Such cracks could provide a pathway for fluids, perhaps explaining what happened to the ocean that some scientists think existed long ago on the surface of Mars.
"That ocean could well be underground," Zuber said.
As the Martian surface dried out over the years, such undergound water may have provided a refuge for surface microbes, if they ever existed. Microbes "could have gone very deep within the crust of Mars," Zuber said.
Ebb and Flow wrapped up their primary science mission in May and are currently embarked on an extended mission that will end in mid-December. Shortly thereafter, they will be crashed intentionally onto the lunar surface; exactly where and when that will happen is still being worked out, researchers said.
The results presented today were from the primary mission. The spacecraft have been circling even closer to the moon during the extended phase — an average altitude of 14 miles (23 km) as opposed to 34 miles (55 km) — so the Grail team thinks the gravity map will get even better.
"We expect a lot more exciting results in the future, so stay tuned," said Grail project scientist and co-investigator Sami Asmar of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
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