97 Fun Facts About Planets

Which planet is nicknamed for its orange-red appearance?

The colour comes from iron oxide dust that coats much of the surface.

What is the largest planet in our solar system?

Jupiter is by far the largest planet in our solar system. It has a mass more than twice that of all the other planets combined and a diameter of about 142,984 km.

How many planets are in our solar system?

The IAU definition adopted in 2006 is what moved Pluto into the dwarf-planet category.

Which planet is closest to the Sun?

Mercury orbits at an average distance of about 58 million km from the Sun, making it the closest planet. Despite this, Venus is actually hotter due to its thick greenhouse atmosphere.

Which planet has the most extensive ring system in the Solar System?

The rings are mostly ice particles with a little rocky debris and dust.

What is the hottest planet in our solar system?

A crushing carbon dioxide atmosphere traps heat so well that Venus averages about 465°C (869°F) at the surface — hotter than Mercury, which sits closer to the Sun.

Which planet's rotation axis lies almost in the plane of its orbit, so it rolls around the Sun on its side?

Uranus's tilt is 97.77 or 82.23 degrees depending on which pole you call north, so each pole gets 42 years of continuous sunlight.

What is the smallest planet in our solar system?

Mercury is the smallest planet in our solar system with a diameter of about 4,880 km. Pluto, once considered the smallest planet, was reclassified as a dwarf planet in 2006.

Which planet is known as Earth's twin due to its similar size?

The resemblance ends at the surface, where a runaway greenhouse effect makes it the hottest planet.

Which planet has the Great Red Spot, a massive storm that has raged for centuries?

Jupiter's Great Red Spot is a persistent anticyclonic storm larger than Earth. It has been observed since at least 1831, and possibly since 1665, though it has been gradually shrinking in recent decades.

Which planet has the most moons in our solar system?

Saturn holds the record for most known moons with over 140 confirmed natural satellites as of 2023. New moons continue to be discovered.

What is the name of the largest moon in our solar system?

Ganymede, a moon of Jupiter, is the largest moon in our solar system with a diameter of 5,268 km. It is even larger than the planet Mercury and is the only moon known to have its own magnetic field.

In which year did the IAU demote Pluto to dwarf planet?

The IAU voted on 24 August 2006 in Prague to define 'planet' in a way that excluded Pluto; the American Dialect Society then made 'plutoed' its 2006 word of the year.

Which planet has the shortest day (fastest rotation) in our solar system?

Jupiter has the shortest day of any planet, rotating once in just under 10 hours (9 hours 56 minutes). Despite being the largest planet, its rapid spin causes a noticeable bulge at its equator.

Which planet spins backward (retrograde rotation) compared to most other planets?

Venus rotates in the opposite direction to most planets (retrograde rotation), meaning the Sun rises in the west and sets in the east. A day on Venus (243 Earth days) is actually longer than its year (225 Earth days).

What is the farthest planet from the Sun in our solar system?

Neptune is the farthest planet from the Sun at an average distance of about 4.5 billion km. Since Pluto was reclassified as a dwarf planet in 2006, Neptune holds this distinction.

Olympus Mons, roughly 2.5 times the height of Everest, is the tallest volcano on which planet?

It is roughly tied with Rheasilvia on the asteroid Vesta as the tallest mountain known in the Solar System.

Which moon of Saturn has a thick atmosphere and liquid methane lakes on its surface?

Titan is the only moon in our solar system with a dense atmosphere, which is primarily nitrogen with methane. The Cassini-Huygens mission revealed lakes and seas of liquid methane and ethane on its surface.

What are the four Galilean moons of Jupiter?

Io, Europa, Ganymede, Callisto are numbered I to IV outward from Jupiter; Galileo saw them in 1609–10, and no other Jovian moon was known until Amalthea in 1892.

Which planet has winds that can reach speeds of over 2,000 km/h, the fastest in the solar system?

Neptune has the fastest winds in the solar system, with speeds exceeding 2,000 km/h (1,200 mph). This is remarkable given how far Neptune is from the Sun and how little solar energy it receives.

Which is the most massive known dwarf planet in the Solar System?

Pluto is slightly larger by diameter, but Eris outweighs it; it is also the largest known object never visited by a spacecraft.

