Scientists took a close look at an extreme case of seasons thanks to a retired NASA telescope.
The researchers used NASA’s Spitzer Space Telescope to film a year on an exoplanet called XO-3b. Conveniently, a year on this world is only three Earth days long. Within that time, the exoplanet experiences a one-day summer and a two-day winter, and while the seasons pass quickly, they’re also terrifyingly dramatic.
“We saw seasonal temperature variations hundreds of times stronger than what we experience on Earth,” Lisa Dang, Ph.D. candidate in astrophysics at McGill University in Canada, during a press conference held by the American Astronomical Society on Thursday (January 13). The investigation was due to be presented at a meeting that the organization canceled due to COVID-19.
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While the concept of seasons is familiar to Earthlings, the dynamics occur differently in XO-3b. Earth’s seasons are caused by the planet’s axial tilt, but XO-3b’s are caused by the planet’s oval orbit around its star, which dramatically affects the amount of radiation received.
“These are not the same seasons that we experience on Earth,” Dang said.
Finding a large planet orbiting so close to its star but in an ellipse is unusual. Because the star and planet are large and close together, their gravitational interactions tend to bring the most distant part of the planet’s orbit closer and closer to the star, resulting in a circular orbit. So scientists think that XO-3b hasn’t been orbiting its star for very long, astronomically speaking.
“The oval shape that we see here on this very short period planet suggests that we are catching it in the middle of migration,” Dang said.
But this strange orbit isn’t the only surprising feature Dang and his colleagues found. NASA’s Spitzer Space Telescope specialized in detecting infrared light, which also manifests as heat. And when Spitzer looked at XO-3b, he saw stronger infrared signatures and thus a hotter planet than scientists expected.
And when the researchers took a closer look, they realized that even the planet’s wild seasons couldn’t explain the unexpected warmth.
“This additional warming that we saw with Spitzer is not seasonal, it is seen throughout the year,” Dang said. “Our investigation of this hot Jupiter finds that it is not only heated by the nearby planet’s star, but is also heated from within the planet.”
Additional observations collected by the European Space Agency’s Gaia mission suggest the planet is also “puffier” than expected, a feature that could be related to the surprising warmth.
Dang and his colleagues have two theories about how the planet may be generating the excess heat. One possibility is tidal heating: as the planet orbits, the star’s gravity pulls on it from different angles, stretching and deforming the planet.
The other possible explanation is that the planet is not actually a planet at all. Instead, Dang and his co-authors argue that it could be a star, with a stack of hydrogen at its core fusing as it does inside our sun. If this is the case, XO-3b would be a brown dwarf, a class of bodies often nicknamed “failed stars.”
“XO-3b might not be a regular planet, but it might not necessarily be a failed star yet, but rather be at the peak of its life as a star,” Dang said.
The research is described in a paper published December 22 in The Astronomical Journal.
Email Meghan Bartels at mbartels@ or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.
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