5 June 2008

Phoenix's Neighborhood (Part I): The Basin

Posted by briony

If you’re like us, you’ve been refreshing the Phoenix news page constantly, looking for the next update from Mars. If you need a little catching up on what’s going on in the mission, here are some recent posts with updates.

But with all the Phoenix coverage, there hasn’t been much talk about the context for the Phoenix landing site. What’s so cool about the north pole of Mars?

The north pole of Mars sits at the lowest elevation of the huge basin that takes up most of the northern hemisphere of Mars:

MOLA elevation map of Mars (credit: NASA)

Like any basin here on Earth, the northern basin acts as a trap for all kinds of materials from elsewhere on the planet: wind-blown sand, water and debris from outflows, groundwater, and maybe even precipitation. The idea that the northern basin may have once held water has made it the prime location for a possible ancient martian ocean.

While observations of features that look like shorelines and deltas support the concept of an ancient northern ocean on Mars, the evidence is not conclusive. Right now, the consensus in the scientific community is that the northern ocean may have never existed, and if it did, that it was pretty short-lived on geologic timescales.

Possible deltas and shorelines at the edge of the northern basin (Pablo and Pacifici, 2008).

Even if there never was an ocean, there has still been a huge amount of material deposited by wind and outflows in the northern basin. In the shaded elevation map above, did you notice how smooth the northern plains look compared to the southern highlands? This indicates that enough material has been added to the northern basin to smooth over and obscure the ancient cratered terrain – many, many kilometers of sediments.

The northern basin has gotten much more interesting in the past decade. Until high resolution images came back from Mars Global Surveyor in the late 90’s, it was thought that vast floods of lava had smoothed out the plains a few billion years ago, and not much had changed since. Our new picture of the northern plains is a vast stack of sediments that have been constantly reworked by erosion and permafrost processes for potentially billions of years.

In the next installment, we’ll look at the evidence for ice in the northern plains before Phoenix landed on it.