Living in the Universe

Dust Storms and the Mars Rovers

Fourth Week of July 2007

Dust storms on Mars have been in the news for the last few weeks. A series of severe Martian summer dust storms has blocked ninety-nine percent of the direct sunlight to the Opportunity rover, and its companion Spirit has been affected to a lesser extent. Both rely on solar panels to charge their batteries. Scientists think these storms could continue for several days or even weeks. Alan Stern, who is the associate administrator of the science directorate of NASA said, “We’re rooting for our rovers to survive these storms, but they were never designed for conditions this intense.” NASA says the rovers won’t be able to generate enough power to keep themselves warm and operating under reduced sunlight for much longer.

Before the dust storms, Opportunity’s solar panels had been producing about seven hundred watt-hours of electricity per day. The dust has reduced daily output to less than four hundred watt-hours, prompting the rover team to suspend driving and most observations. Last Wednesday, Opportunity’s solar output dropped even further to a measly hundred and thirty watt-hours. Remember, the rovers have been exploring Mars since landing in 2004 for a mission originally planned for only three months. So the rovers are being maintained on minimal life support as they fight conditions that stop them getting their precious lifeblood.

Meanwhile, scientists up the road from me at Arizona State University are using the thermal imaging system on NASA’s Mars Odyssey to monitor these large dust storms on the red planet. Their instrument, which is a multi-wavelength camera sensible to five different wavebands, provides scientists and spacecraft controllers with global maps that track the amount and the distribution of atmospheric dust obscuring the planet. The current dust storm erupted during the last week of June, and it’s affecting operations of all five spacecraft at Mars. The fleet currently includes two NASA rovers on the ground, Spirit and Opportunity, plus three orbiters, two of which belong to NASA, Mars Odyssey and Mars Reconnaissance Orbiter, and one to the European Space Agency, Mars Express.

Being on the surface of the planet, the rovers have been directly affected by the storm, and Opportunity has had to postpone its descent into Victoria Crater. Scientists are anxious to enter this crater because it will give them a chance to investigate the compositions and textures of exposed minerals in the crater’s depth for clues about ancient wet environments. These clues are an important step in determining whether or not the planet has supported life in its past. Beginning in Mars’ heavily cratered Southern Highlands the dust storm took a week to grow large enough, but it currently encircles the planet and dust has now drifted into the northern hemisphere as well.

This is the traditional time of the Martian year for dust storms. It’s summer in the southern hemisphere. That’s when Mars lies closest to the Sun, and the solar heating is the greatest. We can watch the weather fronts spreading and kicking up dust in a big way. As winds sweep dust into the atmosphere, the atmosphere gets warmer. This adds to the storm’s power, helping it pick up more dust, but the process does have a built-in limitation. When the dust becomes thick enough, it reflects sunlight from the atmosphere allowing the air near the surface to cool, and that’s why the dust storms eventually abate. As seen from orbit the dust storm has the effect of veiling surface features and sometimes econcealing them completely, which hasn’t yet happened.

This storm isn’t as big or as severe as one that occurred in 2001. All the other orbiters can still see the surface, but from the ground the dust in the air cuts the amount of sunlight and reduces the electrical power to the rovers. If you were standing next to the rovers, you’d see the sky looking tawny with haze. The Sun would appear as a sharp-edged disk, but the light level would be visibly lower. Luckily summer is a time when the rovers can best survive under reduced power. If the storm had struck during the local winter, the rovers might not get enough power during the day to stay alive through the cold Martian night. How long will this storm last? Nobody knows for sure, but its effects probably won’t disappear as quickly as the storm erupted and Mars is likely to remain dusty for a couple of months more.

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Giant Outer Exoplanets are Rare

Third Week of July 2007

I’m pleased to be able to report this week on major research done by my colleagues at the University of Arizona, in particular by professor Laird Close in the department, and by one of our best young graduate students, Beth Biller. These astronomers and others in their team have used powerful new telescopes in Arizona and Chile to survey planets around other stars, and they’ve discovered that extrasolar planets more massive than Jupiter are extremely rare in other outer solar systems.

Unlike most of the studies done for extrasolar planets that have led to their discovery using the Doppler method, this was an imaging survey using highly sophisticated techniques to cheat the atmosphere and its blurring and produce exceptionally sharp images that would allow the detection of a planet near a distant star. These astronomers just concluded a benchmark three-year survey using direct detection techniques better than anyone has used before to look at fifty-four young nearby stars. These stare are among the best candidates for having detectable Jupiter-like planets at distances beyond five astronomical units or the distance between Jupiter and the Sun. As a reminder, One A.U. is the distance between the Earth and the Sun.

