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Tilting toward life
But Mars goes through cycles of obliquity, or changes in its orbital tilt. Currently, Mars is wobbling back and forth between 15 and 35 degrees' obliquity, on a timescale of about 100,000 years. But every million years or so, it leans over as much as 60 degrees. Along with these changes in obliquity come changes in climate and atmosphere. Some scientists speculate that during the extremes of these obliquity cycles, Mars may develop an atmosphere as thick as Earth's, and could warm up considerably. Enough for dormant life to reawaken.
"Because the climate can change on long terms," says Clark, ice in some regions on Mars periodically could "become liquid enough that you would be able to actually come to life and do some things—grow, multiply, and so forth—and then go back to sleep again" when the thaw cycle ended. There are organisms on Earth that, when conditions become unfavorable, can form "spores which are so resistant that they can last for a very long time. Some people think millions of years, but that's a little controversial."
Desulfovibrio is not such an organism. It doesn't form spores. But its bacterial cousin, Desulfotomaculum, does. "Usually the spores form because there's something missing, like, for example, if hydrogen's not available, or if there's too much [oxygen], or if there's not sulfate. The bacteria senses that the food source is going away, and it says, 'I've got to hibernate,' and will form the spores. The spores will stay dormant for extremely long periods of time. But they still have enough machinery operative that they can actually sense that nutrients are available. And then they'll reconvert again in just a matter of hours, if necessary, to a living, breathing bacterium, so to speak. It's pretty amazing," says Clark.
That is not to say that future Mars landers should arrive with life-detection equipment tuned to zero in on species of Desulfovibrio or Desulfotomaculum. There is no reason to believe that life on Mars, if it ever emerged, evolved along the same lines as life on Earth, let alone that identical species appeared on the two planets. Still, the capabilities of various organisms on Earth indicate that life on Mars—including dormant organisms that could spring to life again in another few hundred thousand years—is certainly possible.
Clark says that he doesn't "know that there's any organism on Earth that could really operate on Mars, but over a long period of time, as the martian environment kept changing, what you would expect is that whatever life had started out there would keep adapting to the environment as it changed."
Detecting such organisms is another matter. Don't look for it to happen any time soon. Spirit and Opportunity were not designed to search for signs of life, but rather to search for signs of habitability. They could be rolling over fields littered with microscopic organisms in deep sleep and they'd never know it. Even future rovers will have a tough time identifying the martian equivalent of dormant bacterial spores.
"The spores themselves are so inert," Clark says, "it's a question, if you find a spore, and you're trying to detect life, how do you know it's a spore, [and not] just a little particle of sand? And the answer is: you don't. Unless you can find a way to make the spore do what's called germinating, going back to the normal bacterial form." That, however, is a challenge for another day.
Read the original article at http://www.astrobio.net/news/article1163.html.
NASA SATELLITES DETECT "GLOW" OF PLANKTON IN BLACK WATERS

NASA release 2004-280


31 August 2004
For the first time, scientists may now detect a phytoplankton bloom in its early stages by looking at its red "glow" under sunlight, due to the unique data from two NASA satellites. According to a study conducted in the Gulf of Mexico, this phenomenon can forewarn fishermen and swimmers about developing cases of red tides that occur within plumes of dark-colored runoff from river and wetlands, sometimes causing "black water" events.


