By Paul Rincon
Science reporter, BBC News
The icy feature has been spotted in images from the European Space Agency's (Esa) Mars Express spacecraft.
Ancient glaciers, many millions of years old, have been seen before on the Red Planet, but these ones may only be several thousand years old.
The young glacier appears in the Deuteronilus Mensae region between Mars' rugged southern highlands and the flat northern lowlands.
"If it was an image of Earth, I would say 'glacier' right away," Dr Gerhard Neukum, chief scientist on the spacecraft's High Resolution Stereo Camera (HRSC) told BBC News.
"We have not yet been able to see the spectral signature of water. But we will fly over it in the coming months and take measurements. On the glacial ridges we can see white tips, which can only be freshly exposed ice.
This is found in very few places on the Red Planet because as soon ice is exposed to the Martian environment, it sublimates - or turns from a solid state directly into gas.
In Deuteronilus Mensae, Dr Neukum estimates that water came up from underground in the last 10,000 to 100,000 years.
"That means it is an active glacier now. This is unique, and there are probably more," said Dr Neukum.
The water subsequently froze over and glaciers developed, the researcher from the Free University in Berlin, Germany, explained.
Not all researchers share his view of events. Some believe that snowfall causes glaciers to develop on Mars, as it does on Earth. But Gerhard Neukum thinks there is too little precipitation on the Red Planet for this to be the case.
Glacial features have been seen before on the Olympus Mons volcano. But these are thought to be about four million years old.
Dr Neukum said glacial features would be prime locations for robotic rovers to look for evidence of life on Mars.
If microbes survive deep below Mars, they could be transported to the surface by water gushing up from deep underground.
Last month, Esa celebrated Mars Express's five thousandth orbit of the Red Planet. The unmanned probe arrived at Mars on 25 December 2003.Paul.Rincon-INTERNET@bbc.co.uk