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[ Posted : 04.14.04 ]


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Methane on Mars: Or … “Back to the Future …?”


By Richard C. Hoagland
© 2004 The Enterprise Mission



Part 1

 

It was one of those sunny, Southern California days that songwriters have made famous.

The group of us gathered at NASA’s Jet Propulsion Laboratory that morning, just north of Los Angeles, in Pasadena, were still slightly in a daze; just a week or so before, this same diverse assembly – veterans of America’s fledgling space program ranging from space scientists to space journalists, from network anchors to their production staffs and advisors – had been uniquely privileged to witness firsthand the modern culmination of a Dream:

Neil Armstrong’s first immortal footprints on the Moon.

Now, seemingly but an eye blink later, this same diverse group was gathering for an equally unprecedented encore … the flyby of an even farther planet by twin unmanned NASA spacecraft: Mariners 6 and 7. The destination this time?

Mars.

This was not the first visit by an American spacecraft to the mysterious Red Planet. That honor was reserved for a previous unmanned mission – Mariner 4 – which flew only 6000 miles away in July of 1965. But now, only four years later – literally, as Neil and Buzz were being simultaneously debriefed in their quarantine in Houston from their extraordinary human adventures on the Moon just days beforethose of us covering the on-going NASA program were anticipating the impending reconnaissance of the next “obvious destination” for human beings beyond the surface of the Moon (as viewed from the unbelievable perspective of “the Summer of 1969”)—

Mars itself.

 

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Now just days away from Mars this late July, the two new unmanned spacecraft (above) were far more sophisticated than the pioneering Mariner 4; instead of a single television camera as the major “science instrument,” Mariner 6 & 7 carried dual television systems (for narrow and wide-angle imaging) – including, a capability for the first close-up color images of Mars; in addition, as opposed to the set of interplanetary “particle and field” experiments carried by Mariner 4, these spacecraft focused solely on an array of sophisticated additional instrumentation for the first detailed close-up spectral analysis of Mars atmosphere and surface.

These “ultraviolet and infrared spectrometers” -- capable of detecting extremely low concentrations of a range of atmospheric gases – were co-mounted with the cameras on a movable “scan platform,” which hung below the main body of the spacecraft (above). It was through searching for key “biomarkers” in the Martian atmosphere, gases that on Earth are created by living organisms, that the NASA scientists hoped to find out if Mars might be “alive.” In particular, the Mariner instruments were searching for two key hydrogen compounds -- methane and ammonia -- known to be given off by living systems ….

 


 

The twin Mars exploration spacecraft – Mariners 6 and 7 – were launched just a month apart, in February, and again in March, of 1969. They arrived at Mars just four months later; Mariner 6 flying within ~2000 miles of Mars’s surface on July 30th, Mariner 7, following at about the same distance, passing Closest Approach on August 4th.

Unfortunately, during the July 30th flyby, critical refrigeration of the Mariner 6 infrared spectrometer (IRS) malfunctioned – thus preventing the recording of long-wave spectral information. This meant that, if we were going to discover any “biomarkers” indicative of living organisms currently on Mars, we would have to await Mariner 7’s imminent encounter … fortunately, only four days later.

 


 

I will always remember that packed JPL Auditorium, 48 hours after Mariner 7 successfully flew by the planet Mars. Its IRS instrument had worked perfectly, but it had taken almost two additional days for the Berkeley science team (whose experiment it was) to fly to and from Berkeley to reduce their preliminary spectra. Now, they were back at JPL … about to tell us what they’d found.

First up, however, was a display of the spectacular fly-by Mariner 7 images (below). The classic, enigmatic dark markings had never been this clear; the rotation of the planet so easily discerned -- as the distances, image resolution, and early questions raised by never-before-seen details were patiently explained by the Imaging Team Leader and his colleagues.

Soon – for those of us waiting impatiently for the crucial spectrometer results – the picture show was over. Now, another side of history was about to begin ….


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As Science Advisor for the Special Events Unit of CBS News, I was standing at the back of Von Karman this particular morning, beside veteran CBS reporter Bill Stout, both of us taking in the scene. My job: interpret the technical jargon coming from the NASA panel that Stout didn't understand … which left me with a lot of time to examine the new images and observe the reactions in the room; for I’d quickly learned that Bill Stout – whom I’d met for the first time just weeks before, for our historic coverage of Apollo 11’s landing on the Moon -- knew almost everything about the space program … if not this new Mars mission. Luckily – because of this -- I was free to truly focus on what was going on … and what it felt like to be a witness to space history.

