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Asked by purplebug123 to Adam, Catherine, Karen, Leila, Nazim on 15 Mar 2012.
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Adam Stevens answered on 15 Mar 2012:
Two things –
At the beginning of the solar system, the planets were formed out a big spinning disc of dust and gas.
Due to the conservation of angular momentum, all the bits would have carried on spinning even after they clumped together (the angular momentum, or spinning, couldn’t just disappear).
However, all the planets would have been hit by other bits of rock and smaller planets that added to their mass. We think the Earth was hit by a big bit of rock that eventually caused the moon to form – this would have affected how fast we were spinning (maybe faster, maybe slower).
In fact, we think Venus was probably hit by something REALLY big at some point, as it spins in the opposite direction to all the other planets, and the same for Uranus, which spins sideways!
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Leila Battison answered on 15 Mar 2012:
What he said!
Also, did you know that the earth’s spin is slowing down, so our days are a little bit longer than they were, and you get fewer days in a year than you used to. This is only a very tiny change, but you can tell by counting the growth rings in shells in the sea and counting the numbers of days per year.
We don’t really know why this is, but it might be because the moon is stealing a bit of our angular momentum every time it goes round, and uses it to edge further and further away from us. The moon is moving away at about 2 cm a year!
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Karen Masters answered on 18 Mar 2012:
Oooh great question. Definitely a scientist in the making asking this one.
My answer might be unsatisfying though, but ultimately the answer is we don’t know, but we can go back a few steps before getting there.
The Earth is spinning because the disc of material it formed from was orbiting (spinning around) the Sun.
The disc of material (and the Sun) got spinning, because the gas cloud they formed out of was spinning.
The gas cloud they formed out of was spinning because it was in our Galaxy which is spinning.
The Galaxy was spinning because….. well here we’re not quite sure.
It’s hard not to spin if you form out of something much bigger which collapsed – because even a tiny spin in the big thing turns into a big spin when it gets smaller. This is called “conservation of angular momentum” and you might have played with it on an ice rink – spin with your arms out and pull them in and you speed up spinning a lot.
But the question of where those original tiny spins came from is still an active area of research – so something scientists do wonder all the time.
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Nazim Bharmal answered on 21 Mar 2012:
When the solar system was formed, there was a big cloud of spinning dust, ice, and gas around the Sun. (If it didn’t spin, it would have been sucked into the Sun.)
As it all stuck together to form the planets, to conserve the angular momentum (or the spinningness, if you like 🙂 ), the planets had to spin even faster.
That is why most planets spin more quickly than they go around the Sun (a shorter day than their year), and they spin into the direction of their orbit too.
Comments
purplebug123 commented on :
Ok. thanks!