May 27, 2020

Meet the Neighbors- Probing Proxima Centauri B

An artist’s conception of the strange surface of Proxima Centauri B.

Image credit: ESO

By now, you’ve heard the news.

Yesterday, astronomers at the European Southern Observatory made the formal announcement that we expected was forthcoming: our nearest stellar neighbor, Proxima Centauri, hosts an exoplanet.

And of course, the SEO-hungry media quickly morphed the announcement from ‘Planet Found Around Nearest Star,” to “Earth’s Twin Discovered Next Door!”

First off, let me say that this is indeed an amazing discovery. Although Proxima is only just over four light years distant, the detection was right on the edge of what current radial velocity detections could see. And there’s a good chance that this world orbiting close in to its star should transit from our line of sight, allowing us to further refine its mass and orbit.

But I wouldn’t build an interstellar ark and head off there just yet. Though Proxima Centauri B is only 30% more massive than the Earth, it orbits its host star in only 11 days at 0.05 AU or just under five million miles distant. A tempestuous red dwarf star like Proxima would subject the world to life sterilizing solar flares many times more powerful than the Earth’s Sun.

Of course, it’s fun to imagine what could be. Maybe Proxima Centauri B is cocooned safely inside a robust magnetic field. Or Maybe its tidally locked, with a safe habitable zone nestled on its far side. Or maybe it hosts extensive underground oceans, such as those imagined on Europa…

All big maybes that are, thus far, backed up with little evidence. Maybe it’s simply a sun-baked rock. Red dwarfs do have one thing going for them, in that the miserly stars have life-spans measured in hundreds of billions of years, and are by far the most populous type of star in the Universe.

The Universe isn’t old enough for a single red dwarf to have burned out, giving the chemistry of life a longer chance to get going, longer than its had on Earth. And though they’re the most populous, not a single one is visible with the naked eye from the Earth. Proxima shines at magnitude +11, and doesn’t even break the top 14 in terms of red dwarf stars visible to backyard telescopes.

I also feel that the idea of finding an ‘Earth twin’ is a dangerous thing to promote. I suspect that we’ll find that even Earth-sized planets come in a variety of flavors, not all of them habitable. Witness the vast difference between Venus and Earth, right here in our own solar system. Maybe we will, with the help of superior technology, head off to the stars. Maybe this will happen with multi-generational star ships traveling at an appreciable fraction of the speed of light, or perhaps encampments we’ve established in hollowed out asteroids will just ‘leak out’ into the galaxy.

But I hear the idea that we’ll soon move to a ‘new Earth’ lots at star parties, and I think promoting this is a cop out. Folks need to know that we evolved here, and if we trash our home, there isn’t another one waiting in the wings. Earth is the only place we can thrive without massive technological assistance. Even most of the Earth is uninhabitable ocean or windswept tundra, places we can only visit but never live.

And even though it’s the closest, Proxima Centauri is far. New Horizons took a decade to reach Pluto, which is 40 times as far away from the Sun as the Earth; Proxima is 1,580 times more distant.

Still, if anything good comes from the discovery, perhaps public imagination will finally turn towards the idea of interstellar travel. If we could even accelerate a spacecraft to 10% the speed of light, we could reach Proxima in a generation. Ideas such as the original Project Orion or Breakthrough Starshot seek to do just this. These are worth looking at, as they would work using known technology.

Kuddos to the Pale Red Dot team… and may Proxima Centauri B finally set our dreams on the stars.


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