Meeting and Greeting the Nearest Aliens Will Take Centuries

Although our telescopes will likely become good enough to detect signs of life on exoplanets within the next 100 years, it would probably take many centuries before we could ever get a good look at the aliens.

"Unfortunately, we are perhaps as far away from seeing aliens with our own eyes as Epicurus was from seeing the first other worlds when, 23 centuries ago, he predicted the existence of these planets," said astrobiologist Jean Schneider at the Paris Observatory at Meudon. He and his colleagues discussed the difficulties of studying distant alien life in the journal Astrobiology.

Schneider and his colleagues say that in the next 15 to 25 years, there will likely be two generations of space missions able to analyze exoplanets in greater detail. The first generation will feature 1.5-to-2.5-meter-wide coronagraphs to block out the direct light from a star to help search for giant planets and nearby super-Earths.

The second generation will feature interferometers, coronagraphs and other equipment to better analyze the light reflected off these exoplanets. These missions could reveal what the planets might look like, and what they might have in their atmospheres or on their surfaces. At the same time, there will likely be coronagraphic cameras on extremely large ground-based telescopes.

After these projects, future missions could search for more potentially habitable planets either by peering at more distant stars more than 50 parsecs away or at rocky moons of giant planets seen in the habitable zones of nearby stars. The follow-up missions also could deeply investigate any exoplanets that display potential signs of life.

Such missions will require much larger arrays in space - for instance, taking a 100-pixel image of a planet twice the width of Earth some 16.3 light years away would require the elements making up a space telescope array to be more than 43 miles apart.

Such pictures of exoplanets could make out details such as rings, clouds, oceans, continents, and perhaps even hints of forests or savannahs. Long-term monitoring could reveal seasonal shifts, volcanic events, and changes in cloud cover. One might even detect the presence of moons by shadows they project on the planets.

More sensitive instruments could hunt for the wavelengths of infrared light associated with carbon dioxide, which could tell a lot about the atmosphere.

Beyond conventional signs of life as we know it, such as oxygen in atmospheres, another type of signal could be "technosignatures," features that cannot be explained simply by complex organic chemistry. Technosignatures could include laser light, chlorofluorocarbon gases, or even artificial constructions.

"Looking for aliens is philosophically important - it would tell us what is essential in the human condition," Schneider said.

However, if scientists actually detect signs of life, it will frustratingly take many centuries before humanity can realize the hope of seeing what these aliens might actually look like, Schneider and his colleagues explained.

"It is very disappointing," Schneider said.