Have you ever seen wispy arcs and rings in astronomical images taken by the Hubble Space Telescope and other observatories? These unusual features are caused by a quirk of nature called gravitational lensing, which occurs when light from a distant object is distorted by a closer massive object along the same line of sight. This distortion effectively creates a giant lens which magnifies the background light source, allowing astronomers to observe objects embedded within those lens-created arcs and rings that are otherwise be too far and too dim to see.

A group of researchers are working on plans to build a spacecraft that could apply this quirk by using our Sun as a gravitational lens. Their goal is to see distant exoplanets orbiting other stars, and to image an Earth-like exoplanet, seeing it in exquisite detail, at a resolution even better than the well-known Apollo 8 Earthrise photo.

Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory has spearheaded research into this proposed concept, called the Solar Gravity Lens (SGL). The idea would be to send a spacecraft to the exact location where it could use the focal region of our own Sun to bend the light from an exoplanet, magnifying it into a gigantic image.

Hubble image of a luminous red galaxy (LRG) gravitationally distorting the light from a much more distant blue galaxy, a technique known as gravitational lensing. Credit: ESA/Hubble & NASA
Hubble image of a luminous red galaxy (LRG) gravitationally distorting the light from a much more distant blue galaxy, a technique known as gravitational lensing. Credit: ESA/Hubble & NASA

“Using the solar gravitational lens is similar to using a conventional lens with a diameter equal to that of the Sun, which is 1.4 million km,” Turyshev told me. “The physics is there, now it’s just figuring out the engineering.”

Turyshev and fellow researchers say they could potentially image an Earth-sized exoplanet up to 100 light-years away, detecting surface features as small as 10 kilometers across.


This image taken by The Planetary Society’s LightSail 2 spacecraft on May 31, 2021 shows Afghanistan, Pakistan, and the Arabian Sea. The Caspian Sea is at lower left. The shadows of the spacecraft’s solar panels can be seen on the sail. North is approximately at the top left. This image has been color-adjusted and some distortion from the camera’s 180-degree fisheye lens has been removed. Credit: The Planetary Society

Turyshev said the spacecraft architecture is still being studied and debated but instead of using a single large spacecraft like Voyager or Cassini, the SGL concept could rely on a fleet of smaller satellites that would use solar sails for propulsion. One intriguing flight plan for SGL is to use a gravity assist from the Sun to reach speeds where it would take just 25 years to travel 60 billion miles to the focal point destination in interstellar space.

“You don’t need to fly systems like the size of Voyager, or Galileo, etc, but can use smaller spacecraft,” Turyshev said. “There are alternative options like assembling in space, so if you need to build a larger aperture. Or if we have smaller, multiple spacecraft we can use different means of taking them to space, such as rideshare opportunities to get to low Earth orbit or geostationary orbits where we have our system self-assembled and then use solar sails for propulsion to deep space.”

If the idea sounds fantastical, the NASA Innovative Advanced Concepts (NIAC) Program – which funds research on visionary ideas that could transform future missions with breakthrough

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