Friday, 12 August 2011

TrES-2b, the black planet.

TrES-2b was discovered by the in 2006 by the Trans-Atlantic Exoplanet Survey, using telescopes at the Palomar Observatory in California and the Lowell Observatory in Arizona. It was the second planet discovered by the survey, hence its name, TrES from Trans-Atlantic Exoplanet Survey, 2 for the second planet discovered and b for a planet which is the second object in the system (a second star would get the designation B). The discovery was announced in a paper in The Astrophysical Journal by a team lead by Francis T. O'Donovan of the California Institute of Technology. The Trans-Atlantic Exoplanet Survey used simultaneous observations several relatively small (& therefore cheap) telescopes to identify regular drops in light intensity from stars, which might indicate planets passing in front of the star. The discovery was confirmed by the Keck Observatory.

TrES-2b was discovered by the very slight dimming it causes when it passes in front of its host star.

The planet orbits the star GSC 03549-02811, a yellow-dwarf main sequence star 718 light years away in the constellation of Drago. For this reason the planet could be referred to as GSC 03549-02811b and the star as GSC 03549-02811A, but this is unwieldily so it is not normally used. GSC stands for Guide Star Catalogue, a catalogue of stars designed for the Hubble Space Telescope. The numbers are co-ordinates, rather than numbers from a list, enabling the list to (potentially) include every object in the sky.

TrES-2b was the first transiting exoplanet (planet detected transiting across the disk of its star) discovered within the Kepler Field. This is the area of space which the Kepler Space Telescope is permanently trained upon. Unlike Hubble, Kepler does not move. It points permanently at the same point in space to build up a very detailed picture of the star systems in its field, and any planets they have. Since the Kepler team were forwarded as to the existence of TrES-2b, they were able to quickly identify it when Kepler came on line in 2009. Thus it was the first planet imaged by Kepler and is sometimes referred to as Kepler-1b (making the star Kepler-1A).

In February 2009 a team led by Sebastian Daemgen of the Max-Planck-Institut für Astronomie published a paper in the journal Astronomy & Astrophysics in which they announce the discovery of a second star in the TrES system using the Calar Alto telescope in Almeria, Spain. This second star is a dim K-type star orbiting TrES-2A at a distance of 232 AU (i.e. 232 times as far from the main star as Earth is from the sun, or nearly 5 times as far away as Pluto at its furthest from the sun). Since it was more distant than and discovered after TrES-2b it was given the designation TrES-2C, though it is unusual for a star to have a designation lower than a planet in the same system. A K-type star is a star with a surface temperature between 3700 and 5200 K; in contrast our sun is a G-type star, which implies a star with a temperature between 5,200 and 6000 K. K-type stars tend to be older stars running out of fuel or much smaller stars that have never got as hot as our sun, as is the case with TrES-2C.

TrES-2b is a 'hot jupiter' type planet; a gas giant twice the mass of Jupiter orbiting its star at a tenth of the distance at which Mercury orbits the sun.

In August 2011 The Royal Astronomical Society issued a press release announcing a forthcoming paper in the journal Monthly Notices of the Royal Astronomical Society, in which a team led by David Kipping of the Harvard-Smithsonian Center for Astrophysics detail the results of a long-term spectrographic study of TrES-2b using the Kepler Space Telescope. This has revealed that the planet is inexplicably dark in the visible part of the spectrum, emitting almost no light whatsoever. The planet is known to have a surface temperature of around 1000°C, and to have an atmosphere containing gaseous sodium, potassium and titanium oxide, all of which absorb light in the visible part of the spectrum and emit it at other wavelengths, but this cannot account for the darkness of the planet, which remains a mystery.

An artists impression of TrES-2b.

1 comment:

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