Astronomers have been able to detect scores of exoplanets in orbit of distant stars, but actually taking pictures of them is extremely difficult. To date, only a few dozen exoplanets have been directly imaged, and only those with very large diameters can be spotted at all. A new technology discussed at the American Geophysical Union’s annual conference could help us spy on smaller planets like the Earth-sized Proxima Centauri b.
All of the large exoplanets images thus far have been captured with the aid of a device called a coronagraph. This instrument blocks out the light from a star, allowing the telescope to zero in on the far dimmer planet orbiting the star. However, minute imperfections in the coronagraph mean some light from the star will inevitably leak out, and even a little light can make it impossible to see a smaller planet. Even using multiple coronagraphs in a single imaging system comes with too much uncertainty.
The solution could be a new technology called multi-star wavefront control. Rather than search for a perfect light blocker, this system uses deformable mirrors to bounce light from stars and planets into multiple sensors. The mirrors essentially correct for imperfections in the optical components in a telescope. This system can also account for the light from multiple stars at once, which is important as many solar systems are binary or trinary systems (like Centauri).
An example of a coronagraph and the sun.
Filtering out the light from stars more efficiently could allow astronomers to take a closer look at exoplanets that are small and rocky like Earth. Astronomers are particularly interested in taking a look at Proxima Centauri b, which is just a little over 4 light years away and 1.3 times more massive than Earth. The exoplanet orbits the red dwarf Proxima Centauri, but the other two stars in the Centauri system are larger and brighter. Multi-star wavefront control would be an ideal way to filter out the light from all three stars to image Proxima Centauri b directly. The resulting images would not provide high detail, but rather points of light. However, there’s a great deal scientists can learn from a few points of light when they come from exoplanets.
According to Ruslan Belikov from NASA’s Ames Research Center, multi-star wavefront control is compatible with many projects that are currently under construction, like ACESat and Project Blue. Adding a deformable mirror is all that’s required. Telescopes with multi-star wavefront control could enter service in the mid-2020s.