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A Quarter of Sun-Like Stars Host Earth-Size Worlds
astroengine writes "Although there appears to be a mysterious dearth of exoplanets smaller than Earth, astronomers using data from NASA's Kepler space telescope have estimated that nearly a quarter of all sun-like stars in our galaxy play host to worlds 1-3 times the size of our planet. These astonishing results were discussed by Geoff Marcy, professor of astronomy at the University of California, Berkeley, during a talk the W. M. Keck Observatory 20th Anniversary Science Meeting on Thursday. '23 percent of sun-like stars have a planet within (1-2.8 Earth radii) just within Mercury's orbit,' said Marcy. 'I'll say that again, because that number really surprised me: 23 percent of sun-like stars have a nearly-Earth-sized planet orbiting in tight orbits within 0.25 AU of the host stars.'"
As Carl said, "...billions and billions..."
When Fascism comes to America, it will call itself Anti-Fascism, and tell you to give up your guns.
...that's translated as "lots of stars have planets in orbits which can in no way sustain life". Dims my hopes rather than the other way around.
Also: would that not decrease the chance of planets in goldilocks range overall, since planet material in that system was partly used to give birth to close orbiters?
...gis sdrawkcab (usually not responding to ACs; don't bother posting as AC)
Actually, "within 0.25 AU" puts them too close to their star to be habitable... i.e. not in the goldilocks zone :(
PS 1 A.U. is the distance of the Earth to the Sun, just in case you didn't/don't know.
It depends upon the size and temperature of the star - a planet that is 0.25 AU from a star half the size or half the "temperature" of the sun may very well be in the goldilocks zone of the star. (Remember the inverse square law!) But in this case, it looks like they are talking about earth-sized planets that are within 0.25 AU of sun-sized stars, and those are not in the goldilocks zone - but they are also a lot easier to find than earth-sized planets in the goldilocks zone are (the inverse square law strikes again!). So the question is, what does this finding suggest about how common terrestrial (i.e., non-Jovian) planets with relatively round orbits in the goldilocks zone are?
In 30 years we will be able to detect planetesimals smaller than the moon orbiting stars out to 300 LY. This is of course just a guess.
I am very small, utmostly microscopic.
How much harder would be to find planets of those sizes if they were at a bigger distance from their sun?
I am confused... can someone explain how this report is not selection biased against distant or small planets?
To put it another way, we started by finding huge planets. As we have gotten better methods, we have found successively smaller planets. The three factors that make a planet easy to find are its diameter (occlusion of star), gravitational effect (how much the star wobbles), and distance (how likely that the planet will occlude the star from our perspective, and also factoring into the gravitational effect).
Distant, small planets simply won't be detected from our perspective. So the report is not really saying 'Only 23% of stars have earth sized planets'. It's really saying 'We know that about 23% of stars have rocky planets that are really close. Since we have no reason to believe our solar system is extremely unique, that makes it very likely that an even greater percentage of stars have rocky planets that are farther out'.
This is probably a huge boost to the 'how many stars have possible life sustaining planets' factor in that oft derided formula, the Drake equation.
"I will trust Google to 'do no evil' until the founders no longer run it." Hello Alphabet.
What are you basing that guess on?
Quite an experience to live in fear, isn't it? That's what it is to be a slave.
Absolutely. Present technology is strongly biased towards detecting large planets orbiting close to their stars in a plane we're looking at nearly edge-on. This is a recognized weakness among astronomers, and means that planets that depart from any of those criteria will be less likely/take longer to be detected. It typically take at least 3-5 orbits worth of observations to confirm a planet detection, and smaller or more distantly-orbitting planets will be harder to detect (lower signal-to-noise ratio), so more orbits are required for confirmation. Something like an exo-Jupiter with it's multiple-century orbit won't be directly* detected for a thousand years or so using current technology, despite it's large mass. And an exo-Earth with it's small signal and longer year will take much longer to detect than say an exo-Mercury.
We can make educated guesses about what other system are actually like, but for the immediate future the only planets types we can make any sort of statistical extrapolation about are the kinds that are easiest to detect. On the bright side as the length of observation increases not only can we detect more planets directly, we can also more accurately characterize the orbits of previously detected planets, including the perturbations caused by other planets in the system too small or slow to detect directly.
* technically what I'm calling direct detection is via the Doppler shift it causes in its star's spectrum
--- Most topics have many sides worth arguing, allow me to take one opposite you.
"Alone In The Universe: Why Our Planet Is Unique" by John Gribbin. I've just finished it. Those who've always hoped to one day chat with a Wookie or a Klingon (not to mention SETI-types) will find it thoroughly depressing, but it's filled with excellent science. There's a good review of it here:
http://freethoughtblogs.com/bluecollaratheist/2012/05/29/alone-in-the-universe-why-our-planet-is-unique-part-1
Computer geeks will like it because many of its conclusions are based on cluster-run computer simulations. :) The results of the simulations are nothing short of amazing.
Example: Earth's molten iron core is what gives us a strong magnetic field that protects our atmosphere. The only way they could get that to work out was to put a supernova(!!!) .1 light years (that's not a typo) from the solar system at a critical time while it was forming. This also helps answer why our system has an unusual mix of elements compared to other stellar systems (particularly of radioactives such as Aluminum 26 and Iron 60).
Example: we're actually a binary planet -- Earth and Moon. The moon is thought to have formed from a planet in the Langrange point, called "Theia," that would have fractured our thick crust, making continental drift possible; the moon's gravitational effects on Earth are also critical.
Read the book. Even if you disagree with it (and I know many here will, especially my good friends who love SETI), but it's an excellent read.
Cogito, igitur comedam pizza.
Greg01851 noted:
Actually, "within 0.25 AU" puts them too close to their star to be habitable... i.e. not in the goldilocks zone :(PS 1 A.U. is the distance of the Earth to the Sun, just in case you didn't/don't know.
Yep. Important datum, that.
However ... since this announcement ONLY applies to 1-3 Earth-mass planets within .25 AU of G-type stars (because it's the result of occulation observations, and that's the limit of resolution for any current telescope), it says nothing whatsoever about Earth-ish planets that obit in the "Golidlocks zone". OTOH, I think it's not unreasonable to extrapolate that, if there're appropriately-sized worlds in too-close orbits around that high a proportion of G-type stars, there's a pretty good likelihood that there're just as many (or more) in the zone where life could evolve.
Perhaps we'll find out when/if the James Webb telescope is launched.
Exciting stuff, regardless.
Check out my novel.