Posted on by Fraser Cain

The Ends of the Earth

Antarctic ice sheets. Image credit: NASA Click to enlarge
Pamela Conrad, an astrobiologist with NASA’s Jet Propulsion Laboratory, has traveled to the ends of the Earth to study life. Conrad recently appeared in James Cameron’s 3-D documentary “Aliens of the Deep,” where she and several other scientists investigated strange creatures that inhabit the ocean floor.

On June 16, 2005, Conrad gave a lecture entitled, “A Bipolar Year: What We Can Learn About Looking for Life on Other Planets by Working in Cold Deserts.”

In part 1 of this edited transcript, Conrad describes what sort of signs we could look for to see if there is life in an alien environment.

“In the past three years, I’ve been engaged in a project with several of my colleagues that takes us to hot and cold deserts. We want to observe the signatures of life, and see if we can tell the difference between places where life is and where life isn’t. The reason we go to deserts is to cut down on the number of confounding variables that are introduced by all kinds of life. Basically, we don’t want to be scraping away the dog poop to find the bacteria in the dirt.

This past year we were privileged to go to both the Arctic and the Antarctic. So this is my bipolar year, and what we were doing there is relevant to space exploration because, like a desert, the conditions on the surface of other planets are very harsh.

We look at rocks because, if life had been and is already gone – in other words, it’s dead, or it’s so dead it’s been fossilized and altered – you can find that in the rock record.

To detect life anywhere, you need to be able to investigate the environment and find measurable clues. If it’s not something you can define in measurable terms, it’s not science. So by definition, we’re kind of out in the cold, so to speak.

One of the challenges is coming up with measurable terms by which you could define life. The terms have to be universal enough to not miss life on another planet, if it was unlike the life we have here. We have a sample set of one: the biosphere on the Earth. We try to use the knowledge we have about life here to come up with those terms, and so we try to think about life in the most general descriptive terms we can.

We look for life in places that are habitable; places that are capable of supporting life. But habitability is difficult to define, because we only have a vague notion of what makes an environment habitable. At NASA, we’re very big on looking for water as one of the facets of habitability.

Water is as important to life in the desert as it is to us. After a fresh snowfall, when rocks get heated up and melt the ice, you see a bloom of cyanobacteria on the surface of the rock. Yet they are able to maintain a minimal existence when there’s not much precipitation.

One reason metabolism has to slow down in the Antarctic winter is because the water is in a solid phase and it’s not accessible. Living things can only use ice when it melts and becomes a good solvent. Using ice is like using a mineral in the crystal phase — when it’s in the solid form, you’ve got to use some energy to bust up those bonds to do something with it. There are organisms in Antarctica that have antifreeze types of molecules in them, fish that possess molecules called glycoproteins. When an ice crystal forms in the fish, the molecule grabs hold of the ice crystal as it starts to grow, and doesn’t let it grow in the direction that its energetically most easily grown. Because it can’t grow, the ice crystal gives up the ghost and turns back into water.

Besides water, we think that certain kinds of chemical elements are important for life elsewhere. Life on Earth is made of carbon and hydrogen and phosphorus and a few other important things, and we need the oxygen in the air. But there are microbes on Earth that breathe metal, and they don’t care about oxygen.

So habitability is really habitable in the eyes of the beholder. When you’re defining it, you’ve got to think about the broadest set of terms you can in order to encompass any kind of life you might be able to imagine. The ultimate assessment of whether a place is habitable is, of course, to see if it is inhabited.

You ask one set of questions if you want to know, “Can I set up housekeeping here?” You might ask another set of questions if you want to know, “Is anybody home?” But at the heart of it all, whether or want to live there or just see if anyone’s home, you have to know something about the neighborhood. You’ve still got to do all the experiments that tell you about the geophysical, mineralogical, and atmospheric properties of the planet. If you’re looking for life, you’ve got to have some notion about what sort of thing you’re trying to support with that environment.

Erupting about 5 million years ago, from a series of fractures known as the Cerberus Fossae, the water flowed down in a catastrophic flood, collecting in an area 800 x 900 km and was initially an average of 45 meters deep. Click image for larger view.Credit: ESA/Mars Express

So what would constitute proof? If you want to say that something has been proven, you have to achieve a certain level of consensus in the scientific community, otherwise your peers will tear you into little bits and pieces in the literature. Of course, there is never a complete consensus: that’s why we nasty scientists fight with each other endlessly. But we have to at least come up with terms. We can agree or disagree with each other’s theories, but we have to agree on the terms and the measurements.

