New findings
New findings
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Existing knowledge
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Technology and methods
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Issues and applications
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Existing knowledge
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Technology and methods
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
Issues and applications
First habitable Earth-like planet
Astronomers have discovered the most Earth-like planet yet outside our solar system. It has a radius just half again as big as Earth’s. Conditions there are suitable for liquid water. So there could be life on this planet.
The star is called Gliese 581. It is among the closest of stars to us, just 20.5 light-years away in the constellation Libra. It is a red dwarf.
These are small and faint, but they are the most common stars in our galaxy. Among the hundred closest stars to us, eighty are red dwarfs.
A team of Swiss, French and Portuguese scientists discovered the new planet using the European Southern Observatory 3.6-metre telescope. They also have strong evidence for the presence of a third planet with a mass about 8 Earth masses. Gliese 58 was already known to have a planet, a gas giant about the same mass as Neptune.
This new exoplanet is the smallest yet found. It completes a full orbit in 13 days. It is 14 times as close to its star as the Earth is to the sun.
But Gliese 581 is much smaller and colder than the Sun. This makes it far less bright. So although the planet is so close to its sun, it does lie in the habitable zone. This is the region around a star in which water on a planet would be liquid, rather than steam or ice.
“Liquid water is critical to life as we know it,” says Xavier Delfosse. He is a member of the team from Grenoble University (France).
Because of its temperature and nearness to Earth, this planet will be an important target for future space missions looking for extraterrestrial life, he added. “On the treasure map of the Universe, one would be tempted to mark this planet with an X.”
Red dwarfs are ideal targets for the search for planets like Earth, says Xavier Bonfils, of Lisbon University. “Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun.”
Planets close to their suns are much more easily detected with the radial velocity method, the most successful method for detecting exoplanets. This looks for wobbles in the motion of the star caused by the planet, by studying small changes in the star’s light.
“We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explains Stéphane Udry. He is from Geneva Observatory (Switzerland) and is lead author of the paper that reports the result.
Its radius should be only 1.5 times the Earth’s radius, he added. “And models predict that the planet should be either rocky, like our Earth, or covered with oceans.”
The same team of astronomers found a planet around Gliese 581 two years ago. It is 15 times as massive as the Earth. It is similar to Neptune, and has a year that is just 5.4 days long. At the time, the astronomers had hints of another planet. So they obtained a new set of measurements.
With these they found the new super-Earth. They also found clear indications of another planet, around 8 times the mass of Earth. This completes its orbit in 84 days.
This means that the planetary system surrounding Gliese 581 has three planets of 15 Earth masses or less.
The discovery was made using HARPS (High Accuracy Radial Velocity for Planetary Searcher). This is perhaps the most precise spectrograph in the world. It is located on the ESO 3.6-m telescope at La Silla, Chile.
HARPS can measure velocities with a precision better than one metre per second. It is one of the most successful instruments for detecting exoplanets, and holds several recent records. These include the discovery of a ‘trio of Neptunes’.
The new planet was detected through small changes it caused in the speed of motion of its star. These were only about 2 to 3 metres per second. This is the speed of a person walking fast. Such tiny signals could not have been detected with most spectrographs.
“HARPS is a unique planet-hunting machine,” says Michel Mayor, from Geneva Observatory. He is the HARPS principal investigator.
Of the thirteen known planets with a mass less than 20 Earth masses, eleven have been discovered with HARPS, he added.
“We are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach.”
This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics.
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