Living in the Universe

A Proxy for Europa

Fourth Week of May 2007

At a place called El Zacaton in Mexico, NASA is testing an underwater robot in one of the Earth’s deepest sinkholes as a first step towards searching for life on Jupiter’s icy moon Europa. El Zacaton is near the Gulf Coast of northeastern Mexico. It’s about three hundred and thirty feet wide and more than thirty-three hundred feet deep. It could easily hold the Washington Monument or the Eiffel Tower. Scientists plan to map and take samples in this dark water-filled fissure with the one and a half ton DEPTHX robot over the next two weeks, as a prelude to navigating Europa’s ice capped oceans in about twenty years.

That mission is the latest step in a four hundred year old endeavor to understand Jupiter and its distant moons. Chris McKay of NASA Ames Center in California says we’re so sure there’s water on Europa that the real question is whether there is also life, whether there’s something in the ocean that bugs can eat. The robot is the ideal way to search. The robot is lowered by a sixty ton crane, and it’s powered by batteries. It’s nicknamed Clementine for its round shape and orange color, and it’s going to make daily descents into the vertical cave known in Mexico as a cenote. In fact the cenotes known in this part of Mexico are often formed from the debris of giant impacts, and many were caused by the impact that extinguished dinosaurs and other mammals sixty-five million years ago.

The robot will take three dimensional images, collect rock samples, and using floodlight film nooks and crannies too deep for divers to reach. Plants, animals, fungus, microbes, and bacteria are the known forms of life, but there may be more branches to the tree of life on Europa. Learning more about life tells us about our own heritage and the benefits for health and medicine that it could bring, according to researchers in the project.

The idea of mapping Europa’s oceans with an automated robot was dreamed up by a Texas scientist called Marcus Gary at a barbeque in 2001. Two years later his team won NASA funding for the five million dollar project. Gary chose El Zacaton for the first major test of the robot, which is about the size of a small car, because its sheer depth at the site was an unknown quantity. In 1994, an American diver died trying to swim to the bottom. According to Gary, it’s an ideal testing ground because we can test the robot’s mapping powers in untried waters. Its great depth means that many of its microbes live without oxygen or light and could be similar to that which could exist on Europa.

Europa’s thought to have twice as much water as the entire Earth, and it’s intrigued scientists ever since Italian astronomer Galileo Galilei observed Jupiter’s large four moons for the first time in 1610. NASA has hopes to take the probe to Antarctica in November 2008 to test it in the much colder waters below the frozen ice that resembles Europa, and if funding can be found, the scientists could send a much smaller version of the robot to Europa in about twenty years. That’s a long time to wait for a measurement of life, but water much closer at hand features in another story from this week, further evidence of a wet past on Mars.

The Mars rover Spirit has uncovered possibly the strongest evidence that the planet was much wetter than previously thought, by analyzing a patch of soil in Gusev crater and finding it unusually rich in silica. The presence of water would have been necessary to produce such a large silica deposit, according to team scientists. Principle Investigator Steve Squyres of Cornell University said in a statement to the news media, “This is a remarkable discovery. It makes you wonder what’s still out there.”

Spirit previously found clues of ancient water in the crater through the presence of sulfur rich soil, water altered minerals, and explosive volcanism, but this latest find is compelling because of the high silica content, which raises the possibility that conditions may have been favorable for the emergence of primitive life. It’s not clear how silica deposits form. One possibility is that the soil mixed with acid vapors in the presence of water. Others believe the deposit was created from water in a hot spring surrounding. The durable Spirit and its twin Opportunity have been working on overtime since completing their primary three month mission all the way back in 2004. For eight months opportunity has explored the rim of Victoria Crater on the opposite side of the planet. Scientists are exploring for a safe opening to send the rover in. These missions are managed by NASA’s JPL laboratory, and we can expect further discoveries from these intrepid rovers searching for evidence of previous life and wet conditions on Mars.

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A Hot Ice Giant

Third Week of May 2007

With over two hundred exoplanets or planets around other stars known, it takes a pretty special exoplanet to rate a news story, but a very exciting planet was found last week, a hot ice giant around the star Gliese 436. This odd planet is the size of Neptune, and it’s made mostly of hot, solid water, it was discovered not too far from Earth, and it offers evidence that other planets may be covered with oceans. European astronomers reported the discovery this week.

The planet is called Gliese 436b. “It orbits around a cool, red star just thirty light years away,” said the team from the Geneva observatory led by Frederic Pont, an astronomer who helped make the discovery. He said, “It’s not a very welcoming planet.” It’s hot because it’s near its star and under high pressure because of its mass. In this strange state of matter the water is frozen by the pressure but it’s hot, hot enough to boil. It’s a very strange world. We’re used to seeing water changing conditions because of temperature, but in fact water can be solidified by pressure. “The planet is also likely to be blanketed by hydrogen,” said the researchers.

These conditions are hardly conducive to life, but if there is water there could be water on planets in other solar systems and then life as we know it. Not all the water on this big planet is likely to be frozen. Some of it could be liquid, and where there’s liquid water we believe there can be life. This planet is particular because it also passes in front of its parent star causing a mini-eclipse with an amount of light diminishing in proportion to its size. Knowing the size of the planet helps a lot with the interpretation because among the two hundred or so exoplanets known only a dozen or so have size variations measured by their eclipses.

