WASHINGTON -- Working late in their laboratory, two NASA scientists were startled when their electron microscope scanned across a tiny, segmented structure that looked for all the world like a string of primitive bacteria, fossilized in rock.
"Is this for real?" they asked themselves.
What stunned them that night a year ago, and what has stunned the world this week, is that the rock was from Mars.
And what they saw looked like signs of Martian life.
The 4.5 billion-year-old meteorite almost certainly was blasted off the surface of Mars by an asteroid or comet collision millions of years ago and fell onto Antarctic ice 13,000 years ago.
The structures and associated organic compounds would constitute the first physical evidence for the existence of life beyond Earth, with implications not just for science, but for philosophy and theology as well.
Assuming that further scientific studies don't reveal it all to be the product of lifeless inorganic chemistry, it would be one of the most momentous scientific discoveries -- and one of the biggest news stories -- of all time.
The discovery surely thrilled NASA geochemists David S. McKay and Everett K. Gibson Jr.
"When I went home, I had difficulty sleeping," Gibson told a packed news conference yesterday at NASA headquarters.
News of their discovery was too hot to contain. It was scheduled for publication in the scientific journal Science on Aug. 16, but word of it had already set the Internet abuzz.
The story hit the news wires Tuesday, forcing NASA to schedule yesterday's news conference.
NASA Administrator Daniel S. Goldin hastily briefed President Clinton, Vice President Al Gore and the congressional leadership this week, and consulted with leaders of the space community around the world.
NASA already had a series of unmanned Mars missions planned, including two due for launch late this year, and Goldin promised a scientific review of their objectives in light of the new discovery.
"What a time to be alive," he said.
If the scientists are right, Clinton said yesterday, "it will surely be one of the most stunning insights into our universe that science has ever uncovered. Its implications are as far-reaching and awe-inspiring as can be imagined."
He said he was "determined that the American space program will put its full intellectual power and technological prowess behind the search for further evidence of life on Mars."
He called for a November White House "space summit" to discuss how the nation should respond to the discovery.
The initial reaction from the Roman Catholic Church -- which reacted with hostility to discoveries by the likes of Galileo and Copernicus that seemed to reduce Earth's supposedly unique status in the universe -- was calm, even cheerful.
The Rev. James A. Wiseman, chairman of the Theology Department at the Catholic University of America in Washington, said, "Theologically, I see no problem. Personally, I have always suspected that there are forms of life elsewhere in this immense universe.
"If theologians, or theists in general, take seriously what is meant by the phrase 'an omnipotent God,' it should not be surprising at all if signs of this creator and life-giver's power were to be found throughout the universe."
A skeptical approach
The scientific community will take a more skeptical approach, however, and Goldin yesterday urged researchers to scrutinize the data and the meteorite.
Dr. William Schopf, a paleobiologist at the University of California in Los Angeles who is not connected with the NASA team, called the NASA investigation "a fine piece of work" and said, "This is not easy science."
But noting that it remained a "preliminary report," he urged caution.
"Extraordinary claims require extraordinary evidence," he said.
Although he agreed that the meteorite is "quite probably" from Mars, and that organic compounds probably formed there 3.6 billion years ago, Schopf said it was too soon to say the compounds got there by way of biological processes.
"The mere presence of organic matter by itself is not definitive of life," he said. Inorganic chemistry could explain everything the NASA team found.
Likewise, the structures identified by the NASA team as fossil bacteria are one-hundredth the size of most terrestrial bacteria, Schopf said, and could be "mineralogic pseudo-fossils," or "foolers."
He said McKay and his colleagues at the Johnson Space Flight Center in Houston and at Stanford University in California must conduct further studies, especially some that would establish whether the supposed Martian bacteria show any fossil evidence of the cell walls and interior chemistry of once-living microbes.
The NASA scientists agreed there are inorganic processes that could produce the compounds and structures they saw combined in spaces just a few hundred-thousandths of an inch across.
"None of this is, by itself, definitive," McKay said. "But taken together, the simplest explanation is that they are the remains of Martian life."
The gray, 4.2-pound, softball-sized meteorite is one of just 12 found in Antarctica that are believed to have originated on Mars.
But it is by far the oldest, and the only one found so far with carbonate minerals -- a compound like that produced by microorganisms on Earth, and which accumulates to become limestone.
Scientists seem to be in general agreement, based on chemical analyses, that the meteorites condensed from molten rock on Mars 4.5 billion years ago, at about the same time that Earth was forming.
About 3.6 billion years ago, while the first primitive life was appearing on Earth, McKay said, golden-colored globules of carbonate minerals were forming in microscopic cracks in the rock.
Using high-resolution scanning and transmission electron microscopy that became possible only in the past few years, McKay's team found those globules. At their edges were black and white structures that turned out to be magnetite and other fine-grained minerals that team member Kathie L. Thomas Keprta said are "very similar" to minerals associated with bacterial processes on Earth.
Close by, or embedded within the globules, the scientists also found tiny structures -- fields of spheres, ovoids and rod-shaped objects -- that closely resemble fossils of primitive bacteria found in ancient rocks on Earth.
If these minerals and fossils were the result of contamination on Earth after the meteorite's fall, the scientists argue, they would be concentrated in the outer portions of the rock. But just the opposite is true.
Stanford chemistry professor and team member Richard Zare suggested that life on Earth might even have originated with bacteria brought to Earth in such a manner. "Who is to say we're not all Martians?" he said.
The process could work in reverse, he said. "How do we know that what we are seeing on Mars didn't first come from Earth?"
For McKay, "The question is, what happened to this early life?"
Life might survive on Mars
While there is evidence that liquid water once existed on Mars' surface, "at some point things went bad." The planet today is very inhospitable to life, with a thin atmosphere of carbon dioxide and no liquid surface water.
Bacterial life could have retreated deep into the Martian rocks, extracting energy from geo-thermal sources. Similar bacteria have been found on Earth, a mile or more below the surface.
"The only way we will know," McKay said, "is to go there." NASA plans to send 10 small unmanned probes to Mars in the next 10 to 15 years.
Two are due for launch late this year: Mars Pathfinder, with a lander and robot rover; and Mars Global Surveyor, a high-resolution orbital mapping mission. A later probe is designed to return a sample of Martian rock to Earth.
There are no current plans for a manned mission to Mars. Goldin has been steering the space agency away from that kind of big-budget mission.
Instead, he said, scientists should first resolve the inevitable controversy the new discoveries will spark.
"Our mission should be driven by the scientific potential" and economic implications of space exploration, he said.
"Let's not get to Mars as fast as we can and not know what we're doing once we get there."
Pub Date: 8/08/96