Martian Moons May Have Formed Like Earth's

sciencehabit writes: Astronomers have long believed that Mars snatched its two moons — Phobos and Deimos — from the asteroid belt. That would explain why the objects look like asteroids—dark, crater-pocked, and potato-shaped. But computer simulations by two independent teams of astronomers (abstract 1, abstract 2) indicated that Mars's moons formed much like ours did, after a giant space rock smashed into the planet and sprayed debris into orbit.

Comments

Aphelion vs Parhelion

[TWX]

Phobos and Deimos both have nearly circular orbits, with aphelions and parhelions that are not very far apart:

Phobos:
9,234 km min
9,376 km average
9,518 km max


Deimos:
23,453 km min
23,458 km average
23,463 km max


Compared to our Moon:
384,400 km min
363,104 km average
405,696 km max


I can see how one could say that Phobos and Deimos, like our Moon, have extremely regular orbital distances, but given that the science that has stated that our Moon was caused by an impactor is still itself being both refined and challenged, I wonder if it's a little premature to conclude that based on orbital characteristics alone the two Martian moons derived from the same sort of event as our Moon. After all, many of the planets have orbits that are very near circular, but we do not interpret their existence in a similar fashion.

Re:Aphelion vs Parhelion

[painandgreed]

I can see how one could say that Phobos and Deimos, like our Moon, have extremely regular orbital distances, but given that the science that has stated that our Moon was caused by an impactor is still itself being both refined and challenged, I wonder if it's a little premature to conclude that based on orbital characteristics alone the two Martian moons derived from the same sort of event as our Moon. After all, many of the planets have orbits that are very near circular, but we do not interpret their existence in a similar fashion.

The impactor theory for the origin of the moon is being refined, but AFAIK, it really hasn't been challenged seriously since the early 90's. Before that there were many competing theories for the origin of the moon from forming at the same time as the earth, captured by there earth, formed from impact, and a few others. Meanwhile there are various criteria such scenarios must meet dealing with angular velocity of the moon, composition, etc. In the early 90's computer modeling got to the point that they could do such for impactor theory and resulted with a model of an impact of another body of similar composition that would collide with the proto-Earth, split off a glob that would become the moon while leaving it's own iron core to explain the Earth's relative large one. At that point, while not perfect, the impactor theory was basically doing better over all in the criteria than the other options. I remember seeing the presentation and video of the computer simulation while an undergrad in physics in the early 90's. I've been keeping up with the subject when I see it, and it has been modified, mainly that two moons were formed and then they recombined in a rather low energy collision to form the moon. I have not heard any serious competition by the other theories since then.

Re:Wou would have thought.

[antiperimetaparalogo]

"Mars snatched its two moons — Phobos and Deimos — from the asteroid belt."

So there really _are_ (astronomical) body snatchers from outer space.

I am full of Fear and Dread right now...