HARPS Bags 32 New Exoplanets

by Paul Gilster on October 19, 2009

More than 75 exoplanets in thirty different planetary systems is an impressive score, and that’s what HARPS has compiled since its installation in 2003. The High Accuracy Radial Velocity Planet Searcher is the spectrograph for the European Southern Observatory’s 3.6-meter telescope at La Silla (Chile). Built by a consortium led by Michel Mayor (Geneva Observatory), HARPS does its work by measuring the minute changes in a star’s radial velocity that flag the presence of an unseen companion.

Most of the roughly four hundred exoplanets discovered to date have been found through radial velocity methods. The figure of 400 includes the latest results from HARPS, which is back in the news with the announcement of 32 new exoplanets, found as part of a five year program using observing time given to the HARPS consortium in return for building the instrument. One of the new worlds is Gliese 667 Cb [see andy's note below], a six Earth-mass planet in a triple star system. The planets announced today range from five times the mass of Earth to up to five times the mass of Jupiter.

Discussing the low-mass worlds HARPS has located, Stephane Udry (Geneva University) draws an interesting conclusion, as quoted in this BBC story:

“From [our] results, we know now that at least 40% of solar-type stars have low-mass planets. This is really important because it means that low-mass planets are everywhere, basically. What’s very interesting is that models are predicting them, and we are finding them; and furthermore the models are predicting even more lower-mass planets like the Earth.”

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At a stroke, HARPS has boosted the known population of low-mass planets by thirty percent. No wonder Udry is encouraged. HARPS’ long suit is its sensitivity, enabling it to detect the signature of these smaller worlds. 28 planets with a mass of less than twenty times that of Earth have been found, and HARPS is responsible for 24 of them. Most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system.

The new planets were announced today at the ESO/CAUP conference Toward Other Earths: Perspectives and Limitations in the ELT Era, now taking place in Portugal. Out of the work, eight papers are in the submission process at Astronomy & Astrophysics. We’ll know more as these papers become available, but we do know the HARPS consortium’s target list focused on solar-like stars, low mass dwarfs and stars with lower metal content than the Sun. The results include several giant planets in M-dwarf systems and, interestingly enough, three candidate exoplanets that showed up around metal-deficient stars.

Addendum: This ESO news release has more, including a brief video interview with Michel Mayor.

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djlactin October 19, 2009 at 12:07

Earth-sized planet in 3, 2, 1…

Administrator October 19, 2009 at 13:10

Getting close. And we still have active campaigns looking at the Alpha Centauri stars. You’re right, djlactin, it can’t be long.

kurt9 October 19, 2009 at 13:53

The articles say that some of these planets have been found around stars that are low in “metals”. What are the correlation trends between planets and stellar metallicity? Perhaps metallicity is more relevant for formation of larger planets and not as significant for smaller planets. Or stars with greater metallicity have more planets than those with less metallicity. It does appear that planets are very common, almost ubiquitous.

How well are these discoveries matching the computer modeling of planet formation? The scientist quotes in the BBC article says this is considerable. However, I have seen a large number of models and simulations posted here in this blog, many of them with conflicting results. Which models is she referring to?

tacitus October 19, 2009 at 14:46

I think we still need the Kepler Mission to come through in a big way regarding “Earth-like” planets. If Kepler can bag a decent number of them, it would give great impetus towards space missions that would actually have a chance of imaging some of them directly (not the same ones, obviously, since they are too far away). That should be the main goal we’re working towards in the next decade or so.

yeti101 October 19, 2009 at 14:58

more encouraging signs rocky worlds are common. But who really doubted it? :)

Now if we could only scrap the moon missions and go all out for exoplanets, maybe once kepler gets some positive results more attention will be given to this field of astronomy. So depressing TPF has been mothballed indefinitley. Roll on SIM lite

andy October 19, 2009 at 16:58

One of the new worlds is Gliese 667 c, a six Earth-mass planet in a triple star system.

Gliese 667 C is the star. The planetary designation would be Gliese 667 Cb.

kurt9 October 19, 2009 at 17:05

more encouraging signs rocky worlds are common. But who really doubted it? :)

The first serious searches for exoplanets came up negative in the late 70′s.

Kepler should provide enough finds that make for statistically meaningful analysis (several thousand data points).

Mike October 19, 2009 at 17:38

Wow over 400 now! Good work from all the ground-based observatory stalwarts who have teased out the data using incredibly precise techniques and stubborness. They all have so very much to celebrate. It seems like the commonality of exoplanets has been confirmed.
We all have high hopes for Kepler too, don’t we. It may very well provide the proof that Earth mass planets are indeed ubiquitious. And perhaps that might spark some reappraisal of NASA’s priorities.
I must admit I’d rather see NASA’s resources being used to develop space-based telescopes that can analyse Earth mass exoplanet atmospheres for bio-markers and even achieve direct imaging of exoplanets then used for a human crew return to the moon and a moon base.
In any event there are more interesting places in our solar system to explore.
And more interesting places outside our solar system to observe now,explore
later.

Administrator October 19, 2009 at 18:22

Gliese 667 C is the star. The planetary designation would be Gliese 667 Cb.

Ouch. Will fix this pronto.

fbj October 19, 2009 at 20:21

Why do I get the feeling that these are the 32 most uninteresting exoplanet candidates that the Geneva group has in store? World history’s longest “shortcut to happiness” continues :-)

Ronald October 20, 2009 at 4:28

With regard to small planet detection and direct imaging, maybe some interested people could also have a look at the previous article:
http://www.centauri-dreams.org/?p=9865&cpage=1#comment-75471

In it I refer to the recent discovery of a near-ideal location for telescopes on Antarctica and ask the question whether this could actually enable direct imaging of (earthlike) planets with ground-based ELTs.

