54 Fun Facts About Comets

What are comet nuclei mostly made of?

Ice and dust: comets have been called 'dirty snowballs', but later observations suggested 'icy dirtballs' fits them better.

Why did the Philae lander soon fall silent after touching down on a comet in 2014?

It came to rest in shadow: its harpoons failed, so it bounced into a shaded spot where its solar panels got too little light, though it woke again in June 2015.

In which direction does a comet's ion tail point?

Directly away from the Sun: sunlight ionises the gas and the solar wind sweeps it outward, while the separate dust tail curves.

Which process builds a comet's coma as sunlight warms it?

Outgassing: the material it frees streams out from the comet and forms its tails.

The name comet comes from a Greek term meaning what?

The Greeks called it the long-haired star.

Where do most short-period comets originate?

The Kuiper belt and scattered disc lie beyond Neptune, where the gravity of the giant planets nudges icy bodies inward to become short-period comets.

The Oort cloud is named after an astronomer from which country?

Jan Oort of the Netherlands proposed the cloud in the 1950s as the distant reservoir that keeps sending long-period comets toward the Sun.

Many Romans believed the comet that shone over Rome in 44 BC was whose soul?

Julius Caesar's statues were given a star on the head, because Romans took the comet seen during games Augustus held in his honour as Caesar's soul.

In which 2021 Netflix satire do two astronomers struggle to warn the world about a planet-killing comet?

Don't Look Up used its comet as an allegory for climate change, mocking how politicians and the media shrug off scientists' warnings.

In 2014, NASA spacecraft took shelter behind which planet as Comet Siding Spring's dust swept past?

Mars passed through the comet's dust for hours, so NASA parked its Mars orbiters on the planet's far side at the riskiest moment, then used them to study the flyby.

Which Sun-watching spacecraft, launched in 1995, had discovered its 5,000th comet by 2024?

SOHO mostly spots sungrazers, and most of its comets, including the 5,000th, were found by volunteer citizen scientists combing its images.

Which was the first detected interstellar comet, spotted in 2019?

2I/Borisov was spotted by Crimean amateur astronomer Gennadiy Borisov, and astronomers worldwide then confirmed its path came from interstellar space.

After comets appeared, which Roman emperor reportedly had prominent nobles executed to deflect the omen from himself?

Nero took comets as omens that a ruler would fall, and reportedly deflected them by executing prominent nobles.

Which amino acid was confirmed in 2009 in comet dust returned to Earth by a NASA sample-return mission?

Glycine could have come from handling the spacecraft, so scientists checked its carbon isotopes, which showed it formed in space rather than on Earth.

What surprising radiation were comets found to emit in 1996?

X-rays arise when solar wind ions steal electrons from a comet's gas, a surprise because comets were thought far too cold for such energetic emission.

Which August meteor shower is debris from Comet Swift-Tuttle?

The Perseids seem to streak out of the constellation Perseus, which gives them their name, as Earth ploughs through the comet's dust each August.

The Andromedid meteor shower is the remains of which body, which split in two in 1846 and was never seen after 1852?

Spectacular showers appeared in 1872 and 1885 when the comet should have returned.

Which comet broke apart and crashed into Jupiter in July 1994?

Comet Shoemaker-Levy 9 had been torn apart on a close pass of Jupiter in July 1992, so it struck the planet as a string of separate fragments.

Which ancient philosopher argued that comets were atmospheric phenomena?

Aristotle reasoned that comets could not be planets because many appear outside the zodiac, so he placed them in the upper atmosphere.

Giotto saw a comet, probably Halley's, in 1301 and painted it in Padua as which biblical sign?

The Star of Bethlehem in Giotto's Adoration of the Magi takes the shape of a comet, and ESA later named its 1986 Halley's Comet probe Giotto in his honour.

Who used the parallax of the Great Comet of 1577 to show comets lie beyond Earth's atmosphere?

Tycho Brahe's measurements placed the comet beyond the Moon, which showed that the heavens were not unchanging after all.

Edmond Halley used whose theories to show that three comet sightings were one returning comet?

Isaac Newton's theory of gravitation let Halley compute comet orbits, even allowing for Jupiter's pull on the comet's path.

Which three French mathematicians refined the predicted return date of Halley's Comet?

Clairaut, Lalande and Lepaute spent six months calculating from morning to night, and the comet reached perihelion on 13 March 1759, a month before their mid-April forecast.

About how often does Halley's Comet return?

Every 76 years is only an average, because the pull of Jupiter and Saturn delays or hastens each return.

Which famous medieval tapestry shows Halley's Comet as a sign in the sky?

The Bayeux Tapestry shows the comet of 1066, which some took as an omen, shortly before William the Conqueror invaded England.

Which toxic gas found in Halley's tail in 1910 caused panic buying of gas masks and anti-comet pills?

By then most scholars had long since dismissed comets as omens.

Which writer was born two weeks after Halley's 1835 perihelion and died the day after its 1910 return?

Mark Twain said in 1909 that he had come in with Halley's Comet and expected to go out with it, and his prediction came true.

Who proposed the dirty snowball model of comets in 1950?

