New study show Earth could have multiple large moons

[tjoneslo]

This is a summary of an study done by a group of study how many moderate to large sized moons an earth sized planet could host. It's a surprisingly large number.

New study examines how many moons an Earth-mass planet could host

Astrophysicists conduct simulations to determine limits to the existence of exomoons

www.uta.edu

The team used moons with the mass of Ceres, Pluto, and Luna (Earth’s own moon) as prototype masses to compute orbital stability constraints. They found an upper limit of three Luna-mass moons, four Pluto-mass moons, and seven Ceres-mass moons which could orbit an exoplanet with the mass of Earth.

So all those sci-fi pictures with two moons in the sky for an alien world are more accurate and possible than previously believed.

 

[mike wightman]

The thing is we don't actually know how the Earth ended up with a moon and yet Venus lacks one.

The leading theory at the moment is that the proto-Earth was in collision with another proto-planet in its orbit and from the collision the Earth and the Moon formed. Even this scenario requires a lot of 'ifs' - if the object was just the right size, if the object hit at such and such an angle if....

The other mechanism is gravitational capture, but that also has issues.

It's a very interesting model though.

 

[Condottiere]

“We went to the lab right after that seminar and Martin coded up the moon being hit by a companion moon,” Asphaug says. The result of those computations was a novel interpretation of lunar asymmetry. In Asphaug’s view, the jumbled lunar highlands are the wreckage of a second moon that once orbited the Earth, pasted onto the surface of the moon. Small wonder that the far side looks like a different world; it is a different world. The new model provides an integrated description of the moon’s ancient origin and its modern appearance, but to Asphaug the concept goes deeper than that. It showcases a broader, and largely overlooked, process in planetary formation: the gentle collision, in which two bodies come together in a kiss.

When the Earth Had Two Moons

A new model—“The Big Splat”—explains the strange asymmetry of the moon.

nautil.us

 

[Spinward Flow]

The thing is we don't actually know how the Earth ended up with a moon and yet Venus lacks one.

Current speculation is that the slow rotation of Venus (and Mercury for that matter) are contributing factors explaining why Venus (nor Mercury) has a natural satellite.

Even more interesting is the fact that Venus is tidally locked ... not to the Sun, but rather to the Earth ... such that the same side of the Venusian surface is always oriented towards Earth. Venus is the one planetary body in the solar system with a retrograde planetary rotation (1 year orbit is faster than 1 day rotation), so the planet "spins backwards" relative to its orbital path. That slow rotation then creates conditions under which an orbiting satellite will be more easily perturbed and destabilized from sustaining a stable orbit around Venus. Gravity disruptions from Earth and Jupiter would be more easily able to "strip" a natural satellite out of orbit around Venus, partly due to the slow rotation speed of Venus.

 

[whartung]

Even more interesting is the fact that Venus is tidally locked ... not to the Sun, but rather to the Earth ... such that the same side of the Venusian surface is always oriented towards Earth.

Man, I did not know that. That's pretty fascinating. I wouldn't think we'd have enough impact on Venus. (or, more, why doesn't it have its impact on us?)