A few weeks ago, astronomers discovered what is being called the “Most distant object in the Solar System”. It’s another dwarf planet, a small body like Pluto, out in the vast outer reaches of the solar system, but it tells a more interesting story than Pluto.
I tend to think of the Solar System as being
- terrestrial planets
- then an asteroid belt
- then the gas giant planets (intermixed with a couple comets),
- then a cloud of objects at and beyond the orbit of Neptune,stretching off into the
- probable sea of comets and potential comets that are out there.
This isn’t exactly WRONG, but it basically betrays that it’s been a while since I really paid attention to the outer reaches of the Solar System. As it is, there’s enough objects out there that astronomers have identified multiple distinct regions of the outer solar system: There are the trans-Neptunian objects (like Pluto), then there’s the Edgeworth-Kuiper Belt, which is like an asteroid belt except there are more asteroids, and the asteroids are actually chunks of ice and not rock, then there’s the ‘scattered disk’ (which may or may not be a thing), and then far beyond that, there is the hypothetical Oort cloud. The object that’s just been found is not like Pluto. It is, apparently, outside even the Kuiper Belt.
Claiming that this is the most distant known object in the Solar System is actually a more specific claim: It’s the most distant known object in the Solar System at the time of discovery. We know about more distant objects – Sedna will eventually get farther from the Sun than anything else we know about and have a good orbit for. Famous comets like West, Kohoutek and Hale-Bopp are more distant now… but they weren’t at time of formation (Halley’s comet actually never gets much farther from the Sun than Neptune, believe it or not… but it comes back every 76 years, whereas the others take millions of years if they even come back at all). Even the Voyager 1 spacecraft (120 AU) is now more distant than this object. But this thing was DISCOVERED at an extremely large distance, which is an even greater feat.
What does this mean, in the grander scheme of things? Well, one of the outstanding questions of the outer solar system is still: are there any more planets in the solar system? People have been looking for planets beyond Neptune for over a century. We now know that Pluto and Eris aren’t quite what we’re looking for… And we know from various infrared satellites that there aren’t any large warm gas or ice giants out there… But there could still be smaller, Earth sized worlds.
The best evidence that such worlds might exist is if there’s a sharp outer edge to the Kuiper Belt- for the asteroid belt and extrasolar disks, sharp edges (as opposed to gradually petering out) mean something massive is shaping the far side. Therefore, the existence of very distant solar system objects like V774104 (what their orbits actually are, how many of them there are, how sharp the edge of the Kuiper Belt really is) is directly relevant to finding any new outer planets.
Other posts about the edge of the Solar System: Pluto was Never a Planet, on the Exploration of Pluto, in which Pluto is Revealed, on the Saga of Planet Nine, on the Search for Planet Nine (Part 2), on the Secrets of Pluto