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HD 209458 System

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Exoplanetary Scratchpad

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Has first discovered transiting planet which was nicknamed Osiris due to the (first detected) comet-like tail detected and the first exoplanet around a normal star to have its mass directly measured. Also the first Inflated Hot Jupiter found. The planet may be losing its outer atmosphere, or magnetism may prevent the ions from escaping. They detected water in its atmosphere (they had failed earlier), the first time this has been done for any exoplanet. 2nd Exoplanet with detected organic compounds; like HD 189733b, it has water and carbon dioxide, but it has a lot more Methane. Was one of 2 planets to have light directly taken and thus their temperatures read (over 1000K). Tracking carbon molecules with dopplar spectrometry caused it to be the first exoplanet detected to have winds, which are raging at 5,000 to 10,000 km/h. This is believed to cause hotspots to appear at terminators rather than at the star-ward facing point. Had one of the strongest water detection of the 5 exoplanets contrasted by Hubble in 2013, though still less intense than expected, probably due to dust clouds or a haze blocking its detection.

HD 209458 System Web PagesEdit

HD 209458 System In the NewsEdit

First Transiting Planet Ever Detected (Nov 1999)Edit

Others Indicate they Saw Transits Also (Nov 1999)Edit

Transit Detected by Amateurs (Sep 2000)Edit

HD 209458 b becomes the first exoplanet whose transit is detected by amateur astronomers.

Precovery Transits by Hipparcos in 1991 Found (2000)Edit

Hubble Detects First Exoplanetary Atmosphere (2001)Edit

Finds Sodium

Hyedrogen Envelope and Tail Detected (Feb 2003)Edit

Unknown Agent Increasing Radius (May 2003)Edit

Baraffe study

Oxygen and Carbon Found in Envelope (Jan 2004)Edit

Planet Infrared Light Detected, Temperature Taken(Mar 2005)Edit

MOST Rules Out Earth-Like Planet (Jan 2006)Edit

Upper Atmosphere Transition Zone Probed (Oct 2006)Edit

Gilda Ballester is lead scientist

Infrared Spectrum Taken, Silicate Clouds found, Water Not (Dec 2006)Edit

Richardson's team

Supersonic Wind Causes Uniform Temperature (Jan 2007)Edit

Eric Agol, Nicolas Cowan (lead poster), David Charbonneau

Water Not Detected in Atmosphere (Feb 2007)Edit

Mark Swain's team also does not detect water

Water Detected in Atmosphere (Apr 2007)Edit

Barman's study

Atmosphere of HD 209458 probed - Extrasolar Visions BBS Thread

Surface Gravity Calculated to be Near Earth's (May 2007)Edit

Magnetic Field May Prevent Stripped Ions From Escaping (2009)Edit

Atmospheric Evaporation Explored (2008)Edit

Water Confirmed in Atmosphere (Dec 2008)Edit

Deming commented, but wasn't part of new study

Organic Compounds Detected (CO2, CH4) (Oct 2009)Edit

Swain's team

Temperature Time Variation (Weather) Studied (Jan 2010)Edit

Magnetic Explanation for Inflated Hot Jupiters (Feb 2010)Edit

First Winds Detected around an Exoplanet (2010)Edit

Tail Confirmed (2010)Edit

Winds Cause Shift in Hot Spots (2011)Edit

Hubble Finds Water and Haze in 5 Exoplanet Atmospheres (2013)Edit

See also WASP-17 System, HD 209458 System, WASP-12 System, XO-1 System, WASP-19 System

More Precise Measurements Still Yield Less Water Than Expected (2014)Edit

See also HD 189733 System, HD 209458 System, WASP-12 System

Hubble Observes 10 Hot Jupiters (Dec 2015)Edit

See WASP-12 System, WASP-6 System, WASP-31 System, WASP-33 System, HD 189733 System, HAT-P-12 System, WASP-17 System, WASP-19 System, HAT-P-1 System, HD 209458 System



