The ancient Martian climate was thought to be a hot one, full of oceans, rivers, and rainfall. Evidence of ancient icebergs suggests these oceans were much colder than suspected - not to mention bad news for an ancient Martian Titanic.
We don't know what Mars looked like three billion years ago, but planetary scientists had settled into one of two basic camps. The more popular current theory is that Mars was once a warm, wet world full of liquid water, which is what carved the planet's complex valley systems and other features likely created by erosion. The other theory holds that Mars was never consistently warm enough to support oceans long-term, and instead these features indicative of water were caused during very brief, hot bursts n the planet's life.
That second theory was bolstered by investigations into a giant stretch of Martian lowlands thought to be a possible site of a great Martian ocean. This was seemingly disproved - and the entire notion of long-term Martian liquid water cast into doubt - when giant rocks and craters were discovered on the lowlands, which don't fit easily with the fine sediments one would expect to find on a former ocean bed.
But astrobiologist Alberto Fairen has another theory that restores the Martian ocean, just at a much colder temperature than once thought. He suggests icebergs and glaciers could have moved giant rock fragments through the ocean, depositing breakaway boulders in clumps and craters tha form the features we now observe today. That's precisely the same process that occurs on Earth.
In this model, glaciers would have slowly moved across the Martian surface, then broken up into icebergs that drifted thousands of miles across the ancient oceans. That would have been a very gradual process, meaning the oceans would have had to have been a long-term feature of the Mars climate, not something formed briefly during a short period of increased heat.
For more information on Fairen's research, check out the original report at Space.com.