The Asteroid that Flattened Mars
In 1080p. Did Mars long ago develop far enough for life to arise? If so, does anything still live within Mars’ dusty plains, beneath its ice caps, or somewhere underground?
In 1964 the Mariner Four spacecraft flew by Mars and got a good look. What it saw looked more like the Moon than the Earth. Then, in the mid-1970′s, two lander-orbiter robot teams, named Viking, went in for an even closer look. The landers tested the soil for the chemical residues of life. All the evidence from Viking told us: Mars is dead. And extremely harsh.
The mission recorded Martian surface temperatures from -17 degrees Celsius down to -107. We now know it can get even colder than that at the poles. The atmosphere is 95% carbon dioxide, with only traces of oxygen. And it’s extremely thin, with less than one percent the surface pressure of Earth’s atmosphere.
And it’s bone dry. In fact, the Sahara Desert is a rainforest compared to Mars, where water vapor is a trace gas in the atmosphere. On Earth, impact craters erode over time from wind and water… and even volcanic activity. On Mars, they can linger for billions of years.
Earth’s surface is shaped and reshaped by the horizontal movement of plates that make up its crust driven by heat welling up from the planet’s hot interior. At half the width and only 11% the mass of Earth, Mars doesn’t generate enough heat to support wide-scale plate tectonics.
Nor does it have the gravity to hold a thick atmosphere needed to store enough heat at the surface to allow liquid water to flow. Nonetheless, some areas that looked to Viking-era scientists like craters and volcanic areas, were later shown to be riverbeds, lake bottoms, and ocean shorelines.
If water once flowed on Mars’ surface, where did it all go?
This was the scene at NASA’s Jet Propulsion Lab in 2004. The twin rovers Spirit and Opportunity had just bounced down on the Red Planet. When the excitement died down, the rovers were set off on one of the most remarkable journeys in th