6degrees Astroblog

Life on Mars?

By Irwin Horowitz, 6-01-08

	First image from Phoenix landing site Copyright: NASA/JPL-Caltech/University of Arizona

With last Sunday’s landing of the Mars Phoenix mission in the north polar regions of the Red Planet, there is once again a renewed interest in the exploration of our planetary neighbor.  The history of Martian exploration is a fascinating story.  It is filled with tall tales and wild speculation, spectacular failures and awe-inspiring successes.  The role played by Mars in the development of human understanding of the universe and our place within it cannot be underestimated.

The Death of Geocentrism

The story begins, as all good stories must, a long time ago.  The birthplace of western civilization is generally regarded to be the ancient cultures of Greece and Rome.  In those times, there were seven known “planetes” or wanderers visible in the sky.  These were the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn.  They were different from the fixed stars because they appeared to change their positions over time.

Most of the time, five of the seven objects appeared to move from west to east across the sky (the Sun and Moon always move in this direction).  However, every so often, this motion would slow down, come to a stop and reverse itself for a few months. Then once again, the reversed motion would slow down, stop and return to the original direction.  This process is known as retrograde motion.

Numerous individuals tried but failed to explain these motions within the prevailing geocentric paradigm of that era.  The Egyptian philosopher Ptolemy created an elaborate set of “epicycles” in order to explain retrograde motion among the planets.  His “model” managed to survive as the prevailing explanation for nearly fourteen hundred years.

In 1543, Nicolas Copernicus published his masterpiece De revolutionibus orbium coelestium in which he posited that the Sun rather than the Earth lay at the center of the universe.  By placing our world in orbit around the Sun along with the other planets, he could explain retrograde motion as an effect which occurred when the Earth would pass one of the outer planets.  He could also explain why Mercury and Venus never appeared to stray very far from the Sun, as they were located closer to it than the Earth.

It was the observational work of Tycho Brahe and the subsequent analysis performed by Johannes Kepler that thrust Mars into the center of the debate between the two vastly different world views of the geocentric versus the heliocentric model of our solar system.  Tycho spent decades carefully observing the position of Mars against the background stars at his observatory in Denmark.  Kepler utilized this data set to derive his three laws of planetary motion:

1) Planets orbit the Sun on ellipses with the Sun at one focus;
2) The line between a planet and the Sun sweeps out equal areas in equal time; and
3) The square of the period of the orbit is proportional to the cube of the semi-major axis.

The success of Kepler’s three laws along with the telescopic observations made by Galileo at the same time represented the final triumph of the heliocentric model over the geocentric model.  A large part of that result can be traced back to the positional data of Mars acquired by Tycho.

“Canals” on Mars

By the late-nineteenth century, telescope technology had advanced to the point where observers could discern features on the surfaces of other planets.  In 1877, Italian astronomer Giovanni Schiaparelli noted a number of thin straight lines on the surface of Mars.  He coined the term “canali” or channels, to describe what he believed he observed.  Subsequent analysis has shown that these were merely an optical illusion.

At the end of the nineteenth century, American astronomer Percival Lowell established an eponymous observatory in the northern Arizona desert near Flagstaff.  Having read about Schiaparelli’s observations, he convinced himself that not only were these features real, but that they were an indication of the presence of an advanced civilization.  He conjectured that they may have been attempting to stave off extinction by bringing water from the polar ice caps to more temperate latitudes for the purposes of agricultural cultivation.

He utilized the telescopes at Lowell Observatory to carefully study Mars and discern the nature of this civilization.  He made detailed maps showing not only canals, but also large dark “oases” where he believed the Martians resided.

While many of his contemporaries disputed Lowell’s fanciful notions, it was several decades before they were finally tossed into the dust bins of history.  Before our first space probes in the 1960s provided the reality of the planet, there were still many who believed that we were not alone in our own solar system. 

Indeed, on Halloween eve in 1938, famed actor Orson Welles directed a live radio rendition of H.G. Wells’ “The War of the Worlds,” which dealt with a fictional invasion of Earth by ruthless denizens of the red planet.  The performance was so realistic and the belief in intelligent Martians so prevalent that a mass panic ensued in many communities across the United States.

A Frozen, Arid Wasteland

In 1965, after a string of failures by the Soviets (a recurring theme regarding their Mars exploration program) and one by the United States, Mariner 4 successfully flew past Mars and returned 21 images of the Red Planet.  What was immediately clear was that the advanced civilization imagined by Percival Lowell was precisely that.  The images revealed a cold, dry surface pockmarked with impact craters.  Subsequent flybys by Mariners’ 6 and 7 in 1969 showed no evidence for any “canali” on the surface.

It wasn’t until Mariner 9 successfully entered Martian orbit in 1971 that some of the true surface features of the planet began to be revealed.  After waiting for a global dust storm to subside, the cameras on this probe revealed volcanic mountains like Olympic Mons which are taller than Everest and a vast canyon system (Valles Marineris) that dwarfs the Grand Canyon.  It imaged the entire accessible surface of Mars and clearly showed that the planet was not habitable.

We learned that Mars has a thin atmosphere consisting mostly of carbon dioxide, but with a surface pressure so low that liquid water could not exist.  Its two small moons, Phobos and Deimos, appear to be captured asteroids.  It has no appreciable magnetic field to protect the surface from cosmic rays and gave every indication that even simple life forms could not survive in that environment.

