Astronomers at San Francisco StateUniversity (SF State) have observed an exoplanet located just 117light-years from Earth, which exhibits the most eccentric orbit yetfound. The light reflected as the planet passed close to its parentstar is providing researchers with clues as to the make up of thebody's atmosphere, which is thought to be similar to that of Jupiter.
All of the planets in our home solarsystem have almost entirely circular orbits around the Sun, but somedistant planets take a much less ordinary route around their ownstars. Known as HD 20782, the exoplanet observed by the SF Stateastronomers has the single most eccentric orbit known, travellingalong an almost flat path away from and towards its star, which itpasses at extremely high speeds.
At its farthest point, HD 20782 isaround two and a half times the distance from its star than the spacebetween Earth and the Sun. But it was at its closest point, when itpasses much closer to its star than the orbit of Mercury around theSun, that the astronomers took their chance to take a peek at theobject. Timing their observations, the scientists were able to watchthe brightness of the exoplanet change as light from the starreflected off its atmosphere.
Planets with thick layers of cloudscontaining large amounts of icy particles, such as Venus or Jupiter,are usually very reflective. However, if they were to pass closer toa star, the heat would melt the icy particles and the planet wouldappear much darker when observed.
So, why doesn't HD 20782 dim as itpasses by its parent star? Well, astronomers theorize that the highspeed of the planet as it sling-shots around the star means that notall of the icy material has time to be removed, giving it the opportunity to reflect light out into space.
The observations provided a lot of newinformation about the planet, but the team wasn't able to work outthe exact makeup of its atmosphere. At this point, they believe thatthe environment is probably similar to that of Jupiter's atmosphere,with thick, highly reflective cloud cover.
Similarly, the astronomers aren'texactly sure why the planet travels along such an eccentric orbit.Possible theories are that HD 20782 collided with another object andwas ejected out onto its current path, or that the second star in thesystem – it being a binary system – might have passed close tothe planet and thrown it out of an original, more circular orbit.
The findings of the research arepublished online in The Astrophysical Journal.
Source: SF State