Epimetheus

Objects shown in this view

Sun (G2V star)

The Sun holds 99.86% of the Solar System’s mass. Its core reaches about 15 million degrees Celsius, where hydrogen fuses into helium, powering its energy output. Its light takes about 8 minutes and 20 seconds to reach Earth from 150 million kilometers away. It is about 4.6 billion years old and roughly halfway through its life - in about 5 billion years it will swell into a red giant. Its visible surface (photosphere) is around 5,500°C, while the outer atmosphere, the corona, is paradoxically far hotter, reaching millions of degrees. Its activity follows a roughly 11-year cycle, reflected in the number of sunspots and space-weather events. Its chemical composition is about 74% hydrogen and 24% helium, with trace amounts of heavier elements. Its diameter is about 1.39 million km, roughly 109 times Earth's, with a volume that could hold about 1.3 million Earths. It holds 99.86% of the Solar System's total mass; the planets, moons and everything else make up only the remaining fraction. Its solar flares and coronal mass ejections can disrupt satellites and power grids on Earth. It rotates once roughly every 25-35 days, with the rate varying by latitude (differential rotation).

Mercury (rocky planet)

Its solar day is longer than its year. The smallest planet in the Solar System, smaller even than Jupiter's two largest moons, Ganymede and Callisto. It has the most extreme surface temperature swing of any planet: around 430°C by day and minus 180°C at night, since it has virtually no atmosphere. Water ice has been found in permanently shadowed polar craters, despite Mercury being the closest planet to the Sun. Its iron core is disproportionately large, making up about 85% of the planet's volume - possibly the result of an ancient impact that stripped away its mantle. Only two spacecraft have visited it closely: Mariner 10 (1974-75) and MESSENGER, which orbited it from 2011 to 2015. Its orbital period is 88 days, but its solar day (sunrise to sunrise) lasts 176 Earth days because of its slow rotation. Its orbit is in a 3:2 spin-orbit resonance: it rotates exactly three times for every two orbits around the Sun. Its surface is heavily cratered; the largest, the Caloris Basin, spans about 1,550 km. It has a weak but genuine magnetic field, surprising for such a small, slowly rotating planet. The BepiColombo mission is currently en route and will enter orbit around it in 2026.

Venus (rocky planet)

The hottest planet (~465 °C), and it spins backwards. Its atmosphere is 96% carbon dioxide, with surface pressure about 92 times Earth's - equivalent to being 900 meters deep in Earth's oceans. Thick sulfuric-acid clouds hide its surface almost completely, so it has mostly been mapped by radar, notably by the Magellan probe (1990-94). It has the most circular, least elongated orbit of any planet in the Solar System. Often called Earth's twin because of its similar size and mass, though its runaway greenhouse effect makes its surface hellish. Its brightness often causes it to be mistaken for a UFO - it's the brightest natural object in the sky after the Sun and Moon. Its day (between successive solar noons) is longer than its year: 243 days to rotate, but only 224.7 days to orbit. Thousands of volcanoes dot its surface, and recent observations suggest some may still be active today. In antiquity it was thought to be two separate objects (the Morning Star and Evening Star) before astronomers realized they were the same planet. High in its atmosphere, around 50-60 km altitude, pressure and temperature are Earth-like, inspiring proposed future balloon missions. Several Soviet Venera probes landed on it in the 1970s-80s, providing the only surface photographs ever taken there.

Earth (rocky planet)

The only world known to harbour life. About 71% of its surface is covered by ocean, and its single natural satellite, the Moon, stabilizes its axial tilt, helping keep the climate relatively steady. Its atmosphere is 78% nitrogen and 21% oxygen - the oxygen is almost entirely the result of billions of years of photosynthetic life. Its magnetic field, generated by the churning liquid iron-nickel outer core, deflects charged particles streaming from the Sun like a protective shield. It is about 4.54 billion years old, and the only known rocky planet with a surface shaped by active plate tectonics. Its atmosphere's ozone layer filters out most of the Sun's harmful ultraviolet radiation, a key condition for life on land. It is the only planet in the Solar System known to have large, stable quantities of liquid water on its surface. Its interior has four main layers: inner core, outer core, mantle and crust - the crust is the thinnest, yet it's where we live. A single rotation (one day) takes 23 hours 56 minutes relative to the stars, though we round it to 24 hours because of the Sun. Its axial tilt of 23.4 degrees causes the seasons - without it Earth's climate would be far more uniform. Its atmosphere is generally considered to extend to about 100 km altitude (the Kármán line), beyond which space begins.

Moon (moon)

It drifts ~3.8 cm farther from Earth every year. The fifth largest moon in the Solar System, and it has the largest size ratio to its parent planet of any major moon. The leading theory holds it formed about 4.5 billion years ago from debris after a Mars-sized body, Theia, collided with the young Earth. Tidally locked, it always shows the same face to Earth - its far side was first seen only in the space age. Twelve people have walked on its surface, all during the Apollo program between 1969 and 1972. Its gravity drives Earth's tides and stabilizes Earth's axial tilt, which helps keep the seasons steady. Its surface is a mix of dark, lava-filled plains (maria) and brighter, mountainous highlands. It has essentially no atmosphere, so temperatures swing from about 127°C by day to minus 173°C at night. Its gravity is about one-sixth of Earth's, giving Apollo astronauts their distinctive bouncing gait. Water ice has been found in permanently shadowed polar craters, a potential resource for future lunar bases. The age of its rocks makes it a key record of the early Solar System's history, including the era of heavy bombardment.

Phobos (moon)

It orbits faster than Mars rotates, so it rises in the west and sets in the east. It is spiralling inward and will break apart in a few tens of millions of years. It orbits so close to Mars that from most points on the planet it is below the horizon at its own zenith. Its surface is scarred by deep grooves, likely fractures from the Stickney impact. Japan's MMX mission aims to collect a sample from it and return it to Earth in the late 2020s. Its average diameter is about 22 km, an irregular, potato-shaped body. Its surface is covered by a thin layer of dust, and its largest crater, Stickney, nearly shattered it. Discovered by American astronomer Asaph Hall in 1877, in the same month as Deimos. Its origin is debated: it may be a captured asteroid or a body that formed from debris orbiting Mars. In roughly 50 million years it will either be torn apart by tidal forces or crash into Mars.

Deimos (moon)

So small that from the surface of Mars it looks like little more than a bright star. One of the smallest known moons in the Solar System, its surface covered by a thin layer of dust (regolith). Its orbital period is close to Mars's rotation period, so from the surface it appears nearly stationary in the sky for days. Discovered in 1877 by American astronomer Asaph Hall, in the same month as Phobos. Its average diameter is about 12.4 km, even smaller and more irregular than Phobos. Its surface is smoother than Phobos's because a thicker layer of dust covers it. Its orbital radius is about 23,460 km, nearly three times that of Phobos. It's named after Deimos, the personification of dread in Greek mythology, son of Ares. The Mariner 9 probe took the first close-up photographs of it in 1971.

Metis (moon)

One of Jupiter's innermost, tiny moons: together with Adrastea it supplies the material for the planet's main ring, orbiting faster than Jupiter itself rotates. Discovered in March 1979 by the Voyager science team. An irregularly shaped body, too small in mass to pull itself into a sphere. The Galileo spacecraft revealed impact craters, hills and valleys on its surface. Scientists believe it likely maintains synchronous rotation, always showing the same face toward Jupiter.

Amalthea (moon)

The reddest known object in the Solar System, redder than Mars. It radiates more heat than it receives from the Sun. Jupiter's fourth largest moon, though tiny compared to the large Galilean moons. Discovered by Edward Emerson Barnard in 1892, the last moon ever discovered purely by visual telescopic observation. An irregular, potato-shaped body, likely the remnant of a larger object that broke apart. It orbits between the four large Galilean moons and Jupiter, much closer to the planet. Its red surface likely results from sulfur compounds originating from Io's volcanoes. The Galileo probe studied it up close in 2002-2003. Its density is lower than water's, suggesting a loose, porous internal structure.

Thebe (moon)

Dust knocked off Thebe by impacts feeds one component of Jupiter's outer, so called gossamer ring, forming its thicker, more tilted part because Thebe's orbit is more inclined than Amalthea's. Discovered in 1980 by the Voyager science team from images taken by Voyager 1. Jupiter's seventh largest satellite, with a mean radius of about 49 km. Follows a prograde, nearly circular orbit in Jupiter's equatorial plane, alongside three other inner moons.