Florida red tide bloom of Karenia brevis, and Karenia brevis under a microscope (inset). Image credit: Woods Hole Oceanographic Institute/NOAA and NOAA/CHBR.
Dark-colored river runoff includes nitrogen and phosphorus, which are used as fertilizers in agriculture. These nutrients cause blooms of marine algae called phytoplankton. During extremely large phytoplankton blooms where the algae is so concentrated the water may appear black, some phytoplankton die, sink to the ocean bottom and are eaten by bacteria. The bacteria consume the algae and deplete oxygen from the water that leads to fish kills.
Chuanmin Hu and Frank Muller-Karger, oceanographers at the College of Marine Science of University of South Florida, St. Petersburg, FL, used fluorescence data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard both NASA's Terra and Aqua satellites. MODIS detects the glow or phytoplankton fluorescence, from the plant's chlorophyll. The human eye cannot detect the [far-]red fluorescence.
The ability to detect glowing areas of water helps researchers identify whether phytoplankton are present in large dark water patches that form off the coast of Florida. Without these data, it is impossible to differentiate phytoplankton blooms from plumes of dark river runoff that contain few individual phytoplankton cells. Because colored dissolved organic matter that originates in rivers can absorb similar amounts of blue and green color signals as plants do, traditional satellites that simply measure ocean color cannot distinguish phytoplankton blooms within such patches.



The image on the left was captured by the MODIS instrument on October 19, 2003. Overlaid were the locations where water samples were collected to determine their Karenia brevis (toxic phytoplankton) abundance between September 19 and October 19, 2003. Large circles mean higher abundance. Smallest circles mean "not present." The dark plume flows from the central Florida coast to the Dry Tortugas. The image on the right is from the same time period. The fluorescence increases from dark blue to green, yellow and red. Image credit: NASA/USF.
Although satellites cannot directly measure nutrients in lakes, rivers, wetlands and oceans, remote sensing technology measure the quantities of plankton. Scientists can then calculate how much nutrient might be needed to grow those amounts of plankton. Hu and others used this technique to study the nature and origin of a dark plume event in the fall of 2003 near Charlotte Harbor, off the south Florida coast. Moderate concentrations of one of Florida's red tide species, were found from water samples.
"Our study traces the black water patches near the Florida Keys to some 200 kilometers (124 miles) away upstream," said Hu. "These results suggest that the delicate Florida Keys ecosystem is connected to what happens on land and in two remote rivers, the Peace and Caloosahatchee, as they drain into the ocean. Extreme climate conditions, such as abnormally high rainfall in spring and summer 2003, may accelerate such connections," he added.


The left image is a MODIS image which shows dark water on October 9, 2003. The arrows show the average wind speed and direction (day and night) from the QuikScat scatterometer. October 8-14 is in black, October 15-19 is in red. Areas of low salinity or salt usually occur near the mouths of rivers. In the image on the right, the white lines on this color enhanced image depict the approximate locations of Everglades rivers. Image credit: NASA/USF/NOAA/UM.
These findings are based on scientific analyses of several things. Data used include satellite ocean color from MODIS and Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and wind data from NASA's QuikSCAT satellite. U.S. Geological Survey, National Oceanic and Atmospheric Administration (NOAA), Florida's Fish and Wildlife Research Institute, and other organizations provided rain, river discharge, and field survey information. By knowing which way the winds blow and the currents flow, Hu and colleagues can predict where black water may move.
Red tides occur every year off Florida and are known to cause fish kills, coral stress and mortality, and skin and respiratory problems in humans. Previous studies show that prolonged "black water" patches cause water quality degradation and may cause coral death. The use of remote sensing satellites provides effective means for monitoring and predicting such events.
The link between coastal runoff and black water events is an example of how land and ocean ecosystems are linked together. "Coastal and land managers over large areas need to work together, to alleviate more black water events from taking place in the future," said Muller-Karger.
This study appeared in a recent issue of the American Geophysical Union's Geophysical Research Letters. Coauthors of the article include Gabriel Vargo and Merrie Beth Neely from University of South Florida and Elizabeth Johns from NOAA's Atlantic Oceanographic and Meteorological Laboratory. NASA's Science Directorate works to improve the lives of all humans through the exploration and study of Earth's system, the solar system and the Universe.
For more information and images on the Internet, visit http://www.gsfc.nasa.gov/topstory/2004/0826planktonglow.html.
Gretchen Cook-Anderson

NASA Headquarters, Washington, DC

Phone: 202-358-0836)



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