# Runaway Planets Zoom at a Fraction of Light-Speed

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Here is the press release.

"
Seven years ago, astronomers boggled when they found the first runaway star flying out of our Galaxy at a speed of 1.5 million miles per hour. The discovery intrigued theorists, who wondered: If a star can get tossed outward at such an extreme velocity, could the same thing happen to planets?
New research shows that the answer is yes. Not only do runaway planets exist, but some of them zoom through space at a few percent of the speed of light - up to 30 million miles per hour."

Okay, so I just lazily plugged in some values on wolframalpha and I'm a little alarmed at the result.

http://www.wolframalpha.com/input/?i=13000000m+asteroid+impact+6000000+km%2Fs

Earth vs. Earth's evil twin travelling at 0.02 c: The "ideal/imaginary" (I realize the problems here, it's just quick and dirty and only for fun) impact energy would be around 5.6x10^43 J? That's like a gamma ray burst. What's wrong with this picture? Really? Damn.

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Well, I am not familliar with the WolframAlpha site, but from a quick glance there seems to be two problems:

First, 6000000 km/s is a total closing speed that is 20 times faster than light and not the double of a few percent.

Secondly, an asteroid with twice the Earth's diameter, (13000000m), contain 4 times more mass than two Earths.

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How do astronomers actually manage to see these planets without a lot of light to shine on them?

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Well, I am not familliar with the WolframAlpha site, but from a quick glance there seems to be two problems:

First, 6000000 km/s is a total closing speed that is 20 times faster than light and not the double of a few percent.

Secondly, an asteroid with twice the Earth's diameter, (13000000m), contain 4 times more mass than two Earths.

The diameter of the Earth is pretty close to 13000 km. I just double checked on wikipedia and it says the average diameter is 12,742 km. But yes, in my haste and inattention I plugged in a m/s value where km/s would be correct. Derp. Epic fail. lol. Thanks.

Here's round two with a result that is much more in keeping with reality. Impact energy of 5.6x10^36 J, which is much more reasonable.

http://www.wolframalpha.com/input/?i=1.3x10%5E4km+asteroid+impact+6x10%5E6+m%2Fs

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How do astronomers actually manage to see these planets without a lot of light to shine on them?

This is all theoretical. That "New research shows that the answer is yes. Not only do runaway planets exist ..." in the press release is truth spaghettification. I don't like this over the top hyperbole that one sees in scientific press releases as of late. It ultimately gives science a bad image.

Here is what the press release should have said:

Seven years ago, astronomers boggled when they found the first runaway star flying out of our Galaxy at a speed of 1.5 million miles per hour. The discovery intrigued theorists, who wondered: If a star can get tossed outward at such an extreme velocity, could the same thing happen to planets? New research shows that this might be the case. A simulation of the same kind of event that might be responsible for runaway stars resulted in the formation of runaway planets. In this simulation some of these runaway planets zoom through space at a few percent of the speed of light - up to 30 million miles per hour.

Edited by D H
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Indeed, hypervelocity planets have not been observed. However, it is possible that they will be someday. The press release indicates the plausibility of detecting a hypervelocity planetary system, within certain parameters, using the transit method. Just something else worth noting for the questionposter.

P.S. JWST could potentially detect an unbound hypervelocity runaway planet. Or so I've heard.

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The diameter of the Earth is pretty close to 13000 km. I just double checked on wikipedia and it says the average diameter is 12,742 km. But yes, in my haste and inattention I plugged in a m/s value where km/s would be correct. Derp. Epic fail. lol. Thanks.

Hehe, I was not much better, I went to wikipedia to check the size of Earth too... and I mixed up the radius as the diameter... Epic fail for me too...

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