Astrobiology Universe findings

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The Astrobiology Universe

Artist's representation of a human mission to Mars. Image credit:
NASA/ David Mattingly and Pat Rawlings.
By Leslie Mullen, Henry Bortman and Aaron Gronstal
for Astrobiology Magazine
Moffett Field CA (SPX) Apr 30, 2008
The opening speaker at the 2008 Astrobiology Science Conference, Lord
Martin Rees of the University of Cambridge, said that our universe may
just be one of many. Multiple universes could be stacked sideways like
sheets of paper, separated by only a thin margin of space. We would
never know they were there unless we could be awakened to the
existence of that other dimension.
This could have been the theme of the conference. Every morning and
afternoon, nine separate talks were given simultaneously, often just
separated by thin walls through which applause could be heard.
Although aware of these separate astrobiology multiverses,
participants could not attend most sessions due to the constraints of
space and time. Perhaps Lord Rees should have helped us transcend our
limited 3-dimensional existence. After all, when he received his work
visa for the United States, he was classified as "an alien of
extraordinary abilities."

It's difficult to pick just a few galaxies of thought from the
universe of ideas presented at the conference. Below is an attempt to
highlight those where the stars seemed to shine the brightest.

Humans Will Explore Mars
In 2007, the Human Exploration of Mars Science Analysis Group (HEM-
SAG) set out to define the science goals for NASA's human exploration
of Mars. Joel Levine of NASA's Langley Research Center said the
group's report is now online.

The group decided the first three human missions to Mars should have
three different landing sites, and the sites should represent three
different geological epochs in martian history. There are currently 58
possible sites, and Levine feels that biologists and life scientists
should "have the highest priority" in site selection.

It takes six months to travel to Mars, and the explorers would stay on
the planet for at least 500 days. For humans to travel around the
surface, a pressurized rover would be needed. This vehicle would
probably need to be very massive, weighing several thousand kilograms.

Such missions would have to bring a lot of equipment to Mars for in
situ analysis, because it's too expensive to bring mass back to Earth.
Levine said that "when we go to Mars, it's going to be such an
important event that it'll be an international effort." No details
about this have been worked out yet, but a Mars sample return mission
should set precedents for such international collaboration.

Four Months on Mars
What would it be like to live on Mars? The Mars Society recently sent
seven people to Devon Island in the Canadian Arctic to simulate a
martian colony. For four months they lived in a "tin can" habitat,
wore space suits when venturing outside, and ate freeze-dried food.
They could communicate with Earth, but there was the same time delay
Mars colonists would experience.

They also gained 39 minutes each day, since Mars has longer days than
Earth. Participants conducted science experiments, but also were
experiment subjects: their sleep patterns were studied, as was their
water use. The overall experience must have been good because one of
the participants, Kim Binsted of the University of Hawaii,
enthusiastically said she would volunteer for a real Mars mission.

Do We Need to Come Back?
Given the difficulties of returning humans back from Mars, Paul
Davies, a physicist at Arizona State University, said a "one-way
ticket" to Mars should be considered for future explorers. Going to
Mars is risky, and would shorten your life expectancy. But "this is
not a suicide mission," he stressed.

The riskiest parts of space travel are the take off and landing, and
by not coming back to Earth you reduce your risk by half. You also
reduce the amount of zero gravity you are exposed to during space
travel, which has significant hazards for health. Mars is the second
safest place in the solar system, said Davies, and lava tube caves
would make a good protected habitat.

The first four-person crew would establish and maintain a base, and
additional people would join them over time. The initial mission
"would be the first step in establishing a permanent human presence on
another world," he said.

Establishing a Mars colony also would provide humans with a lifeboat
away from Earth disasters, such as asteroid impacts, plagues, or war.
"But in my view, the reason to go is not to avoid disaster, but
because it is the most likely object beyond the Earth to have life,"
said Davies.

Scientists would do a great deal of research on Mars, and would have
awards and accolades heaped upon them. "I don't envision four
miserable people sitting around on the surface waiting to die, but
doing useful work," he said.