From the size and the mass we can get the density, and the density of Gliese 436 suggests that it is made mostly of water. The researchers are not absolutely sure that the composition is water, but with this kind of density, and if you take the materials that usually make a planet, it’s very typical of water planets. What the researchers actually say in their report is that the mass and radius that we measure for Gliese 436b indicate that it is mainly composed of water ice. It is an ice giant planet like Uranus and Neptune rather than a small mass gas giant or a very heavy super-Earth. It’s also very close to its star which is an M dwarf or a cool red star, meaning a small star a hundred times less bright than the Sun and about half the Sun’s mass. Smaller stars are cooler and redder. They also live longer which is an interesting possibility as far as life’s concerned because this star may have lived a significant fraction of the age of the universe since the big bang, about fourteen billion years. The coolness of a red star is why water can persist, albeit in a hot and solid state on the planet. The astronomers estimate its temperature at five hundred and twenty degrees Kelvin which is two hundred and fifty degrees Celsius or five hundred and forty degrees Fahrenheit.

Gliese 436b is by far the closest, smallest, and least massive transiting planet detected so far. It’s only thirty-three light years away. Last month members of the same team said they had found the most Earth-like planet outside our solar system with balmy temperatures orbiting another red dwarf star called Gliese 581. The planet hunting game is “heating up,” and as we find planets like this, exotic water worlds, we have to wonder how strange life might be to inhabit such locales in the universe.

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Finding Clones of Home

Second Week of May 2007

NASA researchers have demonstrated that a space telescope rigged with the right equipment could actually photograph an Earth-like planet orbiting a nearby star. This is major news because as you probably know virtually all of the planets found so far are about the size of Jupiter, and virtually all of them have been found with the Doppler method, an indirect technique where the planet is revealed by the fact that it wobbles the star that it orbits. That wobble is detected as a periodic Doppler signal.

Imaging Earth-like planets is extremely difficult. They reflect less than a billionth of the light of their parent star, and they sit projected incredibly close to the star, when seen from far away. NASA researchers have made lab experiments as work in preparation for the Terrestrial Planet Finder, which is designed to hunt for an Earth twin that might harbor life. Trying to image an exoplanet is a daunting task because of the relatively dim glow and how much it’s overpowered by the bigger, brighter star. The challenge is often been compared to looking for a firefly next to a searchlight.

But two researchers at the JPL facility in Pasadena, California, have shown that a fairly simple coronagraph, an instrument used to mask a star’s glare, paired with an adjustable mirror could enable a space telescope to image a distant planet that’s ten billion times fainter than its central star. John Trauger, who’s the lead author of a paper in Nature magazine describes the work, “Our experiment demonstrates the suppression of glare extremely close to a star, clearing a field dark enough to allow us to see an Earth twin. This is a thousand times better than anything demonstrated previously.” The paper describes a new system called the High Contrast Imaging Testbed and how this technique could be used with a telescope in space to see exoplanets. The lab experiment used a laser as a simulated star with fainter copies of the laser star serving as the planets.

In the lab demonstration, the High Contrast and Imaging Testbed overcame two significant hurdles all telescopes face when trying to make images of Earth-like planets: diffracted and scattered light. When starlight hits the edge of a telescope’s primary mirror it becomes slightly disturbed in accordance with the wave nature of light, producing a pattern of rings or spikes around the major source of light in the focused image. This diffracted light could completely obscure any planets in the field of view. To address this problem Trauger and his colleagues fashioned a pair of masks for their system. The first, which resembles a blurry barcode, directly blocks most of the starlight while the second clears away the diffracted rings and spikes. The combination creates enough darkness to allow the light of any planets to shine through. “Mathematically, this coronagraph blocks the central star and its rings,” says Wesley Traub, another member of the team.

Scattered light presents an additional hurdle. Minor ripples on a telescope’s mirror produce speckles or faint copies of the star shifted to the side which can also hide planets. In fact they look planet-like, so speckles are often confused with planets. In the High Contrast Imaging Testbed a deformable mirror the size of a large coin limits scattered light with a surface that is altered slightly by computer controlled actuators. Many times a second this mirror compensates for the effects of minor imperfections in the telescope and instrument. Traub said, “This result is important because it points to the way to building a space telescope with the ability to detect Earth-like planets around nearby stars.”

Trauger and Traub plan to improve the suppression of speckles by a further factor of ten and extend the method to accommodate many wavelengths of light from red to blue simultaneously. I should also point out that this is not entirely a job for space alone. Here at the University of Arizona, we’re building a telescope called the Large Binocular Telescope. Its twin mirrors, giving it an effective aperture of 11.4 meters, work in concert. With an instrument called a nulling interferometer as its instrument, a similar suppression of the central starlight is possible. Deformable secondary mirrors correct for fluctuations in the Earth’s atmosphere, allowing this very large telescope, much larger than anything that can be launched into space, to separate a planet from the much brighter nearby star. Then, clever use of optics to overcome diffraction and scattered light, as with the JPL experiment, sufficiently blots out the central star to reveal the Earth-like planet.

