"Tens of Billions of Earth-like Rocky Planets Orbit Milky-Way Red Dwarf Stars"
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December 03, 2012

"Tens of Billions of Earth-like Rocky Planets Orbit Milky-Way Red Dwarf Stars"

 

          GJ876b

 

Data released early this year from the European Space Agency's (ESO) HARPS planet finder shows that rocky planets not much bigger than Earth are very common in the habitable zones around faint red stars. The international team estimates that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about one hundred in the Sun’s immediate neighbourhood. This was the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.  

This first direct estimate of the number of light planets around red dwarf stars was announced early this year by an international team using observations with the HARPS spectrograph on the 3.6-metre telescope at ESO's La Silla Observatory in Chile. A prior announcement, showing that planets are ubiquitous in our galaxy used a different method that was not sensitive to this important class of exoplanets.

The HARPS team has been searching for exoplanets orbiting the most common kind of star in the Milky Way — red dwarf stars (also known as M dwarfs). These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.

"Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet," says Xavier Bonfils (IPAG, Observatoire des Sciences de l'Univers de Grenoble, France), the leader of the team."Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone."

The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of Gliese 581 and Gliese 667 C respectively. The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are around red dwarfs. They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare around red dwarfs. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1000 times that of the Earth).

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about one hundred super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

"The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun," says Stephane Udry (Geneva Observatory and member of the team). "But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."

One of the planets discovered in the HARPS survey of red dwarfs is Gliese 667 Cc. This is the second planet in this triple star system and seems to be situated close to the centre of the habitable zone. Although this planet is more than four times heavier than the Earth it is the closest twin to Earth found so far and almost certainly has the right conditions for the existence of liquid water on its surface.

This is the second super-Earth planet inside the habitable zone of a red dwarf discovered during this HARPS survey, after Gliese 581d was announced in 2007 and confirmed in 2009.

"Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet's atmosphere and searching for signs of life," concludes Xavier Delfosse, another member of the team.

The image at the top of the page is an artist's conception of the planetary system around the M dwarf Gliese 876. Currently, 3 planets are known to be orbiting this low mass M star, which is only 15.3 lightyears away.
The Daily Galaxy via ESO
Image credit: http://physics.rice.edu/Content.aspx?id=363 and The Astrophysical Journal

Comments

It is simply amazing that we are living in an age where we are learning such novel things about the existance of potentially habitable planets in the galaxy. This is the stuff that should be making the evening news. Billions of rocky planets in the habitable zone, a virtual certainty! Wow.

With each new discovery it seems both our galaxy and our own solar system may be a perfect melting pot for at the very least simple forms of life. At this point i would be willing to conclude that the Milky Way is home to a wide variety of life forms in every stage of development including intelligent. I feel like its only a matter of time before we make contact. It seems to only be a matter of gaining the technology advanced enough to detect them.

It is my great pleasure to visit your website and to enjoy your great post here. I like it very much.

Which account for 80% of the stars in the Milky Way.

I can easily imagine planets friendlier to life than this planet, where the climate is always 72 degrees. Whatever species is now at the top of the food chain there, the least intelligent of its kind could be more intelligent than Einstein, depending on how far back their civilization goes.

The day we discover life beyond Earth will be a great day indeed. I think it will change Humanity for the better, less people will move towards the Superstitions of religion and that can only be an improvement for our Species. I think microbes abound in the Universe and intelligent life must have evolved somewhere out there, it's all just waiting for us to find.


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