By Professor Mark R....
| June 14th 2020 09:06 AM | Print
Jupiter has captured an icy comet from the outer solar system in a bizarre orbit that will bring it back to within 3 million kilometres of the giant planet in 2063. The only Sun orbiting objects known to come closer were the fragments of Comet Shoemaker Levy 9, which plunged into the Jovian cloud deck in July 1994.
A CENTAUR, NOT A TROJAN:
During 2019 NASA's asteroid hunting ATLAS project in Hawai'i discovered 2019 LD2, and further observations showed it was a comet. New observations confirmed it as a periodic comet and placed its orbit near Jupiter, leading (Denneau, L.) to announce that P/2019 LD2 was the first comet among the Trojans. This family of several thousand asteroids shares Jupiter's orbit but stays steady at approximately 60° ahead or behind of the planet. The discovery of a comet among Trojan asteroids was surprising because most of them are thought to have been captured in the solar system’s early years, any ice should have evaporated long ago.
However, when amateur astronomer Sam Deen used software on the Jet Propulsion Laboratory's (JPL) solar system dynamics website to calculate the object’s orbit, he found P/2019 LD2 had a close encounter with Jupiter that left its orbit unstable. The model showed that the comet had likely been a Centaur, part of a family of outer solar system asteroids, with an orbit reaching out to Saturn. On February 17th, 2017, it passed approximately 14 million kilometres from Jupiter, an encounter that sent the comet on a wild ride and inserted it into an odd Jupiter like orbit.
Although the swing past Jupiter put P/2019 LD2 into a Jupiter like orbit, it did not move it near to one of the two Lagrange points where the combination of gravitational forces from Jupiter and the Sun hold Trojan asteroids. Instead of being 60°, one sixth of the giant planet's orbit, from Jupiter, P/2019 LD2 is only 21° ahead of Jupiter. The model predicts the comet will drift to no more than 30° ahead before the two begin converging again.
The comet will pass within approximately 18 million km on May 13th, 2028. That will alter the orbit again (Deen, S.). That makes P/2019 LD2 a Jupiter family comet, but not a Jupiter Trojan, as the Hawaii group now acknowledges. Project Pluto's Find Orb model gives similar results to JPL’s model.
Also, amateur astronomer, Tony Dunn, found similar results. He illustrated the orbit using his own model to show the path of the object as seen from Jupiter.
The 2028 encounter will shift the comet from an orbit close to a 1:1 resonance with Jupiter to one near a 2:3 resonance. But that orbit will not last, because it will put P/2019 LD2 on course for a much closer planetary encounter.
"From Jupiter's perspective the comet will appear to slowly move around the Sun before coming back," (Deen, S.).
In January 2063, it will pass approximately 3 million kilometres from Jupiter, just outside the orbits of its Galilean satellites, close enough to cause a major redirection of the comet's orbit.
2063 AND BEYOND:
Where P/2019 LD2 will go from there is unclear. The orbital uncertainties are large enough to make the results of that encounter difficult to predict (Gray, B.). "It could get tossed almost anywhere," (Gray, B.) depending on how close it comes to Jupiter. The closer the encounter, the more dramatic the results could be.
Another wild card, is that comets eject gas from various points on their surfaces, and it is difficult to model the impact of the resulting non gravitational effects on their orbits. Such effects could enhance or diminish the effect of Jupiter’s gravitational force and could send it veering off in an unexpected direction. Strong forces can also fragment a comet, as happened to Shoemaker Levy 9 before its impact (Gray, B.).
The 2063 approach should yield new insight into a process that has helped shape the solar system: intense interactions between planetesimals and the gravitational giant of the solar system. The event should give "a detailed look at the dynamics that convert Centaurs and long period comets into short period comets," (Deen, S.).
"Odds are that we will have some spacecraft orbiting Jupiter by then that will be able to visit the interplanetary visitor close up." That would give a much better view of the action than we had for Shoemaker Levy 9, when the collision itself happened on the side of Jupiter hidden from terrestrial observers and spacecraft.
Deen, S. (Minor Planet Mailing List).
Denneau, L. (University of Hawaii).
Gray, B. (Project Pluto).
Heinze, A. (Asteroid Terrestrial impact Last Alert System/ Institute for Astronomy (ATLAS/ IfA)).