In 1992, astronomers discovered
three objects roughly the size of Earth orbiting another star, the first known
exoplanets. No one expected life on those objects because the star was a
pulsar, the remains of a star that blew up as a supernova, and the “planets”
had actually formed from the debris of that explosion.
Three years later, astronomers
found the first true exoplanets orbiting the sun-like star 51 Pegasi. Now, the
NASA Exoplanet Archive lists 4113 confirmed exoplanets with more than 3600
exoplanet candidates awaiting confirmation. Astronomers believe that we have
only touched the tip of the exoplanet iceberg. Data suggests that our Milky Way
galaxy alone contains some two hundred billion planets. As of now, there’s no
solid evidence suggesting that life exists on any of them.
But some scientists believe that we
already found life on another planet, one much closer to home. In 1976, NASA
landed twin spacecraft on Mars, Viking 1 and 2. Each included automated
laboratories designed to search for microscopic life on the Red Planet.
Both craft, which landed 4000 miles
apart, included a simple test called the Labeled Release experiment. It added a
nutrient broth to a small amount of Martian soil and checked to see if any
metabolic byproducts, like carbon dioxide, were released. Every test by both
landers reported positive results. However, the other experiments on both
landers found no organic chemicals, which seemed to preclude any lifeforms.
Since then, most scientists decided that some odd chemistry in the Martian soil
falsely mimicked those life signs.
Viking Lander, credit NASA
But not all scientists. Gilbert Levin was the principal
investigator for the Labeled Release experiment for both landers. In a recent
article in Scientific American, he wrote “The Viking LR (experiment)
sought to detect and monitor ongoing metabolism, a very simple and fail-proof
indicator of living microorganisms. Several thousand runs were made, both
before and after Viking, with terrestrial soils and microbial cultures, both in
the laboratory and in extreme natural environments. No false positive or false
negative result was ever obtained. This strongly supports the reliability of
the LR Mars data.”
It may be
decades or centuries before we confirm life on an exoplanet, if we ever do. But
we may have already discovered life on another planet, right next door.
