Gliese 436 b

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Gliese 436 b
Exoplanet List of exoplanets
300px
Size comparison of Gliese 436 b with Neptune
Parent star
Star Gliese 436
Constellation Leo
Right ascension (α) 11h 42m 11.0941s[1]
Declination (δ) +26° 42′ 23.652″[1]
Apparent magnitude (mV) 10.68
Distance 33.4 ± 0.8 ly
(10.2 ± 0.2 pc)
Spectral type M2.5 V[1]
Mass (m) 0.41 ± 0.05 M☉
Radius (r) 0.42 R☉
Temperature (T) 3318 K
Metallicity [Fe/H] -0.32
Age 7.41–11.05[2] Gyr
Orbital elements
Semi-major axis (a) 0.0291±0.0004[3] AU
(4.35 Gm)
    2.85 mas
Periastron (q) 0.0247 AU
(3.70 Gm)
Apastron (Q) 0.0335 AU
(5.01 Gm)
Eccentricity (e) 0.150±0.012[3]
Orbital period (P) 2.643904±0.000005[4] d
(0.00723849 y)
    (63.4537 h)
Inclination (i) 85.8+0.21
−0.25[4]°
Argument 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[3] M⊕
Radius (r) 4.327±0.183[3][5] R⊕
Stellar flux (F⊙) 29.5 ⊕
Density (ρ) 1.51 g cm−3
Surface gravity (g) 1.18 g
Temperature (T) 712±36[3]
Discovery information
Discovery date August 31, 2004
Discoverer(s) Butler, Vogt,
Marcy et al.
Discovery method Radial velocity, Transit
Discovery site California, USA
Discovery status Published
Other designations
Ross 905 b, GJ 436 b,[6] 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
Database references
Extrasolar Planets
Encyclopaedia		 data
SIMBAD data
Exoplanet Archive data
Open Exoplanet Catalogue data

Gliese 436 b /ˈɡliːzə/ (sometimes called GJ 436 b[7]) is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436.[8] It was the first hot Neptune discovered with certainty (in 2007) and was among the smallest known transiting planets in mass and radius, until the much smaller Kepler exoplanet discoveries started coming in by 2010.

In December 2013, NASA reported that clouds may have been detected in the atmosphere of GJ 436 b.[9][10][11][12]

Discovery

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.[13] 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 characteristics

File:GJ436interior.jpg
Possible interior structure of Gliese 436 b
Formation of a helium atmosphere on a helium planet, possibly like Gliese 436 b.

The planet's surface temperature is estimated from measurements taken as it passes behind the star to be 712 K (439 °C).[3] 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 tidal effects deliver to the planet, it does not affect its temperature significantly.[14] A greenhouse effect could raise the temperature to much higher degrees than the predicted 520–620 K.[15]

Its main constituent was initially predicted to be hot "ice" in various exotic high-pressure forms,[15][16] which would remain solid despite the high temperatures, because of the planet's gravity.[17] 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.[18]

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.[3][4] This obviates the need for an ice core. Alternatively, the planet may be a super-earth.[19]

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.[20][21][22][23]

In June 2015, scientists reported that the atmosphere of Gliese 436 b was evaporating,[24] resulting in a giant cloud around the planet and, due to radiation from the host star, a long trailing tail 14×10^6 km (9×10^6 mi) long.[25]

File:Artist impression of Gliese 436b.jpg
Artist impression of Gliese 436b shows the enormous comet-like cloud of hydrogen boiling off.[26]

Orbital characteristics

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.[22]

The eccentricity of Gliese 436 b's orbit is inconsistent with models of planetary system evolution. To have maintained its eccentricity over time requires that it be accompanied by another planet.[3][27]

See also

References

  1. ↑ 1.0 1.1 1.2 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ 4.0 4.1 4.2 Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Confirmed, Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ 15.0 15.1 Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found. By analogy with Gliese 876 d.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ GJ436b - Where's the methane? Planetary Sciences Group at the University of Central Florida, Orlando
  22. ↑ 22.0 22.1 Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found., abstract in the arXiv titled "Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b"
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  27. ↑ Lua error in package.lua at line 80: module 'strict' not found.

Selected media articles

External links

Media related to Lua error in package.lua at line 80: module 'strict' not found. at Wikimedia Commons

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

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