Fred Whipple also invented the Whipple shield, a thin outer metal skin that shatters incoming particles before they can damage a spacecraft.

How close did ESA's Giotto probe pass to Halley's nucleus in March 1986?

About 600 km was close enough that planners feared dust would destroy Giotto, and a large particle did knock it off balance seconds before closest approach.

Which two Soviet probes joined Giotto in the Halley Armada of 1986?

Vega 1 and 2 first dropped landers and balloons at Venus, then swung on to fly past Halley's Comet.

Which spacecraft became the first to land a robotic probe on a comet?

Rosetta slept in hibernation on the far leg of its ten-year chase, woke in January 2014, and dropped its Philae lander that November.

On which comet did the Philae lander touch down in 2014?

After Philae, its mother ship ended the mission in 2016 by deliberately descending onto 67P/Churyumov-Gerasimenko, studying the comet all the way down.

Into which comet did NASA's Deep Impact fire an impactor on 4 July 2005?

Tempel 1 took the hit on its sunlit side, and the impact blasted a huge cloud of fine, powdery material out from beneath the comet's surface.

Which sungrazing comet was torn to pieces as it neared the Sun in late November 2013?

ISON, a newcomer from the Oort cloud, was shredded by the Sun's heat just before its closest approach.

For how long was Comet Hale-Bopp visible to the naked eye in 1996 and 1997?

18 months of naked-eye visibility came from Hale-Bopp's unusually huge nucleus, about 60 km across.

Which cult carried out a mass suicide of 39 members in 1997 timed to Hale-Bopp's closest approach?

Heaven's Gate members believed a UFO was hiding behind the comet and that leaving their bodies would let them board it.

Which 1996 comet's tail did the Ulysses spacecraft fly through, far from the comet itself?

Hyakutake's tail reached so far that Ulysses, a solar probe not built to study comets, crossed it by chance in 1996.

Which bright comet has the shortest known orbital period, about 3.3 years?

Encke keeps shedding dust along its short orbit, and Earth's passage through that debris produces the Taurid meteor showers each autumn.

Which 1973 comet was hyped as the Comet of the Century but disappointed the public?

Kohoutek was forecast to be visible in daylight but ended far fainter than predicted, and the best views of it went to astronauts aboard Skylab.

The Kreutz sungrazers are thought to be fragments of what?

One large comet that broke up centuries ago would explain why the Kreutz comets all follow almost the same orbit.

Which comet, found in 2020 by a NASA space telescope hunting asteroids, was the brightest in northern skies in over 20 years?

NEOWISE was found by a space telescope that NASA had put into hibernation in 2011 and then brought back to life in 2013.

Under the IAU's 1995 naming scheme, what does the prefix P/ denote?

A periodic comet keeps coming back, which is why Halley's Comet, the first known to return, carries the designation 1P/Halley.

What most likely gave 2023's 'green comet' ZTF the green glow around its head?

Diatomic carbon molecules likely lit up ZTF's head, and a burst of solar wind appears to have torn off part of its tail.

What are Manx comets?

Long-period bodies with asteroid-like traits, like the tailless C/2014 S3, may be rocky leftovers from where Earth formed, kept in cold storage in the Oort cloud.

Which spacecraft returned samples from the coma of Comet Wild 2 to Earth in 2006?

Stardust trapped the comet's particles in aerogel, an ultralight material built to catch them as they struck, then brought them back to Earth.

The Great Comet of 1811 streaks across the sky in which Tolstoy novel?

War and Peace has Pierre gaze at the comet that people said foretold woes and the end of the world, yet it fills him with hope instead.

Which 18th-century comet hunter compiled his famous catalogue of nebulae so they would not be mistaken for comets?

Charles Messier started the catalogue after a fuzzy patch he found in 1758, while hunting comets, first fooled him into thinking it was one.

Which astronomer discovered eight comets between 1786 and 1797 while working alongside her brother?

Caroline Herschel began as her brother William's housekeeper and singer, then became his astronomy assistant before hunting comets in her own right.

Which NASA probe photographed the nucleus of Comet Borrelly during a 2001 flyby?

Deep Space 1 was really a test flight for new technology such as ion engines, and it visited Borrelly only as a bonus during an extended mission.

The first exocomet system beyond the Solar System was detected in 1987 around which young star?

Eleven such systems were known by 2013, and in 2018 citizen scientists spotted the first transiting exocomets in Kepler light curves.

In 1711 William Whiston blamed the Great Comet of 1680 for which biblical event?

He gave the comet a 574-year period and claimed it poured water onto Earth, reviving cometary fear as a direct physical threat for another century.

The first certain record of Halley's Comet, from 240 BC, appears in which Chinese chronicle?

The 164 BC apparition survives only on two Babylonian tablets rediscovered in the British Museum in 1984.

Which pope, alarmed by a comet in 1456, reportedly ordered prayers that any coming evil fall on the Turks?

Callixtus III also had a bell rung around noon each day to call Christians to prayer while the Ottomans besieged Belgrade.

In 2010, a NASA flyby found jets on Comet Hartley 2 powered by which frozen substance?

Dry ice, frozen carbon dioxide, turned straight to gas on Hartley 2, and its jets hurled out fluffy chunks of ice and dust.