The other big attraction on Mars is the largest volcano, and highest mountain in the solar system. Olympus Mounts towers at an astounding 17 miles, 3 times higher than Everest, its base covers more ground than the United Kingdom, and the massive caldera(火山口) at its submit could easily swallow Greater London, Paris and New York. 

 

Things tend to be big on Mars. I think in part that is because the planet has lower gravity. That is / when you pile up lava, you can pile it 3 times higher because the gravity is 3 times less before all starts to collapse on its own weight. 

 

Mars is a far more active world than previously thought. We see landslides of dust, and gullies(沟壑)freshly carved by outflows of mysterious fluids. And this peculiar region has been claimed as flash frozen sea, complete with fossil icebergs. Likewise, there are glaciers, geologically recent, but now buried beneath protective blanket of dust, waiting for the next change of the climate, still, most of defining surface features of Mars were carved away back in the good old days. 

 

Certainly, something happened in the early history of Mars that led to / great release of / water, and of course people wonder, without that much water, could there have been / ancient oceans? Could there have been an environment that was very much like life environments on the early earth. 

 

Early Mars was a different world, a world with a thicker atmosphere, with weather and water, possibly a vast / shallow northern ocean. This was really the time to go to Mars, when you did not need a spacesuit, perhaps just an oxygen tank and some warm clothes