When Murrary first proposed this hypothesis about 20 years ago, it didn't receive much attention.
"It just took its place with the other seven or eight major ideas out there at the time," he said.
But new images from Mars Expressallowed Murray and Heggie to map virtually the entire surface of Phobos in high detail, and take a close look at the grooves' features. With the new data and models, the researchers argue that this hypothesis can explain all of the grooves' morphological characteristics, unlike other hypotheses.
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What's more, the pair was able to pinpoint launch latitudes on Mars from which the groove-forming ejecta could have come. Murray is now working to determine specific source craters on Mars.
An Ongoing Debate But not everyone agrees that the hypothesis advanced by Murray and Heggie makes sense.
Last year, Kenneth Ramsley and James Head, researchers at Brown University in Providence, Rhode Island, tested the hypothesis and found it wanting for numerous reasons. For example, they argue that if the grooves were produced by Mars ejecta, then the so-called zone of avoidance - the region of Phobos where grooves are absent - shouldn't exist, because it's an area where Mars ejecta could actually strike, according to their calculations.