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Asked by jparness12 to Dilwar, Lou, Rachel, Simon, Susan on 12 Nov 2013.
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Simon Langley-Evans answered on 12 Nov 2013:
Really it is all about gravity. Gravity comes about because of the massive size and weight of the material that makes up the planet, especially the core of molten iron that lies at the centre of the Earth. This gravitational pull holds the solid part of the planet together. We also have to think about the atmosphere as well because if there was nothing to hold the gases to the planet, everything would die. The atmosphere doesn’t leak into space partly because gravity can also act upon the gases, but also because the iron core has creates a magnetic field. That magnetism acts upon the gases to keep them in place. Mars doesn’t have an atmosphere that could support life anymore because its core cooled too quickly and it lost the magnetic field.
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Susan Skelton answered on 13 Nov 2013:
Hi Jparness!
Yes, as Simon said, it is down to gravity. Gravity is very important because it is the glue that holds together entire galaxies and planets, including the Earth!!Anything that has mass has some gravity, so every object in the universe (no matter how big or small) exerts a gravitational force on everything else. Even you and I are exerting a small gravitational force on each other! Basically, everything on Earth – the atoms, the soil, the grass, the cars, the mountains – all exert a gravitational force on everything else. This force pulls everything together and makes it stick!
Gravity even acts on the gas molecules in the atmosphere which stops the air that we breathe from drifting off in to space.
Because gravity acts on everything, other planets and stars also have gravitational fields. 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.
Comments
Susan commented on :
I want to comment on Simon’s point about the magnetic field from the Earth’s core holding the gases in the atmosphere in place, as this isn’t really the case and I don’t want anyone to get the wrong idea!
A magnetic field cannot hold air molecules – the gases are only held by gravity.
Having said that, the Earth’s magnetic field does have a useful purpose, because it shields the Earth from lots of harmful charged particles which come from the sun, called the “solar wind”. If we didn’t have the magnetic field barrier, this solar wind would blow away all our atmosphere and we would have nothing left to breathe!
Simon commented on :
@susan Thanks. I am just a humble biologist who dabbles with a telescope!
I think what I was trying to say was that without the magnetic field, that solar wind could strip the Earth’s atmosphere away.