Microbe Travel Aboard Meteorites Possible, Study Says
For two centuries, scientists have suspected that life might be able to travel between planets via meteorites, and even suggested that life on Earth may have originated elsewhere in the solar system.
But there’s been one problem. All meteorites are generated by explosive impacts on their home planets. Could any living organism survive the massive shock and heat of such a blast?
Now, a team led by three Caltech scientists says that any contents in the rocks could indeed survive. Conducting an extremely precise magnetic analysis of a Martian meteorite, the group found that the core of the meteorite did not reach more than 104 degrees Fahrenheit--far below the sterilization temperature of 230 degrees.
“Thirty years ago, it was thought a rock could not be ejected from a planet without melting or vaporizing it,” said Benjamin Weiss, a Caltech graduate student and lead author of the research published in today’s issue of Science. “This is the first evidence a rock was blasted off Mars and got to Earth without being heated beyond 104 degrees, and perhaps not even above room temperature.”
Weiss’ team studied a controversial meteorite known as ALH84001, a 4 1/2-billion-year-old rock from Mars that has been extensively studied and vigorously debated since 1996 because it appeared to contain microfossils created by extraterrestrial life.
The issue has not been resolved, and many scientists remain skeptical of the assertion. The new study did not address the question of whether the meteorite had ever contained life, but answered a broader question of whether life could theoretically be transferred between planets.
“There’s every reason to think life can go back and forth,” said Joseph Kirschvink, a professor of geobiology at Caltech and coauthor of the paper.
In the 1980s, H. Jay Melosh, a professor of planetary sciences at the University of Arizona in Tucson, was the first to suggest that meteorites might be able to evade heat sterilization. Rocks near the surface, he surmised, could be ejected from a planet with very little shock damage. Though this might occur in only 2% of ejected material, it held open the possibility that life on those surface rocks could survive the blast as well.
Until now, Melosh never had any proof his theory was correct.
After the ejection blast, microbes atop a meteorite traveling through space would still face a deadly barrage of cosmic rays. Those within the meteorite could be killed off by the rock’s own radiation.
Entry into Earth’s atmosphere does not turn out to be so hazardous. The passage generally takes less than 20 seconds. While heat might cause the surface of the rock to boil off, that heat wouldn’t penetrate too deeply. When meteorites land on earth, they are generally covered with frost.
“People have gotten frostbite picking them up,” said Kirschvink.
To test how hot the rock had been, the scientists analyzed the magnetism in a small chip. A meteorite heated to high temperatures would lose its original magnetism and instead reflect the magnetism present where it landed.
They found that the outer surface of the meteorite was aligned with the Earth’s magnetic field. The interior, however, retained a randomly oriented magnetism. When the researchers heated a slice of the meteorite, it started to demagnetize at 104 degrees--showing the interior had never reached that temperature.
The subtle measurements were possible due to a machine developed by study coauthor Franz J. Baudenbacher at Vanderbilt University in Nashville. The machine, an “ultrahigh resolution scanning superconducting quantum interference device microscope,” detects microscopic changes in magnetism, said Kirschvink, and is 10,000 times more sensitive than similar machines.
Other questions center on just how long microbes could stay alive in space. Bacteria on a satellite have survived the vacuum of space for more than five years. Some bacteria on Earth have shown a remarkable ability to survive desiccation and radiation, both in nature and the laboratory. “We do all sorts of things to insult them, and they do just fine,” said Melosh.
