Near Gigapixel Imaging of Exoplanets from the Gravity Lens Regions

Exoplanets are planets in other solar systems. They are very faint but they are even harder to see because of the much brighter star they are orbiting. If we send a telescope to the solar gravitational lens (SGL) point on the opposite side of our sun then light from objects like exoplanets will be focused to provide 100 billion times more magnification. The Sun becomes a telescope that is 1.4 million kilometers wide for the SGL regions.

We could resolve exoplanets around Proxima B to 450-meter resolution using a one-meter telescope SGL mission. If there was an earth-sized planet around Proxima B, we could resolve to 800 megapixels. We would only be able to resolve 10 square kilometers at a time. The space telescope would have to roam around the einstein-ring image of the target object to assemble the full image. The image would need to be converted from an einstein ring back into the image of the exoplanet. A giant 1.3 kilometer focus line diameter space telescope would be able to resolve an entire einstein-ring image of an earth-sized exoplanet at 100 light years from the right SGL location.

There are ten known stars within ten light years. There are over 150 stars and white and brown dwarfs known to be located within 20 light-years.

One light year is 63,241 AU (astronomical units, distance from Earth to the sun.) The gravitational lens points are 200 to 420 times closer than the nearest star and would be 4000 to 8000 times closer than starts that are 100 light years away.

Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year. Voyager 2 is escaping the solar system at a speed of about 3.3 AU per year. If we went 10 times faster than Voyager then we could have missions reach the SGL areas in about 20 to 40 years. Ideally, we would want to decelerate and keep space telescopes moving around the lensing locations for each target solar system. You would only be able to resolve 10 square kilometers at a time. You would need to precisely move around the image area to take millions of picture to form the full picture of the planet. You could move along the focus line to form the full picture. You would not have to completely stop the telescope. The SGL reduces the image of the exo-Earth by a factor of ~6,000. An orbital radius of 1 AU becomes ~2.25´104 km and an orbital velocity of 30 km/s translates into 5 m/s. Solar gravity accelerates the Earth at 6 mm/s2. The imager spacecraft needs to accelerate at ~1 µm/s2 to move in a curved line mimicking the motion of the exoplanet. Even if the probe mass is ~1,000 kg, the corresponding force is 1 mN, which may be achieved with electric propulsion. Electric propulsion should be able to move the space telescope to sample the pixels in the Einstein ring needed for imaging. JPL we could potentially reach velocities of roughly 60 to 70 kilometers per second with planned solar sails. This would be 5 times faster than Voyager. A rocket could perform a slingshot around the sun to send a mission to the SGL in 27 to 35 years. An new megawatt laser and lithium-ion drive combination could reach 45 AU per year in speed. This could send missions to the SGL with 15-25 year trip times and the beamed power could be used to slow down and move around. There are a few thousand stars within 100 light years. Light from the parent star is typically focused many tens of thousands of kilometers away from the focal line that corresponds to the instantaneous position of the exoplanet. Light contamination due to the parent star is not a problem when imaging with the SGL. A regular telescope has an optical lens with a single focal point. A gravitational lens has no single focal point but a focal line. A mission to the SGL carrying a modest telescope and coronagraph opens up a possibility for direct megapixel imaging and high-resolution spectroscopy of a habitable Earth-like exoplanet at a distance of up to 100 light years. The entire image of such a planet is compressed by the SGL into a region with a diameter of ~1.3 km in the vicinity of the focal line. The telescope, acting as a single pixel detector while traversing this region, can build an image of the exoplanet with kilometer-scale resolution of its surface, enough to see its surface features and signs of habitability.

The gravitational lens regions are from 550 AU to 1200 AU. We would need to send one or more mission for each solar system we would want to study.

Propulsion Technology Possible by 2030

There is a NASA NIAC phase 2 study to use lasers to beam 10 megawatts of power to power new ion drives. This will enable a system to go ten times faster than any previous space mission. This will go 40 AU per year. It would take less than year to get to Pluto.

They are building and proving out the various components of this system. The sail and the ion drives are coming together. The hard part is the phased array lasers.

They are boosting the testing voltage up to 6000 volts so the lithium ion drives can be directly driven. Direct drive eliminates the need for a lot of heavy electronics which would kill the performance.

The phased array lasers will increase the power density over the solar density by 100 times.

Going from a laser wavelength of 1063 nanometers down to 300 nanometers would reduce the needed power and system size.

SOURCES- NASA, Arxiv, Slava G. Turyshev (Physicist, JPL), Louis Friedman (Co-Founder and Executive Director Emeritus, The Planetary Society)

Written By Brian Wang.