Not like Earth
On Thursday, NASA will announce a planet orbiting Proxima Centauri
- the star closest to our Sun, 4.24 light years away. They're trying to make this planet sound like Earth... and that's cool. But I'll tell you some ways it's got to be different.
Mainly, Proxima Centauri is really different from our Sun!
It's a red dwarf. It puts out just only 0.17% as much energy as our Sun. So any planet with liquid water must be close to this star.
And because it's cooler than the Sun, Proxima Centauri mainly puts out infrared light - in other words, heat radiation. Its visible
luminosity is only 0.005% that of our Sun!
So if you were on a planet as warm as our Earth orbiting Proxima Centauri, it would look very dim - about 3% as bright as our Sun.
Of course, if there's life on this planet, it would probably evolve to see infrared.
But there's a more serious problem. Proxima Centauri sometimes puts out big flares, with lots of X-rays! That's not very nice.
Why does a wimpy little red dwarf have bigger flares than the Sun?
The Sun has a core where fusion happens, and helium produced down in the core mainly stays there. A red dwarf doesn't have a core: it's fully convective
. In other words, heat moves through the star not by radiation, but by hot gas actually moving up to the surface.
All this ionized gas moving around makes big magnetic fields. The magnetic field lines get twisted up and sometimes explode out in flares! These flares get so hot that they emit X-rays. That's very
The same thing happens in our Sun but on a smaller scale. Even on a calm day, Proxima Centauri puts out as much X-ray energy as our Sun. But when a big flare occurs, it can put out 10 times more. This happens pretty often.
So: any "Earth-like" planet orbiting this star will be a lot closer than the Earth is to our Sun, and get a lot more X-rays. Puzzle 1.
Use what I've told you to estimate how much closer a planet must be, to be at the same temperature as the Earth.Puzzle 2.
Estimate how much more X-rays it will get.
On top of this, Proxima Centauri could be part of a triple star system!
The closest neighboring stars, Alpha Centauri A and B, orbit each other every 80 years. One is a bit bigger than the Sun, the other a bit smaller. They orbit in a fairly eccentric ellipse. At their closest, their distance is like the distance from Saturn to the Sun. At their farthest, it’s more like the distance from Pluto to the Sun.
Proxima Centauri is fairly far from both: a quarter of a light year away. That’s about 350 times the distance from Pluto to the Sun! We’re not even sure Proxima Centauri is gravitationally bound to the other stars. If it is, its orbital period could easily exceed 500,000 years.
On the bright side, Proxima Centauri will last a lot longer than our Sun. As it ages, it will get smaller and hotter, gradually changing from red to blue. After about four trillion years
it will grow to 2.5% of the Sun's luminosity. When its hydrogen is exhausted, it will then become a white dwarf, without ever puffing out into a red giant like our Sun.
So, any planet orbiting this star will be a weirdly different world. But if we ever get there, we could stay for trillions of years, long after our Sun has become a red giant, roasting life on Earth.
For rumors of NASA's announcement, see this:http://phys.org/news/2016-08-scientists-unveil-earth-like-planet.html
For more on Proxima Centauri, try this:https://en.wikipedia.org/wiki/Proxima_Centauri #astronomy