UNITED STATES, WASHINGTON (OBSERVATORY) — Mars rover “Curiosity” (Curiosity) found methane on the Red Planet. But the TGO orbiter , specifically designed to search for rare gases, did not find this substance. How did it happen that methane disappeared somewhere? Can two missions simultaneously “tell the truth”? Astronomers have proposed a simple and elegant answer to this question.
Details are set out in a scientific article published in the journal Geophysical Research Letters by an international group of astronomers.
Methane in the atmosphere of Mars is of great interest to scientists. According to calculations, it should be destroyed by solar radiation in about 300 Earth years. In addition, its concentration is also subject to seasonal fluctuations.
Both mean that organic gas has not been present in the planet’s atmosphere since ancient times. There is its source, acting right now.
Perhaps this substance is secreted by bacteria, how does this happen on Earth? Or volcanoes (and Mars is considered to be a geologically dead body)? Or is it about the gradual melting of ancient methane ice, and then it turns out that in the past the Red Planet was very rich in organic matter? Any answer would be a sensation.
Mars rover discovered in the Gale crater a concentration of methane in the Martian atmosphere of 410 parts per trillion. At the same time, TGO would notice methane, even if its content was 50 parts per trillion, but would not register this substance. How could this happen?
The authors of the new study drew attention to a simple circumstance. Curiosity made all measurements of the level of methane in the atmosphere at night. In the dark, the rover stands still and charges the batteries (recall that the Curiosity power source is based on the decay of radioactive elements). This is the right moment for atmospheric measurements.
At the same time, TGO performed all measurements during daylight hours. And no wonder: this orbital apparatus determines the composition of the atmosphere according to the characteristics of its translucent sunlight.
Maybe methane concentration depends on the time of day? This is exactly what the experts suggested.
Researchers have built a mathematical model of the circulation of Martian “air.” According to their calculations, the source of methane (whatever it is) in Gale Crater can work around the clock and give out 0.15 millionths of a gram of methane per square meter in one Martian day (sol).
At night, when the atmosphere is calm, this gas accumulates at the surface and reaches the concentration measured by the rover. When the sun rises, the surface heats up. Upward flows of relatively warm “air” appear and downward flows compensating for them. As a result, methane is effectively mixed with the surrounding carbon dioxide (constituting, recall, more than 95% of the Martian atmosphere). So the concentration of matter so interesting to astronomers drops to undetectable values.
However, this elegant model has a drawback, and the authors, as befits in science, themselves point to it.
The researchers hypothesis suggests that there are rare oases of methane emission on the entire Red Planet. Their total area is only 1.5 times larger than that of Gale Crater alone. Otherwise, gas would still accumulate a lot for detection from orbit. The alternative is that on the rest of Mars, methane is released much less intensively than at the Curiosity measurement point.
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