Which NASA rover landed on Mars in February 2021?

Perseverance touched down in Jezero Crater, an ancient lake-delta site, on February 18, 2021, to drill and cache rock cores for a future Mars sample-return mission.

What is the name of the asteroid belt's only dwarf planet?

Ceres is the only dwarf planet located in the asteroid belt between Mars and Jupiter. With a diameter of about 940 km, it is also the largest object in the asteroid belt, containing about a third of the belt's total mass.

Which moon of Jupiter is considered the likeliest home for life elsewhere in our solar system?

Europa's smooth young surface points to a water ocean beneath the ice; sea salt on the surface suggests that ocean touches a rocky sea floor.

What is the densest planet in our solar system?

Earth averages 5.51 g/cm³ thanks to an iron-nickel core that makes up about a third of its mass.

Which planet did Urbain Le Verrier discover by calculation before it was observed?

Neptune was predicted mathematically by Urbain Le Verrier in 1846 based on irregularities in Uranus's orbit. Johann Galle then observed it at the Berlin Observatory within 1 degree of Le Verrier's predicted position.

What is the main component of Jupiter's atmosphere?

By mass the split is nearer 76% hydrogen and 24% helium, close to the composition of the Sun.

Which planet has the longest year (orbital period) in our solar system?

Neptune has the longest orbital period of any planet, taking about 165 Earth years to complete one orbit around the Sun. It only completed its first full orbit since discovery in 2011.

What feature on Mars is the largest canyon system in the solar system?

Valles Marineris stretches over 4,000 km along the Martian equator, reaching depths of up to 7 km. It is roughly 10 times longer and 5 times deeper than the Grand Canyon on Earth.

Which spacecraft flew past both Uranus and Neptune?

Voyager 2, launched in August 1977, flew past Uranus in January 1986 and Neptune in August 1989; no other spacecraft has visited either ice giant.

What phenomenon causes Io, Jupiter's moon, to be the most volcanically active body in the solar system?

Tidal heating: Jupiter's gravity and Io's orbital resonance with Europa and Ganymede flex the moon's interior continuously, generating the heat that powers more than 400 active volcanoes.

How long does it take light from the Sun to reach Earth?

Light from the Sun takes about 8 minutes and 20 seconds to reach Earth, traveling at approximately 299,792 km/s across the roughly 150 million km distance between the two.

Which planet has a hexagonal storm pattern at its north pole?

David Godfrey spotted it in 1987 by piecing together Voyager fly-by images from 1981; Cassini revisited it in 2006.

How long is a Mercury year — one lap of the Sun?

A Mercury year is 88 Earth days, the shortest orbital period of any planet, because Mercury circles the Sun at about 47 km/s on the innermost orbit.

Which planet is classed as an ice giant rather than a gas giant?

Neptune is the other one; both hold only a few Earth masses of nebular gas around icy interiors.

Which moon of Saturn shoots geysers of water ice into space from its south pole?

Enceladus vents plumes of water ice and vapour from 'tiger stripe' fractures near its south pole; the jets carry roughly 200 kg of material a second and feed Saturn's E ring.

What makes Neptune appear blue?

Rayleigh scattering contributes too, which is why the option about scattering alone is only half the story.

How many Earth-sized planets could fit inside Jupiter?

About 1,300: Jupiter's volume is roughly 1,321 times Earth's, since its equatorial diameter of about 143,000 km is eleven times Earth's, though its mass is only 318 Earths.

Which planet has the longest day (slowest rotation)?

Its day outlasts its 224.7-day year, and because it spins backwards a solar day is only about 116 Earth days.

What is the Great Dark Spot?

Voyager 2 saw the first one in 1989, and Hubble has since shown Neptune spends more than half its time with one.

Which planet has two small moons named Phobos and Deimos?

They may be captured asteroids or fragments of an older moon shattered by an impact.

What is the Roche limit?

The Roche limit is the distance within which tides tear a moon apart: inside it a planet's tidal pull exceeds the moon's self-gravity, so material spreads into rings rather than coalescing.

Which planet was the first to be discovered using a telescope?

Herschel spotted it from his garden in Bath on 13 March 1781 and at first reported it as a comet.

What is the Kuiper Belt?

