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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]

[♪ INTRO]

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3つの新しい太陽系外惑星が身近に (Three New Exoplanets Close to Home)

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    林宜悉 に公開 2021 年 01 月 14 日
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