However, Davies thinks NASA will not fund such a mission, so money
would have to come from private enterprise and philanthropy. For
example, "The TV rights [to] a spectacular like this, a real-life soap
opera from another planet, I would think would be worth a lot of
money." The stars of the show might be all elderly people, since their
life span would not be too greatly shortened by living on Mars. Davies
asked for a show of hands for volunteers, and about one-third of the
audience were up to the task.

Davies said he'd rather head straight to Mars and skip the moon bases
planned by NASA. "Been there, done that," he said.

The Moon Before Mars
Paul Davies might not be excited by a moon colony, but Chris McKay of
NASA's Ames Research Center thinks a human base on the moon is a
necessary first step toward the human exploration of Mars.

If we wanted to send humans to Mars just to "collect some rocks, get
back in the space ship and come back to Earth, we could probably do
that without going to the moon," he said. But the most effective way
to search for martian life would be to establish a long-term human
base there, and "we don't know how to operate [an off-world] base for
years on end." The best place to learn what will be required, he
argued, is on the moon.

Although NASA is formulating plans to send humans back to the moon,
and hints at the eventual human exploration of Mars. "Mars is really
the interesting world" for astrobiologists, McKay said. It's likely
that evidence of Martian life is buried below the surface, or deep
within southern polar ice, accessible only by deep drilling, "maybe as
deep as a kilometer."

Have Drill, Will Explore
Since there is much less risk involved in having robots explore the
other planets, one of the main goals of HEM-SAG was to define
experiments humans can do that robots cannot. Peter Doran of the
University of Illinois at Chicago made the case that to drill on Mars,
humans will have to do it. Recent discoveries of microbes living below
the surface of Earth have shown that microbial life can grow deep
within a planet, protected by layers of rock and soil.

Astrobiologists hope that life on Mars might live in a similarly
protected niche. But deep-drilling projects are "almost an
impossibility without humans" according to Doran. Because of this,
human explorers could be essential in answering the question of
whether Mars can support life as we know it.

Mojave Lava
A Mars-like drilling project was reported by Henry Sun, a
microbiologist with the Desert Research Institute in Las Vegas,
Nevada. His team wants to drill into a "natural experiment" in the
Mojave Desert, a series of lava flows that occurred in the Cima
Volcanic Field about a million years ago. The lava flows entombed
layers of desert soil beneath them, perhaps isolating the soil layers
from access to water.

He's interested in drilling into the ancient soil layers to see, after
so much time has passed, what biosignatures have been preserved. The
difficulty will be to perform the drilling without contaminating the
ancient soils with present-day organisms. The Cima field, Sun said, is
a good "training ground" for future missions to Mars that will drill
into the subsurface in search of signs of life.

Cliffbot
Robots are being used to explore places humans can't get to. The Cliff-
bot rover was tested during the 2007 field season of the AMASE (Arctic
Mars Analog Svalbard Expedition) project.Developed at NASA's Jet
Propulsion Laboratory (JPL), as a prototype for a possible future
mission to Mars, Cliff-bot is one of a trio of rovers that work
together to access interesting rock and soil samples on steep
hillsides.

Two of the three rovers are anchored at the top of the cliff, and the
third, which contains a set of scientific instruments, is lowered down
the cliff face on tethers.

Paulo Younse, a JPL engineer working on the Cliff-bot project, said
the field test included an 11-meter (35-foot) climb down an 85-degree
cliff face. "Any typical rover, MER, MSL - no way they'd be able to go
down" such a steep incline, Younse said, pointing out that "a lot of
the interesting science" on Mars can be found along steep crater and
chasm walls that have, so far, been inaccessible.

Hot Rocks
We could send robots to explore regions of our solar system that are
far too cold for humans, but would the robots find any evidence of
life there? We think liquid water is needed for life to exist, so the
habitable zone is the region of space where water stays liquid on the
surface of a rocky planet.

In our solar system, the habitable zone roughly extends from Venus'
orbit out to Mars (with Earth smack in the middle). But if a planet
undergoes tidal heating, it may not need to be in the habitable zone
for its water to stay liquid.

According to Wade Henning of Harvard University, the gravitational
influence of a star or giant planet can create a great deal of tidal
heat on a rocky planet. "If you've got a rocky planet, I can melt it
for you," he said. That could mean there are more regions in any given
solar system suitable for life as we know it. For instance, the moon
Europa receives so much tidal heating from orbiting Jupiter that it
has a global ocean of liquid water, even though Europa is far away
from the habitable zone.

