## The Sky That Touches the Star

Literally.

A newly recently discovered gassy planet that is being eaten by its star. It is so close to it that it orbits in around 1.1 days. In around 10 million years, all the fluff from the huge atmosphere will be gone, and all that will remain is its central rocky core, which will probably orbit around as a giant glob of lava, being so close and all. (the mental image of the giant lava glob orbiting the star is quiet tantalizing, isn’t it?)

(Concept art of what the planet looks like)

I wonder, how close is the planet to the star? Well, that’s why the use of handy dandy physics is in order. So, let’s see, day 1.1 is 95040 seconds, and according to badastronomy (hat tip to the blog also), it orbits with a velocity of 220 km/sec, assuming its orbit is circular, and plugging it all in Kepler’s third law, and I get:

3 million km!

Holy cramolly! It is so close that I imagine that the star would fill pretty much a huge portion, if not, all of the sky. Aside from the fact that my eyeballs would be melting from the brightness (metaphorically, of course), what a view it would be! Especially from a moon of the planet, if any remains that is. Now, I know that 3 million sounds like a lot, but in the cosmic scales, the planet is practically touching the star. You would be amazed at how far away planets in our own Solar System are from the star and from each other. Consider Mercury, whose orbiting distance is 88 days. How much farther is Mercury from the sun? Well, using Kepler’s third law:

$R=T^{2/3}$

Plugging T for time, 88, since Mercury’s period is 88 times larger, I see that it is around 20 times farther. Which makes sense, since 3 million times 20 is 60 millions and Mercury’s semi major axis*  is around 58 million km, I guess it is a reasonable approximation. Although I would like to remind you that Mercury’s somewhat wild elliptical orbit makes the fact that it matches with the semi-major axis somewhat coincidental.

Awesome planet, by the way, along with that awesome illustration above. Almost makes me want to be there and smell the sweet scent of searing, poisonous gas of hydrogen and heavy metal. Don’t you?

By the way, if any of you want to do the calculation I did above regarding the distance too, you can use the following equation, another more precise form of Kepler’s third law:

$T*v_{orb}=2*\pi*R$

T being the period, v being the orbital velocity, and r being the radius of the orbit. So, pretty much solve for r, and you will find the distance of the planet from the star. Assuming, of course, that the orbit is nearly circular, instead of yucky oval like Mercury’s. Oh, and one final advice. Remember when calculating to beware of units. Covert km/second to meters/second by multiplying by a thousand when necessary, and if you want to know the result in km instead of meters, just divide by a thousand. Pretty easy, right? (I hope so, I tend to horribly underestimate what is difficult for everyone else since I find this stuff second nature)

*which is basically the farthest distance from the center in an ellipse, not necessarily the star, the star is at a focus, and I decided to use that type of distance because Mercury’s distance varies quiet wildly in its orbit