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TESS found 3 new exoplanets around a strangely calm m-dwarf star, and it's possible they could be habitable!

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[♪ INTRO].

We know about thousands of planets around other stars in the Milky Way, but most of them are really far away. That makes them pretty hard to study in enough detail to answer questions like whether or not any of them are habitable.

Fortunately, NASA has a satellite on the job, and this week it dropped a shiny new planetary system right in our laps; one that's close enough and cooperative enough to carry out those detailed studies. In a paper in the journal Nature Astronomy, a team of researchers described three planets around the nearby star TOI-270. That's a small m dwarf star, more commonly referred to as a red dwarf, just 73 light-years from Earth.

The planets were found with TESS, the Transiting Exoplanet Survey Satellite, which has been searching for planets since 2018. And in that time, it's been logging new discoveries at a steady clip. As its name suggests, TESS looks for exoplanets with the transit method, which searches for dips in a star's light as a planet passes in front of it.

It's the same principle that was used by the Kepler Space Telescope, but TESS takes a slightly different approach. While Kepler stared at the same patch of sky for years on end,. TESS looks somewhere new about once a month.

The shorter viewing window means it can only spot the easy ones: close-in planets around bright, nearby stars. But those it does find will be among the easiest for scientists to investigate further. And the planetary system around TOI-270 should be particularly easy to study because the star itself is unusually tame.

Most m dwarfs live turbulent lives, frequently experiencing powerful storms and emitting violent solar flares. That all leads to ongoing fluctuations in brightness, which is kind of a problem when you're searching for planets using a method that specifically looks for changes in brightness. TOI-270 doesn't fit this pattern though, possibly because it's older than many other nearby dwarf stars.

TESS found three planets orbiting close to the star, creatively named TOI-270 b, c, and d. “b” is a so-called super-Earth, about 1.2 times the radius of our planet. The others are categorized as sub-Neptunes and are a bit more than two times bigger than Earth, but smaller than Neptune. These kinds of planets are especially exciting to astronomers because planets in between Earth and Neptune in size might represent the most common types in the galaxy.

But neither super-Earths nor sub-Neptunes are found in our own solar system. All three of these new worlds orbit TOI-270 with periods of 11 days or less, which means they're probably too close to fall in the star's habitable zone. But that doesn't mean that there can't be any habitable planets here.

Since TESS only observed this system for about 27 days, it could only detect planets with periods of a couple weeks or less. That's because ideally, you need to see a planet pass by several times to be certain it's there. Follow-up observations by other telescopes might reveal additional planets farther from the star.

If there are habitable worlds, TOI-270's quiet nature means life would probably have an easier time getting started. And even if there aren't any others, there's still a lot more that astronomers can learn from these three that we've already found. These 3 are all in resonance with one another, which means each orbits the star in a length of time that's roughly a whole number multiple of one of its counterparts.

The closest makes five orbits in the same time the middle one needs to make three. And that middle one goes around twice for every one orbit made by the outermost planet. This intricate dance is similar to motion in our own solar system.

The three inner moons of Jupiter have a similar relationship, as do Neptune and Pluto. Such resonances help stabilize the system, but they're also useful to astronomers as a tool for weighing the planets themselves. In systems with multiple planets, the gravitational tug each exerts on the others causes slight wobbles in their orbits.

And astronomers see these wobbles as slight timing errors between when a planet's transit is expected to start and when it actually does. Record enough of these errors and you can figure out how much mass each planet must have to cause the wobbles. And because they line up repeatedly, planets in resonance show more variation than those that don't.

Although TESS didn't collect enough data to make this calculation, the paper's authors believe it should be pretty straightforward for someone else to do. They're also looking forward to making observations with NASA's upcoming James Webb Space Telescope, and these measurements will help reveal the composition of each planet's atmosphere and shed further light on whether they could be at all habitable. All these future opportunities suggest that TOI-270 will continue to be a favorite of scientists for years to come! [♪ OUTRO].