So what kind of measurements could we make if we were looking for life? Does a planet look different if life has been there? For example, if you go into my kitchen after I’ve eaten, you might see a plate or a crumb. That’s a clue that I was there. There are clues at the planetary level too. A biomarker – a clue that says life was there – can be anything that was produced by life. The clue can be chemical, because chemicals comprise everything. I am a sack of chemicals, just like this podium is a sack of chemicals. Just what chemicals there are, and in what proportion to each other, and how they’re arranged in 3-D, is what distinguishes me from this. It’s a simple way of distinguishing categories of things.

Chirality is a biomarker as well. What chirality means is that some molecules are mirror images of each other, and the living molecules tend to be a certain handedness. When it comes to amino acids, which are the constituents of the proteins that make up life, living things like to use the left-handed form. And when it comes to the sugars, living things like to use the right-handed form. There are exceptions to these, but that’s a general case.

Isotopes also can be a biomarker. Some molecules come in different isotopic flavors, where some are slightly heavier than others. Living things like the lighter variety, probably because it’s energetically less expensive to process.

Complex polymers also could be biomarkers. Of course, plastic is a complex polymer. The again, we made the plastic. So this whole distinction between natural and unnatural – if humans made it, it’s still biogenic. So think about that. My car is a biosignature. What kind, I’m not sure.

If you’re going to define life in measurable terms, I’d like to keep it really simple. You could define life by what it’s made of, or you could define life by what it does. I like to define life by what it’s made of, because as soon as you say the “does” word, you’re talking about a process. A process is something that happens through time. Then you’ve got to figure out what the sampling rate should be. How often should you look, and how long should the whole experiment take? A process is a little more problematic because it takes time, and you may be wrong about how often to look, or how long you should look for.

Processes – making stuff, reproducing, or evolving – can take place over different time scales. So if you’re only looking at processes, and you have two that are vastly different in their time scales, you won’t be able to do the same experiment to look at them both. So I like to look at life in terms of what it is. Not to say we couldn’t add in a little bit of process-based stuff, but when you look at what life is, it gets simple really fast. It’s unique chemistry, some kind of proportionate chemicals, arranged in some way, and the “arranged in some way” is what I call structure.

If I were looking for life on another planet or a moon, I would look for places where interesting chemistry could happen, so that the ultimate evolution of that chemistry could create a living system. I would think about places like Europa, which has an ocean beneath ice. I would think about other places where ice exists, like comets. I would think about Titan, Saturn’s moon. I would think about all those places where interesting chemistry occurs, because chemistry is clever. You can get all kinds of interesting molecules.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Supernova Shockwave Slams into Stellar Bubble

X-ray image of SN 1987A. Image credit: NASA/CXC/PSU Click to enlarge
Recent Chandra observations have revealed new details about the fiery ring surrounding the stellar explosion that produced Supernova 1987A. The data give insight into the behavior of the doomed star in the years before it exploded, and indicate that the predicted spectacular brightening of the circumstellar ring has begun.

The supernova occurred in the Large Magellanic Cloud, a galaxy only 160,000 light years from Earth. The outburst was visible to the naked eye, and is the brightest known supernova in almost 400 years. The site of the explosion was traced to the location of a blue supergiant star called Sanduleak -69? 202 (SK -69 for short) that had a mass estimated at approximately 20 Suns.

Subsequent optical, ultraviolet and X-ray observations have enabled astronomers to piece together the following scenario for SK -69: about ten million years ago the star formed out of a dark, dense, cloud of dust and gas; roughly a million years ago, the star lost most of its outer layers in a slowly moving stellar wind that formed a vast cloud of gas around it; before the star exploded, a high-speed wind blowing off its hot surface carved out a cavity in the cool gas cloud.

The intense flash of ultraviolet light from the supernova illuminated the edge of this cavity to produce the bright ring seen by the Hubble Space Telescope. In the meantime the supernova explosion sent a shock wave rumbling through the cavity.

In 1999, Chandra imaged this shock wave, and astronomers have waited expectantly for the shock wave to hit the edge of the cavity, where it would encounter the much denser gas deposited by the red supergiant wind, and produce a dramatic increase in X-radiation. The latest data from Chandra and the Hubble Space Telescope indicate that this much-anticipated event has begun.

Optical hot-spots now encircle the ring like a necklace of incandescent diamonds (image on right). The Chandra image (left) reveals multimillion-degree gas at the location of the optical hot-spots.

X-ray spectra obtained with Chandra provide evidence that the optical hot-spots and the X-ray producing gas are due to a collision of the outward-moving supernova shock wave with dense fingers of cool gas protruding inward from the circumstellar ring (see illustration). These fingers were produced long ago by the interaction of the high-speed wind with the dense circumstellar cloud.