So far we’ve found over two hundred and thirty planets around other stars. Many of them are super-Jupiters orbiting very close to their parent stars. Scientists have written over two thousand papers about these giant Jupiter-like planets within a few Earth-to-Sun distances of their stars. However, the radial velocity method presently used is most sensitive to planets close to their stars moving on fairly rapid orbits. The technique has not been going long enough to reveal extrasolar planets further out. Remember that Jupiter in its orbit of the Sun takes twelve years. So even more distant planets would take decades to complete an orbit and we simply don’t have enough Doppler data to find them. Astronomers need other techniques to map extrasolar planets at those large distances, and they then determine what the average planetary system looks like and whether ours is a typical solar system.

The three-year survey had a very strong and unequivocal result. It didn’t turn up even one giant extrasolar planet in the outer part of any of these nearby solar systems. According to Laird, “We certainly had the ability to detect super-Jupiters at ten A.U. and further out around young Sun-like stars.
The odds are extremely slight that planets larger than four or five Jupiter masses exist at distances greater than twenty A.U. from these stars, and so there is no planet oasis between twenty and a hundred A.U.” Another member of the team, grad student Eric Nielsen, who is also from Steward Observatory, said, “We achieved contrasts high enough to find these super-Jupiters but didn’t.”

Astronomers were surprised in the early days of planet hunting to find this population of massive super-Jupiters within the orbit of Mercury taking only a few days to orbit their planet. Now we know from this survey that there aren’t large numbers of giant planets lurking at large distances from their stars. We now have a much more complete picture of giant planet formation. The team used Laird Close’s novel Simultaneous Differential Imager, SDI, for observations made with the European Southern Observatory’s VLT, or Very Large Telescope in Chile, and they also used the six and a half meter MMT observatory in Mt. Hopkins here in Arizona. The new measurements show the power of imaging to weigh in on the demographics of extrasolar planets, and we can expect more results like this in the months and years to come.

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An Extreme Microbiologist

Second Week of July 2007

I’d like to note the passing and celebrate the career of Imre Friedmann, an extreme microbiologist who died at the age of eighty-five. Conventional wisdom says that life stands no chance at all on the surface of Mars. Fields of reddish oxidized rock stretch to the horizon. Carbon dioxide fills the atmosphere, and UV radiation burns through it. Deep cold and dryness are everywhere. There may have been water, for the poles have icecaps and the ground shows channels, gullies, and shifting shorelines, but water alone is no proof of life. That’s what science says, but human curiosity and hope say otherwise.

For Imre Friedmann hope lay in a squarish grey lump of rock known as ALH84001, the meteorite picked up in 1984 in the Allan Hills of Antarctica. Traces of gas inside it seemed to prove that it came from Mars, and there were also microscopic strings of pearls, as Friedmann described it, flexible chains of crystals that seemed to have been formed by an organic process. They were like fossilized internal compasses of magnetotactic bacteria of which kind examples still exist on Earth, and since such bacteria need oxygen their presence suggested that photosynthesizing organisms must have lived on Mars too.

Well, the promise of the life in the Mars rock faded away and Friedmann was disappointed too, but his long search for life in the most daunting places on Earth mirrored the bleakness of the Martian terrain. The organisms he studied were nothing much to see. They lay under the stony floor of deserts like the Negev, the Gobi, and the Atacama, or in the bone-dry valleys of the Antarctic. He called them cryptoendoliths or hiders in rocks. Most of them were cyanobacteria, familiarly known as blue-green algae, organisms that cling precariously to life in the most extreme conditions of heat, cold, dryness, or salinity.

For many years the scientific world was indifferent to Doctor Friedmann’s studies of these organisms. Fame engulfed him in 1978 not long after the first Viking lander when Mars had disappointingly concluded that the planet’s soil was sterile. So NASA scientists recalled that two years before Friedmann with his wife, also a microbiologist, had published a paper on bacteria surviving in terrain almost as hostile as Mars, and suddenly the dead rocks began to suggest a different story. Friedmann always felt a certain tenderness for his cryptoendoliths. “Always hungry, always too cold, in this grey zone,” he said. In human terms, you could compare them to the most miserably living generations of pariahs in India. They are born. They live, and they die in the gutter like pariahs, or like him when as a Jew growing up in Budapest he was debarred from university, then forced into a labor camp, driven into a life of hiding from both Germans and Russians bent on killing him as though he was the most contemptible form of life.

