Water-bearing salt crystals come from dawn of solar system, UK researchers report in Science

June 08, 2000

Washington D.C. -- Brine-pocketed salt crystals within the "Zag" meteorite may be among the oldest materials found in the solar system, a U.K. research team has found. This surprisingly old age could spur scientists to speed up the prevailing scenario of the solar system's evolution, and opens the possibility that hospitable conditions for life might have arisen earlier than previously thought. The researchers report their findings in the 9 June issue of Science.

Using radioisotope dating, scientists at the University of Manchester and the Natural History Museum in London determined that the salt crystals probably formed within about two million years of the solar system's birth. If this age is correct, it means that the dust, gas, and ice swirling around the newborn sun clumped together into rocky fragments far more quickly than researchers have assumed. These fragments were the parent bodies for primitive meteorites like Zag and the essential building blocks for asteroids and planets.

In the scenario proposed by first author James Whitby and his colleagues, Zag's parent body accreted rapidly into a rocky mass containing water and radioactive isotopes. The isotopes' decay generated enough heat to melt any ice within the rock matrix, and soon caused the liquid to evaporate altogether. The salt crystals, (mainly sodium chloride, or "halite,") precipitated during the evaporation process, similar to the way halite forms when sea water evaporates on Earth.

The Zag meteorite, which fell in Morocco in 1998, was the second meteorite found carrying halite crystals. Like those in the Monahans meteorite (see Science, 27 August, 1999, p. 1364 and 1377), these crystals contained microscopic inclusions of water, the key ingredient for life. Both finds have raised hopes of learning more about the possibility that life might have evolved elsewhere in the solar system. To do so, researchers would first have to determine when water existed in these parent bodies and for how long.

Previous studies of other meteorite minerals could only place the time of liquid water within 100 million years after the solar system's formation, explains Ulrich Ott, of the Max-Planck-Institut für Chemie in Mainz, Germany, in a Perspective article that accompanies the research paper. Rubidium dating of the halite in Monahans had suggested that the crystals might be some of the oldest materials in the solar system, but this dating method is less precise than the one used by Whitby and his colleagues.

"Those results showed that this was interesting halite. Immediately, our next question was, 'how old is it?'" Whitby said.

A second crucial task was to make sure that the halite hadn't precipitated from water on Earth that contaminated the meteorite after it landed.

To tackle both these questions, Whitby and co-authors Ray Burgess, Grenville Turner and Jamie Gilmour, of the University of Manchester, and John Bridges, of the Natural History Museum, analyzed xenon, iodine, and argon isotopes extracted from a minute sliver of a Zag halite crystal. They found a surprisingly large amount of xenon-129, which forms when iodine-129 decays. Iodine-129 was present in the early solar system but is not found on Earth.

"I popped the halite in the machine and got this amazing peak showing an abundance of xenon-129. That told us immediately it wasn't terrestrial material. I hadn't really expected that, so it was quite stunning, really," said Whitby.

Because scientists know the rate at which iodine-129 decays into xenon-129, Whitby and his co-authors could then calculate the age of the halite. They estimate that the crystals formed about two million years after the birth of the solar system 4.57 billion years ago, suggesting that liquid water departed from its parent body soon after it had appeared.

"The results from the I-Xe dating by Whitby et al. are particularly astonishing," writes Ott in the Perspective article.

Until the discovery of halite in Monahans and Zag, the oldest materials in the solar system were thought to be chondrules, glassy spheres that make up much of the mass in primitive meteorites. Although the origins of these particles are still under debate, many scientists believe that chrondrule formation continued for about 5 million years after the solar system's birth.

From their analysis of the crystals and the rocky matrix around them, the research team proposes that the halite grew very quickly on a newly formed asteroid that had just formed by the collision of smaller particles. About 300 million years later, another large impact smashed the loose fragments together into a more solid conglomerate, a piece of which became the Zag meteorite.

The presence of liquid water also has important implications for understanding the geology of moons and planets with large amounts of heat in their interiors. Volcanic activity is closely tied with the availability of water, which plays a major role in the formation of magma.
-end-


American Association for the Advancement of Science

Related Solar System Articles from Brightsurf:

Ultraviolet shines light on origins of the solar system
In the search to discover the origins of our solar system, an international team of researchers, including planetary scientist and cosmochemist James Lyons of Arizona State University, has compared the composition of the sun to the composition of the most ancient materials that formed in our solar system: refractory inclusions in unmetamorphosed meteorites.

Second alignment plane of solar system discovered
A study of comet motions indicates that the Solar System has a second alignment plane.

Pressure runs high at edge of solar system
Out at the boundary of our solar system, pressure runs high.

What a dying star's ashes tell us about the birth of our solar system
A UA-led team of researchers discovered a dust grain forged in a stellar explosion before our solar system was born.

What scientists found after sifting through dust in the solar system
Two recent studies report discoveries of dust rings in the inner solar system: a dust ring at Mercury's orbit, and a group of never-before-detected asteroids co-orbiting with Venus, supplying the dust in Venus' orbit.

Discovered: The most-distant solar system object ever observed
A team of astronomers has discovered the most-distant body ever observed in our solar system.

Discovery of the first body in the Solar System with an extrasolar origin
Asteroid 2015 BZ509 is the very first object in the Solar System shown to have an extrasolar origin.

First interstellar immigrant discovered in the solar system
A new study has discovered the first known permanent immigrant to our solar system.

A star disturbed the comets of the solar system in prehistory
About 70,000 years ago, when the human species was already on Earth, a small reddish star approached our solar system and gravitationally disturbed comets and asteroids.

Scientists detect comets outside our solar system
Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets -- comets outside our solar system -- orbiting a faint star 800 light years from Earth.

Read More: Solar System News and Solar System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.