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HD 209458 b

HD 209458 b
Size comparison of HD 209458 b with Jupiter
Discovery[1][2]
Discovered byD. Charbonneau
T. Brown
David Latham
M. Mayor
G.W. Henry
G. Marcy
R.P. Butler
S.S. Vogt
Discovery siteHigh Altitude Observatory
Geneva Observatory
Discovery dateSeptember 9, 1999
Radial velocity
Orbital characteristics[3]
0.04707 AU (7,042,000 km)
Eccentricity<0.0081
3.52474859(38) d
84.59396616 h
Inclination86.710°±0.050°
2452826.629283(87) JD
83[citation needed]
Semi-amplitude84.27+0.69
−0.70 m/s
StarHD 209458
Physical characteristics[3]
1.359+0.016
−0.019 RJ
Mass0.682+0.014
−0.015 MJ
Mean density
0.333+0.014
−0.013 g/cm3
9.2 m/s2 (0.94 g)
Albedo0.096±0.016 (geometric)[4]
Temperature1499±15 K (1,226 °C; 2,239 °F, dayside)[5]
972±44 K (699 °C; 1,290 °F, nightside)[5]

HD 209458 b is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some 157 light-years (48 parsecs) from the Solar System. The radius of the planet's orbit is 0.047 AU (7.0 million km; 4.4 million mi), or one-eighth the radius of Mercury's orbit (0.39 AU (36 million mi; 58 million km)). This small radius results in a year that is 3.5 Earth-days long and an estimated surface temperature of about 1,000 °C (1,800 °F; 1,300 K). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and volume of HD 209458 b indicate that it is a gas giant.

HD 209458 b represents a number of milestones in exoplanetary research. It was the first of many categories:

  • a transiting extrasolar planet
  • The first planet detected through more than one method
  • an extrasolar planet known to have an atmosphere
  • an extrasolar planet observed to have an evaporating hydrogen atmosphere
  • an extrasolar planet found to have an atmosphere containing the elements oxygen and carbon
  • one of the first two extrasolar planets to be directly observed spectroscopically
  • The first extrasolar gas giant to have its superstorm measured
  • the first planet to have its orbital speed measured, determining its mass directly.[6]

Based on the application of newer theoretical models, as of April 2007, it is thought to be the first extrasolar planet found to have water vapor in its atmosphere.[7][8][9][10]

In July 2014, NASA announced finding very dry atmospheres on HD 209458 b and two other exoplanets (HD 189733 b and WASP-12b) orbiting Sun-like stars.[11]

HD 209458 b has been nicknamed "Osiris" after the Egyptian god.[12][13] This nickname has been acknowledged by the IAU, but as of 2023 it has not yet been approved as an official proper name.[14]

  1. ^ Cite error: The named reference Charbonneau2000 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Henry2000 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Bonomo2017 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Brandeker2022 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Zellem2014 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Ignas was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Space.com water was invoked but never defined (see the help page).
  8. ^ Signs of water seen on planet outside solar system, by Will Dunham, Reuters, Tue Apr 10, 2007 8:44PM EDT
  9. ^ Cite error: The named reference NASA-20131203 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference ApJ-20130910 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference NASA-20140724 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Vidal-Madjar2004 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Vidal-Madjar2008 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference IAUnaming was invoked but never defined (see the help page).

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