Spectrum of Light Captured From Distant World

An anonymous reader writes with this excerpt from Cosmos: "Astronomers have made the first direct capture of a spectrum of light from a planet outside the Solar System and are deciphering its composition. The light was snared from a giant planet that orbits a bright young star called HR 8799 about 130 light-years from Earth, said the European Southern Observatory (ESO). ... The find is important, because hidden within a light spectrum are clues about the relative amounts of different elements in the planet's atmosphere. 'The features observed in the spectrum are not compatible with current theoretical models,' said co-author Wolfgang Brandner. 'We need to take into account a more detailed description of the atmospheric dust clouds, or accept that the atmosphere has a different chemical composition from that previously assumed.' The result represents a milestone in the search for life elsewhere in the universe, said the ESO. Until now, astronomers have been able to get only an indirect light sample from an exoplanet, as worlds beyond our Solar System are called. They do this by measuring the spectrum of a star twice — while an orbiting exoplanet passes near to the front of it, and again while the planet is directly behind it. The planet's spectrum is thus calculated by subtracting one light sample from another."

Comments

NOT first spectrum of planet's atmosphere

[StupendousMan]

Astronomers have measured transmission spectra of a planet circling the star HD 209458 and a planet circling the star HD 189733 (and probably others). The first successful measurements, which found sodium in the spectrum of HD 209458b, were published by Charbonneau et al. in 2002. See ApJ 568, 377 (2002).

Re:NOT first spectrum of planet's atmosphere

[floateyedumpi]

The article is wrong on many levels. The key word here is "direct". The 2002 transmission spectra you mention (and others like it) consist of light from the host star, passing through the atmosphere of the planet as it passes in front of it, which imprints spectral signatures of the planetary atmosphere on that stellar spectrum. So in this sense, its not a direct spectrum of the planet's own light, but of the star, modified by the planet in front of it.

The first spectrum of a planet, consisting only of planetary light, came from the Spitzer Space Telescope, which used a differencing technique:

planet + star [out of eclipse] - star [when planet eclipsed] = planet only

The star and planet could not be resolved (separated) by the telescope, but by using the known orbit of this eclipsing planetary system, and timing the observations carefully, a spectrum of the "planet's own light" was obtained.

The novelty of this latest result is that no differencing of this sort was required. Using adaptive optics to correct distortions due to Earth's atmosphere, the light from a star and the light from its associated giant planet where physically resolved, and a spectrum of the planet, all by itself, was obtained. Even with adaptive optics, however, very few systems have star-planet separations on the sky large enough to permit this technique.

Re:Reflected Light

[Nadaka]

To be a smart ass, no, not all light from a planet is indirect. For instance Jupiter is releasing light in the infra-red spectrum that is not reflected nor absorbed & re-radiated from the sun. Due to its size and mass it retains a great deal of heat from its gravitational contraction and any internal radioactive decay. Jupiter is currently emitting more energy that it is receiving form the sun.

Though in this case I believe they are refering to reflected | absorbed & re-radiated light instead of starlight filtering through the atmosphere. The first produces chemical emission lines while the later negates them from the stars emissions.