HD 209458 b
453959
226140050
2008-07-17T00:17:44Z
GabrielVelasquez
6054809
moved diagrams to relevant paragraphs
{{Planetbox begin
| name = HD 209458b
}}
{{Planetbox image
| image = Transiting planet HD 209458b.png
| caption = Artist's conception of HD 209458b transiting its star.
}}
{{Planetbox star
| star = [[HD 209458]]
| constell = [[Pegasus (constellation)|Pegasus]]
| RA = {{RA|22|03|10.8}}
| DEC = {{DEC|+18|53|04}}
| dist_ly=154
| dist_pc=47.1
| class = F8-G0V
}}
{{Planetbox orbit
| semimajor = 0.045
| eccentricity = 0.00
| period = 3.52474541 ± 0.00000025
| inclination = 86.1 ± 0.1
| ang_dist = 0.957
| long_peri = 83
| t_peri = 2,452,854.825415<br />± 0.00000025
| semi-amp = 84.26 ± 0.81
}}
{{Planetbox character
| mass = 0.69 ± 0.05
| radius = 1.35 ± 0.05
| density = 370
| gravity_earth = 0.89
| temperature = 1,130 ± 150
}}
{{Planetbox discovery
| discovery_date = [[5 November]] [[1999]]
| discoverers = [[David Charbonneau|D. Charbonneau]]<br>[[Timothy Brown (astronomer)|T. Brown]]<br>[[David Latham|D. Latham]]<br>[[Michel Mayor|M. Mayor]]<br />[[Gregory W. Henry|G.W. Henry]]<br />[[Geoffrey Marcy|G. Marcy]]<br />[[R. Paul Butler|R.P. Butler]]<br />[[Steven S. Vogt|S.S. Vogt]]
| discovery_method = [[Astronomical transit|Transit]] and [[Radial velocity]]
| discovery_site = {{flagicon|United States}} [[Lowell Observatory|Lowell]]<br />{{flagicon|France}} [[Geneva Observatory|Geneva]]
| discovery_status = Published
}}
{{Planetbox catalog
| names = Osiris, V376 Pegasi b
}}
{{Planetbox end}}
'''HD 209458b''', also unofficially named '''Osiris''', is an [[extrasolar planet]] that orbits the [[Solar twin]] [[star]] [[HD 209458]] in the constellation [[Pegasus (constellation)|Pegasus]], some 150 [[light-year]]s from Earth's solar system, with evidence of water vapor.<ref name="barman">Barman, T.S. (2007) [http://fr.arxiv.org/abs/0704.1114 "Identification of Absorption Features in an Extrasolar Planet Atmosphere"] ''Astrophysical Journal Letters'' (accepted for publication)</ref>
The radius of the planet's orbit is 7 million kilometers, about 0.047 [[astronomical unit]]s, or one eighth the radius of [[Mercury (planet)|Mercury's]] orbit. This small radius results in a year that is 3.5 Earth days long and an estimated surface temperature of about 1,000 degrees [[Celsius]] or 1,800 degrees [[Fahrenheit]]. Its mass is 220 times that of Earth (0.69 [[Jupiter]] masses). Its volume is some 146% greater than that of Jupiter. The high mass and great volume of HD 209458b lead to its classification as a [[gas giant]].
