Marcus MacGregor wrote:
I'd just like to point out ahead of time that Mars has a fairly high density so the Roche limit does not come into play.
The Roche limit does not "go away" if the planet has a high density. Dense planets break up inside the Roche limit as readily as less dense planets.
Furthermore, no one has come close to providing any sort valid counter-argument.
The counter-argument to explain the Hellas Basin is that it is an impact crater, due to an asteroidal impact during the late heavy bombardment.
The surface of Mars looks almost as if two different planets have been sutured together. The northern hemisphere consists of smooth, low-lying plains; the southern hemisphere is mostly rocky highlands. These highlands are heavily cratered and include several basins— vast circular impact craters that formed relatively early in Martian history. . . .
The Hellas Planitia basin is one of the most spectacular features on Mars—a circular crater, 1,300 miles across, with a brightly reflective floor and raised terrain all around it. Planitia is a Latin term often applied to Martian basins: It simply means "low plain/' The bottom of the Hellas basin is no exception, lying an average nine miles below the surrounding highlands.
Hellas has been known to astronomers for over a century—it is easily spotted as a bright circular feature through a small telescope. But it took close-up images from the Mariner space probes to reveal that Hellas is actually a crater formed by a massive meteorite impact. The impact site is circled by a rim of material that towers 1.25 miles above the surrounding highlands, which themselves extend for nearly 2,000 miles on every side.. . .
It seems that the basins are among the oldest features on Mars, and date from a time when large, partially formed planetoids were still flying around the inner solar system. The sheer size of the craters, as well as their appearance, suggests that they were formed before the amount of meteorite bombardment in the solar system suddenly tailed off about 4 billion years ago