The Kuiper Belt is a disc of icy bodies beyond Neptune, stretching from about 30 to 50 AU from the Sun; Pluto is its best-known member and Neptune's moon Triton may have come from it.

Which NASA spacecraft radar-mapped about 98% of Venus's surface in the early 1990s?

Magellan orbited Venus from 1990 to 1994 and used synthetic-aperture radar to map about 98% of the surface through the clouds, revealing volcanoes, vast lava plains and few impact craters.

Which planet has the strongest magnetic field in the Solar System?

It is generated by eddy currents in the fluid metallic-hydrogen interior, and its magnetosphere is the second-largest contiguous structure in the Solar System.

What is the largest impact basin on Mercury called?

Caloris Basin, about 1,550 km across, is Mercury's largest impact basin; the impact was so violent that seismic waves converged on the opposite side of the planet, leaving the jumbled 'weird terrain' there.

In which direction does Triton, Neptune's largest moon, orbit its planet?

Retrograde, against the host's spin, makes Triton the only large moon in the Solar System to orbit that way, which suggests it was captured from the Kuiper belt.

Jupiter's mass is roughly how many times the mass of all the other planets combined?

About 2.5 times: Jupiter's 318 Earth masses outweigh the other seven planets' combined total of roughly 128 Earth masses, yet Jupiter is less than a thousandth of the Sun's mass.

In which year did William Herschel first observe Uranus and report it as a comet?

Herschel spotted Uranus on 13 March 1781 from the garden of his house in Bath, England; it took months of orbit calculations before astronomers accepted it was a planet, not a comet.

What name did Herschel propose for the planet he had discovered?

Herschel named it Georgium Sidus ('George's Star') after his patron George III; the name lingered in Britain until HM Nautical Almanac Office finally switched to Uranus in 1850.

The lowest temperature recorded in Uranus's tropopause is roughly how cold?

About 49 K (−224 °C), colder than anything measured on Neptune despite Uranus orbiting closer to the Sun; Uranus radiates unusually little internal heat.

Which is the largest moon of Uranus?

Titania, about 1,578 km across, is the largest moon of Uranus and the eighth-largest in the Solar System; Herschel discovered it and Oberon on the same day in 1787.

Verona Rupes, possibly the tallest cliff in the Solar System, is on which moon of Uranus?

Verona Rupes is on Miranda, the innermost of Uranus's five major moons; the scarp may be about 20 km high, and in Miranda's feeble gravity a dropped rock would take several minutes to reach the bottom.

Uranus's moons are named after characters from Shakespeare and which poet?

Alexander Pope: Ariel and Umbriel take their names from his poem The Rape of the Lock. John Herschel began the Shakespeare-and-Pope naming tradition in 1852, breaking with Greek and Roman mythology.

Which was the first spacecraft to visit Mercury, flying past it in the mid-1970s?

Mariner 10 flew past Mercury three times in 1974–75; it was also the first probe to visit two planets, using a Venus gravity assist and steering partly with sunlight pressure on its solar panels.

In which year did MESSENGER become the first spacecraft to orbit Mercury?

MESSENGER entered Mercury orbit on 18 March 2011 after six planetary flybys — one of Earth, two of Venus, three of Mercury — to shed the speed a probe gains falling sunward.

The BepiColombo mission to Mercury is a joint project of ESA and which agency?

JAXA, Japan's space agency: BepiColombo carries two orbiters stacked together — ESA's Mercury Planetary Orbiter and JAXA's Mio magnetospheric orbiter — which separate on arrival at Mercury.

How many rotations does Mercury complete during two orbits of the Sun?

Three: Mercury's 3:2 spin-orbit resonance means it rotates three times for every two orbits. Radar measurements in 1965 proved it; earlier astronomers assumed Mercury kept one face toward the Sun.

How long is a solar day on Mercury, from one sunrise to the next?

A single sunrise-to-sunrise cycle lasts two full Mercury years, because the planet's slow spin and fast orbit nearly cancel each other out.

Craters on Mercury are named after what kind of people?

Mercury's craters honour artists, musicians and authors — hence Beethoven, Tolkien and Disney. IAU rules require the honouree to have been famous for more than fifty years and dead for at least three.

Venus's planet-wide cloud layer is made mostly of what?