Io (moon)

The most volcanically active body in the Solar System: over 400 active volcanoes, kneaded from within by Jupiter's tides. Jupiter's tidal forces constantly knead it from within, driving extreme volcanism with sulfur dioxide plumes reaching up to 500 km high. Sulfur and sulfur dioxide paint its surface yellow, orange and red, earning it the nickname 'pizza moon'. It has almost no impact craters because constant volcanic resurfacing erases them. The fourth largest moon in the Solar System, and it has the highest density of the four Galilean moons. Its surface has almost no water ice, unlike Jupiter's other large moons. Its volcanoes eject sulfur dioxide into space, some of which feeds Jupiter's magnetosphere, forming a plasma torus. Discovered by Galileo Galilei in 1610, along with Jupiter's other three large moons. Its average surface temperature is about minus 143°C, but active volcanic vents can reach up to 1,600°C.

Europa (moon)

A salty ocean hides beneath its icy crust, holding more water than all of Earth's seas combined. Its surface is nearly featureless ice with very few impact craters, a sign of a geologically young, active surface. NASA's Europa Clipper probe, launched in 2024, will arrive in 2030 to study its potential habitability up close. The ocean beneath its icy shell is considered one of the most promising places in the Solar System to search for microbial life. A network of reddish-brown fracture lines crisscrosses its surface, one of the smoothest known surfaces in the Solar System. Discovered by Galileo Galilei in 1610, along with Jupiter's other three large moons. It is slightly smaller than Earth's Moon. It has a thin oxygen atmosphere, released from its icy surface, though extremely tenuous.

Ganymede (moon)

The largest moon in the Solar System, bigger than Mercury, and the only moon with its own magnetic field. Its own magnetic field generates auroras above its surface, which have been observed by Hubble. A salty ocean may lie beneath its icy crust, potentially holding more water than all of Earth's oceans combined. ESA's JUICE probe, launched in 2023, will enter orbit around it in 2034 - the first spacecraft ever to orbit a moon other than our own. The largest moon in the Solar System, bigger than the planet Mercury, though less massive. Discovered by Galileo Galilei in 1610. Its surface alternates between darker, cratered regions and lighter, grooved terrain. Its interior is layered: an iron core, a rocky mantle, then a thick layer of ice and ocean.

Callisto (moon)

The most heavily cratered surface in the Solar System, essentially unchanged for four billion years. The outermost of Jupiter's four Galilean moons, and the least affected by the planet's tidal forces. A salty ocean may also lie beneath its surface, though its icy crust is thought to be much thicker than Europa's. Its relatively low radiation levels once made it a candidate site NASA considered for a future crewed outpost. Discovered by Galileo Galilei in 1610, one of Jupiter's four large moons. The third largest moon in the Solar System, nearly the size of Mercury. Its Valhalla impact basin is one of the largest known crater systems in the Solar System, about 3,800 km across.

Himalia (moon)

Jupiter's largest irregular moon is not tidally locked: it spins on its own in just 7.8 hours while taking about 250 days to circle the planet. Discovered on 3 December 1904 by Charles Dillon Perrine using the 0.9 meter Crossley reflector at Lick Observatory. Its albedo of only about 4 percent points to a dark, C or D type asteroid-like composition. By far the largest member of the Himalia group, which also includes Leda, Lysithea and Elara. Ground-based light-curve photometry in 2012 refined its rotation period to 7.7819±0.0005 hours, correcting an earlier, erroneous value of about 9.5 hours.

Pan (moon)

Pan orbits inside the Encke Gap of Saturn's A ring; its prominent equatorial ridge gives it a flying-saucer or ravioli shape, and as a shepherd moon it keeps the roughly 325 km wide gap open. Discovered by M. R. Showalter in 1990 in Voyager 2 images taken nine years earlier. Its gravity raises wave patterns, called wakes, in the ring material along the gap that extend hundreds of miles into the rings. Ring particles orbiting closer to Saturn move faster and get a gravitational kick from Pan as they pass, generating the wakes. Named after Pan, the goat legged god of the wild in Greek mythology.

Daphnis (moon)

Cassini found it from the telltale rippled edges of the Keeler Gap: its gravity keeps raising waves along the gap’s rim, which even cast shadows at Saturn’s equinox, when the Sun is in line with the ring plane. Identified by the Cassini team on 1 May 2005, after ripples along the Keeler Gap's edge had already hinted at a moon's presence. Known as a 'wavemaker moon': waves on the gap's inner edge lead the moon's orbit, while those on the outer edge trail it. Its gravitational pull perturbs the orbits of particles in Saturn's A ring, sculpting the wavy edge of the Keeler Gap. Named after Daphnis, a shepherd and pipe playing pastoral poet from Greek mythology, son of Hermes.

Prometheus (moon)

Acting as a shepherd moon, Prometheus constrains the inner edge of Saturn's F Ring; unlike its neighbors Pandora, Janus and Epimetheus, its surface is noticeably less cratered. Discovered by the Voyager 1 science team in October 1980. An extremely irregular, potato-shaped body with visible craters up to about 20 km across. Likely a porous, icy body of low density. Named after Prometheus, the Titan of Greek mythology who stole fire from the gods and gave it to humanity.

Pandora (moon)

Pandora is the F Ring's other shepherd moon alongside Prometheus: while Prometheus helps keep the ring in place, Pandora tends to disrupt it. Discovered by the Voyager 1 science team in October 1980. A potato-shaped body whose surface is coated in fine, dust-sized icy material, blanketing even its impact craters. Its surface is crossed by grooves and ridges. Named in 1985 after Pandora of Greek mythology, whose curiosity released both misfortune and hope into the world.

Janus (moon)

Janus and Epimetheus form the only known pair in the solar system that swap orbits roughly every four years: as the inner moon catches up with the outer one, their gravitational interaction trades their orbits. First observed by Audouin Dollfus on 15 December 1966, though for years it was thought to be a single moon; in 1978 Stephen M. Larson and John W. Fountain realized the observations showed two separate bodies, Janus and Epimetheus. Voyager 1 confirmed this in 1980. A potato-shaped body, extensively cratered with several craters larger than 30 km, including Castor, Phoebe, Idas and Lynceus. Orbits in the gap between the F and G rings, with a surface temperature of about -195 degrees Celsius. Even at closest approach the two moons stay about 10,000 km apart, the only such orbital configuration known in the solar system.

Epimetheus (moon)

Together with Janus, Epimetheus forms the solar system's only known co-orbital moon pair: roughly every four years, as the inner moon catches up with the outer one, their gravity trades their orbits. Independently observed twice in December 1966, by Audouin Dollfus (Dec. 15) and Richard Walker (Dec. 18); the fact that two distinct moons were involved was only recognized in 1978 by Stephen M. Larson and John W. Fountain, and confirmed by Voyager 1 in 1980. A potato-shaped body with a pronounced flattening at its south pole, the remnant of a large crater. Orbits in the gap between the F and G rings, with a surface temperature of about -195 degrees Celsius. Along with Janus, it is likely a loosely bound 'rubble pile' held together by gravity.

Mimas (moon)

The huge Herschel crater makes it look uncannily like the Death Star. An ocean may hide under its icy shell. The smallest known body shaped into a sphere by its own gravity. Discovered by William Herschel in 1789. The Herschel crater spans about a third of the moon's diameter - a slightly larger impact could have shattered it. Its diameter is about 396 km, making it the smallest known body shaped into a sphere by its own gravity. It orbits close to Saturn's inner rings, and its gravity helps carve out the Cassini Division gap in the rings. Its surface temperature shows an unusual pattern that some have nicknamed the 'Pac-Man' pattern.

Enceladus (moon)

Water geysers erupt from its south pole and feed Saturn's E ring. One of the most promising places to look for life. The Cassini probe discovered its south polar geysers in 2005, which contain organic molecules and silica particles. Its surface is one of the most reflective (highest-albedo) in the Solar System, coated in fresh ice. Material ejected from its geysers feeds Saturn's E ring. Discovered by William Herschel in 1789. Part of its surface is nearly crater-free, evidence of ongoing geological renewal. In 2015 the Cassini probe flew directly through its geyser plume and detected molecular hydrogen, hinting at hydrothermal activity.

Tethys (moon)

Almost pure water ice, so light it would float on water. The Ithaca Chasma canyon runs three quarters of the way around it. Its Odysseus crater spans about two-thirds of the moon's diameter, one of the largest known craters relative to its parent body. Its density suggests it is composed almost entirely of water ice, with very little rock. Discovered by Giovanni Cassini in 1684. Its density is only about 0.98 g/cm3, suggesting it's nearly pure water ice with almost no rock. Two tiny companion moons, Telesto and Calypso, share its orbit at its Lagrange points. Its surface is heavily cratered, with Odysseus being the largest crater.

