The incredible shrinking Moon
Astronomers studying pictures from a NASA orbiter have announced that wrinkles on the surface of the Moon is evidence it is still geologically active and that it is not the dead, inactive lump of rock that we have previously thought.
The team has calculated that the ridges, some up to ten metres tall and several miles long, are less than 1 billion years old and that the Moon has shrunk by 200m in diameter during this time.
Seismometers on the Moon’s surface that were placed there by NASA in the 1970s have also recorded activity.
This evidence combined suggests that the process may be ongoing and the ridges may be still growing.
These ridges would not be at all unusual on Earth – mountain ridges are being constantly formed because of plate tectonics. However, on the Moon there must be another explanation for them.
This could be a good introduction to a lesson on how the Moon was formed. One theory is that it happened 4.5 billion years ago when a body smashed into Earth, throwing a huge cloud of debris into space. Heat was created as the particles bashed against each other whilst gathering to form the Moon. Students can be asked how this new evidence backs up this theory.
Even though plate tectonics is now an accepted theory it was not so long ago that students were being taught the ‘shrinking earth theory’. It was thought that mountains and trenches on the Earth were caused by the inside of the Earth cooling, and the crust was wrinkling much like the skin of an old apple. Even though this has been disproved, it is interesting that scientists are accepting this theory when it comes to the Moon.
Students can take a look at why the ‘apple skin’ process was disproved as an explanation of features on the Earth’s crust but could reasonably be accepted as what is happening to the Moon.
Another story this week could make an engaging start to any lesson on the Moon. Tell students that this photo was taken from Mercury and ask them what they think the two brightest objects are.
It was taken by NASA’s MESSENGER probe which is 114 million miles from Earth. They are in fact the Earth and its Moon. Makes you realise how insignificant our planet and its Moon really are doesn’t it?
Story from the New Scientist on the shrinking Moon
Website of the MESSENGER probe