Last week, NASA’s Innovative Advanced Concept program announced its new cohort of scientists who will spend the next year developing space mission concepts that sound like they were plucked straight from science fiction. Among this year’s NIAC grants are proposals to turn a lunar crater into a giant radio dish, to develop an antimatter deceleration system, and to map the inside of an asteroid. But the most eye-popping concept of the bunch was advanced by Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory who wants to photograph an exoplanet by using the sun as a giant camera lens.It’s an idea based on a century-old theory first floated by Albert Einstein, who calculated that a star’s gravity would cause light from another star to bend around it, effectively creating a giant lens. If you were to stand at the focal region where the bent light converges, the “solar gravitational lens” would significantly magnify whatever was behind the star. Einstein’s theory about gravitational lensing is now a well-established fact. Observational cosmologists regularly use the gravitational lensing from galaxies and galaxy clusters to study more distant objects.
Turyshev’s plan would take advantage of this effect by sending a telescope on a 60 billion-mile journey to the sun’s focal region to photograph a habitable, Earth-like exoplanet that is up to 100 light years away. He calculates that sending a telescope just one-third the size of the Hubble Space Telescope to the sun’s focal region could produce a megapixel-quality image of an exoplanet after a few years of snapping photos. If the targeted exoplanet is about the size of Earth, each pixel would cover 35 square kilometers. Turyshev says that would be better resolution than the famous “Earthrise ” photo taken by Apollo 8 astronauts, and more than enough definition to make out surface features and any signs of life on the exoplanet’s surface.
“The primary motivation for everyone contributing to this project is to move this idea from science fiction to reality, so that the current generation of people living on this planet can enjoy images of an alien world,” says Turyshev. “‘Are we alone?’ is a question we all ask, and we may be able to answer it within our lifetime.”Snapping photos of our extraterrestrial neighbors is an enticing idea, but the technological challenges involved with this mission are staggering. First, consider the sheer distance: 60 billion miles is about 16 times further from the sun than Pluto. If you were traveling at the speed of light, it would take more than three days to cover this distance. Voyager 1, which has ventured further into interstellar space than any other human-made object, has only traveled about 13 billion miles—and it took the spacecraft 40 years to get there.
Simply getting the spacecraft to the right place is a major challenge. Unlike a camera lens, the sun doesn’t have a single focal point, but a focal line that starts around 50 billion miles away and extends infinitely into space. The image of an exoplanet can be imagined as a tube less than a mile in diameter centered on this focal line and located 60 billion miles away in the vast emptiness of interstellar space. The telescope must align itself perfectly within this tube so that you could draw an imaginary line from the center of the telescope through the center of the sun to a region on the exoplanet.