A team of astronomers led by Dr Stephen Kane of San Francisco State University has discovered a new giant extrasolar planet circling the nearby G5 star HD 4203.
The newly discovered alien world, named HD 4203c, orbits its host star every 18.2 years, and has a minimum mass about 2.17 times that of Jupiter.
The star, HD 4203, lies in the constellation Pisces, around 250 light years from our planet.
The star system harboring HD 4203c contains only one star, as do the other three systems with extrasolar planets, HD 168443, HD 1690 and HD 137759, analyzed by Dr Kane and his colleagues using Gemini North observatory in Hawaii.
“And at the same time, the planets that had already been discovered in these systems followed eccentric orbits, swinging away from their stars in a less circular and more elliptical fashion, more like that of a comet,” Dr Kane said.
With these two clues, the scientists wondered if the radial velocity and eccentric orbits might be explained by the presence of another star in the system.
But when they took a closer look at the systems, they were able to rule out the possibility that another star was perturbing the system.
“I thought we were likely to find stellar companions, and when all four didn’t have a binary star, that did surprise me,” said Dr Kane, who is the lead author of a paper submitted for publication in the Astrophysical Journal (arXiv.org).
But in the case of HD 4230, the unexplained radial velocity appears to be coming from the pull of a previously undiscovered giant planet.
The astronomers confirmed the presence of HD 4203c with additional radial velocity data collected at Hawaii’s Keck observatory.
Given that the astronomers did not find any stellar companions it is very likely that the leftover radial velocity is instead a signal that there are additional planets to be found in all four systems.
They feel this is especially true for the system called HD 168443, where their ability to detect a companion star was very strong.
Kane SR et al. 2014. Limits on Stellar Companions to Exoplanet Host Stars With Eccentric Planets. ApJ, submitted for publication; arXiv: 1401.1544