NASA wants to use the sun as a giant telescope to view the surfaces of alien planets

In 1936, Albert Einstein published what he described as a “little calculation,” which showed how the sun could one day be used as a giant telescope. As incredible as it may sound, the concept isn’t that far out of our reach, and an idea for how to make it a practical reality is in Phase III of NASA’s Institute for Advanced Concepts.

“Some time ago RW Mandl visited me and asked me to publish the results of a small calculation I had made at his request,” Einstein wrote in the journal Science. “This note fulfills his wish.”

As implied by Einstein’s theory of general relativity, giant objects in the universe bend space-time, changing the path of light. This is not an abstract idea, but something we can do quite regularly using telescopes like the JWST, essentially extending the range of the telescope by viewing light diffracted by massive objects on its path to Earth.

Einstein realized – although he had clearly calculated this only under pressure from Mandl – that this meant that there is a region in our solar system where light from behind the sun is focused because it has been bent by the gravity of our star.

A diagram showing how light can bend around massive objects.

How Gravitational Lenses Work.

Image credit: NASA, ESA and Goddard Space Flight Center/K. Jackson

The area where this effect occurs is about 550 astronomical units (AU) from the Sun, where one AU is the distance between the Earth and the Sun. Place a telescope in that area, and we can use it to view the surfaces of exoplanets, without the need to build the mind-bogglingly large space telescopes (or telescope arrays) that would otherwise entail.

“The Sun’s gravitational field acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line,” wrote Von Russel Eshleman, who first proposed a mission to create such a telescope, in an article. ‘A spacecraft anywhere along that line could, in principle, observe, eavesdrop and communicate across interstellar distances, using equipment comparable in size and power to what is now used for interplanetary distances. If one neglects coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to the wavelength, being 100 million to 1 millimeter.”

Currently, we can use gravitational lensing to see incredibly distant objects, but we are limited by the location of these objects and objects beyond them. With the help of spacecraft, we can place our telescope on the opposite side of the sun from the distant object we want to view, dramatically increasing our viewing distance. A Phase III project from NASA’s Institute for Advanced Concepts proposed that we could use this method to image the surfaces of exoplanets in our stellar neighborhood.

“Even in the presence of the solar corona, the [signal-to-noise ratio] is so high that one can reconstruct the exoplanet image by ~25 km in six months of integration time [15.5 mile]-scale surface resolution,” NASA explains, “sufficient to see surface features and signs of habitability.”

“There is of course no hope of directly observing this phenomenon,” Einstein added. “We will almost never get close enough to such a central line.”

While that’s still a huge distance—Voyager I has reached just over 160 AU since its launch in 1977—it seems a lot more feasible than when Einstein ruled out such a mission. The NASA project proposes to use a “swarm architecture” of smallsats using solar sails to propel them to the required position in less than 25 years.

While there are still astronomical challenges ahead for such a mission (including significant distortion caused by gravitational lensing, and moving spacecraft over great distances to observe the object you’re interested in behind), it’s possible that we’ll get images of the actual surfaces of alien exoplanets could build up within our lifetime. That’s pretty cool, even if Einstein found it a distracting chore to write down and publish.

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