Scientists ponder plant life on extrasolar planets
dool...@rock.com
to imagine weird creatures like Jar Jar Binks, Chewbacca, and, if
those are not bizarre enough, maybe even the pointy-eared Vulcan,
Spock, of Star Trek fame.
But scientists seeking clues to life on extrasolar planets are
studying various biosignatures found in the light spectrum leaking out
to Earth to speculate on something more basic and essential than the
musical expertise of Droopy McCool. They are speculating on what kind
of photosynthesis might occur on such planets and what the extrasolar
plants might look like.
Paint it black
It could be the plants are black, says Robert Blankenship, Ph.D.,
Lucille P. Markey Distinguished Professor in Arts & Sciences at
Washington University in St. Louis. But it all depends on what size
and light intensity of star - or sun - the planet feeds off, and the
extrasolar planet's atmospheric chemistry.
Plants on Earth are green because of chlorophyll, which harnesses the
energy of the sun to make sugars for metabolism. But our plants aren't
completely efficient - they waste a little bit of light.
"Ideally, what you want is a black molecule that absorbs all of the
light," Blankenship said. "There could be another system developed on
an extrasolar planet where plants are completely black if the spectrum
of light that's available to organisms is different from the light
available to organisms on Earth.
"Then, for sure, the plants will have different types of pigments
tuned to absorb those wavelengths of light available on the other
world."
Blankenship is co-author of two papers recently published in the
journal Astrobiology. The papers detail the kinds of clues that
researchers are looking for and explore theories of what these other
worlds might be like.
Blankenship is part of a NASA working group based at the Jet
Propulsion Laboratory called the Virtual Plant Laboratory. He and his
colleagues are studying light that comes from stars and extrasolar
planets to infer their composition. They can see clues that suggest
the presence of water vapor, oxygen or carbon dioxide, for instance.
One key biosignature is the existence of disequilibrium - the
simultaneous presence of things that should not coexist on a dead
world. The presence of methane and oxygen together on an extrasolar
planet, for instance, would be a strong smoking gun for the possible
existence of life.
Life on the edge
They also are looking into the "red edge" effect. Seen at 700
nanometers out, beyond the limit of normal human vision, this
reflectance spectrum is a signature of the fact that there is very
intense chlorophyll absorption going on.
A third way to find extrasolar planets is to look for wobbly stars. As
a planet - especially a massive planet - goes around the star it
causes the star to wobble a bit. The Hubble Space Telescope has found
wobbly stars.
NASA has two missions in the works designed to find possible evidence
for life on extrasolar planets. One features a space-based instrument
that will make measurements in the near infrared region; the other
measures longer wavelengths to get good biosignatures for things like
methane and oxygen.
Blankenship said that speculation about the natural world of
extrasolar planets is at this point speculative, but that it is
important to get a handle on what the possibilities are, how things
might look, what measurements to make and what experiments to do to
conclude whether there is life on another world.
"I think that everyone thinks that there are Earth-like ones out
there, but very few have been detected so far," he said. "One of the
things that I've learned is that you have to free your mind from the
constraints of thinking that life elsewhere has to be like life
here."
Energy on any world is critical, he said, and there has to be some
system on an extrasolar planet that involves light capture and
storage.
"When you consider another world you've got to find that life there
depends on photosynthesis in the broad sense, but it's probably not
identical to the way that photosynthesis works here," Blankenship
said. "You'll need molecules that absorb light that are highly
colored, but whether they have the same green colors we know on Earth
is unlikely."
Similarly, on Earth life depends on DNA and proteins. But out there?
"I don't think that there is anything magical about DNA in that it has
to be the same out there as here," he said. "But there has to be some
sort of information-carrying molecule - again, highly unlikely the
same as our DNA - that has information coded in a way that allows the
ability to transfer information. We've got proteins that do all of the
dirty work in the cell in terms of chemistry. You can imagine a
different sort of molecule that would do that sort of chemistry. Maybe
it would have the same protein backbone with peptide bonds and so
forth. But there's no reason to think it would be comprised of the
same 20 amino acids that we have on Earth. It's intriguing to
speculate, and I think we'll know more when we get more clues."
