Commentary Magazine

Promise and Peril of a New Planet

To take a brief break from the horrible politics of 2016, a new planet has swum into our ken. What’s more it’s earth like—i.e. rocky, not gaseous like Jupiter—and only a little larger than earth itself. What’s more still, it’s very close, orbiting a star called Proxima Centauri–the closest star to our solar system at a mere 4.2 light years away. What is still more than that, it orbits Proxima Centauri in that star’s habitable zone, which is to say at a distance where liquid water—essential to life—can exist.

While this is exciting news, don’t fire up the rocket ship for a visit quite yet. The fastest rocket that has ever flown would need 78,000 years to get to the new planet. Space is incredibly empty. Just consider: if the sun were one inch in diameter—the size of a walnut—earth would be a poppy seed orbiting a little less than eight feet away. Jupiter would be a French pea orbiting 37 feet away. Proxima Centauri would be a large pea, 400 hundred miles away.

Despite the possible presence of liquid water, the chances of life arising on this new planet are not good. Proxima Centauri is a very dinky little star, a red dwarf, only twelve percent the mass of the sun. As a result it is very dim, eleventh magnitude. Indeed it is so dim it was only discovered in 1915. That has consequences. For one thing, the new planet must orbit very close to be in the habitable zone. It’s only five million miles away from Proxima Centauri (earth is 93 million miles from the sun). That means that it is in all probability tidally locked, like the moon. In other words, one side always faces the star. So one side would be very hot and the other very cold. Life might be possible in the twilight zone between the two halves, but, assuming the planet has an atmosphere, the winds would surely be ferocious there as the two sides try to equalize temperatures.

And Proxima Centauri is a flare star, as many red dwarfs are. Every so often a huge eruption sends a massive burst out into space. If the new planet were in its path, the northern lights would be spectacular, but the intense X-rays would fry anything not sheltered.

We will soon have the capacity to explore this planet more closely, if still at a distance, and it will have much to teach us about the exciting new field of exoplanets. That, in turn, will teach us more about planet earth and our solar system. But don’t expect to find any little green men.

OK, sigh, back to politics.

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