As with everybody else gathered in Von Karman on that morning, though mightily impressed by the new images – which showed Mars with a clarity no human eyes had ever seen before (Lowell included …) – Bill and I ... and a thousand other folks .... were impatiently awaiting the BIG show … the one Mariner scientist guaranteed to make the CBS Evening News that night (after we sent our story to New York), regardless of his results:

George Pimentel.

Dr. Pimental was the literal creator and Principal Investigator (chief scientist) for the Mariner 6& 7 Infrared Spectrometers (IRS, below). As each Mariner flew by the planet at about 2000 miles, the infrared spectra recorded by the spacecraft were supposed to tell his team (and us!) if the Martian atmosphere did indeed contain any of the key “biomarkers” just discussed … potential signatures for a “living, breathing Mars.” This (below) is the remarkable instrument that Pimental and his Berkeley Team devised.

 

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Several years earlier, an obscure, visiting JPL medical technology specialist, James Lovelock – who would later gain world wide recognition as author of the then highly controversial “Gaia Hypothesis” – wrote a letter to Nature, the preeminent British science journal. In it Lovelock recommended--

 

“… some physical tests for the presence of planetary life. One of these was a top down view of the whole planet instead of a local search at the site of landing. The test was simply to analyze the chemical composition of the planet's atmosphere. If the planet were lifeless then it would be expected to have an atmosphere determined by physics and chemistry alone and be close to the chemical equilibrium state. But if the planet bore life, organisms at the surface would be obliged to use the atmosphere as a source of raw materials and as a depository for wastes. Such a use of the atmosphere would change its chemical composition. It would depart from equilibrium in a way that would show the presence of life. Dian Hitchcock joined me then and together we examined atmospheric evidence from the infra-red astronomy of Mars (Hitchcock and Lovelock 1967). We compared this [ground-based, telescopic] evidence with that available about the sources and sinks of the gases in the atmosphere of the one planet we knew bore life, Earth. We found an astonishing difference between the two atmospheres. Mars was close to chemical equilibrium and dominated by carbon dioxide, but the Earth was in a state of deep chemical disequilibrium. In our atmosphere carbon dioxide is a mere trace gas. The coexistence of abundant oxygen with methane and other reactive gases, are conditions that would be impossible on a lifeless planet. Even the abundant nitrogen and water are difficult to explain by geochemistry. No such anomalies are present in the atmospheres of Mars or Venus, and their existence in the Earth's atmosphere signals the presence of living organisms at the surface. Sadly, we concluded that Mars is lifeless now, although it may once have had life [emphasis added] ….”

 

Lovelock’s pessimism notwithstanding -- obviously based on the technological limitations to finding those key biological indicators, methane, ammonia, etc. in the Martian atmosphere up to that time from Earth – his revolutionary “biomarker” ideas were actually at the heart of Pimental’s Mariner ‘69 experiment. For, Pimental’s spacecraft-based, infrared detectors were now thousands of times closer to Mars … and thus potentially millions of times more sensitive than the best Earth-based telescopic IR observations. If these tell-tale “biomarkers” were present in the Martian atmosphere – even in significantly lower concentrations than on Earth -- this new NASA Mission had the best chance in history of detecting this evidence of living “Martians” ….

 

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Pimental began to speak, and a classic hush fell over the crowded Auditorium. One way or another, we were about to know. He called for his first slide ….

On the giant projection screen that spanned the whole width of Von Karman, a montage of new close-in Mariner 7 images appeared (below). Using this mosaic, Pimental explained the geometry of the simultaneous IRS spectral observations – a swath that took the instrument’s field of view down across the southern Martian latitudes … then across the Pole.

 

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A new graphic appeared (below) -- a squiggly line … depicting Mariner’s read-out of the Martian atmosphere during this imaging sequence. The IRS Principal Investigator carefully explained that, as the instrument crossed the darkened band hugging the edges of the bright white polar cap of solid CO2 (above), two anticipated absorptions suddenly appeared – at 3.0 and 3.3 microns (below).


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Quoting from a recent history of Pimental’s Experiment:

 

“[The] spectra … crossed the south polar cap edge and then continued deep into the polar cap. IRS spectra from the cap edge showed bands at 2.0, 3.0 and 3.3 µm (4900, 3300 and 3020 cm -1 ). They [the IRS Team] knew C O2 ice had a band at 2.0 µm, and this band appeared in all their polar cap spectra, indicating IRS measured C O2 ice the entire time it viewed the cap. However, when moving from the cap edge toward the cap center, both the 3.0 and 3.3 µm bands disappeared. If C O2 ice caused these two bands, then it somehow caused them at the cap edge but not farther into the cap.

