TAU-led team discovers new planet outside solar system

HAT-P-2b rotates its 'mother star' in an elliptical orbit and has a 'year' of 5.6 days.

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May 6, 2007 01:15
2 minute read.
TAU-led team discovers new planet outside solar system

solar system 88. (photo credit: )

An international team headed by a Tel Aviv University astronomer has discovered a new planet, HAT-P-2b, outside our solar system. The planet's "mother star" is some 400 light years from Earth. Prof. Zvi Mazeh and doctoral student Avi Shporer discovered the planet, which moves in an elliptical orbit, after carrying out more than 26,000 measurements of the intensity of the light of its mother star - HD 147509. The researchers used three identical small telescopes located in Israel, Hawaii and Arizona to take round-the-clock measurements. When the sun rose in Hawaii, monitored by the world's largest telescope (at Keck Observatory), the Israeli telescope - located at TAU's observatory outside Mitzpe Ramon - was able to continue measuring the planet's light intensity. The international team has been following the light intensity of tens of thousands of stars for a year in an effort to discover small cyclical changes. Mazeh's researchers found that the intensity of HD 1475098 decreases by 1 percent for four hours and 15 minutes, then regains its original intensity. This phenomenon repeats itself every 5.6 days. This can happen when a planet that revolves around a star hides a small section of the mother star from Earth's view, similar to what occurs during a solar eclipse. The data showed clearly that a planet moved in an elliptical orbit around the star. About 200 planets outside our solar system have been identified so far, and 14 of them take an elliptical orbit around the mother star. All of these planets have been found to have similar density to that of Jupiter, and to that of water. But the newly discovered planet has an average density 6.6 times that of water, denser than Earth. This density, said Mazeh, was connected to HAT-P-2b's mass, which is eight times greater than Jupiter's, the largest planet in our solar system. The newly-discovered planet's orbit is also unusual. It moves closer to its mother star than any planet in our solar system moves to the Sun - 7% of the distance between Earth and the Sun. It also circles its mother star very closely, in cycles of 5.6 days, causing the temperature to reach an average 1,500 degrees Celsius; when the planet is at the far end of its orbit, its temperature drops hundreds of degrees. As the planet's "year" is only 5.6 days, there are radical changes in its climate throughout its orbit. The planet's discovery, said Mazeh, strengthens astronomers' impression that space encompasses many planetary systems significantly different from those we have known. Astronomers who study these systems are like the great explorers like Ferdinand Magellan and Christopher Columbus, who discovered new lands, Mazeh said. "The phenomena we have discovered makes us feel man's greatness, for his ability to investigate the vastness of space, and also the insignificance of man in the vast reaches of space and its thousands of worlds," the astronomer said. •


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