At least we now have a number. It happens to be completely huge.
What is more, this is likely the minimum number of planets that can
be terraformed and are likely been terraformed or have been.
In our own solar system Earth has long been effectively terraformed
and is now in the process of been redone after the Pleistocene
nonconformity some 13,900 years ago.
On top of that Venus was likely ejected from Jupiter quite recently
and now needs to be bombarded with volatiles to cool down the crust
and provide enough water and carbon. We will eventually get the job.
Otherwise subsurface colonies are plausible on the moons of Jupiter
and Saturn if needed for any reason. The same technology supports
subsurface establishments on Mercury, the Moon and on Mars.
In short, our solar system can be reasonably infested with life.
Kepler telescope:
Earth-sized planets 'number 17bn'
By Jason Palmer
8 January 2013
Astronomers say that one in six stars hosts an Earth-sized planet
in a close orbit - suggesting a total of 17 billion such planets in
our galaxy.
The result comes from
an analysis of planet candidates gathered by Nasa's Kepler space
observatory.
The Kepler scientists
also announced 461 new planet candidates, bringing the satellites'
total haul to 2,740.
Their findings were
announced at the 221st meeting of the American Astronomical
Society in California.
Transit
Since its launch into
orbit in 2009, Kepler has stared at a fixed part of the sky, peering
at more than 150,000 stars in its field of view.
It detects the minute
dip in light coming from a star if a planet passes in front of it, in
what is called a transit.
But it is a tricky
measurement to make, with the total light changing just tiny
fractions of a percent, and not every dip in light is due to a
planet.
So Francois Fressin of
the Harvard-Smithsonian Center for Astrophysics - who discovered
the first Earth-sized planets set about trying to find out not
only which Kepler candidates might not be planets, but also which
planets might not have been visible to Kepler.
"We have to correct for two things - first [the Kepler
candidate list] is incomplete," he told BBC News.
"We only see the
planets that are transiting their host stars, stars that happen to
have a planet that is well-aligned for us to see it, and [for each of
those] there are dozens that do not.
"The second major
correction is in the list of candidates - there are some that are not
true planets transiting their host star; they are other astrophysical
configurations."
These might include,
for example, binary stars, where one star orbits another, blocking
some of the light as the stars transit each other.
"We simulated all
the possible configurations we could think of - and we found out that
they could only account for 9.5% of Kepler planets, and all the rest
are bona fide planets," Dr Fressin explained.
The results suggest
that 17% of stars host a planet up to 1.25 times the size of the
Earth, in close orbits lasting just 85 days or fewer - much like the
planet Mercury.
That means our Milky
Way galaxy hosts at least 17 billion Earth-sized planets.
In the zone
Even as Dr Fressin
reported an analysis of the most recent Kepler catalogue, it was
increased substantially by results reported by Christopher Burke of
the Seti Institute.
Dr Burke announced 461
new candidate planets, a substantial fraction of which were
Earth-sized or not much larger - planets that have until now been
particularly difficult to detect.
"What's
particularly interesting is four new planets - less than twice the
size of Earth - that are potentially in the habitable zone, the
location around a star where it could potentially have liquid water
to sustain life," Dr Burke told BBC News.
One of the four,
dubbed KOI 172.02, is a mere 1.5 times the size of the Earth and
around a star like our own Sun - perhaps as near as the current data
allow to finding an "Earth 2.0".
"It's very
exciting because we're really starting to pick up the sensitivity to
these things in the habitable zone - we're just really getting to the
frontier of potentially life-bearing planets."
William Borucki, the
driving force behind and principal investigator on the Kepler
mission, said he was "delighted" by the fresh batch of
results.
"The most
important thing is the statistics - not to find one Earth but to find
100 Earths. That's what we'll be seeing as the years go on with the
Kepler mission, because it was designed to find many Earths."
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