To test that hypothesis, NASA launched a pair of missions in the mid-1970s with the goal of landing on the surface and carrying out a series of tests to explore the feasibility of biological systems evolving on the planet.  The Viking landers performed these experiments and while they found evidence for unusual chemical activity in the soil, there was no evidence of living microorganisms.  Analysis of the soil and surface conditions suggested that the environment was too harsh for life as we understand it to have survived.

The Little Rover that Could

Following the loss of Mars Observer in 1992 and the continued string of mission failures from the Russian space program, the next successful explorers were Mars Global Surveyor and Pathfinder in 1996 and 1997.  At the time these missions were undertaken, an astonishing announcement had been made here regarding the analysis of a meteorite found in the frozen wasteland of Antarctica.

ALH84001 was a piece of space debris about 2 kilograms in mass.  It was discovered in the Allan Hills region of Antarctica in 1984 and was brought back to a NASA laboratory for study.  It was quickly determined that the rock originated on Mars based on the chemical abundances of certain trapped gases.  It was blasted off the surface about 16 million years ago (most likely by a comet/asteroid impact) and landed on Earth about 13,000 years ago.

NASA scientists announced during the summer of 1996 that they had discovered evidence that suggested the presence of fossilized microbial life within the core of the meteorite.  There were some dramatic photographs presented along with a very technical description of biochemical reactions to explain the presence of carbonate globules.  However, subsequent analyses have demonstrated that all of this evidence could be explained using non-biological processes.  As a result, scientists no longer believe this object is an example of extra-terrestrial life.

Meanwhile, back on the planet, tiny Sojourner rumbled to life and drove off of Pathfinder’s platform to explore the region around the landing site.  Expected to last for only one week, it continued to radio data back to Earth for three months.  The pair made several scientific discoveries regarding atmospheric conditions and surface chemistry.

The end of the 90s saw a pair of spectacular mission failures for NASA in their Mars exploration program.  The more noteworthy was the loss of Mars Climate Orbiter, which apparently burned up in the atmosphere during the orbital insertion.  The cause of this was the use of non-metric units by the contractor, where NASA specified the use of metric units.  This resulted in a navigational error that put the satellite into an orbit that passed through the thin Martian atmosphere.  The second mission, the Mars Polar Lander apparently crash landed near its landing site in the south polar region of the planet.

A New Millennium…a New Dawn

Since the arrival of Mars Odyssey in 2001, there have been seven successful missions to Mars, including three landers (the British lander Beagle 2 apparently crashed landed in 2004).  In January 2004, NASA successfully returned to the surface with a pair of rovers called Spirit and Opportunity.  These two were supposed to survive on the surface for about three months but are still functioning and returning useful scientific data.  They have traversed several miles from their initial landing sites, sending back hundreds of thousands of images as well as spectroscopic analyses of the chemical makeup of rocks and soil samples found in both locations.  They have found evidence that liquid water did flow on the surface of Mars in the distant past.  This is a key finding as it is more likely that biological activity could have occurred in the presence of these streams.

High above both rovers, the Mars Reconnaissance Orbiter (MRO) has joined Mars Odyssey to perform global measurements of the planet and to take images of unprecedented detail of the surface features.  As mentioned at the start of this article, Mars Phoenix landed in the North Polar Region last Sunday.  During its descent, MRO acquired this amazing image of the craft suspended beneath its parachute. 

Over the past week, there have been a few minor technical glitches that the wizards at the Lunar and Planetary Lab (LPL) at the University of Arizona are analyzing and working around.  But there are already science results being reported.  The camera mounted on the robotic arm has snapped a picture of the surface beneath the lander and has found what appears to be water ice that was exposed by the retrorockets firing to soft land the craft.  Yesterday, they tested the robotic arm by leaving a foot-shaped impression in the surface to learn how to properly operate and control the equipment.

During its projected three month life, Phoenix will use the scoop on its arm to dig below the surface and bring up material for analysis in its sophisticated experimental labs.  It should be able to determine whether water ice is present and if it could have sustained simple life forms.  The lander will also take first-of-its-kind measurements of the atmosphere in the polar region of the planet.

The next mission to Mars is currently en route and should flyby the planet next February.  The Dawn spacecraft is on its way to enter orbit around two of the largest members of the asteroid belt, the asteroid Vesta and the dwarf planet Ceres.
---------------------------------------------------------------------------------------------
This month in our skies we see that Mars is gradually dimming as we pull further away in our annual trek about the Sun.  By month’s end it will be setting around midnight local time.  Saturn continues to be the dominant planet during the early evening, but now Jupiter starts to rival it in the hours following midnight.  You can spot Jupiter low in the southeast after 11 p.m. and it will traverse the southern sky all the way until dawn.

The Boise Astronomical Society will be meeting on Friday, June 13th.  The meeting will start at 7 p.m. in Classroom #2 of the Discovery Center of Idaho.  This month, I will be the featured speaker.  My presentation is entitled “Cosmic Fireworks: From Supernovae to Gamma-Ray Bursts.” The public is invited to attend.

On Saturday, June 28, we will be holding our annual Bogus Basin Star Party.  It runs from 7 p.m. until midnight.  It is free to the general public.

Like this story? Get more! Sign up for our free newsletters.