A dry planet, after all

This picture shows the size of a sphere that would contain all of Earth's water in comparison to the size of the Earth. The blue sphere sitting on the United States, reaching from about Salt Lake City, Utah to Topeka, Kansas, has a diameter of about 860 miles (about 1,385 kilometers) , with a volume of about 332,500,000 cubic miles (1,386,000,000 cubic kilometers). The sphere includes all the water in the oceans, seas, ice caps, lakes and rivers as well as groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant.

All of Earth's Water in a Single Sphere. Credit: Jack Cook, Woods Hole Oceanographic Institution (© Howard Perlman, USGS)

Sources:

• Water Science for Schools, USGS, May 10, 2012
• All the Water on Planet Earth, APOD, May 15, 2012

Zooming on craters and rivers in Acidalia Planitia

There are numerous river valleys in this section of the transition zone from the Martian highlands to the northern lowlands of Acidalia Planitia. Some of these valleys show what is referred to as a dendritic pattern, imitating the shape of the uniform branching of a tree. Such flow patterns occur as a result of precipitation, in the form of rain or snow, for example. The existence of dendritic outflow systems on Mars indicates that the planet once had a different, presumably warmer and more humid, climate – at least at some point in time.

Dendritic river valleys and craters in Acidalia Planitia on Mars. Credit: ESA/DLR/FU Berlin (G. Neukum)

A bomb sag provides more evidence of water on early Mars

Georgia Tech Assistant Professor Josef Dufek is attempting to learn more about the past atmospheric conditions of Mars. Dufek’s first research tool was a rock fragment propelled into the Martian atmosphere during a volcanic eruption roughly 3.5 billion years ago. The deposit landed in the volcanic sediment, created a divot (or bomb sag), eventually solidified and remains in the same location today. Dufek’s next tool was the Mars rover. In 2007, Spirit landed at that site, known as Home Plate, and took a closer look at the imbedded fragment. Dufek and his collaborators at the University of California-Berkeley received enough data to determine the size, depth and shape of the bomb sag.

This bomb sag on the surface of Mars was created during a volcanic blast approximately 3.5 billion years ago. Assistant Professor Josef Dufek has replicated the sag in his lab while studying the possibility of water and atmospheric conditions of early Mars. Credit: NASA/JPL

Former lakes and rivers in Acidalia Planitia

The images from the High Resolution Stereo Camera (HRSC), carried on board ESA’s Mars Express spacecraft and operated by the German Aerospace Center, were acquired on 21 June 2011 and show the transition zone between the western edge of Acidalia Planitia and the Martian highlands. 

This colour view was created using the nadir channel, which is directed vertically down onto the Martian surface, and the HRSC camera system colour channels on ESA's Mars Express spacecraft; north is to the right in the image. The image section shown here covers an area of around 11,000 square kilometres. Numerous river valleys can be made out in this section of the transition zone between the Tempe Terra region in the Martian highlands and the northern lowlands of Acidalia Planitia. The dendritic pattern of these river valleys suggests that these structures formed a long time ago by surface water, which presumably precipitated onto Mars in the form of rain or snow. Many of the large craters are filled with sediment that the water transported into these impact structures, which were once much deeper. Credit: ESA/DLR/FU Berlin (G. Neukum)