[meteorite-list] Hanging By A Thread On Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:15 2004
Message-ID: <200404211556.IAA29229_at_zagami.jpl.nasa.gov>

http://www.spacedaily.com/news/mars-life-04e.html

Hanging By A Thread On Mars
for Astrobiology Magazine
April 21, 2004

Moffett Field - One engineering obstacle to overcome when landing on
Mars is the treacherous descent and landing. From start to finish,
this mission phase can last six minutes. Because of its nail-biting
drama, it is often referred to as the six minutes of hell.

If horizontal winds blow the rover's parachute sideways during
descent, the precious payload
might scrape rather than bounce. That possibility of shear against
sandpaper-like soil prompted a relatively late addition to the mission
planning. Stabilizing horizontal thrusters were added to compensate if any
wind started to tilt the otherwise vertical path.

This attention to detail proved invaluable during the first landing attempt.
When the Spirit rover descended towards Gusev crater, just such
unpredictable winds had to be corrected for. If all had not gone according to
plans, the airbag fabric might have ripped catastrophically.

On February 12th, the nineteenth day on the other side of the planet for the
Opportunity rover, one curious image stood out. The picture was
downloaded in the daily batch from a microscopic imager peering onto the
pebbly surface. On Sol 19, a long, thin feature surprised the science team.

Measuring 6 millimeters long and 60 micrometers across, this thread was
smaller than the size of an average human hair. At first glance, many
speculated whether the thread might point towards some strange biological
origin.

The lack of another microscopic image capturing such a thread in view,
however, made the science and engineering team's detective work difficult.
But using their expertise from so many landing simulations, the rover team
set out to test if they could reproduce this feature in the JPL sandbox.

A best first guess was that when the rover's airbag hit the surface, tiny
threads had been stripped from the fabric and laid out across the martian
soil. Their experiment entailed a grab bag of starting materials: Mars soil
simulant and airbag fabric made of Vectran (a synthetic material stronger
than Kevlar, which is tough enough to qualify for bulletproof vests).

Placing Vectran threads against the backdrop of simulated Mars soil gave
the team a first view of what the microscopic imager might have seen.

To recreate similar conditions, the team still needed to know exactly where
the rover was on Sol 19. They also wanted to know how its robotic arm
turret was positioned for such an extended camera view.

The rover's navigation and front hazard avoidance cameras narrowed down
their choices to the rim of Eagle Crater. Two airbag marks could be seen
nearby. Suddenly two lines of forensic evidence came together: a location
near bounce marks and a recreated microscopic scene on Earth with
Vectran threads.

The threads in Pasadena's sandbox closely resembled what had first
surprised scientists nearly a month earlier at Eagle Crater on Mars.

The threads of this mystery seemed not to show martian biology in
microscopic view, but another kind of throw-away terrestrial biology at
work: the airbags had shed fabric and the camera showed human
engineering in action.

What lesson can be learned from the thread mystery? How does shape
itself guide a biological interpretation?

One answer is the Knoll criterion. Named after Harvard paleontologist
Andrew Knoll, the methodology is cited as one example of not just how a
shape might be similar to something biological, but whether a presumption
is given to another explanation in the absence of biology.

"You do your exploration," said Knoll, "and if, in the course of that
exploration, you find a signal that is (a) not easily accounted for by physics
and chemistry or (b) reminiscent of signals that are closely associated with
biology on Earth, then you get excited.

"What will happen then, I can guarantee you, is that 100 enterprising
scientists will go into the lab and see how, if at all, they can simulate what
you see - without using biology."

This is an extension of Carl Sagan's classic comment, that extraordinary
claims require extraordinary evidence.
Received on Wed 21 Apr 2004 11:56:46 AM PDT


Help support this free mailing list:



StumbleUpon
del.icio.us
reddit
Yahoo MyWeb