The Sun could be used as a gravitational lens to magnify normally hard-to-image targets such as exoplanets. The catch? The equipment needs to be 550 AU away from the Sun:
Now Leon Alkalai from the Jet Propulsion Lab and his co-authors have picked up an earlier suggestion from Italian physicist Claudio Maccone to use our Sun, rather than a distant star, to create what might be the ultimate telescope based on the microlensing principle. Alkalai's team has investigated the viability of the method in detail as a breakthrough mission concept. They also presented their findings at NASA's recent Planetary Science Vision 2050 workshop in Washington, D.C.
To build such a "telescope," detecting instruments would be placed at a point in space where the Sun's gravity focuses lensed light from distant stars. Not only is the idea viable, according to the Alkalai team, it would produce images that separate the distant star from its exoplanet, a critical observation that is the goal of future space telescopes equipped with Starshades. And using the Sun as a lens would result in much greater magnification. Instead of a single pixel or two, astronomers would get images of 1,000 x 1,000 pixels from exoplanets 30 parsecs, or about 100 light years, away. That translates to a resolution of about 10 kilometers on the planet's surface, better than what the Hubble Space Telescope can see on Mars, which would allow us to make out continents and other surface features.
[...] There is a downside, however. The telescope's focal plane instruments would have to be at least 550 AU from the Sun (1 AU, or astronomical unit, is the distance from the Sun to Earth), which is well into interstellar space. The only spacecraft that has reached interstellar space so far is Voyager 1, which covered approximately 137 AUs in 39 years. So we would need a spacecraft that is at least 10 times faster, but Alkalai and his colleagues say this is within the reach of current technology.