The highly elliptical orbit of the newly discovered planet HD 20782 makes it the most eccentric orbit yet found, with an eccentricity of up to .96. According to the report of San Francisco State University astronomers, this “eccentricity” means that the extrasolar planet moves in an almost flattened ellipse, passing a long path far from its host star before making a quick slingshot around the star at its closest approach.
Eccentricity is how elliptical a planet’s orbit is around its star. The scientists explain in their study published on Feb. 28 in The Astrophysical Journal that HD 20782 separates from its star with a distance 2.5 times the distance between the Sun and Earth during its furthest point in its orbit and closes in as near as .06 the distance between the Sun and Earth at its closest approach.
The planet is 117 light-years away from Earth. Lead scientist Stephen Kane, an assistant professor of physics and astronomy at the university, adds that it is around the mass of Jupiter.
Moreover, the team has also observed a reflected light from the planet. This could help them learn how its atmosphere changes during the time away from its host star.
They explain that a planet’s atmospheric composition dictates how bright a planet appears or the percentage of light it reflects. They say that planets like Venus and Jupiter are reflective when far away from the sun due to its icy clouds. However, these ice particles get heated up and disappear when these planets move too close to the Sun.
These observations led the team to believe that HD 20782 might have the same highly reflective clouds of Jupiter. Still, its exact atmospheric composition remains unknown.
Apart from this, they are also uncertain about how this planet’s orbit became this way. Although they suggested that HD 20782 could have been pushed by another planet into its eccentric path, they admit more studies are needed to solve this.
“When we see a planet like this that is in an eccentric orbit, it can be really hard to try and explain how it got that way,” Kane says. “It’s kind of like looking at a murder scene, like those people who examine blood spatter patterns on the walls. You know something bad has happened, but you need to figure out what it was that caused it.”