The dense fingers and the visible circumstellar ring represent only the inner edge of a much greater, unknown amount of matter ejected long ago by SK -69. As the shock wave moves into the dense cloud, ultraviolet and X-radiation from the shock wave will heat much more of the circumstellar gas.

Then, as remarked by Richard McCray, one of the scientists involved in the Chandra research, “Supernova 1987A will be illuminating its own past.”

Original Source: Chandra X-ray Observatory

Posted on by Fraser Cain

Saturn’s Rings Have an Atmosphere of their Own

Spectrum indicating atmosphere over rings. Image credit: NASA/JPL/SSI/SWRI/UCL Click to enlarge
Data from the NASA/ESA/ASI Cassini spacecraft indicate that Saturn’s majestic ring system has its own atmosphere – separate from that of the planet itself.

During its close fly-bys of the ring system, instruments on Cassini have been able to determine that the environment around the rings is like an atmosphere, composed principally of molecular oxygen.
This atmosphere is very similar to that of Jupiter’s moons Europa and Ganymede.

The finding was made by two instruments on Cassini, both of which have European involvement: the Ion and Neutral Mass Spectrometer (INMS) has co-investigators from USA and Germany, and the Cassini Plasma Spectrometer (CAPS) instrument has co-investigators from US, Finland, Hungary, France, Norway and UK.

Saturn’s rings consist largely of water ice mixed with smaller amounts of dust and rocky matter. They are extraordinarily thin: though they are 250 000 kilometres or more in diameter they are no more than 1.5 kilometres thick.

Despite their impressive appearance, there is very little material in the rings – if the rings were compressed into a single body it would be no more than 100 kilometres across.

The origin of the rings is unknown. Scientists once thought that the rings were formed at the same time as the planets, coalescing out of swirling clouds of interstellar gas 4000 million years ago. However, the rings now appear to be young, perhaps only hundreds of millions of years old.

Another theory suggests that a comet flew too close to Saturn and was broken up by tidal forces. Possibly one of Saturn’s moons was struck by an asteroid smashing it to pieces that now form the rings.

Though Saturn may have had rings since it formed, the ring system is not stable and must be regenerated by ongoing processes, probably the break-up of larger satellites.

Water molecules are first driven off the ring particles by solar ultraviolet light. They are then split into hydrogen, and molecular and atomic oxygen, by photodissocation. The hydrogen gas is lost to space, the atomic oxygen and any remaining water are frozen back into the ring material due to the low temperatures, and this leaves behind a concentration of oxygen molecules.

Dr Andrew Coates, co-investigator for CAPS, from the Mullard Space Science Laboratory (MSSL) at University College London, said: “As water comes off the rings, it is split by sunlight; the resulting hydrogen and atomic oxygen are then lost, leaving molecular oxygen.

“The INMS sees the neutral oxygen gas, CAPS sees molecular oxygen ions and an ?electron view? of the rings. These represent the ionised products of that oxygen and some additional electrons driven off the rings by sunlight.”

Dr Coates said the ring atmosphere was probably kept in check by gravitational forces and a balance between loss of material from the ring system and a re-supply of material from the ring particles.

Last month, Cassini-Huygens mission scientists celebrated the spacecraft’s first year in orbit around Saturn. Cassini performed its Saturn Orbit Insertion (SOI) on 1 July 2004 after its six-year journey to the ringed planet, travelling over three thousand million kilometres.

The Cassini-Huygens mission is a co-operative project of NASA, ESA and ASI, the Italian space agency.

Original Source: ESA Science

Posted on by Fraser Cain

Predicting Times for Clear Space Weather

Biggest solar flare recorded by SOHO. Image credit: SOHO Click to enlarge
Scientists funded by NASA have made big strides in learning how to forecast “all clear” periods, when severe space weather is unlikely. The forecasts are important because radiation from particles from the sun associated with large solar flares can be hazardous to unprotected astronauts, airplane occupants and satellites.

“We have a much better insight into what causes the strongest, most dangerous solar flares, and how to develop forecasts that can predict an ‘all clear’ for significant space weather, for longer periods,” said Dr. Karel Schrijver of the Lockheed Martin Advanced Technology Center (ATC), Palo Alto, Calif. He is lead author of a paper about the research published in the Astrophysical Journal.

Solar flares are violent explosions in the atmosphere of the sun caused by the sudden release of magnetic energy. Like a rubber band twisted too tightly, stressed magnetic fields in the sun?s atmosphere (corona) can suddenly snap to a new shape. They can release as much energy as one, 10 billion megaton nuclear bomb.