“To further complicate the issue, the IRS group could not find any reports in the literature of bands in C O2 ice at 3.0 and 3.3 µm. Therefore, the disappearance of those two bands while IRS still viewed C O2 ice, combined with the lack of reports of C O2 ice bands at those wavelengths led the group to conclude that something which occurred only at the polar cap edge caused the two bands [Pimentel corr., 18 Jul 1972 ].

“To investigate the puzzle in the few hours before the upcoming the Mariner 7 press conference, they spent the night measuring spectra. They were not yet set up to measure sprayed-on C O2 ice in the lab,and so they measured it as a solid block. When they did this, they found no bands at 3.0 and 3.3 µm. On the other hand, their [laboratory] spectra of methane and ammonia gas showed bands at 3.0 and 3.3 µm. Therefore, less than 48 hours after receiving their data, they reported at the Mariner 7 press conference that IRS had measured methane and ammonia at the polar cap edge [Mar. 7 Press Conf. Transcript, 1969]. This created quite a stir because of its implications for life ….”

 


 

It was Percival Lowell, the famous 19th Century astronomer -- literal founder of the modern science of “comparative planetology” -- who made the first detailed observations of this mysterious “transition zone” around the annually melting Martian polar caps.

Although Lowell believed, based on the technology of the time and analogy with Earth, that these caps were water ice (we now know – in large part because of Mariners 6 & 7 -- that they’re frozen CO2), other aspects of Lowell’s late 1800’s observations were remarkably accurate – judging by the results of thousands of professional and amateur astronomers’ recent electronic Mars imaging, made during the opposition and closest approach of 2003 (below). (These images are reversed -- with the south Martian polar icecap at the top – as seen in a normal telescopic view.)

 

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As important as his pioneering Mars work would become, Lowell left an even more valuable contribution to this fledgling science of planetology: he made his observations (and that of his colleagues at the Lowell Observatory -- which he founded at Flagstaff, Arizona in the late 1800’s), available to a world wide, general audience. From this, we now have an invaluable public record of the earliest years of planetary science … to compare with modern observations, such as the Mariner ’69 fly-bys … or last years’ closest approach in over 60,000 years.

Writing in his first book in 1895, “MARS,” Lowell observed:

 

“On May 1, then, Martian time, the cap was already in rapid process of melting; and the speed with which it proceeded to dwindle showed that hundreds of square miles of it were disappearing daily. As it melted, a dark band appeared surrounding it on all sides [above]. Except, as I have since learned, at Arequipa , this band has never, I believe, been distinctively noted or commented on before, which is singular, considering how conspicuous it was at Flagstaff . It is specially remarkable that it should never have been remarked upon elsewhere, in that a similar one girdling the north polar cap was seen by Beer and Madler as far back as for it is, as we shall shortly see, a most significant phenomenon. In the first place, it was the darkest marking upon the disk, and was of a blue color. It was of different widths at different longitudes, and was especially pronounced in tint where it was widest, notably in two spots where it expanded into great bays, one in longitude 270 degrees and one in longitude 330 degrees. The former of these was very striking for its color, a deep blue, like some other-world grotto of Capri . The band was bounded on the north, that is, on the side toward the equator, by the bluish-green areas of the disk. It was contrasted with those both in tone and tint. It was both darker and more blue ….

“What can explain so general and so consecutive a change in hue? Water suggests itself; for a vast transference of water from the pole to the equator might account for it. But there are facts connected with the change which seem irreconcilable with the idea of water. In the first place, Professor W. H. Pickering found that the light from the great blue-green areas showed no trace of polarization. This tended to strengthen a theory put forth by him some years ago, that the greater part of the blue-green areas are not water, but something which at such a distance would also look blue-green, namely, vegetation. Observations at Flagstaff not only confirm this, but limit the water areas still further; in fact, practically do away with them entirely ….”


Lowell’s observations conditioned later generations of astronomers and readers to anticipate that the “dark band” observed around the shrinking polar cap each Martian spring was likely melting water, which was vital (on the arid planet) to supporting some kind of seasonal vegetation.

As Mariner 7’s IRS instrument swept across this dark transition to the icy polar cap, the sudden appearance of spectral features indicative of well-known byproducts of decomposing vegetation, or colonies of certain microorganisms, seemed to clinch it:

Mariner 7’s remarkable infrared observations, through detection of one of Lovelock’s crucial “biomarkers,” had all-but-confirmed current life on Mars ….

