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Asked by jakedunne13 to Dilwar, Lou, Rachel, Simon, Susan on 12 Nov 2013.
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Simon Langley-Evans answered on 12 Nov 2013:
Any solid body in space will attract material to it through the force of gravity, even fairly small rocks. The bigger an object is, the more gravitational pull it gives. The Earth is bigger than the moon, which is why gravity on Earth is 6 times greater than on the moon. Bigger planets like Jupiter have a much greater gravity than Earth does. As a result Jupiter gets bombarded by huge meteors and comets that approach too close and get captured by the gravity. Luckily these things don’t happen to Earth because we are smaller.
The biggest objects in space are the stars and their gravitational pull is vast. Our sun can pull in objects from orbits that are further out even than Pluto. This is purely due to the size of the sun. Every star and every planet will have a gravitational pull, creating gravity in space.
The biggest gravitational pull of all comes from the centre of the Galaxy which is powerful enough to pull on all of the billions of stars that make the Galaxy. Just as our planet orbits the Sun, the Sun orbits the galactic centre because of this gravity.
Big galaxies also pull on other galaxies. Our Milky Way galaxy is pulling on the nearest galaxy to us, which is called Andromeda and one day the two will come together. All because of gravity.
Complicated and mind-blowing isn’t it?
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Susan Skelton answered on 13 Nov 2013:
Great question, Jake!
Gravity is very important because it is the glue that holds together entire galaxies and planets!
Actually gravity doesn’t only exist in space – it is everywhere. There are four main forces which control everything in the universe. Gravity is the weakest of all the forces but it acts everywhere in the universe; the other three forces are stronger but can only act over short distances. Because space is so big, only gravity can reach so far!
Every object in the universe exerts a gravitational force on everything else. Even you and I are exerting a small gravitational force on each other! Big objects make a bigger gravitational force, so the force from planets and galaxies is huge, which makes them attracted to each other. The gravitational force from massive stars (like our sun) is even big enough to keep planets (like the Earth) in orbit around it.
Although we can describe what gravity does, scientists still don’t understand exactly how it works – it is a really interesting question that still needs to be answered!
Comments
Susan commented on :
@simon:
Simon mentioned that Jupiter gets bombarded by meteors more often that Earth because of it’s high gravity.
Although gravity can cause meteors to crash in to planets, the main reason Jupiter gets hit more often than Earth does, is because Jupiter lies very close to the asteroid belt.
The asteroid belt is a vast ring between the orbits of Mars and Jupiter where most of the asteroids and meteors in the solar system lie. This belt holds more than 200 asteroids larger than 60 miles in diameter, more than 750,000 asteroids larger than three-fifths of a mile in diameter, and millions of smaller ones.
So Jupiter has no chance! Many asteroids even lie just outside the asteroid belt, right in Jupiter’s path, so crashes happen very often!
Luckily the Earth lies far away from the asteroid belt so there are much fewer asteroids in our path. We sometimes do still get hit though!
Simon commented on :
@susan
But the reason the asteroid belt is where it is, is that Jupiter is so big and such a big gravitational pull. If Jupiter didn’t hold those asteroids there, or act as a big juicy target, they would come our way more often. When big objects come into the solar system they get the biggest gravitation tugs from the two biggest objects which are the sun and Jupiter. Great news for Earthlings
Susan commented on :
Yes, scientists think that the asteroid belt was created long long ago (4.6 billion years!) when our solar system was being formed. One theory is that a tenth planet tried to form between Mars and Jupiter, but the gravity from Jupiter was too strong so the material was unable to stick together to form a planet. That material still exists between Mars and Jupiter – it is the asteroids in the asteroid belt. Most of the asteroids remain orbiting on the same elliptical paths around the sun, due to the massive gravitational force of the sun!
What a great question from jakedunne13 to have caused a discussion between scientists! 🙂
Simon commented on :
Yes, nice one Jakedunne13. We got great value from your question