The type of body a rocky world orbits makes a big difference in how
much tidal heating the planet will experience. For a G-type star like
our sun and also for the slightly cooler K stars, the tidal zone and
the habitable zone do not overlap (in other words, a planet in the
habitable zone will not experience tidal heating as well). For M-type
red dwarf stars, however, the zones do overlap. They do so for moons
as well, which receive most of their tidal heating forces from the
planet they orbit.

Henning said that one interesting result of his analysis is that it is
possible to envision a habitable planet with no star. "It would be
very dark, but warm enough," he said.

Is There Life in Alpha Centauri?
Alpha Centauri, a triple-star system only four light years from Earth,
contains our closest stellar neighbors. To date, no planets have been
found around these stars. Computer models suggest that gas-giant
planets like Jupiter and Saturn would be unlikely to form there, and
these giant planets are the easiest to detect with the radial-velocity
technique that has been used to discover most of the known extrasolar
planets. But models also show that Earth-like planets could form
within the habitable zone around Alpha Centauri B.

Terrestrial-size planets are far more difficult to detect with radial-
velocity measurements, but a group of planet-hunters thinks it may be
possible if enough measurements are taken. "We're talking about taking
over 100,000 data points" over a five-year period "to detect an Earth-
size planet," said Elisa Quintana, an astronomer with the SETI
Institute. Quintana and her colleagues will use a 1.5-meter telescope
in Chile to make the observations, a much smaller telescope than those
typically used for radial-velocity measurements.

"We're doing this from the backyard," she said. "Hopefully, five years
from now ... we're going to be able to report the detection or the non-
detection" of one or more terrestrial planets around Alpha Centauri
B."

Galactic Habitable Zones
Charley Lineweaver, a cosmologist with The Australian National
University, is investigating the habitable zone of galaxies. One thing
that could be life-limiting on a galactic scale would be the elements
available to form planets and life. Life as we know it primarily uses
carbon, hydrogen, oxygen and nitrogen, but will life do so everywhere?
Elements are made by stars, especially in the later years of their
life.

So the older a region of space, the more elements will be available.
Lineweaver noted that 75 percent of stars in the galactic habitable
zone are older than our sun, and this suggests that life with a far
more ancient heritage than life on Earth could be out there.

Another limiting factor for life in a galaxy would be the location of
the star relative to the galactic center. You want to be far enough
away to avoid intense radiation and so that you're not crowded by
other stars (thereby also avoiding the supernova explosions of dying
stars). How a star orbits the galactic center may be important as
well. Our sun has a relatively circular orbit, while other stars do
not.

Lineweaver thinks perhaps a circular galactic orbit is a requirement
for life to appear in a solar system, or at least survive over large
time scales. Ultimately, Lineweaver said that life may be possible for
less than 10 percent of all the stars ever formed in the Milky Way
Galaxy.

Cycles of Diversity
Richard Muller of the University of California, Berkeley said that our
place in the galaxy could influence the evolution of life on Earth. He
noted that there are 62-million-year and 140-million-year cycles of
fossil diversity on Earth (depending on which species you look at).
Ticking down a list of possibile causes, he said that for the 140-
million-year-cycle one cause could be the sun's passage through the
arms of the Milky Way.

This passage would increase the possible number of comet impacts on
our planet, and such impacts can lead to extinction events. As for the
62-million-year cycle, as yet no plausible causes have been found.
Muller did say that strontium isotopes in the rock record also show a
62-million-year cycle. Strontium tracks weathering (the slow break-
down of rocks through rain, wind, and other natural phenomena), so
this could be an indication of some as-yet unknown climate cycle on
Earth.

Evolving Minerals
Do minerals evolve like life does? Robert Hazen of the Carnegie
Institution of Washington proposed a new way to look at mineralogy on
terrestrial worlds: as an evolutionary process.

