Scientists have discovered a strange planet that may raise questions about the origins of so-called "hot Jupiters." The new planet has a highly eccentric orbit which raises questions about how it achieved it in the first place.
Over the last 20 years, more powerful telescopes have revealed a host of exotic systems with unexpected configurations. Hot Jupiters, as an example, are massive planets that can be found extremely close to their stars. It's likely that these planets actually form far from their stars but then, somehow, moving closer into the system.
In this case, though, the researchers found a hot Jupiter that's even more unusual than most. This particular planet is named HD 80606 b, and is about the size of Jupiter. While it's the size of Jupiter, though, it's about four size as massive, and resides in a system that's located in the constellation Ursa Major. The planet itself has a highly eccentric orbit; instead of a circular path, the planet spends about 100 days of its year traveling an oblong route away and then returning to its star-rather like the trajectory of a comet. Within 20 hours it sweeps around the star before swinging away again.
The researchers spent over 85 hours examining this planet during its closest approach to its star. They found that the star-facing side of the planet boils to about 2,000 degrees Fahrenheit. However, these temperatures are short-lived and the planet cools is fewer than 10 hours as it orbits away.
In the past, the researchers thought that the planet was slowly moving from an elliptical to a circular orbit; the more pliable a planet is, the better it is as dissipating mechanical energy as heat. Based on the "squishiness" of the giants in our solar system, the circularization phase is expected to occur over a relatively short period of hundreds of millions of years. This could explain how hot Jupiters evolve their close-in orbits.
However, new observations have shown that this particular hot Jupiter isn't as squishy as expected, which means it's not migrating as fast. This means that it's likely to retain its eccentric orbit, and scientists may need to rethink their theories on how hot Jupiters form.
"This system is undoubtedly very unique as it seems to challenge in many ways our understanding of planet-star interactions and planet formation," said Julien de Wit, one of the researchers. "Hopefully, future studies of similar systems will help us evaluate how special this system is and how far off our initial theories were."
The findings are published in the March 2016 journal Astrophysical Journal Letters.
