What do we expect to find in the asteroid belt between Mars and Jupiter? The correct answer, and one that wouldn’t surprise anyone, would be: asteroids—millions of pieces of rocky debris. Recently, however, astronomers have identified some odd objects hidden among the debris, apparently lost: comets.
Now, as disclosed on the last day 7 in a study published in the Monthly Notices of the Royal Astronomical Society, research that sought to locate these heterodox objects may have found another icy individual spewing its own matter into space.
Scientists identified the suspected comet with the wide-angle camera of the Isaac Newton telescope in La Palma, Canary Islands. During three observing sessions between 2018 and 2020, they observed 534 different asteroids, looking for signs of a comet’s coma — the ephemeral gaseous cloud that coats it — or a tail formed by a comet’s dust being pushed by radiation from the Sun.
Conventionally, comets are composed of a nucleus — a solid core made up of various ices and dust. When a comet approaches the Sun, its most volatile gases convert to vapour, creating a coma and two types of tail.
It is believed that comets came from the outskirts of the solar system and further afield. Unlike their icy “cousins” that often reside in the icy outer reaches of our star system, the asteroid belt or main belt, comets reside at the hottest edge of the inner solar system. These comets are as old as neighboring asteroids, which is why their frozen matter is an enigma.
“We need to be able to explain how their ice has survived for so long,” said Léa Ferellec, a graduate student in astronomy at the University of Edinburgh and an author of the study.
Solving this mystery will help explain not only planetary diversity and the layout of the solar system, but also one of astronomy’s biggest riddles: where did Earth’s water come from?
Astronomers suspect that at least part of Earth’s water came from a bombardment by comets from far away. But exploratory robotic missions and observations from a distance have demonstrated that the chemical fingerprints of cometary water often do not match those of terrestrial water. Also, it is easier for asteroid belt objects to collide with the planet.
This means that objects like main-belt comets “could be a source of Earth’s water,” said astronomer Colin Snodgrass of the University of Edinburgh and co-author of the study.
As is the case with other comets, ice from a main-belt comet converts to vapor and forms a coma as it passes close to the Sun. Bizarrely, they orbit in the asteroid belt, a graveyard of debris that didn’t merge to form planets.
The first major comet belt was discovered in 1996, but “you always find an explanation for an object that is out of place,” Snodgrass said, suggesting that the belt may have captured a rogue comet. Since then, however, eight others have been detected. About 20 other objects linked to the belt seen to be shedding mass — possibly due to periodic vaporization of ice, as comets do, because of disorderly spinning or recent impacts with asteroids — are considered candidates to become comets. .
Study researchers, hoping to locate more unique objects in the main belt, found only one new candidate: 2001 NL19.
“This is the only one that seems to have something,” Ferellec said, describing what looks like a faint tail as the object moves away from the Sun. It may have originated from the vaporization of ice, making the object cometary. More observations will be needed as it re-approaches the Sun, when a coma or tail is more likely to appear.
Regardless of how 2001 NL19 is classified, the number of confirmed main-belt comets suggests that “these things are native to the asteroid belt,” Snodgrass said. Its origin is still unknown, although some hypotheses have already been suggested.
It is possible that main-belt comets, like their more distant and conventional counterparts, formed far from the Sun during the solar system’s chaotic early days, but instead of remaining remote, they were pulled by the gravity of other objects and placed in the solar system. what is now the asteroid belt. After billions of years, any remaining primordial ice would be buried deep beneath its rocky surfaces. If they are hit by another asteroid, some of that ice will be brought to the surface, exposing it to blazing starlight.
Uncertainties aside, one thing is clear: the existence of eccentric asteroid-comets complicates our desire to classify natural phenomena into tight categories.
“I always say, ‘Everything is a comet,'” said astronomer Kacper Wierzchos of the Lunar and Planetary Laboratory at the University of Arizona and not involved in the study. “If we took my sofa close enough to the sun, it would start melting and go into a coma.”