Extra Solar Planets
New Planets Discovered
Gliese 581e
Four Planet System
Image credit:  Artist's impression of the newly discovered planetary system Gliese 581 ESO
After more than four years of observations using the most successful low-mass-exoplanet hunter in the world, the HARPS spectrograph attached to the 3.6-metre ESO telescope at La Silla, Chile, astronomers have discovered in this system the lightest exoplanet found so far: Gliese 581 e (foreground) is only about twice the mass of our Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, centre), and 7 Earth-masses (planet d, with the bluish colour). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days, while Gliese 581 e completes its orbit in 3.15 days. - ESO

April 21, 2009

Gliese 581e or Gl 581e is the fourth extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra. At a minimum of 1.9 Earth masses, it is the smallest extrasolar planet discovered around a normal star and the closest in mass to Earth. However, at an orbital distance of just 0.03 AU from its parent star it is well out of the habitable zone, and unlikely to possess an atmosphere due to its high temperature and strong radiation from the star. Although, scientists say the planet probably has a rocky surface similar to Earth. Gliese 581e is known to orbit its sun approximately every 3.15 days.


The planet was discovered by the team of Michel Mayor of the Observatory of Geneva in Switzerland using the HARPS instrument on the European Southern Observatory 3.6 m (140 in) telescope in La Silla, Chile. The discovery was announced on 21 April 2009. Mayor's team employed the radial velocity technique, in which the orbit size and mass of a planet are determined based on the small perturbations it induces in its parent star's orbit via gravity.

Source: Wikipedia Gliese_581e

Related Links: Papers:
Lightest exoplanet is discovered

By Paul Rincon and Jonathan Amos
Science reporters, BBC News

Astronomers have announced the discovery of the lightest planet ever detected outside our Solar System.

Situated in the constellation Libra, it is only about twice as massive as the Earth, whereas most other exoplanets identified have been far bigger.

The scientists say the planet's orbit takes it far too close to its star Gliese 581 for life to be possible.

The detection was made by an international team of researchers using a 3.6m telescope at La Silla, Chile.


  • From closest in to furthest out Planet e is 1.9 Earth masses 
  • Planet b is 16 Earth masses - The first planet to be found is always given the 'b' designation
  • Planet c is 5 Earth masses
  • Planet d is 7 Earth masses 
"This is by far the smallest planet that's ever been detected," said group member Michel Mayor, from the Geneva Observatory, Switzerland.

"This is just one more step in the search for the twin of the Earth.

"At the beginning, we discovered Jupiter-like planets several hundred times the mass of the Earth; and now we have the sensitivity with new instruments to detect very small planets very close to that of the Earth," he told BBC News.

Habitable zone

The planet joins three others previously detected around its star and takes the designation Gliese 581 e.

As with the previous discoveries, its presence was picked up using the so-called wobble technique. This is an indirect method of detection that infers the existence of orbiting planets from the way their gravity makes a parent star appear to twitch in its motion across the sky.

Astronomy is working right at the limits of the current technology capable of detecting exoplanets and most of those found so far are Jupiter scale and bigger.

To discover one so small is a major coup. The previous record holder was about four times as massive as the Earth.

Because Gliese 581 e takes just 3.15 days to orbit its host star, it lies beyond what scientists call the habitable, or "Goldilocks", zone, where it is neither too hot nor too cold for liquid water to exist.

But one of the other planets in this system does appear to be. Gliese 581 d was first discovered in 2007. The latest research has allowed scientists to refine details of its orbit.

The team now believes planet d (which is about seven Earth-masses in size) circles Gliese 581 in 66.8 days.

"This planet is probably not just rocky; it's very probably an icy planet - but relatively close to the star so at the surface, we should have some big ocean," said Professor Mayor.

"Maybe, it's the first candidate in a new class of planet called an 'ocean planet'."

