Neptune May Have Eaten a Planet and Stolen Its Moon

jitendraharlalka noted a piece about the origins of Neptune. There is a theory now that it once ate a super-earth in the outer solar system, and kept its moon as some sort of macabre trophy to make sure that Mars and Venus didn't get any big ideas.

Comments

This should be tagged Om-nom-nom.

[timepilot]

This story should be tagged om-nom-nom.

Re:amphromoporthizing

[Hatta]

You should never anthropomorphize planets. They hate that.

Re:Next

[oldspewey]

Dude, you're posting AC. You don't have to use the "my buddy" cover.

Re:Nuclear?

[oldspewey]

If you're willing to classify radioisotope decay as a form of "fission," then not only is it likely, it's highly probable.

http://www.physlink.com/News/121103PotassiumCore.cfm
http://en.wikipedia.org/wiki/Radioactive_decay

Some orbital dynamics

[Michael Woodhams]

Some may wonder what need there is for a third body at all - Triton wanders too close to Neptune, it gets captured, right?

The reason is conservation of energy: as Triton wanders near Neptune, it falls into Neptune's gravity well and accelerates, so it is going too fast to remain in orbit. Triton at infinity has more energy than Triton in orbit, so to get captured it has to lose energy, and that energy has to go somewhere.

With a few exceptions, three body interactions (e.g. Neptune, Superearth, Triton) are chaotic, and often end with one of the bodies being expelled and the remaining two left in orbit. The lightest body is the most likely to be expelled. This scenario has Superearth being expelled rather than Triton, which is somewhat unlikely but not impossible. (It is too long since I studied this for me to quantify 'most likely to be expelled'.)

It really doesn't seem to me that you need Superearth to explain Triton. The third body could very easily have been a normal Neptunian moon, which is now unobserved somewhere in the Oort cloud or expelled from the solar system entirely. (Could it be Pluto? This was thought of and rejected a long time ago.)

Disclaimer: All these comments are on the basis of reading the New Scientist summary, not the real paper.

Re:Some orbital dynamics

[simonbp]

The reason we invoked the extra planet was that in these three-body encounters, it's much more likely that the more massive object gets ejected and the smaller captured. However, the surveys of the Kuiper Belt are such that if Triton had larger twin, we'd have found it by now. But noone has, so a different capture method remains plausible. The existence of the extra planet isn't actually the hard part to prove, but rather that it impacted instead of being tossed by Neptune down to Saturn or Jupiter, who could then throw it out of the solar system.

Still lots of work to be done...

-Simon Porter, Coauthor

Re:Some orbital dynamics

[simonbp]

what happens in these binary captures is that you have two objects orbiting around each other and falling at essentially escape velocity towards Neptune. If it were just one object, it would either hit Neptune or zoom past and leave Neptune's sphere of influence. But since there are two objects, one is going slightly faster than escape velocity, and the other slightly slower. If there is no collision, then one that is going slower can be captured, while the other is ejected from the system. If the two objects are not of equal mass, then the smaller is going to be moving faster than the larger, and thus there is much wider window of opportunity for it to be captured. So, it's not impossible for the larger to be captured, just much less likely.

In the case of a collision, it is more like likely that the larger will impact, as the center of mass is closer to it, and impacts are the merging of centers of mass. In this case, we think that Triton would be in a sufficiently wide orbit that it would watch the impact from a distance, and then either ejected (if its orbital velocity was in the impact direction) or captured (if its orbital velocity was in the opposite direction). So, Amphtrite could have had multiple moons, but Triton was the one on the correct quarter of the orbital phase to be captured.

Simon Porter

Re:Worlds In Collision

[spacemandave]

Ugh. Every time one of these stories comes up, someone has to bring up Velikovsky. As someone who studies early solar system evolution, I've had the "pleasure" of talking with Velikovsky supporters on numerous occasions. What Velikovsky wrote about was wide-scale rearrangements of the architecture solar system WITHIN HISTORICAL TIMES, based on nutty interpretations of classical mythology. What the article here discusses is a hypothesis for the formation of Triton during an event called the Nice model that is thought to have happened about 3.9 billion years ago (based on dating of large lunar basins from Apollo samples). During this time, a much more massive precursor to the Kuiper belt fueled the migration of the outer four giant planets, disrupting stable reservoirs of small bodies throughout the solar system. Once the ancient Kuiper belt was depleted of mass, the migration stopped (so the "fuel" is gone, and therefore this process can only occur once in the lifetime of the solar system). Had planetary migration occurred within historical times, then we would currently be in the midst of a massive bombardment of comets and asteroids, and the Earth's oceans would currently reside in the atmosphere (along with perhaps some rock vapor clouds). The Nice model and Late Heavy Bombardment is backed up by observations of the structure of the Kuiper belt, observations of other solar systems around other stars, radioisotope dating of lunar rocks (in a variety of isotope systems, but most especially K-Ar, and U-Pb), observations of the structure of the asteroid belt, dynamical models based on plausible initial conditions for the early solar system (constrained by aforementioned observations), observations of zircon crystals found in ancient Earth rocks, cratering chronologies of the rocky planets, the Moon, and icy satellites. Basically it's a preponderance of evidence pointing toward plausible models for the early history of the solar system. Velikovsky has tortured interpretations of ancient literature. Who do you think is more likely to be closer to describing reality?