PT143 · S1 · Q15 Astronomer: In most cases in which

This answer is describing what would happen if two planets had a close encounter, but we're trying to find an answer that makes us more likely to think that two planets had a close encounter. This isn't ruling out an alternate explanation for the oval orbits, nor is it giving us any additional plausibility for the author's explanation. If we had more data to pair with this (i.e. if we knew, in these distant solar systems, that the smaller of the two planets who we think had a close encounter was the more affected one, then this answer would be adding some plausibility to the close encounter hypothesis).

For the sake of the 4 or so planets that have circular orbits around the Sun, this answer would strengthen. A lot of plausibility-strengtheners take the form of "where cause is absent, the effect is absent" (or No Cause No Effect for short). Since our author thinks that Cause Effect Close encounter w/ other planet Oval orbit She would be thinking that in situations where planets did not have close encounters with other planets, they would not be likely to have oval orbits. This answer is telling us that no planet in our solar system had close encounters w/ a planet, so if all the planets in our solar system were non-ovals, this would be a decent strengthener. But we were only told that Earth and several (~3) other planets are circular. So the other four are probably ovals, just like most of the planets we observe distantly. If Neptune and Uranus have oval orbits, but no planet in our solar system has ever had a close encounter with another planet in this solar system, then this answer would actually Weaken the argument. So because of its mixed / unclear impact, it's kind of a wash.

We're only concerned with planets here. We're interested in hearing about Alternate Explanations for how these distant planets got oval orbits, and this answer is not referring to any alternate storyline for the planets' oval orbits. Or we're interested in making the author's story seem more plausible, and this answer has nothing to do with helping to persuade us that these distant planets had close encounters with other planets in their same solar system.

This annihilates the plausibility of the author's hypothesis. There's no way these oval orbits were caused by a planetary close encounter if, according to this answer, there are no other objects large enough to affect that planet's orbit.