TAU-led team discovers extra-solar planet

Planet has unusual density and unusual orbit.

planet 88 (photo credit: )
planet 88
(photo credit: )
An international team headed by a Tel Aviv University astronomer has discovered a new planet outside our solar system that moves in an elliptical orbit. Designated HAT-P-2b, its "mother star" is some 400 light years from Earth. Prof. Zvi Mazeh and doctoral student Avi Shporer discovered the unique planet after carrying out more than 26,000 measurements of the intensity of light of its mother star, HD 147509. This was made possible by the use of three identical small telescopes located in Israel, Hawaii and Arizona. As most heavenly bodies can be seen only at night, three different locations were needed to take around-the-clock measurements. When the sun rose in Hawaii, where the world's largest telescope (Keck) was monitoring it, the Israeli telescope - located at TAU's observatory outside Mitzpe Ramon - kept measuring the planet's light intensity. The planet's discovery, Mazeh said, strengthened the impression that there were many hidden planetary systems that were significantly different from what we have known until now. Astronomers who study them, he said, were like the great explorers of the 16th century, such as Ferdinand Magellan and Christopher Columbus, who discovered new lands about whose existence no one knew. "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," Mazeh said. The international team has been following the light intensity of tens of thousands of stars for about a year in an effort to discover small cyclical changes. Mazeh's team found that the intensity of HD 1475098 decreases by 1 percent for four hours and 15 minutes, and then regains its original intensity. This phenomenon repeats itself every 5.6 days. This can happen when a planet hides a small amount of its mother star from Earth - just like what occurs during a solar eclipse. The data showed clearly that the planet moves in an elliptical orbit around its star. Approximately 200 planets outside our solar system have been identified so far, and 14 of them follow an elliptical orbit around their star. All of these have been found to have density similar to that of Jupiter, which is like that of water. But the newly discovered planet has an average density 6.6 times that of water, even denser than Earth. HAT-P-2b's density, said Mazeh, was eight times greater than that of Jupiter. Its orbit is also unusual. It moves much closer to its mother star - only 7% of the distance from the Earth to the sun. No planet in our solar system comes so close to the sun. HAT-P-2b also circles its mother star very closely in cycles of 5.6 days, causing its temperature to average 1,500 degrees Celsius. When it is at its farthest from its star, the 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.