Astronomers find exoplanet with most eccentric orbit
An artist's rendering shows the planet HD 20782, the most eccentric planet ever known, passing its star in close orbit. Credit: NASAA team of astronomers has discovered an exoplanet with the most eccentric orbit ever observed.
According to Phys.Org, the planet called HD 20782 lies about 117 light-years from Earth and boasts an extremely elliptical orbit around its host star.
Planets in our own solar system have nearly circular orbits, while HD 20782 maintains an elliptical orbit so wide as to be in the shape of a very flattened oval. The highly eccentric orbit more closely resembles the typical orbit of a comet than that of a planet, with HD 20782 whipping quickly around its star in a slingshot maneuver then shooting far out into space before its return.
“It’s around the mass of Jupiter, but it’s swinging around its star like it’s a comet,” Stephen Kane of San Francisco State University said.
If HD 20782 were to orbit the Sun, its farthest point of orbit would be 2.5 times as far as Earth orbits the Sun, and its closest approach would bring it to within just .06 of the Earth-Sun distance.
The team was able to spot the planet by way of a flash of starlight that reflected off the planet’s atmosphere as it passed by the star in its closest orbital approach. Further study of the light passing through the atmosphere of HD 20782 may help scientists understand what kind of atmosphere can withstand such close approaches to a star.
Jupiter-sized exoplanets with very close orbits to their host stars seem to typically lose the reflective ice in their atmospheres to the stars’ radiation. In the case of HD 20782, however, “the atmosphere of the planet doesn’t have a chance to respond,” Kane said. “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.”
Just how HD 20782 ended up with such an eccentric orbit remains a mystery for the moment. One possibility is that a now-absent second planet with an unstable orbit knocked HD 20782 onto its current course. Another scenario has the host star’s binary partner affecting HD 20782’s orbit at some point in the past.
“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 said.
The study was published in The Astrophysical Journal.
Kathy Fey
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