Starts With A Bang!

Boiling Planets may be Chillin’

Alright, folks, I know it’s Monday, and that you were looking forward to some awesome space stuff, and so I’m taking the thing I was going to write for today, and I’ll have it for you tomorrow, so that I can bring you a little bit of the Universe right now.

Apparently, scientists have just announced the discovery of three rocky planets orbiting a nearby star! How do you find them? The key is to remember Kepler’s first law and Newton’s third law:

Kepler #1: Planets orbit around the center of mass of their Solar System in ellipses.
Newton #3: For every action, there is an equal and opposite reaction.

What this means, when we put these together, is that if a star accelerates a planet, causing it to move in an ellipse, the planet will accelerate the star, and cause it to move in an ellipse (just a much smaller one).

So they went and looked at the star HD 40307, and saw three superimposed signals, one with a period of 4.3 days, one with a period of 9.6 days, and one with a period of 20.4 days. That means there are three planets really close to this star. Remember, the closer you get to a star, the faster you revolve around it. And for comparison, Mercury takes 88 days to revolve around the Sun.

These planets were found to be somewhat more massive than Earth, ranging from 4.2 to 9.4 Earth masses. I think that it’s likely that they were once gas giant planets similar to Uranus or Neptune with a thick gas atmosphere and a big solid rocky core. Then, they had their thick gas atmospheres blown and boiled off by the intense radiation and heat coming from their star. There are some good, detailed writeups of this at Universe Today and Bad Astronomy.

But what I found super interesting about this is that there’s a good chance that these planets aren’t boiling, they’re only halfway there. Why? Because they’re almost definitely tidally locked to their Sun. That means they orbit the star so that the same side always faces towards their Sun and the same side always faces away, just like the same side of the Moon always faces Earth and the same side always faces away.

Well, you know what this means? One side of these planets will always be ridiculously hot, probably on the order of 1,000 degrees Celcius, and the other one will be ridiculously cold, just a few degrees higher than absolute zero. And there will probably be some narrow ridge where it’s just perfectly room temperature; the perfect place to hang out and set up your solar panels! Neat, hmm? Just make sure to bring your own atmosphere…