BEIJING, Aug. 4 (Xinhua) -- Martian meteorites, seen as gifts from Mars and also a way to study the red planet, have attracted increasing interest from Chinese scientists in the past decades.
Recently, researchers from the Institute of Geology and Geophysics (IGG) under the Chinese Academy of Sciences (CAS) discovered coesite, a form of silicon dioxide, in a Martian meteorite for the first time, said a report by the Science and Technology Daily.
In the country's first Mars exploration mission, China launched its Tianwen-1 probe, heading for the red planet, on July 23. The study on the "precious stones" has been moving forward since the first known Martian meteorite landed on Earth in 1815.
As of Aug. 2, a total of 276 pieces of Martian meteorites have been discovered on Earth, according to the meteorite database of the Meteoritical Society. However, more than 70,000 named meteorites in the world are contained in the database.
"In all, the number of Martian meteorites found on Earth is very small and the total weight is only over 200 kg," said Xu Weibiao with the Purple Mountain Observatory under the CAS, adding that a Martian meteorite is less likely to fall to Earth than other asteroid meteorites.
In the database, the heaviest Martian meteorite, which landed in Nigeria in 1962, has a weight of 18 kg, and the lightest only weighs about 0.48 g.
Methods for identifying Martian meteorites are also constantly being updated with scientific and technological advances.
Initially, one method of identification was to measure whether the gas in the meteorite glass was consistent with the composition of the Martian atmosphere, said Zhang Aicheng, a professor from Nanjing University.
Asteroids landing on Mars at high temperatures would form molten glass, which would contain Martian gases. Consisting of gases like carbon dioxide, nitrogen, neon and krypton, the composition of the Martian atmosphere was analyzed by a U.S. Mars exploration rover in 1975.
Another method is to confirm the meteorite's age by measuring its radioisotopic composition, Xu said.
Mars was volcanically active even 200 million years ago. Therefore, Martian meteorites are generally between 200 million and 2 billion years old, whereas the age of meteorites from asteroids or the Moon are much older.
In addition, the content of specific elements in Martian meteorites also provides support for identification. For example, a Martian meteorite has a different composition of oxygen isotopes from that of the Moon and Earth, Xu added.
At present, Martian meteorites are mostly found in deserts and the Antarctic region, said Zhang, adding that with a thick ice sheet, Antarctica can bury the fallen meteorites, and preserve them well for a long time.
Also, meteorites can be preserved in deserts owing to a dry environment for hundreds of thousands of years. But compared to the Antarctic region, where solid ice holds meteorites in place, they will not be concentrated in one area, said Lin Yangting with the IGG .
For years, Chinese scientists have devoted themselves to exploring clues about Martian life and evolution with the meteorites as a medium.
In 2014, Lin's team discovered that the Martian mantle contained about a tenth as much water as Earth's mantle, indicating that Mars is a very dry planet.
About 3 billion years ago, there was running water on the surface of Mars. As it gradually cooled, some of the water escaped from the red planet and some turned into underground glaciers and frozen soil, according to their research results.
"We always wish to know what major geological changes took place on Mars and whether it is habitable for human beings, and we are expected to find more answers from Martian meteorites," said Xu. Enditem