SISTINE

Of the over 5,000 exoplanets known throughout across the galaxy, only Earth is known to host life. In the search for other exoplanets that could host life as we know it, astronomers have focused on planets that orbit in the habitable zone – defined as the distances from a star where a planet’s surface temperature could support water.

While water is one part of making a planet hospitable, for a planet to support an Earth-like biosphere, it also needs an atmosphere. If the habitable zone is bathed in too much ultraviolet radiation, any water vapor in the upper atmosphere could escape, quickly drying out the planet. Atmospheres can also be eroded by radiation and extreme flares from a planet’s host star, exposing the surface to harsh ultraviolet radiation, which can break apart molecules.

The researchers selected Alpha Centauri A and B because they can serve as a useful reference against which to calibrate observations from the Sun – the only other star for which we have complete ultraviolet measurements. Ultraviolet light is absorbed by dust and gas in space. This makes it nearly impossible to measure ultraviolet light from more distant stars at the level needed for these types of analyses. The Alpha Centauri system, however, is just 4.3 light-years away, close enough that much of its ultraviolet light reaches us before being absorbed.

DEUCE and SISTINE will take these important measurements of ultraviolet light to help narrow the search for habitable planets. Launching only a week apart, the two missions will work together (DEUCE will measure the shorter, extreme-ultraviolet wavelengths and SISTINE will measure the longer, far-ultraviolet wavelengths) to get a full picture of the ultraviolet light coming from Alpha Centauri A and B.