More About Mars

Last time talked about the various sorts of surface terrain on Mars revealed by unmanned spacecraft, primarily the Viking orbiters and Mars Global Surveyor. The main types of surface features discussed were the north-south asymmetry in the topography of Mars, impact craters, volcanos, Valles Marineris, water flow channels, (two types, the valley networks and the outflow channels), and evidence of ancient lakes like Hebes Chasma.

Students in this class should explore this web site to see all of the marvelous examples of Martian terrain. Imagine yourself wandering around there!

The Ancient Martian Paleoclimate

We have seen evidence for water flows on Mars in the past. The valley networks

In particular look like river systems. This indicates that in the remote past that the atmosphere of Mars must have been considerably heavier than it is now, and that the surface temperature must have been higher. This is often referred to as the “warm, wet past” of Mars.

This conclusion about a heavier atmosphere is corroborated by other the chemical composition of the atmosphere of Mars. Argon is the third most abundant gas in the atmosphere of Mars, and is much more abundant there than on Earth or Venus. Since a atom of Argon is heavier than nitrogen, a planet with weak gravity could hold on more readily to Argon than lighter gases. The relatively large amount of Argon points to a heavier atmosphere in the past.

The interesting implications of the ancient paleoclimate of Mars is summarized in the paper by McKay and Stoker in the journal Reviews of Geophysics, in 1989. In that article, they show a “geological timeline” for Mars and the Earth.

In the case of the Earth, we believe life arose within 1 billion years of the time that the planet formed and “certainly” by 1.5 billion years after the formation of the planet, i.e. 3.0 billion years ago. At that time, the atmosphere of the Earth was primarily carbon dioxide, and the was substantial liquid water on the surface.

McKay and Stoker make the point that Mars retained a similar atmosphere and surface conditions for 1 to 1.5 billion years after its formation. The questions then arises as to whether life similarly began on Mars, to be later snuffed out by the hostile climate that arose, and which we now see there.