Kepler space telescope peers at hot alien couple Astro-boffins have located an alien planet pair that are orbiting so close to each other, any inhabitants would see a planet-rise as well as sunrise. Gas giant sits on the Seattle skyline Gas giant sits on the Seattle skyline. Pic credit: NASA, Frank Melchior, Eric Agol Both of the planets are a little too toasty to play …
I'm no scientist but I believe they look at how the radiation spectrum differs when the planet is in front of the star.
It's pretty much the only way to tell that a planet even exists - we don't know much if anything about planets that don't happen to orbit between their star and us.
No spectroscopy here (most likely, anyway) - stars have an annoying habit of being so bright that they drown out any light from the planet itself. Instead, you look at how the light from the star dims as the planet passes in front. You can guesstimate the mass of the star quite well, and from that and the orbital period, you can get the star-planet distance. You then know a bigger planet will block more light at a given distance than a tiny one, so you can work out the radius of the planet by the amount of starlight blocked, the radius of the star itself, and how far apart they are. You then use fairly handwavey arguments and say that if it's Earth radius, it's like Earth, and that if it's Neptune radius, it's like Neptune!
That is, of course, much simpler than how it actually is!
And a few notes now I've posted and re-read that:
The Mass/Radius of the star comes from its colour - bluer stars are more massive, larger, and hotter; red stars are smaller and cooler. We've spent a lot of time modelling these! Look up the "Main Sequence" if you want to know a bit about that.
We're not entirely sure on planet compositions for things that aren't represented in the solar system - this is why we're not too sure what a Super-Earth is actually like. When do you stop being a ball of rock and become an ice/gas giant? The theoretical chappies have been having great fun with all that.
Spectroscopy isn't so good for getting actual planet sizes - you can get the mass ratio of the star:planet easily, and if you guess the star's mass, you can get the planet's one too. But as mentioned above, if something is 3 times the mass of the earth, do we model it as a ball of rock or a ball of gassy ice? Ideally you want to combine information from both spectroscopy and transits ("photometry").
*Looks out the window*
Hmm, good point...and here I was looking forward to some blue planet-viewing tonight. ;)
As for the dimness in the city, we Seattleites aren't accustomed to bright light so we have to filter it out to protect our sensitive eyes.
And the Welsh complain about *their* weather. I was in Cardiff in March and it felt like summer!
Probably the smaller planet was knocked out of stable orbit, and was captured by the gas giant. That, or it formed out of a condensate disc around the giant. (Think about Saturn's rings, but a lot lumpier.)
Either way, I'd suggest it's in effect a moon, just vastly larger than we're used to thinking of them.
Kepler 36 ???
Surely planets should be named after their order of orbit from the parent Star ? As in we are living on Sol 3 ...
I can't imagine calling everything Kepler followed by a number is going to stick or even be very easy to understand.
Are the parent stars not even hardly getting a mention now?
Quote: The star itself is Kepler 36 (well, Kepler 36a). You then label planets as b, c, d, and so forth. So we would technically be Sol d, by that naming system!
We are Sol3, you don't give the star the A designation. That goes to first orbiting planet. This particular star is Kepler 36a because there is a different nearby star (maybe locally grouped or optically near to it). So to distinguish between the 2 Kepler 36's, a letter is designated to each. Kepler 36b is therefore a star not a planet.
The system described in the article consists of a star (Kepler 36a) and two planets (Kepler 36a 1 and Kepler 36a 2). If a planet has moons, they are given a letter designation starting with a for the closest moon. Our Moon is therefore Sol 3 a. Spaces are optional, but generally dropped except for a numbered star (Kepler 36a)
No idea where you got that information from! The generally accepted system is:
Kepler 36 is the system. In a binary (or more) star system, the stars would generally be A and B - in a single-star system, it is acceptable to drop the A (so Kepler 36 = Kepler 36A). Objects orbitting around Kepler 36A are labelled with lowercase letters, with the central object (the star) being designated Kepler 36Aa = Kepler 36a. The planets are then Kepler 36Ab and Kepler 36Ac, but again the A can be dropped as there is no ambiguity.
An alternative example would be the 16 Cygni system, consisting of 3 stars (16 Cyg A, B and C), with the 16 Cyg B system containing two components - 16 Cyg Ba, the star, abd 16 Cyg Bb, a planet.
Hessman et al's paper is a good reference for this: http://arxiv.org/pdf/1012.0707v1.pdf
The artist(s) who produced those pictures just didn't grasp the size of gas giants. To say that the gas giant, when seen from the rocky world, would be much larger in the sky than those images suggest would be a gross understatement; the gas giant would fill most of the sky.
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