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May
22, 1998: What started as a hobby for a scientist here has
become a new line of scientific investigation in the newly formed
NASA Astrobiology Institute.
Richard Hoover, a solar physicist at Marshall Space Flight Center, is co-investigator on two astrobiology proposals which NASA has selected for funding.
The poster depicts Hoover's foray into astrobiology, including Europa (background and top), and a cyanobacteria (center) found deep in the Antarctic (bottom). (links to a 900x1281-pixel, 320K JPG. Photo credit: NASA/Marshall Space Flight Center.)
Dr. David McKay of Johnson Space Center is principal investigator on a proposal to look for biomarkers in astromaterials: signs of life in soil, rocks, and other materials from outside the Earth.
Dr. Kenneth Nealson of the Jet Propulsion Laboratory in Pasadena, Calif. is principal investigator on a proposal on a study of the co-evolution of planets and biospheres.
Hoover will be a co-investigator on both proposals.
"This is really exciting," said Hoover, whose primary work at Marshall has been developing advanced telescopes to study the sun. "We are going to look at life on Earth in the most extreme environments - hot volcanic vents, deep ocean ice, and even ancient rocks - and help sharpen our senses when we look for signs of life on Mars, Europa, and other astromaterials."
For Hoover, this journey started years ago when he became fascinated by diatoms (below), the "living jewels of the sea." It became a hobby, then a passion, which has earned him international recognition. Most recently, he has applied knowledge gained in this area to the search for preserved microbes in Antarctic ice cores as a model of extraterrestrial life.
While
Mars has long been thought of as the best chance for life elsewhere
in our solar system, recent evidence of liquid water in Europa,
one of Jupiter's moons, raises the possibility of life there.
In turn, the discoveries over the past few decades of life in
hot springs, deep ocean vents, and even Antarctic ice broaden
the range of conditions where at least basic lifeforms may set
up housekeeping.
In the first investigation, Hoover will work with David McKay who startled the scientific community in 1996 with claims that he had found evidence of microbial fossils in a rock believed to have fallen to Earth from Mars. While the evidence within the Allan Hills meteorite, ALH84001, continues to be debated, pictures and data from the Mars Pathfinder and Mars Global Surveyor missions have added evidence that Mars once had flowing water.
"The primary research that we'll be doing is looking microfossils in ancient rocks," Hoover said. He anticipates analyzing phosphorites from Mongolia, oil shale from Siberia, and other formations dating back about 3.8 billion years. The search for fossils of bacteria and archaea will be of prime importance.
Left: Europa, as seen by the Galileo
spacecraft, is covered with ice, apparently atop a world ocean,
raising the possibility that conditions could be right for life
- and similar to those in Lake
Vostok, hidden under 3 km (1.8 mi) of Antarctic ice (right).Life is divided into three principal domains, eukaryotes (large cells, like plants and animals), bacteria, and archaea. Archaea, only discovered in 1977, normally thrive in extreme conditions like the hot springs of Yellowstone National Park, thermal vents deep underwater in the mid-Atlantic ridge, highly acid and alkaline baths, and deep rocks. These are not normal conditions now, but were more than 3 billion years ago.
"It's now looking like the archaea are among the most ancient forms of life on Earth," Hoover said. And the implication is that if life could originate and then thrive under such conditions here, then it could do the same on Mars and Europa - perhaps even volcanic Io - where conditions are considered inhospitable.
Under the biosphere evolution study with Nealson at JPL, Hoover will develop methods to fix, prepare, and view samples so that unambiguous indications of life - or non-life - can be obtained. He will use advanced tools such as the Scanning Electron Microscope (ESEM) and an atomic-force microscope that NASA/Marshall already has for engineering work.
"One of the things that's important in preparation techniques is making sure that you get no interference from the substrate in the X-ray spectral analysis," Hoover said. NASA/Marshall's ESEM is especially good at analyzing biological materials without the need for special coatings.
The detail revealed by the ESEM offers new challenges.
"The most critical thing is getting to the ability to recognize different types of microorganisms in tools such as the ESEM," Hoover said. "It's a very powerful tool, but it shows you things that you don't see in optical microscopes or conventional electron microscopes." That can mean relearning how to recognize creatures that you already know.
Recognizing and classifying microbes and bacterial fossils in this manner will be doubly important in a field that has thousands of unnamed microbes. The rule in the international microbiology community is that an organism is not named unless it is grown in a pure culture and is lodged - physically - in a recognized cell bank.
"In
many cases, these bugs can't be grown in pure culture," Hoover
said. Asking a bacterium from a deep ocean vent to grow in a lab
culture is like asking a human to breath a vacuum. It takes more
than recreating conditions like water temperatures above boiling
(intense pressure keeps that water from boiling). Some creatures
only survive with certain neighbors, like one bacteria that releases
methane and another that consumes it.
At right, Hoover and Dr. S.S. Abyzov of Russia's Institute of Microbiology use the ESEM to probe deep ice from Antarctica for signs of life. (links to a 1,500x1,082-pixel, 576K JPG. Photo credit: NASA/Marshall Space Flight Center.)
Another challenge will be recognizing life when you see it. Hoover said he was recently stumped by a microsphere with a lot of iron. He was told by a colleague that it was indeed a bacterium that consumes iron sulfate - FeSO3 - to get oxygen.
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"That tells me that we have to learn the kinds of things that go on inside an electron microscope, and in other tools, with respect to microbiology," Hoover said, "because these are the kinds of tools we'll take to Mars and Europa when we look for life." "It's extremely important that we continue to learn and to develop an enhanced knowledge of microfossils, and of bacteria, eukaryotes, and archaea." |
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HeadlinesAuthor: Dave
Dooling
Curator: Bryan Walls
NASA Official: John M. Horack