Predicting space weather is a complicated problem. Solar forecasters focus principally on the complexity of solar magnetic field patterns to predict solar storms. This method is not always reliable, because solar storms require additional ingredients to occur. It has long been known large electrical currents must be present to power flares.

Insight into the causes of the largest solar flares came in two steps. “First, we discovered characteristic patterns of magnetic field evolution associated with strong electrical currents in the solar atmosphere,” said ATC’s Dr. Marc DeRosa, co-author of the paper. “It is these strong electrical currents that drive solar flares.”

Subsequently, the authors discovered the regions most likely to flare had new magnetic fields merge into them that were clearly out of alignment with the existing field. This emerging field from the solar interior appears to induce even more current as it interacts with the existing field.

The team also found flares do not necessarily occur immediately upon the emergence of a new magnetic field. Apparently the electrical currents must build up over several hours before the fireworks start. Predicting exactly when a flare will happen is like studying avalanches. They occur only after enough snow built up. Once the threshold is reached, the avalanche can happen anytime by processes not yet completely understood.

“We found the current-carrying regions flare two to three times more often than the regions without large currents,” Schrijver said. “Also, the average flare magnitude is three times greater for the group of active regions with large current systems than for the other group.”

The researchers made the discovery by comparing data about magnetic fields on the sun?s surface to the sharpest extreme-ultraviolet images of the solar corona. The magnetic maps were from the Michelson Doppler Imager (MDI) instrument on board Solar and Heliospheric Observatory (SOHO) spacecraft. SOHO is operated under a cooperative mission between the European Space Agency and NASA.

The corona images were from the NASA Transition Region and Coronal Explorer spacecraft (TRACE). The team also used computer models of a three-dimensional solar magnetic field without electrical currents based on SOHO images. Differences between images and models indicated the presence of large electrical currents.

“This is a result that is more than the sum of two individual missions,” said Dr. Dick Fisher, Director of NASA’s Sun-Solar System Connection Division. “It’s not only interesting scientifically, but has broad implications for society.”

For imagery about the research on the Web, visit: NASA News Release

Posted on by Fraser Cain

Rhea’s Southern Pole

Southern polar region of Rhea. Image credit: NASA/JPL/SSI Click to enlarge
Like the rest of Rhea’s surface, the southern polar region of this Saturn moon has been extensively re-worked by cratering over the eons. This close-up shows that most sizeable craters have smaller, younger impact sites within them. Near the left lies an intriguing gash.
The largest well-defined crater visible here is an oval-shaped impact toward the upper right. The crater is 115 by 91 kilometers (71 by 57 miles) in size.

Cassini acquired this view during a distant flyby of Rhea (1,528 kilometers, or 949 miles across) on July 14, 2005.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera at a distance of approximately 239,000 kilometers (149,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 56 degrees. The image was obtained using a filter sensitive to wavelengths of infrared light centered at 930 nanometers. The image scale is about 1 kilometer (0.6 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Sea Ice May Be Increasing in the Antarctic

Antarctic Snow Depth on Sea Ice. Image credit: NASA Click to enlarge
A new NASA-funded study finds that predicted increases in precipitation due to warmer air temperatures from greenhouse gas emissions may actually increase sea ice volume in the Antarctic?s Southern Ocean. This adds new evidence of potential asymmetry between the two poles, and may be an indication that climate change processes may have different impact on different areas of the globe.

“Most people have heard of climate change and how rising air temperatures are melting glaciers and sea ice in the Arctic,” said Dylan C. Powell, co-author of the paper and a doctoral candidate at the University of Maryland-Baltimore County. “However, findings from our simulations suggest a counterintuitive phenomenon. Some of the melt in the Arctic may be offset by increases in sea ice volume in the Antarctic.”

The researchers used satellite observations for the first time, specifically from the Special Sensor Microwave/Imager, to assess snow depth on sea ice, and included the satellite observations in their model. As a result, they improved prediction of precipitation rates. By incorporating satellite observations into this new method, the researchers achieved more stable and realistic precipitation data than the typically variable data found in the polar regions. The paper was published in the June issue of the American Geophysical Union’s Journal of Geophysical Research.

“On any given day, sea ice cover in the oceans of the polar regions is about the size of the U.S.,” said Thorsten Markus, co-author of the paper and a research scientist at NASA?s Goddard Space Flight Center, Greenbelt, Md. “Far-flung locations like the Arctic and Antarctic actually impact our temperature and climate where we live and work on a daily basis.”

