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Astronomers detect smallest extrasolar planets yet
Bob Kopp writes "A team of astronomers using Keck Observatory has discovered the smallest extrasolar planets yet: one with 80% of Saturn's mass, orbiting HD46375, and one with 70% of Saturn's mass, orbiting 79 Ceti. These are the first extrasolar planets discovered with masses less than that of Jupiter. Both are, however, quite close to their parent stars; the HD46375 planet has a period of 3 days, while the 79 Ceti planet has a period of 75 days. CNN has coverage. "
OK, here is a thought problem for any astronomy buffs. How would a gas planet orbiting so close to a star be different from Jupiter et al? The one with the 3 day period must be experiencing a much larger gravitational pull and much higher temperature as well. It must be stable if they found it, but it is pretty wild stuff for a layman such as myself to think about.
Laugh while you can, monkey boy!
Remember, all these observations are INDIRECT. They are estimating the size of the planet by the solar wobble caused by the tug of gravity by these planets on their suns. Now, whose to say that this tug is caused by 1 super-jovian sized planet or 5-11 terran sized planets? Whose to say these Saturn like and jovian like planets don't have moons in orbit that are in a "habitable zone?".
I wonder if we could detect anything but Jupiter from our ouwn sun's wobble? How big a planet does old Sol's wobble say is in orbit around it - 2 Jupiters or 1 jupiter and 8 to 9 others? How does an Oort cloud or Kuiper belt of material affect these calculations?
Until we have a spaced based interferometer array (which I beleive NASA is trying to get funding for)which can do DIRECT imaging of these planets, we will not know of any reall numbers and sizes.
BTW, NASA's space-based interferometer design is capable of imaging earth sized planets and doing spectral analysis on them.
Any professional asttronomers or planet finders out there care to comment?
Never by hatred has hatred been appeased, only by kindness - the Buddha
1. Saturn is a Jovian planet. Jovian refers to the composition of the planted, not its size or mass.
2. There have been on the order of 100 planets found. There are billions of stars. When we find billions of solar systems and show that none possess terrestrial planets, then we can conclude ours is not typical.
It's been a long time since I had any physics, but I seem to remember that orbital period is a function of the masses of the bodies and how far apart they are.
It seems to me for a gas giant to orbit a sun in 3 days, they would have to be really close, right? My gut reaction is that an orbit that close would be unstable. Has anyone studied the dynamics of a situation like this?
-y
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Oops. The quote is from the CNN article.
Quantum mechanics: the dreams that stuff is made of.
And there are no orbital telescopes that can be tasked for planet searching?
How pathetic is that.
You'd think that might be something we want to find out about so that when our sun blows up in a few million years (if not sooner) we will have some idea of where we can go (let alone how to get there).
But I guess that's a little ways off.
BTW for those who care, is there any realizable time pay off to computing in 0 gravity (I suppose Moore's law keeps relativity (which tells us time goes faster where there is less gravity) in perspective.)
Hmm... gas giant planets so close to a star? You'd think they would have to have one hell of a magnetic field to deflect the stellar wind and retain their atmosphere, regardless of how massive they are. Could that imply a relatively young planet with a hot, active, metallic core? -boredman
But while I'm on the topic: the sun is something like 1050 Jovian masses, dwarfing Jupiter even more than Jupiter does Earth. This ratio is why detecting extrasolar planets smaller than Jupiter is so hard -- it's common to say that the planets orbit the sun, but actually a planet and its sun both orbit their common center of gravity. As it turns out, Jupiter orbits a bit more than 1100 times the sun's radius away from the sun's center, so the center of mass is just about at the sun's surface.
This means, to detect Jupiter at interstellar distances, we'd be looking for a Doppler shift based on a "wobble" about equal to the sun's radius (not quite 700 thousand kilometers) in half of Jupiter's orbital period (six years, since Jupiter's orbit takes 4433 days)... not much variation, over a very long time -- meaning the velocity is small, and therefore difficult to separate from measurement errors. The extrasolar planets we've been finding have mostly been larger than Jupiter, and have all orbited much closer to their stars -- barely a quarter of them have been as far out as Earth, while Jupiter is over five times that distance from Sol.
As I said, it's a difficult task.
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Politics is about making compromises. Religion isn't. --Michael Horton
Don't be so quick to judge. You can't just point the Hubble at a star and see if there are any planets going around it. First of all, since they are so faint and close to the disk of the star, no existing instrument can resolve planets optically.
Secondly, the major method used to find planets (doppler shift in stellar spectra to detect the star's wobble) works as well from the ground as from space, and there are more telescopes on the ground.
Thirdly, you can't find earth-like planets this way, so this won't help any when it comes time to look for other planets to move to. But the sun won't explode, either, so we're fine for quite some time. The gradual heating of the sun will, if anything, probably mean that, in 100 Myr, when the Earth is uninhabitably hot, Mars should be plenty warm enough to support liquid water (just add air).
Fourthly, to see earth-like planets, you need huge interferometers. Look at Deep Space 3 for an example of what NASA is trying to do in this direction. But interferometers are hard, so it'll be a while before the planet finder goes on line, or is even technically feasible, for that matter.
Not really. From the perspective of a zero-g environment, calculations would seem to take longer on the surface of the earth than in space, but by such a miniscule amount that it doesn't matter. For the money spent to develop and orbit the thing, you can probably double many times over the number of processor nodes in your computing system.
Quantum mechanics: the dreams that stuff is made of.
Yes, finding more planets reinforces the notion that planetary systems are relatively common. This theory didn't need a whole lot of shoring up, though ... it's patently obvious by now.
On the other hand, I don't at all see what this discovery has to say about the relative abundance of terrestrial-class planets. In fact, since the current models of planetary formation indicate that these bodies must have migrated in from the outer reaches of their solar systems (via either migration or interaction with other large bodies) we can actually surmise that, in all of the systems thus far examined, any inner, terrestrial planets that once existed have been ejected by interacting with these gas giants.
Remember, in our own solar system, the major reason there are (practically) no small sun-orbiting bodies between the asteroid belt and the Kupier belt is that the gas giants swept up most of the mass and ejected the rest in that zone.
Quantum mechanics: the dreams that stuff is made of.
While I'm glad to see that non-Jovian scale planets have been found, these are obviously still gas giants - and this leads to the conclusion that our solar system may not be typical.
I still intend to look up the characteristics of the stars involved... my guess it they are not sollike... but the fact that gas giants have been detected close enough to their primaries to have 3- and 75- day orbits means that the models that predict gas giants at larger distances and rock/ice bodies in close, with scattered debris interspersed, may be incorrect.
On the positive side, these are only two data points, and the most obvious sort (it's easier to find a planet close to a star, and large, because of reflection), so they may be statistical anomolies yet.
-- Still waiting for the Nike endorsement
Although it is true we are detecting an awful lot of planetary systems that different from our own -- in particular, ones with gas giants in small, eccentric orbits -- we don't yet have the capacity to detect planetary systems like our own.
There are two boundary conditions on what we can detect: the size of the planets and the distance of their orbit from the star. This is because we can detect planets by noting how much their presence causes their parent star to move. At present, we can detect Saturn-class planets with periods of a couple of years or less. With ground based technology, we may eventually be able to detect Neptune-class planets and planets in Jupiter-like orbits. To detect terrestrial planets, we'll need orbital or lunar telescopes designed for planet searching.
Bob Kopp