TRAPPIST-1’s Planets Are Similar to Those in our Solar System, Suggesting Possible Habitable Zone

The TRAPPIST-1 system is an ultra-cool red dwarf system more massive than Jupiter, and it is a hot spot for astronomers. It is located about 40 light-years away, and has seven rocky exoplanets, out of which three are in their star‘s habitable zone.

The system is the most fascinating in our local galactic vicinity, but it needs more than what it currently has in order to be completely habitable. That’s why astronomers have been looking for characteristics that could explain the system’s background.

TRAPPIST-1’s Planets Resemble Our System’s Arrangement

Now, breathtaking new research has discovered that similar to how the Solar System‘s planets orbit around the Sun‘s equator, so do TRAPPIST-1’s exoplanets: they orbit in a flat plane around its core.

This finding will allow scientists to probe the system’s active history, which can help enhance models of the system and figure out if its exoplanets can sustain life. However, detecting the planets around the star’s equator means they are, in essence, rotating at the same tilt on which they formed, making TRAPPIST-1’s primordial state easier to analyze.

Artist’s Concept of TRAPPIST-1. [Image: NASA]
Astronomers have calculated the orbital alignment of a few exoplanets by now, and many close-orbiting gas giants emit what is called stellar obliquity, which happens when a star’s exoplanets are rotating around at an oblique angle to the star’s spin axis.

Multiple-planet systems are usually less oblique, but no one has measured it with rocky worlds before. That is because stellar obliquity is calculated in accordance with something called the Rossiter-McLaughlin effect, which is rather difficult to observe with small, dim stars like TRAPPIST-1.

The latest data collected on the system is not conclusive yet, but it does imply some fascinating possibilities for the TRAPPIST-1.

How Stellar Formation Shapes a System

During stellar formation, a star is encircled by a massive, flat disc of dust and gas coiling into it. When the star is completely filled, that remaining dust and gas are what shapes everything else. That is why the Solar System’s planets are so elegantly ordered, instead of clawing in every which way; nothing appeared to disturb their alignment, so they just remained like this.

Our Solar System is an orderly arrangement of planets orbiting the Sun. [Image: NASA]
If TRAPPIST-1’s exoplanets are in a tidy, flat, equatorial plane, then they, like the planets in the Solar System, probably remained where they took shape. Still, the planets are gathered pretty close to their star, which means that this stiff arrangement was, most likely, the result of a gradual inward migration, instead of any other perturbing factor.

It could also suggest that the lack of massive gravitational disturbances is probably to result in peaceful, habitable-zone planets, even though, obviously, reaching that conclusion would need a lot more examination.

However, for now, the team’s studies are an amazing step forward.

“Despite the limitations of the data, our observation of the Doppler transits in the TRAPPIST-1 system are the first such observations, to our knowledge, for such a low-mass star,” they wrote in their paper. “No other results have been reported for stars cooler than 3500 K. By performing additional observations with the IRD and other new high-resolution infrared spectrographs, a new window will be opened into the orbital architectures of planetary systems around low-mass stars.”

The study has been published in The Astrophysical Journal Letters.

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