Centaur or Comet, LD2

2 Mar 2021

At https://phys.org/news/2021-02-comet-pit-jupiter-asteroids.html ... a comet makes a pit stop near Jupiter, joining the team of Trojan asteroids orbiting in conjunction with the big planet - see also https://wattsupwiththat.com/2020/02/26/comet-makes-a-pit-stop-near-jupit...   .... astronomers have detected a roaming comet taking a rest near Jupiter. It has settled near a family of captured asteroids known as the Trojans that are co-orbiting alongside Jupiter. The Hubble Space Telescope observations seem to show it showing signs of transitioning from a frigid asteroid into an active comet, sporting a long tail and outgassing jets of material. The headline seems to be a bit misleading. How can you spot a comet coming into such an orbit, slowing down, and slinking around with the Trojans. Was it instead a Trojan asteroid showing signs of cometary activity? No. Although commenters at WattsUp seemed to think think a comet could not reduce speed as a result of coming close to the gravity of Jupiter, LD2 was specifically noted as an interloper. It is in fact a centaur. One of those objects that orbit between Jupiter and Neptune, unable to enter the inner solar system as Jupiter presents a barrier, a sort of gate. This one has slipped the leash it seems, spotted first around 2 years ago. It must have had just the right trajectory to have had this kind of configuration. It gives the appearance of slowing its orbit but may simply have become in lock step with Jupiter on a temporary basis. In other words, within several years it may break away and enter the inner solar system, representing the arrival of a new comet that will orbit around the sun. At the moment its tail is estimated at 400,000 miles in length - yet it is a long way from the sun. Computer simulations show the icy object  probably swung close to Jupiter and the planet shunted it into the Trojan asteroid group.

Is it just a pit stop location? Will it pull away on a sunward bound trajectory? There s a possibility it will not remain amongst the Trojans for much longer. Computer simulation shows it will have another encounter with Jupiter in the next few years and be punted into a new orbit. Possibly back into an orbit between Jupiter and Saturn rather than the inner solar system. Then again, it might be years before it is dislodged by Jupiter as it seems at home amongst the Trojans.

For the full pdf go to the abstract is at https://iopscience.iop.org/article/10.3847/1538-3881/abd94b ... and click on the PDF link to the RH side.