Rather than the traditional static view of minerals, which focuses
primarily on their crystal structures, he suggested that "every
mineral is part of a narrative story, a dynamic story." When the Earth
was first coalescing, it contained only a dozen or so "ur-minerals,"
leftovers from stellar explosions. Condensation, heating, pressure,
water-rock interactions and plate tectonics increased that number to
perhaps 1,500 different minerals.

But the saturation of the Earth's atmosphere with oxygen, the
byproduct of oxygenic photosynthesis, was "the most dramatic single
event in mineral diversity on Earth," he said. "Perhaps two-thirds of
all minerals on Earth, if this model is correct, are the indirect
consequence of the biological changes in the atmosphere."

Hazen suggested that different planetary bodies "achieve different
levels of mineral evolution, and this can be a very interesting target
for astrobiology investigation."

Are Brains Necessary?
Some forms of primitive life can teach us about the evolution of
complex life. David Gold of the University of California, Los Angeles
studies cnidarians. These creatures predated the Cambrian explosion
and include the sea anemones, hydras, and jellyfish. Some are
scyphozoan, with primitive slit eyes that can detect light
orientation, while others are cubozoan, with sophisticated lens eyes
extremely similar to our own. But they have no brain.

"One would expect lens eyes to be useless without advanced neural
processing," said Gold. It's not a case of form preceding function,
because they use their eyes to hunt and avoid objects.

Gold has studied the more primitive Aurelia to see how gene networks
that code for eyes develop. The Aurelia nervous system consists of a
Giant nerve net - which may be independent brains that are connected -
and a Diffused nerve net. Head-patterning genes found in bilateral
animals (like humans) are also found in the development of individual
nerve nets in Aurelia.

Perhaps intelligence is limited by body shape. Or perhaps intelligence
is not necessarily a result of evolution -- many organisms have
survived eons without developing "intelligent" hardware, and
evolutionary history has many cases of a species losing intelligence
over time.

The Human Niche
Charley Lineweaver said we are being vain when we assume all forms of
intelligence evolve toward human-like intelligence, such as in the
movie "Planet of the Apes" where primates evolved to be human-like. We
assume that humans occupy the peak of an intelligence hierarchy, and
other species want to evolve to occupy that niche to become our
functional equivalent. Lineweaver said this view is not supported by
the evidence.

If all animals eventually evolved to develop human-like intelligence,
this trait would have appeared over geologic time, especially on
isolated islands that were devoid of humans. Animals had millions of
years to develop, and yet no other human-like intelligences ever
emerged. Lineweaver also noted that large brains are not an inevitable
outcome for animals.

People look to the dolphins and say that is an example of convergent
evolution, since their brains are comparable to ours. However, on the
tree of life humans and dolphins diverged recently, so both species
had the underlying genetic tendency already built in to develop those
brains.

Dolphin Culture
There were broad grins all around as Denise Herzing played a video of
intelligence tests on wild dolphins. The Wild Dolphin Project has been
working with mostly juvenile females in the Bahamas, and they devised
a simple keyboard composed of three large symbols. Each key had a
musical tone that was not a normal sound in the dolphin repertoire.
The key and tone represented a desired behavior, such as retrieving a
brightly colored scarf that the dolphins loved to drag around.

The scientists discovered that the dolphins learned more when the
divers participated in synchronized swims and other forms of mimicry,
and maintained eye contact. When asked why most of the dolphins were
juvenile females, Herzing said they were the only ones who had free
play time. Older females were busy rearing their calves, and the young
males already were fighting for territory.

Herzing said the divers tried to always respect the dolphin's social
rules, but the dolphins themselves also would ensure the cultural
norms were maintained. For instance, when swimming together, if a
diver tried to change her place in the pack the dolphins would adjust
their own positions to maintain the group order.

The Story of the Stars
The cultural aspect of astrobiology was the focus of a talk by
Daniella Scalice, Education and Public Outreach Coordinator for the
NASA Astrobiology Institute (NAI). In 2005, the NAI began working with
the Navajo people to develop hands-on educational programs for Navajo
students -- resulting in what is called "So ba' hane'" or the Story of
the Stars.

These programs weave together astrobiology and Navajo cultural
knowledge, drawing on the experience of Navajo leaders, teachers and
medicine people. Now there are plans for a more focused program on
lunar science. The moon plays an important role in Navajo history and
legend, and so NASA's plan to return humans to the moon provides an
opportunity to explore the cross-cultural implications of lunar
research.

