Living in the Universe

Why It’s Hard to Live Off-Earth

Fifth Week of March 2007

This week I want to talk about a natural consequence of biological evolution when it reaches the level of technology and intelligence. At some point, we might presume, people or other alien creatures will want to go “off world.” They’ll either use up the resources of their home planet or curiosity will take them farther afield. As we’ve just begun the space activity we’re starting to learn all the issues involved and just how hard it can be. The practical issue that arises in space exploration is whether we want to move out there, with humans and all of the infrastructure they require, or do our exploration with robots and remote sensing using telescopes.

NASA is facing this issue right now because of its Moon, Mars, and Beyond initiative. The drive to explore and colonize the Moon is switching into high gear and some scientists worry that exploration will come at the expense of doing science leading to the policy question, which is a better investment: science or exploration? There’s been a continual tension within NASA and in space circles over this issue. Can science benefit from a drive to live off the land in space? It’s not clear.

One key goal for a self-sustaining colony is to find minerals for building materials, such as aluminum for habitats. The best source for aluminum ore on the Moon is in the highland regions where abundant deposits of feldspar average twenty-eight percent aluminum oxide. Collecting this feldspar could produce a science spin-off because the lunar highlands are also studded with boulders that are remnants of the ancient lunar crust. Some of these rocks were studied in the Apollo missions, but they’ve not been sampled in great detail.

Another promising lunar resource is helium 3, an isotope deposited by the solar wind that’s extremely rare on Earth, but is a prime fuel for fusion reactors should such devices ever be developed successfully. Studies by several researchers suggest that helium 3 could be exported to Earth, but it could also be used to generate heat and electricity on the Moon. But either scenario would require the massive extraction of material from the lunar regolith, that granular material sometimes called soil. A regolith mining project would offer a chance to resolve questions about the history of the Moon. There is science there but it’s extremely expensive and scientists continue to argue over whether lunar exploration should be done for its scientific benefit, or just to deserve us a place off-world, an outpost for jumping off into deep space.

A story in Astrobiology Magazine this week with the catchy title “Pizza Delivery in Nine Months or Less” also deals with the issue of going off-world. Researchers have developed a software tool for modeling supply chains between planets in order to better understand the requirements for establishing human bases on the Moon and beyond. If you think shipping freight across the United States is challenging, imagine trying to deliver an oxygen generation unit from the Earth to a remote location on the Moon.

According to current plans, by 2020 NASA plans to establish a long-term human presence on the Moon, potentially centered on an outpost to be built at the rim of the Shackleton Crater near the lunar south pole. To make this scenario possible, a reliable stream of consumables such as food, fuel and oxygen, spare parts, and exploration equipment would have to make its way from the Earth to the Moon as reliably and predictably as any Earth-based delivery system, or even more predictably because a single missed shipment can have devastating consequences when you can’t easily replenish essential supplies.

To figure out how to do this two MIT researchers released some software for modeling interplanetary supply chains. It’s called SpaceNet. That reminds us of the Terminator scenario, doesn’t it? The system is based on a network of nodes on planetary surfaces in stable orbits around the Earth, the Moon, or Mars, or at those well defined points in space where the gravitational force between two bodies, in this case the Earth and the Moon, cancel each other out. These are called Lagrange points. These nodes act as a source, or a point of consumption, or a transfer point for space exploration logistics.

The term supply chain usually refers to the flow of goods and materials in manufacturing facilities, but one of the researchers said that a well-designed interplanetary supply chain could operate on much the same principles with some complicating factors. Transportation delays might be significant, as much as six to nine months in the case of Mars, and shipping capacity will of course be very limited. This requires mission planners to make difficult trade-offs between the competing demands for different types of supplies. SpaceNet evaluates the capability of vehicles to carry both pressurized and unpressurized cargo. It simulates the flow of vehicles, crew, and supplies through the trajectories of the chain, takes into account how much fuel and time are needed, and then costs the whole thing out.

To test in an environment as close as possible to harsh planetary conditions, MIT researchers conducted an expedition to Devon Island in the Canadian Arctic in 2005. The researchers established a semi-permanent shelter at the existing NASA sponsored Haughton-Mars research station and compiled an inventory of materials at the base including key items such as food, fuel, tools, and scientific equipment. They experimented with all the logistic technologies such as radio frequency identification that will track assets.

The goal is to create a smart exploration base that can increase safety and save astronauts and explorers precious time. This interesting research reminds us that the goal of a lunar base is not so far off. We may one day have to face the difficulties, challenges, and thrills of having people living off-world.