Dione (moon)

Bright ice cliffs streak its trailing side. Voyager mistook them for clouds; Cassini revealed walls hundreds of metres high. Discovered by Giovanni Cassini in 1684, the same year as Tethys. It has a thin oxygen atmosphere, though extremely tenuous, trillions of times less dense than Earth's. It has two tiny companion moons sharing its orbit at its Lagrange points. Its surface has both bright ice cliffs and darker, cratered terrain. The Cassini probe made several close flybys, producing detailed maps of it. A faint, dust-based ring arc has also been detected along its orbit, similar to what's suspected at Rhea.

Rhea (moon)

Saturn's second largest moon. It may have a faint ring system of its own, which would be unprecedented for a moon. Saturn's second largest moon, smaller only than Titan. Discovered by Giovanni Cassini in 1672. Its surface is heavily cratered, featuring two large, bright impact basins. Its density suggests it is about two-thirds ice and one-third rock. Two huge impact basins mark its surface, both featuring bright, radiating streaks. The Cassini probe made close flybys of it in 2005 and 2010.

Titan (moon)

The only moon with a thick atmosphere. Its rivers, lakes and rain are made of methane; Huygens landed there in 2005.

Hyperion (moon)

A spongy, porous body that tumbles chaotically: its rotation is literally unpredictable, with no two days alike. The largest known non-spherical moon in the Solar System. Discovered independently by William Cranch Bond, George Bond and William Lassell in 1848. Its spongy structure gives it a lower density than most icy moons - roughly half that of water. Its chaotic rotation makes it unique in the Solar System, with an unpredictable orientation. Its distinctive, deeply shadowed craters give it a spongy, porous appearance. The Cassini probe made its closest flyby in 2005, passing about 500 km away.

Iapetus (moon)

One hemisphere is soot-dark, the other snow-white, and a 13 km high ridge runs along its equator, making it look like a walnut. Discovered by Giovanni Cassini in 1671, who for a long time couldn't understand why it was only visible half the time. Its light-dark split is likely caused by dark dust from Phoebe falling onto its leading hemisphere. Its equatorial ridge is so tall and regular that some researchers have jokingly floated artificial origins - it is, in fact, geological. Its diameter is about 1,470 km, making it Saturn's third largest moon. Its orbit is unusually distant from Saturn and steeply tilted relative to the other major moons. Its dark region is named Cassini Regio, after its discoverer.

Phoebe (moon)

It orbits backwards, so it was not born with Saturn: it is a captured object from the Kuiper belt. Discovered by William Henry Pickering in 1899 on photographic plates - the first moon ever discovered photographically. Its retrograde, highly tilted orbit suggests it is a captured object from the Kuiper Belt rather than having formed in the Saturn system. Its dark surface is coated in carbon-rich material, some of which also darkens one hemisphere of Iapetus. One of the most distant and largest of Saturn's irregular (non-circular, tilted-orbit) moons. The Cassini probe flew past it in 2004, just before entering orbit around Saturn. Water ice and organic materials have been detected on its surface.

Puck (moon)

The largest of Uranus's lesser moons, ranking just behind the planet's five major moons, all of which exceed 400 km in diameter. Discovered by Voyager 2 in December 1985 during its Uranus flyby. Originally designated S/1985 U1. Named after Puck, the mischievous sprite from Shakespeare's A Midsummer Night's Dream. Orbits Uranus in less than one Earth day.

Miranda (moon)

Chasms up to 20 km deep scar its surface, as if it once shattered and reassembled itself at random. First photographed up close by Voyager 2's 1986 flyby, which revealed its extreme, fractured terrain. The smallest and innermost of Uranus's five major moons. Its Verona Rupes cliff is one of the tallest known scarps in the Solar System, possibly up to 20 km high. Discovered by Gerard Kuiper in 1948. Its surface is one of the most varied, chaotic landscapes in the Solar System, with three large oval-shaped regions called coronae. It is known only from Voyager 2's single flyby, so less than half of its surface has ever been mapped.

Ariel (moon)

The brightest of Uranus's moons, with young valley systems probably flooded by ice volcanism. Discovered by William Lassell in 1851. A network of fault valleys (chasmata) crosses its surface, likely once filled by ice-volcanic processes. It has the least cratered surface among Uranus's moons, suggesting a younger, more active history. The brightest of Uranus's five major moons, with the highest albedo. Its density suggests it is roughly half ice and half rock. It is known up close only from Voyager 2's 1986 flyby.

Umbriel (moon)

The darkest of Uranus's moons. A single mysterious bright ring, the rim of Wunda crater, breaks its uniform dark surface. Discovered by William Lassell in 1851, the same time as Ariel. Its name comes from Alexander Pope's poem 'The Rape of the Lock', like the other Uranian moons, which are all named after literary characters. Its dark surface is likely coated in ancient, carbon-rich material largely unchanged since the Solar System's formation. The darkest of Uranus's five major moons, with low reflectivity. Its ancient, heavily cratered surface shows little sign of geological activity. It is known up close only from Voyager 2's 1986 flyby.

Titania (moon)

Uranus's largest moon, with a canyon system nearly 1,500 km long, one of the great fracture networks of the Solar System. Discovered by William Herschel in 1787, on the same night as Oberon. Its surface features icy cliffs and deep canyons, evidence of past internal tectonic activity. It is named after the fairy queen in Shakespeare's A Midsummer Night's Dream. Uranus's largest moon. Its density suggests a roughly equal mix of ice and rock. It is known up close only from Voyager 2's 1986 flyby.

Oberon (moon)

Dark material pools in its crater floors, and an 11 km mountain rises at its limb, spotted in silhouette by Voyager 2. Discovered by William Herschel in 1787. The outermost of Uranus's major moons, its surface heavily cratered. Named after the fairy king in Shakespeare's A Midsummer Night's Dream. Uranus's second largest moon, and the outermost of its five major moons. Its surface is among the oldest and most heavily cratered of Uranus's moons. It is known up close only from Voyager 2's 1986 flyby.

Proteus (moon)

Right at the limit: a little larger and its own gravity would pull it into a sphere. Instead it stayed angular. Discovered by Voyager 2 in 1989 during its Neptune flyby. Neptune's second largest moon, though its dark surface and close orbit make it hard to observe from Earth. Its largest crater, Pharos, nearly shattered the body on impact. The largest irregularly shaped (non-spherical) moon in the Neptune system. Its dark surface makes it only a fraction as bright as the similarly sized Mimas. Its orbit lies very close to Neptune, essentially at the outer edge of the ring system.

Triton (moon)

It orbits backwards, so it is a dwarf planet captured from the Kuiper belt. Its nitrogen geysers still erupt at minus 235 Celsius. The largest retrograde moon (orbiting opposite to its planet's rotation) in the Solar System. Discovered by William Lassell in 1846, just 17 days after Neptune itself was discovered. Its surface is young and active, with very few impact craters, likely due to partial resurfacing. Neptune's tidal forces will eventually tear it apart, possibly into a ring system, in about 3.6 billion years. Its surface temperature is only about 38 kelvin (minus 235°C), one of the coldest known places in the Solar System. Its surface is coated in nitrogen and methane ice, with a pinkish-bluish tint. Voyager 2's 1989 flyby discovered active geysers erupting up to 8 km high.

Nereid (moon)

One of the most eccentric orbits of any moon: it swings between 1.4 and 9.7 million km from Neptune. Discovered by Gerard Kuiper in 1949. Neptune's third largest moon, though its highly elongated orbit means its distance from the planet can vary sevenfold. Such an eccentric orbit suggests a past gravitational disturbance, possibly related to Triton's capture. One of the hardest larger moons in the Solar System to observe, because it is very faint and orbits far out. Its size and orbit suggest it likely did not form on its current path.

Charon (moon)

So large relative to Pluto that their common centre of mass lies outside Pluto: a true binary, each keeping one face turned to the other. Discovered by James Christy in 1978, which led to a much more accurate measurement of Pluto's mass. It has a reddish-brown polar region (Mordor Macula), possibly caused by methane gas escaping from Pluto and freezing onto it. New Horizons' 2015 flyby revealed a vast canyon system on it, possibly from the freezing of a former internal ocean. Its diameter is about half of Pluto's, the largest ratio known between any moon and its parent body. American astronomer James Christy named it after his wife Charlene's nickname and the ferryman of Greek mythology, Charon. It is in a mutual tidal lock with Pluto: both bodies always show the same face to each other.

Styx (moon)

Pluto's smallest known moon, found only in 2012 with Hubble, three years before New Horizons arrived. Discovered by the Hubble Space Telescope in 2012 while mapping the Pluto system. Named after the river of the underworld in Greek mythology, like several other moons in the Pluto system. It is only about 16 km across, one of the smallest known moons of Pluto. The New Horizons probe observed it more closely during its 2015 flyby.

