http://www.bbc.co.uk/news/science-environment-19011013 What is certain is that some sort of impact from another body freed material from the young Earth and the resulting debris coalesced into today's Moon. But the exact details of the impactor's size and speed have remained debatable. In a report online to be published in Icarus, researchers suggest that the crash happened with a much larger, faster body than previously thought. Such theories need to line up with what we know about the Moon, about the violent processes that set off the creation of moons, and what computer simulations show about the more sedate gravitational "gathering-up" that finishes the job. In recent years, scientists' best guess for how the Moon formed has been that a relatively slowly moving, Mars-sized body called Theia crashed into the very young Earth. That would have heated both of them up and released a vast cloud of molten material, much of which cooled and clumped together to give rise to the Moon. That would suggest that the Moon is made up of material from both the early Earth and from Theia, which should be somewhat different from one another. Impact factor What complicates that story is a number of observations of "isotopic compositions" - the ratios of naturally-occurring variants of some atoms - taken from the Earth and from lunar samples. While the Moon has an iron core like Earth, it does not have the same fraction of iron - and computer models supporting the Theia impact idea show just the same thing. However, the ratio of the Earth's and the Moon's oxygen isotopes is nearly identical, and not all scientists agree on how that may have come about. Confounding the issue further, scientists reporting in Nature Geoscience in March said that a fresh analysis of lunar samples taken by the Apollo missions showed that the Moon and the Earth shared an uncannily similar isotope ratio of the metal titanium. That, they said, gave weight to the idea that the Moon was somehow cleaved from the Earth itself. Now, Andreas Reufer, of the Center for Space and Habitability in Bern, Switzerland, and colleagues have run computer simulations that suggest another possibility: that a far larger and faster-moving body made an even more glancing blow with the young Earth. They said this body would have lost only a small amount of material and most of it would have continued on after the "hit-and-run". That results in a much hotter disc of debris from the collision, but matches up with what would be needed to make a Moon-sized body. The authors suggest that since most of what became the Moon would have been liberated by the impact from the Earth, similarities between the isotope fractions should be more pronounced. More analyses of different elements within lunar samples - and a great deal more computer simulations that result in a Moon like our own - will be needed to settle the debate
It is very unlikely that any orbiting planet or moon can sustain their finely balanced orbit after a great collision. Unless we accept the idea that it is not gravity alone that holds them on track...
Don't you know about the importance of magnetism and gravity in formation of such objects? The magnetic field created by the dynamo still remains as a remnant on lunar surface. Studying Rima Sirsalis region can help us understand for example on the collision and ejection trajectories during moon formation. LRO satellite currently in orbit around the moon can possibly help us answer these questions and provide the missing data to these simulations O.P. speaks of. The orbit was achieved after aggregation of ejected debris, obviously the fine tuning for a stable orbit made life on Earth possible, so luck is in it.
I don't find it particularly odd or lucky that two bodies which were both already in orbit, once combined, would tend to remain in orbit. Mass, velocity, orbital potential- these things are generally conserved, aren't they? If some of the velocity canceled itself out, a net change in orbital velocity would just be a slight change in orbit. In order for something to fall out of orbit entirely in a timely manner, doesn't one have to have substantial drag? Planets seem nicely spaced to me; frankly, our solar system is a little unlucky if anything- a slight shift in either direction, and we might have two life bearing planets rather than just one. Mars is a little on the small side, but Venus for sure. However, even if we did think it wasn't probable, I wouldn't call it luck; more like we wouldn't be here to see it if it wasn't so. We have a distinct sample bias in retrospect- naturally any planet being witnessed by a civilization born on that planet will have certain qualities. Please Register or Log in to view the hidden image!
I have no idea what you are talking about. The theory is that a body not in orbit with the earth collided with the earth. This collision obliterated the smaller body and a sizable potion of the earth and the impacting body was thrown into space. some of the material fell back to earth, some of the material was ejected beyond the gravitational pull of the earth, and some of the material remained in orbit. This material that remained in orbit coalesced into the moon. So your comments do not make any sense.
It's always seemed a dodgy theory, the earth must have shifted from it's formation orbit into it's present not-too-hot/cold, life bearing, orbit after the impact, a moon size chunk leaving the earth is definitely something for newtons third law. If I remember correctly the 19th century thinking was that the pacific basin is about moon sized, so it's where the impact was...... If the impact teory is used, mars needed 2 impacts and jupiter needs lots of impacts. Also why would it only form just one moon? The modern notion is that of a moon that was formed just like any other moon is formed. That the sun and planets have 'fields' which allow the formations of planets and moons, and belts. Mercury - no atmosphere - no moon venus - atmosphere - no moon earth - atmosphere - one moon mars - atmsphere - two moons See a pattern? Any pattern to asteroid distribution outside of the kirkwood gaps? Any pattern to the outer planets? My own notion (which belongs entirely in the psuedoscience forum) is that the periodicity of the solar system is reflected and weighted by the position and nature of a planet within that periodicity, which is only slightly supported by the material from the moon attempting to maintain an electronegativity and mars soil being acidic. It does however mean that life would exist on earth because the chemical periodicity of the solar system is 'hydrogen' doped by the earth, meaning that the high vibration of earth chemistry is tempered by a natural tendancy to cancel out the vibration in the form of diatomic bonding, giving rise to the ability to form long chain molecules. There is another planet in our solar system that sits in a 'similar field' to the earth, and has it's own bizarre qualities. I did say psuedoscience.....
I think he is saying: 1. 'At some point something collided with the Earth' 2. 'Earth's orbit is so delicate that if anything so much as brushed up against the planet it would have been knocked out of orbit and plummeted into the sun immediately' 3. 'Earth did not so plummet' Conclusion: 'Therefore science is wrong on this subject.' His premise #2 is incorrect. The context and details of his suggested example for premise #1 may be inaccurate, but that's not entirely relevant to his argument. Although it's also possible that I did not understand his post either. Please Register or Log in to view the hidden image!
Thank you, that's what I wrote. But Origin has smoothed the collision by saying that there was a general swathe of material, possibly lots of molten states that would significantly dampen the flying cracked egg scenario I had imagined!