The exoplanet discovery was announced at the JENAM conference during the European Week of Astronomy & Space Science, which is taking place at the University of Hertfordshire, UK.

A scientific paper detailing the research has been submitted for publication in the journal Astronomy & Astrophysics.

Upcoming challenge

The US space agency (Nasa) recently launched its Kepler telescope dedicated to finding Earth-size planets. It will use a different approach to the HARPS/La Silla set-up.

Kepler will look for the tiny dip in light coming from a star as a planet crosses its face as viewed from Earth.

Michel Mayor commented: "The challenge in coming years will be to find Earth-mass planets in the habitable zones of stars."

He added: "I'm absolutely confident that in one year or two years, we will arrive at [a planet with] the mass of the Earth."

In the future, some of these planets could be imaged in some detail by the next generation of ground telescopes.

One of these projects, the European Extremely Large Telescope (E-ELT) is currently coming to the end of its design process.

"One of the interesting things about today's announcement is that some of the planets in this system would actually be imageable with the next generation of telescopes," said Isobel Hook, from Oxford University and the UK project scientist on the E-ELT.

"The type of technology coming along, such as extreme adaptive optics, will allow you to produce very sharp images. The seven-Earth-mass planet we think could be imaged directly. You would be able to see it go around its star and see what it was made of," she told BBC News.

Tim de Zeeuw, director-general of the European Southern Observatory (Eso) organisation, which will operate the E-ELT, told BBC News: "The E-ELT will make it possible to take images of (Earth-mass planets) and indeed find evidence for many of them.

"This then leads to very interesting questions: do we find many Solar Systems like our own? Or is there only one like us?"

He added: "I don't follow this field daily... (but) the number of cases we have is steadily growing to a size where we can start asking this question and there are some indications that perhaps our Solar System is a little unusual."

The 42m E-ELT comprises five large mirrors. Its adaptive optics system will compensate for the distortions to images of the sky caused by turbulence in the Earth's atmosphere.

Construction of the ground observatory could begin in 2011 if all goes to plan. Eso intends to select a location for the telescope by the end of this year.

Six sites have been shortlisted: three in Chile; one in the Canary Islands, Spain; one in Morocco; and one in Argentina.

Story from BBC NEWS:

Published: 2009/04/21 09:55:10 GMT


Astronomers Find Planet Closer to Size of Earth

April 22, 2009
Article from New York Times

European astronomers said Tuesday that they had discovered the smallest planet yet found orbiting another star. The planet could be as little as only 1.9 times as massive as the Earth and belongs to a dim red star known as Gliese 581, which lies about 20 light-years from Earth in the constellation Libra.

The star was already know to harbor at least three more massive planets. The new planet, known as Gliese 581e, is probably rocky like the Earth, but it lies in such a close orbit — only three million miles from its star — that it is surely blasted with too much radiation and heat to be livable.

Michel Mayor, of Geneva Observatory, and his colleagues announced their results at a conference at the University of Hertfordshire in Britain and in a paper submitted to the journal Astronomy and Astrophysics.

Astronomers said the discovery was more encouragement that the galaxy was full of small-mass planets and that with more time and improved instruments like the Kepler satellite, recently launched by NASA, they would eventually find Earth-like planets in orbits suitable for life around other stars.

“Finding Earth-like planets with lukewarm temperatures is the next great goal,” Geoff Marcy, of the University of California, Berkeley, a planet-hunting rival of Dr. Mayor’s, said in an e-mail message.

“This is the most exciting discovery in exoplanets so far,” Dr. Marcy said.

Dr. Mayor’s group also discovered the first exoplanet, a gas giant 160 times the mass of the Earth, in 1995, using a technique known popularly as the “wiggle” method that detects planets by a slight gravitational tug they give their stars. The method is most sensitive to massive planets in close orbits. In a statement, Dr. Mayor noted that the new planet is only one-eightieth of the mass of the first one, saying, “This is tremendous progress in 14 years.”