The Story of a Meteorite
In 1996, a team of scientists identified potential traces of
microorganisms in the martian meteorite ALH 84001. Their report made
headlines, and since then ALH 84001 has been the subject of heated
discussions concerning life on Mars. New research presented by Andrew
Steele of the Carnegie Institution of Washington identified ways the
controversial 'biosignatures' within ALH 84001 could have been
produced through non-biological chemical reactions.

The new research may appear to be a blow against the idea that Mars
once supported life, but Steele was quick to point out that his work
"doesn't disprove life" -- it simply shows that organic chemistry on
Mars could produce structures that look similar to those produced by
microbes. "If you want to find life," he stated, "you must know what
signs of abiotic chemistry look like."

You must first "assume that abiotic chemistry is ubiquitous," and then
search for biosignatures that could not be formed by any processes
other than biological activity. Ultimately, Steele feels that "if
there is not life on Mars, it isn't a negative result." Understanding
how the structures in ALH 84001 could've formed without biological
activity is essential in determining how to accurately discover
biosignatures on planets beyond Earth.

Life Needs Liquid
William Baines of the Institute of Biotechnology said that although we
can describe life in exquisite detail, we don't really know what it is
because we can't make any predictions about it.

Life implies a code (genetic info) and requires catalysis for all
metabolic steps. This does not require evolution or carbon chemistry,
but it does imply a solvent because for things to react, they need to
move around. That solvent does not need to be water, however. "Water
is a dreadful solvent," said Baines.

"Chemists try to keep water out of their experiments because it reacts
with everything and rips molecules apart." Possible bio-solvents other
than water include methane, ammonia, neon, argon, carbon dioxide,
ethane, hydrogen, nitrogen, and sodium.

The temperature, pressure, and density of a planet will determine
whether a liquid stays fluid. Solubility declines with temperature,
but biochemistry still can occur in very cold places, like Jupiter's
moon Ganymede or Saturn's moon Titan, although life there would not be
as productive as life on Earth.

What We Choose to Believe
Steven Benner, a chemist with the Foundation for Applied Molecular
Evolution, said exobiology is a science without a subject matter. But
that's nothing new -- Galileo wanted to know whether the Earth circled
the sun, but he couldn't study that directly so he rolled balls down
inclined planes to answer the question. Benner said that we often
can't rely on established science to be a guide.

Lord Kelvin said the Earth and sun could NOT be billions of years old,
when Darwin was arguing they were. "Who are you going to believe?"
asked Benner. "The gentleman who had a temperature scale named after
him, or this guy who makes a living studying bird beaks?" So science
is often what we choose to believe.

To make new discoveries, we can try to prove false some of our chosen
beliefs. So is there anything we can prove false in the possibility of
life elsewhere? "Astrobiologists everywhere have daily evidence of the
persistence of life," said Benner, "but we have little constructive
knowledge of how frequently life emerges."

We may never have direct evidence for life elsewhere, said Benner, but
models are accepted by communities when they interconnect sufficient
threads of evidence. For astrobiology, the threads include
paleogenetics (tracing the tree of life backwards through time),
searching the cosmos, prebiotic chemistry (trying to trace life's
origin forward in time), and synthetic biology (creating alternative
life forms).

According to Benner, chemists don't believe that life can emerge from
a prebiotic soup. The Miller-Urey experiments showed that energy plus
organics equals tar without evolution. "We put energy in complex
chemical systems, we get pavement, not life," said Benner. "Do an
experiment. Use some glucose to make a souffle, and leave it in the
oven a little too long. [You get] asphalt."

The RNA world preceded DNA life, but it was not necessarily the first
living system. The big problem is with ribose, the "R" in RNA, which
falls apart when heated and forms tar. So life may have formed with a
sugar other than ribose, but in lab tests nothing else works. However,
ribose-borate is a stable mineral, and Benner believes that boron
makes an RNA prebiotic world more possible. Boron is associated with
deserts on Earth.

Benner suggested that because Mars had deserts long before Earth did,
perhaps life originated there and was somehow transported to Earth
(making us, in effect, Martians).