The Exciting Plan to Photograph an Alien Continent

Every exoplanet discovered so far has been invisible, detected only by their gravitational pull on their host star or their faint reflection of starlight. NASA has funded a concept study aiming to photograph alien worlds, not just detect them. The ambitious goal is to resolve the surface of an Earth-like planet orbiting another star, mapping its continents and oceans from vast distances.

The star in question is roughly ten billion times brighter than the Earth-sized planet, making the task seem impossible with current technology. Physicist Paul Stankus leads the effort, proposing a two-part solution. First, a new instrument called a dynamic hierarchical nulling interferometer, which combines light from multiple telescopes to cancel out starlight, allowing faint planetary light to pass through.

The contrast ratio needed is ten billion to one, comparable to the difference between a firefly next to a lighthouse and turning the lighthouse off. Second, fly two nulling instruments on separate spacecraft 100 kilometers apart, using Michelson interferometry to act as one larger virtual telescope from a distance. The starlight is kept as a separate reference beam for alignment.

This approach, still in a NASA Innovative Advanced Concepts study, aims to shift exoplanet science from proving worlds exist to mapping them.