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Every 120 thousand years the climate on Mars becomes more Earth-like. During these periods Mars is tilted in the direction of the sun, which causes polar ice to move towards the equator. The surface of Mars then contains large amounts of snow, and meltwater causes debris flows to occur at Earth-like frequencies and magnitudes on some crater walls, concludes , PhD. Unfortunately, it may take a few hundred thousand years for Mars to have so much flowing water again. The results were published in on June 23.

Periodic appearance of water on Mars

A great deal of information about the past, present and future of Mars is available via satellite photographs as long as you know how and where to look. Based on these photographs, Tjalling de Haas concluded that over the past million years there have been regular occurrences of flowing water on the surface of Mars. However, we are currently in a long period in which flowing water is not possible.

The right circumstances

The conditions must be just right for liquid water to occur. Like Earth, Mars is tilted towards the sun. The approximate tilt on Mars varies between 15 and 35 degrees, leading to extreme climate fluctuations (in comparison, the Earth tilts by only 2 degrees during ice ages). The climate is more Earth-like when the tilt of Mars is greater than 30 degrees; a stronger water cycle emerges with snow covering more than half of the planet. Furthermore, some of this snow can melt on crater walls.

Streams of sand, mud, rocks and flowing water

In a large crater that was once covered with snow, De Haas found traces of debris flows: streams of sand, mud and rocks of which about half consists of liquid water. “In a geological time frame the flows are very recent” says De Haas. "The oldest is up to one million years old, formed at intervals of about one hundred thousand years in short periods when the tilt of Mars exceeded 30 degrees. During these periods snowmelt resulted in the presence of liquid water and the formation of debris flows."

Debris flows with Earth-like regularity

Previous research had already shown that liquid water was present on Mars in the last million years. “But no one has yet been able to figure out how much or how often it appeared" explains De Haas. “At least one and a half to five centimeters of meltwater is needed for a large debris flow. That means that the thickness of the layer of snow in the crater must have been tens of centimeters deep. Additionally, we can calculate that during the short periods when the tilt of Mars was greater than 30 degrees, the debris flow occurred just as often as it now does in desert areas on Earth. To be clear, this type of activity only occurred locally on crater walls as most of the surface of Mars was bone-dry."

A few hundred thousand years

Mars has tilted less in the last 400 thousand years, and it is already almost half a million years ago since the conditions allowed for liquid water on the planet. "It will take some time before these conditions will be present again" concludes De Haas. "It may well take a few hundred thousand years."

Meer informatie

• , Global Change Geomorphology, faculty of Geosciences, Utrecht ľ�ϸ���Ӱ��, T.deHaas@uu.nl, +31 30 253 4014
• , press officer faculty of Geosciences, Utrecht ľ�ϸ���Ӱ��, T.deKievith@uu.nl, +31 30 253 5593

Faculty of Geosciences: a sustainable Earth for future generations