Gliese 436 b
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| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
 |
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| Parent star | ||
| Star | Gliese 436 | |
| Constellation | Leo | |
| Right ascension | (α) | 11h 42m 11.0941s[1] |
| Declination | (δ) | +26° 42′ 23.652″[1] |
| Distance | 33.4 ly (10.2 pc) | |
| Spectral type | M2.5 V[1] | |
| Orbital elements | ||
| Semimajor axis | (a) | 0.0291±0.0004[2] AU |
| Eccentricity | (e) | 0.150±0.012[2] |
| Orbital period | (P) | 2.64385±0.00009 d |
| Inclination | (i) | 86.5° |
| Angular distance | (θ) | 2.794 mas |
| Longitude of periastron |
(ω) | 351±1.2° |
| Time of periastron | (T0) | 2,451,551.716 ±0.01 JD |
| Semi-amplitude | (K) | 18.68±0.8 m/s |
| Physical characteristics | ||
| Mass | (m) | 22.2±1.0[2] M⊕ |
| Radius | (r) | 4.327±0.183[2] R⊕ |
| Density | (ρ) | 1510 kg/m3 |
| Surface gravity | (g) | 1.18 g |
| Temperature | (T) | 712±36[2] K |
| Discovery information | ||
| Discovery date | August 31, 2004 | |
| Discoverer(s) | Butler, Vogt, Marcy et al. |
|
| Detection method | Radial velocity, Transit | |
| Discovery site | California, USA | |
| Discovery status | Published | |
Gliese 436 b (IPA: /ˈgliːzə/) (GJ 436 b)[3] is a Neptune-sized extrasolar planet orbiting the red dwarf star Gliese 436.[4] Discovered in August 2004, it was the first extrasolar planet determined to contain water. As of May 2007, it is the smallest planet known to transit its star.
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[edit] Discovery
Gliese 436 b was discovered in 2004 by the planet-hunting team of Dr. Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and University of California, Berkeley, respectively. Together with 55 Cancri e, it was the first of a new class of planets with a size similar to Neptune.
In 2007, the planet was observed to transit its star. Transit observations led to the determination of Gliese 436 b's radius and mass, both of which are very similar to Neptune. Gliese 436 b is thus the smallest known transiting extrasolar planet. The planet is about 4,000km larger in diameter than Uranus and 5,000km larger than Neptune but a bit more massive.
[edit] Physical characteristics
One orbit around the star takes only about 2 days, 15.5 hours. The planet's surface temperature is estimated from measurements taken as it passes behind the star to be 712 K (439 °C).[2] This temperature is significantly higher than would be expected if the planet were only heated by radiation from its star, implying that strong tidal heating as a result of the planet's eccentric orbit is occurring. Its main constituent is likely to be hot "ice" in various exotic high-pressure forms,[5] which remains solid because of the planet's gravity despite the high temperatures.[6] An outer layer of hydrogen and helium up to ten percent in mass is probably needed on top of the ice to account for the observed planetary radius.
[edit] References
- ^ a b c LHS 310. Simbad. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-11-28.
- ^ a b c d e f Deming, D. et al. (2007). "Spitzer Transit and Secondary Eclipse Photometry of GJ 436b" arxiv:0707.2778 [astro-ph].
- ^ Maness et al. (2006). "The M Dwarf GJ 436 and its Neptune-Mass Planet". Submitted to Publications of the Astronomical Society of the Pacific.
- ^ Butler et al. (2004). "A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436". The Astrophysical Journal 617: 580 – 588. doi:.
- ^ Shiga, David. "Strange alien world made of "hot ice"", New Scientist, 6 May 2007. Retrieved on 2007-05-16.
- ^ Fox, Maggie. "Hot "ice" may cover recently discovered planet", Science News, Scientific American.com, May 16, 2007. Retrieved on 2007-05-17.
[edit] Selected media articles
- Hot "ice" may cover recently discovered planet, Reuters, 16 May 2007.
- Astronomers Detect Shadow Of Water World In Front Of Nearby Star (from Science Daily).
