Scientists who think about the possibility of
extraterrestrial life need data to estimate those possibilities. Because Earth
is the one and only known example of a life-bearing planet, it seems logical,
therefore, to use ours as a model for life-bearing planets. The first, best
place to hunt for alien life would be on planets like Earth
And this is where data is needed. Just how many
Earth-like planets exist in our Milky Way galaxy? Fortunately, we have reams of
data on planets orbiting other stars from the Kepler space telescope. It spent
more than nine and a half years doing nothing but searching for extrasolar
planets. It discovered more than 2,600 planets with nearly 3,000 still awaiting
confirmation. That’s a lot of data.
One thing astronomers learned from a statistical analysis
of that data is that Earth-like planets are rather common. Twenty billion
sun-like stars call the Milky Way home, and Kepler teaches us that one in four
of them have planets roughly the size of Earth orbiting in the habitable zone,
where, as on Earth, liquid water can exist. That’s five billion Earth-like
planets in the Milky Way. And that’s not even counting the billions of other
stars of different sizes than our sun that also possess Earth-sized planets in
their habitable zones.
Artist depiction of
a habitable exoplanet. Credit NASA-JPL
That sure sounds like the potential exists for a galaxy
teeming with life.
Now, astronomers want to check for the actual existence
of alien life. We can’t yet send probes to examine those planets. But we can examine
the atmosphere of an alien planet for life-supporting gases. According to Eric B. Ford, professor of
astronomy and astrophysics at Penn State, “Scientists are particularly
interested in searching for biomarkers – molecules indicative of life – in the
atmospheres of roughly Earth-size planets that orbit in the ‘habitable zone’ of
sun-like stars.”
With five billion planets to examine, the search might
be tedious, but the payoff will be the most amazing scientific discovery ever.
And it appears to be only a matter of time before we discover alien life.
The map shows the sky at 10:00 early in the month, 9:00 in the middle of the month, and 8:00 at the end of the month. Map produced using Night Vision star mapping software.
On or about the first Tuesday of each month, I write an
astronomy-related column piece for the Oklahoman newspaper. On the following
day, I post that same column to my blog page.