HD 209458b represents a number of milestones in extraplanetary research. It was the first [[Astronomical transit|transiting]] extrasolar planet discovered, the first extrasolar planet known to have an [[atmosphere]], the first extrasolar planet observed to have an evaporating [[hydrogen]] atmosphere, the first extrasolar planet found to have an atmosphere containing [[oxygen]] and [[carbon]], and one of the first two extrasolar planets to be directly observed [[Spectroscopy|spectroscopically]]. Based on the application of new, [[theoretical]] models, as of April [[2007]], it is alleged to be the first extrasolar planet found to have [[water vapor]] in its atmosphere.<ref name="Space.com water"> [http://www.space.com/scienceastronomy/070410_water_exoplanet.html Water Found in Extrasolar Planet's Atmosphere] - Space.com </ref><ref>[http://www.reuters.com/article/scienceNews/idUSN1043498020070411 ''Signs of water seen on planet outside solar system''], by Will Dunham, Reuters, Tue Apr 10, 2007 8:44PM EDT</ref><ref>[http://www.lowell.edu/press_room/releases/recent_releases/extrasolar_water.html ''Water Identified in Extrasolar Planet Atmosphere''], [[Lowell Observatory]] press release, April 10, 2007</ref>
HD 209458b has been informally referred to as ''[[Osiris]]'', though this name was not given by the astronomers credited with its discovery. The use of the Osiris nickname has faded among astronomers and the media.<ref name="osiris_leaks">{{cite web | title= Dying Planet Leaks Carbon-Oxygen | date = [[2004-02-19]] | year = 2004 | url = http://www.nasa.gov/vision/universe/newworlds/Osiris_leaks.html | work = [[NASA]] | accessdate = 2007-04-11}}</ref><ref>[http://www.journals.uchicago.edu/cgi-bin/resolve?doi=10.1086/383347 University of Chicago Press - Oxygen and Carbon in HD 209458b - 10.1086/383347<!-- Bot generated title -->]</ref> HD 209458 is an [[Apparent magnitude|8th magnitude star]], visible from Earth with binoculars.
== Detection and discovery ==
=== Transits ===
[[Astronomical spectroscopy|Spectroscopic]] studies first revealed the presence of a planet around HD 209458 on [[November 5]] [[1999]]. Astronomers had made careful [[photometry (astronomy)|photometric]] measurements of several stars known to be orbited by planets, in the hope that they might observe a dip in brightness caused by the [[astronomical transit|transit]] of the planet across the star's face. This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected.
Soon after the discovery, separate teams, one led by [[David Charbonneau]] including [[Timothy Brown (astronomer)|Timothy Brown]] and others, and the other by [[Gregory W. Henry]], were able to detect a [[transit (astronomy)|transit]] of the planet across the surface of the star making it the first known transiting extrasolar planet. On September 9 and 16, 1999, Charbonneau's team measured a 1.7% drop in HD 209458's brightness, which was attributed to the passage of the planet across the star. On November 8, Henry's team observed a transit ingress.<ref name="transit">Henry et al [http://cfa-www.harvard.edu/iauc/07300/07307.html#Item1 IAUC 7307: HD 209458; SAX J1752.3-3138] 12 November 1999, reported a transit ingress on Nov. 8. David Charbonneau et al, [http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v529n1/995832/995832.html Detection of Planetary Transits Across a Sun-like Star], November 19, reports full transit observations on September 9 and 16.</ref> Each transit lasts about three hours, during which the planet covers about 1.5% of the star's face.
The star had been observed many times by the [[Hipparcos]] satellite, which allowed astronomers to calculate the orbital period of HD 209458b very accurately at 3.524736 days.<ref>{{cite journal
| last =Castellano
| first = T.
