'Glowing planet' baffles scientists
Updated on 09 May 2007
A strange distant planet that behaves like a glowing hot coal in space is puzzling scientists.
Experts have calculated that the planet has a surface blacker than charcoal and as hot as 3,700C.
To reach such a blistering temperature, the planet must absorb virtually all the starlight reaching it and then re-radiate the energy.
Professor Joseph Harrington, from the University of Central Florida in Orlando, US, whose team described the find in the journal Nature, said: "The high heat would make the planet glow slightly, so it would look like an ember in space, absorbing all incoming light but glowing a dull red."
The planet orbits the star HD 149026, 257 light years away in the constellation of Hercules.
It is one of around 230 extra-solar planets discovered by astronomers, but only the fourth to have its temperature measured directly.
Spitzer, the American space agency Nasa's infrared space telescope, was used to observe the planet as it vanished behind its star and then reappeared.
The dimming of the light that reached the telescope allowed astronomers to work out the planet's temperature.
Discovered in 2005, the planet is slightly smaller than Saturn but contains a super-dense core with 70 to 90 times the Earth's mass.
The unusual nature of the planet, designated HD 149026b, has left scientists scratching their heads.
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