In dozens of sci-fi stories, heroes and villains alike have ventured to the Centauri system. There’s a good reason: it’s the nearest star to the sun. To be accurate, its the nearest stars to the sun, and of the three stars making up that system, the nearest one is Proxima Centauri, a mere 4.24 light-years away instead of 4.37 light-years for the larger, more sun-like binary stars called Centauri A and B.
Proxima is part of that three-star system, but it’s isolated enough that it could probably host a full system of planets similar to our own without much chance of constant perturbations and collisions with debris from the planetary disks or solar systems of the other two stars. So this news is big, exciting stuff for sci-fi readers and astronomers alike:
The ante for hyping a new exoplanet discovery is a little higher these days, but if rumors are true, this one makes the grade: astrophysicists from the European Southern Observatory (ESO) plan to announce they’ve spotted an Earth-like exoplanet orbiting the nearest star, Proxima Centauri, in its habitable zone. This, according to an anonymous source quoted in a report that appeared Friday in Der Spiegel.
If you read that link and others like it you’ll soon know as much about this possible planet as anyone else, because there’s not much info out there—yet. But if you want to follow below, we can sure speculate and use our imaginations on what such a world might be like and how we might someday learn a lot more about it, if it does turn out to exist. We can even suggest names for it!
Proxima Centauri is a teeny, tiny red dwarf in the Southern Cross. You can’t see the constellation Centaurus from the northern hemisphere, and Proxima is too dim to see with your unaided eye, anyway. But a decent pair of binoculars might reveal a pale red-orange point if you knew exactly where to look on a very clear night.
Proxima is estimated to be about five billion years old, roughly the same age as our sun, but it’s way smaller and its light is much, much redder. Despite that small size, stars like Proxima are notorious for big flares, big enough to cause problems for life—that is, if it were our kind of life, sitting out on a surface under a relatively thin, transparent atmosphere vulnerable to solar activity.
Because it’s so much smaller and dimmer then the sun, any planet orbiting in Proxima’s habitable zone would have to be much closer to it than the Earth is to our star. Something like 2.5 million to 3 million miles away would probably do the trick (compared to an orbital radius of about 93 million miles for Earth). That means this hypothetical planet’s “year” would be measured in Earth-days. It also means the planet would be tide-locked, one side forever facing the star in the same way our moon is tide locked to Earth. Because stars like Proxima are prone to periodic violent flares, astronomers theorize it could constantly thin an atmosphere out, or even strip it away completely over time.
It’s debatable if life could develop or persevere on a planet orbiting a red-dwarf because of those big flares. But some astronomers figure a respectable atmosphere combined with a healthy pond, a thin crust of ice on a puddle, or a convenient rocky overhang might be enough to shield Earth-like microorganisms from the worst of Proxima’s stellar outbursts. And that’s assuming terrestrial life, i.e., life as we know it. Life that evolved on a planet orbiting a red-dwarf flare star might not only tolerate flares—it could find them positively delightful, maybe even necessary for an alien lifecycle to thrive, in much the same way Arctic and Antarctic life has adapted to big, seasonal variations in terrestrial sunlight on Earth.
Given a largish, geologically active terrestrial world, perhaps a little lighter in metals than our own and maybe a little bit heavier in silicates and carbon, and with a healthy three-phase water cycle biased toward the icy end, what might it look like from the surface?
In the image at the top, courtesy of graphic artists Karen Wehrstein and our own DemFromCT, we see one guess at such a hypothetical world. We chose to make it between two and three Earth masses with a deep atmosphere composed largely of nitrogen, a respectable amount of carbon-dioxide, streaked with smaller amounts of water vapor, and hydrocarbons like methane and traces of argon, at about twice the pressure of our own. Since the planet spins in sync with its “year,” the molten core still provides a respectable magnetic field protecting the upper layers of the atmosphere from stellar stripping.
We assumed the planet orbits at the outer edge of the system’s habitable zone, making one orbit every 10 to 11 Earth-days, putting it on the colder side of comfortable when the star isn’t flaring, and made it on average drier than Earth, giving us a surface scoured by wind lit in cool reds and browns under Proxima’s filtered, ruddy glare. It rarely snows even the tiniest flakes on this relatively arid super-earth, but ice regularly heaves up in the lowlands, breaking through the frozen subsurface to melt and flow whenever the planet is warmly caressed by the occasional super-flare and associated sleet of recently liberated electrons and nucleons.
We see the cooling aftermath of such an event as an icy, muddy stream flowing briskly alongside a shallow glacier in a broad valley carved out of rugged hills and small mountains. Presumably, larger ice and melt-water flows and a chaotic weather cycle complete with gale force winds would be driven by more intense flaring episodes that would distribute heat and precious water vapor over both the dark and light sides. Hydrocarbon clouds, wisps of high cirrus, and faint, shimmering aurora mingle with the blues and reds of scattered star-light providing a somber suite of pastel colors overhead.
That’s all pure speculation, we have little confirmation that a planet even exists, let alone anything in the way of physical details. As far as getting a probe there to learn more, that’s a whole different story. Proxima is 4.24 light-years away; that’s more than 25 trillion miles to us civilians, roughly 5,000 times farther away that the dwarf planet Pluto—and it took NASA’s New Horizons 10 years of hauling ass to reach that mini world! Proxima is close in interstellar terms, but it’s beyond a giant leap compared to any journey our most ambitious interplanetary machines have ever undertaken. We would need a propulsion system that gets up to at least 5 to 10 percent of the speed of light. The only drive we have dreamed up and halfway sketched out that might do that is the old Project Orion concept that could use nukes as propulsion. Still, there are plenty of other ideas that are not quite as fleshed out.
We’d probably be better off studying this hypothetical world, and many planets around other stars, by building a large, comprehensive observatory in our own solar system. The James Webb Space Telescope would be a great start and that is scheduled to go into space in 2018, if all goes well.
But eventually, who knows? Let’s be optimistic about humanity. Maybe some of the youngest people reading this will live long enough to see a spacecraft take shape in Earth orbit, whip through the inner solar system on sophisticated chemical or ion rockets, blaze deep into the Oort Cloud, light up an as yet undiscovered new propulsion method, and finally, for the first time, set course for the stars.
There’s no hurry: long after humans have come and gone — or transformed into something else entirely -- Proxima will shine on. It will outlast the Earth by orders of magnitude, it will outlast its twin companions A and B, it will outlast our sun, the Milky Way galaxy, and even our local corner of the universe as we know it. When all the other, brighter stars have burned out, and all their mighty descendants have likewise churned through their recycled stellar endowments until there is nothing left worth fusing, Proxima Centauri will still burn. Modest red stars like it will be the very last ones to fade away and that won’t happen for trillions of years. Their passing will mark the formal end of the well-lit, star-filled stellar epoch our universe currently enjoys and signal final entry into an eternal cosmic night — assuming the Rippers are wrong.
In the meantime, we can at least have some fun: what do you think we should we call this new planet, if it does turn out to exist?