New class of exoplanets discovered

Smaller than Jupiter and maybe rock

The size of Neptune orbits the star Gliese 436. © NASA JPL
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Astronomers first discovered a new kind of planet outside our solar system. The "new ones" are only about ten to twenty times the size of the earth and about the size of the planet Neptune. All previously detected were gas giants at least the size of Jupiter. One of the new exoplanets, along with three other planets previously discovered, is the first clearly-detected extrasolar four-planetary system.

The two new planets were found by the renowned planet hunter team Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and the University of California, as well as Barbara McArthur of the University of Texas. So far you know almost 140 extrasolar planets - but so far all gas giants. "These Neptune-sized planets prove that Jupiter size gas giants are not the only planetary species out there, " explains Marcy. Butler adds: "We are starting to see smaller and smaller planets. Earth-like planets are our next destination. "

In close contact with the central star

Both new planets are very close to their central star and only need a few days to orbit around. The first planet orbiting a small star named Gliese 436 every two and a half days at a distance of only 4.1 million kilometers. He is the second known planet ever to have a so-called M-dwarf, a low-mass star of only four-tenths of the sun's size. Gliese 436 is located about 30 light-years away from Earth in the constellation Leo - in our galactic backyard.

The entomologist Benjamin Wipfler with a model of the now extinct insect. © Jan-Peter Kasper / FSU

The second planet, discovered by McArthur, races in about three days around the star 55 Cancri, at a distance of just 5.6 million kilometers. Further outside, three other planets orbit this approximately 55 billion year old star. It is 41 light-years away in the constellation Cancer and lighter than the sun. "55 Cancri is an excellent laboratory for studying the evolution and formation of planetary systems, " explains McArthur.

Rock instead of gas?

Because the new planets are smaller than Jupiter, it could be that they are made of rock or rock and ice, in contrast to this. According to the scientists, they could have formed like the earth through the gradual accumulation of stony space chunks. "A Neptune planet could not have enough mass to capture gas, but at this point we do not know yet, " said Butler. display

The planets were discovered using the so-called "radial velocity" technique, in which the slight tumbling of the central star, which is generated by the attraction of the planets, dissipates the presence of the satellites. The scientists found their extrasolar planets by observing hundreds of nearby stars using the WM Keck Observatory in Hawaii and the hobby Eberly at the McDonald Observatory in West Texas.

(NASA JPL, 02.09.2004 - NPO)