| authorlink =
| coauthors = J. Jenkins, D. E. Trilling, L. Doyle, D. Koch
| title = Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set
| journal = The Astrophysical Journal
| volume = 532
| issue = 1
| pages = L51–L53
| publisher = University of Chicago Press
| date = March 2000
| url = http://adsabs.harvard.edu/abs/2000ApJ...532L..51C
| doi =
| id = 2000ApJ...532L..51C
| accessdate = 2007-04-17 }}</ref>
=== Spectroscopic ===
{{Planetary radius
| align = left
| radius = 135
}}
Spectroscopic analysis had shown that the planet had a mass about 0.69 times that of [[Jupiter (planet)|Jupiter]].<ref name="mass">[http://exoplanet.eu/star.php?st=HD+209458 Notes for star HD 209458<!-- Bot generated title -->]</ref> The occurrence of transits allowed astronomers to calculate the planet's radius, which had not been possible for any previously known [[exoplanet]], and it turned out to have a radius some 35% larger than Jupiter's. It had been previously hypothesised that [[hot Jupiter]]s particularly close to their parent star should exhibit this kind of inflation due to intense heating of their outer atmosphere. Tidal heating due to the planet's eccentric orbit may also play a role.<ref>{{cite journal|title=Tidal Heating of Extra-Solar Planets| first= Brian| last= Jackson| coauthors= Richard Greenberg, Rory Barnes| journal=ApJ| id={{arXiv|0803.0026}} | year=2008 }}</ref>
Observations by the orbiting [[Microvariability and Oscillations of STars telescope]] has shown that the planet has an [[albedo]] (or reflectivity) that is less than 30%, making it a surprisingly dark object. In comparison, Jupiter has a much higher albedo of 52%. This would suggest that HD 209458b may not be covered with clouds (which are in general quite reflective), against expectations. At these high temperatures the cloud material would likely be silicate rocks and iron<ref name="albedo">Matthews J.,(2005), [http://www.astro.umontreal.ca/~casca/PR/Casca2005_Matthews.html MOST SPACE TELESCOPE PLAYS `HIDE & SEEK' WITH AN EXOPLANET; LEARNS ABOUT ATMOSPHERE AND WEATHER OF A DISTANT WORLD'']</ref>
It is assumed that HD 209458b's days are the same length as its years; that is, it rotates about its axis every time it rotates around its star due to [[tidal locking]].{{Fact|date=August 2007}}
== Physical characteristics ==
=== Atmosphere ===
[[Image:209458b.jpg|thumb|300px|right|HD 209458b atmosphere currents.]]
On [[November 27]] [[2001]] the [[Hubble Space Telescope]] detected [[sodium]] in the planet's atmosphere, the first planetary atmosphere outside our solar system to be measured. This detection was predicted by [[Sara Seager]] in late 2001.<ref name="seagerprediction"> {{cite journal | url=http://www.journals.uchicago.edu/doi/full/10.1086/309292 | author=Seager ''et al.'' | title=Photometric Light Curves and Polarization of Close‐in Extrasolar Giant Planets | journal=The [[Astrophysical Journal]] | volume=540 | year=2000 | pages=504 – 520 | doi=10.1086/309292 <!--Retrieved from URL by DOI bot-->}}</ref> In 2003-4, astronomers used the Hubble Space Telescope Imaging Spectrograph to discover an enormous [[ellipsoid]]al envelope of [[hydrogen]], [[carbon]] and [[oxygen]] around the planet that reaches 10,000 K. At this temperature, the [[Maxwell-Boltzmann distribution]] of particle velocities gives rise to a significant 'tail' of atoms moving at speeds greater than the [[escape velocity]], and the planet is estimated to be losing about 100-500 million (1-5×10<sup>8</sup>) kg of hydrogen per second. Analysis of the starlight passing through the envelope shows that the heavier carbon and oxygen atoms are being blown from the planet by the extreme "[[hydrodynamic]] [[drag (physics)|drag]]" created by its evaporating hydrogen atmosphere. The hydrogen tail streaming from the planet is approximately 200,000 kilometers long which is roughly equivalent to its diameter.
It is thought that this type of atmosphere loss may be common to all planets orbiting Sun-like stars closer than around 0.1 AU. HD 209458 b will not evaporate entirely, although it may have lost up to about 7% of its mass over its estimated lifetime of 5 billion years.<ref name="loss">Hébrard G., Lecavelier Des Étangs A., Vidal-Madjar A., Désert J.-M., Ferlet R. (2003), [http://arxiv.org/abs/astro-ph/0312384 ''Evaporation Rate of Hot Jupiters and Formation of Chthonian Planets''], Extrasolar Planets: Today and Tomorrow, ASP Conference Proceedings, Vol. 321, held [[30 June]] - [[4 July]] [[2003]], Institut d'astrophysique de Paris, France. Edited by Jean-Philippe Beaulieu, Alain Lecavelier des Étangs and Caroline Terquem.</ref>
=== Direct detection ===
On [[March 22]], [[2005]], [[NASA]] released news that [[infrared]] light from the planet had been measured by the [[Spitzer Space Telescope]], the first ever direct detection of light from an extrasolar planet.