Nix (moon)

It tumbles chaotically in the double gravity field of Pluto and Charon, so it has no regular day-night cycle. Discovered by the Hubble Space Telescope in 2005 while mapping the Pluto system. It has a surprisingly reddish surface compared to the more neutral-colored moons elsewhere in the system. It is about 50x35 km, an irregularly shaped body. Its chaotic rotation results from the strong combined gravity of the Pluto-Charon pair.

Kerberos (moon)

It is made of two lobes stuck together, as if two smaller moons collided gently and merged. Discovered by the Hubble Space Telescope in 2011. Named after the three-headed dog guarding the underworld in Greek mythology. It has a surprisingly dark surface compared to the brighter moons elsewhere in the system. The New Horizons probe took the first close-up photos of it in 2015.

Hydra (moon)

Pluto's outermost moon. Its surface is almost pure water ice, making it strikingly bright, like fresh snow. Discovered by the Hubble Space Telescope in 2005, at the same time as Nix. The outermost known moon in the Pluto system, with a chaotic rotation. It is about 51x33 km, one of the larger small moons in the Pluto system. The New Horizons probe photographed it in detail during its 2015 flyby.

Dysnomia (moon)

Tracking its orbit is what made it possible to weigh Eris: a moon’s orbit directly gives the mass of the body it circles, and for Eris only Dysnomia provides that. Its discovery was announced in September 2005; researchers initially nicknamed it 'Gabrielle', after Xena the warrior princess's sidekick on the TV show. Its permanent name honors Dysnomia, the Greek goddess of lawlessness and daughter of Eris. Follows a nearly circular, prograde orbit tilted about 78 degrees to Eris's own orbital plane around the Sun. 2023 light-curve studies found that Eris's own rotation is tidally locked to Dysnomia's orbital period, an unusual arrangement in the solar system.

Namaka (moon)

Haumea's smaller, inner moon has an unusually eccentric orbit (about 0.25) tilted roughly 13 degrees from Hiʻiaka's, as the two moons continuously perturb each other gravitationally. Discovered in 2005 and named after Namaka, a water spirit of Hawaiian mythology. Its mass is only about 0.05 percent of Haumea's, so its orbit could only be pinned down with a fully interacting three-point-mass model that includes Hiʻiaka. Over timescales of more than a few weeks, no simple Keplerian orbit describes Namaka's motion because of Hiʻiaka's gravitational perturbations.

Hiʻiaka (moon)

Haumea’s larger, outer moon spins surprisingly fast, once every 9.8 hours or so, while it takes 49 days to circle the dwarf planet: it is not tidally locked. Discovered in 2005 and named after Haumea's mythological daughter, patron goddess of the island of Hawaii and of hula dancers. Follows a nearly circular orbit with an eccentricity of only about 0.05. Hiʻiaka and the smaller Namaka orbit close to an 8:3 mean-motion resonance with each other. Its surface is dominated by water ice, consistent with both of Haumea's moons having formed from a collision-generated debris disk.

Vanth (moon)

An unusually large moon relative to its dwarf planet: the Vanth-Orcus mass ratio is the highest of any known planet or dwarf planet system, and the pair has likely evolved into a mutually tidally locked, double synchronous state. Discovered in 2005 and named after Vanth, a goddess of the underworld in Etruscan mythology. Follows a nearly circular, nearly face-on orbit around Orcus. A 2017 stellar occultation directly constrained its diameter to 443±10 km, assuming a spherical shape. ALMA measurements give a Vanth-to-Orcus mass ratio of 0.16±0.02, suggesting the system has likely evolved to a double synchronous state.

Weywot (moon)

Weywot is an unusually dark body, with a geometric albedo of only about 0.024-0.078, far lower than its parent Quaoar's (about 0.124), a trait that may point to a captured origin rather than formation from shared collisional debris. Its discovery was announced in 2006, and it was named in 2007 after Quaoar's son, a creator figure in Tongva mythology. Stellar occultation observations show it follows a nearly circular orbit around Quaoar. The most recent occultations (from 2023 onward) constrain its size to 116-172 km at 95 percent confidence.

Mars (rocky planet)

Olympus Mons is the largest volcano in the Solar System. Olympus Mons stands about 22 km tall, nearly three times Mount Everest, and is roughly the size of the state of Arizona. Its red color comes from iron oxide (rust) coating its surface. It has two tiny, irregularly shaped moons, Phobos and Deimos, likely captured asteroids. Significant water ice has been found beneath the surface and in its polar caps, a potential resource for future crewed missions. Its day (a 'sol') is remarkably close to Earth's, at 24 hours and 37 minutes. Its atmosphere is 95% carbon dioxide, extremely thin, with surface pressure less than 1% of Earth's. Like Earth, its seasons result from its axial tilt (25.2 degrees), but they last about twice as long because its year is nearly twice Earth's. Its giant dust storms can occasionally engulf the entire planet for weeks or months. Ancient river and lake beds found on its surface suggest it once had a much wetter climate. It has had nine successful landers/rovers to date: Viking 1-2, Pathfinder, Spirit, Opportunity, Phoenix, Curiosity, InSight, Perseverance.

Jupiter (gas giant)

More than twice as massive as all other planets combined. More than twice as massive as all other planets combined. The largest planet in the Solar System - its mass is about 318 times that of Earth. It also has a faint, thin ring system, discovered only in 1979 by Voyager 1. NASA's Juno probe has orbited it since 2016, mapping its interior structure and magnetic field. Sometimes called a 'failed star', since with roughly 80 times more mass it could theoretically have ignited nuclear fusion. It takes 11.9 Earth years to orbit the Sun, but spins faster than any other planet, completing a rotation in under 10 hours. Its atmosphere is primarily hydrogen and helium, similar in composition to the Sun. Its four largest moons (Io, Europa, Ganymede, Callisto) are called the Galilean moons, discovered by Galileo Galilei in 1610. It radiates more heat than it receives from the Sun, the leftover warmth of its slow gravitational contraction. Fragments of Comet Shoemaker-Levy 9 spectacularly struck its atmosphere in 1994, observed live by astronomers worldwide.

Saturn (gas giant)

Less dense than water, so in theory it would float. Its rings are mostly made of water ice, and though they can span up to 280,000 km wide, they are often only tens of meters thick. It has more than 82 known moons, the most of any planet in the Solar System. The Cassini-Huygens mission studied its system from 2004 to 2017, before being deliberately plunged into the planet's atmosphere. A striking hexagon-shaped jet stream pattern persists in its atmosphere at the north pole. Its average density is lower than water's, so in theory it would float on a large enough ocean. It is named after the Roman god of agriculture, the same root as the English word 'Saturday'. Its atmosphere is primarily hydrogen and helium with banded cloud patterns, though less dramatic than Jupiter's. Besides Titan, dozens of smaller moons orbit it, many discovered by the Cassini mission. Galileo Galilei first observed its rings in 1610, though he didn't recognize their true nature. The origin of its rings is debated: they may be the remnant of a shattered moon or comet, or material as old as the planet itself.

Uranus (ice giant)

It orbits lying on its side, tilted by 98°. The only planet named after a Greek deity rather than a Roman one, like the rest of the planets. Discovered by William Herschel in 1781 - the first planet ever discovered with a telescope. Its atmosphere contains methane, which absorbs red light, giving it a blue-green color. Only one spacecraft, Voyager 2, has ever visited it, in 1986. It has 13 known faint rings, discovered in 1977 while astronomers observed it passing in front of a star. Because of its extreme axial tilt, its poles experience about 42 years of continuous daylight followed by 42 years of continuous night. Its atmosphere is primarily hydrogen, helium and methane; as an ice giant it contains less hydrogen than Jupiter or Saturn. Its internal heat output is lower than the other giant planets', for reasons not yet fully understood. It has 27 known moons, most named after characters from the works of Shakespeare and Alexander Pope. Its extreme tilt may have been caused by an ancient, massive impact early in the Solar System's history.

Neptune (ice giant)

Home to the strongest winds in the Solar System (~2,100 km/h). The only planet discovered through mathematical prediction before it was observed: irregularities in Uranus's orbit hinted at its existence. German astronomer Johann Galle first identified it in 1846, within about one degree of its predicted position. Only one spacecraft, Voyager 2, has ever flown past it, in 1989. Its largest moon, Triton, is likely a captured dwarf planet from the Kuiper Belt. It has a faint ring system, notable for arcs of denser material within the rings. Its atmosphere is primarily hydrogen, helium and methane, with the methane giving it its distinctive blue color. Its internal heat output significantly exceeds the energy it receives from the Sun, unlike Uranus. It has 14 known moons, by far the largest of which is Triton. With an orbital period of 165 years, each of its seasons lasts about 41 years. It is named after the Roman god of the sea, chosen for its blue color.

