Spectrum of young extrasolar planet reveals its uniqueness

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Washington, Aug 31 (ANI): By measuring the temperature of a young gas-giant planet around another star using the W. M. Keck Observatory, University of Hawaii astronomers have unveiled surprising results.

They have found that its atmosphere is unlike that of any previously studied extrasolar planet.

By obtaining a spectrum of its emitted light, the astronomers determined the temperature of the planet.

Thus, they found that current theoretical models of gas-giant planets did a poor job of explaining all the data.

The team suspects that the reason is dust in the planet's atmosphere.

Models with normal amounts of dust do not resemble this planet, but models with exceptionally thick dust clouds do a much better job.

It therefore appears that young gas-giant planets are extremely cloudy.

"We are at a point where not only can we directly image planets around other stars, but we can begin to study the properties of their atmospheres in detail. Direct spectroscopy of exoplanets is the future of this field," said Brendan Bowler, a graduate student at the University of Hawaii and the lead author of the study.

The planet, known as HR 8799 b, is one of three gas-giant planets orbiting the star HR 8799, located 130 light-years away from Earth in the constellation Pegasus.

HR 8799 b is the lowest-mass planet around the star, about 7 times the mass of Jupiter.

This multiplanet system was discovered by direct imaging in 2008, and now, only a year and a half later, astronomers have obtained a spectrum of one of its planets.

The spectrum of a planet contains much more information than a single image- it can reveal the temperature, chemical composition, and cloud properties of the planet.

The technique the team used to determine the planet's temperature relies on the chemistry of the planet's atmosphere.

Specifically, the presence or absence of gaseous methane can be used as a thermometer.

The team found that HR 8799 b shows little or no methane in its atmosphere.

Based on their spectrum and previously obtained images of the planet, and by comparing the observations to theoretical models of low-temperature atmospheres, they estimate the coolest possible temperature for the planet is about 1,200 Kelvin (about 1,700 degrees Fahrenheit).

A paper describing the study will be published in the Astrophysical Journal later this year. (ANI)

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