There was a theory that a long time ago, a volcano exploded on Mars. Though Mars has no active volcanoes today, scientists hypothesize that such was not the case during the early days of Mars and there are some evidences which could point to a huge volcanic explosion occurring on Mars' surface.
From Mars' volcanic activity, some remnants might have lingered including the recently discovered mineral deposit near the landing site for NASA's next Mars rover. Scientists say these might be volcanic ash.
“This is one of the most tangible pieces of evidence yet for the idea that explosive volcanism was more common on early Mars,” said Christopher Kremer, a graduate student at Brown University who led the work. “Understanding how important explosive volcanism was on early Mars is ultimately important for understand the water budget in Martian magma, groundwater abundance and the thickness of the atmosphere.”
(Image credit: NASA)