  • April 17 1991 - Earliest precovery detection of transit by Hipparcos satelite
  • Aug/Sep 1999 - Transits detected by David Charbonneau and David Latham
  • Nov 5 1999 - The first dopplar spectrometry wobbles are detected for Planet b by Marcy Butler et. al.
  • Nov 7 1999 - Telescope detected wobble
  • Nov 1999 - Marcy Butler announces discovery of planet
  • Jan 2000 - Precovery transits by Hipparcos satellite found
  • Sep 16 2000 - Becomes first exoplanet whose transit is detected by amateur astronomers
  • Nov 2001 - Hubble detects Sodium in atmosphere
  • Jan 2003 - Second transiting planet OGLE-TR-56 System] detected
  • Feb 2003 - Hydrogen Envelope detected, planet appears to be evaporating
  • May 2003 - Baraffe Study finds that stellar irradiation alone does not explain planets large radius; 20% deviation from model prediction
  • Oct/Nov 2003 - Hubble Telescope detects Oxygen and Carbon in the envelope
  • Aug 2004 - Planet found in TrES-1 System found. It has about the same mass as HD 209458b and similar irradiation, but for unknown reason, is considerably smaller. HD 209358 will remain the only "puffed up" planet known for a while.
  • Oct 2004 - Spitzer detects Infrared emitted by TrES-1b
  • Dec 2004 - Spitzer detects Infrared emitted by HD 209458b
  • Mar 2005 - Infrared radiation from this planet and TrES-1b detected for first time using Spitzer Space Telescope
  • Sep 2006 - Second "Inflated Hot Jupiter" in HAT-P-1 System thought to be discovered (but later turned out to not be so puffed up)
  • Jan 2006 - MOST observations show no habitable Earth-like planets in the system by attempting to detect gravitational effects on transit timing of any nearby planet
  • Dec 2006 - Infrared spectrum taken by Jeremy Richardson, doesn't comply with Water-rich theories, silicate clouds possibly detected
  • Jan 2006 - Gilda Ballester detects hot Hydrogen in upper atmosphere
  • Jan 2007 - Temperature found to be uniform on day and night side, indicating supersonic winds go from hot side to the cold side
  • Feb 2007 - Richardson/Seager (Goddard) and Swain's (JPL) teams fail to detect water, methane, or carbon using Spitzer Space Telescope. Richardson's team only detected sandy Silicate Clouds, thought to be hiding the water (looked just before planet disappears behind star)
  • Apr 2007 - Barman's study detects water in the atmosphere (looked during transit)
  • May 2007 - Surface Gravity found to be near Earth's, leading insight into escape velocity
  • Dec 2008 - Water detected before, during, and after transit by a team (Demen commented, but wasn't part of it), confirming water's presense
  • Oct 2009 - Carbon Dioxide and Methane detected by Swain's team, who had earlier detected them in the HD 189733 System.
  • Jan 2010 - Temperature variations (weather) found on dark side of planet, but not day side.
  • Jun 2010 - Carbon Monoxide movements detected revealing supersonic winds. Orbital speed calculated, yielding exact mass for the first time for any exoplanet(before it was based on inferred stellar mass).


  • First planet detected with the transit technique
  • First planet found with Dopplar Spectrometry that was confirmed with a transit
  • First visual evidence for an exo-planet
  • First visual evidence for Hot Jupiters
  • First Hot Jupiter shown to have the predicted bloatedness
  • First planet to have its temperature measured
  • First transiting planet and hot Jupiter close enough to make good observations
  • First exoplanet proven to be gaseous rather than solid
  • First planet whose transit detected by amateur astronomers
  • First planet whose molecules in its atmosphere are detected
  • First planet found to have Sodium, Hydrogen, Oxygen, Carbon, Water
  • First evaporating planet found
  • First exoplanet to have its mass directly measured (via orbit speed measurements)

Not Firsts:

  • 30th Exo-planet discovered
  • 2nd planet to have detected infrared light and thus direct temperature measure
  • 2nd planet to have Methane and Carbon Dioxide detected

Other Records:

  • Least dense planet known at time of discovery (less than Saturn)

Unusual "Puffed Up" Size:

  • At first, thought to be 1.6 RJ, which confirmed theories that hot Jupiters would be "puffed up"
  • Found to be 20% larger than models predicted in 2003 report, prior to discovery of any other transiting exoplanets
  • Radius reduced to 1.3 RJ eventually, but other planets were found to not be as puffed up. Why was it so much bigger than the 7 other known transiting planets, including TrES-1, which had similar temperature and mass.
  • Orbit confirmed to be circular via transit techniques, so an explanation that it was eccentric and thus stressed more went out the window
  • Second "puffed up planet" HAT-P-1 was thought to be found in 2006, but turned out to be not so puffed up

Outer Envelope (Full Extended Upper Atmosphere):

  • Contains an outer envelope of atomic Hydrogen, Oxygen, Carbon, and theoretically heavier atoms like Iron in an extended gas envelope
    • This envelope is being ripped away at speeds of 35,000 km/h
    • Envelope is 3 times the planet's diameter
    • Envelope trails off into a tail
    • Envelope and tail are both completely transparent
    • Eventually, the planet may be stripped bare, leaving only a 10 Earth Mass core in orbit (a "Cthonian planet")
    • Hydrogen boiling off at rate of 10,000 tons a second
    • Tail extends 125,000 miles
    • Hydrogen moving quickly relative to planet, therefore it is escaping
    • Escaping Hydrogen is "blowing off" the Oxygen and Carbon, which are too heavy to leave the planet by themselves
    • It will take 5 Billion years for the atmosphere to be completely lost

