Gliese 581 d

Extrasolar planet		List of extrasolar planets
An artist's impression of Gliese 581 d and speculative moons.
Parent star
Star		Gliese 581
Constellation		Libra
Right ascension	(α)	15h 19m 26s
Declination	(δ)	−07° 43′ 20″
Apparent magnitude	(mV)	10.55
Distance		20.3 ± 0.3 ly (6.2 ± 0.1 pc)
Spectral type		M3V
Orbital elements
Semimajor axis	(a)	0.22[1] AU (33 Gm)
		35 mas
Periastron	(q)	0.14 AU (21 Gm)
Apastron	(Q)	0.30 AU (49 Gm)
Eccentricity	(e)	0.38 ± 0.09[1]
Orbital period	(P)	66.80 ± 0.14[1] d (0.1829 y)
Inclination	(i)	≥30[1]°
Argument of periastron	(ω)	−33 ± 15[1]°
Time of periastron	(T0)	2,454,603.0 ± 2.2[1] JD
Physical characteristics
Minimum mass	(m sin i)	7.09[1] M⊕
Discovery information
Discovery date		24 April 2007
Discoverer(s)		Udry et al.
Detection method		Radial velocity
Discovery site		La Silla Observatory, Chile
Discovery status		Published[2]
Database references
Extrasolar Planets Encyclopaedia		data
SIMBAD		data

Gliese 581 d (pronounced /ˈɡliːzə/) or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. Because of its mass, nearly 8 times that of Earth, the planet is classified as a super-Earth. In late April 2009, new observations by the original discovery team concluded that the planet is within the habitable zone where liquid water and, therefore, life could exist.

[edit] Discovery

The planet was discovered by the team of Stéphane Udry of the Geneva Observatory in Switzerland using the HARPS instrument on the European Southern Observatory 3.6 meter telescope in La Silla, Chile on 24 April 2007. Udry's team employed the radial velocity technique, in which the size and mass of a planet are determined based on the small perturbations it induces in its parent star’s orbit via gravity.^[2]

Dynamical simulations of the Gliese 581 system assuming that the orbits of the three planets are coplanar show that the system becomes unstable if the masses of the planets exceed 1.6 – 2 times the minimum values. The upper mass limit for Gliese 581 d is 13.8 Earth masses.^[1]

[edit] Climate and habitability

Gliese 581 d's orbit compared to Mercury's orbit (0.38AU) in our Solar System.

It was originally thought that Gliese 581 d orbits outside the theoretical habitable zone of its star. Further studies released in April 2009 confirmed that the planet is within the habitable zone where liquid water could exist. According to Stephan Udry, "It could be covered by a 'large and deep ocean'; it is the first serious Ocean planet candidate."^[3] Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to the star."^[4][5] Scientists originally believed that Gliese 581 d would be too cold for liquid water to exist, and therefore could not support life in forms as existing on Earth. However, since Earth's temperature would be about -18°C^[6] without any greenhouse gases, and due to a theorized greenhouse effect of Gliese 581 d, research now suggests that atmospheric conditions on the planet could create temperatures at which liquid water can exist, and therefore the planet may be capable of supporting life.^[7][8][9]

On 21 April 2009, ESO announced, together with the discovery of Gliese 581 e, that they had refined the models of Gliese 581 d's orbit, discovering it lay well within the habitable zone.^[1][10] Calculations by Barnes et al. suggest, however, that tidal heating is too low to keep plate tectonics active on the planet, unless radiogenic heating is somewhat higher than expected.^[11]

[edit] Messages from Earth

In October 2008, members of the networking website Bebo beamed A Message From Earth, a high-power transmission at Gliese 581, using the RT-70 radio telescope belonging to the National Space Agency of Ukraine. This transmission is due to arrive in the Gliese 581 system's vicinity by the year 2029; the earliest possible arrival for a response, should there be one, would be in 2049.^[12]

As part of the 2009 National Science Week celebrations in Australia, Cosmos Magazine launched a website called Hello From Earth to collect messages for transmission to Gliese 581d. The maximum length of the messages was 160 characters, and they were restricted to the English language. In total, 25,880 messages were collected from 195 countries around the world. The messages were transmitted from the DSS-43 70 m radio telescope at the Canberra Deep Space Communication Complex at Tidbinbilla, Australia on the 28th of August, 2009. ^[13]

[edit] References

[edit] External links

Wikinews has related news: Discovery of smallest exoplanet yields 'extraordinary' find

Wikimedia Commons has media related to: Gliese 581

• National Science Week 2009 - Send A Message To Gliese 581d

v • d • e The Gliese 581 system Star Gliese 581 Planets Gliese 581 e • Gliese 581 b • Gliese 581 c • Gliese 581 d

Coordinates: 15^h 19^m 26^s, −07° 43′ 20″