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Gliese 436 b
Extrasolar planet List of extrasolar planets
300px
Size comparison of Gliese 436 b with Neptune
Parent star

<tr> <td colspan="2">Star</td> <td>Gliese 436</td></tr><tr> <td colspan="2">Constellation</td> <td>Leo</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>11h 42m 11.0941s[1]</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>+26° 42′ 23.652″[1]</td></tr><tr> <td>Apparent magnitude</td> <td style="text-align: center">(mV)</td> <td>10.68</td></tr><tr><td colspan="2">Distance</td><td>33.4 ± 0.8 ly
(10.2 ± 0.2 pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>M2.5 V[1]</td></tr><tr> <td>Mass</td> <td style="text-align: center">(m)</td> <td>0.41 ± 0.05 M</td></tr><tr> <td>Radius</td> <td style="text-align: center">(r)</td> <td>0.42 R</td></tr><tr> <td>Temperature</td> <td style="text-align: center">(T)</td> <td>3318 K</td></tr><tr> <td>Metallicity</td> <td style="text-align: center">[Fe/H]</td> <td>-0.32</td></tr><tr> <td>Age</td> <td style="text-align: center"></td> <td>6.5–9.9 Gyr</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>0.0291±0.0004[2] AU
(4.35 Gm)</td></tr><tr><td> </td> <td style="text-align: center"> </td> <td>2.85 mas</td></tr><tr> <td>Periastron</td> <td style="text-align: center">(q)</td> <td>0.0247 AU
(3.70 Gm)</td></tr><tr> <td>Apastron</td> <td style="text-align: center">(Q)</td> <td>0.0335 AU
(5.01 Gm)</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0.150±0.012[2]</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>2.643904±0.000005[3] d
(0.00723849 y)</td></tr><tr><td> </td> <td style="text-align: center"> </td> <td>(63.4537 h)</td></tr><tr> <td>Inclination</td> <td style="text-align: center">(i)</td> <td>85.8+0.21
−0.25
[3]°</td></tr><tr> <td>Argument of
periastron
</td> <td style="text-align: center">(ω)</td> <td>351±1.2°</td></tr><tr> <td>Time of periastron</td> <td style="text-align: center">(T0)</td> <td>2,451,551.716
±0.01 JD</td></tr><tr> <td>Semi-amplitude</td> <td style="text-align: center">(K)</td> <td>18.68±0.8 m/s</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>22.2±1.0[2] M</td></tr><tr><td>Radius</td><td style="text-align: center">(r)</td><td>4.327±0.183[2][4] Template:Earth radius</td></tr><tr><td>Stellar flux</td><td style="text-align: center">(F)</td><td>29.5 </td></tr><tr><td>Density</td><td style="text-align: center">(ρ)</td><td>1.51 g cm-3</td></tr><tr><td>Surface gravity</td><td style="text-align: center">(g)</td><td>1.18 g</td></tr><tr> <td>Temperature</td> <td style="text-align: center">(T)</td> <td>712±36[2] K</td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>August 31, 2004</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Butler, Vogt,
Marcy et al.</td></tr><tr> <td colspan="2">Discovery method</td> <td>Radial velocity, Transit</td></tr><tr> <td colspan="2">Discovery site</td> <td>California, USA</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr>

Other designations
Ross 905 b, GJ 436 b,[5] LTT 13213 b, GCTP 2704.10 b, LHS 310, AC+27:28217 b, Vyssotsky 616 b, HIP 57087 b, GEN# +9.80120068 b, LP 319-75 b, G 121-7 b, LSPM J1142+2642 b, 1RXS J114211.9+264328 b, ASCC 683818 b, G 147-68 b, UCAC2 41198281 b, BPS BS 15625-0002 b, G 120-68 b, 2MASS J11421096+2642251 b, USNO-B1.0 1167-00204205 b, CSI+27-11394 b, MCC 616 b, VVO 171 b, CSI+27-11395 b, HIC 57087 b, NLTT 28288 b, Zkh 164 b, CSI+26-11395 b, [RHG95] 1830 b, GCRV 7104 b, LFT 838 b, PM 11395+2700 b

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
Encyclopaedia
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>

Gliese 436 b Template:IPAc-en (sometimes called GJ 436 b[6]) is a Neptune-sized extrasolar planet orbiting the red dwarf star Gliese 436.[7] It was among the smallest known transiting planets in mass and radius until the much smaller Kepler discoveries started coming in 2010.

In December 2013, NASA reported that clouds may have been detected in the atmosphere of GJ 436 b.[8][9][10][11]

DiscoveryEdit

File:GJ 436 b rv.pdf

Gliese 436 b was discovered in August 2004 by R. Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and University of California, Berkeley, respectively, using the radial velocity method. Together with 55 Cancri e, it was then the first of a new class of planets with a minimum mass (M sini) similar to Neptune.

The planet was recorded to transit its star by an automatic process at NMSU on January 11, 2005, but this event went unheeded at the time.[12] In 2007, Gillon led a team which observed the transit, grazing the stellar disc relative to Earth. Transit observations led to the determination of Gliese 436 b's exact mass and radius, both of which are very similar to Neptune. Gliese 436 b then became the smallest known transiting extrasolar planet. The planet is about 4000 km larger in diameter than Uranus and 5000 km larger than Neptune and a bit more massive. Gliese 436b (also known as GJ 436b) orbits its star at a distance of 4,000,000 km or 15 times closer than Mercury's average distance from the sun.