Pluto (dwarf planet)

Counted as the ninth planet until 2006. Discovered by Clyde Tombaugh in 1930; its name was suggested by an 11-year-old English girl, Venetia Burney. Its orbit is so elongated that it sometimes moves closer to the Sun than Neptune - most recently between 1979 and 1999. The New Horizons probe photographed it up close for the first time in 2015, revealing the heart-shaped plain Tombaugh Regio. It has five known moons; the largest, Charon, forms with it what is effectively a double dwarf-planet system. In 2006 the International Astronomical Union reclassified it as a dwarf planet because it hasn't cleared its orbital neighborhood. Its atmosphere is primarily nitrogen, which periodically freezes onto the surface as it moves farther from the Sun. Mountains have been found on its surface, some up to 3,500 meters tall, likely built from water ice. New Horizons revealed that a liquid water ocean may lie beneath its surface, under the Tombaugh Regio plain. It is in a mutual tidal lock with its largest moon, Charon - both always show the same face to each other. A year on Pluto lasts 248 Earth years - since its discovery in 1930, it still hasn't completed a full orbit of the Sun.

Ceres (dwarf planet)

The largest object in the asteroid belt. Discovered by Giuseppe Piazzi in 1801 - the first asteroid ever discovered, long classified as a planet. It accounts for roughly a third of the total mass of the asteroid belt. NASA's Dawn probe studied it from 2015 to 2018, discovering bright salt deposits in the Occator crater. Water ice, and possibly some remaining liquid water, may lie beneath its surface, hinting at unusual activity for a dwarf planet. A salty water ocean may once have existed, or possibly still exists, beneath its surface, supported by Dawn's data. It is the only body in the asteroid belt classified as a dwarf planet. Giuseppe Piazzi originally identified it as a planet; only decades later was it reclassified as an asteroid, then in 2006 as a dwarf planet.

Eris (dwarf planet)

Its discovery led to Pluto’s reclassification. Discovered in 2005 by Mike Brown's team, its mass is nearly identical to Pluto's. Its discovery directly triggered the debate that led to Pluto's reclassification as a dwarf planet in 2006. Its one known moon, Dysnomia, is named after the daughter of the goddess of strife, personifying lawlessness. Its surface is extremely bright, likely coated in fresh methane ice that continually freezes and sublimates along its orbit. Orbiting at an average distance of about 68 AU from the Sun, it's one of the most distant known large dwarf planets.

Makemake (dwarf planet)

Named after the creator god of Easter Island. Discovered in 2005 by Mike Brown's team, shortly after Easter, hence its name. One of the brightest known objects in the Kuiper Belt after Pluto. A tiny moon was discovered orbiting it in 2016. Spectroscopic observations have detected methane ice on its surface. It may have a very tenuous atmosphere that appears near its closest approach to the Sun and freezes out farther away.

Haumea (dwarf planet)

The fastest-rotating large body: the spin stretched it egg-shaped, and it has its own ring. Its elongated, cigar-like shape results from its rapid, roughly 4-hour rotation. Its ring, discovered in 2017, was the first ring ever found around a classical Kuiper Belt object. It has two moons, Hi'iaka and Namaka, named after Hawaiian deities, as is Haumea itself. Its density is unusually high among dwarf planets, suggesting a mostly rocky interior. Its rapid rotation may be the result of an ancient, major impact that could also have created its moons and ring.

Quaoar (dwarf planet candidate)

A ring was found around it in 2023, far outside the Roche limit, where the debris should have coalesced into a moon instead. Discovered in 2002 by Chad Trujillo and Mike Brown. Named after the creation deity of the Tongva people, indigenous to the Los Angeles basin. Its one known moon is named Weywot. Its ring, discovered in 2023, surprised astronomers because it lies far outside the Roche limit, where debris should theoretically have coalesced into a moon. Crystalline water ice, and possibly ammonia, have been detected on its surface, suggesting recent cryovolcanic activity.

Orcus (dwarf planet candidate)

It sits in the same 2:3 resonance with Neptune as Pluto, but always in the opposite phase, which earned it the nickname anti-Pluto. Discovered in 2004 by Chad Trujillo, Mike Brown and David Rabinowitz. Named after an Etruscan-Roman underworld deity, a kind of 'dark mirror' to Pluto. Its one known moon, Vanth, is roughly half its size. Water ice and ammonia hydrate have been detected on its surface, suggesting past geological activity. Based on its size and brightness, it is one of the largest known classical Kuiper Belt objects.

Gonggong (dwarf planet candidate)

One of the reddest large bodies in the Solar System; its slow spin was probably braked by its moon, Xiangliu. Discovered in 2007 by Megan Schwamb, Mike Brown and David Rabinowitz. Named after a Chinese water god said to have thrown the heavens off balance. Its one known moon, Xiangliu, is named after a mythological companion of Gonggong. Its reddish surface color likely comes from organic compounds (tholins) altered by solar wind exposure. Its highly inclined, elongated orbit is typical of 'scattered disk' objects.

Sedna (dwarf planet candidate)

Even at its closest it stays 76 AU from the Sun, so Neptune cannot have put it there: a passing star or an undiscovered planet may have. Discovered in 2003, it was the most distant known solar system object at the time. Its extremely elongated, roughly 12,700-year orbit means it's currently in the relatively close portion of its path - at its farthest it recedes to about 900 AU. Its reddish surface has led some astronomers to consider it the first known member of the sparsely populated 'inner Oort cloud' between the Kuiper Belt and the Oort Cloud. Discovered by Mike Brown, Chad Trujillo and David Rabinowitz. It's named after an Inuit sea goddess who dwells in the depths of the Arctic Ocean - a fitting name for such a cold, distant world. Its surface is one of the reddest known in the Solar System, comparable only to Mars and a few other KBOs. It has no known moon, which is unusual given its size and slow rotation compared to similar distant objects.

Halley's Comet (comet)

Next returns to the inner Solar System in 2061. It's the only short-period comet visible to the naked eye, observable roughly twice in a human lifetime. Its earliest recorded sighting dates to 240 BCE, noted by Chinese astronomers. During its 1986 return, five spacecraft (including ESA's Giotto) approached it, capturing the first close-up images of a comet's nucleus. It is named after English astronomer Edmond Halley, who in 1705 first calculated that the comets seen in 1531, 1607 and 1682 were the same object, and predicted its 1758 return. Its nucleus is a dark, peanut-shaped body with a surface reflectivity lower than coal's. Its nucleus is about 15x8 km, made of dark, carbon-rich, porous material. It will next return to the inner Solar System in 2061, when it should again be well placed for observation from Earth.

Comet Encke (comet)

The shortest orbital period of any known comet: it laps the Sun more than twenty times in a human lifetime. It is named after German astronomer Johann Franz Encke, who calculated its orbit in 1819, though Pierre Méchain first discovered it in 1786. It has one of the lowest known albedos (least reflective surfaces) of any comet. It is thought to be the source of the November Taurid meteor shower. Its orbit stays entirely within Jupiter's, unusually compact for a short-period comet. Astronomers link at least one branch of the Taurid meteor shower to this comet.

Tempel–Tuttle (comet)

Parent of the Leonids, which in 1833 threw tens of thousands of meteors an hour across the sky. Discovered independently by Wilhelm Tempel and Horace Parnell Tuttle in 1865. Its roughly 33-year returns can turn the Leonid meteor shower into an intense 'meteor storm'. Its nucleus is relatively small, about 3.6 km across. Its most recent return was in 1998, which also produced a significant Leonid meteor outburst.

Swift–Tuttle (comet)

Parent of the Perseids, the best known meteor shower of the year. Discovered independently by Lewis Swift and Horace Parnell Tuttle in 1862. Its nucleus, about 26 km across, is among the largest of any comet that approaches Earth's orbit. Some long-range calculations suggest a future return, thousands of years from now, could bring it uncomfortably close to Earth, though there is no near-term risk. It's the largest known object that regularly comes close to Earth's orbit. It most recently returned to the inner Solar System in 1992.

Churyumov–Gerasimenko (comet)

Rosetta escorted it for two years, and in 2014 Philae became the first craft to land on a comet nucleus. Discovered by Ukrainian astronomers Klim Churyumov and Svetlana Gerasimenko in 1969. Its distinctive 'rubber duck' shape suggests it formed from two separate bodies that merged. Data from Rosetta and Philae revealed organic molecules and water ice on its surface. The Rosetta mission launched in 2004 and reached the comet in 2014, escorting it until 2016. After a rough landing, the Philae lander ended up in the shadow of a cliff, which limited its solar power.