According to Markus, the impact of the northernmost and southernmost parts on Earth on climate in other parts of the globe can be explained by thermal haline (or saline) circulation. Through this process, ocean circulation acts like a heat pump and determines our climate to a great extent. The deep and bottom water masses of the oceans make contact with the atmosphere only at high latitudes near or at the poles. In the polar regions, the water cools down and releases its salt upon freezing, a process that also makes the water heavier. The cooler, salty, water then sinks down and cycles back towards the equator. The water is then replaced by warmer water from low and moderate latitudes, and the process then begins again.

Typically, warming of the climate leads to increased melting rates of sea ice cover and increased precipitation rates. However, in the Southern Ocean, with increased precipitation rates and deeper snow, the additional load of snow becomes so heavy that it pushes the Antarctic sea ice below sea level. This results in even more and even thicker sea ice when the snow refreezes as more ice. Therefore, the paper indicates that some climate processes, like warmer air temperatures increasing the amount of sea ice, may go against what we would normally believe would occur.

“We used computer-generated simulations to get this research result. I hope that in the future we?ll be able to verify this result with real data through a long-term ice thickness measurement campaign,” said Powell. “Our goal as scientists is to collect hard data to verify what the computer model is telling us. It will be critical to know for certain whether average sea ice thickness is indeed increasing in the Antarctic as our model indicates, and to determine what environmental factors are spurring this apparent phenomenon.”

Achim Stossel of the Department of Oceanography at Texas A&M University, College Station, Tex., a third co-author on this paper, advises that “while numerical models have improved considerably over the last two decades, seemingly minor processes like the snow-to-ice conversion still need to be better incorporated in models as they can have a significant impact on the results and therefore on climate predictions.”

Original Source: NASA News Release

Posted on by Fraser Cain

New Look for the Milky Way

Artist’s impression of the Milky Way. Image credit: NASA/JPL-Caltech/R Click to enlarge
With the help of NASA’s Spitzer Space Telescope, astronomers have conducted the most comprehensive structural analysis of our galaxy and have found tantalizing new evidence that the Milky Way is much different from your ordinary spiral galaxy.

The survey using the orbiting infrared telescope provides the fine details of a long central bar feature that distinguishes the Milky Way from more pedestrian spiral galaxies.

“This is the best evidence ever for this long central bar in our galaxy,” says Ed Churchwell, a UW-Madison professor of astronomy and a senior author of a paper describing the new work in an upcoming edition of Astrophysical Journal Letters, a leading astronomy journal.

Using the orbiting infrared telescope, the group of astronomers surveyed some 30 million stars in the plane of the galaxy in an effort to build a detailed portrait of the inner regions of the Milky Way. The task, according to Churchwell, is like trying to describe the boundaries of a forest from a vantage point deep within the woods: “This is hard to do from within the galaxy.”

Spitzer’s capabilities, however, helped the astronomers cut through obscuring clouds of interstellar dust to gather infrared starlight from tens of millions of stars at the center of the galaxy. The new survey gives the most detailed picture to date of the inner regions of the Milky Way.

“We’re observing at wavelengths where the galaxy is more transparent, and we’re bringing tens of millions of objects into the equation,” says Robert Benjamin, the lead author of the new study and a professor of physics at the University of Wisconsin-Whitewater.

The possibility that the Milky Way Galaxy has a long stellar bar through its center has long been considered by astronomers, and such phenomena are not unheard of in galactic taxonomy. They are clearly evident in other galaxies, and it is a structural characteristic that adds definition beyond the swirling arms of typical spiral galaxies.

The new study provides the best estimates for the size and orientation of the bar, which are far different from previous estimates.

It shows a bar, consisting of relatively old and red stars, spanning the center of the galaxy roughly 27,000 light years in length – 7,000 light years longer than previously believed. It also shows that the bar is oriented at about a 45-degree angle relative to a line joining the sun and the center of the galaxy.

Previously, astronomers debated whether a presumed central feature of the galaxy would be a bar structure or a central ellipse – or both. The new research, the Wisconsin astronomers say, clearly shows a bar-like structure.

“To date, this is the best evidence for a long bar in our galaxy,” Benjamin asserts. “It’s hard to argue with this data.”

The Spitzer Space Telescope was lofted into orbit in August of 2003. It consists of a telescope and three science instruments, including the Infrared Array Camera, the primary instrument used for the new survey, known as GLIMPSE for Galactic Legacy Mid-Plane Survey Extraordinaire.

NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center in Pasadena. JPL is a division of the California Institute of Technology.

Original Source: UW-Madison News Release