Israeli astrophysicists help find oldest-known planet outside solar system

Sep 16, 2007 1:04 | Updated Sep 16, 2007 1:04
Israeli astrophysicists help find oldest-known planet outside solar system
By JUDY SIEGEL-ITZKOVICH
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The discovery of the oldest planet yet identified outside our solar system - just announced in the prestigious journal Nature - illustrates the process that is likely to lead to the sun burning out in approximately five billion years.

The planet V391b Pegasi, whose discovery was made possible by an international team of astrophysicists including researchers at Tel Aviv University, revolves around a "pulsating" star (V391 Peg) that is mutating from its "red giant" status to a shrunken "white dwarf."

The discovery means that astrophysicists can now measure the star's radiation and investigate the planet's characteristics, instead of just theorizing about the distant future of Earth and other planets when their suns reach the end of their existence.

Prof. Elia Leibowitz of TAU's Department of Astrophysics and Astronomy (and son of the late philosopher and biologist Prof. Yeshayahu Leibowitz) is a permanent participant in the international team whose paper in Nature included 23 authors linked in the Whole Earth Telescope project.

Leibowitz told The Jerusalem Post on Saturday night that "no one has actually seen any of the exoplanets, thus there are no photographs, but the data proves that they have to be there."

The Pegasi star, part of the constellation of Pegasus, is "a very weak star and can't be observed by the naked eye. After putting out data together about three or four months ago, we had long discussions of whether it was in fact a planet. Gradually, more people became convinced, and we presented our data to Nature, which accepted our conclusion," he said.

After the embargo on the article was lifted on Wednesday at 8 p.m. Israel time, the astrophysicists who participated broke open bottles of champagne and communicated via e-mail. They have never all met in one place, Leibowitz said. The research was led by Prof. Roberto Silvotti of the observatory in Naples.

As stars can be observed only at night, observatories around the world - including TAU's Wise Observatory located five kilometers west of Mitzpe Ramon in the Negev - coordinate to watch a specific star continuously through 24 hour cycles several times a year and measure its radiation.

V391b Pegasi and its sun are located some 4,500 light years from our solar system, and the planet is three times heavier than Jupiter, the largest planet revolving around the sun. It takes about 3.2 years, or 1,170 Earth-days, for the planet to make one revolution around its sun. The distance between the planet and the sun is 1.7 times that between the Earth and our sun (150 million kilometers).

But these characteristics do not make V391 Peg and V391b Pegasi very different from the 200 exoplanets that have already been discovered. It is very unlikely to have residents, because its surface temperature is about 200 degrees Celsius. Its sun pulsates, meaning that the power of its light rises and falls at a rate of one percent, pulsating every six minutes. It loses one second every 22,000 years. The radius of its sun is only a quarter of our sun's, and it is white-blue in color, with a temperature of 30,000 degrees (compared to our sun's 6,000 degrees). The main difference, however, is in V391b Pegasi's age - it is the oldest exoplanet ever discovered.

Our sun is a "primary series" star that creates nuclear energy through most of its lifespan. It has been doing so for some five billion years, and has about the same amount of time to go, astronomers say. At that point, within several million years, according to astrophysicists, it will turn into a "red giant," swelling to a radius 100 its current one and turning red. It will then swallow up Mercury and Venus, causing major changes in Earth and the other planets in our solar system. The sun will start to shrink and within a few hundred million years, it will turn into a "white dwarf" no bigger than Earth.

Leibowitz said Israel was ideally located for the research, as there are few observatories in the Middle East, and none of those that exist, including the Egyptian one, participated in the Whole Earth Telescope project. "Thus there were certain hours when we were the only one or one of the few able to observe the star. But the research continues, as we are due to meet at a conference in Egypt in the near future," he said.

Leibowitz was assisted by Ezra Mishal, the technical director of the Wise Observatory, and by Sami Ben-Gigi, the manager of the Mitzpe Ramon facility, along with John Dunn, the chief observer.