Astronomers are puzzled. Asteroids and comets are two different objects. Asteroids are usually dry, inert, with orbits similar to those of the planets; Comets, on the other hand, have long, looped orbits and carry volatile ice that generates a long, dusty tail that grows closer to a star. But … what do my eyes see? An asteroid that behaves like one but with a comet-like tail.
This is 2019 LD2.
A new type of space rock that is a cross between an asteroid and a comet, an active asteroid. It is a unique stellar object – the first of its kind seen spewing gas like a comet. The object shares its orbit with Jupiter, in a swarm of asteroids known as the Trojans.
Although other “active asteroids” with properties similar to those of comets are not unknown, it has never been a Jupiter Trojan before.
First observed in June 2019 by the University of Hawaii’s Asteroid Land Impact Last Warning System (ATLAS), 2019 LD2 was initially believed to be a faint asteroid that shared Jupiter’s orbit around the Sun. But when The Trojan asteroid reappeared last month, ATLAS surveys confirmed that almost a year later it still looked like a comet.
Discovering such behavior from a Jupiter Trojan is momentous. Jupiter is believed to have captured them in orbit billions of years ago; These asteroids should have been rid of any surface ice that could vaporize and form “tails” by now, so astronomers are puzzled.
They suggest that the sudden cometary behavior of this active asteroid could indicate that Jupiter recently captured it from a more distant orbit where ice could exist. Alternatively, it could have recently had a landslide or collision that uncovered ice underneath its protective rock layers.
What is certain is that the universe is full of surprises, and surveys to protect Earth from dangerous asteroids often make unexpected discoveries of harmless but fascinating objects that can reveal more about the history of our solar system.
“We have believed for decades that Trojan asteroids should have large amounts of ice underneath their surfaces, but we never had any evidence until now,” said Alan Fitzsimmons of Queen’s University Belfast, Northern Ireland, who helped reveal the cometary side of the asteroid . “ATLAS has shown that predictions of its icy nature can be correct.”
Fortunately, the first Trojan asteroid mission will launch next year, in 2021, so researchers are hoping to get a closer look at the mysterious behavior of 2019 LD2. For now, the focus remains on ATLAS, which has already discovered more than 40 comets.
“Although the ATLAS system is designed to search for dangerous asteroids, ATLAS sees other rare phenomena in our solar system and beyond while scanning the sky ,” ATLAS project principal investigator Larry Denneau said in a statement. “It is a real advantage for ATLAS to make these kinds of discoveries.”
Reference: NASA
