NEA 1998 SH2 is Really a Comet

[PMSchu]

Here's an article describing new work about a new type of solar system objects called "dark comets". The NEA 1998 SH2 was reclassified as a dark comet because it had changed its orbit due to sublimating ice. 

https://www.sciencealert.com/a-near-eart...ry-defense

This is going to make predicting their orbits more difficult.

Hope you find it interesting,

Phil S.

[theskyhound]

Hi Phil,

Some thoughts.

I think "Dark Comet" is a poor term for this, likely invented by a journalist. These objects have been known for a long time, and are usually called extinct or dormant comets. There is also a family called Damocloids. Even if it was invented by the authors of a paper, the last thing we need is yet another name for them, especially a bad one, so I would avoid it.

As for the orbits, as long as the MPC doesn't start treating these like comets, e.g. with a single epoch at periastron, there shouldn't be much trouble with the orbits. That shouldn't be much of a worry, because if they did come close to the sun enough for that, they likely wouldn't be dormant.

[PMSchu]

Hi Greg,

I think what the authors of the paper were getting at was that these "dark comets" look like asteroids, but that their orbits can be altered by sublimating ice jets that change their motion slightly. Perhaps the author of the posted article didn't dig deeply enough. There was no mention of Damocloids. It looked interesting.

1998 SH2 is classified as an Apollo-class NEA with a 4.7 AU aphelion. Aren't the Damocloids much farther out?

Phil S.

[theskyhound]

I had a look at the paper. They failed to fully appreciate the minor planet observation community (which is typical) and ignored much of the previous research, much of which has been published in specialty amateur/professional literature rather than Nature. When you do that, you end up reinventing the wheel and then giving it a new name.

What's new here is the idea that you could use signs of outgassing, based on an analysis of the orbit, as a diagnostic for determining if the object was historically a comet. I suspect this isn't as useful as they suggest it to be, because orbital data that is consistent and accurate enough over long periods of time is not generally available--at least not quite yet.