Chuck Bednar for redOrbit.com – Your Universe Online
A meteorite discovered in the Sahara Desert three years ago could hold the secrets to the climate history of Mars, and may ultimately help answer the question as to whether or not the now cold, dry Red Planet was once home to a warm environment capable of supporting life, an international team of researchers claim in a new study.
That meteorite, which is known as both Black Beauty and NWA 7533, is currently being analyzed by Florida State University professor Munir Humayun and his colleagues at the National High Magnetic Field Laboratory in Tallahassee. Chemical clues contained within that meteorite could be the key to unraveling the planet’s climatic history, and could hold key evidence supporting the existence of surface water on ancient Mars.
In research published online Sunday in the journal Nature Geoscience, the scientists report that they’ve discovered evidence for the climate shift in minerals known as zircons that are embedded deep inside the dark, glossy object. Zircons form when lava cools and are extremely long lasting – a feature that allows scientists to use them as a sort of record of the passage of time.
Last year, researchers tested samples from Black Beauty and confirmed that it did actually come from Mars, and Humayun and his colleagues determined that the zircons found in the meteorite were 4.4 billion years old. That is significant, the geochemistry professor explained, because it means that the object formed during the earliest stages of the Red Planet, and might have come from a time when the planet was capable of sustaining life.
“First we learned that, about 4.5 billion years ago, water was more abundant on Mars, and now we’ve learned that something dramatically changed that,” Humayun explained in a statement Wednesday. “Now we can conclude that the conditions that we see today on Mars, this dry Martian desert, must have persisted for at least the past 1.7 billion years. We know now that Mars has been dry for a very long time.”
The zircons found in NWA 7533 (ZrSiO4) contain oxygen, an element with three isotopes. Isotopes are atoms of the same element that have the same number of protons but a varying number of neutrons, the researchers explain. On Mars, oxygen is distributed in the atmosphere (as carbon dioxide, molecular oxygen and ozone), in the hydrosphere (as water) and in rocks. Since the planet’s atmosphere is thin and dry, the sun’s UV light causes unorthodox shifts in the proportions in which each of those three oxygen isotopes occur in different atmospheric gases.
“So when water vapor that has cycled through the Martian atmosphere condenses into the Martian soil, it can interact with and exchange oxygen isotopes with zircons in the soil, effectively writing a climate record into the rocks,” Florida State’s Kathleen Laufenberg explained. “A warm, wet Mars requires a dense atmosphere that filters out the ultraviolet light making the unique isotope shifts disappear.”
In order to measure the proportions of the oxygen isotopes in the zircons, Humayun, Alexander Nemchin of the Swedish Museum of Natural History, and institutions in the US, Australia and France used a device called an ion microprobe. Using that instrument, the researchers applied a focused beam of particles to the sample, obtaining precise measurements that they said have helped them craft an accurate isotopic record of the atmospheric changes that have taken place on Mars, complete with dates.
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