Wild 2 (comet)

Stardust caught grains from its tail and brought them back to Earth in 2006. Discovered by Swiss astronomer Paul Wild in 1978. A close 1974 encounter with Jupiter dramatically altered its orbit, bringing it closer to the Sun. Samples returned by Stardust included presolar interstellar grains older than the Solar System itself. Its nucleus is about 5.5 km across, with steep cliffs and deep pits visible on its surface. The Stardust probe flew past it in 2004, before returning the collected samples to Earth in 2006.

Tempel 1 (comet)

Deep Impact fired a projectile into it in 2005 to expose the pristine material below the surface. Discovered by Wilhelm Tempel in 1867. The Deep Impact collision created a crater roughly the size of a football field and about 30 meters deep. In 2011 the Stardust-NExT mission also visited it to document changes since the impact. Its nucleus is about 7.6x4.9 km, with layered structures visible on its surface. Material ejected by the impact revealed water ice and organic compounds.

Hartley 2 (comet)

EPOXI flew within 700 km in 2010: carbon dioxide jets blast out of the tiny nucleus. Discovered by Australian astronomer Malcolm Hartley in 1986. Its distinctive, peanut-shaped nucleus consists of two separate lobes joined by a narrower 'neck'. EPOXI, the repurposed Deep Impact spacecraft, flew past it in 2010. Its nucleus is unusually small, only about 1.6 km across, yet it has active jets. EPOXI data showed its carbon dioxide jets also eject ice grains into the space near its surface.

Hale–Bopp (comet)

It stayed visible to the naked eye for 18 months in 1997, still a record. Discovered independently by Alan Hale and Thomas Bopp in 1995, unusually far out, beyond Jupiter's orbit. Its nucleus is exceptionally large, about 60 km across, a major reason for its remarkable brightness. It is not due to return to the inner Solar System until around the year 2534. Near the Sun it displayed three distinct tails at once: a dust tail, an ion tail, and a rare sodium tail. At the time of its discovery it was beyond Jupiter's orbit, unusually far out for a comet spotted by amateur astronomers.

NEOWISE (comet)

The brightest comet of the decade in the northern hemisphere, in the summer of 2020. Discovered by NASA's NEOWISE (formerly WISE) space telescope in March 2020. It survived its close solar approach, a passage that destroys many smaller comets. It won't return to the inner Solar System for roughly another 6,800 years. Its nucleus is about 5 km across, unusually large among comets bright enough to see with the naked eye. Within weeks of its discovery it became easily visible to the naked eye in the evening sky of the northern hemisphere.

James Webb Space Telescope (space telescope)

The largest space telescope ever built (2021). Launched on December 25, 2021, aboard an Ariane 5 rocket from French Guiana. It observes primarily in infrared light, letting it peer through dust and see the most distant, oldest galaxies. It consists of 18 hexagonal beryllium mirror segments, coated in gold for better infrared reflectivity. Its sunshield is a tennis-court-sized, five-layer structure that maintains a temperature difference of hundreds of degrees between its sun-facing and shaded sides. It orbits about 1.5 million km from Earth, around the Sun-Earth L2 point, never passing into Earth's shadow. It took about 25 years to develop and build, at a cost of roughly $10 billion, making it one of the most expensive scientific instruments ever built. Its first science images were released in July 2022, including the deepest and sharpest infrared image of the Universe ever taken.

Euclid Space Telescope (space telescope)

ESA's dark matter and dark energy mapping mission: since 2023 it has been surveying a third of the sky, charting the shapes and distances of 1.5 billion galaxies. Launched in July 2023 aboard a SpaceX Falcon 9 rocket. Its goal is to build a 3D map of the Universe's large-scale structure to better understand the nature of dark matter and dark energy. Its mission is planned to run through 2030. It is named after the ancient Greek mathematician Euclid, one of the founders of geometry. Over its 6-year primary mission it will map about a third of the sky, avoiding the bright plane of the Milky Way.

Gaia Space Telescope (space telescope)

ESA's star-mapping mission: spinning once every 6 hours, it charted the positions, motions and distances of nearly 2 billion stars; science operations ended in 2025. Launched in December 2013 aboard a Soyuz rocket. The star catalog it produced gave the most precise 3D map of the Milky Way ever made. Its data has also led to the discovery of numerous exoplanets and previously unknown objects. It is named after the ancient Greek Earth goddess. Its precision is so high that, in principle, it could measure the width of a human hair from the distance between the Earth and the Moon.

Voyager 1 (space probe)

The most distant human-made object, now in interstellar space. Launched on September 5, 1977, just over two weeks after Voyager 2, but overtook it on a faster trajectory. In 1990, from the edge of the Solar System, it took the famous 'Pale Blue Dot' photo of Earth, at Carl Sagan's suggestion. It crossed the heliopause into interstellar space in 2012, the first human-made object ever to do so. It carries a Golden Record with sounds, music and images from Earth, in case it is ever found by an alien civilization. Its radio signal currently takes about 23 hours to reach Earth, reflecting its current distance. Its plutonium-powered generators are slowly losing output, expected to keep enough instruments running until roughly the late 2020s.

Voyager 2 (space probe)

The only probe to have visited Uranus and Neptune. Launched on August 20, 1977, two weeks before Voyager 1. It followed the 'Grand Tour' trajectory, exploiting a rare planetary alignment to visit all four giant planets. It crossed the heliopause into interstellar space in 2018, six years after Voyager 1. It carries the same Golden Record as Voyager 1. The only spacecraft to have flown past all four giant planets (Jupiter, Saturn, Uranus, Neptune). In 2023 an incorrect command temporarily severed contact with Earth, but NASA successfully restored communication.

New Horizons (space probe)

The first spacecraft to photograph Pluto up close (2015), later visiting the Kuiper Belt object Arrokoth (2019) as well. Launched on January 19, 2006, it was the fastest spacecraft ever to launch directly from Earth. In 2007 it used a Jupiter gravity assist to speed its journey toward Pluto. After its 2015 Pluto flyby, in 2019 it also visited the Kuiper Belt object Arrokoth, the most distant object ever explored up close. It carries a small portion of the ashes of Clyde Tombaugh, the discoverer of Pluto. It remains operational, continuing to study the Kuiper Belt as it heads farther out of the Solar System.

Parker Solar Probe (space probe)

The fastest human-made object ever built: it reaches about 430,000 mph (192 km/s) at closest approach, passing closer to the Sun than any spacecraft before it, about 4.3 million miles (6.9 million km) from its surface. Launched on August 12, 2018, it is named after physicist Eugene Parker, who theoretically predicted the solar wind - the first NASA spacecraft ever named after a living person. Its heat shield, made of carbon-composite material, withstands around 1,370°C while the instruments behind it stay at room temperature. Seven Venus gravity assists gradually tighten its orbit, bringing it ever closer to the Sun's corona. Its goal is to gather data directly from the Sun's corona, helping scientists understand the origin of the solar wind. In December 2024 it made a historic close approach, passing about 6.1 million km from the Sun's surface.

BepiColombo (space probe)

A joint ESA/JAXA mission: after nine gravity assists (Earth, Venus, then Mercury six times) it enters orbit around Mercury in November 2026, when the two probes it carries (MPO and MMO) will separate. Launched on October 20, 2018, aboard an Ariane 5 rocket. It's named after Giuseppe 'Bepi' Colombo, the Italian scientist who worked out the gravity-assist trajectory used by Mariner 10 at Mercury. It carries two separate orbiters: Europe's MPO (Mercury Planetary Orbiter) and Japan's MMO (Mio, formerly Mercury Magnetospheric Orbiter). Its route uses seven gravity assists (Earth once, Venus twice, Mercury six times) to slow down enough to enter orbit so close to the Sun. By 2025 it had already completed several successful Mercury flybys, gathering scientific data along the way.

Nancy Grace Roman Space Telescope (space telescope)

NASA's newest wide-field survey telescope, with a field of view roughly 100 times larger than Hubble's - launched to map dark energy and dark matter and hunt for exoplanets, heading to a halo orbit around the Sun–Earth L2 point, just like James Webb. Named after Nancy Grace Roman, NASA's first chief astronomer, often called 'the mother of Hubble' for her early advocacy of space telescopes. It shares Hubble's mirror diameter but has a far wider field of view, letting it map much larger areas of sky in a single image. One of its key goals is discovering exoplanets via gravitational microlensing, a technique barely used by Hubble or Webb. Launched on August 30, 2026, as NASA's newest major wide-field survey telescope. One of its main goals is mapping the nature of dark energy by observing supernovae and galaxy clusters.

