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M. Kornmesser / ESO
A cartoon view of the Milky Way shows stars bristling with planets. The planets, their orbits and the sizes of their host stars are all vastly magnified in the cartoon.
A statistical analysis based on a survey of millions of stars suggests that there's at least one planet for every star in the sky, and probably more. That would add up to 160 billion planets or so in the Milky Way.
"We conclude that stars are orbited by planets as a rule, rather than the exception," an international research team reports today in the journal Nature.
The estimate may sound amazing: Just a year ago, the world was wowed by the claim that at least half of the 100 billion or more stars in the Milky Way possessed planets, yielding a figure of 50 billion planets. The latest survey now suggests that there's an average of 1.6 planets per star system, which would work out to 160 billion. But perhaps the most amazing thing about the findings is ... astronomers don't find them amazing at all.
"I am not surprised by the numbers," Didier Queloz, a planet-hunter at the Geneva Observatory who was not involved in the survey, told me in an email. Back in 2008, Queloz was part of a different research team that concluded one-third of the stars like our sun harbored super-Earth-size planets — the kinds of planets that could support life.
Over the past couple of years, findings from a variety of planet-hunting missions — including NASA's Kepler space telescope, the European Space Agency's COROT telescope and ground-based telescope surveys — have reinforced the view that planets are plentiful.
"Results from the three main techniques of planet detection are rapidly converging to a common result: Not only are planets common in the galaxy, but there are more small planets than large ones," Caltech astronomer Stephen Kane, a member of the team behind the findings reported in Nature, said in a news release from the Space Telescope Science Institute. "This is encouraging news for investigations into habitable planets."
Six years' worth of data
The new findings draw upon six years' worth of data from two wide-field surveys known as PLANET and OGLE. These surveys use a network of telescopes around the world, scanning the night sky for very rare events in which the light from one star system is amplified by the gravitational-lensing effect of another star (and perhaps a planet) passing in front of it. This particular planet-hunting method is known as microlensing, as opposed to the transit method (which looks for telltale dips in starlight as a planet crosses its parent star's disk) or the radial-velocity method (which looks for the slight gravitational wobble in a star that has a planet in orbit).
A. Feild / STScI / NASA / ESA
This graphic explains how microlensing is used to detect planets. Click on the image for a larger version.
During their six years of searching, the microlensing researchers identified only three actual planets. But they combined those detections with seven earlier detections, plus all the data about non-detections, to arrive at an estimate of how probable it is that planets of different types would be found around a star.
They estimated that about 17 percent of the stars in the Milky Way should host planets in the Jupiter range (0.3 to 10 times as massive as Jupiter), 52 percent should have planets in the Neptune range (10 to 30 times Earth's mass), and 62 percent should have super-Earth-size planets (five to 10 times Earth's mass).
All these figures are surrounded by wide bands of uncertainty. For example, the researchers say their estimate of 1.6 planets per star system could actually be anywhere between 0.7 and 2.5. But the lead author of the Nature study told me that his team's estimate is the best guess yet.
"The average number we find is higher than estimates derived by other methods," said Arnaud Cassan, an astronomer at the Institut d'Astrophysique de Paris. That's because the microlensing method can detect planets as small as five times Earth's mass up to 10 times Jupiter's mass, in orbits ranging from 0.5 to 10 times as wide as Earth's. Other methods aren't that sensitive, Cassan said.
"If they could detect planets with a range farther out, our guess is that they would find more planets," Cassan said.
What are the chances?
The big issue would have to do with how precise the statistical analysis can be with such a small sample of actual detections. Microlensing events are so rare that coming upon even one is like winning the lottery, and that makes the numbers difficult to crunch. But after reviewing the Nature paper, Queloz told me that Cassan and his colleagues conducted "a very good statistical analysis of the microlensing surveys."
Whether the actual number of planets in the Milky Way is 70 billion or 250 billion, it's a big, big number — 10 to 30 planets for every human on Earth. And the number doesn't even count worlds that are less than five times as big as Earth (such as Mercury, Venus, Mars and our own planetary home), inside the orbit of Venus or beyond the orbit of Saturn (such as Uranus, Neptune and the icy dwarfs on the solar system's edge).
Still more revelations about planets beyond our own solar system are coming up this week, but the bottom line for all this is that there's a big cosmos out there — with plenty of opportunities for planets and even life to develop. And that'll always be amazing.
"We used to think that the Earth might be unique in our galaxy," Daniel Kubas, a colleague of Cassan's at the Institut d'Astrophysique de Paris and a co-author of the Nature paper, said in a news release from the European Southern Observatory. "But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way."
