I cannot imagine any news as exciting and profound as
finding extraterrestrial life. If we find it---or should I say when we find it---we will finally have
an undisputable proof that we are not alone and indeed our universe may be
teeming with life.
In that context, the recent finding of a system of seven planets
around a star called Trappist-1, which is “only” 40 light-years away, is quite
significant. Three of these planets are orbiting in the so-called “Goldilocks”
zone, not too far from the star they are circling to be frozen wasteland, and yet
not too close that any water on it would boil and evaporate. Like, earth, in other words. So, if we assume
that water is necessary for any life to exist, and that is not too bad an
assumption, there could be life on one or more of these planets. The problem is
how can we know one way or another.
For many years, the plan was to listen to the
electromagnetic signals coming form space and see if there is a pattern that
would indicate that they are being sent by some intelligent creature. After
listening for over 50 years (under a program called SETI---Search for
Extraterrestrial Intelligence), we haven’t found any such signals. Also, many
believe that this is not the way we will detect intelligence. Given how long
universe has been around, it is highly unlikely that the extraterrestrial
beings, if they exist, are at the same stage of civilization as us. They could
be much more advanced, and don’t rely on electromagnetic signals for
communications, or much more primitive.
So we need to find other methods. It would be great to send
a probe to one of these exoplanets, but the distances are just too great. At 40
light years, it would take that many years for a probe travelling at the speed
of light to reach there, and equal number of years to send back signal. That is
absolutely minimum amount of time---the actual time would be much greater. We
would all be dead by then.
There are stars that are not that far, and in fact a star
only 4 light years away, Proxima Centauri, a companion of the more famous Alpha
Centauri, has a planet worth examining. A very wealthy Russian entrepreneur is
funding a project to investigate the feasibility of sending a series of probes
to take a closer look at that planet. These probes would accelerate close to
the speed of light using earth-based lasers and “light sails” that catch those
beams and accelerate. Such an audacious endeavor is still considered an
extremely challenging and expensive. Even for a billionaire.
Instead of going there, one can look at these candidate-for-harboring-life
planets from here and see what is going on. Of course, one would need extremely
powerful telescopes, like the James Webb Space Telescope currently under
construction, and, besides, what would you look at? A very advanced
civilization would construct something on a huge scale to, say, harvest energy
from the star. Such a structure may be visible from great distances; otherwise
we are out of luck. On the other hand, a spectroscopic analysis of these
planets’ atmosphere may yield some tantalizing clues, in form of biosignature
gases. That alone would not prove that life does
exists, but indicate that life could exist.
My feeling is that in the short term, we are better off
focusing on finding life closer by---on our fellow planets circling sun or one
of their moons. Of the planets, Mars has the highest likelihood of harboring
life. Even if nothing is alive now, finding evidence that life did exist in the past would be a great
discovery.
Then there is the possibility of finding something currently alive on one of the moons
circling Jupiter or Saturn. The two most likely candidates are Enceladus,
circling Saturn, or Europa, which orbits Jupiter.
Europa has a crust of frozen water with a high probability
of a liquid ocean underneath. Enceladus is similar but has become a more exciting
target because Cassini spacecraft orbiting Saturn recently saw icy jets spewing
from its surface, much like geysers. That indicates there may be liquid water
underneath and hydrothermal vents. This is significant because on earth,
hydrothermal vents are an important story in the emergence of life. At many
locations in our ocean, scientists have found a whole new ecosystem that is
based on energy from these vents and not sun. The same can be true on Enceladus.
To determine if life truly exists on Europa or Enceladus, we
may need to drill through the icy surface and peek inside, which is hard to do.
However, the icy plumes of Enceladus provide a simpler way. Collecting samples
from the plume and testing for building blocks of life may give a strong
indication of whether this planet harbors something alive. Such a test may happen in our
lifetimes---NASA is thinking of sending a probe as soon as within the next five
years.
So, it is quite likely that we may discover that we are not
alone, as soon as in the next few years. How great would that be?