Juno (space probe)

A solar-powered probe that skims just a few thousand km above Jupiter's cloud tops on every orbit to map the planet's interior and magnetic field. Launched on August 5, 2011, and entered orbit around Jupiter on July 4, 2016. It's the first solar-powered spacecraft to operate this far from the Sun, powered by three massive solar panels. Named after the Roman goddess Juno, who could see through the clouds Jupiter, her husband, used to hide his mischief. Its mission has been extended multiple times, and it continues actively gathering data on Jupiter and its moons. Its electronics are protected inside a radiation-hardened titanium vault, shielding them from Jupiter's intense radiation belts.

Galileo (space probe (NASA))

The first spacecraft to orbit an outer planet, Jupiter; it found evidence of a salty ocean beneath the icy crust of Europa. Launched on October 18, 1989 aboard space shuttle Atlantis (STS-34), it swung by Venus and twice by Earth to gain speed for Jupiter. On the way it became the first spacecraft to visit asteroids: Gaspra (1991) and Ida, where it discovered Dactyl, the first known moon of an asteroid. In 1994 it provided the only direct view of fragments of comet Shoemaker-Levy 9 striking the far side of Jupiter. It entered orbit around Jupiter on December 7, 1995; the same day its released atmospheric probe sent data from inside Jupiter's atmosphere for 58 minutes. Running low on propellant, it was deliberately plunged into Jupiter on September 21, 2003, so it could never contaminate Europa.

Cassini (space probe (NASA/ESA/ASI))

It studied Saturn, its rings and moons for thirteen years and delivered the Huygens lander to Titan. Launched on October 15, 1997, it gained speed from Venus (twice), Earth and Jupiter and entered orbit around Saturn on June 30, 2004. The European Huygens probe it carried descended to Titan on January 14, 2005: the first landing in the outer Solar System. It discovered water-ice geysers erupting from the south pole of Enceladus and mapped lakes and seas of hydrocarbons on Titan. In its final phase, the Grand Finale, it dived 22 times through the gap between the planet and its innermost ring. On September 15, 2017 it was deliberately steered into Saturn's atmosphere to avoid contaminating its potentially habitable moons.

Rosetta (comet probe (ESA, with NASA instruments))

The first spacecraft to orbit a comet, escorting 67P along its path around the Sun for two years. Launched on March 2, 2004, it flew past Earth three times and Mars once on a ten-year journey to its target. It arrived at comet 67P/Churyumov-Gerasimenko on August 6, 2014. Its Philae lander became the first craft to reach the surface of a comet nucleus, on November 12, 2014. It carried three NASA instruments: the Alice ultraviolet spectrometer, the MIRO microwave instrument and the IES ion and electron sensor. On September 30, 2016 it ended its mission with a controlled descent onto the comet, where it still rests on the nucleus.

Dawn (space probe (NASA, ion propulsion))

Thanks to its ion propulsion, the only spacecraft to have orbited two different bodies: asteroid Vesta and dwarf planet Ceres. Launched on September 27, 2007, it flew past Mars on February 17, 2009 on its way to the asteroid belt. It entered orbit around Vesta on July 15, 2011, the first probe to orbit an object in the main asteroid belt between Mars and Jupiter. It departed Vesta on September 4, 2012 and entered orbit around dwarf planet Ceres on March 6, 2015. In Ceres' Occator crater it found bright salt deposits, signs of briny water beneath the surface. Its mission ended on November 1, 2018 when it ran out of hydrazine; the silent spacecraft remains in a stable orbit around Ceres.

OSIRIS-REx (asteroid sample-return probe (NASA))

The first U.S. mission to return a sample from an asteroid: in 2020 it collected rocks and dust from the surface of Bennu. Launched on September 8, 2016, it arrived at asteroid Bennu in December 2018. On October 20, 2020 it briefly touched Bennu's surface and collected a sample (the TAG maneuver). It left for home in May 2021, and on September 24, 2023 its sample capsule landed at the Department of Defense's Utah Test and Training Range. After the capsule release, the spacecraft was renamed OSIRIS-APEX and sent to asteroid Apophis, which it will reach in 2029.

Pioneer 10 (space probe (NASA))

The first spacecraft to fly through the main asteroid belt and the first to visit Jupiter. Launched on March 2, 1972, it became the first spacecraft to cross the asteroid belt, between July 1972 and February 1973. On December 4, 1973 it passed within 130,354 km of Jupiter. It carries an aluminum plaque showing a man and a woman, the Solar System and the location of the Sun relative to 14 pulsars. It was the first spacecraft to use all-nuclear electrical power, from two SNAP-19 radioisotope generators. Its last signal was received on January 23, 2003 from 12.23 billion km away; it will pass near Aldebaran in about two million years.

Vesta (asteroid (4 Vesta))

The second most massive body in the asteroid belt; NASA's Dawn orbited it in 2011-2012. Discovered by Heinrich Wilhelm Olbers in 1807. The Rheasilvia basin at its south pole is nearly as wide as the asteroid itself, with one of the tallest mountains in the Solar System at its center. Some meteorites found on Earth (the HED meteorites) come from Vesta, debris of an ancient impact. Dawn orbited it from July 15, 2011 to September 4, 2012, the first orbit around a main-belt asteroid.

Bennu (near-Earth asteroid (101955 Bennu))

A carbon-rich rubble-pile asteroid; OSIRIS-REx sampled its surface in 2020 and brought the sample to Earth in 2023. Discovered in 1999 by the LINEAR sky survey, with the provisional designation 1999 RQ36. It is not a solid rock but a loose rubble pile held together by gravity, with a surprisingly boulder-strewn surface. OSIRIS-REx studied it from December 2018 to May 2021 and collected a sample on October 20, 2020. It is classed as a potentially hazardous asteroid: in the distant future (late 2100s) it has a small chance of hitting Earth.

International Space Station (space station)

Continuously inhabited for over 25 years. Its first module, Zarya, launched in 1998, and it has been built out since with participation from 15 countries. It's about the size of an American football field, and one of the brightest artificial objects visible to the naked eye from Earth. Orbiting at about 400 km altitude, it circles Earth roughly every 90 minutes - astronauts aboard see about 16 sunrises and sunsets a day. Its mass is about 420 tonnes, making it the largest human-made structure ever built in space. It is typically home to a crew of six to seven, conducting scientific experiments in microgravity.

Tiangong (space station)

Its name means “heavenly palace” (built since 2021). Its core module, Tianhe, launched in April 2021. China's first long-term, independently operated space station, after being excluded from the ISS for political reasons. It orbits somewhat lower than the ISS, at roughly 340-450 km altitude. It consists of three main modules: the Tianhe core module, plus the Wentian and Mengtian science labs. It is regularly crewed by three Chinese astronauts (taikonauts) on long-duration missions.

Curiosity (Mars rover)

The Mars Science Laboratory mission’s rover, still operating today - use the buttons above to switch between its "stowed" (travel) and "deployed" (driving) configuration. Launched on November 26, 2011, and landed on Mars on August 6, 2012, using a unique rocket-powered 'sky crane' maneuver. It's powered by a plutonium radioisotope generator (RTG) rather than solar panels, letting it operate at night and through dust storms. One of its key findings confirmed that Gale Crater once held a lake, in conditions suitable for microbial life. It's about the size of a small car, carrying laboratory-grade instruments for analyzing rock samples. Its wheels gradually wear down on Mars's rough terrain, so NASA uses careful route planning to minimize damage.

Perseverance (Mars rover)

Collects rock samples for a future sample-return mission to Earth - use the buttons above to switch between its "stowed" (travel) and "deployed" (driving) configuration. Launched on July 30, 2020, and landed in Jezero Crater on February 18, 2021. It carried the small helicopter Ingenuity, which achieved the first powered flight on another planet. It leaves sealed rock samples on the surface for a future Mars Sample Return mission, which could bring them to Earth sometime in the 2030s. It shares the same basic design as Curiosity but carries more advanced instruments and the sample-caching system. Its microphones made the first-ever audio recordings from the surface of Mars, capturing the sound of wind and its own wheels.

Ingenuity (Mars helicopter)

The first aircraft to make a powered, controlled flight on another planet. It landed attached to Perseverance’s belly on February 18, 2021, and was set down on the surface on April 3, 2021, after the rover drove about 4 meters away. Its first flight was on April 19, 2021; its 72nd and final flight was on January 18, 2024. It has a mass of 1.8 kg, and its rotors span about 1.2 meters tip to tip. In total it flew 128.8 minutes, covered 17.0 km and climbed as high as 24 meters. NASA announced the end of the mission on January 25, 2024; the helicopter remains in Jezero Crater.

