Study says solar systems like ours may be common

Oct 28, 2010 by Robert Sanders

(PhysOrg.com) -- Nearly one in four stars like the sun could have Earth-size planets, according to a University of California, Berkeley, study of nearby solar-mass stars.

UC Berkeley astronomers Andrew Howard and Geoffrey Marcy chose 166 G and K stars within 80 of Earth and observed them with the powerful for five years in order to determine the number, mass and orbital distance of any of the stars' planets. The is the best known of the G stars, which are yellow, while K-type dwarfs are slightly smaller, orange-red stars.

The researchers found increasing numbers of smaller planets, down to the smallest size detectable today – planets called super-Earths, about three times the mass of Earth.

"Of about 100 typical sun-like stars, one or two have planets the size of Jupiter, roughly six have a planet the size of Neptune, and about 12 have super-Earths between three and 10 Earth masses," said Howard, a research astronomer in UC Berkeley's Department of Astronomy and at the Space Sciences Laboratory. "If we extrapolate down to Earth-size planets – between one-half and two times the mass of Earth – we predict that you'd find about 23 for every 100 stars."

The sizes of planets around 166 nearby, sun-like stars show a clear trend: small planets outnumber larger ones. Each bar on the chart represents the percentage of planets within a specific range of masses. Astronomers extrapolated from these data to estimate that nearly one in four sun-like stars 23 percent host close-in, Earth-size planets. (NASA/JPL & Caltech/UC Berkeley)

"This is the first estimate based on actual measurements of the fraction of stars that have Earth-size planets," said Marcy, UC Berkeley professor of astronomy. Previous studies have estimated the proportion of Jupiter and Saturn-size exoplanets, but never down to Neptunes and super-Earths, enabling an extrapolation to Earth-size planets.

"What this means," Howard added, "is that, as NASA develops new techniques over the next decade to find truly Earth-size planets, it won't have to look too far."

Because the researchers detected only close-in planets, there could be even more Earth-size planets at greater distances, including within the habitable zone located at about the same distance as the earth is from our sun. The habitable, or "Goldilocks," zone is the distance from a star neither two hot nor too cold to allow the presence of liquid water.

The researchers' results conflict with current models of planet formation and migration, Marcy noted. After their birth in a protoplanetary disk, planets had been thought to spiral inward because of interactions with the gas in the disk. Such models predict a "planet desert" in the inner region of solar systems.

"Just where we see the most planets, models predict we would find no cacti at all," Marcy said. "These results will transform astronomers' views of how planets form."

Howard and Marcy report their results in the Oct. 29 issue of the journal Science.

The astronomers used the 10-meter Keck telescopes in Hawaii to measure the minute wobble of each star. Current techniques allow detection of planets massive enough and near enough to their stars to cause a wobble of about 1 meter per second. That means they saw only massive, Jupiter-like gas giants up to three times the mass of Jupiter (1,000 times Earth's mass) orbiting as far as one-quarter of an astronomical unit (AU) from the star, or smaller, closer super-Earths and Neptune-like planets (15-30 times the mass of the earth). An AU is 93 million miles, the average distance between the earth and the sun.

The W.M. Keck Observatory, atop Mauna Kea in Hawaii, was used to survey 166 sun-like stars for planets of different sizes. (WMKO photo)

Only 22 of the stars had detectable planets – 33 planets in all – within this range of masses and orbital distances. After accounting statistically for the fact that some stars were observed more often than others, the researchers estimated that about 1.6 percent of the sun-like stars in their sample had Jupiter-size planets and 12 percent had super-Earths (3-10 Earth masses). If the trend of increasing numbers of smaller planets continues, they concluded, 23 percent of the stars would have Earth-size planets.

Based on these statistics, Howard and Marcy, who is a member of NASA's Kepler mission to survey 156,000 faint stars in search of transiting planets, estimate that the telescope will detect 120-260 "plausibly terrestrial worlds" orbiting some 10,000 nearby G and K dwarf stars with orbital periods less than 50 days.

"One of astronomy's goals is to find eta-Earth (ηEarth), the fraction of sun-like stars that have an earth," Howard said. "This is a first estimate, and the real number could be one in eight instead of one in four. But it's not one in 100, which is glorious news."

Twelve possible planets also were detected, but they need further confirmation, Marcy said. If these candidate planets are included in the count, the team detected a total of 45 around 32 .

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Provided by University of California -- Berkeley

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User comments : 13

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Tangent2
3.9 / 5 (7) Oct 28, 2010
What does this do for the Drake equation I wonder? It must give it one hell of a boost.
ThanderMAX
4.5 / 5 (2) Oct 28, 2010
Reminds me of StarGate series....