The discovery also cements the Gliese system as one of the most promising exoplanet systems. Two years ago, the third planet from that star was hailed as a ”Goldilocks” planet, where liquid water and thus life might be possible, until calculations showed that the greenhouse effect would broil it.

But the new data also shifted the orbit of the star’s outermost planet inward so that it now appears to revolve in the so-called habitable zone where liquid water is possible, according to Stéphane Udry of Geneva University, one of the team members.

That planet, 581d, is about seven times as massive as the Earth, Dr. Udry explained, which is too big to be just rock. It probably formed as a combination of ice and rock farther out in the Gliese system and then migrated inward, according to various planetary formation models, and melted. He called it the first serious “water world candidate.”

Sara Seager, a planet theorist at the Massachusetts Institute of Technology, said in an e-mail message that the Gliese planetary system “is like the gift that keeps on giving.”

SOURCE: New York Times

Most Earthlike Planet Yet Found May Have Liquid Oceans

Kate Ravilious
April 21, 2009
for National Geographic News

It probably wouldn't feel exactly like home. But the planet known as Gliese 581d has a lot more in common with Earth than astronomers first thought.

New measurements of the planet's orbit place it firmly in a region where conditions would be right for liquid water, and thus life as we know it, astronomer Michel Mayor, from Geneva University in Switzerland, announced today.

"It lies in the [life-supporting] habitable zone, and it could have an ocean at its surface," Mayor said during the European Week of Astronomy and Space Science conference, being held this week at the University of Hertfordshire in the U.K.

First discovered in 2007, Gliese 581d was originally calculated to be too far away from its host star—and therefore too cold—to support an ocean.

But Mayor and colleagues now show that the extrasolar planet, or exoplanet, orbits its host in 66.8 days, putting it just inside the cool star's habitable zone.

At the same time, Mayor and colleagues announced that they have spotted a fourth planet orbiting in the Gliese 581 star system—and it's the lightest exoplanet found so far.

The planet, dubbed Gliese 581e, is only about twice the mass of Earth and is the closest planet to the star, completing its orbit in about 3.15 days.

"It brings down the mass [of the lightest known exoplanet] by more than a factor of two. The previous smallest was around five Earth masses," said Andrew Collier Cameron, an astronomer at the University of Saint Andrews in the U.K. who was not involved in the find.

(Related: "Mysterious 'Super Earth' Is Smallest Known Exoplanet?")

Near Neighbor

Gliese 581, a red dwarf star in the constellation Libra, lies around 20.5 light-years from Earth.

"In astronomical terms it is one of our near neighbors, the 87th closest known star system to the sun," said Carole Haswell, an astronomer at the Open University in Milton Keynes, U.K.

Since planets orbiting Gliese 581 are too far away to be seen directly, Mayor and colleagues originally spotted Gliese 581d by searching for tiny wobbles in the host star's motion using the European Southern Observatory (ESO) telescope at La Silla in Chile.

Weighing in at around seven Earth masses, Gliese 581d is unlikely to be made of rocks alone, the team believes.

"We can only speculate at this stage, but it may have a rocky core, encased in an icy layer, with a liquid ocean at the surface and an atmosphere," Mayor said.

Meanwhile, the much smaller and lighter Gliese 581e "probably doesn't look too different to Earth, except that it will be very hot, because it is so close to its host star," said Andrew Norton, an astronomer also at the Open University.

Norton's colleague Haswell added: "It is very exciting that such a promising candidate for an Earthlike planet has been found so close to us. It means there are likely to be many more when we search further."

And the more Earthlike planets there are, the greater the chance of discovering one that harbors life.

"I think it is only a matter of time," Norton said. "If life really does exist elsewhere in the universe, then within the next 10 to 15 years I expect we may see the first signs of life, via spectroscopic signals from exoplanets."

© 1996-2008 National Geographic Society. All rights reserved.

SOURCE: National Geographic News

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