Beachcombing On the Shores of Barsoom
“The shores of the ancient seas were dotted with just such cities, and lesser ones, in diminishing numbers, were to be found converging toward the center of the oceans, as the people had found it necessary to follow the receding waters until necessity had forced upon them their ultimate salvation, the so-called Martian canals.”
– A Princess of Mars, Edgar Rice Burroughs
For centuries we could only visit Mars, that bright red dot in the sky, with our minds. With the advent of telescopes we could use reflected and concentrated light from Mars to slowly unravel its secrets. But we still did most of our exploration with our imagination filling in the blanks.
With only one world close at hand to go by we projected our own expectations on those photons from Mars.
We always seemed to call Mars a “dead world”. But “dead” always carries within itself the notion that it was once alive. Some called it a “dying” world – one with “dried up” oceans long gone.
Then we began to visit the planet with machines. While our minds still did the exploring, we had mechanical proxies to prod Mars with – and sensors to reveal its secrets. At first it looked sterile – not even dead – like our moon.
Then we began to see things that spoke of the signs of water. After two landings did not suggest life’s presence we lost interest.
We soon found it again. This time the interest seems to be here to stay.
Mars was very, very wet
This morning in Washington DC, on the 198th anniversary of the start of the long trek home by Lewis and Clark, NASA revealed evidence that the Mars Opportunity rover landed on what they believe to be “the shoreline of a salty sea on Mars” according to Rover Principal Investigator Steve Squyres.
Opportunity was sent to the plains of Meridiani Planum where hematite, a mineral often formed on Earth in the presence of water was known to be in abundance.
Unlike its twin Spirit which landed in the midst of a large boulder strewn plain, Opportunity managed to roll into the best possible spot – a small crater named “Eagle crater”. The impact which created Eagle crater was energetic enough to expose rock layers several meters below the surface. Indeed, some of the very first photos from Opportunity sent its operators into a frenzy as they revealed rock out croppings extending from one side of the crater to the other.
Upon close examination things began to reveal themselves. So called “blueberries” were found to be made of hematite. Moreover, they formed within rocks after the rocks were laid down . Closer examination of the rocks inside Eagle crater showed that they had been altered by the presence of water – water that had to have been present in significant amounts for some period of time.
As to where the rocks had originally come from – while they hinted at a watery origin, a final determination required several more weeks before it was agreed. Soon after announcing that rocks at Eagle Crater had been “drenched” in water the team went back to Pasadena to pour over new data.
The evidence
Two factors led the team to decide that these rocks had indeed been laid down in the presence of standing water.
First, spectral data showed the presence of Bromine. Moreover, the levels of Bromine varied from one part of a rock layer to another by a factor of ten. This is something that is common to so called “evaporite deposits” on Earth – mineral layers that form as sea water evaporates leaving suspended materials behind which eventually become rock.
This evidence alone was enough to convince some but Sqyuyres said that more was needed. That additional evidence came from the identification of crossbeds in the layered construction of rocks in Eagle crater. Layers such as those seen in the rocks on Earth and at Eagle crater can be laid down by a variety of means – all of them fluidic in one or more ways via the action wind or water.
While there are similarities between the two modes of deposition, there are great differences. How the fluid moves helps make the distinctions even greater. Running water has a tendency to move particles along a path down stream such that they avalanche over one another in a series of waves. Over time, the particles are deposited in a very distinct three dimensional fashion.
In order to examine the rocks at the highest possible resolution, the team used Opportunity’s Microscopic Imager and slowly “wallpapered” their way across the face of one rock so as to construct a large mosaic. Examining these high resolution mosaics showed clear evidence of cross bedding thus providing a second peg to hang their theory on.
But this was still not enough. The team was in a position several weeks back to make this announcement. Instead, they felt that this was an important enough finding that they needed to get a sanity check by outside experts. A peer review panel of six individuals was assembled to look over the data.
After two weeks they reported back that the Rover team’s initial conclusions were indeed sound – that the data provided ample evidence that the rocks had been laid down in standing bodies of water.
What does this all mean?
The significance of this announcement, while diluted by previous announcements from this mission, and from observations made from orbit by Mars Global Surveyor and Mars Odyssey, couldn’t be more profound. According to Squyres these findings show that conditions once existed on Mars which biologists consider to be “habitable”. While Squyres was quick to caution that no evidence of life – past or present – had been found, the conditions it would enjoy had been verified as having once existed on a world other than our own. Up until now this has just been conjecture. This is backed by data.
