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Gliese 581 d is an extrasolar planet
Extrasolar planet

An extrasolar planet, or exoplanet, is a planet beyond the Solar System, orbiting a star other than the Sun. As of February 2009, 342 exoplanets are listed in the Extrasolar Planets Encyclopaedia....
 approximately 20 light-year
Light-year

A light-year or light year is a Units of measurement of length, equal to just under ten orders_of_magnitude_%28numbers%29#1012 kilometres....
s away in the constellation
Constellation

A constellation is a group of stars that appear to have a physical proximity in the sky. The stars in a constellation are often vastly distant from each other, but they appear close to each other from the perspective of Earth....
 of Libra
Libra (constellation)

Libra...
. Because of its mass, the planet is classified as a super-Earth
Super-Earth

A Super-Earth is an extrasolar planet more massive than the Earth but less massive than a gas giant. The term "super-Earth" refers only to the mass of the planet and does not imply anything about the surface conditions or habitability: in particular it does not imply that the planet would have a similar temperature or environment to Earth....
 planet. Because the planet orbits in the outer edge of its parent star's habitable zone
Habitable zone

The habitable zone in astronomy is a region of space where stellar conditions are favorable for life as it is found on Earth. There are two regions that must be favorable, one within a planetary system and the other within the galaxy....
, it is thought that the planet may be similar to Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
.

Discovery
The planet was discovered by the team of Stéphane Udry
Stéphane Udry

St?phane Udry is an astronomer at the University of Geneva in Switzerland, whose current work is primarily the search for extra-solar planets. He and his team have recently discovered a possibly terrestrial planet in the habitable zone of the red dwarf star Gliese 581, approximately 20 light years away in the constellation Libra ....
 of the Geneva Observatory in Switzerland
Switzerland

Switzerland is a landlocked Swiss Alps country of roughly 7.7 million people in Western Europe with an area of 41,285 km?. Switzerland is a federal republic consisting of 26 states called Cantons of Switzerland....
 using the HARPS
Harps

Harps is the plural of harp, a stringed musical instrument.Harps can also refer to:*Harps GAA, an Irish sports club* High Accuracy Radial Velocity Planet Searcher, a spectrograph used for research in astronomy....
 instrument on the European Southern Observatory
European Southern Observatory

The European Southern Observatory , is an intergovernmental research organization for astronomy, composed and supported by fourteen countries from Europe....
 3.6 meter telescope
Telescope

A telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century....
 in La Silla, Chile
Chile

Chile, officially the Republic of Chile , is a country in South America occupying a long and narrow coastal strip wedged between the Andes mountains and the Pacific Ocean....
 on 24 April 2007.






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Encyclopedia


Gliese 581 d is an extrasolar planet
Extrasolar planet

An extrasolar planet, or exoplanet, is a planet beyond the Solar System, orbiting a star other than the Sun. As of February 2009, 342 exoplanets are listed in the Extrasolar Planets Encyclopaedia....
 approximately 20 light-year
Light-year

A light-year or light year is a Units of measurement of length, equal to just under ten orders_of_magnitude_%28numbers%29#1012 kilometres....
s away in the constellation
Constellation

A constellation is a group of stars that appear to have a physical proximity in the sky. The stars in a constellation are often vastly distant from each other, but they appear close to each other from the perspective of Earth....
 of Libra
Libra (constellation)

Libra...
. Because of its mass, the planet is classified as a super-Earth
Super-Earth

A Super-Earth is an extrasolar planet more massive than the Earth but less massive than a gas giant. The term "super-Earth" refers only to the mass of the planet and does not imply anything about the surface conditions or habitability: in particular it does not imply that the planet would have a similar temperature or environment to Earth....
 planet. Because the planet orbits in the outer edge of its parent star's habitable zone
Habitable zone

The habitable zone in astronomy is a region of space where stellar conditions are favorable for life as it is found on Earth. There are two regions that must be favorable, one within a planetary system and the other within the galaxy....
, it is thought that the planet may be similar to Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
.

