From: LARRY KLAES (ljk4@msn.com)
Date: Wed May 15 2002 - 07:23:17 PDT
The original article can be found on SFGate.com here:
http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2002/05/13/MN185465.DTL
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Monday, May 13, 2002 (SF Chronicle)
Airborne search for life on Venus
Keay Davidson, Chronicle Science Writer
Is there life in "hell"?
It's an old question being dusted off and re-examined in a new way by
space scientists, who jokingly use the label for hellish Venus, our
nearest planetary neighbor.
Glowing like a brilliant diamond at sunset, Venus is the brightest of the
five "naked-eye" planets, all now grouped in a spectacular western-sky
alignment. For space scientists, though, earthly views only hint at what
may be lurking beneath the planet's thick cover of white clouds.
The heat on Venus -- close to 900 degrees Fahrenheit -- far exceeds the
heat within a standard domestic oven. Surface air pressure is about 90
times greater than Earth's. Immense clouds of acid race overhead at
hurricane speed.
Four decades ago this year, most space scientists ruled out the
possibility of life on Venus, the second world from the sun. In December
1962 -- just as the Cuban missile crisis was winding down, easing fears of
earthly annihilation via nuclear war -- the Mariner 2 space probe radioed
to Earth an ominous message.
GREENHOUSE EFFECT MODEL
It seemed our "sister" planet Venus, victim of a runaway greenhouse
effect, had beaten us to extinction, offering what some still consider to
be a reasonably close approximation of what Earth may eventually be like.
Now, a few space scientists are taking a second look at the life-on-Venus
question. At an April astrobiology conference at NASA's Ames Research
Center in Mountain View, two Texas scientists proposed a robotic search
for microbes floating in the Venusian atmosphere.
"Surface conditions of Venus are now too extreme for life as known on
Earth, but early in the solar system when the sun was fainter, Venus likely had
abundant water and favorable conditions for the origin of life, or may
have provided a life-friendly environment for microbes dislodged from
Earth" by asteroid impacts, Dirk Schulze-Makuch and Louis N. Irwin of the
University of Texas at El Paso wrote in a paper have submitted for peer
review.
LIFE ON VENUS THINKABLE
The idea draws support from a small "back-to-Venus" movement among space
scientists, including Charles Cockell, formerly of NASA-Ames and Stanford
University. Cockell, now with the British Antarctic Survey, wrote a paper
titled "Life on Venus" for the journal Planetary and Space Sciences in 1999.
Another Venus enthusiast is David Grinspoon, co-author of a major 1998
study, "Venus," published by Yale University Press and a popular book,
"Venus Revealed" (1997).
"Venus should not be declared off limits in the search for alien life,"
Grinspoon, principal scientist in the department of space studies at
Southwest Research Institute in Boulder, Colo., said in an e-mail exchange
with The Chronicle. "In my (distinctly minority) opinion, Venus is at
least as likely to harbor life, at present, (as) Mars."
Schulze-Makuch and Irwin are both members of NASA's Europa Focus Group.
Their article on the possibility of organisms in the hypothetical ocean of
the Jovian moon Europa appears in the Spring issue of Astrobiology.
Schulze-Makuch obtained his doctorate in geosciences at the University of
Wisconsin. Irwin, a neurobiologist who received his doctorate at the
University of Kansas, is former chairman of biological sciences at the El
Paso campus.
They cite several reasons for focusing on Venus:
EVIDENCE OF WATER
-- Indirect evidence suggests that Venus had large, watery oceans early in
its existence, when it was much cooler. Such oceans may have been
cauldrons for evolution of early microbial life forms. Later, when the
planet grew hotter, hardier species of microbes might have retreated to
the cool upper atmosphere.
"It is now considered likely that a proto-ocean existed on Venus for a
limited time early in its history," Schulze-Makuch and Irwin wrote.
Some supporting evidence has been gleaned from chemical sensors aboard
exploratory spacecraft.
Ordinary water contains two types of hydrogen -- the ordinary "H" in
H2O,referring to hydrogen with a single proton, and its much less common
isotope deuterium, which has a proton and a neutron.
As the Venusian atmosphere warmed billions of years ago, hydrogen and
deuterium molecules vibrated violently, and some escaped into space.
That may have produced a measurably higher ratio of deuterium to hydrogen,
which, according to some interpretations, could be taken as evidence of
the past presence of water on Venus.
HARSH SURVIVAL
-- Since Mariner 2, scientists have learned that microbes can withstand
much worse environments than previously thought. For example, on the ocean
floor, exotic-looking creatures hang around ocean-bottom hot springs,
where they are nourished by acidic chemicals that would kill surface animals.
So-called "extremophile" bacteria endure the intense radiation within a
nuclear reactor and the high pressure within subterranean rocks.
Indeed, Venusian bugs might enjoy a fairly cozy life, Schulze-Makuch and
Irwin speculate. The planet's permanent cloud layer is more stable than
clouds in Earth's atmosphere. Microbes might also be nourished by sulfuric
acid, like some of their counterparts on Earth.
Schulze-Makuch and Irwin propose sending a space robot through the upper
Venusian atmosphere. There, it would unveil a panel of "aerogel," an
extremely lightweight substance that materials scientists call "solid smoke."
It's so low-density as to be almost transparent. The aerogel could "catch"
microbes like a catcher's mitt, which the spaceship could haul back to
Earth for analysis.
There's a precedent. The Stardust space robot is now hauling a panel of
aerogel toward a rendezvous with Comet Wild in January 2004. If all goes
as planned, the aerogel will catch cometary particles to be brought back
to Earth by 2006.
RESEARCH BALLOONS
Might Venusian microbes vaporize on hitting the aerogel? If that's a risk,
then there's a safer alternative: have a spaceship release balloons into
the Venusian atmosphere. There, they could drift for weeks, seeking
microbes, examining them and transmitting the findings back to Earth.
Some scientists react warily to talk of Venusian microbes. Geoscientist
and Mars expert Norman Sleep of Stanford cautions there is no terrestrial
analogy for microbes that live their entire lives in a planetary
atmosphere and never touch ground.
"Clouds on the Earth are not green," he said. "There are no Earth microbes
that pass their whole life cycle in the air and clouds."
FURTHER STUDY NEEDED
Dale Cruikshank, a noted NASA-Ames expert on the quest for organic
molecules in space, says: "The authors' ideas are not outlandish, but some
(further) lab work would be useful before committing to send a $300
million- plus probe to Venus (to seek life)."
"We just don't know enough about Venus' surface and its history to develop
a case for or against liquid water," Cruikshank said in an e-mail
interview. "In the Venus atmosphere, there may indeed be a 'habitable
zone' where the pressure and temperature are clement, but the amount of
water in that (atmospheric) layer is still vastly less than in a zone of
comparable temperature and pressure on Earth."
Schulze-Makuch replied that life's limits are unknown, even on Earth. Lab
experiments, he said, have shown that microbes can withstand air pressures
500 times as great as the pressure at Earth's surface.
Even if the Venusian atmosphere is uninhabited now, some scientists argue
that NASA still has some down-to-Earth reasons to take a look at what
happened on the second planet from the sun.
By robotically studying the Venusian atmosphere, Cockell said, we might
learn "why it ended up with this runaway greenhouse effect, which will
eventually happen to the Earth in maybe 2 to 3 billion years as the sun
expands and heats up."
E-mail Keay Davidson at kdavidson@sfchronicle.com.
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Copyright 2002 SF Chronicle
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