Adam October 20, 2009 at 7:11

Hi All

Amazingly… more of the same! Which is very cool, but kind of ho-hum too. There’s far too many exoplanets to even try to remember now, though they are generally rather far away compared to most SF exoplanets. Exoplanets around our near neighbours will be more interesting than those a hundred or more light-years/parsecs away.

Thomas October 20, 2009 at 8:19

@ Kurt9:
“Perhaps metallicity is more relevant for formation of larger planets and not as significant for smaller planets. ”
Yes, that does seem to be the correlation.

@ fbj:
From what I can gather, the HARPS GTO Programme is divided into two groups, a low-sensitivity survey to boost the statistics of giant planets, and a high-sensitivity survey to boost the statistics of low-mass planets. These 30 planets (the other two are brown dwarfs) appear to be from the low-sensitivity survey. Very little has been released about the high-sensitivity GTO Programme, but the HD 40307, HD 181433 system, and HD 47186 systems announced last June are examples from that programme. We were told that they have about 30 or so low-mass planets, so if HD 40307 et al are just a taste of the high-sensitivity programme, than the best is yet to come.

@ Administrator:
“Most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system.”
The largest solar system announced in these new 30 planets is that of HD 125612A, a three-planet system (of which 2 have been discovered by HARPS, N2K discovered the first back in 2007). Do you happen to know which five-planet system is being referred to here?
The only published five-planet system is 55 Cancri. It’s low-mass planet was found by HET. So there must be another five-planet system floating around somewhere.

Thomas October 20, 2009 at 8:21

“so if HD 40307 et al are just a taste of the high-sensitivity programme, than the best is yet to come.”

Should be

“so if HD 40307 et al are just a taste of the high-sensitivity programme, then the best is yet to come.”

Then/Than fail.
Sorry about that.

James M. Essig October 20, 2009 at 8:57

Hi Folks;

Forrest Noble had mentioned to me that planets around M-class are most likely to have advanced civilizations.

As I was pondering how advanced civilizations around M-class stars might now have become, I began to imagine the possibilities of civilizations developing around M class stars on super Earths. Just think of the intellectual, psychological, spiritual, and social development such beings could attain, as well as the scientific and technological developments within any such civilizations as they develop over the following trillions of years, perhaps 10s of trillions of years for the smallest M class stars.

These possibilities, although perhaps obvious, have profound implications for the development of ETI and human civilizations in the comming Gyrs and Tyrs. Look how far we humans have come in just the past 2 Centuries. Sure, we have had our conflicts, social problems, and the like, but when I imagine the crude balloon born cameras used during the American Civil War vrs the modern spy sattelites, or the modern f-MRI scans verses blood letting during the Medieval times, or the Space Shuttle verses the Wright Brothers’ first sucessfull flight, and the list goes on and on, I have to remain hopefull that human progress on all of the above mentioned fronts can continue.

The fact that M-class dwarfs are the most numerous stars, and can last for trillions if not tens or trillions of years gives me great hope. The unburned hydrogen gas in the interstellar and intergalactic medium is perhaps 5 to 10 times more abundant than the gas currently incorporated into stars, and so perhaps this alone might permit stars to form or some how be artificially constructed long after the last of the current M class stars burn out.

Truly, the discovery of super Earth’s around M class stars offers the civilization of humanity great up for a temporally virtually unbounded future.

spaceman October 22, 2009 at 20:47

I would just like to take a minute to try to dispel the notion that there exists a tension between the recent HARPS results and other high-precision RV searches. During the same conference, another presenter produced the following result : “~17% of stars have planets down to 3-earth-masses within 16 day orbital period.” The HARPS results which have been almost 5 years in the making are a perfectly believable valid extrapolation of the aforementioned numbers: ~30-40% of stars have planets between several and 50 Earth masses within 100 day orbital periods. Here is the abstract for the talk upon which the 17 percent figure is based:

The Frequency of Low-mass Exoplanets

We report first results from the Anglo-Australian Telescope Rocky Planet Search
– an intensive, high-precision Doppler planet search targeting low-mass exoplanets in
contiguous 48 night observing blocks. On this run we targeted 24 bright, nearby and
intrinsically stable Sun-like stars selected from the Anglo-Australian Planet Search’s
main sample. These observations have already detected one low-mass planet reported
elsewhere (HD16417b), and here we reconfirm the detection of HD4308b. Further, we
have Monte-Carlo simulated the data from this run on a star-by-star basis to produce
robust detection constraints. These simulations demonstrate clear differences in the
exoplanet detectability functions from star to star due to differences in sampling, data
quality and intrinsic stellar stability. They reinforce the importance of star-by-star
simulation when interpreting the data from Doppler planet searches. The simulations
indicate that for some of our target stars we are sensitive to close-orbiting planets as
small as a few Earth masses. The two low-mass planets present in our 24 star sample
indicate that the exoplanet minimum mass function at low masses is likely to be a flat
 −1 (for dN/dM / M ) and that between 15±10% (at = −0.3) and 48±34% (at
= −1.3) of stars host planets with orbital periods of less than 16 days and minimum
masses greater than 3M⊕.

spaceman October 30, 2009 at 9:38

Has anyone heard anything as to when the scientific papers describing these exoplanet discoveries are due out? I heard that there are 8 papers to be published, but I am not sure when. Thanks.

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