Tumbleweeds on Mars

Quick, pilgrim! Think of a Western movie!

What do you see? A gunfight at high noon? Perhaps a tall saguaro cactus, inexplicably growing in Texas? I’ll bet you picked a moment of breath-holding suspense, taut as a pulled rope, as the white hat and black hat share an intimate gaze from fifty paces. And in the background of this nauseating tension, like crickets in a bad joke, is a rolling tumbleweed.

Little-known fact: Tumbleweeds can levitate.

Tumbleweeds: the rolling punctuation marks of awkward silences. They are the harmonica’s dog, the cough in the crowd in the pause before the gallows trapdoor drops. And out here in the day-to-day life of the American West, they’re practically an animal of their own. You swerve to avoid hitting them on the highway. They nuzzle the barbed-wire fences, sniffing out an opening. They show up mysteriously like stray cats in your yard overnight. Though native Westerners give them scant notice, transplants like me still have a starstruck fondness for them, as if they were some B-list actor from a John Ford movie that we’d discovered, lost and drunk, making a cameo in the alley behind our house. But despite their scruffy aimlessness, tumbleweeds are one of the great success stories of the American West, and may someday follow us to even wild, wilder Wests and further frontiers.

Like most modern drifters, many of them will take the bus.

The first thing you must understand about tumbleweeds is that they’re not a plant, but a habit of plants. (Like a “tree.”) Plants, as you know, rarely travel themselves; they leave that to their seeds. But a tumbleweed, or rather, a plant that tumbleweeds, uses its own dead and desiccated body as the seed disperser, and so gets to see a little bit of the world. There are tumbleweed forms among the asters, the plantains, the ferns, the mustards, the nightshades, and a dozen other families across Eurasia, Africa, Australia and the Americas.

Tumbleweeds are also transported over land masses by establishing a symbiotic relationship with a vector.

But the one you’re probably thinking of is Salsola tragus, also known as Russian Thistle. As the name implies, this weed is like most of us here in the West: not from ’round these parts. Most sources trace its arrival from the windy steppes of Russia to 1870, when a contaminated shipment of flax seed was planted in South Dakota. (For you botany-minded Western movie nerds, note that this makes tumbleweed in most Westerns set before 1900 an historical anachronism.)

Salsola tragus in bloom.

Evolution has endowed the ambling Salsola with two gifts: drought tolerance and locomotion. Both were perfectly suited to the American West, where hardiness and nomadism are the parents of survival. There is a third key to the tumbleweed’s success: a Taoist-like desirelessness, the willingness to wander with the wind. After the pretty white or pink flowers have been pollinated, Salsola gives up any desire to live, drying out while its seeds form and then cutting its own stalk. Its spherical shape lets it spread between 20,000 and 50,000 tiny seeds as it bounces along. The fences that smothered the migrations of the buffalo have little effect on them; planting the remainder of their seeds on both sides of the barbed wire, the tumbleweed’s children pick up where their parents left off, rolling to the next fence or, hopefully, an irrigated cotton field. So tumbleweeds are the plant kingdom’s high plains drifters, or as one species is called, their tumbling oracles.

"But they never attack the same place twice. They were testing the fences for weaknesses. Systematically. They remembered."

From Russia to America, then to the Australian outback. Another tumbleweed species, also in the Amaranth family, traveled from Central America to Europe. Another, from Africa to America. There are many ways to define a “weed,” but my favorite has generally been a non-native and aggressively invasive species out of balance with the local ecosystem. By this definition, most of us are weeds. And we bring our weeds with us. (Especially our tumbleweeds, if we are flax farmers or hot naked women.) The tumbleweed is perhaps one of the greatest of colonizers: highly mobile, thirsty yet motiveless, and best of all, ready to roll. So of course, NASA is studying them to learn how better to colonize the New American West: the outback of Mars.

Mars rovers are built to traverse rocky and uneven terrain, but there are places on the Red Planet where even rovers cannot tread. The Spirit rover, for example, has been stuck in a sand trap in the Gusev Crater since May 2009. Current rovers are solar-powered, and it’s possible for rovers’ solar panels to become so dusty as to shut down the whole machine. But we know that Mars’ thin, carbon-dioxide based atmosphere is actually quite windy, and there’s nothing for being blown up hills, down ravines, and over boulders in a desert like a tumbleweed.

NASA technology finally catches up with that of "American Gladiators."

Instead of putting one very expensive tank-like rover on Mars, scientists could learn more about the surface from a whole fleet of wind-blown balls rolling all over the planet. If one gets stuck, an auxiliary motor could make it self-rolling until it’s freed. The idea is controversial and not yet approved by NASA, but someday we may very well plant our tumbleweeds in the red dirt of a new planet. And with tumbleweeds usually come cowboys.

Prepare to be broken in and saddled, you ornery varmint.

Call me cynical, but I don’t believe we’ll ever colonize Mars. For one thing, it’s pointless. A mission to Mars would be just another example of Americans’ weird compulsion to touch everything. (And you know that if anyone plays “tag” with Mars, it will be America.) For another thing, it would be so unbelievably expensive that politics and economics would strangle such an effort in its crib. But most importantly, Mars is a terrible place to live: It’s frigid, it has no breathable atmosphere, the weak gravity would unknit our bones, the solar radiation would poison us from inside our cells, and if Ray Bradbury is to be believed, we’ll all turn into effete, golden-eyed aliens. If all those things don’t kill us, the homesickness will.

And if not the homesickness, than this guy.

But human exploration, for all we talk about its nobility, has often had the aggressive aimlessness of weeds. The American soul in particular is restless, rarely satisfied in its place, and for all its speechifying about Manifest Destiny, the responsibility to civilize the wildnerness, and the “human spirit” yearning to “reach for the stars,” it is often surprisingly undirected. A controversial study [which I could not find on the internet, sorry] has correlated the frequency of ADHD levels worldwide with the amount of exploration by each ethnic group, reaching the conclusion that cultures seem more driven to colonize when their leaders are just impulsive spazzes. And so we may reach Mars and other planets not just through the concerted effort of thousands of highly focused scientists and engineers, but through random and misplaced willpower. I’m betting against it, personally, but it’s not inconceivable that one day cryonically frozen astronauts will drift across the solar system in sailships powered by cosmic winds, like dead cowboys riding thirsty horses across the desert. Like the colonization of the American West, corporations will build the cities and railways to space, and settlers without any better prospects will follow them and call themselves intrepid. We are a weedy species, for the most part, and a tumbleweed species at that. Should the first one-horse town ever set up its saloon in the valleys of Mars, we may be greeted with a familiar compliment to the New Arizona landscape: the tumbling oracles wandering the plains, the oracles that had long foretold our coming.

If we can populate Nevada...