The highly elliptical orbit of exoplanet HD 20782, located about 117 light-years away from Earth, is unlike anything seen in our solar system. It is, in fact, touted as the most eccentric orbit known to scientists.
This eccentric-orbit planet presents “a particularly lucrative opportunity” to study planetary atmospheres, specifically one that can hurdle a brief yet blistering exposure to its host star. Its reflected light may play quite an important role here, according to researchers discussing their findings in the Astrophysical Journal.
HD 20782 moves in an almost flattened ellipse, journeying a long path from its host star before making a rapid, intense slingshot around the star at the closest approach.
When it spends most of the time far from its star yet becomes “flash-heated” at a very close approach, how then does HD 20782’s atmosphere behave? The researchers probed its bright reflected light, because the percentage of light a planet reflects — or its level of brightness in the sky — is partly determined by its atmospheric makeup.
Venus and Jupiter, for instance, are highly reflective since they are covered in clouds filled with icy particles. Moving too close to the sun, however, will strip icy particles in the planet’s clouds.
Some extrasolar, Jupiter-sized planets treading short and circular orbits do appear “dark” as this phenomenon seems to remove reflective material from the atmosphere.
But HD 20782 is deprived of the chance to respond, explains lead researcher and San Francisco State University astronomer Stephen Kane.
"The time it takes to swing around the star is so quick that there isn't time to remove all the icy materials that make the atmosphere so reflective,” he says.
The researchers speculate that the exoplanet's atmosphere, after all, just might have a greatly reflective cloud cover not unlike that of Jupiter. And due to its eccentricity, HD 20782 flashes bright reflected light whenever it gets close to its star.
Planetary atmospheres have always captured great interest. For instance, one intriguing mystery is why Earth maintains a nitrogen-oxygen atmosphere, while Venus has a thick carbon dioxide one with no oxygen but with sulfuric acid clouds.
The answer appears to be linked to the latter’s very hot surface conditions (in fact the hottest in the solar system), leading to a striking difference even when both planets have practically the same mass, are made out of the same material and have roughly the same solar distance.
Eccentric heavenly bodies like HD 20782 are an altogether different story, fueling further investigation.