In addition to being ‘habitable’, the nature of how these rocks formed provides a good place to preserve evidence of past life – should it have existed on Mars. On Earth, such deposits allow the biochemistry as well as the outward structural features of microorganisms to be preserved in rock for vast periods of time.
How long ago these deposits were made, and what the environmental conditions were at the time is still open to debate. While the prevailing view seems to be that there was a large body of water that dried up – perhaps repeatedly, Squyres offered a theory that what happened here could also be the result of ice-covered bodies of water.
Jim Garvin remarked that layers such as these speak to a process – with a beginning and an end – one which apparently happened over and over again. As to whether this was over a short or a long period of time no one is certain. There are a number of cycles at work here – the Martian day/night cycle, the planet’s annual cycle (a year complete with seasons), and a much larger one wherein the rotational axis of the planet moves about – much like a spinning top. This causes the amount of light that hits the planet to vary greatly – and solar energy is what pumps planetary climate. More data will be needed before time frames and ages can be applied to what has been discovered.
Hopefully, Opportunity will be able to make the 700 meter trek to Endurance crater and peer inside at what may well be a much deeper hole in the surface. “Looking at a larger slice of rock” was how Squyres suggested geologists best find the age of a particular specimen. Endurance may provide enough of a record to make a better guess as to when conditions on Mars were habitable.
In their opening comments both Squyres and Office of Space Science associate Administrator Ed Weiler made mention of fossils and that this location would be a good one to go looking for them. I asked if Opportunity had the ability to detect fossils (assuming of course there was life that died to leave fossils to begin with). Squyres was reluctant to speculate beyond saying that the rovers were unlikely to be able to provide evidence at the microscopic level of small fossils. Since this is what is commonly found in such deposits on Earth this suggest that fossils, if they are present, will have to be much larger to be seen. While not saying “Yes”, Opportunity could detect larger fossils, Squyres did admit that if something is large enough you are going to see it.
What’s next
Initially designed to last 90 days, the rovers are both working so well that extended missions – perhaps into September 2004 – are now being considered. After visiting Endurance crater – and perhaps going down into the crater, Opportunity’s plans are TBD. As for Spirit, there is a lot of rocky terrain ahead. Squyres spoke of the hope that Spirit could travel the 3.5 km to reach the Columbia Hills wherein some layering has been hinted at from long distance photos.
Beyond that the rovers will eventually fade. If it isn’t the motors then the batteries will eventually lose their ability to hold a charge. At some point the rovers will stop moving. Sometime after they will stop working all together.
The future
The next mission to Mars, the Mars Reconnaissance Orbiter, which will be launched in 2005 will build upon what Opportunity and Sprit find. Using the data the rovers gather as ground truth, the high resolution capabilities of MRO will allow a much more detailed survey to be made of the entire planet.
Following MRO in 2007 will be the Phoenix Lander. While it won’t be moving around, it will land three microscope systems with an immense increase in resolution and analytical power on the surface of Mars.
Next comes the Mars Science Laboratory. This vehicle will serve in many ways as the inheritor of all that came before it. Equipped with a nuclear power source it will prowl the surface of Mars for an entire Martian year, carry a full suite of astrobiology gear, and seek to take that step that many have been waiting for: to make a determined effort to look for the presence of life using the best that 21st century technology has to offer. While the landing site has not been chosen, Office of Space Science associate Administrator Ed Weiler said that Meridiani Planum is now the prime candidate until a better one comes along.
After that, a Mars Sample Return mission is being contemplated which would allow the collective analytical power of Earth to be focused on pieces of Mars.
Where do we go from here?
Of course, there is only so much you can do by proxy or with little pieces of Mars. Even the most sophisticated rover can only cover so much ground and is reliant upon how smart its developers can make it. At some point people will have to using their own hands to over turn rocks on Mars. Once seen as separate, mutually exclusive notions, the human and robotic exploration of Mars is now spoken of as a collaborative marriage in the context of the President’s space initiative.
When asked if the possibility that these findings may have direct bearing on the question as to whether Mars ever supported life – and if that will, in turn, affect the pace of the President’s new space initiative, Sean O’Keefe said that it could since the agenda “is driven by the science as you go along”.
Opportunity certainly added to that science drive today.
