Gliese 581 d (pronounced /ˈɡliːzə/) or Gl 581 d is an extrasolar planet 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.
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.
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 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
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, "d could be
covered by a 'large and deep ocean'; it is the first serious Ocean planet candidate."
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." 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 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.
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. 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
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.
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.
Details of GL581D
Gliese 581 d
Extrasolar planet List of extrasolar planets
An artist's impression of Gliese 581 d and speculative moons.
Star Gliese 581
Right ascension (α) 15h 19m 26s
Declination (δ) −07° 43′ 20″
Apparent magnitude (mV) 10.55
20.3 ± 0.3 ly
(6.2 ± 0.1 pc)
Spectral type M3V
Semimajor axis (a) 0.22 AU
Eccentricity (e) 0.38 ± 0.09
Orbital period (P) 66.80 ± 0.14 d
Inclination (i) ≥30°
(ω) −33 ± 15°
Time of periastron (T0) 2,454,603.0 ± 2.2 JD
Minimum mass (m sin i) 7.09 M⊕