Sun's Twin Discovered In Star Cluster; Planets Around It Too Hot For Liquid Water
Turns out the Sun has a twin. Not in the sense that it was born from the same mother nebula (that's something else, which I'll get to). Rather, this star, about 2,500 light-years away from Earth, is almost exactly the same size, temperature, and composition as the Sun. Nevertheless, its solar system is very different. Like twins separated at birth, the discovery can teach scientists lessons about nature vs. nurture and what a difference the environment makes.
This solar doppelganger is remarkable, first of all, because solar twins are so rare to begin with, and this is one of the most similar ever found. On Wednesday, scientists in Germany announced the discovery of yet another reason HIP 102152 is so fascinating: it's got a planet. The star and the planet are part of a larger star cluster — a close grouping of stars that formed from the same nebular dust — called Messier 67. Two other stars in the cluster also have planets.
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"In the Messier 67 star cluster the stars are all about the same age and composition as the Sun," said Anna Brucalassi of the Max Planck Institute for Extraterrestrial Physics in Germany, in a statement. Brucalassi was the lead author of a paper describing the find. "This makes it a perfect laboratory to study how many planets form in such a crowded environment, and whether they form mostly around more massive or less massive stars."
Two of the planets were orbiting stars similar to the Sun. Another is orbiting a Red Giant, which is a very old star, nearing the end of its life, that has swelled and cooled. Even though the first two stars are so much like the Sun, their planets were very different. Two of the planets they identified were about one-third of Jupiter's mass; the third was more massive than Jupiter. And all three were very close to their stars. They made complete orbits in five days, seven days, and 122 days. In theory, that could mean they're moving extremely fast, or they're extremely close.
In this case, they're close. Two of the planets are among a category called "hot Jupiters" because they're similar to Jupiter in size, but hot like Mercury (which orbits the Sun in 88 days). So even though the stars are like ours, the planets are not — and they're probably not habitable. "All three are closer to their host stars than the habitable zone where liquid water could exist," according to the European Southern Observatory, or ESO, which published the research.
It took six years using a telescope in Chile to find these three planets in the Messier 67 star cluster. The scientists who worked on it say that the difficulty in finding the planets isn't because planets are less common around stars in these kinds of clusters. Actually, they're "about as common as they are around isolated stars — but they are not easy to detect," co-author Luca Pasquini, of the ESO, said in the statement. She added that the group is "continuing to observe this cluster to find how stars with and without planets differ in mass and chemical makeup." Maybe that's the key to looking for more stars with hidden planets.
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