Kepler’s Exoplanets: A map of the locations of exoplanets, of
various masses, in the Kepler field of view. 1,235 candidates are
plotted (NASA/Wendy Stenzel)
Just in case you haven’t heard, our galaxy appears to be teeming with small worlds,
many of which are Earth-sized candidate exoplanets and dozens appear to
be orbiting their parent stars in their “habitable zones.”
Before Wednesday’s Kepler announcement, we knew of just over
500 exoplanets orbiting stars in the Milky Way. Now the space telescope
has added another 1,235 candidates to the tally — what a difference 24 hours makes.
Although this is very exciting, the key thing to remember is that we are talking about exoplanet candidates,
which means Kepler has detected 1,235 exoplanet signals, but more work
needs to be done (i.e. more observing time) to refine their orbits,
masses and, critically, to find out whether they actually exist.
But, statistically speaking, a pattern is forming. Kepler has opened our eyes to the fact our galaxy is brimming with small worlds — some candidates approaching Mars-sized dimensions!
Earth-Brand™ Life
Before Kepler, plenty of Jupiter-sized worlds could be seen,
but with its precision eye for spotting the tiniest of fluctuations of
star brightness (as a small exoplanet passes between Kepler and the
star), the space telescope has found that smaller exoplanets outnumber
the larger gas giants.
Needless to say, all this talk of “Earth-sized” worlds (and the much-hyped “Earth-like” misnomer)
has added fuel to the extraterrestrial life question: If there’s a
preponderance of small exoplanets — some of which orbit within the
“sweet-spot” of the habitable zones of their parent stars — could life as we know it (or Earth-Brand™ Life as I like to call it) also be thriving there?
Before I answer that question, let’s turn back the clock to Sept. 29, 2010, when, in the wake of the discovery of the exoplanet Gliese 581 g,
Steven Vogt, professor of astronomy and astrophysics at University of
California Santa Cruz, told Discovery News: “Personally, given the
ubiquity and propensity of life to flourish wherever it can, I would say
that the chances for life on [Gliese 581 g] are 100 percent. I have
almost no doubt about it.”
Impossible? Or 100 Percent?
As it turns out, Gliese 581 g may not actually exist — an
excellent example of the progress of science scrutinizing a candidate
exoplanet in complex data sets as my Discovery News colleague Nicole
Gugliucci discusses in “Gliese 581g and the Nature of Science” — but why was Vogt so certain that there was life on Gliese 581 g? Was he “wrong” to air this opinion?
Going to the opposite end of the spectrum, Howard Smith, an
astrophysicist at Harvard University, made the headlines earlier this
year when he announced, rather pessimistically, that aliens will
unlikely exist on the extrasolar planets we are currently detecting.
“We have found that most other planets and solar systems are
wildly different from our own. They are very hostile to life as we know
it,” Smith told the UK’s Telegraph.
Smith made comparisons between our own solar system with the interesting HD 10180 system, located 127 light-years away.
HD 10180 was famous for a short time as being the biggest star system
beyond our own, containing five exoplanets (it has since been trumped by
Kepler-11, a star system containing six exoplanets as showcased in
Wednesday’s Kepler announcement).
One of HD 10180′s worlds is thought to be around 1.4
Earth-masses, making it the smallest detected exoplanet before
yesterday. Alas, as Smith notes, that is where the similarities end; the
“Earth-sized” world orbiting HD 10180 is too close to its star, meaning
it is a roasted exoplanet where any atmosphere is blasted into space by
the star’s powerful radiation and stellar winds.
The Harvard scientist even dismissed the future Kepler
announcement, pointing out that upcoming reports of habitable exoplanets
would be few and far between. “Extrasolar systems are far more diverse
than we expected, and that means very few are likely to support life,”
he said.
Both Right and Wrong
So what can we learn about the disparity between Vogt and
Smith’s opinions about the potential for life on exoplanets, regardless
of how “Earth-like” they may seem?
Critically, both points of view concern Earth-Brand™ Life (i.e.
us and the life we know and understand). As we have no experience of
any other kind of life (although the recent eruption of interest over
arsenic-based life is hotly debated), it is only Earth-like life we can
realistically discuss.
We could do a Stephen Hawking and say that all kinds of life is possible anywhere in the cosmos,
but this is pure speculation. Science only has life on Earth to work
with, so (practically speaking) it’s pointless to say a strange kind of
alien lifeform could live on an exoplanet where the surface is molten
rock and constantly bathed in extreme stellar radiation.
If we take Hawking’s word for it, Vogt was completely justified
for being so certain about life existing on Gliese 581 g. What’s more,
there’s no way we could prove he’s wrong!
But if you set the very tight limits on where we could find
Earth-like life, we are suddenly left with very few exoplanet candidates
that fit the bill. Also, just because an Earth-sized planet might be
found in the habitable zone of its star, doesn’t mean it’s actually
habitable. There are many more factors to consider. So, in this case,
Smith’s pessimism is well placed.
Regardless, exoplanet science is in its infancy and the
uncertainty with the “is there life?” question is a symptom of being on
the “raggedy edge of science,” as Nicole would say.
We simply do not know what it takes to make a world habitable for any
kind of life (apart from Earth), but it is all too tempting to speculate
as to whether a race of extraterrestrials, living on one of Kepler’s
worlds, is pondering these same questions.
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/dqvWnKM2lCA/chances-of-exoplanet-life-impossible-or.html
Chances of Exoplanet Life 'Impossible'? Or '100 percent'?
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