The incredible shrinking Moon
The story
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.
Teaching ideas:
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?
Weblinks
Story from the New Scientist on the shrinking Moon
Website of the MESSENGER probe
Wow! I guess I have always thought of the moon as more like a giant inactive rock, too. I wonder whether these new findings shed light on the interior make up of the moon or the weathering processes that happen there. I also wonder whether the earth’s gravity may cause geologic events on the moon.
When the word theory is used in the article, do you mean hypothesis or could it best be characterised by theory with a small ‘t’ rather than Theory with a capital T. I prefer hypothesis to keep the difference more clear in students heads.
Keep the always fascininating science coming my way!
Steve
Hi Steve,
Interesting point about the Earth’s gravity affecting the Moon – hadn’t thought of that as a possible hypothesis for these observations. We know that the Moon’s gravity has an effect on the Earth so it would make sense that the Earth would have more of an effect on the Moon. That would be a grest way of using the story in a lesson – give the students lots of hypotheses and ask them to decide which they think is most likely and why.
Yes – this will be some great evidence when it comes to working out the interior of the Moon. It seems that it is much more ‘Earth-like’ then we previously thought.
Hmm…the difference between theory and hypothesis. I always thought that hypothesis was a scientific question that a scientist hopes to answer by conducting an investigation and a theory was the claim made from analysing the data collected during the investigation – does this sound about right?
Keep reading and I’ll keep writing!
Gemma
Yes, I agree with your definitions. In the US we have difficulty with the word ‘theory’, especially as related to Evolution. We often hear the phrase “Evolution is JUST a theory” as if it is just an idea, rather than a broad, well tested explanation of a natural phenomenon. As a biology teacher in the US, I am perhaps oversensitive to the use of the word. Some here are pushing for theory to be capitilized when it is used in the context of evolution or atomic theory, etc. Ahhh, semantics! Or the evolution of a word?!
I think you’ll find this debate goes on on both sides of the Atlantic!
Great post on why evolution can be considered both fact and theory: http://sciencevideos.wordpress.com/2010/09/16/tok-just-a-theory/