60 Fun Facts About Comets

What are comet nuclei mostly made of?

Fred Whipple's 1950 dirty snowball model was later refined to icy dirtball after Deep Impact.

What is the huge, thin atmosphere that surrounds a comet's nucleus called?

It can grow up to 15 times Earth's diameter, and mostly consists of water and dust.

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

Radiation pressure and the solar wind push the tail outward whether the comet is approaching or leaving.

What is the release of gases from a comet as it warms near the Sun called?

It produces the coma and, sometimes, the tail.

The name comet comes from a Greek term meaning what?

The Greeks called it the long-haired star.

Where do short-period comets originate?

Long-period comets are thought to come from the far more distant, spherical Oort cloud.

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

Jan Oort revived the idea in 1950 to resolve a paradox about where comets come from.

Roughly how many comet-like bodies are thought to sit in the Oort cloud?

Only 4,584 comets were actually known as of November 2021.

Bodies with orbital periods under 200 years are known as what kind of comet?

Their aphelia usually lie out among the giant planets; Halley's is just beyond Neptune.

Traditional Jupiter-family comets have orbital periods of less than how many years?

They also have low inclinations to the ecliptic, up to 30 degrees; Halley-type comets run 20 to 200 years.

Roughly what fraction of long-period comets are ejected from the Solar System on their first pass by the Sun?

The planets' gravity does the flinging.

Which was the first detected interstellar comet, found by a Crimean amateur in 2019?

ʻOumuamua showed no optical cometary activity; Borisov clearly had a coma.

How reflective did Giotto find the nucleus of Halley's Comet to be?

That makes comet nuclei darker than asphalt, which reflects seven percent.

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

The samples came from the coma of Comet Wild 2 and landed on Earth in 2006.

Comet 17P/Holmes briefly grew a coma larger than what after an outburst in 2007?

The Great Comet of 1811 also had a coma roughly the diameter of the Sun.

What surprising radiation were comets found to emit in 1996?

They come from charge exchange when solar wind ions steal electrons from cometary atoms.

Which meteor shower, peaking around 9 to 13 August, is debris from Comet Swift-Tuttle?

Earth crosses the trail of dust the comet left behind.

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 over six days in July 1994?

It was the first collision between two Solar System objects ever observed.

At roughly what speed did the fragments of the 1994 comet hit Jupiter?

That is Jupiter's escape velocity, about 216,000 kilometres per hour.

Which ancient philosopher argued that comets were atmospheric phenomena?

Seneca the Younger questioned his logic in the 1st century CE.

In Giotto's 1301 Adoration of the Magi, the first accurate painting of a comet, what does the comet stand in for?

ESA later named its Halley probe after the painter.

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

He and Michael Maestlin found the comet must be at least four times farther than the Moon.

Newton used which year's great comet in the Principia to show how to fit a parabolic orbit?

The Great Comet of 1680, also called Kirch's Comet, was the first discovered by telescope.

Which three earlier apparitions did Halley identify in 1705 as one returning comet?

He predicted its return in 1758-59, and it duly appeared.

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

Nicole-Reine Lepaute was one of the few women doing such calculations at the time.

About how often does Halley's Comet return?

The period varies between 72 and 80 years; the next apparition is in mid-2061.

Halley's Comet appears on which famous embroidery, described in its captions as a star?

It records the comet's 1066 apparition before the Battle of Hastings.

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?

He had predicted he would go out with the comet.

Who proposed the dirty snowball model of comets in 1950?

The model was supported by the spacecraft armada that flew through Halley's coma in 1986.

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

It surprisingly survived being hit by small particles.

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

They flew through the coma, photographed the nucleus and saw jets of evaporating material.

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

Its Philae lander touched down on 12 November 2014.

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

The mother ship found the nucleus has no magnetic field.

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

The results suggested most of a comet's water ice lies below the surface and feeds the jets.

A 2001 flyby found the surface of Comet Borrelly to be how hot?

The dark, dry surface suggested the ice had been driven off or hidden under soot-like material.

For how long was Comet Hale-Bopp visible to the naked eye, a record?

That was twice as long as the previous record holder, the Great Comet of 1811.

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

The group believed a spacecraft trailing the comet would carry them to salvation.

Which 1996 comet is known to have had the longest tail ever recorded, at least 570 million kilometres?

The Ulysses spacecraft crossed the tail far from the nucleus.

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

It gives its name to the Encke-type class whose orbits never reach Jupiter.

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

Early predictions suggested it could be among the brightest of the 20th century.

The Kreutz sungrazers are thought to be fragments of what?

They are named after Heinrich Kreutz, who first showed they were related.

Comet NEOWISE in 2020 was the brightest comet in the northern hemisphere since which comet?

It was discovered by the NEOWISE space telescope.

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

C/ marks single-apparition comets and I/ interstellar objects such as 2I/Borisov.

Roughly how many comets per year are visible to the naked eye?

Many of those are faint and unspectacular; the bright ones are called great comets.

What are Manx comets?

Twenty-seven were found between 2013 and 2017, named for the tailless cat.

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

Possible interstellar dust particles were identified in the capsule in 2014.

The great comet of which year was visible to the naked eye for around 260 days, a record until 1997?

Its coma was roughly the diameter of the Sun.

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

Near the end of his life he linked the great comet of 1769 to the birth of Napoleon.

Who is often credited as the first woman to discover a comet, though Maria Kirch preceded her?

Kirch's early-1700s discovery was attributed to her husband Gottfried.

Which single-apparition comet acquired the largest known eccentricity, 1.057, after an encounter with Jupiter?

Its orbital period had been about 7.1 million years before Jupiter flung it out.

A comet's dust tail contains particles roughly the size of what?

Radiation pressure pushes them into a gentle arc, while pebble-sized particles stay on the comet's orbit.

Which spacecraft in 2001 imaged the surface of Comet Borrelly and found it reflects less than 3 percent of light?

That makes it one of the least reflective objects in the Solar System.

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.

Per an 18th-century embellishment, which pope supposedly 'excommunicated' Halley's Comet in 1456?

He really did order prayers for Belgrade against the Ottoman siege; the excommunication tale was likely a French anti-Church invention.

In which year is Halley's Comet next due to reach perihelion?

It should shine at about magnitude -0.3, far brighter than the +2.1 of the poorly placed 1986 pass, with closest approach a day after perihelion.

In 2010, sublimation of what frozen substance was found to power jets from a comet nucleus?

Infrared images of Hartley 2 caught such carbon-dioxide jets carrying dust into the coma; jets can even spin or split a nucleus.