Venus's clouds are droplets of concentrated sulfuric acid; they evaporate in the scorching lower atmosphere before reaching the ground, and any floating habitat would have to resist their corrosion.

Surface air pressure on Venus is roughly how many times that of Earth at sea level?

At 92 times Earth's pressure, standing on Venus is like being about 900 metres underwater; the crushing pressure destroyed the early Soviet landers within an hour or two.

In which year did Venera 7 make the first successful soft landing on another planet?

Venera 7 landed on Venus on 15 December 1970 and survived about 23 minutes on the surface, long enough to send back the first data ever transmitted from another planet's surface.

What is the highest mountain on Venus, rising about 11 km above the mean surface?

Maxwell Montes rises about 11 km on the northern highland Ishtar Terra; it is named for James Clerk Maxwell, whose physics made radar, and thus the mapping of Venus, possible.

Venus's northern highland, Ishtar Terra, is about the size of which landmass?

Ishtar Terra is about the size of Australia; the larger southern highland, Aphrodite Terra, is closer to South America in extent. Both are named for goddesses of love.

What is the largest clearly exposed impact basin on Mars, about 2,300 km across?

Hellas Planitia, about 2,300 km across and more than 7 km deep, is Mars's largest unambiguous impact basin; air pressure on its floor is high enough for liquid water to exist briefly.

In which year did Viking 1 make the first successful landing on Mars?

Viking 1 touched down on July 20, 1976 — seven years to the day after Apollo 11 landed on the Moon — and kept working on the surface for more than six years.

What was the first wheeled vehicle to operate on a world other than Earth or the Moon?

Sojourner, a microwave-oven-sized rover, arrived with Mars Pathfinder in July 1997 and worked for about 83 sols, far beyond its planned seven-day mission.

NASA's Curiosity rover landed in 2012 inside which Martian crater?

Gale Crater: Curiosity was lowered to its floor on a tether by a rocket-powered 'sky crane' in August 2012. The crater holds Mount Sharp, a 5 km mountain of layered sediment.

What did NASA's Ingenuity achieve on Mars in April 2021?

Ingenuity made the first powered, controlled flight on another planet on 19 April 2021, spinning its blades at over 2,400 rpm to get lift in air about 1% as dense as Earth's; it went on to fly 72 times.

Which 1965 mission returned the first close-up pictures of the Martian surface?

Mariner 4 flew past Mars on 15 July 1965; its 22 grainy images showed a cratered, seemingly dead world and deflated hopes of finding canals or vegetation.

A Martian solar day, called a sol, lasts about how long?

Only about 2.75% longer than Earth's day. Rover teams on Earth who work on 'Mars time' drift 40 minutes later every day.

Seen from the surface of Mars, Phobos does what that no moon does on Earth?

Phobos rises in the west and sets in the east because it orbits faster than Mars rotates, circling in just 7 hours 39 minutes — it crosses the sky 'backwards' about twice each sol.

Which year did Juno enter a polar orbit around Jupiter?

Juno found that Jupiter's core is diffuse, mixing into the mantle for 30–50% of the planet's radius, and it measured the Great Red Spot as 300–500 km deep.

Which spacecraft was the first to orbit an outer planet, arriving at Jupiter in 1995?

Galileo entered orbit around Jupiter in December 1995, the first spacecraft to orbit an outer planet; it dropped a probe into Jupiter's atmosphere on arrival and spent eight years studying the Galilean moons.

In which year did Comet Shoemaker–Levy 9 crash into Jupiter?

In July 1994 more than 20 fragments of Shoemaker–Levy 9 struck Jupiter — the first collision between Solar System bodies ever observed directly — leaving dark scars in the clouds larger than Earth.

Which probe was the first to cross the asteroid belt and reach Jupiter?

Pioneer 10, launched in March 1972, was the first probe through the asteroid belt and passed Jupiter in December 1973; it carries a plaque showing a man, a woman and Earth's location.

Which moon of Jupiter has the oldest and most heavily cratered surface in the Solar System?

Unlike its neighbour Io, it sits far enough from Jupiter to escape strong tidal heating, so its icy crust has barely changed in four billion years.

Jupiter's faint ring system was discovered in 1979 by which spacecraft?

