Gliese 581 c
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Extrasolar planet | List of extrasolar planets | ||
---|---|---|---|
![]() around the red dwarf star Gliese 581, with Gliese 581 c in the foreground. | |||
Parent star | |||
Star | Gliese 581 | ||
Constellation | Libra | ||
Right ascension | (α) | 15h 19m 26s | |
Declination | (δ) | −07° 43′ 20″ | |
Spectral type | M2.5V | ||
Orbital elements | |||
Semimajor axis | (a) | 0.073 AU | |
Eccentricity | (e) | 0.16±0.07 | |
Orbital period | (P) | 12.93 d | |
Inclination | (i) | ?° | |
Longitude
of periastron |
(ω) | ?° | |
Time of periastron | (τ) | ? JD | |
Physical characteristics | |||
Mass | (m) | > 5 ME | |
Radius | (r) | ~1.5 RE | |
Density | (ρ) | ? kg/m3 | |
Temperature | (T) | ~290 K | |
Discovery information | |||
Discovery date | 2007-04-04 | ||
Discoverer(s) | Udry et al. | ||
Detection method | Radial Velocity | ||
Discovery status | published |
Gliese 581 c (IPA: [ˈgliːˌzə]) is an extrasolar planet orbiting the red dwarf star Gliese 581[1]. It appears to be in the habitable zone of space surrounding the star, where the surface temperatures of any planets present might maintain liquid water[1][2]. The planet is relatively close, at 20.5 light years (190 trillion kilometres) from Earth in the constellation of Libra[3]. Its star is identified as Gliese 581 by its number in the Gliese Catalogue of Nearby Stars.
Contents |
[edit] Characteristics
[edit] Physical
Gliese 581 c may be the first discovered extrasolar planet similar in temperature to Earth. It is the smallest extrasolar planet around a main sequence star discovered to date[1].
The calculation of its mass depends on the presence of other planets in the Gliese 581 system. Using the already known mass of Gliese 581 b, and assuming the existence of Gliese 581 d, Gliese 581 c would have a mass 5.03 times that of Earth.[4]
Under the assumption that it is a rocky planet, rather than an icy planet, Gliese 581 c has a radius 50% larger than that of Earth[5]. Gravity on such a planet's surface would be approximately 2.1 times as strong as on Earth.
The Gliese 581 system is believed to be ~4.3 billion years old.
[edit] Orbital
Gliese 581 c has an orbital period ("year") of 13 Earth days and its orbital radius is only about 7% of that of the Earth,[3] about 11 million km (6.8 million miles), while the Earth is 150 million km (93.2 million miles) from the Sun. Since the host star is smaller and colder than the Sun — and thus less luminous — this distance places the planet in the habitable zone. This proximity also means that the primary star is several times larger in the planet's sky than the Sun is in Earth's sky.
The free fall accelerations on the day and night sides of the planet would differ by approximately 0.7m/sec² because of the high orbital velocity. For earth, this difference is about 0.01m/sec².
[edit] Climatic

Gliese 581 c has a projected equilibrium surface temperature between 0°C and 40°C[3]. However, the actual temperature on the surface depends on the planet's atmosphere, which remains unknown. Research team member Xavier Delfosse expects that the actual surface temperatures will only be hotter; for instance, the corresponding calculation for Earth yields an "effective surface temperature" of 256 K (−17°C), yet Earth's true surface is 32 K warmer, an average of 288 K (15°C), due to the greenhouse effect of its atmosphere. [6]
Because of its close orbit around its parent star, the planet would experience tides about 400 times as strong as those that the Moon causes on the Earth. It may be tidally locked to the star, with one hemisphere always lit and the other always dark[7]. The lit hemisphere might be extremely hot and the dark hemisphere extremely cold, while the narrow terminator or "twilight zone" between them might have a moderate climate more suitable for life similar to Earth's.[8]
A theoretical model predicts that volatile compounds such as water and carbon dioxide might evaporate in the scorching heat of the sunward side, migrate to the cooler night side, and condense to form ice caps. Over time, the entire atmosphere could become frozen as ice caps on the night side of the planet. Alternatively, if it has an atmosphere large enough to be stable, it should circulate the heat more evenly, allowing for a wider habitable area on the surface.[9]
[edit] Discovery
The discovery of the planet by the team of Stéphane Udry of the Geneva Observatory in Switzerland was announced on April 24, 2007. The team used the HARPS instrument on the European Southern Observatory 3.6 m Telescope in La Silla, Chile. The team employed the radial velocity technique. The team now intends to use the Canadian-built MOST space telescope to conduct follow-up studies of the planet as it passes in front of the star.

[edit] Liquid water
Gliese 581 c is within the habitable zone where liquid water—a necessary ingredient for life as we know it—could exist.[1][10]
Although the potential for liquid water is predicted by the habitable-zone
model, no direct evidence has been found. Techniques like the one used to
measure HD
209458 b could be applied to determine the existence of water vapor in an
extrasolar planet's atmosphere, but this method
requires the rare coincidence of a planet whose orbit causes it to transit directly
between its star, and our planet; this is something Gliese 581 c is not known to
do.
[edit] Difficulty of exploration
Gliese 581 c presents several challenges for study or exploration. It has not been directly observed, and the development of equipment sensitive enough to look for signs of life will take several years.[11] However, according to the research-team member Xavier Delfosse:
Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the universe, one would be tempted to mark this planet with an X. [11][5]
If a probe were sent from Earth to explore Gliese 581 c, it would take 20.5 years to reach it if it could travel at the speed of light; scientists observing Gliese 581 c are seeing what happened to it 20.5 years ago because Gliese 581 c is 20.5 light years away[12][3].
[edit] See also
[edit] References
- ^ a b c d http://www.space.com/scienceastronomy/070424_hab_exoplanet.html
- ^ http://www.space.com/scienceastronomy/070424_exoplanet_side.html
- ^ a b c d "New 'super-Earth' found in space", BBC News, 25 April 2007. Retrieved on 2007-04-25.
- ^ Udry et al. (2007). "The HARPS search for southern extra-solar planets, XI. An habitable super-Earth (5 M⊕) in a 3-planet system". Astronomy and Astrophysics preprint: preprint.
- ^ a b http://www.eso.org/outreach/press-rel/pr-2007/pr-22-07.html
- ^ "More Earthlike Planets to Come", Wired Science, [1]
- ^ http://www.usatoday.com/printedition/news/20070425/1a_bottomstrip25_dom.art.htm
- ^ Perlman, David. "New planet found: It might hold life", San Francisco Chronicle, 2007-04-24. Retrieved on 2007-04-24.
- ^ Alpert, Mark (2005-11-07). Red Star Rising. Scientific American. Retrieved on 2007-04-25.
- ^ http://www.nbc4.tv/technology/13023236/detail.html
- ^ a b Earth-like planet found that may support life. CTV News. Retrieved on 2007-04-25.
- ^ http://www.esa.int/esaSC/SEMU3QS1VED_extreme_0.html
- Hazel Muir (April 25, 2007). 'Goldilocks' planet may be just right for life. NewScientistSpace.
- Astronomers find first habitable Earth-like planet. Scientificblogging.com (April 24, 2007).
- Ian Sample (April 24, 2007). 'Second Earth' may mean we're not alone. The Hindu.
- J.R. Minkle (April 24, 2007). All Wet? Astronomers Claim Discovery of Earth-like Planet. Scientific American.
- ANI (April 23, 2007). First habitable Earth like planet outside Solar System discovered. DailyIndia.com.
- Joe Campbell (April 26, 2007). Meet the neighbours. BBC Magazine.