Physical characteristicsEdit

File:GJ436interior.jpg

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 (which had been, in a Reuters article from a month prior to this measurement, estimated at 520 K). Whatever energy that tidal effects deliver to the planet does not notably affect its temperature.[13] Its discoverers allowed for a temperature increase due to a greenhouse effect.[14]

Its main constituent was initially predicted to be hot "ice" in various exotic high-pressure forms,[14][15] which remains solid because of the planet's gravity despite the high temperatures.[16] The planet could have formed further from its current position, as a gas giant, and migrated inwards with the other gas giants. As it arrived in range, the star would have blown off the planet's hydrogen layer via coronal mass ejection.[17]

However when the radius became better known, ice alone was not enough to account for it. An outer layer of hydrogen and helium up to ten percent in mass would be needed on top of the ice to account for the observed planetary radius.[2][3] This obviates the need for an ice core. Alternatively, the planet may be a super-earth.[18]

Observations of the planet's brightness temperature with the Spitzer Space Telescope suggest a possible thermochemical disequilibrium in the atmosphere of this exoplanet. Results published in Nature suggest that Gliese 436b's dayside atmosphere is abundant in CO and deficient in methane (CH4) by a factor of ~7,000. This result is unexpected because, based on current models at this temperature, the atmospheric carbon should prefer CH4 over CO.[19][20][21][22]

Orbital characteristicsEdit

One orbit around the star takes only about 2 days, 15.5 hours. Gliese 436 b's orbit is likely misaligned with its star's rotation.[21]

This planet should not be as eccentric as is measured. To have maintained its eccentricity over time requires that it be accompanied by another planet.[2][23]

In 2012 two candidate planets were proposed.[24]

See alsoEdit

ReferencesEdit

  1. 1.0 1.1 1.2 LHS 310. Simbad. Centre de Données astronomiques de Strasbourg. Retrieved 2007-11-28.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 (2007). Spitzer Transit and Secondary Eclipse Photometry of GJ 436b. The Astrophysical Journal 667 (2): L199–L202.
  3. 3.0 3.1 3.2 Bean, J.L. et al. (2008). A Hubble Space Telescope transit light curve for GJ 436b. Astronomy & Astrophysics.
  4. Confirmed, (2008). Transit infrared spectroscopy of the hot neptune around GJ 436 with the Hubble Space Telescope. Monthly Notices of the Royal Astronomical Society: Letters 393: L6–L10.
  5. Maness et al. (2006). The M Dwarf GJ 436 and its Neptune-Mass Planet. Submitted to Publications of the Astronomical Society of the Pacific 119 (851): 90–101.
  6. (August 1, 2012)Dynamical evolution of the Gliese 436 planetary system - Kozai migration as a potential source for Gliese 436b's eccentricity. arXiv.
  7. Butler et al. (2004). A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436. The Astrophysical Journal 617 (1): 580–588.
  8. Release 13-383 - NASA's Hubble Sees Cloudy Super-Worlds With Chance for More Clouds. NASA (December 31, 2013). Retrieved January 1, 2014.
  9. Moses, Julianne (January 1, 2014). Extrasolar planets: Cloudy with a chance of dustballs. Nature (journal) 505 (7481): 31-32.
  10. (January 1, 2014)A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b. Nature (journal) 505 (7481): 66-68.
  11. (January 1, 2014)Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b. Nature (journal) 505 (7481): 69-72.
  12. (2008). New observations and a possible detection of parameter variations in the transits of Gliese 436b. The Astrophysical Journal 689 (2): L149–L152.
  13. (2008). Tidal Heating of Extra-Solar Planets. The Astrophysical Journal 681 (2): 1631–1638.
  14. 14.0 14.1 M. Gillon et al. (2007). Detection of transits of the nearby hot Neptune GJ 436 b. Astronomy and Astrophysics 472 (2).
  15. Template:Cite news
  16. Template:Cite news
  17. H. Lammer et al. (2007). The impact of nonthermal loss processes on planet masses from Neptunes to Jupiters. Geophysical Research Abstracts 9 (07850). By analogy with Gliese 876 d.
  18. E. R. Adams, S. Seager, and L. Elkins-Tanton (February 2008). Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres. The Astrophysical Journal 673 (2): 1160–1164.
  19. (22 April 2010)Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b. Nature 464 (7292): 1161–1164.
  20. GJ436b - Where's the methane? Planetary Sciences Group at the University of Central Florida, Orlando
  21. 21.0 21.1 (2011). A Spitzer Transmission Spectrum for the Exoplanet GJ 436b. Astrophysical Journal 735, 27.
  22. (2011). Thermochemical and Photochemical Kinetics in Cooler Hydrogen Dominated Extrasolar Planets. Astrophysical Journal 738, 32., abstract in the arXiv titled "Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b"
  23. Template:Cite arXiv
  24. Reuters (July 2012). Alien exoplanet smaller than Earth discovered. Sydney Morning Herald. Retrieved 19 July 2012.

Selected media articlesEdit

Template:Wikinewsart

External linksEdit

Template:Commonscat-inline

Coordinates: Sky map 11h 42m 11.0941s, +26° 42′ 23.652″

Template:Star systems within 30 – 35 light-years

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