In previous blogs I’ve lamented that it would take incredibly large telescope arrays to try and see any details on planets orbiting nearby stars. Even space telescopes envisioned for the next 20-30 years from now could only tease out information about a planet by studying how its light fluctuates, and what colors of light it reflects or absorbs. But the planet will remain a dot of faint light in the largest imaginable telescopes.
However, astronomers have exploited “God’s zoom lens” in space to see details in some a the farthest galaxies every detected. It’s called a gravitational lens.
First predicted by Einstein’s General Relativity, gravity warps space like a funhouse mirror. This result is that the gravity of a foreground galaxy will amplify — and distort — the light from a very distant background galaxy. When chance alignments do happen, astronomers can peruse the details of very distant galaxies that would be unreachable with conventional large telescopes.
You can simulate a gravitational lens by looking at Halogen desk lamp through the base of a wine glass. The curved glass is an analog to the warping of space. (It helps the experiment if you fill the glass with wine first, drink it, and proceed to make the observation.) The bulb will smear into bright arcs around the glass base.
For years astronomers have toyed with the idea of using the sun as a gravitational lens for spying on nearby stars. The trick is that the sun needs to be reduced to a pinpoint on the sky rather than a blinding photosphere. This means placing a space telescope very far from the sun, about 50 billion miles.
Getting the telescope there would take a while depending on the propulsion system. 100 years might be a safe bet except the project would span at least two generations. Engineers would be motivated to build something moving fast enough to complete the trip within a career lifetime.
The beauty is that the telescope would not have to decelerate to stay at that location but continue racing away from the sun and a radial trajectory. Unlike a conventional lens everything would stay in focus regardless of distance.
A specific target on the sky than lines up precisely on the opposite side of the sun from the telescope’s path would have to be picked for the first experiment. My bet is on the Alpha Centauri binary system. This is the closest star system to Earth. Within a few years we’ll know if one or both sunlike stars have accompanying planets. Building a gravity lens telescope for scrutinizing Alpha Centauri’s planets would be the next big step before trying to travel there.
The amplification by the sun could yield detailed images of planetary surfaces. Like a kid perusing an ant colony with a magnifying glass, the space telescope would have to slightly shift it position relative to the sun to scan the Alpha Centauri system. It might trace out a search spiral pattern that is perpendicular to its direction of motion.
An even more ambitious use of the sun’s lensing abilities would be to locate a radio or optical transmitter 50 billion miles out to send a SETI message, or eavesdrop on the communications of an alien civilization. The advantage is that the transmitter would not need much power because of the sun’s amplification. The disadvantage is that only one nearby star system could be targeted, at least for starters.
Transmitter/receiver probes could be mass-produced so that they are stationed all around the sun to have various sightlines to specific stars. Taking this idea a step further, two neighboring stellar civilizations might set up pairs of antennas at their respective gravitational lensing points. You might even imagine a galactic Internet where gravity lens amplified transmissions are a common strategy among chit-chatting civilizations.
An extraterrestrial probe visiting Earth might drop off an interstellar transmitter that exploits the sun’s gravitational lensing. This would efficiently serve as a power-saving transponder for relaying information the probe collects about us to the home civilization. Even extraterrestrials may worry about being energy frugal.
Image Credits: NASA, ESA, British Interplanetary Society