“I’m almost on the Martian equator. To give you some reference, the great Tharsis Bulge, with its three huge shield volcanoes, is a couple of thousand miles to the east of me; and Olympus Mons, the greatest volcano in the Solar System, is about the same distance to the north. But I can’t see the volcanoes, or the Bulge, from here; although this is a small world, Martian features are too huge, overwhelming on a human scale.

“We’re close enough to Tharsis for this region to have been affected by the uplift of the Bulge. So, although the surface here looks as flat as a beach at low tide, I know that when I look away from the MEM I’m probably looking down a slope of a few tenths of a degree.”

She took a long, slow look around at the panorama of Mangala Vallis.

“The MEM is standing on a surface which is littered with rocks. The rocks, I would say, range in size from maybe half a yard up to two yards. The rocks show vesicles. That is, there are small bubbles in the surface of the rocks; it means the rocks are probably bits of frozen lava, and the bubbles were caused by the escape of gases from within the molten rocks. Gases lost maybe a billion years ago. The rocks are uniformly pitted and fluted, I would guess by wind erosion. I can see smaller formations that look like pebbles, but I’m pretty sure they are duricrust aggregate. Just bits of the surface stuck together. The surface is not like sand; it’s evidently much finer-grained. The grains are no more than a micron or so wide. I’m sure that the dust is the result of the slow weathering of the rocks, with much oxidation having occurred; the rocks have the characteristic deep red-brown coloration of smectite clays…

“I can see how geological processes are continuing to shape this landscape. The surface has clearly been scoured by wind: the landscape is eroded, and the dust under my feet has surely been transported from around the planet. From a geological point of view, there is clearly a sequence of events represented here: impact, wind, volcanic activity, possibly flooding, probably ground ice.

“The Moon is an old world; we think its story ended, essentially, a billion or more years ago. But it’s obvious to me, standing here, that Mars, like Earth, is still evolving. Still alive.”

There was a long silence on the radio link.

“Natalie,” Stone said gently. “Are you all right?”

“Yes. Yes, I’m fine, Phil.”

She thought of her words dispersing, radiating away to Earth and beyond; she wished she could call them back. It’s not enough. It could never be enough.

But, I guess, it was the best I could do.

It was time.

She said, “I’ll step off the footpad now.”