Voyager 1 photographed Jupiter's faint rings in March 1979. They are made of dust knocked off small inner moons by meteoroid impacts, not ice like Saturn's, which is why they are so dark.

Saturn is the only planet less dense than what?

Its mean density is about 30% below that of water, so in a big enough bathtub it would float, though it still has 95 times Earth's mass.

Which moon of Saturn bears the giant crater Herschel, giving it a Death Star look?

Mimas: the crater Herschel is 139 km wide, about a third of the moon's 396 km diameter, and an impact much bigger would have shattered Mimas entirely.

Which moon of Saturn has one dark hemisphere and one bright one?

Iapetus: Giovanni Cassini deduced its two-tone surface in the 1670s because the moon vanished from view on one side of Saturn. It also has a ridge running along its equator.

The Cassini Division, the largest gap in Saturn's rings, separates which two rings?

The Cassini Division separates the A and B rings; Giovanni Cassini spotted the gap in 1675. Rings are lettered in order of discovery, so the main rings run C, B, A outward from Saturn.

Which probe was the first to reach Saturn, flying past it in 1979?

Pioneer 11 flew past Saturn in September 1979, discovering the F ring and a small new moon; its flight path tested whether later probes could safely pass through the ring plane.

How did NASA end the Cassini mission on September 15, 2017?

Cassini was deliberately plunged into Saturn's atmosphere and burned up, protecting potentially habitable moons like Enceladus and Titan from contamination by any microbes on board.

Which sponge-looking moon of Saturn tumbles chaotically, so its rotation is unpredictable?

Hyperion's deep, sharp-edged craters and very low density suggest it is a loose rubble pile that is roughly half empty space, and its irregular shape and Titan's tugs make its spin chaotic.

Triton was found by William Lassell how soon after Neptune itself was discovered?

Just 17 days: Neptune was found on 23 September 1846 and Lassell, a brewer turned astronomer using a telescope he built himself, spotted Triton on 10 October. Neptune's next moon, Nereid, waited until 1949.

In which year did New Horizons fly past Pluto, the first spacecraft ever to do so?

New Horizons flew past Pluto on 14 July 2015, passing about 12,500 km above the surface after a nine-year journey, then went on to fly by the Kuiper belt object Arrokoth on New Year's Day 2019.

What is Pluto's largest moon, with a diameter just over half of Pluto's own?

Charon, about 1,212 km across, is so large that the pair's centre of mass lies outside Pluto, earning them the label 'double dwarf planet'; its 1978 discovery let astronomers finally weigh Pluto.

Who discovered Pluto at Lowell Observatory in 1930?

Clyde Tombaugh, a young Kansas farm boy hired after sending Lowell Observatory his amateur drawings, spotted Pluto on photographic plates in February 1930. Some of his ashes travel aboard New Horizons.

Pluto's largest bright surface feature is nicknamed for what shape?

Its western lobe, Sputnik Planitia, is a 1,000 km basin of slowly churning nitrogen ice. A nearby dark region is nicknamed 'the Whale'.

Which elongated dwarf planet was found in 2017 to have its own ring system?

Haumea spins so fast, once every four hours, that it is stretched into an egg shape about twice as long as it is wide; its ring, found by stellar occultation in 2017, was the first around a trans-Neptunian object.

Which was the first exoplanet found orbiting a Sun-like star, in 1995?

51 Pegasi b is a 'hot Jupiter' racing around its star every four days; its discoverers, Michel Mayor and Didier Queloz, shared the 2019 Nobel Prize in Physics.

How many known planets, all roughly Earth-sized, orbit the red dwarf star TRAPPIST-1?

Seven roughly Earth-sized planets are packed so tightly that each completes an orbit in between 1.5 and 19 days; the star is barely larger than Jupiter.

After the 2012 event, when is the next transit of Venus across the Sun?

The next transit of Venus is in December 2117: transits come in pairs eight years apart, separated by gaps of more than a century. Edmond Halley proposed using them to measure the Solar System's scale.

In the leading theory of the Moon's origin, what is the Mars-sized impactor called?

Theia is named for the Greek Titan who was mother of the Moon goddess Selene; Canadian geologist Reginald Daly first floated the giant-impact idea in 1946, and Hartmann and Davis developed it in 1975.