This is what researchers from the harvard smithsonian center for astrophysics (cfa) concluded from an analysis of data from the "kepler" space telescope of the u.S. Space agency nasa. The team led by courtney dressing presented its research on wednesday in cambridge, u.S.A.
"We have always thought we had to travel immeasurable distances to stumble upon an earth-like planet," dressing emphasized in a release from her institute. "Now we realize that another earth is probably already waiting to be discovered in our cosmic neighborhood."
The scientists had searched for red dwarf suns with planets in the data of the planet hunter "kepler. Red dwarfs are the most common type of star in our galaxy: they account for about three out of four stars in the milky way.
Dressing’s team had analyzed all 158,000 stars targeted by "kepler" and identified 95 planet candidates in red dwarfs – including three about earth size with a temperature that allows for runny water. Flowing water is a basic requirement for life as we know it.
Researchers assume, however, that with "kepler" they have by no means discovered all the planets in the stars under investigation. Telescope can only show planets passing directly in front of stars. An extrapolation shows that about six percent of all red dwarfs have terrestrial planets, as the group writes in the journal "the astrophysical journal". With at least 75 billion red dwarfs in the milky way, that was 4.5 billion terrestrial planets in our galaxy. The next of these is expected to be just 13 light years away. By way of comparison, the diameter of the milky way is about 100,000 light years.
These worlds will be very different from ours, say astronomers. For red dwarfs are much cooler than our sun. Accordingly, planets must orbit them much more closely to be in the so-called habitable zone, where water would be plentiful. At such short distances, however, planets would usually perform a bound rotation around their star, always turning the same side to it – just as the moon does to the earth.
However, according to the researchers, this does not diminish the chances for life. "You don’t need an earth clone to make life possible," dressing emphasized. A dense atmosphere or a deep ocean could distribute the warmth over the whole planet.
"We now know the abundance of habitable planets in the most common stars of our galaxy," explained cfa co-author david charbonneau. "This abundance suggests that it will be much easier to search for life beyond our solar system than we previously thought."Since red dwarfs live to be much older than our sun, life on their planets could even be more advanced than ours, researchers speculate. However, they did not find evidence of extraterrestrial life.
Already at the beginning of this year, a team around geoff marcy from the university of california in berkeley presented similar results after the evaluation of "kepler" data: presumably, about every second star of the milky way has approximately earth-sized planets orbiting their home star at a maximum of the same distance as the earth orbits the sun, the group reported on 8. January at the annual meeting of the american astronomical society (AAS). This does not necessarily mean that there is life on one of these planets.