Earth-like Planets May Have Older and More Evolved Life

Planet With Two Moons Orbiting a Red Dwarf Star

This artist’s conception shows a hypothetical habitable planet with two moons orbiting a red dwarf star. Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. Credit: David A. Aguilar (CfA)

Astronomers at the Harvard-Smithsonian Center for Astrophysics believe that six percent of red dwarf stars have habitable, Earth-sized planets. Since red dwarfs live much longer than Sun-like stars, this discovery raises the possibility that some of these planets may have much older and more evolved life than on Earth.

Using publicly available data from NASA’s Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have found that six percent of red dwarf stars have habitable, Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away.

“We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted,” said Harvard astronomer and lead author Courtney Dressing (CfA).

Dressing presented her findings today in a press conference at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Red dwarf stars are smaller, cooler, and fainter than our Sun. An average red dwarf is only one-third as large and one-thousandth as bright as the Sun. From Earth, no red dwarf is visible to the naked eye.

Despite their dimness, these stars are good places to look for Earth-like planets. Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The signal of a transiting planet is larger since the star itself is smaller, so an Earth-sized world blocks more of the star’s disk. And since a planet has to orbit a cool star closer in order to be in the habitable zone, it’s more likely to transit from our point of view.

Dressing culled the Kepler catalog of 158,000 target stars to identify all the red dwarfs. She then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than previously thought.

Since the size of a transiting planet is determined relative to the star size, based on how much of the star’s disk the planet covers, shrinking the star shrinks the planet. And a cooler star will have a tighter habitable zone.


By analyzing publicly available Kepler data, CfA astronomers identified 95 planetary candidates circling red dwarf stars. Of those, three orbit within the habitable zone (marked in green) – the distance at which they should be warm enough to host liquid water on the surface. Those three planetary candidates (marked with blue dots) are 0.9, 1.4, and 1.7 times the size of Earth. In this graph, light received by the planet increases from left to right, and therefore distance to the star decreases from left to right. Planet size increases from bottom to top. Credit: C. Dressing (CfA)

Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren’t quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that six percent of all red dwarf stars should have an Earth-like planet.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said co-author David Charbonneau (CfA). “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Our Sun is surrounded by a swarm of red dwarf stars. About 75 percent of the closest stars are red dwarfs. Since 6 percent of those should host habitable planets, the closest Earth-like world is likely to be just 13 light-years away.

Locating nearby, Earth-like worlds may require a dedicated small space telescope, or a large network of ground-based telescopes. Follow-up studies with instruments like the Giant Magellan Telescope and James Webb Space Telescope could tell us whether any warm, transiting planets have an atmosphere and further probe its chemistry.

Such a world would be different from our own. Orbiting so close to its star, the planet would probably be tidally locked. However, that doesn’t prohibit life since a reasonably thick atmosphere or deep ocean could transport heat around the planet. And while young red dwarf stars emit strong flares of ultraviolet light, an atmosphere could protect life on the planet’s surface. In fact, such stresses could help life to evolve.

“You don’t need an Earth clone to have life,” said Dressing.

Since red dwarf stars live much longer than Sun-like stars, this discovery raises the interesting possibility that life on such a planet would be much older and more evolved than life on Earth.

“We might find an Earth that’s 10 billion years old,” speculated Charbonneau.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5,700 and 5,900 degrees Fahrenheit or 3,150 to 3,260 degrees Celsius. (For comparison, our Sun’s surface is 10,000 degrees F or 5,500 degrees C.)

These results will be published in The Astrophysical Journal.

Reference: “The false positive rate of Kepler and the occurrence of planets” by Francois Fressin, Guillermo Torres, David Charbonneau, Stephen T. Bryson, Jessie Christiansen, Courtney D. Dressing, Jon M. Jenkins, Lucianne M. Walkowicz and Natalie M. Batalha, 12 March 2013, The Astrophysical Journal.
DOI: 10.1088/0004-637X/766/2/81

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

11 Comments on "Earth-like Planets May Have Older and More Evolved Life"

  1. These are still speculations. Sure, there might be all kinds of life out there – that’s easy to say. – And it’s easy to make up stories. But the hard truth is we cannot say anything definite.

  2. how are we gonna get there? that’s what we should be working on right now.

  3. its easy to get there,bud first we must have solutions for earth,and we have to learn to go in peace into space.mind well one damaged planet is enough…

  4. Madanagopal.V.C | February 7, 2013 at 12:53 am | Reply

    The sun’s closest stars being red dwarfs swarming can hold more habitable planets as told in the article. But the probable planetary candidates 300 to 600 light years away claiming a warm temperature of 5700 to 5900 degrees Fahrenheit puts an end to the probable communication between our world and them. If the evolution had been advanced in them being 10 billion years old as against 4.6 billions years of our earth, there won’t be any concurrence of the intelligent beings who were there and and who are now occupying our earth. Everything appears theoretical only, when one planet becomes barren the other one becomes lively in the time scale. Thank You.

  5. hans-dieter otto | February 9, 2013 at 9:37 am | Reply

    when i was 10 years old in 1952i read a science fiction story about the first flight to the moon. 17 years later it happenend in reality.then isaac asimovs stories about satelites which became reality even faster. then orwells 1984 which is happening in north korea. the computer, the handphone, bbs etc. acc to some astrophysicists humanity will spread all over the galaxie within the next 3500 years. if we dont, we will vanish and die out within the next 1000 years. we will probably never meet another intelligence because within 3,5 bio years our intelligence exists for not even one million years. on another planet 5 billion years ago there was an intelligence that existed may be for 2 million years. so the sea of time between the existence of intelligence and the short time of life and intelligence make it highly improbable for a meeting at the same moment in time. its a pity, but i dont think, we will ever meet the little green men.

    • Well can we communacate and bring the little green men here to earth.

      • 1) where do you point the antenna at?
        2) where do you get the energy for it?
        3) radio travels 1 ly per year.. in 300-600 years we should be way more advanced, why wasting time with broadcasts now?

  6. I truly believe the WOW signal was a snippet of a signal generated by a intelligent species of some kind, saying were here.It was excatly as predicted,on the hydrogen line[something that would pertain to the most abundent chemical in the universe]Many have said,why wasn’t there a repeat signal ? We have sent a couple of signals outbound and guess what,we did the same thing.Of course we don’t have proof positive as of yet,but with the James Webb telescope coming on line in a few years,will learn a little more.Its just a matter of time.

  7. Many other factors may account for if a planet has life within the goldilock zone. The speed at which it rotates, its axis and its moon or moons.

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