Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 07/08/2011 16:59:43

Title: Did Earth once have two moons?
Post by: thedoc on 07/08/2011 16:59:43

A paper published in this week's issue of the Journal Nature presents evidence that the Earth might once have had a second moon, based on a puzzling problem with the geology of the Moon's surface...

Read the whole story on our  website by clicking here (http://www.thenakedscientists.com/HTML/content/news/news/2334/)

  

Title: Did Earth once have two moons?
Post by: graham.d on 07/08/2011 18:30:37

Yes, it's an interesting hypothesis. Jutzi and Asphaug (University of California) produced a computer simulation and concluded that the present disparity between the terrain in areas on the moon may have resulted from this conjoining of two orbiting moons relatively soon after the moon(s)' initial creation (this resulting from a large, planet sized, impact with the earth). To give the desired results the second moon would have to have been around 3% of the mass of the moon and have had an impact velocity of around 2.4km/sec, which is considered to be slow.

Previous theories have included heating effects on the nearside from the earth's tidal forces. I am not sure what practical tests could be done (other than modelling) to give support to one theory over another, but I expect they would not be possible without sending more probes there to investigate the comparative geological structures.

Title: Did Earth once have two moons?
Post by: CliffordK on 07/08/2011 18:35:01

I saw notes about the article a while ago.  It is most interesting, and could help explain some of the mass asymmetries in the moon, and why it is tidally locked with Earth.

Once the moon became tidally locked with the Earth, it is likely that there were many more far-side impacts than near-side impacts as I would imagine that the Earth would offer substantial protection from meteorites impacting the Earth side of the moon.  If there is too much material build-up on one side of a planet or moon, it is quite possible that gravity would pull it back into a rough sphere shape, causing significant tectonic activity.  And, thus the super-collision would end up with a round body, as would millions of small collisions.

Would earth's gravity and the departure of the moon's center of gravity from the middle of the moon account for some of the off center core?