[meteorite-list] New System Would Assess Odds of Life on Other Worlds

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 22 Nov 2011 14:13:33 -0800 (PST)
Message-ID: <201111222213.pAMMDXWY013217_at_zagami.jpl.nasa.gov>

http://news.wsu.edu/pages/publications.asp?Action=Detail&PublicationID=28889&TypeID=1

New system would assess odds of life on other worlds
By Robert Strenge
Washington State University
November 21, 2011

PULLMAN, Wash. - Within the next few years, the number of planets
discovered in orbits around distant stars will likely reach several
thousand or more. But even as our list of these newly discovered
"exoplanets" grows ever-longer, the search for life beyond our solar
system will likely focus much more narrowly on the relatively few of
these new worlds which exhibit the most Earth-like of conditions.
 
For much of the scientific community, the search for alien life has long
been dominated by the notion that our own planet serves as the best
model of conditions best suited to the emergence of life on other
worlds. And while there's anundeniable logic to seeking life in the same
sort of conditions in which you already know it to be successful, there
are scientists like Dirk Schulze-Makuch, an astrobiologist with the
Washington State University School of Earth and Environmental Sciences
and Abel Mendez, a modeling expert from the University of Puerto Rico at
Aricebo, who also see such a model as the product of a potentially
limiting form of earthling-biased thinking.
 
To Schulze-Makuch and his nine fellow authors - an international working
group representing, NASA, SETI,the German Aerospace Center, and four
universities - the search for life on other worlds is really driven by
two questions.
 
"The first question is whether Earth-like conditions can be found on
other worlds, since we know empirically that those conditions could
harbor life," Schulze-Makuch said. "The second question is whether
conditions exist on exoplanets that suggest the possibility of other
forms of life, whether known to us or not."
 
In a paper to be published in the December issue of the journal
Astrobiology, Schulze-Makuch and his co-authors propose a new system for
classifying exoplanets using two different indices - an Earth Similarity
Index (ESI) for categorizing a planet's more earth-like features and a
Planetary Habitability Index (PHI) for describing a variety of chemical
and physical parameters that are theoretically conducive to life in more
extreme, less-earthlike conditions.
 
Similarity indices provide a powerful tool for categorizing and
extracting patterns from large and complex data sets. They are
relatively quick and easy to calculate and provide a simple quantitative
measure of departure from a reference state, usually on a scale from
zero to one. They are used in mathematics, computer imaging, chemistry
and many other fields.
 
The two indices proposed by the group mark the first attempt by
scientists to categorize the many exoplanets and exomoons that are
expected to be discovered in the near future in accordance with their
potential to harbor some form of life.
 
"As a practical matter, interest in exoplanets is going to focus
initially on the search for terrestrial, Earth-like planets," said
Schulze-Makuch. "With that in mind, we propose an Earth Similarity Index
which provides a quick screening tool with which to detect exoplanets
most similar to Earth."
 
But the authors believe that focusing exclusively on earth-based
assumptions about habitability may well be too restrictive an approach
for capturing the potential variety of life forms that, at least in
principle, may also exist on other worlds.
 
"Habitability in a wider sense is not necessarily restricted to water as
a solvent or to a planet circling a star," the paper's authors write.
"For example, the hydrocarbon lakes on Titan could host a different form
of life. Analog studies in hydrocarbon environments on Earth, in fact,
clearly indicate that these environments are habitable in principle.
Orphan planets wandering free of any central star could likewise
conceivably feature conditions suitable for some form of life."
 
The paper's authors concede that attempting to rate the probability that
life of some unknown form could exist on any given world is an
intrinsically more speculative endeavor. But the alternative, they
argue, is to risk overlookingpotentially habitable worlds by using
overly restrictive assumptions.
 
"Our proposed PHI is informed by chemical and physical parameters that
are conducive to life in general," they write. "It relies on factors
that, in principle, could be detected at the distance of exoplanetsfrom
Earth, given currently planned future (space) instrumentation."
 
The paper, entitled A Two-Tiered Approach to Assessing the Habitability
of Exoplanets, was written by Alfonso Davila, of SETI; Alberto Fairen,
of NASA; Abel Mendez of the University of Puerto Rico at Aricebo; Philip
von Paris, of the German Aerospace Center; David Catling, of the
University of Washington; Louis N. Irwin, of the University of Texas-El
Paso, and Marina Resendes de Sousa Antonia, Carol Turse, Grayson
Boyer and Dirk Schulze-Makuch, all of Washington State University.
 
-----------------------
 
Source:
Dirk Schulze-Makuch, WSU School of Earth & Environmental Science,
509-335-1180, dirksm at wsu.edu
Received on Tue 22 Nov 2011 05:13:33 PM PST