It's the fourth anniversary of the Mars Exploration Rovers. The twin rovers have operated now 16 times longer than the original three-month prime mission and they're still going.

Transcript:

Mars 4 th Anniversary:

This is the fourth anniversary of both rovers operating on the surface of Mars.

These rovers have told us so much about Mars and about its past history.

Hi this is John Callas, project manager for the Mars Exploration Rovers at the Jet Propulsion Laboratory.

Well, these rovers have operated now 16 times longer than the original three-month prime mission and they're still going. In the past four years on Mars, each rover has returned over 100,000 images. Spirit has traveled over seven-and-a-half kilometers. That's over four-and-a-half miles. Opportunity has traveled over eleven-and-a-half kilometers.

That's over seven miles on the surface of Mars.

The first rover to land, Spirit, is right now on Home Plate, preparing for her third Martian winter. We were able to collect some outstanding color images of the west valley of the region west of our current location.

We're concerned because there's a lot of dust that's on the solar arrays that provide the power to the rover. So we're having to take and tilt the rover towards the sun to maximize the amount of energy that the arrays will produce as we get into the deep, dark winter.

Opportunity on the other side of the planet is deep within Victoria Crater exploring the past history of Mars. And it is exploring a bright band, a region within the crater, which may tell us something about the ancient surface of Mars. It's also collecting some super-resolution imagery of a promontory called Cape Verde.

I'm very fond of the rovers. I'm very attached to them and I worry about them, and they are getting older. And things are aging on each rover.

These rovers have told us so much about the past history of Mars. What they're telling us is that at one time in the ancient past, Mars was a warmer, wetter environment. It was more Earth-like and so it's natural to ask the question: Was there life on Mars? Is there life there today? Can we find evidence of past life on Mars? These are very tantalizing and exciting questions.

I think what people will remember about them is that they are almost like people on the surface of Mars. They are our proxies. These are intrepid explorers that are dutifully following our commands and exploring this alien and hostile world for our benefit.

In the meantime, we're going to keep these rovers going. We're going to keep them exploring, and there's a lot of work to do. And both of these rovers are eager to carry out those duties.

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