 


 

That summer night in 1969, while Walter Cronkite summarized our breaking “possible life on Mars” story from New York, Bill and I watched the west coast network feed – once again from the back of JPL’s Von Karman. As the piece ended, I turned and couldn’t help observing with a wry smile:

“Well, look at that – ‘life on Mars’ ... and we got all of 15 seconds on the Evening News. I wonder what we’d get if they invaded …?”

 


 

A few weeks after his remarkable, historical announcement … George Pimental had a sudden “change of heart.”

At a specially-called press conference at NASA Headquarters, in Washington DC, Pimental publicly retracted his previous assertion that Mariner 7 “had discovered methane and ammonia on Mars,” explaining instead that the anomalous lines were more likely due to “C O2 ice when it has lattice imperfections" [Herr and Pimentel, 1969]. The date of Pimental’s retraction?

September 11, 1969 .

Fast forward the film ….

 


 

… to, September 2003.

Dr Michael Mumma, of the Center for Astrobiology at NASA’s Goddard Space Flight Center, announces -- at the annual meeting of the Division for Planetary Sciences -- the preliminary results of a new, far more sensitive Earth-based search for methane in the atmosphere of Mars. Utilizing NASA’s Infrared Telescope Facility in Hawaii (below, left), and the “Gemini South” Telescope in Chile (below, right), Mumma and his team carried out a detailed new infrared survey of the Red Planet early in 2003 … with remarkable result.

 

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Mumma’s preliminary analysis (below) reveals a methane concentration of about 10.5 parts per billion. Under current Martian temperatures and pressures, this translates to about 90,000 tons ….


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More intriguing -- unlike Pimental’s Mariner ’69 polar observations, the methane in the current NASA study seems to be concentrated in the equatorial regions of the planet (above) -- the enhanced methane, according to Mumma, being greatest over the two equatorial locations of “anomalous hydrogen” previously localized by the Mars Odyssey GRS experiment (below) –

Precisely the locations of our two projected “ancient tidal oceans” … and (coincidentally?) the sites of the current rover missions. Where one of them has just uncovered robust “ground truth” of a former “ancient salty sea ….”

 

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A few months later, a second team -- this one headed by Vittorio Formisano, of the Institute of Physics and Interplanetary Science in Rome – announced their independent discovery of Martian methane. The new detection was made by the Planetary Fourier Spectrometer (PFS), aboard ESA’s Mars Express spacecraft.

According to Formisano, the results were obtained by averaging over 1700 atmospheric scans, made of the planet between January and February, 2004.

Then, a few days later, a third team reported its separate discovery of methane on Mars as well – this time led by Vladimir Krasnopolsky, of the Catholic University of America in Washington DC . Krasnopolsky and his team used the Canada-France-Hawaii 3.6 meter telescope (below, right) to accomplish their detection … again, at about 10.5 parts per billion. The Krasnopolsky team will formally present their results at the European Geophysical Union's meeting in Nice, France, in late April.

 

 

 

Three independent teams … three independent results … all affirming the presence of methane in the current atmosphere of Mars.

So ... what does it mean?

Methane normally has a very limited lifetime, exposed in an atmosphere such as Earth’s or Mars’ – only a few hundred years at best – before it is destroyed from various chemical reactions. Thus, if three teams are detecting methane now on Mars, somehow that means (at the very least) that the methane is being replaced as fast as it is disappearing.

Production mechanisms for methane on Earth (or Mars) are limited, there being essentially only three known sources: 1) volcanic emissions, 2) certain geochemical reactions, and … 3) biological activity.

On Earth, essentially all the methane present in the atmosphere comes from living organisms – either as direct emission by certain species of bacteria (even in the guts of cows!), or as fermentation by bacteria of previously living planet life after it has died. This applies – and is critically important -- even to that methane released through “geological activity,” including volcanism.

As Prof Colin Pillinger, the Open University space scientist behind England ’s Beagle 2 Mars lander explained it:

 

"This may not say that there's life on Mars, but it doesn't half get close. Whether it is produced by organisms now or from volcanic activity, the primary source of methane is microbes . Most of the natural methane gas released during geological activity on the Earth [volcanism] originally comes from the decomposition of organic matter. On a planet like Mars, methane doesn't hang around so you have to find a way of constantly replenishing it. It is very difficult to produce except from a biological source … [emphasis added]."

 

It is therefore quite probable, based on this terrestrial geological analogy, that the three independent teams’ new methane discovery has one root cause – either present (or past) biological activity on Mars … or both.

 

Parts 1 | 2 | 3 | ^

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