Looks like “KEPLER did HIT THE BULLSEYE” …

http://blogs.discovermagazine.com/badastronomy/2011/12/05/kepler-confirms-first-planet-found-in-the-habitable-zone-of-a-sun-like-star/

Dear Mr. Plait,
My recent issue of “Sky and Telescope” shows an astonishing image of a “binary asteroid” as shadows cast by the light of a single star. Can you comment on this interesting application of stellar occultation? How accurate is the resulting image? Since the light rays from a distant star are nearly parallel, the size of the shadow should just about match that of the asteroid! It would seem to me that the precision is almost entirely dependent on the astronomers clocks. (and, of course the number of observation locations) So we should be able to “see” any occulting object regardless of distance. Perhaps groups of stars could be used as a kind of “telescope”? Note: This last would require special camera software to assign timing to each star imaged on the camera chip! (A cute trick. Scanning won’t do it, well . . . maybe super fast scanning.)

Here’s a great opportunity for another organization of amateur and pro astronomers.

Sincerely
Albert J. Hoch Jr.

“Although it does seem to be the latest and one of the more massive of what I think of as “Mustafar” class worlds joining the likes of Corot-7b, 55 Cancris e and Kepler-10 b.”
Thing is, those planets do not naturally group together. Kepler-10b is consistent with being a rocky planet, i.e. a super-Earth, it probably fits the lava-ocean planet model. 55 Cancri e on the other hand is not: it requires at the very least a deep layer of supercritical water to explain the observations, i.e. a mini-Neptune (initially it was announced to be a high-density rocky planet, but this was swiftly contradicted by Spitzer measurements and subsequently an error was found in the data-analysis pipeline that led to the initial underestimate of the planet’s radius). CoRoT-7b has somewhat uncertain mass, lately the estimates have led towards the high end of the scale which suggests it groups with Kepler-10b rather than 55 Cancri e. The remaining low-mass planets for which we have both mass and radius measurements have all turned out to be in the mini-Neptune class: GJ 1214b, the Kepler-11 system, HD 97658b, Kepler-18b.

Thanks for that informative comment. Much appreciated.

I like exoplanet hunter Sara Seager’s term for such mini-Neptunes – “Gas Dwarfs” & guess that may make many of the rocky or lava worlds “Rock Giants” by extension.

@47. andy : Cheers for your greatly informative comment too.

~20 Earth-masses for a pure iron “theorists’ planet”
~10 Earth-masses for a Mercury-like compositon (67.5% iron, 32.5% silicate)
~6.4 Earth-masses for an Earth-like composition (30% iron, 70% silicate)
~4.8 Earth masses for a pure silicate “theorists’ planet”

Not much point doing the calculation for icy compositons because these would not be solid at the temperatures of Kepler-21b, violating the assumptions of the mass-radius relationship. Nevertheless any mass below 4.8 Earth masses essentially must include volatiles. Above that there is a degeneracy between volatile content and iron core fraction.

SOMEONE NEEDS TO TAKE THESE STELLAR SOUNDWAVES, MAKE AN EPIC, SPACEY AMBIENT TRACK FROM IT, AND NAME IT MUSIC OF THE SPHERES. IT MIGHT EVEN BE ME. WHAT IS THIS I DON’T EVEN….DAMN….THE UNIVERSE ITSELF MIGHT BE MUSICAL….

Thanks for the tip! The Kepler sit itself has some of these: http://kepler.nasa.gov/multimedia/Audio/sonifications/“
Even without the different overtones that we can detect in the sun, those are some surprisingly complex sounds!

(For the record, I think links from nasa.gov should just automatically bypass moderation )

It is due to compression (and the resultant changes in the matter equation of state) that the exponent, alpha, that appears in the radius — mass relation:
R ~ M^{alpha}
becomes smaller for ever more massive planets, depending on their composition. alpha is 1/3 for gravitationally uncompressed objects (like a rock). This is the exponent the BA took, when he estimated 4 Earth masses (he simply cubed the radius ratio). For a (cold) object whose mass is in the range of several Earth’s, alpha is ~ 0.27 (i.e., R ~ M^{0.27}), meaning then that the mass might easily be 6 Earth masses, even if its density were exactly that as Earth. Of course, then there’s the possible effect of bloating via sufficient heating by the parent star, but this may not be very important for terrestrial-like exo-planets.

btw: Planets of roughly a Jovian mass and greater have an exponent alpha ~ 0 — that is, they are all about the size of Jupiter. This includes brown dwarf stars with masses up to 80 Jovian masses.

…And since I have mentioned sound waves: Those are actually the most exciting results from Kepler. We can very accurately measure the standing sound waves of stars, which means we can do astero-seismology…

I really wish we could post pictures, so I could post a picture of my gobsmacked face. This is the coolest thing I’ve read all week! For example, I’ve heard of low frequency solar waves, but it never occurred to me that each star would have a distinct frequency. As a musician, this really excites me. Each star has a different pitch, like strings on an galactic harp (even if they’re a few dozen octaves below anything audible). I love it!

