Press Release

A Bit of Titan on Earth Helps in the Search for Life’s Origins

By SpaceRef Editor
May 17, 2004
Filed under , , ,
A Bit of Titan on Earth Helps in the Search for Life’s Origins
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While the Cassini spacecraft has been flying toward Saturn, chemists on
Earth have been making plastic pollution like that raining through the
atmosphere of Saturn’s moon, Titan.

Scientists suspect that organic solids have been falling from Titan’s sky
for billions of years and might be compounds that set the stage for the
next
chemical step toward life. They collaborate in University of Arizona
laboratory experiments that will help Cassini scientists interpret Titan
data and plan a future mission that would deploy an organic chemistry
lab to Titan’s surface.

Chemists in Mark A. Smith’s laboratory at the University of Arizona create
compounds like those condensing from Titan’s sky by bombarding an analog of
Titan’s atmosphere with electrons. This produces “tholins” — organic
polymers (plastics) found in Titan’s upper nitrogen-methane atmosphere.
Titan’s tholins are created by ultraviolet sunlight and electrons streaming
out from Saturn’s magnetic field.

Tholins must dissolve to produce amino acids that are the basic building
blocks of life. But chemists know that tholins won’t dissolve in Titan’s
ethane/methane lakes or oceans.

However, they readily dissolve in water or ammonia. And experiments done 20
years ago show that dissolving tholins in liquid water produces amino
acids.
So given liquid water, there may be amino acids brewing in Titan’s version
of primordial soup.

Oxygen is the other essential for life on Earth. But there is almost no
oxygen in Titan’s atmosphere.

Last year, however, Caitlin Griffith, of UA’s Lunar and Planetary
Laboratory, discovered water ice on Titan’s surface. (See ‘Titan Reveals a
Surface Dominated by Icy Bedrock’ online at http://uanews.org – the article
search number is 7248.) UA planetary scientist Jonathan Lunine and others
theorize that when volcanoes erupt on Titan, some of this ice could melt
and
flow across the landscape. Similar flows could result when comets and
asteroids slam into Titan.

Better still, Titan’s water may not immediately freeze because it’s
probably
laced with enough ammonia (antifreeze) to remain liquid for about 1,000
years, Smith and Lunine noted in a research paper published in last
November’s issue of “Astrobiology.”

So although Titan is extremely cold — about 94 degrees kelvin (minus 180
degrees Celsius or minus 300 degrees Fahrenheit) — water may briefly flow
across the surface, supplying oxygen and a medium for chemistry, they
conclude.

To further understand how all this might work together, Smith’s group is
generating tholins in the lab, analyzing their spectroscopic properties,
and trying to understand their chemistry.

“We’re trying to learn how the compounds will react with molten water on
Titan’s surface, what compounds they’ll make, and, therefore, what we
should
really be looking for,” Smith explained. “We’re not just looking for
atmospheric plastic sitting on the surface, but the result of time and
energy input over billions of years.

“We want to know what sorts of molecules have evolved, and whether they’ve
evolved along pathways that might provide insights into how biological
molecules developed on primordial Earth,” he said.

“Some of what we’ve learned so far in our experiments is that these
materials are gross mixtures of incredibly complex molecules,” Smith added.
“Carl Sagan spent the last 10 years of his life studying these compounds in
experiments like ours. What we’ve found complements his work. We see the
same spectroscopic signatures.”

But Smith’s group also has found that there is a component of these
molecules that is very reactive and could easily, within a reasonable time
frame, react on the surface of Titan to yield oxygenated compounds.

“And that’s what we’re just starting to unravel now,” Smith said.

“Our work will get much more interesting this fall, in our experiments at
the Advanced Light Source of the Lawrence Berkeley Lab,” he added. “We’ll
be
using a synchrotron to create tholins photochemically, using very energetic
photons to break up this Titan gas by vacuum ultraviolet radiation.”

Vacuum ultraviolet radiation hits nitrogen and methane molecules in Titan’s
upper planetary atmosphere and blasts them apart. Scientists don’t know if
this produces the same kinds of polymers that are formed from an electrical
discharge.

“When you can crack nitrogen and methane molecules with light, you might
get polymers similar to those formed when an electrical discharge cracks
them
apart,” Smith said. “Or you may get different polymers. The chemistry is
quite complex, and we just don’t know the answers to so many of the simplest
questions. But that’s one of the reasons we’ll conduct the experiments at
Berkeley.”

The work going on in Smith’s lab is important to scientists on NASA’s
Cassini Mission and possible follow-up missions to Saturn. The Cassini
orbiter was launched in 1997 and is to launch a probe into Titan’s
atmosphere in December. This Huygens probe will float to Titan’s surface
next January.

“Titan’s thick orange aerosol haze layer is basically a bunch of organic
plastics — polymers of carbon, hydrogen and nitrogen,” said Smith, head of
UA’s chemistry department. “The particulates eventually settle on Titan’s
surface, where they produce the organic feedstock for any organic chemistry
going on.”

Cassini’s Huygens probe will be the first instrument to actually sample
this
aerosol. It will give scientists some rudimentary chemical information on
this material. But the probe won’t tell them much about organic chemistry
at Titan’s surface.

A follow-up mission to Titan that includes a robotic organic chemistry
laboratory will give scientists a much more detailed look at the surface.
The experiment is being designed by Lunine and Smith in collaboration with
researchers from Caltech and NASA’s Jet Propulsion Laboratory.

Lunine leads NASA’s Astrobiology Institute focus group on Titan and is one
of three interdisciplinary Cassini mission scientists for the Huygens
probe.

“We don’t really know how life formed on the Earth, or on whatever planet
it
formed,” Lunine said. “There are no traces left of how it happened on
Earth,
because all of Earth’s organic molecules have been processed biochemically
by now. Titan is our best chance to study organic chemistry in a planetary
environment that has remained lifeless over billions of years.”

SpaceRef staff editor.