Exploration of the Solar System

Week 6, Topic 8 (continued)

A summary of what we have learned from spacecraft observations of the surface of Mars

In this brief lecture, I will pull together the main results from observations by spacecraft over a nearly 40 year period.

• We saw that there is evidence for liquid water having existed in the past on Mars. The extreme suggestion of this sort is that the large, flat, craterless northern plain represents an ancient ocean floor. If this were the case, early Mars would have been a “waterworld” like the Earth, but this idea is controversial and far from universally accepted.
• All of this constitutes a somewhat confusing picture for the question of water on Mars. On one hand, the current low surface temperature and extremely low atmospheric pressure of Mars preclude the possibility of surface water. On the other hand, spacecraft photos show clear evidence of past water flows on the surface, some of which were quite big. In addition, there is photographic evidence of past bodies of water. Very recent information from the Opportunity spacecraft on the surface of Mars shows mineralogical evidence that demonstrates, almost without a doubt, that the Martian surface was submerged for long periods of time. So what’s the right answer? Remember, the reason we are interested in this is the relevance to life on Mars. Water is crucial for the existence of life.
• The scientific discussion of the possibility of life on Mars concentrates on Mars in the remote past. Like the Earth, Mars has been around for 4.5 billion years. Although presently inhospitable to life, it may be that the climate on Mars was more suitable for life long ago. Intriguingly, the most interesting features on Mars, the valley networks, are found in the oldest terrain on the planet.
• It is not presently known what the hydrological conditions of Mars have been during its 4.5 billion year history. A major goal of the NASA program of solar system exploration is to find out. With present information, scientists have tended to divide into two camps. The warm, wet Mars school believes that for a significant period of time early in the history of the solar system, say 4.2 to 3.5 billion years ago, the atmosphere of Mars was much denser and surface temperatures much warmer. They contend that during this time, liquid bodies of water could have existed on the surface of Mars. They also point out that life on Earth originated in this period, so it might have on Mars as well. In the opposite corner are the proponents of the cold, dry Mars view, who doubt that conditions on Mars were ever favorable for water to exist in liquid form for sufficiently long periods of time. In the next lecture, I will elaborate on these two points of view, particular the warm, wet Mars viewpoint.
• The Mars Exploration Rover spacecraft seem to provide very strong support for the Warm Wet Mars theory. It seems rather clear that the Meridani Planum landing site of the spacecraft Opportunity was submerged for a long period of time. Similar but less striking data has been returned by Spirit.