Question: HI i am krystal and im with my friend antonia and we was just wondering about the solar system and we wanna ask you how are new planet being made if it has been their for 100 and thouseands of years,. Antonia and i are very confused and NEED your help.

Hywel Owen answered on 16 Jun 2012:

The short answer: the planets in the solar system have been around for billions of years, and there aren’t any new planets being formed right now.

The long answer:

All the planets in the solar system, the Earth, Mars etc. and all the other lumps of rock like the moon, are made of elements like iron, carbon, aluminium. Those elements weren’t around at the beginning of the Universe just after the Big Bang, so the first question is: where did they come from?

The answer is that they came from a supernova, which is when a star explodes at the end of its life. Supernovas are where pretty much all the heavy elements in the Universe come from. Since the Earth we’re standing on is made of these elements, we know that there must have been a star before our own Sun, that was shining billions of years ago.

But hang on a second! So this star exploded and made all these heavy atoms, how come they’re collected together into one big lump called the Earth, and other lumps which are the other planets? The answer is gravity.

Gravity is a weak force that acts on anything with mass, i.e. all those atoms we were just talking about. If you leave things for long enough, all the atoms from the supernova (and from others too probably) will gradually draw together. Because most of these ‘clouds’ of atoms are spinning slightly, you don’t just get one big lump in the middle, but instead you get a few lumps – planets. The whole process took a few million years. After that, the planets have just carried on spinning around the Sun, which they have been doing for over 4 billion years.

Occasionally one of these lumps (say, an asteroid) goes ‘rogue’, leaves its normal orbit, and strikes one of the other lumps. One of these lumps was a moon orbiting around Saturn – that moon got destroyed and turned into the little bits that are the rings around Saturn we see today. The gravity of Saturn stops the little lumps drawing back together and making that moon again.