A major methane gas leak that released thousands of tons of potent greenhouse gases might have gone unnoticed if not for a satellite study more than a year later.

The study, published this week in the Proceedings of the National Academy of Sciences, documents the leak at an Exxon Mobil fracking well in Belmont County, Ohio in the eastern US in February 2018.  The blown well was pumping 132 tons of methane into the atmosphere every hour, give or take 35 tons, for 20 days - possibly around 63,360 tons of methane.  That far outpaces the methane emissions from the entire oil and gas industries of many countries like Norway and France.   And Methane is 80 times more potent at warming the planet than carbon dioxide in the first decade after the substance released.

And few knew about it until environmentalists and scientists decided to tap into the European Space Agency's newly-launched a satellite with a new monitoring instrument called Tropomi, which provides accurate methane readings.  

"We're entering a new era.  With a single observation, a single overpass, we're able to see plumes of methane coming from large emission sources," said Dr. Ilse Aben of the Netherlands Institute for Space Research, an expert in satellite remote sensing and one of the authors of the new research.  "That's something totally new that we were previously not able to do from space."

Exxon disagreed with the findings and said the company determined that the amount of the greenhouse gas released was lower than the numbers in the scientists' report.

But for the researchers, the report reinforces the view that these sorts of leaks are more widespread than oil companies previously reported.

"Right now, you have one-off reports, but we have no estimate globally of how frequently these things happen," said Dr. Steven Hamburg with the Environmental Defense Fund.  "Is this a once a year kind of event?  Once a week?  Once a day?  Knowing that will make a big difference in trying to fully understand what the aggregate emissions are from oil and gas."