[[Image:Planetary transit.svg|thumb|300px|right|The transit of HD 209458b.]]
This was done by subtracting the parent star's constant light and noting the difference as the planet transited in front of the star and was eclipsed behind it, providing a measure of the light from the planet itself. New measurements from this observation determined the planet's temperature as at least 750 °C (1300 °F). The circular orbit of HD 209458b was also confirmed.
=== Spectral observation ===
On [[February 21]], [[2007]], [[NASA]] and ''[[Nature (journal)|Nature]]'' released news that HD 209458b was one of the first two extrasolar planets to have their spectra directly observed, the other one being [[HD 189733b]].<ref>[http://www.spitzer.caltech.edu/Media/releases/ssc2007-04/release.shtml NASA's Spitzer First To Crack Open Light of Faraway Worlds]</ref><ref>[http://www.nature.com/nature/journal/v445/n7130/abs/nature05636.html A spectrum of an extrasolar planet] - [[Nature (journal)|Nature]]</ref> This was long seen as the first mechanism by which extrasolar but non-sentient life forms could be searched for, by way of influence on a planet's atmosphere. A group of investigators led by Dr. Jeremy Richardson of NASA's [[Goddard Space Flight Center]] spectrally measured HD 209458b's atmosphere in the range of 7.5 to 13.2 [[micrometre|micrometers]]. The results defied theoretical expectations in several ways. The spectrum had been predicted to have a peak at 10 micrometers which would have indicated water vapor in the atmosphere, but such a peak was absent, indicating no detectable water vapor. Another, unpredicted peak was observed at 9.65 micrometers, which the investigators attributed to clouds of silicate dust, a phenomenon not previously observed. Another unpredicted peak occurred at 7.78 micrometers, which the investigators did not have an explanation for. A separate team led by Mark Swain of the [[Jet Propulsion Laboratory]] also observed HD 209458b's spectrum, and had not yet published their results when the Richardson et al. article came out, but made similar findings.
=== Atmospheric water vapor ===
On [[April 10]], [[2007]], [[Travis Barman]] of the [[Lowell Observatory]] announced evidence that the atmosphere of HD 209458b contained water vapor. Using a combination of previously published Hubble Space Telescope measurements and new [[theoretical]] models, Barman found strong evidence for water absorption in the planet's atmosphere.<ref name="barman"/><ref name="Space.com water"/><ref>[http://news.yahoo.com/s/nm/20070411/sc_nm/planet_water_dc ''Signs of water seen on planet outside solar system'']</ref> <ref>[http://space.newscientist.com/article/dn11576-first-sign-of-water-found-on-an-alien-world.html First sign of water found on an alien world - space - 10 April 2007 - New Scientist Space<!-- Bot generated title -->]</ref> His method modelled light passing directly through the atmosphere from the planet's star as the planet passed in front of it. However, this hypothesis is still being investigated for confirmation.
Barman drew on data and measurements taken by Heather Knutson, a student at [[Harvard University]], from the [[Hubble Space Telescope]], and applied new [[theoretical]] models to demonstrate the likelihood of water absorption in the atmosphere of the planet. The planet orbits its parent star every three and a half days, and each time it passes in front of its parent star, the atmospheric contents can be analysed by examining how the atmosphere absorbs light passing from the star directly through the atmosphere in the direction of Earth.
According to a summary of the research, atmospheric water absorption in such an exoplanet renders it larger in appearance across one part of the infrared spectrum, compared to wavelengths in the visible spectrum. Barman took Knutson's Hubble data on HD209458 b, applied to his [[theoretical]] model, and allegedly identified water absorption in the planet's atmosphere.