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A Land That Time Forgot

Fourth Week of March 2007

Come with me to a lost world, a place that time forgot. It’s a valley in the Chihuahua desert of Mexico where there are strange formations surrounded by looming mountain ranges where we find evidence of the earliest life on Earth, or rather life that lives under conditions very similar to early life on Earth. In addition to the tall mountains and gypsum dunes, this arid region is speckled with spring-fed pools called posas that vary in size, color, and in the complexity of the species they contain.

Posas have become living laboratories for astrobiologists. They are home to stromatolites, the kind of life form that exists early on the Earth billions of years ago. The first life on Earth was microbial and remained single-celled for most of the Earth’s history. This life evidence crops up in the first 3.8 billion years, and life was single-celled for over two billion years. Most organisms lived in communities during that time, forming bacterial mats that trap dirt and nutrients. Modern stromatolites are rare because many modern organisms compete with them for food and space. The Quatro Cienegas region of Mexico is unusual because stromatolites persist there and manage to live with other species.

It’s likely that the early stromatolites on Earth were anoxic, given the small amounts of oxygen in the atmosphere, but the Quatro Cienegas stromatolites produce oxygen. Scientists taking core samples of these stromatolites have found that the top layer of the mat is composed of diatoms. Beneath those are oxygen-producing photosynthetic cyanobacteria. There are purple sulfur bacteria in the third layer and sulfur-reducing bacteria in a last layer. Each layer obtains and processes energy in a different way and makes different waste products, yet it is a symbiotic community where each layer contributes to the survival of the mat as a whole. These living laboratories allow us to understand how life worked early on Earth.

Water in the posas is exceptionally low in phosphorous, which is vital for many functions of life and even forms the backbone of DNA, but life in Quatro Cienegas has evolved to compensate for the lack of that element. Understanding how life is able to survive such conditions could help scientists understand the limitations of life in chemical environments elsewhere. In fact, the scarcity of phosphorous also makes Quatro Cienegas a good analog of the Precambrian Earth. About six hundred million years ago the fossil record suddenly filled with the profusion of different life forms, an event that’s called the Cambrian explosion. There was also a spike of phosphorous in the rock record at that time and some scientists think the two events may be related.

A second story that emerged this week also involves primitive life forms of extraordinary durability. In this case it’s the very resilient bacterium called Deinococcus radioduran, which is sometimes given the nickname Conan the Bacterium. Deinococcus radioduran can protect itself from extraordinarily high doses of ionizing radiation. The paper under review has the indigestible title: Protein Oxidation Implicated as the Primary Determinant of Bacterial Radioresistance. Fifty years ago when scientists discovered Deinococcus radioduran it led to speculation that the incredible resistance exhibited by bacteria had to do with its mechanism of DNA repair, and most research has centered on this hypothesis.

However recent research shows nothing unusual in the microbe’s DNA repair mechanisms, and it appears that other bacteria at different level of resistance sustain the same amount of DNA damage from a given dose of radiation. Additionally, many bacteria are killed by radiation doses that actually cause very little DNA damage. In this study, the scientists found that resistant and sensitive bacterial cells had different metal concentrations pointing to high levels of manganese and low iron levels, and this was a possible influence on cellular recovery. The team showed that the most resistant bacterial species contained three hundred times more manganese and three times less iron than the most sensitive species. It turns out that these bacteria withstand extraordinarily harsh conditions by protecting their proteins rather than repairing their DNA rapidly. This new study is casting light on the varied mechanisms by which bacteria on Earth and maybe in other solar systems may survive, endure, and persist.

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The Cost of Saving the Earth

Third Week of March 2007

I want to return to a subject that I’ve covered once before, the idea of major impacts from space debris. These impacts have caused mass extinctions in the history of life on Earth, and we believe similar debris will cause impacts and extinctions on other terrestrial planets. It’s something that life in the universe just has to deal with. Of course when life gets advanced or complex or intelligent as we are, it has the possibility to circumvent or prevent these impacts, and that’s the basis of the story.

Back in 2004 astronomers discovered that an asteroid called Apophis, named after the Greek god for destruction, had a chance of hitting the Earth. Back then it was given a one or two percent chance of colliding with the Earth in 2029. Well new observations and new simulations have shown that it will pass within twenty thousand miles of the Earth in 2029. That concentrates the mind wonderfully because if it did hit the Earth, someone would get a very nasty headache indeed. It’s two hundred and fifty meters across, five times larger than the objects which produced the Meteor Crater north of me in Arizona and the Tunguska blast back in 1908 in Siberia.

