The planet CoRoT-2 b has puzzled astronomers for nearly a decade, but new data may have solved its mystery
A team of astronomers, including Emily Rauscher of the University of Michigan, appears to have solved a mystery they uncovered eight years ago in observing a planet about 700 light-years away.
In resolving this particular puzzle for this peculiar planet outside our solar system, known as CoRoT-2 b, astronomers can build a better understanding of all exoplanets, the team said.
CoRoT-2 b is a type of exoplanet known as a hot Jupiter. It's a giant gaseous planet, like Jupiter, that is closer to its star than Mercury is to our sun and, thus, hot. All hot Jupiters observed prior to CoRoT-2 b have had planetary winds blowing to the east, which agrees with theoretical predictions for these scorching gas giants. But CoRoT-2 b's winds appeared to be blowing westward, creating a quandary that's puzzled astronomers since.
Now, astronomers have data that support an earlier explanation proposed by Rauscher and her colleagues thanks to new observations led by the NASA Exoplanet Science Institute, or NExScI. Based on this new data from the Very Large Telescope at the European Southern Observatory, CoRoT-2 b is rotating much slower than other hot Jupiters.
"We really, really think that winds on these planets should blow to the east, so this is unexpected and it seems really weird. My default position is to come from a place of skepticism and to be very hesitant to believe a result like this," said Rauscher, an associate professor in the U-M Department of Astronomy. "But I find the data really compelling. We could be wrong-that always happens in science-but this actually does make sense."
The research was presented at the 248th meeting of the American Astronomical Society in Pasadena, California, by team leader Aurora Kesseli, a staff scientist at NExScI. NExScI is hosted by IPAC, a science and data center for astrophysics and planetary science at the California Institute of Technology.
"I really like looking at the weird ones-finding planets that don't fit the standard picture-and doing some mystery solving," Kesseli said. "Now we can see that a one-size-fits-all model does not work, even for planets that we've been studying for a long time."
Hot Jupiters orbit so closely to their host stars that astronomers assume they are always tidally locked, meaning the same side of the planet always faces the star. Us earthlings have a very familiar example of tidal locking in our moon, which is tidally locked to our planet and explains why we always see the same side of it.
When tidally locked, a hot Jupiter will have one side that's in perpetual daytime, being blasted by its star's radiation, leaving the opposite side in a constant, cooler nighttime. But its swirling atmosphere blurs the boundaries between these zones. It ends up with a large hot spot on its dayside, shifted slightly towards the direction of its planetary rotation due to its eastward winds.
CoRoT-2 b-so named because it was first discovered by the Convection, Rotation and planetary Transits, or CoRoT, space telescope-defies this pattern and previous assumptions made in models of hot Jupiters. Its hot spot is in the opposite direction and has westward winds.
Rauscher was part of the team on this initial discovery in 2018, led by Lisa Dang, a professor at the University of Waterloo. In that study, the team outlined three possible hypotheses for this: there could be clouds obscuring our view, there could be complex magnetic field interactions, or the planet could be rotating slower than it is orbiting the host star.
Kesseli measured the planet's velocity, and with a back-of-the-envelope calculation, she found that one day on CoRoT-2 b is equivalent to about three Earth days, but one year on CoRoT-2 b is half of that-about 1.5 days. That means the hot Jupiter will have orbited its host star twice by the time it completes one rotation on its axis, or one CoRoT-2 b day.
"I was very pleasantly surprised when I tried a bunch of methods, and I was like, 'Aha! This is actually like one of the three hypotheses,'" Kesseli said. "Seeing the data pretty clearly pointing towards one of them was just really exciting."
Confirming this result, however, will require further observations with different tools, such as the Extremely Large Telescope that's currently being built, the researchers said.
"As convincing as I find the data, it would be good to observe the system with another instrument-maybe with a different team entirely-to see if the results can be reproduced," Rauscher said.
Written by Isabel Swafford, Caltech IPAC
