In 1960, the renowned astronomer Frank Drake turned the radio telescope at the Green Bank Observatory in West Virginia toward two nearby stars in hopes of discovering some indication of intelligent alien life. Although Drake was unsuccessful in this venture, his effort did mark the beginning of the Search for Extraterrestrial Intelligence (SETI), a global scientific effort to determine whether or not we're alone in the universe.
SETI has come a long way since its humble beginnings over half a century ago, and nowhere is this more apparent than in the technology that is being deployed in the hunt for life beyond Earth. Today, astronomers are using telescopes more powerful than Drake could've ever imagined, and astrobiologists are commandeering rovers that are collecting samples on the Martian surface, a region of the solar system that wouldn't be explored for almost 15 years after Drake's original SETI experiment.
According to Eric Korpela, the director of UC Berkeley's SETI@home project, one of the biggest leaps forward in SETI tech has been in the telescope department. He cited the ALMA Array, the Square Kilometer Array and the Allen Telescope Array as just a few of the examples of the new generation of telescopes that are making the possibility of contact seem closer than ever before.
"The common theme in all these telescopes is that they're arrays," said Korpela. "That's a big change from the way SETI has done most of its work in the past, which was with fairly large, single-dish telescopes that point at a single spot in the sky. The arrays that are coming online have the capability to point at multiple spots on the sky simultaneously and have much higher spatial resolution, meaning you're just focusing tightly in on a single star, rather than surveying a large area."
The reason these telescope arrays represent an advance over their predecessors is because they are able to leverage a relatively new surveying technique called interferometry. In essence, this technique combines the radio signals being received at each of the smaller telescopes so that it provides a really find-detailed version of a single signal.
But even with these new radio telescope arrays coming online, SETI hasn't abandoned its roots in single dish telescopes—it's merely changed the way it's putting them to use. Case in point is SETI@home, a distributed computing initiative launched in 1999 that has enlisted the help of tens of thousands of people around the world in the search for alien life.
"Maybe 5 to 10 percent of stars have an Earth-like planet in orbit that is also in the habitable zone"
Every day, the SETI researchers at UC Berkeley receive dozens of gigabytes worth of radio signal data collected from the Arecibo telescope in Puerto Rico and the Green Bank telescope in West Virginia. Filtering through all this cosmic noise for some small indication of an intelligent signal is a big task, even with state of the art computing technology—there's simply too much to look through. But by linking together the processing power from individual laptops and PCs all around the world, the task has become infinitely more manageable. It also means that anyone can help look for aliens while they sleep.
At the same time, advances in optical telescope technologies have also revealed a universe overflowing with potentially habitable planets orbiting other stars, which are known as exoplanets. The first exoplanet discovery occurred in 1995 and several thousand others have been discovered since then, although most of these were far larger than Earth and unlikely to support life.
It wasn't until 2014 that the Kepler Space Telescope, launched into space in 2009 with the largest camera ever put on a spacecraft, discovered the first Earth-like planet in the habitable region (where liquid water is possible) of another star. In the three years since, well over a dozen other potentially earth-like exoplanets have been discovered, each of which could potentially host extraterrestrial life. The most recent Earth-like exoplanet discovery occurred last month, when NASA announced that seven potentially habitable planets had been discovered in the Trappist-1 star system, the most ever found to be orbiting a single star. Now, according to Korpela, "we can estimate that maybe 5 to 10 percent of stars have an Earth-like planet in orbit that is also in the habitable zone."
SETI astronomers like Korpela are looking at stars and planets that are dozens, if not hundreds of light years away. But a little bit closer to home, astrobiologists are also looking for extraterrestrial life in our own solar system—albeit of the non-intelligent sort.
The tools of choice for these alien hunters are not telescopes, but the new generation of rovers and planetary probes that are on the hunt for microbial life on the planets and moons in our solar system. The leading candidates in this respect are Mars, Saturn's moons Enceladus, and Jupiter's moon Europa because each has water on its surface.
With the exception of Mars, there has yet to be any missions launched to these destinations in search of life. The first mission to Mars in search of life was the Viking missions in the 1970s, but the most recent was a joint mission between the European Space Agency and Roscosmos called ExoMars, which consists of two phases. In the first phase, the Trace Gas Orbiter (which just arrive at Mars last October) will examine the constituency of the Martian atmosphere. Although the atmosphere of Mars is dominated by carbon dioxide, the presence of trace amounts of other gases, such as methane or water vapor, could point to the possibility of life on the surface of the Red Planet. The second part of the mission will see a rover touchdown on Mars in 2021 and will use a 6-foot long drill to sample water beneath the surface of the planet.
As for Enceladus and Europa, they remain enticing destinations for future exobiology-oriented missions.
Just last month, NASA put forward a proposal for a lander on Europa, which is bound by a 10-15 mile thick icy crust that researchers think may hide an ocean of liquid water beneath its surface that is twice as large as the oceans on Earth combined. In the early 2020s, NASA plans to launch an orbiter to Jupiter, which will perform 45 close fly-bys of the moon equipped with instruments capable of measuring the thickness of the ice crust, determining whether there is liquid water beneath its surface, as well as the saltiness and temperature of this water. But NASA doesn't plan to stop there. It's most recent proposal calls for a lander that would be lowered to the moon's surface using a "sky crane" (parachutes would be unnecessary since the moon has no atmosphere) and then proceed to collect samples from the top few centimeters of the moon's surface.
As for Enceladus, NASA's plan to visit this icy moon isssss much less well-defined. In 2015, following a flyby of the moon by the Cassini spacecraft which took photos of water-rich plumes erupting from Enceladus' surface, a scientist from Cornell University proposed the Enceladus Life Finder (ELF) which would make its primary mission sampling these plumes to determine their chemical makeup. A second proposal to fly through the plumes called Life Investigation for Enceladus (LIFE) was also made, differing from insofar as the samples collected by the craft would be returned to Earth for analysis.
As of the time of this writing, neither ELF nor LIFE has advanced beyond the initial mission proposal. But in any case, there has never been a busier or more promising time to be hunting for life beyond Earth, a development which is largely due to the awesome new technologies being developed by space agencies and researchers around the world.