As it passes close to us it stays in orbit with some probability that will bring it back much closer in 2036, on April 13 to be precise. If it passes through this “gravitational keyhole” then its chances of hitting us on 2036 are one in forty-five thousand; that’s low enough not to worry, but it’s a worrying issue anyway. So NASA commissioned a survey to find ninety percent or more of all objects that are a kilometer or more in diameter. Such a survey had been requested by Congress a decade ago, spurred by Shoemaker-Levy where we watched the comet plunge into Jupiter and cause a huge impact much larger than the size of the Earth. In 2005 Congress ordered the survey that is now about to start, aimed at extending the ninety percent coverage by 2020 to smaller nearby objects, everything bigger than a hundred and fifty meters across. NASA’s charter has been changed explicitly to include responsibility for providing advanced warning of potential devastating impacts.

So how do we deal with them? The preferred way is a Hollywood-style heroic space mission to knock the object off course or blow it up, through what would almost surely be an unmanned effort. At a conference just last week in Washington all the latest ideas were discussed. The standard idea, using a nuclear bomb, as Bruce Willis did in the 1998 film Armageddon, is to land on the asteroid, drill into the rock, leaving a bomb behind. Trouble is, asteroids are strange rocks. They are porous agglomerations of smaller bits, more like balls of popcorn loosely held together than baseballs. So a blast from within an asteroid would just break it into pieces, each of which would hit the Earth continuing on their same trajectory. Not smart.

Another option is a nuclear detonation on the asteroid’s surface or above it. Such a blast would cause some of the rock on one side to vaporize and send the asteroid in the other direction. Given enough lead time, even a slight course change would be more than enough to send the rock out of harm’s way. Yet another scheme calls for a ballistic impact, hurling a few tons of non-explosive material at high speed to knock it off course. There are even some really crazy ideas out there, the most far-fetched being a proposal to change the color of the asteroid making it lighter or darker so it absorbs and reradiates more or less sunlight affecting its spin and eventually its orbit. This is what might be called the rolling stones approach. I see an asteroid, and I want it painted black.

Perhaps the best option is something called a gravity tractor, a hovering spacecraft that would use only its gravitational pull to tug the rock into a different orbit. That’s very elegant. A gravitational tractor has the advantage that it’s more likely to leave the asteroid intact. Since they’re held together so weakly, an explosion is definitely not the way to go. But a scientist from NASA’s JPL pointed out at the conference, there’s a trade-off to be made when deciding what to do about an asteroid. The faster the gravitational tractor is dispatched, the cheaper it needs to be to achieve its goal. However, a long wait means a more accurate gauge of the asteroid’s orbit and thus of the need to do anything at all, because in most cases the asteroid will miss. Even a small mission to an asteroid costs hundreds of millions of dollars so this is not an easy choice, especially considering the number of potential collisions that a detailed survey will uncover.

So what do we do? It’s not even clear who should make the choice. Rusty Schweickart, a member of the Association of Space Explorers, a club of ex-astronauts and cosmonauts, has been working with his colleagues to lobby the U.N. to put asteroid impact planning on the agenda, but given the glacial pace at which the UN approaches its work, that’s probably not going to be a good enough emergency response. NASA has no plans to test an asteroid deflection scheme.

Luckily, the Europeans do. The European Space Agency has a project in the pipeline with an irony that maybe even the organizers and planners didn’t appreciate. It’s known as Don Quixote. The mission will have two craft, Hidalgo and Sancho, and as in Cervantes’ novel, the servant will observe while his master makes a fool of himself by crashing blindly into the target asteroid. If all such asteroids turn out to be harmless windmills, it will have been a wasted effort, but if one does turn out to be a threatening giant, future generations may be very glad of the Don’s headlong challenge.

So there are ways to avoid the worry of a meteoric or asteroid impact on the Earth. These odds are small enough that it shouldn’t prey on anyone’s mind. We should be thankful that astronomers and the world’s planners are taking these threats seriously.

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Mission to Alpha Centauri

Second Week of March 2007

Today I want to talk about a wild but exciting idea that was presented in a talk given by Debra Fischer here in my university, in a lecture series that I organize, a few weeks ago. Debra Fischer is one of the most illustrious of the planet hunters. She started her work with Geoff Marcy in the mid-1990s just at the time the first exoplanets were being discovered. She’s continued and moved on to form her own research team and has been involved in the discovery of a good fraction of all the two hundred exoplanets known.

She gave a wonderful talk, and at the end of the talk she threw out an idea that excited and provoked everyone in the audience. It’s the subject of a white paper that she’s currently writing. She developed this idea with her colleague Greg Laughlin. It’s a mission to Alpha Centauri. As you know, there are two hundred exoplanets, but none of them are Earth-like planets. Most are Jupiter-sized or maybe a little bit smaller, and the Doppler method that’s responsible for finding most of those planets runs out of steam or is unable to detect signatures of planets smaller than about Neptune or Uranus.