BradGuth
> "I don't think that there is anything magical about DNA in that it has
> to be the same out there as here," he said. "But there has to be some
> sort of information-carrying molecule - again, highly unlikely the
> same as our DNA - that has information coded in a way that allows the
> ability to transfer information. We've got proteins that do all of the
> dirty work in the cell in terms of chemistry. You can imagine a
> different sort of molecule that would do that sort of chemistry. Maybe
> it would have the same protein backbone with peptide bonds and so
> forth. But there's no reason to think it would be comprised of the
> same 20 amino acids that we have on Earth. It's intriguing to
> speculate, and I think we'll know more when we get more clues."
I agree, that a water+carbon limited form of life isn't all that
essential, but then either is this water+cabon life terrestrial
limited. For all we know, God could be made of silly puddy.
Earth's form of ETI is primarily in the format of bugs and the likes
of diatoms, and especially dependent of those nifty diatoms. Humans
don't hardly account for much of the total span or scope of life
that's available, most of which has been a whole lot smarter than us
humans, and would otherwise get along just fine and dandy without our
ever having been here.
Lets hope the next available planet or moon that's in any way capable
of sustaining intelligent other life has no such supposedly
intelligent humans of their own.
-
Brad Guth
BradGuth
>Lucille P. Markey Distinguished Professor in Arts & Sciences at
>Washington University in St. Louis. But it all depends on what size
>and light intensity of star - or sun - the planet feeds off, and the
>extrasolar planet's atmospheric chemistry.
>"Ideally, what you want is a black molecule that absorbs all of the
>light," Blankenship said. "There could be another system developed on
>an extrasolar planet where plants are completely black if the spectrum
>of light that's available to organisms is different from the light
>available to organisms on Earth."
I totally agree, that depending upon the spectrum of available energy
as light (much of which is outside the threshold of human vision), the
forms of plant/microbe/animal life should have adapted, as do our
terrestrial diatoms for taking the fullest advantage of the given
energy spectrum that's in charge of illuminating a given environment,
including everything from UV starshine to that of a brown dwarf's
black IR/FIR radiating sun (aka 'hot rock') should do just fine as
long as the local, solar, moon and cosmic dosage of gamma and hard-
Xrays are within the scope of whatever such ET DNA or whatever
alternative can cope with.
How about our best of science wizards pondering on behalf of other
intelligent life that's either evolved or having been one way or
another transported onto intrasolar planets or moons, meaning the
likes of Venus or a few of those interesting Saturn or Jupiter moons
seems every bit as worthy as for any little frozen to death Ceres
dwarf of a planet, and otherwise certainly a whole lot better off than
anything Mars could sustain without imported resources.
At most a planet that's hosting intelligent other life needs merely a
brown dwarf of a sun, or at least having a Saturn+ or Jupiter+ class
of a mother planet from which to draw energy from. In the case of
Venus being of such a newish planetology, chances are that it could
have survived an extended interstellar trek pretty much all by itself,
perhaps bringing along its own icy moon and whatever collection of
complex life that's capable of having survived where most terrestrial
forms of life from Earth simply would never have survived, much less
having evolved into the sorts of life as we know it.
Just because a given planet or moon is not 100% suited to our butt
naked and often dumbfounded usage as is, doesn't exclude such other
orbs from having their own populations of weird or even somewhat
terrestrial forms of survival intelligent other life to behold, much
like there being complex life within terrestrial ice or having been
surviving within certain places similar to being as hot as hell on
Earth, as well as within testy environments under the depths of an
ocean that would just as easily crush your typical submarine that's
accommodating us wussy humans, along with terminating our extremely
frail DNA that hasn't hardly evolved for the better since the last ice
age this planet is ever going to see, that is as long as we're going
to keep putting up with that massive and fast moving moon of ours
that's cruising so close to our home world that's 98.5% fluid and thus
unavoidably affected by those horrific tidal forces at play.
-
Brad Guth