The High Accuracy Radial Velocity Planet Searcher (HARPS) is located at the European Southern Observatory’s La Silla facility in Chile. It has been scouring space for planets and the scientists involved with the project say they have located 32 new exoplanets – these are planets outside our solar system.
Increasing Numbers of Planets Discovered
Astronomers are finding more and more planets outside our solar system; the latest discovery, brings the number up to more than 400 so far. Obviously, there are many thousands more yet to be spotted. The HARPS instrument has already discovered 75 exoplanets in 30 different planetary systems.
According to BBC News (October 19, 2009), “The 32 ‘exoplanets’ ranged in size from five times the mass of Earth to 5-10 times the mass of Jupiter.” These are known as low-mass planets and one of the researchers, Stephane Udry of Geneva University, Switzerland, is quoted as saying: “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.”
Planets Found by “Wobble” Technique
The latest batch of planets to be found, like other exoplanets, are not actually visible from Earth. They are detected by something called the “wobble” technique.
Using the HARPS technology, sciencedaily.com reports that scientists are “able to measure the back-and-forward motions of stars by detecting small changes in a star’s radial velocity - as small as 3.5 km/hour, a steady walking pace.”
This slight wobble in radial speed indicates the star has been deflected very slightly by the gravitational pull of an exoplanet. So, the existence of an exoplanet is inferred.
The Search for Low-mass Planets
Most of the exoplanets found so far have been of the Jupiter scale or bigger, which is 11 times larger in diameter than Earth and 300 times bigger in mass. Comparatively, that’s similar to the difference between a basketball and a ping-ping ball.
The HARPS project, writes the BBC’s Jonathan Amos, “has focussed its efforts on small, relatively cool stars - so-called M-class stars - in the hope of finding low-mass planets, ones most likely to resemble the rocky planets in our own solar system.”
So far HARPS has found 24 of the 28 exoplanets known with masses 20 times below that of Earth, usually referred to as “super-Earths.”
A news release from the European Southern Observatory (October 19, 2009) points out that, “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.”
Lightest Planet Found
In April 2009, the European Southern Observatory announced the discovery of the lightest known exoplanet yet found: “The planet, ‘e’, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist.”
Such a finding is often described as the Holy Grail of exoplanet research.
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