More about the planet quest:
- Three newfound worlds are smaller than Earth
- Flash interactive: How other worlds are found
- Two new 'Tatooine' planets with two suns
- SETI researchers check signals in exoplanet study
- Microlensing turns up rocky, low-mass world
- Cosmic Log archive on planets
In addition to Cassan, Kubas and Kane, authors of the Nature paper, "One or More Bound Planets Per Milky Way Star from Microlensing Observations," include J.-P. Beaulieu, M. Dominik, K. Horne, J. Greenhill, J. Wambsganss, J. Menzies, A. Williams, U. G. Jørgensen, A. Udalski, D.P. Bennett, M.D. Albrow, V. Batista, S. Brillant, J.A.R. Caldwell, A. Cole, Ch. Coutures, K.H. Cook, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouqué, K. Hill, N. Kains, J.-B. Marquette, R. Martin, K.R. Pollard, K.C. Sahu, C. Vinter, D. Warren, B. Watson, M. Zub, T. Sumi, M.K. Szymanski, M. Kubiak, R. Poleski, I. Soszynski, K. Ulaczyk, G. Pietrzynski and L. Wyrzykowski.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
Leave a Comment:
wonder which one of the planets God lives on, surely not earth, we are about to discover something big, possibly finding a way to travel from planet to planet, maybe we do that when we die, soul speed, need to do it when we are alive.
The possibility of life on any number of the planetary bodies orbiting other stars, and indeed, even some of the moons orbiting those planets, will be the subject of debate and discussion for years to come. As the line dividing the known from the unknown moves, those arguing for the presence of life elsewhere will have stronger and more plentiful facts from which to draw support for their position. I for one see the question as already settled - a mathematical certainty.
Sadly, those who prefer to see humanity as somehow the point of the universe as ordained by one or more imaginary "god/s" will forever struggle, strain and strive to hold back that line so their sense of self-importance and their god can forever exist on the unenlightened side of that line - the unknown. They will have some success, as they always have. After all, the unknown will always exist for us, we can not know everything there is to know about our vast universe. But that line keeps moving, doesn't it? If I have faith in anything, anything at all, it is that progress in moving that line ever forward is unavoidable and inevitable.
Moons indeed. We need only look to Europa, orbiting Jupiter, as a potential candidate for life. The entire moon may be similar to the deepest part of our own oceans where life is abundant. I only hope that we find out for sure during my lifetime.
all these worlds are yours except europa. attempt no landing there.
Of course if there is more intelligent life than ours out there then it is most likely that they will find us before we find them.
I just wonder if there is yet any statistics relative to finding planets around stars in a multiple star system. How do companion stars effect planet formation? The closest star system to our solar system includes two sun like stars that come within the distance of Saturn to each other but to my knowledge we have yet to detect any planets around them. These stars may currently be more than 4 light years away but they are the closest.
They just reported finding 2 more planets in binary systems. I believe the prevailing thought was that binary stars would not have planets because of the complex gravity between 2 stars and the planets and keeping it in a stable orbit. Again, we find a few cases where the conventional wisdom gets overturned and we're off hunting in another direction now. Look for a new crop of Tatooine's in the coming year.
Anyone else here hearing Carl Sagan's voice saying "billions and billions"?
Yes indeed.
The weird question is how are the giant spacecraft like seen and chased over Belgium and Alaska, are getting here? The nearest stars are very far away. The aliens must have mastered the use of the recently discovered 'dark energy' or found a way to manipulate space or time.
Like a lot of people I grew up watching Sagan on PBS. I miss that guy.
And people really believe that God put all those stars and planets out there just so we'd have something pretty to look at at night?
I'll bet the Mormons and Muslims see these planets as something to convert or conquer! Submit!
Well, if we spent the same amount of money on advanced propulsion and FTL theory that we do buying flatscreen televisions, maybe we'd get there in a decade or two.
OH MAN! Did I really just type that?
@peteMT
The whole discussion about why 'they' haven't contacted us yet hinges around the very point you make. Until we learn the futility of wealth acquisition, we are under quarantine. Personal aggrandizement is the thing that makes us one of the most amusing soap-operas in the universe.
SETI and the Goldilocks Zone search are looking for life as we know it. They won't find a Bank Of America, so it isn't there. Life is something that science can identify only in as much as it is within the bounds of what we know. We have a long way to go before the white mice are satisfied with the output.
So, where did the Romulans and Klingons et al originate?
Huh?
You so dern' smart answer that question!!!
Where are the aliens????
