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Space Matter(s): Proxima b

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Space Matter(s): Proxima b

Space Matter(s) is a weekly column that delves into space science and the mechanics of spaceflight. From the latest discoveries in the universe around us to the fits and starts of rocket test flights, you’ll find analysis, discussion, and an eternal optimism about space and launching ourselves into the cosmos.

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Proxima b. The name sounds so unassuming, and yet it holds so much promise.

In August, scientists using the ESO telescope in Chile found a planet in the “habitable zone” of our nearest star system, just over 4 light years away. The star in question, Proxima

1. proxima centauri.jpg Image credit: ESA/Hubble & NASA

Let’s break down what this means (and what it doesn’t).

If you think of our own solar system, Earth is (probably) the only planet capable of supporting life. Mercury and Venus are too close to the sun, while the planets beyond ours are too far removed from the sun’s warmth. Earth is a “Goldilocks” planet. We have liquid water on our surface, which is a key ingredient in the evolution of life. We’ve had trouble finding other planets in this habitable zone, especially Earth-sized rocky planets. Most of what we’ve discovered are gas giants.

That doesn’t mean that scientists haven’t been convinced of the existence of these kinds of exoplanets (planets outside our solar system), but they’re hard to find. To understand why, we need to discuss how scientists actually discover other planets. Even through a powerful telescope, direct visual observation of planets is virtually impossible. The sky is just too big. So scientists (and planet-hunting spacecraft like Kepler) turn to other methods to find planets.

When a planet crosses in front, or “transits,” a star, there is a change in light output from our point of view. Scientists use this “wobble” in light to detect planets. Now, the vast majority of the planets we detect through the transit method are giant—much, much larger than Earth. This is because large planets create a larger wobble, or change in the star’s light output from our perspective, and are therefore easier to detect. Until the detection of Proxima b, we hadn’t found a planet that was rocky, Earth-sized, and within the habitable zone of a star.

2. ISS transiting the sun.jpg Image credit: NASA/Joel Kowsky

This is why Proxima b is a big deal. We don’t know if it can support life. We don’t know if it already has life on it. But the point is, it could. The potential is there. And what’s more, it likely means that habitable-zone planets are as common as we’ve hoped, especially in red dwarf systems. Red dwarfs are the most common star in the Milky Way, but very dim; we can’t even see our neighbor, Proxima Centauri, from Earth with the naked eye. These stars are much cooler than yellow dwarfs (like our Sun) because of their low fusion rate, but it also means they have incredibly long lives.

But there are some challenges to orbiting a red dwarf star. Red dwarfs give off superflares, much more powerful than the solar flares emitted from our sun. The most powerful solar flares we’ve experienced have affected the electric grid, technology, and satellites (though never catastrophically). But we’re a good distance from our star; to be in the habitable zone of a (much cooler) red giant, Proxima b must be very close to Proxima Centauri, possibly even tidally locked.

Multiply the much shorter distance between planet and star, plus superflares thousands of times more powerful than ours, and you get a troubling conclusion: superflares may wipe out all life on the planet. It’s possible that life has evolved on Proxima b, but a superflare from Proxima Centauri has ended it.

3. solar flare.jpg Image credit: NASA’s Goddard Space Flight Center/SDO/Genna Duberstein

A strong magnetic field (like Earth’s) would likely protect Proxima b, so all hope is not lost. But there’s also a challenge if Proxima b is tidally locked to Proxima Centauri. Proxima b is much closer to its star than even Mercury is to the Sun. If you think about our relationship with our moon, it’s comparable: the moon is tidally locked to the Earth. This means that we only ever see one side of the moon; the only people who have ever seen the “dark side of the moon” are the astronauts who’ve orbited it. Similarly, if Proxima b and its star are tidally locked (which is likely), then one side of it always faces Proxima Centauri. This could mean that one half of the star is scorching hot, while the other side is frigid, never seeing the light of its sun.

There’s a lot we don’t know about Proxima Centauri. We only know the most basic, minimal facts. But the potential of what this discovery holds, and what it means for the universe at large, is incredibly exciting. Breakthrough Starshot, in partnership with Stephen Hawking, wants to send a tiny robotic spacecraft to Proxima Centauri (using lasers to send it to near-light speeds) in just 20 years. It’s an exciting time to be a fan of space, and I’m excited to see what further study of Proxima b brings.

Top image: NASA

Swapna Krishna is a freelance writer, editor, and giant space/sci-fi geek.

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