A year on this exoplanet only lasts about 8 hours

By Ashley Strickland, CNN

If you think there aren’t enough hours in the day on Earth, this newly discovered planet will make your head spin. On an exoplanet called GJ 367 b that’s orbiting a star 31 light-years away from our sun, a year only lasts for about eight hours. The discovery could shed light on these mysterious, rapidly orbiting worlds.

The rocky exoplanet is considered an ultra-short period planet, or USP, that whips around its host star and completes a single orbit every eight hours. But GJ 367 b is intriguing for other reasons as well.

The planet is about the size of Mars, so it’s only half the mass of Earth, which makes it one of the lightest exoplanets discovered so far. About 86% of the planet’s interior is made of an iron and nickel core, which also makes it very similar to Mercury. In our solar system, Mercury is closest to the sun, and a year for the planet lasts 88 days.

Exoplanet GJ 367 b is extremely close to its M dwarf star. These cool red dwarf stars are common in our galaxy and have been known to host multiple planets in a single system, with an average of about two to three planets. Even though they are smaller and cooler than our sun, cool red dwarfs can still heat up planets when they are as close as GJ 367 b is to its star.

During the day, this planet reaches 2,732 degrees Fahrenheit (1,500 degrees Celsius), which is hot enough to melt rocks and metals. The planet is also bombarded with 500 times more radiation than Earth receives from the sun.

All of these factors suggest that the planet lacks a substantial atmosphere, likely vaporized a long time ago, and isn’t a place that would be friendly to life. A study detailing the findings about the planet published Thursday in the journal Science.

Astronomers are eager to learn more about these small planets that quickly spin around their stars in less than 24 hours because they are not sure how they form and end up in such an extreme orbit. This newly discovered planet is close enough to our solar system that researchers were able to gather more data than with other known ultra-short period planets.

“We already know a few of these, but their origins are currently unknown,” said lead study author Kristine W. F. Lam, a postdoctoral researcher at the German Aerospace Center’s Institute of Planetary Research, in a statement. “By measuring the precise fundamental properties of the USP planet, we can get a glimpse of the system’s formation and evolution history.”

Just because GJ 367 b isn’t habitable doesn’t mean there aren’t other planets in the same system that could support life.

“For this class of star, the habitable zone would be somewhere between a two- to three-week orbit,” said study coauthor George Ricker, a senior research scientist in Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, in a statement. “Since this star is so close by, and so bright, we have a good chance of seeing other planets in this system. It’s like there’s a sign saying, ‘Look here for extra planets!'”

Scientists found GJ 367 b using NASA’s planet-hunting TESS mission, which stands for Transiting Exoplanet Survey Satellite. Ricker is the principal investigator for TESS, which looks for changes in brightness of the nearest stars.

When researchers spot dips in starlight, it suggests that a planet is crossing in front of the star, which is known as a transit. In 2019, TESS stared for a month at a patch of the sky that included the red dwarf star GJ 367, which led to the discovery of its very close planetary companion. Follow-up observations with ground-based telescopes helped them pin down measurements of its mass, radius and density, which helped the researchers to determine the composition of the core.

Scientists plan to continue studying the exoplanet and its star so they can find out whether there are any other planets in the system. Those potential exoplanet siblings and their orbits could help reveal how GJ 367 b came to be.

“Understanding how these planets get so close to their host stars is a bit of a detective story,” said Natalia Guerrero, research associate for TESS at the MIT-Kavli Institute, in a statement. “Why is this planet missing its outer atmosphere? How did it move close in? Was this process peaceful or violent? Hopefully this system will give us a little more insight.”

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