Asteroids are generally considered rocky, inert, and dry, with orbits in the Solar System comparable to those of the planets. On the other hand, comets have big, looping orbits and are full of volatile ices that discharge a dusty, misty halo and tail when approaching the Sun.
A recent discovery, however, challenges those definitions. Here is what astronomers found.
New Type of Asteroid Intrigues Astronomers
A newly spotted asteroid dubbed 2019 LD2 is genuinely fascinating. It appears to have a comet-like tail, and an orbit, similar to an asteroid. That’s unique, but not unknown – astronomers call asteroids that display comet-like features (such as sublimation and outgassing) active asteroids. So, it’s not the “what,” but the “where” that makes 2019 LD2 special.
2019 LD2 shares its orbit with Jupiter, in an asteroid colony known as the Jupiter Trojans. And it’s the first Jupiter Trojans astronomers have ever spotted discharging out gas like a comet.
The space object was first detected last year in June when the University of Hawaii’s ATLAS (Asteroid Terrestrial-Impact Last Alert System) captured a faint signal that seemed to be an asteroid in the Trojan category.
Other observations came quickly. But, it wasn’t until June 10, astronomers observed what appeared to be comet-like activity. Then, on June 11 and 13, they used the Las Cumbres Observatory and discovered the same behavior. Finally, the July 2019 results showed a trialing comet-like trail.
There are lots of asteroids in the Jupiter Trojan category, divided into two groups. One of it orbits in front of Jupiter, where 2019 LD2 is, and the other trails behind it, in curved areas concentrating on the planet’s Lagrangian edges. These are points where the mixed gravitational forces of two larger bodies (Jupiter and Saturn, in this case) develop a small area of gravitational balance. The Jupiter Trojans are challenging to study, but astronomers could find out a lot from taking a closer look at 2019 LD2.
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