Doesn't matter how many planets there are in the galaxy. We don't even have a base on the moon yet! Hell, we don't even have spaceships anymore!! We have to hitch rides with the Russians!!!
Jojo, as long as We, The Russians, The Chinese, and other arbitrary groupings are a part of the thinking, we will not get off the planet, or be contacted by another species. We ALL are too young.
The alien teenager who wrapped their new Mustang around a tree in 1947 were a good indication of what kind of development we lack. Give humanity the toys and we will put somebody's eye out.
It is possible, of course, that a life form we might recognise is learning about being a bus driver in New York in the late 1950s as we speak, and thinks we are all Ralph Kramden. Would you drop by?
So, what is the ultimate form of evolution/adaptation in this so called "lucky" universe we live in? God is, plain and simple. Whether it be through technology, or some deeper understanding of a spiritual or quantum connection to the universe, God is the only answer. And if God is the ultimate answer, then He is the only answer. God is complete understanding with complete power.
For those of you that have "science" as your religion, where did you get your morals from? With no God, why not lie, cheat, steal and kill to make yourself happy? What is it in you that makes you do the the right thing? Science?
Empathy.
2012 now, BRING ON THE METEORS!
Lol........
ROFL! you guys think you are soooo smart... yet the truth is that you could not be more ignorant.
The FOOL has said in his heart "THERE IS NO GOD"
Which one of these 160 billion planets can we ship Obama off to? and is there room for the rest of the congress? (except for Ron Paul, we can keep him here)
The FOOL has said in his heart "THERE IS NO GOD"----Sorry but that doesn't get it anymore That's no more than saying you're a fool if you don't believe as I do. Intimidation,and threats such as "hell" doesn't convince people of anything. Dorthy may have gone down the yellow brick road in search of the wizard, but that won't work for religion anymore. Some of humanity has started to grow up and think for themselves! Knowledge is a flood that won't be stopped.
OK, I guess it's time mankind heard the truth. The question is not "is their a God" but rather - -"who is God?" Consider this, the universe is 15 billion years old , but only the universe that we know. The universes are infinite in number and time itself is infinite. There was no "beginning" and there is no end--of time. During this infinite time evolution has progressed beyond our ability to comprehend. God, or life, exists throughout infinite time in whatever form amuses Him. We are presently one of those forms. Prove me wrong--you can't
How come every TV show I watch on the science channel or Discovery has a different total for the amount of stars in our galaxy? I heard for long time that there were 200 billion stars in this galaxy. Then for a while people were saying on these shows only 100 billlion. The other night, on a show about the birth and death of a star.....400 billion stars was what one of the female scientists said when speaking of our galaxy..which is it already?
According to Monty Python it's 100 billion. That settles it.
The Kepler telescope finds new stars every day. Knowledge moves too fast to keep up with. Scientists are just people--no one's perfect.
Science, remember, is merely the pursuit of knowledge. Some spend their lives working out which question to ask. As it stands, the religious precepts saying that god (and I will not use a capitalization for what is not a proper name) made the earth are in line with the "Finite" view we have of the universe today from science. The aim of those in the field is to disprove every theory. If you find out why this hypothesis doesn't work, you have asked another question by answering that disproven one.
160 Bn planets means more than 20 for each one of us. Statistically, that means there are two inhabitable pllanets for each of us. Our Sol system has eight or nine (Pluto, remember). Another bunch of physicists have work to do now, and part of that work is to disprove the work of Peter Higgs et al and keep the number of guage bosons at 4. That would stop us looking for Jetson superfuel.
If anything, the god cheerleaders should get behind the science and push for further work. After all, Archaeologists found evidence of human habitation 500 feet below the surface of the Black Sea, and off the southern English coast bearing out the story of the great flood at about 6000BCE. No evidence of Noah yet, but wait.
It strikes me that we're not being reasonable about things such as life after death, much as we haven't been (till recently) about planets & life on other planets, etc. My point? Scientists tend to be skeptical. This serves them well on a micro-level (when determining the validity of test data, for example). However, it misleads the public about the likelihood of phenomena we have yet to unequivocally prove. Carl Sagan's comment that extraordinary claims require extraordinary evidence does not help in determining the likelihood of these phenomena. In other words, there's an abundance of evidence from thousands of people who've had 'near-death' experiences that are both varied enough and similar enough to reasonably rule-out coincidence or random hallucination. These images tend to be quite lucid, despite lack of oxygen to the brain, and the random firing of neurons that have been discussed as the likely cause. Furthermore, in many cases, the subject in question has been 'dead' for upwards of 40 minutes, eliminating the possibility of fuel required for brain activity!
Chester-1902974, Go talk to John Edward.
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