Astronomers have detected the first exoplanetary system with regularly aligned orbits similar to those in our Solar System.
In this artist interpretation, the planet Kepler-30c is transiting one of the large starspots that frequently appear on the surface of its host star. The authors used these spot-crossing events to show that the orbits of the three planets, color lines, are aligned with the rotation of the star, curly white arrow (Cristina Sanchis Ojeda)
At the center of this faraway system is Kepler-30, a star as bright and massive as the Sun. After analyzing data from NASA’s Kepler Space Telescope, the team discovered that the star 10,000 light-years away rotates around a vertical axis and its three planets have orbits that are all in the same plane.
“In our Solar System, the trajectory of the planets is parallel to the rotation of the sun, which shows they probably formed from a spinning disc,” said Roberto Sanchis-Ojeda, a graduate student at Massachusetts Institute of Technology (MIT) who led the research effort. “In this system, we show that the same thing happens.”
The findings, published in the journal Nature (arXiv.org), may help explain the origins of certain far-flung systems while shedding light on our own planetary neighborhood.
“It’s telling me that the Solar System isn’t some fluke,” said Dr Josh Winn, an associate professor of physics at MIT and co-author of the paper. “The fact that the Sun’s rotation is lined up with the planets’ orbits, that’s probably not some freak coincidence.”
“The team’s discovery may back a recent theory of how hot Jupiters form,” Dr Winn said. These giant bodies are named for their extremely close proximity to their white-hot stars, completing an orbit in mere hours or days. Hot Jupiters’ orbits are typically off-kilter, and scientists have thought that such misalignments might be a clue to their origins. Their orbits may have been knocked askew in the very early, volatile period of a planetary system’s formation, when several giant planets may have come close enough to scatter some planets out of the system while bringing others closer to their stars.
Dr James Lloyd, an assistant professor of astronomy at Cornell University who was not involved in this study, said that studying planetary orbits may shed light on how life evolved in the Universe – since in order to have a stable climate suitable for life, a planet needs to be in a stable orbit.
“In order to understand how common life is in the Universe, ultimately we will need to understand how common stable planetary systems are,” Dr Lloyd said. “We may find clues in extrasolar planetary systems to help understand the puzzles of the Solar System, and vice versa.”
The findings from this first study of the alignment of a non-hot Jupiter system suggest that hot Jupiter systems may indeed form via planetary scattering. To know for sure, Dr Winn said he and his colleagues plan to measure the orbits of other far-off solar systems.
“We’ve been hungry for one like this, where it’s not exactly like the Solar System, but at least it’s more normal, where the planets and the star are aligned with each other,” Dr Winn said. “It’s the first case where we can say that, besides the Solar System.”
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Bibliographic information: Sanchis-Ojeda et al. 2012. Alignment of the stellar spin with the orbits of a three-planet system. Nature 487, 449–453 (26 July 2012); doi: 10.1038/nature11301
