14 December 2009
An international team of planet hunters has found four new planets orbiting
two nearby stars that are very similar to the Sun. These discoveries point
the way to the detection of potentially habitable worlds within a few years.
The planets were found by Australian, American and British astronomers using the Anglo-Australian Telescope in New South Wales and the Keck Telescope in Hawai’i.
To find them, the astronomers employed the “Doppler wobble” technique, which measures how stars are tugged around by their planets’ gravity.
Three planets with masses ranging from 5.3 to 24.9 Earth masses orbit the star 61 Virginis, which is virtually a twin of the Sun.
“These planets are particularly exciting,” said team member Professor Chris Tinney of the University of NSW.
“Neptune in our Solar System has a mass 17 times that of the Earth. It looks like there may be many Sun-like stars nearby with planets of about that mass. They point the way to even smaller planets that could be rocky and suitable for life.”
61 Virginis can be seen with the naked eye. It lies 28 light-years from Earth in the constellation of Virgo, which at this time of year can be seen rising a few hours before the Sun. The findings for 61 Virginis are to be published in The Astrophysical Journal.
The fourth planet the research team found is a Jupiter-mass planet orbiting the Sun-like star 23 Librae.
23 Librae lies 84 light-years away in the constellation of Libra. Another planet was found around this star in 2006: this new one is the second.
The new planet has a 14-year orbit. This makes it very like Jupiter, which has a 12-year orbit.
“In fact, what we detect from this star system is very like what we’d detect from our own Solar System if we were observing it from a distance, because Jupiter has the strongest gravitational effect of all our Sun’s planets,” said Dr Simon O’Toole of the Anglo-Australian Observatory, a member of the planet-hunting team.
“We are now in a position to quantify how common planets like Jupiter are around stars like our Sun,” said team member Hugh Jones of University of Hertfordshire.
“Compared to the Solar System, most extrasolar systems look odd, with planets in very small or very elliptical orbits. In contrast, this new planet has an orbit that is both large, and nearly circular—and for the first time we are beginning to see systems that resemble our own.”
“These detections are truly at the current state-of-the-art,” said team member Dr Paul Butler of the Carnegie Institute of Washington, “The inner planet of the 61 Vir system is among the two or three lowest-amplitude planetary signals that have been identified with confidence. We’ve found there’s a tremendous advantage to be gained from combining data from two world-class observatories, and it’s clear that we’ll have an excellent shot at identifying potentially habitable planets around the very nearest stars within just a few years.”
In addition to Chris Tinney (UNSW), Simon O'Toole (AAO), Hugh Jones (U. Hertfordshire) and Paul Butler (Carnegie Institute), the authors of the 61 Vir and 23 Lib papers are: Steve Vogt, Eugenio Rivera, Greg Laughlin and Stefano Meschiari of the University of California at Santa Cruz; Rob Wittenmyer and Jeremy Bailey of the University of New South Wales; Gregory Henry of Tennessee State University; Brad Carter of the University of Southern Queensland; and Konstantin Batygin of Caltech.
The discovery of three planets around the star HD 1461, found using the Keck telescope, will also be announced.
Professor Chris Tinney, University of NSW
+61 (0)416 092 117 (currently on US West Coast time)
Dr Paul Butler, Carnegie Institute of Washington – currently visiting the Anglo-Australian Observatory (Sydney)
+61 2 9372 4893 (office)
Dr Simon O’Toole, Anglo-Australian Observatory (Sydney)
+61 (0)434 916 378 (mob)
+61 2 9372 4856 (office)
Helen Sim, Anglo-Australian Observatory (Sydney)
+61 (0)419 635 905 (mob)
+61 2 9372 4251 (office)
Dan Gaffney, University of NSW – Media Unit
+61 (0)411 156 015
Graphics of the 61 Vir system
http://www.phys.unsw.edu.au/~cgt/press/61Virbcd_orbits.jpg (850x850 pix)
http://www.phys.unsw.edu.au/~cgt/press/61Virbcd_orbits.ai (Adobe Illustrator)
Caption: A comparison of the orbits of the planets of 61 Vir with the inner planets in our Solar System. All three planets discovered to date in this system would lie inside the orbit of Venus.
Photos of the Anglo-Australian Telescope
Animation of 61 Vir b
Animation Caption: The animation shows a simulation of the hot atmosphere of the 5.3 Earth-mass planet 61 Vir b as it circles around its star in a 4.2 day orbit. The imaginary observer sits in space above the planet, and sees the hot side (which always faces the star) rotate into and out of view.
61 Vir paper (to appear in The Astrophysical Journal)
23 Lib paper (submitted to the Monthly Notices of the Royal Astronomical