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The European Space Agency today released the results of more than a year of observations from its Trace Gas Orbiter (TGO), among which were two significant findings.
First, the orbiter detected no methane in Mars’s atmosphere, contradicting recent results from both Curiosity and Mars Express.
The new results from TGO provide the most detailed global analysis yet, finding an upper limit of 0.05 ppbv, that is, 10–100 times less methane than all previous reported detections. The most precise detection limit of 0.012 ppbv was achieved at 3 km altitude. As an upper limit, 0.05 ppbv still corresponds to up to 500 tons of methane emitted over a 300 year predicted lifetime of the molecule when considering atmospheric destruction processes alone, but dispersed over the entire atmosphere, this is extremely low.
…“The TGO’s high-precision measurements seem to be at odds with previous detections; to reconcile the various datasets and match the fast transition from previously reported plumes to the apparently very low background levels, we need to find a method that efficiently destroys methane close to the surface of the planet.”
It appears they think the Curiosity and Mars Express detections were very localized and occurred close to the surface, where TGO could not detect it.
The second significant finding is indicated by the map below, showing a global map of subsurface water distribution on Mars. I have also posted below this map a global elevation map from Mars Reconnaissance Orbiter (MRO), as the similarities and differences are important.
Click for full TGO water subsurface map.
In the top map, blue means lots of water, while yellow to orange means declining water sources. In the bottom map, blue means lower elevation, while yellow to orange means rising elevations, with the white at the volcano tops the highest.
The similarities are obvious. The northern lowlands, where some scientists believe an intermittent ocean once existed, are also home to a lot of water-rich permafrost. Similarly, the drainage regions to the east of the high volcanoes that includes Marineris Valles is also water rich.
The differences are also important. For example, Hellas Basin, the basement of Mars and seen in the topographical map as the dark blue oval in the southern hemisphere from about 60 to 90 degrees longitude is invisible on TGO’s water map. No subsurface water is detected there, even though it features many flow features draining into it. In fact, it appears drier than the surrounding southern highlands.
Combining this data with all the other data we are accumulating about Mars will help future explorers pick the right spots to settle.
UPDATE: One of the scientists who worked on a similar instrument on Mars Odyssey emailed me to remind me that this TGO result essentially confirmed what they found, ten years earlier. This is great news, because it mean that the existence of this subsurface water on Mars is almost certain. It is the hallmark of good science to doubt every result, until someone confirms it independently. TGO has now done this.