Swiss astronomers have detected three Neptune-mass planets around a star thought to have a super-sized asteroid belt. For more than 2 years, the team studied the Sun-like star HD 69830, located 42 light-years away in the constellation Puppis and faintly visible to the unaided eye.
“The planetary system around HD 69830 clearly represents a Rosetta stone in our understanding of how planets form,” says team member Michel Mayor of the Geneva Observatory. “No doubt it will help us better understand the huge diversity we have observed since the first extrasolar planet was found 11 years ago.”
The astronomers found the planets through precise spectral measurements of the star. Their gravitational influence on HD 69830 give the star a slight wobble, which revealed the presence of three roughly equal-mass companions in orbits lasting 8.67, 31.6, and 197 days.
“This is hot stuff,” Alan Boss, an astronomer at the Carnegie Institution of Washington, tells Astronomy. Finding a system with three “super-Earths” around a star slightly less massive than the Sun “makes the case for there being many Earth-like planets out there all the more compelling,” he says.
The team used the European Southern Observatory’s HARPS instrument installed on the La Silla Observatory, Chile, 3.6-meter telescope to conduct the study. “Without any doubt,” says Mayor, “it is presently the world’s most precise planet-hunting machine.” The planets impart velocity variations to the star that are less than 7 mph (11 km/h) — signals so small they could not have been resolved by most spectrographs available today.
