that are in a zone potentially compatible with life:
Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f and Earth
(named left to right; except for Earth, these are artists' renditions).
that familiar 'science-fiction' trope,
that kitschy fantasy,
that CGI nightmare,
has become a matter of serious discussion,
a "risk factor", a "scenario"...
How has ET gone from sci-fi fairytale to a serious scientific endeavor,
Because, following a string of remarkable discoveries over the past two decades, the idea of alien life is not as far-fetched as it used to seem.
Discovery now seems inevitable and possibly imminent...
It's just chemistry
While life is a special kind of complex chemistry, the elements involved are nothing special:
Habitable planets seem to be common too.
The first planet beyond our Solar System was discovered in 1995. Since then astronomers have catalogued thousands.
Based on this catalogue, astronomers from the University of California, Berkeley worked out there could be as many as 40 billion Earth-sized exoplanets in the so-called "habitable zone" around their star, where temperatures are mild enough for liquid water to exist on the surface.
There's even a potentially Earth-like world orbiting our nearest neighboring star, Proxima Centauri. At just four light years away, that system might be close enough for us to reach using current technology.
With the Breakthrough Starshot project launched by Stephen Hawking in 2016, plans for this are already afoot.
Life is robust
It seems inevitable other life is out there, especially considering that life appeared on Earth so soon after the planet was formed.
The oldest fossils ever found here are 3.5 billion years old, while clues in our DNA suggest life could have started as far back as 4 billion years ago, just when giant asteroids stopped crashing into the surface.
Our planet was inhabited as soon as it was habitable - and the definition of "habitable" has proven to be a rather flexible concept too.
Life survives in all manner of environments that seem hellish to us:
Tantalizingly, some of these conditions seem to be duplicated elsewhere in the Solar System.
Snippets of promise
Mars was once warm and wet, and was probably a fertile ground for life before the Earth.
Besides Earth and Mars, at least two other places in our Solar System might be inhabited.
Russian billionaire Yuri Milner has been so enthused by this prospect, he wants to help fund a return mission.
A second genesis?
A discovery, if it came, could turn the world of biology upside down.
A second independent "tree of life" would mean that the rapid appearance of life on Earth was no fluke.
Life must abound in the universe...
It would greatly increase the chances that, somewhere among those billions of habitable planets in our galaxy, there could be something we could talk to.
Perhaps life is infectious
If, on the other hand, the discovered microbes were indeed related to us that would be a bombshell of a different kind:
When a large meteorite hits a planet, the impact can splash pulverized rock right out into space, and this rock can then fall onto other planets as meteorites.
Life from Earth has probably already been taken to other planets - perhaps even to the moons of Saturn and Jupiter. Microbes might well survive the trip.
In 1969, Apollo 12 astronauts retrieved an old probe that had sat on the Moon for three years in extreme cold and vacuum - there were viable bacteria still inside.
As Mars was probably habitable before Earth, it's possible life originated there before hitchhiking on a space rock to here. Perhaps we're all 'Martians'...
Even if we never find other life in our Solar System, we might still detect it on any one of thousands of known exoplanets.
It is already possible to look at starlight filtered through an exoplanet and tell something about the composition of its atmosphere; an abundance of oxygen could be a telltale sign of life.
A testable hypothesis
The James Webb Space Telescope, planned for a 2021 launch, will be able to take these measurements for some of the Earth-like worlds already discovered.
Just a few years later will come space-based telescopes that will take pictures of these planets directly.
Using a trick a bit like the sun visor in your car, planet-snapping telescopes will be paired with giant parasols called star-shades that will fly in tandem 50,000 kilometers away in just the right spot to block the blinding light of the star, allowing the faint speck of a planet to be captured.
The color and the variability of that point of light could tell us the length of the planet's day, whether it has seasons, whether it has clouds, whether it has oceans, possibly even the color of its plants.
The ancient question "Are we alone?" has graduated from being a philosophical musing to a testable hypothesis.
We should be prepared for an answer...