Posted on by Nancy Atkinson

More Help on the Way for Verifying ExoPlanets in Kepler’s Dataset

The HARPS-N spectrograph will be installed on the 3.6-meter Telescopio Nazionale Galileo in the Canary Islands. Credit: INAF

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With the Kepler spacecraft finding over 1,200 planetary candidates, the next step is verifying their actual status. That will be a big job, but help is on the way. In April 2012, a new spectrograph called HARPS-North will come online to help confirm and characterize Kepler’s planetary candidates. It will be mounted on the 3.6-meter Telescopio Nazionale Galileo (TNG) in the Canary Islands.

“The Kepler mission gives us the size of a planet, based on the amount of light it blocks when it passes in front of its star. Now we need to measure planetary masses, so that we can calculate the densities. That will allow us to distinguish rocky planets and water worlds from ones dominated by atmospheres of hydrogen and helium,” explained astronomer David Latham from the Harvard-Smithsonian Center for Astrophysics (CfA).


If the name HARPS (High-Accuracy Radial velocity Planet Searcher) is familiar, it is because this new instrument is a duplicate the successful design of an existing instrument in the Southern Hemisphere, the original HARPS spectrograph whichoperates on the 3.6-meter European Southern Observatory telescope at La Silla, Chile. At the TNG telescope, the new HARPS-North will be able to study the same region of the sky viewed by the Kepler spacecraft, within the northern constellations of Cygnus and Lyra.

The Harvard-Smithsonian CfA is part of an international collaboration building the new instrument.

Kepler main field of view. Credit: NASA/JPL - Caltech

Verifying a exoplanet can be tricky. In some circumstances, an eclipsing binary star can mimic the shallow dimming due to a planet crossing in front of its star. Ground-based measurements are needed to verify an orbiting world by spotting the gravitational wobbles it induces in its host star, in a method known as radial velocity.

A spectrograph operates by splitting the light from a star into its component wavelengths or colors, much like a prism. Chemical elements absorb light of specific colors, leaving dark lines in the star’s spectrum. Those lines shift position slightly due to the Doppler shift created by the gravitational tug of an orbiting planet on its star.

The new HARPS-North will be augmented by technology now under development, such as a laser comb for wavelength calibration, which will allow it to detect subtle radial-velocity signals.

“We have set up an enthusiastic collaboration among various institutions to build a northern copy of HARPS. We all expect HARPS-N to be as successful as its southern ‘brother,'” said HARPS-N principal investigator Francesco Pepe of the Astronomical Observatory of Geneva.

“HARPS-N will pursue the most interesting targets found by Kepler, at a level that no one else in the world can do,” said Dimitar Sasselov, Director of the Harvard Origins of Life Initiative. “HARPS-N will partner with Kepler to characterize worlds enough like Earth that they might be able to support life as we know it.”

Source: Harvard Smithsonian CfA

Posted on by Nancy Atkinson

Scientists Predict Earth-Like Habitable Exoplanet Will Be Found in 2011

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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Two astronomers have written a paper and say that the first Earth-like, habitable exoplanet will be announced in May of 2011. Do they have inside information, a crystal ball, or amazing powers of prediction? No, they base their projection on math and trends from the past 15 years of exoplanet discoveries. And if the discoveries continue at their present rate, the researchers say next year is the year of the long awaited holy grail of finding another Earth-like planet out in the cosmos.

Samuel Arbesman from Harvard Medical School in Boston and Gregory Laughlin at the University of California, Santa Cruz take a scientometric approach to their prediction. Scientometrics is the science of measuring and analyzing science, and is often done using bibliometrics which is a measurement of the impact of scientific publications. Arbesman and Laughlin said this type of work highlights the usefulness of predictive scientometric techniques to understand the pace of scientific discovery in many fields.

They use the properties of previously discovered exoplanets along with external estimates for the discovery of the first potentially habitable extrasolar planet.

In their paper they indicate that since astronomers have been discovering extrasolar planets at an increasing rate since 1995 and the discoveries follow a well understood pattern, it should be easy to predict when planet searchers will hit the jackpot.

The first exoplanets found were the massive Jupiter or larger-sized planets which were the easiest to find, and then as techniques improved over the past 15 years, astronomers have found smaller planets, some just a few times more massive than Earth.