Discovery


The planet was discovered by the team of Stéphane Udry
Stéphane Udry

St?phane Udry is an astronomer at the University of Geneva in Switzerland, whose current work is primarily the search for extra-solar planets. He and his team have recently discovered a possibly terrestrial planet in the habitable zone of the red dwarf star Gliese 581, approximately 20 light years away in the constellation Libra ....
 of the Geneva Observatory in Switzerland
Switzerland

Switzerland is a landlocked Swiss Alps country of roughly 7.7 million people in Western Europe with an area of 41,285 km?. Switzerland is a federal republic consisting of 26 states called Cantons of Switzerland....
 using the HARPS
Harps

Harps is the plural of harp, a stringed musical instrument.Harps can also refer to:*Harps GAA, an Irish sports club* High Accuracy Radial Velocity Planet Searcher, a spectrograph used for research in astronomy....
 instrument on the European Southern Observatory
European Southern Observatory

The European Southern Observatory , is an intergovernmental research organization for astronomy, composed and supported by fourteen countries from Europe....
 3.6 meter telescope
Telescope

A telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century....
 in La Silla, Chile
Chile

Chile, officially the Republic of Chile , is a country in South America occupying a long and narrow coastal strip wedged between the Andes mountains and the Pacific Ocean....
 on 24 April 2007. Udry's team employed the radial velocity
Radial velocity

Radial velocity is the velocity of an object in the direction of the line of sight . The light of an object with a substantial radial velocity will be subject to Doppler effect, so the frequency of the light decreases for receding objects and increases for approaching objects ....
 technique, in which the size and mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 of a planet
Planet

A planet , as 2006 definition of planet by the International Astronomical Union , is a celestial body orbiting a star or Stellar evolution#Stellar remnants that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared the neighbourhood of planetesimals....
 are determined based on the small perturbations it induces in its parent star’s orbit
ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
 via gravity.

The team is confident that the planet exists but recognizes that unlikely events could mimic its existence. They believe the issue will be settled by upcoming studies.

Dynamical simulations of the Gliese 581 system assuming that the orbits of the three planets are coplanar
Coplanarity

In geometry, a Set of points in space is coplanar if the points all lie in the same geometric Plane . For example, three distinct points are always coplanar; but four points in space are usually not coplanar....
 show that the system becomes unstable if its component masses are so high as to correspond to an overall inclination angle of 10° or less. For Gliese 581 d, the upper bound of its mass must be half that of 581 b; that is, 581 d's maximum is 44 Earth masses. At this mass it must be held together with a central heavy-element core like Saturn
Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant....
 and maybe even HD 149026 b
HD 149026 b

HD 149026 b is an extrasolar planet approximately 257 light-years away in the constellation of Hercules . The planet was discovered after it transit its parent star, HD 149026....
.

Climate and habitability


Although Gliese 581 d orbits outside the theoretical habitable zone
Habitable zone

The habitable zone in astronomy is a region of space where stellar conditions are favorable for life as it is found on Earth. There are two regions that must be favorable, one within a planetary system and the other within the galaxy....
 of its star, scientists surmise that conditions on the planet may be conducive to supporting life. Scientists originally believed that Gliese 581 d would be too cold for liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 to exist, and therefore could not support life
Life

Life is a characteristic of organisms that exhibit certain biological processes such as chemical reactions or other events that results in a transformation....
 in forms as existing on Earth. However, since Earth's temperature would be about -18°C without any greenhouse gases, and due to a theorized greenhouse effect
Greenhouse effect

The greenhouse effect refers to the change in the steady state temperature of a planet or moon by the presence of an atmosphere containing gas that absorbs and emits infrared....
 of Gliese 581 d, research now suggests that atmospheric conditions on the planet could create temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
s at which liquid water can exist, and therefore the planet may be capable of supporting life.