Astronomers spot second smallest exoplanet

Jan 13, 2010
Credit: L. Calcada, ESO

(PhysOrg.com) -- Astronomers from the California Institute of Technology and other institutions, using the highly sensitive 10-meter Keck I telescope atop Hawaii's Mauna Kea, have detected an extrasolar planet with a mass just four times that of Earth. The planet, which orbits its parent star HD156668 about once every four days, is the second-smallest world among the more than 400 exoplanets (planets located outside our solar system) that have been found to date. It is located approximately 80 light-years from Earth in the direction of the constellation Hercules.

The find, made possible through NASA's Eta-Earth Survey for Low-Mass Planets was announced last week at the 215th American Astronomical Society meeting held January 4-7, 2010, in Washington, D.C.

Dubbed HD 156668b, the planet—a so-called "" that would glow with blast-furnace-like temperatures—offers a tantalizing hint of discoveries yet to come. Astronomers hope those discoveries will include Earth-size planets located in the "," the area roughly the distance from the earth to the sun, and thus potentially favorable to life.

HD 156668b was discovered with the radial velocity or wobble method, which relies on Keck's High Resolution Echelle Spectrometer (HIRES) to spread light collected from the telescope into its component wavelengths or colors, producing a spectrum. As the planet orbits the star, it causes the star to move back and forth along our line of sight, which causes the starlight to become redder and then bluer in a periodic fashion.

The color shifts give astronomers the mass of the planet and the characteristics of its orbit, such as how much time it takes to orbit the star. The majority of the exoplanets discovered have been found in this way.

The discovery of low-mass planets like HD 156668b has become possible due to the development of techniques to watch stars wobble with increasing clarity, and of software that can pluck the signals of increasingly smaller planets from amid the 'noise' made by their pulsating, wobbling parent stars.

"If the stars themselves have imperfections and are unstable, their wobbling would cause jumps in velocity that could mimic or hide the existence of a planet," says John A. Johnson, assistant professor of astronomy at Caltech and codiscoverer of the new planet along with Andrew Howard and Geoff Marcy of the University of California at Berkeley, Debra Fischer of Yale University, Jason Wright of Penn State University, and the members of the California Planet Survey collaboration.

"We have been doing simulations to understand the astrophysics of these imperfections, and how to distinguish them from the signals from a planet," says Johnson. "We hope to use these simulations to design even better observing strategies and data-analysis techniques."

The discovery of a planet that is comparable in size to Earth and found within the habitable zone, however, "will require a great deal of work," he says. "If we could build the best possible radial-velocity instrument tomorrow, we might have answers in three years, and a solid census of Earthlike planets within a decade. We'll need gigantic leaps in sensitivity to get there, and we're hot on the trail."

Johnson is also currently building a new camera for the 60-inch telescope at Caltech's Palomar Observatory. The camera will allow astronomers to search for the passages—or transits—of low-mass planets like HD156668 across the faces of their stars.

"If we catch the planet in transit, we can measure the planet's radius and density, and therefore address the question of whether the planet has a composition more like Earth, with a solid surface and thin atmosphere, or is a miniature version of Neptune, with a heavy gaseous atmosphere," he says.

Explore further: Astronomer confirms a new "Super-Earth" planet

More information: For more information about extrasolar planet discoveries, visit exoplanets.org .

Related Stories

Transit Search Finds Super-Neptune

Jan 20, 2009

(PhysOrg.com) -- Astronomers at the Harvard-Smithsonian Center for Astrophysics have discovered a planet somewhat larger and more massive than Neptune orbiting a star 120 light-years from Earth. While Neptune ...

Astronomers spot 'super-Earth' 80 light years away

Jan 08, 2010

US astronomers have detected the second smallest exoplanet ever discovered with a mass just four times heavier than the Earth, adding to a growing number of low-mass planets dubbed "super-Earths."

Wobbly planets could reveal Earth-like moons

Dec 11, 2008

Moons outside our Solar System with the potential to support life have just become much easier to detect, thanks to research by an astronomer at University College London (UCL).

Trio of Neptunes and their belt

May 17, 2006

Using the ultra-precise HARPS spectrograph on ESO's 3.6-m telescope at La Silla (Chile), a team of European astronomers have discovered that a nearby star is host to three Neptune-mass planets. The innermost ...

Scientists discover a nearly Earth-sized planet (Update)

Apr 21, 2009

(PhysOrg.com) -- Exoplanet researcher Michel Mayor announces the discovery of the lightest exoplanet found so far. The planet, "e," in the system Gliese 581, is only about twice the mass of our Earth. The ...

Planet-Finding by Numbers

Oct 18, 2006

More than a decade after the first planets beyond our solar system were found, astronomers have discovered about 200 of these "extrasolar planets," as they're called. Using a common-sense definition of potentially ...

Recommended for you

Kepler proves it can still find planets

Dec 18, 2014

To paraphrase Mark Twain, the report of the Kepler spacecraft's death was greatly exaggerated. Despite a malfunction that ended its primary mission in May 2013, Kepler is still alive and working. The evidence ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

NeptuneAD
5 / 5 (1) Jan 13, 2010
As we find more 'earthlike' planets I can't help but wonder about the Fermi Paradox.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.