Oh yeah, and being able to see inside distant stars. That’s kinda neat too

>>Imagine molten iron rain, at 4 Gs!
What a difference one letter can make: “Singing in the Rain” vs “Singeing in the Rain”.
Hah! Yep, better pack your titanium umbrella and asbestos waders

@29 MTU: Imagines a comet tail atmosphere spiralling around into space as it bubbles off a constantly boiling ever shallowing ocean of metallic hydrogen overlying a core of hyper-pressurised flamed from both sides fluid through to a central plasma core at inconcievably high pressures and temperatures.
A gas giant that has wandered inwards from the Cold Zone where it first formed scattering or engulfing any might-have-been-habitable worlds into the Black. Plunging into its star and stopping just short of being consumed…

You certainly do paint a picture!!
Can you refresh my memory – what exactly is it that can slow something that big enough for it to fall into its primary??

@24 Torbjorn Larsson: Cool, thanks for the elucidation.

The magnetic field/atmospheric erosion issue reminds me of this great series I read: Kim Stanley Robinson’s Mars trilogy. In it, comets are redirected to bring water and other volatiles to Mars. It’s acknowledged that eventually, the water will dissociate into hydrogen and oxygen in the upper atmosphere, and the hydrogen will escape. Apparently it’s only a concern on timescales of millions of years, though. I wonder if a planet with huge amounts of water (say a super-earth with several Earths’ worth of seas) could simply race the process and develop life before the oceans dissociated? Or could it do so if it were hit by a steady stream of comets?
Sheesh. Astronomy always seems to bring up more questions than answers!!

@36 Katherine Lorraine: So all we need to do is find the Mass Relay outside of Pluto and we’re good to go

IIRC, the first mass relay discovered was first taken to be a KBO. Not only that, but asteroids and KBOs are sometimes photographed without the objects being seen for what they are in the images, until later.
We may have pictures of said mass relay, in some astronomical archive somewhere, and not even know it!
/Yes, before my Xbox 360 died, I sat there with Mass Effect 2 and read ALL the historical codex entries

Wikipedia states that Mercury has a density slightly lower than that of Earth, namely 5.427 g/cm3 versus 5.515 g/cm3 for Earth, so your claim that a planet could double in density as a result of all volatiles boiling off into space sounds a bit iffy to me. Perhaps other mechanisms are in play that could explain these results?

The other factor that comes into play is compression. Earth is a more massive planet than Mercury and the interior is under greater pressure. This acts to compress the Earth, increasing its density. The real comparison between the two is uncompressed density, and here Mercury is clearly made of denser material (which would be expected given that a large fraction of Mercury’s mass is the iron core). The uncompressed density of Mercury is around 5.3 g/cm³ while that of the Earth is 4.4 g/cm³.

… wait… I’ve been playing too many video games.

Is the size estimate based upon the full outline of the planet blocking the star’s light and the assumption that we lie in the planet’s orbital plane providing that full outline?

I would imagine the planet’s size estimate could be low if we’re only seeing a portion of the planet eclipsing the star. Chris A calculated the Earth blocks 0.008% of the sun’s light providing it’s the full outline of the Earth. In truth, the Earth could block anywhere from 0% up to 0.008% based on the observation point given intergalactic distance (not counting extremely close perspectives where the Earth could totally block the sun’s face).

Although it does seem to be the latest and one of the more massive of what I think of as “Mustafar” class worlds joining the likes of Corot-7b, 55 Cancris e and Kepler-10 b

Thing is, those planets do not naturally group together. Kepler-10b is consistent with being a rocky planet, i.e. a super-Earth, it probably fits the lava-ocean planet model. 55 Cancri e on the other hand is not: it requires at the very least a deep layer of supercritical water to explain the observations, i.e. a mini-Neptune (initially it was announced to be a high-density rocky planet, but this was swiftly contradicted by Spitzer measurements and subsequently an error was found in the data-analysis pipeline that led to the initial underestimate of the planet’s radius). CoRoT-7b has somewhat uncertain mass, lately the estimates have led towards the high end of the scale which suggests it groups with Kepler-10b rather than 55 Cancri e.

The remaining low-mass planets for which we have both mass and radius measurements have all turned out to be in the mini-Neptune class: GJ 1214b, the Kepler-11 system, HD 97658b, Kepler-18b.

Just as a footnote – is the Alpha Centauri system completely ruled out as far as planets go? Four light years is still pretty far away but it would still be exciting if some kind of terrestrial planet or a gas giant was discovered orbiting Alpha, Beta or Proxima. I recall a while back some Astronomers were studying the system via radial velocity and star transit.

Click on my name or cut’n'paste :

Theoretically, Alpha Centauri should have planets

into this blogs search box for an article the BA posted here on the 7th of March , 2008 at 2:13 PM discussing a study that concluded Alpha Centauri B should – at least in theory – have rocky planets quite likely in the HZ.

I’m sure if they do find something Alpha Centaurian exoplanet~wise we’ll know about it fairly quickly & I’m somewhat surprised there’s been nothing found yet although Earth and smaller mass planets are exceedingly tricky to find even with the technology we have today.

@18. Ken B : What a difference one letter can make: “Singing in the Rain” vs “Singeing in the Rain”.

Good one.

@24. Torbjorn Larsson, OM, #14. Sam H & 22. #Chris A. : Thanks for your informative comments there. This blog needs a ‘like’ button!