Upper Atmosphere

  • A transition area where gas escapes into the hydrogen envelope
  • Outer atmosphere starts at 1,000K to 15,000K (hotter than the surface of the Sun) observed via effects of starlight passing through it
  • Hot Hydrogen detected
  • Observed by Gilda E. Ballester

Lower Atmosphere

  • Hydrogen was detected in it

Heat Distribution

  • Temperature found to be the same on the day side as the night side in 2007, constrasting to the hot/cold atmosphere in the Upsilon Andromedae System
  • Supersonic winds proposed to explain uniform day/night temperatures
  • Temperature near terminator varies by 20% over time
  • Location of coldest spot varies by 20 degrees, occasionally appearing west of the anti-solar point
  • In 2010, wind speed was measured by measuring flow of Carbon Monoxide, at 7,000 km/hour

Elements Detected:

  • Sodium: First element detected. As it has a strong signature, it was the first element to be searched for and found. Finding it proved the planet had an atmosphere, the first time that was done. Had slightly less Sodium than predicted, perhaps hinting at clouds blocking some of it. A rare element, but easy to detect.
  • Hydrogen: Second element detected. First observed in an envelope of escaped Hydrogen. Hydrogen is moving so fast that it pushes heavier elements off the planet into the envelope. Also observed in a tail. Hydrogen also observed in the lower atmosphere. Also observed in the upper atmosphere, where it is "evaporating".
  • Oxygen: First planet where Oxygen was detected. Found being "blown off" the upper atmosphere and into the envelope.
  • Carbon: First planet where Carbon was detected. Also "blown off" the upper atmosphere into the envelope. Atmosphere found to be carbon-rich, similar to Jupiter and Saturn, suggesting it was formed similarly to those planets, and then migrated inward.
  • Water: At first, water was not detected by two studies and a third around another study. It was later detected over a transit (rather than from behind the star like the other studies). Many were still not convinced, so another study confirmed its presence before, during, and after an eclipse.
  • Carbon Dioxide: Detected by the same team who had earlier found it around another star.
  • Methane: Detected by the same team who had earlier found it around another star.
  • Carbon Monoxide: Detected and tracked to determine the speeds of the winds ("poisonous winds"), which blow over 10 times as fast as a tornado from the day side to the night side.


  • Mass = 0.63 Jupiter
  • Radius 1.35 Jupiter
  • Density = 370 kg/m3
  • Surface gravity = 9.39 m/s² (0.96 g)
  • Surface Temperature = 1,130 K
  • Distance from Earth = 150 ly
  • Orbit Period = 3.5 days
  • Distance = 0.045 AU
  • Eccentricity = 0.014
  • Surface Gravity = 9.28 ms-2 (Earth is 9.8, Jupiter is 24.8)


  • Marcy wanted to name it "Shadow" or "Silhouette"
  • Later nicknamed "Osiris"

Observers: Marcy team {announced discovery} -

  • Geoffrey Marcy (professor at Berkeley in California) - head of those who first detected wobble
  • Paul Butler (Department of Terrestrial Magnetism at the Carnegie Institution) - one of those who first detected wobble
  • Steve Vogt (of University of California, Santa Cruz, and Lick Observatory) - one of those who first detected wobble
  • Greg Henry (an astronomer at the Tennessee State University) - first detected transit

American-Swiss Team {first observed planet, but didn't announce it} -

  • David Charbonneau (Harvard-Smithsonian Center for Astrophysics, Massachusetts) - first to detect transit, but didn't announce findings. first used HST to detect its atmosphere and found Carbon
  • David Latham (Harvard-Smithsonian Center for Astrophysics, Massachusetts)
  • Timothy Brown (National Center for Atmospheric research, Colorado)
  • Michel Mayor (Geneva Observatory)


  • Alfred Vidal-Madjar (of the Astrophysical Institute) - Found atomic oxygen, carbon in atmosphere and found it to be evaporating


  • Keck Telescope - first detected dopplar spectrometry
  • Fairborn Observatory in Arizona - first detected transit
  • Nyrölä observatory - used for first amateur detection
  • Hubble Space Telescope (ultraviolet spectrograph) - detected atmospheric molecules (Sodium, Hydrogen, Oxygen, Carbon)

See AlsoEdit

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