HD 189733 b
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HD 189733 b, also cataloged V452 Vulpeculae b, is an extrasolar planet approximately 63 light-years away in the constellation of Vulpecula (the Fox). The planet was discovered orbiting the star HD 189733 on October 5 2005, when astronomers in the United States observed the planet transiting across the face of the star.[1] The planet is classified as a hot Jupiter class Jovial planet, with a close orbit to its parent star. HD 189733 b was the first ever extrasolar planet to be mapped.
Detection and discovery
Transit and Doppler spectroscopy
On October 6 2005, a team of astronomers announced the discovery of transiting planet HD 189733 b. In 2006, a team led by Drake Deming announced a detection of strong infrared thermal emission from the transiting extrasolar planet HD 189733 b, by measuring the flux decrement (decrease of total light) during its prominent secondary eclipse (when the planet passes behind the star).
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The mass of the planet is estimated to be 15% larger than Jupiter's; with the planet completing an orbit around its host star every 2.2 days. It is occasionally referred to as HD 189733 Ab to distinguish it from the red dwarf star HD 189733 B. The HD 189733 star system is 63 light years from Earth in the direction of the constellation Vulpecula.
Infrared spectrum
On February 21, 2007, NASA released news that the Spitzer Space Telescope had measured detailed spectra from both HD 189733 b and HD 209458 b.[2] The release came simultaneously with the public release of a new issue of Nature containing the first publication on the spectroscopic observation of the other exoplanet, HD 209458 b. A paper has been submitted to the Astrophysical Journal Letters. The spectroscopic observations of HD 189733 b were led by Carl Grillmair of NASA's Spitzer Science Center.
On 22 October, a team of astrophysicists at the ETH Zürich managed to "detect and monitor [its] visible light" using polarimetry, the first such success. The authors claim a radius of 1.5+/-.2 Rj: over 30% larger than its transit disc. Its albedo in blue light is greater than 0.14. The planet would appear deep blue to our eyes.[3] ([Press release]) This work will need to be confirmed, however, as the estimated radius is much larger than expected from measurements at other wavelengths.
In mid January 2008, spectral observation during the planet's transit using Rayleigh scattering model found that if molecular hydrogen exists, it would have an atmospheric pressure of 410 ± 30 mbar of 0.1564 solar radii. The Mie approximation model also found that there is a possible condensate in its atmosphere, magnesium silicate (MgSiO3) with a particle size of approximately 10-2 to 10-1 μm. Using both models, the planet's temperature would be between 1340 to 1540 K.Cite error: The <ref> tag has too many names (see the help page).
Physical characteristics
This planet exhibits the largest photometric transit depth (amount of the parent star's light blocked) of any extrasolar planet so far observed, of approximately 3%. While transiting the system also clearly exhibits the Rossiter-McLaughlin effect. Due to its high mass and close orbit the parent star has a very large semi-amplitude (K), the "wobble" in the star's radial velocity, of 205 m/s.[4] The apparent longitude of ascending node of its orbit is 16 degrees +/- 8 away from north-south in our sky. It and HD 209458 b were the first two planets to be directly spectroscopically observed.[2] The parent stars of these two planets are the brightest transiting-planet host stars, so these planets will continue to receive the most attention by astronomers. Like most hot Jupiters, this planet is thought to be tidally locked to its parent star, meaning it has a permanent day and night.
The atmosphere was at first predicted "pL class", lacking a temperature-inversion stratosphere; like L dwarfs which lack titanium and vanadium oxides.[5] Followup measurements, tested against a stratospheric model, yielded inconclusive results.[6]
Map of the planet
In 2007 the Spitzer space telescope was used to map the planet's temperature emissions. The planet+star system was observed for 33 consecutive hours, starting when only the night side of the planet was in view. Over the course of one-half of the planet's orbit, more and more of the day side came into view. A temperature range of 973 ± 33 K to 1,212 ± 11 K was discovered, indicating that the absorbed energy from the parent star is distributed fairly evenly through the planet's atmosphere. Interestingly, the region of peak temperature was offset 30 degrees east of the substellar point.
Assuming the planet is tidally locked with its star, this suggests that powerful easterly winds moving at more than 9,600 kilometers per hour are responsible for redistributing the heat.[7] NASA released a brightness map of the surface temperature of HD 189733 b; it is the first map ever published of an extra-solar planet.[8]
Water vapor and organic compounds
On July 11, 2007, a team lead by Giovanna Tinetti published the results of their observations using the Spitzer Space Telescope concluding there is solid evidence for significant amounts of water vapor in the planet's atmosphere.[9] Follow-up observations made using the Hubble Space Telescope confirm the presence of water vapor and also the organic compound methane.[10] It is currently unknown how the methane originated as the planet's high temperature (700°C, 1292°F) should cause the water and methane to react, replacing the atmosphere with carbon monoxide.[10][11]
See also
References
- ^ Bouchy; et al. (2005). "ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD 189733". Astronomy and Astrophysics. 444: L15–L19.
{{cite journal}}: Explicit use of et al. in:|author=(help) (Preprint) - ^ a b Press Release: NASA's Spitzer First To Crack Open Light of Faraway Worlds
- ^ Berdyugina, Svetlana V. (2008). "First detection of polarized scattered light from an exoplanetary atmosphere" (PDF). The Astrophysical Journal. 673: L83. doi:10.1086/527320.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help) - ^ "HD 189733 page". University of Geneva. 2007-03-05. Retrieved 2008-02-18.
- ^ Fortney, J. J.; Lodders, K.; Marley, M. S.; Freedman, R. S. (2008). "A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres". Astrophysical Journal. 678 (2): 1419-1435.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Ivan Hubeny, Adam Burrows (2008). "Spectrum and atmosphere models of irradiated transiting extrasolar giant planets". arXiv:0807.3588v1 [astro-ph].
- ^ Knutson, Heather A. (2007). "A map of the day–night contrast of the extrasolar planet HD 189733b". Nature. 447: 183–186. doi:10.1038/nature05782.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help) - ^ Image ssc2007-09a
- ^ Press Release: NASA's Spitzer Finds Water Vapor on Hot, Alien Planet
- ^ a b Swain, Mark R. (2008-03-20). "The presence of methane in the atmosphere of an extrasolar planet". Nature. 452: 329–331. doi:10.1038/nature06823.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) arXiv.org link - ^ Stephen Battersby (2008-02-11). "Organic molecules found on alien world for first time". Retrieved 2008-02-12.
External links
- Berdyugina; et al. (2008-02-02). "First Detection of Polarized Scattered Light from an Exoplanetary Atmosphere". arXiv. Retrieved 2008-06-21.
{{cite web}}: Explicit use of et al. in:|author=(help)
- Naeye, Robert (2005-10-07). "The Best Transiting Exoplanet Yet". Sky & Telescope. Retrieved 2008-06-21.
- "Notes for planet HD 189733 b". The Extrasolar Planets Encyclopaedia. Retrieved 2008-06-21.
- "Strong Infrared Emission from the Extrasolar Planet HD189733b". arXiv. 2006-02-20. Retrieved 2008-06-21.
{{cite web}}: Cite uses deprecated parameter|authors=(help)
- HD 189733 b on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images