InSight (Mars lander)

A geophysics lander that studied the deep interior of Mars; its mission ended in December 2022. It landed in western Elysium Planitia on November 26, 2018. Its landed mass was 360 kg; two solar arrays, each 2.2 meters in diameter, powered it, for a total span of about 6 meters. Its main instrument, the six-component SEIS seismometer, recorded marsquakes, while the RISE experiment used its radio link to study the planet’s rotation and interior. The self-hammering “mole” of the HP3 heat-flow probe reached only about 40 cm instead of the planned 5 meters or so. Its last transmission was received on December 15, 2022, and NASA declared the mission over on December 21.

Viking 1 (Mars lander)

The first lander of the Viking program, which worked on Chryse Planitia for more than six years. It touched down on Chryse Planitia on July 20, 1976, at 11:53 UT (22.27° N, 312.05° E). Transmission of the first surface image began 25 seconds after landing. Two plutonium-238 radioisotope thermoelectric generators (RTGs) powered it, each providing 30 W of continuous power. Its launch mass was 572 kg; its three footpads formed an equilateral triangle with 2.21 m sides. Contact with it was lost on November 13, 1982.

Viking 2 (Mars lander)

Viking 1’s twin, which operated on Utopia Planitia for 1281 Mars days. It touched down on Utopia Planitia on September 3, 1976, at 22:58 UT, about 200 km west of the crater Mie. One of its legs came to rest on a rock, leaving it tilted at 8.2 degrees. Its science payload had a mass of about 91 kg, and two 30 W RTGs powered it. Its batteries failed on April 11, 1980, ending the mission.

Apollo 11 (lunar module Eagle)

The first crewed Moon landing. The lunar module Eagle touched down on July 20, 1969 at 20:17 GMT (Sea of Tranquility), carrying Neil Armstrong and Buzz Aldrin. The two astronauts spent 21 h 36 min on the surface, 2 h 31 min of it outside the lunar module. They brought 21.6 kg of lunar rock and soil back to Earth. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Apollo 12 (lunar module Intrepid)

The second crewed Moon landing, a precision touchdown next to the Surveyor 3 probe. The lunar module Intrepid touched down on November 19, 1969 at 06:54 GMT (Ocean of Storms), carrying Charles Conrad and Alan Bean. The two astronauts spent 31 h 31 min on the surface, 7 h 45 min of it outside the lunar module. They brought 34.4 kg of lunar rock and soil back to Earth. The lunar module landed about 160 meters from Surveyor 3, which the two astronauts visited on foot. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Apollo 14 (lunar module Antares)

The lunar module that reached the Fra Mauro highlands, Apollo 13’s original target. The lunar module Antares touched down on February 5, 1971 at 09:18 GMT (Fra Mauro), carrying Alan Shepard and Edgar Mitchell. The two astronauts spent 33 h 30 min on the surface, 9 h 22 min of it outside the lunar module. They brought 42.3 kg of lunar rock and soil back to Earth. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Apollo 15 (lunar module Falcon)

The lunar module of the first Apollo mission with the Lunar Roving Vehicle. The lunar module Falcon touched down on July 30, 1971 at 22:16 GMT (Hadley-Apennine), carrying David Scott and James Irwin. The two astronauts spent 66 h 54 min on the surface, 18 h 34 min of it outside the lunar module. They brought 77.3 kg of lunar rock and soil back to Earth. On their moonwalks they covered about 28 km in total. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Apollo 16 (lunar module Orion)

The lunar module that landed in the Descartes Highlands, one of the Moon’s highland regions. The lunar module Orion touched down on April 21, 1972 at 02:23 GMT (Descartes Highlands), carrying John Young and Charles Duke. The two astronauts spent 71 h 2 min on the surface, 20 h 14 min of it outside the lunar module. They brought 95.7 kg of lunar rock and soil back to Earth. On their moonwalks they covered about 27 km in total. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Apollo 17 (lunar module Challenger)

The last crewed Moon landing, with the longest stay on the surface. The lunar module Challenger touched down on December 11, 1972 at 19:54 GMT (Taurus-Littrow valley), carrying Eugene Cernan and Harrison Schmitt. The two astronauts spent 74 h 59 min on the surface, 22 h 3 min of it outside the lunar module. They brought 110.5 kg of lunar rock and soil back to Earth. On their moonwalks they covered about 36 km in total. The ascent stage returned to the command module waiting in lunar orbit; the descent stage still stands at the landing site.

Hubble Space Telescope (space telescope)

In orbit since 1990, it is one of astronomy’s most influential instruments. Launched on April 24, 1990, aboard the Space Shuttle Discovery. Its first images were blurry due to a mirror flaw, corrected by a spacewalking repair mission in 1993. Five servicing missions, all by Space Shuttle, kept it running and upgraded, the last in 2009. Images like the Hubble Deep Field led to the first estimates that the observable Universe contains roughly 100-200 billion galaxies. It is named after American astronomer Edwin Hubble, who proved that the Universe is expanding. It orbits at about 340 km altitude, requiring periodic boosts via Space Shuttle missions or other means to maintain its orbit.

Terra (Earth observation satellite)

The flagship of NASA's Earth Observing System (EOS): it has watched the land, oceans and atmosphere since 1999. Launched on December 18, 1999. It is about the size of a small school bus: 6.8 m long, 3.5 m across, with a launch mass of 5,190 kg. It carries five instruments (ASTER, CERES, MISR, MODIS, MOPITT) that measure clouds, Earth's radiation budget, aerosols, vegetation and carbon monoxide. It flies a sun-synchronous polar orbit, about 14 orbits a day, originally crossing the equator at 10:30 a.m. local time. Since February 2020 it has been drifting to save fuel: its orbit slowly lowers, its equator crossing gets earlier, and in October 2022 it left the morning satellite constellation.

Aqua (Earth observation satellite)

Its name is Latin for water: it measures Earth's water cycle, from evaporation through clouds and precipitation to ice. Launched on May 4, 2002, it has worked for more than two decades instead of its planned six years. It launched with six instruments (AIRS, AMSU, CERES, MODIS, AMSR-E, HSB); four still work: HSB failed in 2003 and AMSR-E was powered off in 2016. For years it was part of the afternoon 'A-Train' constellation, crossing the equator around 1:30 p.m. local time. With its fuel nearly spent it is now in free drift: it is slowly sinking below the constellation, and its equator crossing keeps getting later.

Landsat 8 (Earth observation satellite)

Part of the Landsat program: it continues the longest continuous space-based record of Earth's land surface. Launched on February 11, 2013, aboard an Atlas V rocket. Its two instruments are OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor). It passes over the same spot every 16 days, completes about 14.5 orbits a day and crosses the equator at about 10:12 a.m. local time. A joint mission: NASA developed the spacecraft and launch, and USGS has operated the satellite since launch. The program began in the early 1970s, and Landsat 8 continues that record of more than four decades.

Landsat 9 (Earth observation satellite)

Landsat 8's near-identical twin: it flies the same orbit eight days out of phase, so together the two satellites revisit every spot on Earth's land surface every eight days instead of sixteen. Launched on September 27, 2021, aboard an Atlas V rocket from Vandenberg Space Force Base. Its design is nearly identical to Landsat 8 - the NASA 3D Resources collection has no separate Landsat 9 model, so the scene shows Landsat 8's model in its place. Its two instruments are OLI-2 and TIRS-2, upgraded, more precise versions of Landsat 8's OLI and TIRS. It flies the same sun-synchronous orbit as Landsat 8, offset by eight days - together the two satellites cover the whole Earth every eight days. A joint mission, like its predecessor: NASA developed the spacecraft and launch, and USGS operates the satellite. It succeeded Landsat 7 as the newest, currently active member of the program.

Chandra X-ray Observatory (X-ray space telescope)

One of NASA's Great Observatories: it watches the hottest, most energetic places in the Universe in X-rays, from the surroundings of black holes to supernova remnants. Launched on July 23, 1999, aboard Space Shuttle Columbia (STS-93). It flies a highly elliptical orbit, reaching about 140,000 km at its farthest, more than a third of the way to the Moon. Its mirrors are barrel-shaped rather than dishes: X-rays graze their atomically smooth surfaces at nearly parallel angles. It gives eight times sharper images and sees sources twenty times fainter than any earlier X-ray telescope. It is named after the Indian-American astrophysicist Subrahmanyan Chandrasekhar.

Suomi NPP (weather and climate satellite)

A joint NASA and NOAA satellite; the daily images from its VIIRS instrument also feed this globe's live cloud layer. Launched on October 28, 2011, as NPP, it was renamed in 2012 after meteorologist Verner E. Suomi, the 'father of satellite meteorology'. Its five instruments (VIIRS, CrIS, ATMS, OMPS, CERES) collect data for weather forecasting and long-term climate monitoring. It flies a sun-synchronous orbit at about 824 km, crossing the equator northbound at 1:30 p.m. local time. According to NASA its data products will cease on November 1, 2026, with NOAA-20 and NOAA-21 taking over.