Asteroids and comets are generally thought to be different classes of celestial objects. But is the strict distinction really justified? The interstellar visitor ʻOumuamua, for example, was initially thought to be a comet, but didn’t develop either a coma or a tail and was then classified as an asteroid. In the meantime, its trajectory has been calculated so precisely that it must have lost mass – which means it is definitely a comet.
The object 2019 LD2 discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) of the University of Hawaii also appears to be some sort of hybrid. Discovered in June 2019, it was thought at first to be an asteroid, but quickly there were indications that it had comet-like properties. In July 2019, it developed a small tail, which it has kept to today. Therefore, 2019 LD2 must be an active object – a comet.