Question: what is the moon?
Keith Brain answered on 15 Jun 2010:
My understanding is that the moon was once part of the early (“primordial”) earth, that broke away from the earth as part of an enormous meteor collision with the earth. Since then it’s been getting steadily rounder (because of its own gravity), its rotation has slowed (because of the effects of gravitational interaction with the earth – the same reason we have tides) and its surface has been bashed by more meteors – hence the craters.
The arguments for the earthly origin of the moon are not straightforward, but I understand have come from studies of the composition of the earth and moon (they’re surprisingly similar in some ways) and from mathematical modeling of the formation of the early planets – two nearby objects couldn’t condense primordial gas clouds and remain separate. The earth is also too small to capture comets and send them into a near-earth orbit … oh, this is stretching my memory …
Alastair Sloan answered on 15 Jun 2010:
The moon is the Earth’s only natural satellite, an astronomical object that rotates with the Earth. It was probably formed around 4 Billion years ago which is about 30 million years after the solar system was formed. There is much debate about how it formed but the most likely cause was that something impacted, or hit the developing Earth blasting some material into space to rotate around the young developing earth. It called the Giant Impact hypothesis.
It has a outer surface, under which is a mantle and an inner core – just like Earth. But, there is a different amount of iron in the moon and different chemicals make up the material and moon rock.
I loved this sort of stuff in A Level physics but that was some time ago!
Hywel Vaughan answered on 16 Jun 2010:
Hi again Saffron,
The moon is actually quite a large body, despite it being so small in our night sky (it is actually about 384,400 kilometres away on average). It is about a quarter of the diameter of Earth and approximately 1/81 of its mass. There are lots of different theories about its formation, but the composition at present is understood to be Argon, Helium, Sodium, Potassium, Hydrogen and Radon.
One of the fascinating questions that science has raised about the moon is about the presence of water – there have always been lots of signs of water being present on the moon, and in 2009 NASA’s LCROSS mission flew its impactor spacecraft into a crater… it detected at least 100kg of water in the plume of material that was ejected!
Emma Carter answered on 16 Jun 2010:
The moon is often described as a natural satellite – something which orbits our planet. We only ever get to see one side of it because of the way it rotates about its own axis as it travels around the earth. Another wierd fact about the moon is that even though it’s loads smaller than the sun, because it’s so much closer, they both appear to be exactly the same size! That’s why we get these really impressive solar eclipses (where the moon is directly in the way of the sun, but you can just see the sunlight showing around the edges).