A previously unknown object in space that is somewhere between comet and asteroid has been spotted in orbit around Jupiter. The University of Hawaii’s Institute for Astronomy has announced that it's the first of its kind ever spotted.
According to the university press release , the object, which is known as 2019 LD2, is part of the Jupiter Trojan cluster. Jupiter Trojans are a large group of asteroids located in the same orbital path as Jupiter, and they’re all dead, inert asteroids. Unlike the rest of the cluster, 2019 LD2 has a comet-like tail. Most small-bodied space objects are either asteroids or comets. Asteroids are essentially big space rocks, but comets shed their volatile surface materials when venturing close to the Sun. This creates a visible tail and a glowing coma around the nucleus. There is an in-between type of celestial body, called active asteroids, that spin more actively.
The object was first observed by astronomers at University of Hawaii’s Asteroid Terrestrial-impact Last Alert System (ATLAS). They typically scan the skies for Earth-threatening objects, but they occasionally find curiosities like this. The Queen’s University Belfast confirmed their observations, which shows that a comet-like object was in the cluster. The movement was unusual because most asteroids are devoid of water and other minerals that would be part of a comet, but this suggests there is more to active asteroids below the surface.
“We have believed for decades that Trojan asteroids should have large amounts of ice beneath their surfaces, but never had any evidence until now,” said Alan Fitzsimmons, an astronomy professor at Queen’s University Belfast who’s been studying 2019 LD2, in the press release. “ATLAS has shown that the predictions of their icy nature may well be correct.”
NASA will be launching a probe to visit the Trojan asteroids. Called Lucy, the spacecraft will investigate a half-dozen Trojans between 2027 and2033. This mission will shed new light on these mysterious objects, including their chemical composition and how they found themselves within Jupiter’s orbital path.