Skip to comments.Astronomers Add at Least 4 New Low-Mass Planets to Their Posse
Posted on 12/15/2009 6:40:11 AM PST by Dallas59
Astronomers announced today the discovery of at least four and as many as six planets orbiting two nearby stars. These planets are relatively low mass, ranging from 5 to 25 times the mass of the Earth. For comparison, Jupiter is over 300 times more massive than the Earth, and Uranus 15 times our mass.
Three of these extrasolar planets orbit the nearby star 61 Virginis, which is only about 28 light years away (thats a stones throw in galactic terms). 61 Vir has been a target for planet hunters for some time because its very much like our Sun: while it has slightly less mass and is a tad less bright, its temperature is almost the exactly the same as the Suns. Its about 6 billion years old, 1.5 billion years older than than the Sun. Its bright (easily visible to the unaided eye from a dark site), making it easy to study. It also has a very similar chemical composition as the Sun, which may be important in the planet-making business. And now we know it has planets! Little ones, too.
Interestingly, recent Spitzer Space Telescope observations indicate a fairly hefty ring of dust around 61 Vir as well, at a distance of about twice the distance of Neptune from the Sun. This probably comes from collisions of comets and asteroids, meaning that this system 300 trillion kilometers away really does look a lot like our own solar system.
On top of that, another sunlike star, HD 1461, was found to have at least one planet orbiting it. The planet has about 7.5 times the Earths mass, and orbits close in, taking six days to circle the star once. There may be two other planets orbiting this star as well, but the signals from them are just a bit too weak to be sure.
All of these planets were found by analyzing the stars light and looking for a periodic Doppler shift. As a planet orbits its star, it in turn pulls the star around very slightly, and that can be seen as a teeny shift in the wavelength of the starlight. And by teeny, I mean really teeny; its only been the past 15 or so years that this method has been refined enough to yield results.
So this is very cool, and brings us another step closer to what we all really want to find: a terrestrial planet orbiting a star in an Earthlike orbit. That doesnt guarantee life heck, it doesnt even guarantee the planet will look anything like Earth at all (just take a peek at Venus and Mars to confirm that), but this new discovery does mean that lower-mass planets are abundant in the galaxy. And thats very cool news indeed.
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