What if we could populate few of those planets?
michaelick
5 / 5 (4) Oct 28, 2010
The good news is that we have me than 100 sun-like stars in the universe. I agree on the Drake equation, I cannot understand how people can still doubt that extraterrestial life exists. Future, here we come!
droid001
4.7 / 5 (3) Oct 28, 2010
As many as 511 or more stars of spectral type "G" are currently believed to be located within 100 light-years. Only around 63 are located within 50 light-years.
Milky Way contains maybe 400 billion stars, about 8% are type G (like our sun), 23 percent host Earth-size planets.
Millions of civilizations?
DamienS
4.8 / 5 (4) Oct 28, 2010
As many as 511 or more stars of spectral type "G" are currently believed to be located within 100 light-years. Only around 63 are located within 50 light-years.
Milky Way contains maybe 400 billion stars, about 8% are type G (like our sun), 23 percent host Earth-size planets. Millions of civilizations?

I doubt it. You can probably exclude a large chunk of the galaxy spanning the central region, as the concentration of stars would create a challenging environment for life, especially complex life to form. That still leaves a lot of real estate with more benign conditions where life could take hold. However, there is a large leap between simple life and complex life (the transition need not occur) and an even bigger leap to intelligent life capable of forming civilizations. I'm not at all optimistic about finding other civilizations, even if they exist(ed).
Gary7
not rated yet Oct 28, 2010
From what i have read, i believe DamienS is correct in his assessment. Multicellular life is probably the exception, rather than the rule. And life with intelligence and manual dexterity similar to humans is probably quite rare.
MaxwellsDemon
3.7 / 5 (3) Oct 29, 2010
With every major advancement in astronomy, spanning hundreds of years, our assumptions about our ‘privileged’ place in the universe have been dashed to ashes, leaving us to confront the rising mountain of evidence that our Sun and Earth, our position in the cosmos, and the conditions that we enjoy on our vivacious planet, are actually very common, if not downright mundane.

And yet still we hear arguments (that carry a growing scent of desperation) defending the notion that we balding hominids are extraordinarily special: a triumph of evolutionary processes acting in concert with nigh-impossibly fortuitous planetary circumstances.

This strikes me as a stance born of either staggering hubris, or the dumbfounding fear that if we are not the miraculously intelligent and graceful creatures of our own imagining, then surely we must be the most primitive and foolhardy sentient beings within dozens if not thousands of light-years of our lovely but largely unremarkable little world.
Digi
4.5 / 5 (2) Oct 29, 2010
We are talking vast numbers here. In my mind there is no doubt many intelligent civilisations exist, and many thousands of planets with multi-cellular life. In the next ten years the first green Earth-type planet will be discovered. I am not being an optimist just a realist.
El_Nose
3 / 5 (1) Oct 29, 2010
considering that no evidence of a green earth like planet other than ours has been found making that statement Digi make you an optimist. I however agree the chances of finding one are increasing every year and the techniques and satelites in orbit capable of detecting a stars wobble grow ever more precise.

In all honesty we are more likely to find that animals are (more) intelligent and cognizent than previously thought years before we establish alien contact.
eachus
not rated yet Oct 29, 2010
In the next ten years the first green Earth-type planet will be discovered. I am not being an optimist just a realist.

Green, or blue-green? Even if Earth-like planets with life, in particular photosynthetic life are common, Earth spent two billion years getting to multi-cellular chlorophyll based life. Before that blue-green algae gradually created an oxygen atmosphere.

It may be that even with a long enough head start, the transition to multi-cellular life doesn't happen everywhere. Also since we see planetary systems of all ages, the likelihood is that the first couple we find will not have gotten to the multi-cellular life stage.
Digi
not rated yet Oct 31, 2010
El Nose - I consider the rate of technological advance and expertese in finding these exoplanets in fact makes me a pessimist - it will be a lot sooner than 10 years! I would settle for blue-green of course!
Newbeak
not rated yet Oct 31, 2010
MaxwellsDemon,I suggest you read The Eerie Silence by Paul Davies ( http://www.physor...5.html). One of his arguments is that if natural selection leads inevitability to intelligence,you would see it happening in every isolated environment.Thus,he argues,Australia should have seen the emergence of tool using sentient beings alongside those that developed in Africa.Needless to say,he is not optimistic that alien civilizations are anything but rare,if they exist at all.
MaxwellsDemon
not rated yet Nov 04, 2010
Ok, but on the other hand, it took about 4 billion years for us to evolve from the first single-celled organisms on Earth, but only about 4 million years for us to evolve from a chimpanzee-like primate. So how sure can we be that if we humans hadn’t evolved, some other form of intelligent life wouldn’t have evolved here in another billion years? Who’s to say that it isn’t happening right now?

There was a Nature episode on crows last week, and I watched in awe as a crow quickly figured out how to get one tool free from a dangling string, to get a second longer tool from the rear of a barred cage, to then use to snatch a piece of food from the rear of a long crevice. I wouldn’t be surprised if we humans are cleaning up after our crow Masters in another hundred million years...