On [[April 24]], [[2007]], the astronomer [[David Charbonneau]], who led the team that made the Hubble observations, cautioned that the telescope itself may have introduced variations that caused the theoretical model to suggest the presence of water. He hoped that further observations would clear the matter up in the following months.<ref>{{cite web | url=http://www.sciam.com/article.cfm?articleID=25A261F0-E7F2-99DF-313249A4883E6A86&chanID=sa007
|title=All Wet? Astronomers Claim Discovery of Earth-like Planet | author=J.R. Minkle
|publisher=Scientific American | date=[[April 24]] [[2007]]}}</ref>
As of April 2007, further investigation is being conducted.
== See also ==
* [[51 Pegasi b]]
* [[HD 189733 b]]
== References ==
{{reflist}}
{{refbegin}}
* Castellano T., Jenkins J., Trilling D.E., Doyle L., Koch D. (2000), ''Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set'', Astrophysical Journal, Volume 532, Issue 1, p. L51-L53
* [[David Charbonneau|Charbonneau, D.]] (2003), ''HD 209458 and the Power of the Dark Side'', Scientific Frontiers in Research on Extrasolar Planets, ASP Conference Series, Vol 294, Edited by Drake Deming and Sara Seager. (San Francisco: ASP) ISBN 1-58381-141-9, 2003, p. 449-456
* Fortney J.J., Sudarsky D., Hubeny I., Cooper C.S., Hubbard W.B., Burrows A., Lunine J.I. (2003), ''On the Indirect Detection of Sodium in the Atmosphere of the Planetary Companion to HD 209458'', Astrophysical Journal, Volume 589, p. 615-622
{{refend}}
== External links ==
{{commonscat|HD 209458b}}
* {{cite web |url=http://www.spacetelescope.org/news/html/heic0303.html |title=European astronomers observe first evaporating planet |accessdate=2008-06-28 |work=[[Hubble Space Telescope]] |publisher=[[ESA]]/[[NASA]] |date=2003-03-12 }}
* {{cite web |url=http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=106 |title=HD 209458 b |accessdate=2008-06-28 |work=Extrasolar Visions |publisher= |date= }}
* {{cite web |url=http://www.newscientist.com/article.ns?id=dn7186 |title=Glow of alien planets glimpsed at last |accessdate=2008-06-28 |work=NewScientiest |date=2005-03-22 |first=Jenny |last=Hogan }}
* {{cite web |url=http://hubblesite.org/newscenter/archive/releases/2001/38/text |title=Hubble Makes First Direct Measurements of Atmosphere on World Around another Star |accessdate=2008-06-28 |work=[[Hubble Space Telescope]] |publisher=[[NASA]] |date=2001-11-27 }}
* {{cite web |url=http://www.newscientist.com/article.ns?id=dn4634 |title=Oxygen seen streaming off exoplanet |accessdate=2008-06-28 |work=NewScientiest |publisher= |date=2004-02-03 |first=Maggie |last=McKee }}
* {{cite web |url=http://www.jpl.nasa.gov/news/news.cfm?release=2005-050 |title=NASA's Spitzer Marks Beginning of New Age of Planetary Science |accessdate=2008-06-28 |work=[[Jet Propulsion Laboratory]] |publisher=[[NASA]] |date=2005-03-22 }}
* {{cite web |url=http://exoplanet.eu/planet.php?p1=HD+209458&p2=b |title=Notes for planet HD 209458 b |accessdate=2008-06-28 |work=The Extrasolar Planets Encyclopaedia |publisher= |date= }}
* {{cite web |url=http://www.spacetelescope.org/news/html/heic0403.html |title=Oxygen and carbon discovered in exoplanet atmosphere 'blow-off' |accessdate=2008-06-28 |work=[[Hubble Space Telescope]] |publisher=[[ESA]]/[[NASA]] |date=2004-02-02 }}
* {{cite web |url=http://www.nature.com/news/2005/050321/full/news050321-9.html |title=Light from alien planets confirmed |accessdate=2008-06-28 |work=Nature |publisher= |date=2005-03-23 |first=Mark |last=Peplow }}
[[Category:Extrasolar planets]]
[[Category:Hot Jupiters]]
[[Category:Pegasus constellation]]
[[Category:Transiting planets]]
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