Sibling Stars Found with Teenage Exoplanets

by | Jul 21, 2021 | Exoplanets, Stars | 0 comments

IMAGE: Short-period planets, or those with orbits shorter than one day, are rare. Potential lava world TOI 1807 b, illustrated here, is the youngest example yet discovered. CREDIT: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

At first glance, this story was interesting because more exoplanets were found, but we’ve been announcing new exoplanets almost steadily for the last decade-plus. Digging a little deeper, this story involves a new paper published in The Astronomical Journal about four new exoplanets that were found orbiting a pair of stars. These stars are related, the planets are teenagers, and they are all giving us more information about a stage of planetary formation we don’t yet understand.

I know. I say all the time that we’re never going to completely understand planetary formation. But with every story that comes out with new information, I’m beginning to think I will be proven wrong. And that’s wonderful.

What makes these stars and their planets so special? According to lead author Christina Hedges: The planets in both systems are in a transitional, or teenage, phase of their life cycle. They’re not newborns, but they’re also not settled down. Learning more about planets in this teen stage will ultimately help us understand older planets in other systems.

The two stars are TOI 2076 and TOI 1807, they are K-type stars or dwarf stars oranger than the Sun, they are 130 light-years away and 30 light-years apart from each other. They are relatively young stars as well, only about 200 million years old. By comparison, that is less than 5% the age of the Sun. And thanks to data from the amazing Gaia satellite, we know they are moving in the same direction, which is how we know they’re related.

As for the planets, TOI 2076 has three mini-Neptunes with the innermost orbiting every ten days. The outer two, per the press release, have “orbits exceeding 17 days”. TOI 1807 has one planet, about twice the size of Earth, and orbiting in 13 hours. So these are incredibly close to their stars. Both stars likely experience flares that give off far more energy than the ones our Sun produces, and they likely produce those flares frequently, so neither system sounds very good for life.

But life isn’t the purpose of studying this system. Again, these planets seem to be at a point in their evolution that is between the point where they have thick atmospheres post-formation and the point where they lose those atmospheres due to stellar radiation. We’ve covered a few studies that indicate that this type of planetary evolution could be how we get some rocky worlds. Now we have four planets in between the two potential stages that we can possibly study further.

First, though, the team needs to determine the masses of the four exoplanets. That would lead to the possibility of Hubble or another space telescope being able to observe the atmospheres. Then the team could use that data to analyze the size and composition and figure out where in the evolutionary process the exoplanets are.

Co-author Trevor David sums up the work: Many objects we study in astronomy evolve on such long timescales that a human being can’t see changes month to month or year to year. If you want to see how planets evolve, your best bet is to find many planets of different ages and then ask how they’re different. The TESS discovery of the TOI 2076 and TOI 1807 systems advances our understanding of the teenage exoplanet stage.

Astronomy is a long game. Here’s hoping this team gets the data they need to complete this analysis. More planetary formation updates, please!

More Information

NASA press release

TOI-2076 and TOI-1807: Two Young, Comoving Planetary Systems within 50 pc Identified by TESS that are Ideal Candidates for Further Follow Up,” Christina Hedges et al., 2021 July 12, The Astronomical Journal

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