A study of P/2019 LD2, the comet that was initially mistaken for an asteroid

Comet P/2019 LD2 seen by Hubble (Image NASA, ESA, STScI, B. Bolin (IPAC/Caltech))
Comet P/2019 LD2 seen by Hubble (Image NASA, ESA, STScI, B. Bolin (IPAC/Caltech))

An article published in “The Astronomical Journal” reports a description of the characteristics of comet P/2019 LD2. A team of researchers used observations conducted with various space and ground-based telescopes to examine P/2019 LD2 while it’s passing near the planet Jupiter in a trajectory that brought it close to the Trojan asteroids to the point that it was initially mistaken for one of them.

Initially cataloged as asteroid 2019 LD2, this object was discovered thanks to the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii in June 2019. ATLAS aims to identify above all the so-called NEOs (Near-Earth Asteroids), the asteroids whose orbit crosses the Earth’s orbit with the consequence that they could represent a danger.

The object discovered was farther from Earth and looked like a Jupiter Trojan, part of a group of asteroids whose orbit is very close to Jupiter’s orbit. Traces of its presence were searched in archive images of observations also conducted using instruments such as the Hubble and Spitzer space telescopes, added to the images obtained thanks to the ATLAS system. To their surprise, astronomers realized that what initially looked like an asteroid had a tail.

Observations of this object, whose nature was at that point in doubt, continued throughout 2020. The line between asteroid and comet may be thin, but in 2020 this object showed it was active by having a coma and a tail months after the identification of its first cometary activity. In short, it was indeed a comet, and consequently, the Minor Planet Center, which deals with the official classification of these small objects, communicated that the protagonist of this research was reclassified as P/2019 LD2, a periodic comet.

The observation of cometary activity in an area close to Jupiter’s orbit is unusual because generally coma and tail form when a comet gets closer to the Sun, to the point that it’s heated enough to cause the sublimation of its water ice. This led the researchers to analyze the data obtained, and Spitzer’s observations actually indicate the presence of carbon monoxide and carbon dioxide in their gaseous state, volatile substances that sublimate at temperatures much lower than water.

Comet P/2019 LD2 probably came from the Kuiper Belt, the area beyond Neptune’s orbit, due to the influence of some other object in that area that altered its orbit. In these cases, an object can get close enough to one of the gas planets for its orbit to be affected again. In this case, P/2019 LD2 was brought close to Jupiter’s Trojan asteroids. It’s a temporary situation because its orbit is not stable.

Simulations conducted on the orbit of comet P/2019 LD2 indicate a very high probability that within 500,000 years it will be projected out of the solar system to become an interstellar comet in the distant future. In the near future, it should get even closer to Jupiter and could be pushed towards the inner solar system. Astronomers may have the opportunity to observe from closer distances an object from the Kuiper Belt, an area of ​​the solar system that’s still poorly known.

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