Wednesday, August 24, 2016

Is Proxima b Our Refuge from Climate Change?

So it's been announced (the rumors were right) that scientists have discovered a potentially Earth-like planet around our nearest star, Proxima Centauri, which is only 4.25 light-years away.

Assuming that's where the last group of surviving humans will go after Anthony Watts' denialism leads to an Earth too hot for habitation, what does this planet look like?

First, I hope nobody suggests calling this planet "Vulcan." For now it's just "Proxima b," which needs improvement; hopefully those who discovered it will get to name it. (Please don't use "Earth 2," "Neoearth," or anything of the sort.)

Nobody knows yet what this planet looks like, though telescopes may be able to able to glimpse it in their next generation. (A proposed $175 million space telescope could help -- surely some billionaire can afford that, right. I mean, just write a check.)

Proxima b is only 0.05 AU from its star, Proxima Centauri, and tidally locked -- like our Moon. One side is in permanent starlight and the other side is permanently dark.

Proxima Centauri has a luminosity of only 0.15% of the Sun, 85% of it in the infrared. So humans, take your night vision goggles.

The irradiance onto the planet is 65% of Earth's, or about 890 W/m2. By comparison, Mars's solar constant is 589 W/m2. So not too shabby.

What's the planet's surface temperature? There isn't enough information to say -- we don't know the planet's albedo, its radius, or the eccentricity of its orbit (the paper says it's < 0.35).

The paper says the equilibrium blackbody temperature of the planet is 234 K. That's -39°C, which is -38°F. But without the above information, the average surface temperature can't be calculated, so we don't know if liquid water can exist there.

I tried calculating the effective blackbody temperature, but got 352 K. I think because an eccentricity of 0.35 is fairly high, and I used the semimajor axis, not the average distance from the star. (That difference increases with eccentricity.)

It seems unlikely advanced life exists there -- else, why haven't they come here, or sent small ships, much like Stephen Hawking and crew want to sent out iPhone sized ships in the next few decades? Planets are old -- a few million years -- the time for our transition from apes to small ship launchers -- doesn't matter much. So it's unlikely they'd be at the same point of development we are, and since we haven't heard from them they must be behind us, if at all.

Speaking of which, the upcoming movie Arrival looks excellent. Trailer:

1 comment:

Brian Schmidt said...

Mercury is in synchronous rotation. Proxima b could be the same.