Gliese 436 b

Planetbox begin
name=Gliese 436 bPlanetbox image

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caption = Artist's impression of Gliese 436 bPlanetbox star
star=Gliese 436
constell=Leo
RA=RA|11|42|11.0941cite web
url=http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=LHS+310
title=LHS 310
work=Simbad
publisher=Centre de Données astronomiques de Strasbourg
accessdate=2007-11-28]
DEC=DEC|+26|42|23.652
dist_ly=33.4
dist_pc=10.2
class=M2.5 VPlanetbox orbit
semimajor=0.0291±0.0004Cite arXiv|author=Deming, D. "et al."|title=Spitzer Transit and Secondary Eclipse Photometry of GJ 436b|eprint=0707.2778|class=astro-ph|year=2007]
eccentricity=0.150±0.012
period=2.643904±0.000005Cite journal|url=http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2008/30/aa10013-08/aa10013-08.html|author=Bean, J.L. "et al."|journal=Astronomy & Astrophysics|title=A Hubble Space Telescope transit light curve for GJ 436b|year=2008]
inclination=85.8±|0.21|0.25
ang_dist=2.794
long_peri=351±1.2
t_peri=2,451,551.716 ±0.01
semi-amp=18.68±0.8Planetbox character
mass_earth=22.2±1.0
radius_earth=4.327±0.183
density=1510
gravity_earth=1.18
temperature = 712±36Planetbox discovery
discovery_date=August 31, 2004
discovery_site=California, USA
discovery_method=Radial velocity, Transit
discoverers=Butler, Vogt,
Marcy et al.
discovery_status=Published

Gliese 436 b (IPAEng|ˈgliːzə) (GJ 436 b) [cite journal | url=http://xxx.lanl.gov/abs/astro-ph/0608260 | author=Maness "et al."| title=The M Dwarf GJ 436 and its Neptune-Mass Planet | journal=Submitted to Publications of the Astronomical Society of the Pacific |year=2006] is a Neptune-sized extrasolar planet orbiting the red dwarf star Gliese 436. [cite journal | url=http://www.journals.uchicago.edu/doi/full/10.1086/425173 | author=Butler "et al."| title=A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436 | journal=The Astrophysical Journal | volume=617 |year=2004 | pages=580 – 588| doi=10.1086/425173 ] As of August 2008, it remains the smallest planet in mass and radius which enters astronomical transit of its star relative to Earth (as recorded in the Extrasolar Planets Encyclopaedia).

Discovery

Gliese 436 b was discovered in August 2004 by the planet-hunting-by-way-of-radial-velocity 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 then the first of a new class of planets with a minimum mass (M sin"i") 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 by humans at the time.Cite arXiv|author=Jeffrey L. Coughlin "et al."|title=New observations and a possible detection of parameter variations in the transits of Gliese 436b| eprint=0809.1664v1| class=astro-ph| year=2008] 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 4,000km larger in diameter than Uranus and 5,000km larger than Neptune but a bit more massive.

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). 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. [Cite arXiv| author=Brian Jackson, Richard Greenberg, Rory Barnes| title=Tidal Heating of Extra-Solar Planets |eprint=0803.0026v1 |class=astro-ph|year=2008] Its discoverers allowed for a temperature increase due to a greenhouse effect.cite journal | url =http://www.aanda.org/articles/aa/pdf/2007/35/aa7799-07.pdf | title=Detection of transits of the nearby hot Neptune GJ 436 b | author=M. Gillon "et al." | journal=Astronomy and Astrophysics | volume=472 2 |year=2007| page=L13-L16 |format=PDF]

Its main constituent was initially predicted to be hot "ice" in various exotic high-pressure forms,cite news| publisher=New Scientist| url=http://space.newscientist.com/article/dn11864-strange-alien-world-made-of-hot-ice-and-steam.html| title=Strange alien world made of "hot ice"| date= 6 May 2007| first= David| last= Shiga| accessdate=2007-05-16 ] which remains solid because of the planet's gravity despite the high temperatures. [cite news | title = Hot "ice" may cover recently discovered planet | first = Maggie | last = Fox | publisher = Scientific American.com | work = Science News | date = May 16, 2007 | url = http://www.reuters.com/article/scienceNews/idUSN1621607620070516 | accessdate = 2008-08-06] 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. [cite journal | journal=Geophysical Research Abstracts | volume=9| issue=07850 |year=2007 | url=http://www.cosis.net/abstracts/EGU2007/07850/EGU2007-J-07850.pdf?PHPSESSID=1eb3a7a98603083dda25d18001ea2a33 | title=The impact of nonthermal loss processes on planet masses from Neptunes to Jupiters |author=H. Lammer "et al." By analogy with Gliese 876 d.]

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. This obviates the need for an ice core. Alternatively, the planet may be a superterrestrial. [cite journal| title = Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres| author=E. R. Adams, S. Seager, and L. Elkins-Tanton| journal=The Astrophysical Journal| volume=673| pages=1160–1164 | year= 2008|month= February | url=http://occult.mit.edu/_assets/documents/publications/Adams2008ApJ673_1160.pdf| accessdate = 2008-08-06|format=PDF]

Kevin Stevenson of UCF "et al." observed the secondary transit under the Spitzer Exoplanet Target of Opportunity program in January and February 2008. On Saturday 11 October 2008, 9:30-9:40 AM, these results will be presented. [ [http://www.abstractsonline.com/viewer/viewAbstractPrintFriendly.asp?CKey={6147211B-803D-4E57-B93E-A43D04C410E1}&SKey={573A774A-97D0-405B-8F88-6603F49651A5}&MKey={35A8F7D5-A145-4C52-8514-0B0340308E94}&AKey={AAF9AABA-B0FF-4235-8AEC-74F22FC76386} Secondary Eclipse Photometry of GJ 436b in Six Spitzer Channels] BAAS , 40, no 3 , 01.07 ]

Orbital characteristics

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. [Cite arXiv|author=Jacob L. Bean and Andreas Seifahrt|title=Observational Consequences of the Recently Proposed Super-Earth Orbiting GJ436|eprint=0806.3270v2|class=astro-ph|year=2008] In September 2008, a formerly-unrecognised transit signature at NMSU from January 11 2005 was incorporated into the data up to then, consistent with a planet at 0.08 AU and under 12 Earth masses.

References

elected media articles

* [http://www.sciam.com/slideshow.cfm?id=how-artists-portray-exoplanets-never-seen&thumbs=horizontal&photo_id=05941D71-E7F2-99DF-36A6A36EADF8F3EA How Do Artists Portray Exoplanets They've Never Seen? 4/9] , Scientific American October 2, 2007.
* [http://www.sciencedaily.com/releases/2007/05/070516151053.htm Astronomers Detect Shadow Of Water World In Front Of Nearby Star] (from Science Daily).

ee also

*55 Cancri e
*Gliese 581 b
*Gliese 876 d
*List of stars with confirmed extrasolar planets

External links

* [http://exoplanet.eu/star.php?st=GJ+436 The Extrasolar Planets Encyclopedia: Gliese 436] [http://exoplanet.eu/planet.php?p1=GJ+436&p2=b planet entry]