A meteorite that whistled into a West Texas yard last year contained the first extraterrestrial water ever captured on Earth, scientists reported yesterday.
Like a cosmic message in a bottle, the microscopic bubbles of primordial water are locked inside crystals of halite, the mineral that makes up table salt, but in this case has been turned blue and purple by radiation. The crystals and their liquid cargo appear to date from the dawn of the solar system about 4.5 billion years ago.
The discovery provides scientists their first chance to study actual samples of water that may have existed in interstellar space before the sun and planets were born. It also suggests that there was much more water on early asteroids than anyone suspected, the researchers said, and it could help reveal the unknown processes by which this essential ingredient of life was distributed in the early solar system.
The processes by which water was acquired by Earth and other rocky inner planets have remained largely unknown. Because water in liquid form is essential to all known forms of life, the search for the origins of life, and for life on other worlds, has centered largely around the search for water. Astrobiologists called the discovery fascinating but said its implications are not yet known.
"The importance of this discovery is that for the first time we have actual samples of [extraterrestrial] water trapped inside mineral grains, which we can have in the lab and study directly -- which is really exciting," said Michael Zolensky, an asteroid specialist and mineralogist at NASA's Johnson Space Center (JSC) and lead author of a report on the discovery in today's issue of the journal Science.
Robert N. Clayton, of the Enrico Fermi Institute at the University of Chicago, who was not involved in the research, wrote in an accompanying commentary: "The existence of water-soluble salt in this meteorite is astonishing" and provides "the first opportunity to study solar nebular water directly."
Based on dating analysis led by JSC scientist Laurence Nyquist, the salt grains appear to have formed at the time the sun, planets and other bodies of the solar system were still tiny seeds coalescing out of a vast cloud, or nebula, of rotating gas and dust. Their presence suggests, among other things, the possibility of previously unsuspected quantities of primordial water flowing through the bits of emerging rubble to form the salt, Zolensky said. "On the earth, sodium chloride usually forms when you have seas evaporating -- huge bodies of water. Well, could that happen on asteroids? Could you have huge bodies of water inside asteroids? Maybe. I don't know."
Scientists have long known that the elements of water -- hydrogen and oxygen -- were plentiful in the solar system from its birth, as they are throughout the known cosmos. And planetary geologists have known that asteroids in the first 10 million or so years of their existence had water running through them. As the solar system formed, much of the available water condensed on the giant outer planets, but some ended up on Earth and the other rocky inner planets.
Researchers have seen indirect evidence of water in meteorites, but never the water itself. "So there was always this big mystery: where this water came from, how it was made, whether it was from the solar system or in the asteroid itself; whether it was delivered by comets, or whether it was from interstellar space. And where it went, what composition it had, things like that," Zolensky said. He added that these tiny pockets of brine -- and others that now may be found in other meteorites -- could help answer all those questions.
The researchers are eager to take the next step: to study the nature of the trapped bubbles of brine. But the droplets are so small -- about an eighth or a tenth the diameter of a human hair -- that they lie beyond the capability of existing technology. A researcher in Cambridge, England, is on the verge of developing an instrument, a highly precise mass spectrometer, that might be able to tackle the problem, Zolensky said.
The meteorite -- white and glowing -- slammed into the ground near the driveway where Alvaro Lyles, 11, and friends were playing basketball on March 22, 1998, in the Texas town of Monahans, according to news reports. JSC geologist Everett Gibson rushed to the site and "sweet talked" the townsfolk into letting him borrow samples, Zolensky said. The 2.2-pound prize was in the lab within a couple of days of impact.
But the scientists who broke the rock sample open might have missed the discovery if they had used traditional methods, and if radiation from its trip through space had not given the normally colorless salt grains what Zolensky called their "lovely" blue and purple hues. Fortunately, he said, the team did not use the traditional method of opening the sample -- a rock saw and water -- or they would have destroyed the blue crystals and their precious cargo. Instead, they used nothing more high-tech than a small hammer and chisel. "We just knocked a little piece off the side. And there was this beautiful blue mineral."
The biggest of the blue crystals of salt, a mineral not expected in such meteorites, is about the size of the nail on a little finger. If the researchers hadn't noticed it and become intrigued, he said, they might have gone on with normal processing, which involves the use of laboratory water, "and we would have destroyed it." Instead, Zolensky identified the crystals as halite. Because halite forms from drying water on Earth, they looked further. Without breaking open the crystals, he said, the team used a form of spectroscopic analysis that involved zapping them with a laser to reveal the signature of the molecules inside.
In the microscope, he said, "what you see are these little rounded [or] square things just floating in the halite, so to speak, and inside of some of those you see these little vapor bubbles just dancing around. The movement of the vapor bubbles proves they are liquid rather than solid."
The research can be tricky, and the researchers said they are extra-sensitive to the possibility of laboratory contamination and error. A mistake of that nature in the early 1980s, in fact, "caused people to drop the whole subject . . . for a generation," Zolensky said. "We've learned just how careful we have to be."
It occurred to the researchers that similar primordial remnants might be getting routinely destroyed in laboratory processing, so they issued a caution. Zolensky was contacted within months by a meteorite dealer who had a specimen that fell in Morocco last year. He had found blue grains. Using the more careful preparation methods, Zolensky said, scientists have confirmed that "lo and behold, it's the same stuff in a different meteorite."