No matter how far we venture into space, there are reminders of Earth. Take Mars, for example. In some ways it's home to such alien landscapes: impact craters, impossibly tall volcanoes, mazes of canyons, ice spiders. Yet it's been widely remarked that some places on the planet look a lot like the deserts we know. If you don't believe me, take a look at these pictures I took not far from my home in Utah.
Mars images: NASA/JPL/Cornell University/University of Arizona. Earth images: Bill Dunford.
Can you tell which is Earth and which is Mars? On the left, images from the Red Planet as captured by the Opportunity rover and the Mars Reconnaissance Orbiter. On the right, locations of roughly the same scale in and around Canyonlands National Park, Utah. Click the image for a longer caption and more details.
Mars even has clouds that sometimes drift lazily through the afternoon sky. In some ways, Mars is not so different from the Earth, and vice versa. They are both very real places. The same laws of light and stone and wind are at work on both worlds, resulting in portraits of recognizable siblings.
I wish there were a word for this sense of alienness-yet-familiarity in the landscapes of other planets. "Terrasimilitude"?
On the other hand, Mars and Earth are very different in such important ways. The air on Mars is thinner than at the top of Mt. Everest, colder than in Antarctica, drier than in Death Valley. In fact, despite decades of science fiction that almost makes one forget it, we have never found, anywhere, sure signs of life beyond the Earth. Despite all our travels, all our straining at the traces of evidence, our planet is--as far as we know--utterly unique.
There is something about studying other worlds that brings the importance of our own sharply into focus. In fact, I think this ranks high among the many benefits that space exploration offers.
After poring over orbital views of Mars' empty plains and pondering the speculative possibilities of underground oceans in the outer Solar System, there is the Earth rising over the lunar horizon in pictures sent by spacecraft. It's a gem. It is immediately obvious that something very strange and almost too wonderful for words is happening within its blue-white curves.
Every trip I take into Earthly deserts reminds me of that singular beauty and the priceless shelter offered by the homeworld. Everywhere, everywhere you look on this planet—even in the desert—there is water, air...and life.
During one expedition in Utah, a cloudburst descended on the mesas and unleashed torrential rain for about ten minutes before it swept on. Then the flash floods came. Dust-red water surged suddenly through every dry channel. We followed it down to the edge of the canyon, and watched it spill over the cliff sides. A few minutes later the entire event ended as fast as it began...but the countryside bloomed for days afterward.
Although the deserts of Earth can look like Mars, reminders that the home planet is a unique oasis are everywhere. Here, a cloudburst passed over the desert at Dead Horse Point, Utah, then was gone within minutes. A surge of mud-red water pushed its way over the cliff side. Half an hour later the stream was dry again, but the entire countryside smelled like flowers for days afterwards.
On Earth Day and every day, it's worth remembering that Mars is nice to visit. But there’s no place like home.