Fischer points out the nearest neighbor to the Sun, Alpha Centauri which is actually a system rather than a single star, has the possibility to host Earth-like planets. Because it’s so near and so bright, Doppler observations can be pushed to the absolute limit to the level where we can detect terrestrial planets. So instead of waiting decades for missions that are actually not yet funded by NASA to find hundreds of Earth clones mostly hundreds of light years away, why not find the nearest Earth now or in a couple of years?

To explore Debra’s idea in more detail, let’s talk a little bit more about the Alpha Centauri system. It’s four and a third light years away and is indeed the nearest star to the Sun. It has three components, so it’s actually a triple system. A and B are in close orbit around each other. A is almost exactly a Sun clone, B is quite similar but a slightly younger star, and C is quite dissimilar. It’s a puny red dwarf, and it’s much wider in orbit around the other two. So let’s toss out C as an unlikely place for life, but notice that A and B are both close enough to the Sun to have the possibility of terrestrial planets. We also use the information from models that suggest that almost every planet that’s been found so far, Jupiter-sized or larger, will also be in systems that harbor terrestrial planets on closer orbits. Terrestrial planets seem to form almost every time planets form.

The two closer stars to each other, twenty astronomical units apart, are nonetheless far enough apart that they would not disrupt the orbits of any planets within four AU. In other words, planets around either of those two stars that are at a Mars distance from their suns or closer would not be disrupted by the fact that it’s a binary system. So we get two bites at the cherry.

Fischer’s idea is to take a two-meter telescope, of which there are several around the world that are not heavily used, and dedicate it to observations of these two stars essentially for two years, night after night, nodding between A and B, taking Doppler high-precision radial velocity measurements of the Alpha Centauri system. Acquiring three hundred thousand observations over two years, the errors can be beat down to the point where the sensitivity far exceeds what is possible today with typical observations. That means that if either Alpha Centauri A or B contained a Mercury, a Venus, an Earth, or a Mars, they could be detected with this data. It gives us two shots at finding terrestrial planets around the nearest stars and in only two years. Which is incredibly exciting. Perhaps we find our Earth clone, and it’s in the nearest star system to ours, and we know the answer within a couple of years.

But Fischer and Laughlin don’t stop there. They say, why not go? Having an Earth clone so close, and the possibility of life on that Earth clone of course, means you would be spurred to investigate. Fischer and Laughlin point out that nanotechnology has improved to the point where we might be able to put a microscopic space orbiting device in a small package, so she imagines launching a fleet of nanobots. Think of them as cell phone-sized objects that contain the capability to analyze the atmosphere of a distant planet or take pictures or movies of it as it approaches.

We launch these nanobots, and here’s the extrapolation part, somehow with a technology like matter/anti-matter drives these nanobots get accelerated to about a tenth the speed of light. There is no fundamental limitation to this technology, but we haven’t developed the propulsion units yet. It seems like it could be done. So a fleet of nanobots accelerated to a tenth the speed of light would take a couple of decades to reach the Alpha Centauri system. Then there’s another problem. How do they send the data back? Once they are several light years away, the signals will be very feeble as heard from Earth. There’s no way to get that data back because there are no high gain antennas so far away, and these devices would be too small to carry a big antenna.

The answer: you send wave after wave of nanobots. Presumably, the unit cost of these devices is pretty small, so there would be hundreds or even thousands in a wave with each wave launched a few months apart. Then the leading wave, once they start arriving at the Alpha Centauri system, beams back at light speed their data to the wave that follows and so on back down the chain, like a fireman’s bucket being passed down a water line. In that way we can get the information back in not much longer than it took the probes to reach there, and actually at more like light speed.

Overall this means the probes would take a few decades to reach there and the information could get back to us within six or seven years. Fischer thinks that within our lifetimes we have the possibility to find an Earth clone, send probes there, and get the information back on what life might exist on those planets. That’s a truly exciting and audacious project.

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Fossil-Hunting on Mars

First Week of March 2007

Mars still represents our nearest and best opportunity for finding life beyond the Earth, and we have a number of missions that are heading there in the next decade. Recent news stories reflect two missions that are heading there. The first is the Mars Science Laboratory, due to launch in 2009.

