Extrasolar planet List of extrasolar planets
Artist's conception of TrES-2b, with unsubstantiated speculation on possible moons
Parent star

<tr> <td colspan="2">Star</td> <td>GSC 03549-02811 A[1]</td></tr><tr> <td colspan="2">Constellation</td> <td>Draco</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>19h 07m 14.035s</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>+49° 18′ 59.07″</td></tr><tr><td colspan="2">Distance</td><td>750±30 ly
(230±10 pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>G0V</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00[1] AU</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00 d</td></tr><tr> <td>Inclination</td> <td style="text-align: center">(i)</td> <td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00[1]°</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00[1] MJ</td></tr><tr><td>Radius</td><td style="text-align: center">(r)</td><td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00[1] Template:Jupiter radius</td></tr><tr><td>Bond Albedo</td><td style="text-align: center">(Ab)</td><td>0.04</td></tr><tr><td>Geometric Albedo</td><td style="text-align: center">(Ag)</td><td>0.0136</td></tr><tr><td>Surface gravity</td><td style="text-align: center">(g)</td><td>Template:Val/delimitnum/gaps00±Template:Val/delimitnum/gaps00[1] g</td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>August 21, 2006
confirmed September 8, 2006</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>O'Donovan et al.</td></tr><tr> <td colspan="2">Discovery method</td> <td>Transit</td></tr><tr> <td colspan="2">Other detection methods</td> <td>Radial velocity,
Reflection/emission modulations,
Ellipsoidal light variations,
Doppler beaming</td></tr><tr> <td colspan="2">Discovery site</td> <td>California & Arizona</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr>

Other designations

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>

TrES-2b (or Kepler-1b) is an extrasolar planet orbiting the star GSC 03549-02811 located 750 light years away from our solar system. The planet has been identified in 2011 as the darkest known exoplanet, reflecting less than 1% of any light that hits it.[2] The planet's mass and radius indicate that it is a gas giant with a bulk composition similar to that of Jupiter. Unlike Jupiter, but similar to many planets detected around other stars, TrES-2b is located very close to its star, and belongs to the class of planets known as hot Jupiters. This system was within the field of view of the now nonoperational Kepler spacecraft.[3]

This planet continues to be studied by other projects and the parameters are being improved continuously. A 2007 study improved stellar and planetary parameters.[4] A 2008 study concluded that the TrES-2 system is a binary star system. This has a significant effect on the values for the stellar and the planetary parameters.[1]


File:TrES-2 b rv.svg

TrES-2b was discovered on August 21, 2006 by the Trans-Atlantic Exoplanet Survey (TrES) by detecting the transit of the planet across its parent star using Sleuth (Palomar Observatory, California) and PSST (Lowell Observatory, Arizona), part of the TrES network of 10–cm telescopes. The discovery was confirmed by the W. M. Keck Observatory on September 8, 2006, by measuring the radial velocity of the star that hosts TrES-2b.[3]

Spin-orbit angleEdit

In August 2008 more details of the relationship between the parent star and the orbit of the planet were published. The orbit was determined to be tilted by −9±12° from the stellar equator. The orbital direction was determined to be in the same direction as the star's rotation (prograde).[5]

The Kepler missionEdit

Main article: Kepler (spacecraft)

NASA launched Kepler in March 2009. The spacecraft is dedicated to the discovery of extrasolar planets by the transit method from solar orbit. In April 2009 the project released the first light images from the spacecraft, and TrES-2b was one of two objects highlighted in these images. Although TrES-2b is not the only known exoplanet in the field of view of this spacecraft it is the only one identified in the first light images. This object is important for calibration and check-out.[6]

File:Kepler First Light Detail TrES-2.jpg

Kepler mission also managed to detect the mass of the planet from Kepler data alone though the analysis of the light curve of the host star. In addition to detecting the planet directly, the planet was also detected by analysis of the star brightness caused by the gravitational tug of TrES-2b by shape distortion of the host star and by light variations due to Doppler beaming. [7]

Darkest planetEdit

The first important result from the Kepler Mission about TrES-2b is an extremely low geometric albedo, measured in 2011.[2] If the entire day-night contrast were due to geometric albedo, it would be 2.53%, but modeling suggests that much of this is dayside emission and the true albedo is much lower. It is estimated to be less than 1% and for best-fit model it is about 0.04%. This makes TrES-2b the darkest known exoplanet, reflecting less light than coal or black acrylic paint.[8] It is not clear why the planet is so dark. One reason could be an absence of reflective clouds such as those which make Jupiter so bright, due to TrES-2b's proximity to its parent star and the consequent high temperature. Another reason could be the presence in the atmosphere of light-absorbing chemicals such as vaporized sodium, potassium, or gaseous titanium oxide.[9] In general, hot Jupiters are expected to be dark, because "absorption due to the broad wings of the sodium and potassium D lines is thought to dominate their visible spectra." Apart from that of Kepler-7b (38±12%), albedo measurements for hot Jupiters have generally given only upper limits.[2]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 (2009). Binarity of transit host stars — Implications for planetary parameters. Astronomy and Astrophysics 498 (2): 567–574.
  2. 2.0 2.1 2.2 David M. Kipping & David S. Spiegel. Detection of visible light from the darkest world. Monthly Notices of the Royal Astronomical Society.
  3. 3.0 3.1 (2006). TrES-2: The First Transiting Planet in the Kepler Field. The Astrophysical Journal Letters 651 (1): L61–L64.
  4. Alessandro Sozzetti et al. (August 1, 2007). Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2. The Astrophysical Journal 664 (2): 1190–1198.
  5. (2008). The Prograde Orbit of Exoplanet TrES-2b. The Astrophysical Journal 682 (2): 1283–1288.
  6. Kepler Eyes Cluster and Known Planet. NASA (2009-04-16). Retrieved 2009-05-09.
  7. Photometrically derived masses and radii of the planet and star in the TrES-2 system: Thomas Barclay, Daniel Huber, Jason F. Rowe, Jonathan J. Fortney, Caroline V. Morley, Elisa V. Quintana, Daniel C. Fabrycky, Geert Barentsen, Steven Bloemen, Jessie L. Christiansen, Brice-Olivier Demory, Benjamin J. Fulton, Jon M. Jenkins, Fergal Mullally, Darin Ragozzine, Shaun E. Seader, Avi Shporer, Peter Tenenbaum, Susan E. Thompson
  8. Coal-Black Alien Planet Is Darkest Ever Seen. Retrieved 2011-08-12.
  9. Baldwin, Emily (2011-08-11). Exoplanet blacker than coal. Astronomy Now. Retrieved 2011-08-12.

External linksEdit

Coordinates: Sky map 19h 07m 14s, +49° 18′ 59″

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