A single realization of the habitability of extrasolar planets over time. H values for the extrasolar planets are plotted, with those of the upper envelope (maximum H for a given year of discovery) indicated in black. The black curve is the logistic best- t curve of the upper envelope, using a nonlinear model, where R = 28:78 and y = 2011:10. The horizontal grey line indicates the maximum value of H = 1, the presence of an Earth-like habitable planet. Credit: Arbesman and Laughlin

Arbesman and Laughlin took that rate of discovery, and they also needed to factor in all the variables for what we think will make a planet habitable: the surface temperature must allow liquid water to exist, so that life as we know it can appear, and that depends on the size of the star, how far the planet orbits from its star, and what type of surface the exoplanet has.

They conclude there is a 66 per cent probability of finding another Earth by 2013, a 75 per cent probability by 2020, and a 95 per cent probability by 2264, but the median date of discovery is in May 2011. And not just sometime in May, but “early May.”

In June 2010, the Kepler Telescope team revealed they had found 750 exoplanet candidates, and a fair number of those confirmed might be Earth-sized. They expect they can confirm and announce some of these candidates in February 2011. But Arbesman and Laughlin predict it might take longer. “Because of the limited time base line of the mission to date, the Kepler planet candidates to published in February 2011 may be too hot to support significant values for H (which is their habitability metric),” they wrote in their paper.

So, if their prediction comes true, that might mean another team, such as the HARPS, or Keck, or CoRoT, or other exoplanet-finding wizards might make the discovery.

“It must be noted that by publicizing our prediction, there is a concern that it will become accurate,” Arbesman and Laughlin write in their paper, “simply due to the well-studied Hawthorne Effect. However, due to the large number of observations and long periods of time required to confirm an extrasolar planet discovery, it is unlikely that our prediction at this time will appreciably affect the announcement of the discovery of an Earth-like planet. Therefore, it is reasonable to use the habitability metric curve as a rough prediction for when the first potentially habitable planet will be discovered, in this case, as early as May 2011, and likely by the end of 2013.”

It will be interesting to see how accurate their prediction turns out to be!

Read the paper: “A Scientometric Prediction of the Discovery of the First Potentially Habitable Planet with a Mass Similar to Earth.”

Additional Source: Technology Review Blog

Posted on by Nancy Atkinson

HARPS Discovers 32 New Exoplanets

A planet 6 times the mass of Earth orbits around the star Gliese 667 C, which belongs to a triple system. Credit: ESO

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Astronomers have found 32 new planets outside our solar system with the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for the European Southern Observatory’s (ESO) 3.6-metre telescope. The number of known exoplanets is now at 406, and HARPS itself has discovered more than 75 exoplanets in 30 different planetary systems. Included in this most recent batch are several low-mass planets – so-called “Super Earths” about the size of Neptune. The image above is an artist’s impression of a planet discovered that is 6 times the mass of Earth, which circles the low-mass host star, Gliese 667 C, at a distance equal to only 1/20th of the Earth-Sun distance. Two other planets were discovered previously around this star.

“HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds,” said ESO astronomer Stéphane Udry. “We have now completed our initial five-year program, which has succeeded well beyond our expectations.”

No Earth-like planets were discovered in this group that was announced today at an exoplanet conference in Portugal.

HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 21 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system. This new group includes a total of 11 planets with masses between 5 and 21 times that of Earth – and 9 in multi-planet systems — and increases the number of known low-mass planets by 30%.

HARPS uses the radial velocity technique which measures the back-and-forward motions of stars by detecting small changes in a star’s radial velocity as it wobbles slightly from a gentle gravitational pull from an otherwise unseen planet. HARPS can detect changes in velocity as small as 3.5 km/hour, a steady walking pace.

Notable discoveries by HARPS during the past five years include the first super-Earth in 2004 (around µ Ara; ESO 22/04); in 2006, the trio of Neptunes around HD 69830 (ESO 18/06); in 2007, Gliese 581d, the first super Earth in the habitable zone of a small star (ESO 22/07); and in 2009, the lightest exoplanet so far detected around a normal star, Gliese 581e (ESO 15/09). More recently, they found a potentially lava-covered world, with density similar to that of the Earth’s (ESO 33/09).

“These observations have given astronomers a great insight into the diversity of planetary systems and help us understand how they can form,” says team member Nuno Santos.

Source: ESO