Proxima Centauri

Proxima is the third member of the Alpha Centauri system, orbiting the bright pair at a great distance, a loop that takes on the order of half a million years to complete. It happens to be on the near side of that orbit at the moment, which makes it, by a small margin, the closest star to us and will keep it so for tens of thousands of years.

It is a small star, about an eighth the mass of the Sun and not much larger than Jupiter, and it burns its fuel so slowly that it will still be shining when the Sun has long since died. It is also violent. Its surface throws off flares that can brighten it many times over in minutes, and those flares bathe anything nearby in ultraviolet and X-rays.

In 2016 astronomers found a planet there, a little heavier than Earth, close enough to its dim star to be in the zone where liquid water could exist. Another, smaller planet was reported in 2022, and a third, farther out, is disputed. Whether anything could live on a world that close to a flaring star is an open question, and it is the first place anyone would look.

The distance is a little over four light-years, which sounds near and is not. The fastest spacecraft ever to leave the Sun would take seventy thousand years to get there. Proposals exist to send gram-scale probes pushed by lasers at a fifth of the speed of light, which would make it a journey of about twenty years, with the pictures arriving four years after that. The star itself is in the southern constellation of Centaurus, invisible to the naked eye from anywhere on Earth.