His enthusiasm for science had started in boyhood in his mother’s kitchen, but his taste for extreme microbiology began in the 1950s at the Hebrew University of Jerusalem. He’d gone there as a refugee to restart his academic career. As a student of seaweed he had the outlandish idea that he might find a single-celled version of seaweed in the desert, and he did indeed find under the limestone surface of the Negev a greenish layer like a copper compound that turned out to be algae alive. When he moved to Florida State University, and with NASA’s interest, money began to come in. He traveled frequently in search of more. Well into old age he could be spotted in bright red parka and frozen beard lying full length on the Antarctic sandstone to snap pictures of some tiny life containing fissure in the rocks, or he could be seen in the Atacama desert gently attaching sensors to rocks as if they were living bodies so his data boxes could record for seven years the least intimation of something interesting happening inside them.

Any such movement on Mars had long since ceased. About three billion years ago, by the best estimates, life has died out there. But Friedmann was fascinated by the thought that Mars might well have been warm, wet, and biologically pulsing before the Earth was. This provided another data point from which to explore the origins of life. It was possible too that life had originally come from Mars, since it was much easier to make that journey that way than in reverse, and that it’d come in the form of bacteria locked in meteorites like Allan Hills 84001. Almost as a dare, Friedmann suggested that future voyagers might try to terraform Mars by reintroducing pioneer organisms, the cyanobacteria he had discovered. Like the Martian dreams of most earthlings, it seemed beyond all bounds of probability, but Friedmann’s plucky little organisms, life at its most resilient, most resistant, could never be counted out for anything.

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Life as We Don’t Know It

First Week of July 2007

This week a panel of senior scientists convened by the country’s leading science advisory group says the hunt for extraterrestrial life should be greatly expanded to include what they call weird life, organisms that lack DNA or other molecules found in life as we know it. The scientists conclude in their report that their investigation makes it likely that life is possible in forms different from those on Earth.

Experts have hailed this report as an important rethinking on the search for life. NASA’s lead scientist for the Mars Exploration Program, Mike Meyer, says, “It’s going to help us a lot to make sure we’re going exploring with our eyes wide open.” Starfish, sequoia, salamanders, and the rest of the Earth’s residents may seem diverse, but they’re surprisingly similar at the molecular scale. All species that scientists have studied need liquid water to survive, for example, and they all rely on DNA to carry genetic information. And they all use that information to build proteins from the same set of building blocks, twenty different amino acids.

NASA has long looked to life on Earth to guide its search for life on other worlds. Planets and moons that have hints of liquid water have always ranked high on the list of potential sites for life detection missions. In fact NASA’s summary of its strategy is: follow the water. But there’s now good reason to suspect that other kinds of chemistry could support life as well, the authors of this new report argue.

Weird life could differ from life as we know it in big or small ways. For example, while DNA uses phosphorous in its backbone, it might be possible to build a backbone out of arsenic instead, and life might exist in liquids other than water, perhaps ammonia or methane. The report even explores the possibility of life based on silicon, not carbon, although Mike Meyer who was not part of this study thinks that astrobiologists should limit their search to carbon-based life forms. “When we look in the universe,” he said, “the only compounds we see with more than six atoms are all based on carbon chemistry. That’s a strong hint that looking for carbon chemistry may be the best bet. There we have some idea what to look for.” The report calls both NASA and the NSF to fund research into weird life.

“Chemists need to investigate chemical possibilities for what life forms might take,” said one member of the committee, Steve Benner, who’s a Distinguished Fellow at the Foundation for Applied Molecular Evolution in Gainesville. Scientists should also continue to search the Earth for weird life. “There’s so much about Earth life we don’t understand,” says the panel’s chairman, John Baross, who’s a professor of oceanography at the University of Washington. Benner also said, “There’s good evidence that the life we know on Earth was preceded by a weird form of life.” It may have been based on RNA, a single stranded form of DNA. Although DNA based life out-competed earlier forms, RNA life may still exist in particular refuges.

One potential hiding place is deep below the ocean floor. “It’s an incredibly primordial world down there,” said John Baross. If you’re going to look for remnants of an RNA world, those are the environments you want to look in. To find weird life, however, scientists will have to build completely new types of detectors. There’s no question that the surveys of life on the planet we’ve done so far would have missed it.

The scientists also said that the possibility of weird life should prompt NASA to reorder its future missions. They’ve singled out Saturn’s moon Titan as particularly promising. The Huygens probe that visited Titan in 2005 found evidence for liquid methane raining down on its surface as well as a mix of water and ammonia seeping out from the interior. Since then we’ve seen large liquid lakes as big as the Great Lakes made of ethane, methane, and ammonia. These large bodies of liquid could conceivably support life, although not necessarily life as we know it. Nothing, the report concludes, would be more tragic in the American exploration of space than to encounter alien life and fail to recognize it.

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