<div><p>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."</p><p>"This is quite a remarkable discovery," said Andrew Howard, an astronomer at the University of California at Berkeley.</p><p>"It shows that we can push down and find smaller and smaller planets," he said in a presentation at the 215th meeting of the American Astronomical Society in Washington DC this week.</p><p>The exoplanet, a name given to planets outside our solar system, has been dubbed HD156668b, and is located around 80 light years from Earth in the direction of the Hercules constellation.</p><p>A light year is rough 9,460 billion kilometers.</p><p>The planet orbits around its parent star in just over four days.</p><p>The smallest exoplanet previously discovered by astronomers was Gliese 581 e, detected by a Swiss astronomer in April 2009 some 20.5 light years from Earth in the Balance constellation.</p><p>But it orbits much closer to its star, making its temperature much higher than that on Earth.</p><p>Earlier this week, the scientific team responsible for the Kepler US space telescope -- launched in March 2009 to find planets similar to Earth outside our solar system -- announced at the same meeting their discovery of five new exoplanets.</p><p>All five planets, dubbed Kepler 4b, 5b, 6b, 7b and 8b, have high masses and very high temperatures, ranging from 1,200 to 1,648 degrees Celsius (2,192 to 2998 degrees Fahrenheit).</p><p>The five Kepler discoveries and HD156668b join more than 400 exoplanets already discovered by astronomers using various terrestrial telescopes since 1995.</p><p>Some 423 exoplanets have been identified by astronomers so far, according to specialist site exoplanet.eu, but none appear to be similar to Earth or capable of supporting life.</p><p>However, astronomers generally express confidence that either the Kepler telescope or the European Corot telescope will eventually find exoplanets like Earth.</p><p>John Morse, head of the astrophysics division at NASA headquarters in Washington, said it was "only a matter of time before more Kepler observations lead to smaller planets with longer period orbits, coming closer and closer to the discovery of the first Earth-analog."</p><p>The team of astronomers who discovered HD156668b used one of two Keck telescopes at the 4,145-meter (13,600-foot) summit of Mount Mauna Kea in Hawaii.</p><p>The astronomers used the so-called wobble method, which measures the gravitational effects of a planet on its star.</p><p>When the planet passes in front of its star it produces a slight change in the star's colour spectrum, shifting it towards blue.</p><img src="http://admatch-syndication.mochila.com/images/ad.gif?aid=66566539&bid=informcom" /></div><div id="copyright"><div>

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