Opposite Orbits Upend Theories
Unlike the planets in our solar system, two of the newly discovered planets are orbiting in the opposite direction to the rotation of their host star. This, along with a recent study of other exoplanets, upsets the primary theory of how planets are formed. There is a preponderance of these planets with their orbital spin going opposite to that of their parent star. They are called exoplanets because they are located outside of our solar system.
These and other related discoveries were presented at the UK National Astronomy Meeting in Glasgow, Scotland. This is the first public mention of the new planets and the research will be described in upcoming scientific journal articles.
"Planet evolution theorists now have to explain how so many planets came to be orbiting like this," said Tim Lister, a project scientist at LCOGT. Lister leads a major part of the observational campaigns along with Rachel Street of LCOGT, Andrew Cameron of the University of St. Andrews in Scotland, and Didier Queloz, of the Geneva Observatory in Switzerland.
After the initial detection of the new exoplanets by the Wide Angle Search for Planets (WASP), the team of astronomers combined data from LCOGT's 2.0-meter Faulkes Telescopes in Hawaii and Australia with follow-up from other telescopes to confirm the discoveries and characterize the planets.
The planets are revolving around nearby stars within 1,000 light years of our galaxy. Their stars are located in the constellations Pegasus, Virgo, Pisces, and Andromeda in the northern hemisphere, and Eridanus, Hydra, Cetus, and Phoenix in the southern hemisphere.
The nine planets are called "Hot Jupiters." These planets are giant gas planets that orbit close to their star. In the 15 years since the first Hot Jupiters were discovered, their origin has been a puzzle. Because they are both large and close, they are easier to detect from their gravitational effect on their stars, and more likely to transit the disk of the star. Most of the first exoplanets discovered were of this type.
The cores of giant planets are thought to form from a mix of rock and ice particles found only in the cold outer reaches of planetary systems. Hot Jupiters, therefore, must form far from their star and subsequently migrate inwards over the course of a few million years. Many astronomers believed this could happen due to gravitational interactions with the disk of dust from which they formed, which might have also subsequently formed Earth-like rocky planets.
According to the research team, the best alternative migration theory suggests that the proximity of Hot Jupiters to their stars is not due to interactions with the dust disk at all, but to a slower evolution involving a gravitational tug-of-war with more distant planetary or stellar companions over hundreds of millions of years. Bounced onto a tilted and elongated orbit, a wandering gas giant would suffer tidal friction every time it swung close to the star, eventually becoming parked in a near circular, but randomly tilted orbit close to the star.
"In this scenario, smaller planets in orbits similar to Earth's are unlikely to survive," said Rachel Street.