According to an article expected to be published in the journal Nature today, Geneva University’s Prof. Michael Mayor and Christopher Lovis, using the HARPS (High Accuracy Radial velocity Planet Searcher), have discovered planets in a solar system in the Argo Navis constellation (“the ship of the Argonauts”). The star (just slightly smaller than our own sun) is classified HD69830 and is located within the sub-constellation Puppis (“The Poop Deck”) some 41 light years away and can only be observed from the southern hemisphere.
The Swiss team based at the Geneva Observatory is renowned for having found more than 95 percent of the 180 solar systems discovered since the first was found eleven years ago. They used the HARPS, located in Chile’s Atacama Desert, to restudy this particular star, because last year astronomers at NASA’s Spitzer Space Telescope found that it has a unique asteroid belt around it (the only star other than our own yet to be discovered with one). The study was to see if there were planets shepherding it, and the rocky belt is believed to be orbiting either between the second and third, or beyond the third, planet.
A closer study by the Swiss team revealed that the Neptune-sized planets are orbiting a sun remarkably like our own. This was done employing a Doppler system of observing the gravitational pull that planets exert on their parent star causing a measurable “wobble.” Recently the team has refined the technique to the point where lower-mass planets are found just as easily as the larger gas giants.
The closest planet has a mass of about ten times that of earth and appears to be like a giant Mercury with a solid core. It has a very swift orbit of only about nine days, approximately seven million miles from its star.
The second planet is about 12 times that of Earth, seventeen million miles from its star, and has an equally swift orbit measured at only around 32 days. It also appears to have a rocky core.
The outermost planet orbits in about 197 days in what’s referred to as the “habitable zone” where its distance from its sun (60 million miles compared to Earth’s 93 million), available light, and approximate temperature might support life. In fact it’s the smallest planet to date yet found within such a zone. It is about 18 times the mass of the earth and has a rocky core with possible ice on the surface, but is shrouded in a thick and high-pressure atmosphere possibly made up of mostly hydrogen. It’s improbable that life could exist there however, because the massive gravitational field and atmospheric pressure would crush it even down to a mere cell’s level.
David Charbonneau of Harvard University is quoted as saying, “The architecture of this particular planetary system bears some intriguing similarities to that of our own solar system.”
The system is also interesting because it’s the first one discovered not to have a gas giant such as Jupiter orbiting it.