Asked by ishwari to Anna, Daniel, Denise, Jesse, Rehemat on 20 Jun 2014.
Keywords: astronomy, colision, planet
planet’s orbits are constrained by the force of gravity.
Knowing the mass of two objects in space, such as planets, and their distance, we can calculate very accurately their position and velocity at any time, that is quite handy when we plan to send satellite or exploring modules on other planets, as we did to Mars.
Usually planets, or at least in our solar system, orbit around one star (the sun, in our case).
If we look at our solar system now, we can then check if planets are going to collide or not, and don’t worry, they won’t. Their orbits do not intersect, so we are safe.
This does not mean that other planets, in other solar systems, will not ever collide!
The Universe is so big that I guess all kinds of collision between any existing object have happened, at least once, since time has started.
Moreover, I am not quite sure about how you define a planet (the definition recently changed, and we lost Pluto, that is not considered a planet anymore…). How would you define a planet?
It seems that there were many collisions during the formation of the Solar System. In fact the best theory to explain the origin of the Moon suggests that it formed from a collision of a planet-sized body (about the size of Mars) with the Earth about 4 billion years ago. The remains of the collision orbited the Earth and fused together to form the Moon.
Now, the planets in our Solar System are pretty fixed in their orbits by the gravity of the Sun and the effect of other planets. It would be unlikely that they will change the orbit in a way that they collide with another planet.
As Daniel mentioned, during the formation of the solar system there were many collisions.
Currently, planetary collisions are quite rare, especially in our developed system, since the solar system can be considered as reasonably stable. In fact, most asteroids that are likely to hit our planet are all too small to be called a planet and produce any significant damage.
Hope this helps! 🙂
As the other geoscientists have mentioned, in order for planets to collide the current state of gravitational forces in the solar system have to be disturbed; I guess this would be a rare occurrence, as planetary orbits right now are stable.
As Denise mentioned, the only things that could collide would be asteroids.
Hi ishwari! I agree with the other geoscientists’ answers. It was especially fun working on research about the formation of the Moon via planetary collisions in my Masters research!
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