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How are planets affected by the Hot Ionised Medium?

Hi, I read at about a recent study of the galaxy NGC 3079, using the Hubble ST together with the Chandra X-ray Observatory. Part of the findings of this study found large structures of gas surrounding the galaxy at 18,000 and 18,000,000 degrees Fahrenheit . That seems pretty hot for a cloud of gas that is almost as big as its host galaxy. My question is this, as hot as these giant clouds are, if planets of some distant solar system in this galaxy passed through any part of these super-hot clouds, would they be incinerated, or affected in any way. It seems to me that even though these clouds are very hot, they must have a very low density, and would likely not cause many problems for such planet systems unfortunate enough to become engulfed in an 18,000,000 deg. F cloud. Am I anywhere near the truth?

You are absolutely right on all accounts!

Although the hot gas in our galaxy (called the Hot Ionized Medium, HIM, by astronomers) contains very energetic particles, their density is extremely low; there are about 100 atoms per cubic meter in this plasma. For comparison, there 10**30 (ten to the thirty) water molecules in a cubic metre of water! Perhaps a better comparison is to the density of energetic particles that come from the Sun and hit the Earth, called the Solar Wind; the density of the Solar Wind is about 1 million particles per cubic metre. This is 4 orders of magnitude greater than the density of the HIM! A direct comparison of the Solar Wind and HIM densities is slightly unfair because the HIM particles are on average more energetic, but it is clear that most planets are much more likely to be bombarded from high energy particles from their parent stars than from the HIM. In the particular case of the Earth, our atmosphere does a good job at keeping these particles from reaching the surface, since the molecules therein dissociate to absorb much of their energy. Inhabitants of planets without atmospheres as substantial as our own, however, would have to possess a means of protection from these particles.

March 2003, Kristine Spekkens (more by Kristine Spekkens) (Like this Answer)

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