Here is Hubble's image of comet P/2019 LD2 (LD2) which currently resides near Jupiter's Trojan asteroid group. Credit: NASA, ESA, and B. Bolin (Caltech)

Massive Comet Near Jupiter’s Trojan Asteroids Photographed by Hubble

In half a million years, the comet will be ejected from the Solar System.


Astronomers studied comet P / 2019 LD 2 (ATLAS) using ground-based telescopes and the Hubble and Spitzer space observatories. The comet initially demonstrated the properties of the Trojan asteroids that share Jupiter’s orbit, and then acquired a cometary tail.

The radius of the comet’s nucleus was estimated from 0.2 to 1.8 kilometers, and in half a million years it will be ejected from the solar system and become an interstellar comet.

When comets arriving from the region beyond the orbit of Neptune, in the course of their movement, cross the orbits of Uranus and Neptune, then a significant part of them turn into centaurs  – unusual bodies that can demonstrate the properties of both asteroids and comets.

What is a centaur?

The classical definition of a centaur says that it is a small body, with a point of perihelion and semi-major axis of the orbit in the range between the semi-major axis of the orbit of Jupiter and Neptune, and the Tisserand parameter more than 3.05 (it shows how strongly the object is influenced by gravitational disturbances from Jupiter).

The average dynamic age of centaurs is about 2.7 million years, after which the vast majority of such bodies are thrown away from the solar system, while comets of the Jupiter family (Tisserand parameter less than 3.05) have a slightly shorter lifetime – about half a million years.

What did astronomers learn about the comet near Jupiter’s Trojan asteroid group?

Comet P / 2019 LD 2 (ATLAS) was discovered in June 2019, when scientists considered it to be the Trojan of Jupiter. However, later it turned out that the object has a faint tail of gas and dust, which made it possible to place it in the transition region between centaurs and comets of the Jupiter family. The semi-major axis of the comet’s orbit was 5.30 AU, its perihelion is 4.57 AU from the Sun, and its aphelion is 6.02 AU from our star.

A group of astronomers led by Bryce Bolin of the California Institute of Technology decided to study the comet for its properties and changes in activity associated with the heating of the core by the Sun. To do this study on the comet, scientists analyzed data from observations of P / 2019 LD 2 (ATLAS) carried out in 2019-2020 using a number of ground-based optical telescopes, as well as the Hubble Space Telescope and the Spitzer Infrared Telescope.

The radius of the comet’s nucleus was estimated from 0.2 to 1.8 kilometers; dust grains of about 100 micrometers in size prevail in its coma, which is ejected from the surface of the nucleus at a speed of about one meter per second. It is unlikely that the emission of dust occurs exclusively due to the rotation of the core; the sublimation of frozen volatile substances, primarily water ice, should also play an important role.

The body became active in November 2018, when it was at a distance of 4.6 astronomical units from the Sun. According to scientists, the rate of loss of dust by the core is about 6 kilograms per second, and water vapor – 80 kilograms per second.

Computer simulations show that the comet will meet Jupiter again in about two years, after which it will go to the inner part of the solar system, and after about 500 thousand years, with a 90 percent probability, it will be ejected from the solar system and become an interstellar comet.

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Bolin, B., Fernandez, Y., Lisse, C., Holt, T., Lin, Z., Purdum, J., . . . Zolkower, J. (2021, January 06). Initial characterization of Active TRANSITIONING Centaur, P/2019 Ld2 (ATLAS), using Hubble, Spitzer, ztf, Keck, APO and GROWTH visible & infrared imaging and spectroscopy.
Jenner, L. (2021, February 24). Comet makes a pit stop near jupiter’s asteroids.


Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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