MSL will have on it a rover that will have the capability to look for existing or fossilized life forms. Jack Farmer, a professor of geological sciences at ASU, up the road from me in Phoenix, gave a talk at the annual meeting of the American Association for the Advancement of Science in San Francisco last week. He said, “Searching for extraterrestrial life must follow two alternative pathways, each requiring different approach and tools. If we are to look for living organisms we’re doing exobiology, but if we’re seeking traces or biosignatures of ancient life, it’s better to call it exopaleontology. Unfortunately,” as he notes, “for the next decade, technological limitations will force us down the exopaleontology path. To find living organisms on Mars, you need to find liquid water, and because liquid water is unstable on the surface today, that means going deep under the subsurface.”

In fact, it’s not even clear how deep we will have to go to find liquid water. Certainly at the higher latitudes in the poles, water exists in the frozen form only a few inches below the surface, but it’s possible that liquid water would be miles deep. There’s no way we can reach that. In practical terms, robotic drilling being limited to a couple of yards, we’re going to look for fossilized or ancient life forms rather than living germs. Finding the signature of an ancient biosphere means exploring old rocks that preserve traces of life for millions or billions of years.

Farmer says the best places to look on Mars are the deposits left by springs and former lakes in the heavily cratered highlands. These rocks date from a period in Martian history when liquid water was common at the surface and conditions on Mars were actually similar to those on the Earth at the same time. He says, “Besides water, life also requires energy sources and organic building blocks.” The Mars Exploration Rover Opportunity found ample evidence for water in the ancient rocks at Meridiani Planum, but the rover’s instruments can’t detect organic materials. Farmer notes that recognizing a Martian fossil could be very difficult. As he puts it, “We’re not talking about stumbling over dinosaur bones.”

In fact the most likely biological formed structures in these sediments will probably be stromatolites like those found on Earth. These are distinctive structures that form in shallow oceans or lakes or streams were microbial colonies trap sediments to form thin, repeating layers. Stromatolites also contain microscopic cellular remains and chemical traces left by the microbes that form them. Taken together, these colonies are already the primary source of evidence for life on ancient Earth, and they may well become the best evidence for ancient life on Mars.

The second Mars story involves a mission that’s even further off. It’s the ExoMars rover, with greatly increased capabilities compared to the rovers we currently have roaming around Mars. It’s not due for launch until 2013, but last week NASA selected one instrument, called Urey or more formally the Mars Organic and Oxidant Detector, for instrument development funds at a level of three quarters of a million dollars. That’s a good sign that this mission is going to go ahead. The European Space Agency is running this mission, and it plans to use the ExoMars rover to grind up samples of the Martian soil into a fine powder and then deliver them to a suite of analytic instruments, including Urey, that will search for signs of life. Each sample will consist of about a spoonful of material dug from the underground by a robotic drill, but of course not very far below the surface as already noted.

Urey is of course named after Harold Urey, the scientist and chemist who developed the famous “life in a bottle” experiments in the 1950s. The Urey experiment is designed to look for organic molecules such as amino acids at incredibly low concentrations, as low as a few parts per trillion. All life on Earth assembles chains of amino acids to make proteins. However amino acids can be made either by living or non-living means. This means it’s possible that Mars has amino acids but has never had life. So how do we distinguish between biological and non-biological amino acids?

The Urey instrument team is going to make use of the knowledge that most types of amino acids can exist in two different forms: left-handed and right-handed. In other words these are molecules that have shapes and they’re distinct just as the hands of a human are distinct between right and left. The right hand of a human mirrors the left, and so the two forms of amino acids mirror each other. Amino acids from non-biological sources come in a fifty-fifty mix of right-handed and left-handed forms. Life on Earth, from the simplest microbes to the largest plants and animals including us, makes and uses only left-hand amino acids, with very rare exceptions. That’s probably because life conserves energy, which made it a favorable choice to pick one handedness and then stick to it for all its chemical functions. Comparable uniformity, either all left or all right, is expected in any extraterrestrial life using building blocks that have mirror image versions because a mixture would complicate biochemistry and make it more inefficient.

According to Dr. Allen Farrington, the Urey project scientist, “The Urey instrument will be able to distinguish between left and right-handed amino acids.” If Urey were to find an even mix of the mirror image molecules on Mars that would suggest life as we know it never began there. All left or all right would be strong evidence that life now exists on Mars, with all right dramatically implying an origin separate from Earth life, which is all left.

It’s also possible that life moved from the Earth to Mars or vice versa being carried by meteorites. Something between fifty-fifty of left and right and uniformity could result if Martian life once existed, because amino acids created biologically gradually change towards an even mixture in the absence of life. Urey is a beautifully designed experiment. Looking at the handedness or shape of molecules can distinguish between current biology, former biology, and no biology at all. It’s going to be hard to wait almost a decade to learn the results.

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