Essentially there’s a race between ground-based facilities like the LBT and space-based projects like the Terrestrial Planet Finder. Both goals are the same, to find twins of the Earth, and it will be an exciting time indeed when astrobiologists find the first clone of our own planet and smear its feeble light into a spectrum to allow astronomers to detect chemical tracers of biology.

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Life and Death on Mars

First Week of May 2007

This week saw the publishing of a report that showed that NASA can be faced with uncomfortable subjects when it considers life and death on Mars. A human mission to Mars is in the offing within the next decade or more, and NASA has suddenly had to realize that it hasn’t answered the questions like: how do you get rid of the body of a dead astronaut on a three year mission to Mars and back? When should the plug be pulled on a critically ill astronaut who’s using precious oxygen and endangering the rest of the crew? Should NASA use DNA testing to weed out astronauts who might get a disease on the long flight?

With NASA planning to someday land on Mars and the recent discovery of the most Earth-like planet ever that I covered last week, the space agency has been forced to consider some of these thorny practical and ethical issues posed by deep space exploration. In fact, the relevant document was obtained by the Associated Press after a Freedom of Information Act request, so NASA isn’t exactly putting it out there for everyone to see. It’s an uncomfortable subject. NASA doctors and scientists with help from outside bioethicists and medical experts plan to answer many of these questions over the next few years. At the moment, they’ve just raised them.

Richard Williams, NASA’s chief health and medical officer, says, “As you can imagine it’s a thing that people aren’t really comfortable talking about. We’re trying to develop the ethical framework to equip future commanders and mission managers to make difficult decisions.” One topic that’s too hot to handle: how do you cope with sexual desire amongst healthy young men and women during a mission years long? We’ve just seen a very recent love triangle involving a crazed astronaut dressed in a diaper traveling halfway across the country to deal violently with a rival. What could happen on a three-year mission to Mars? Hormones will fly. Tempers will flare. Emotions will run strong. Crazy things could happen. But sex is not even mentioned in the NASA document; it is essentially a taboo topic at NASA. That’s pretty short sighted. They’re going to have to face this eventually. Williams said the question of sex in space is not a matter of crew health but a behavioral issue and will have to be taken up by others at NASA. So he basically punted on that one.

Bioethicist Paul Wolpe at the university of Pennsylvania, who’s advised NASA for six years says, “A decision is going to have to be made about mixed-sex crews, and there’s going to be a lot of debate about it,” especially given recent news. But the document does spell out some health policies in detail such as how much radiation astronauts can be exposed to. The answer? No more than the amount that would increase the risk of cancer by three percent over an astronaut’s career. Also, the number of hours crew members should work each week: no more than forty-eight.

But on other topics, such as the steps for disposing of the dead or cutting off an astronaut’s medical care if he or she cannot survive, the document merely says that these are issues for which NASA needs a policy. Here’s Wolpe again, “There may come a time in which a significant risk of death has to be weighed against mission success. The idea that we will always choose a person’s well being over mission success, it sounds good, but it doesn’t really turn out to be necessarily decisions will always be made.” For now astronauts and cosmonauts who become critically ill or injured at the international space station, something that’s never happened, can leave the orbiting outpost, it’s only two hundred and twenty miles above Earth, and return home within hours aboard a Russian Soyuz space vehicle. That simply wouldn’t be possible if a life or death situation were to arise on a voyage to Mars where the nearest hospital is a hundred million miles away. Moreover, Mars-bound astronauts will not always be able to rely on expert advice and instructions from mission control since it might take nearly half an hour for a question to be asked and the answer to come back by the radio.

Astronauts going to the Moon and Mars for long periods of time must contend with basic health risks from space travel multiplied many times over, and those include radiation, loss of muscle and bone, and the psychological challenges that go along with extreme isolation. NASA will consider whether astronauts must undergo preventative surgery such as appendectomy to head off medical emergencies during a mission, and whether astronauts should be required to sign living wills with end of life instructions. The space agency must also decide whether to set age restrictions on the crew and whether astronauts of reproductive age should be required to bank sperm or eggs because of the risk of genetic mutation from radiation exposure during the long trip. These are pretty heavy things to consider.

Already NASA is considering genetic screening in choosing crews for the long duration missions, something that’s currently prohibited. Taking a longer view, NASA’s three major tragedies resulted in seventeen deaths: Apollo 1, Challenger, and Columbia. But they were all caused by technical rather than medical problems. NASA has never had to abort a mission because of health problems, although the Soviet Union has had three such episodes, and some people think the U.S. space agency, coming to these issues so late and so hesitantly, has simply not adequately prepared for the possibility of death during a mission. Listen to former astronaut Story Musgrave, a six-time space shuttle flyer who has a medical degree. “I don’t think they’ve been great at dealing with this type of thing in the past. I guess it’s nice they’re considering it now.” Life and death on Mars: one of the things we’ll have to consider when we look for life in the nearby universe.

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