海角大神

As we push into the final frontier, we are leaving our mark. We have already left more than 400,000 pounds of human-made material on the moon. Rovers and bits of defunct orbiters litter the surface of Mars. And scientists have sent robotic spacecraft hurtling out past Pluto with no final destination.

In our own cosmic backyard, space trash abounds. Between abandoned satellites, pieces of old spacecraft, and spent rocket stages, more than 21,000 pieces of debris orbit Earth. The threat of such debris colliding with expensive satellites or careening to Earth has prompted some wild ideas to tidy the immediate area of space surrounding our planet. Those ideas have ranged from slingshots and nets to gecko-like sticky pads and lasers.

As we explore beyond our own backyard, the stuff we leave behind may not have an effect on us as directly. So should we care? Is it our ethical responsibility to minimize the space junk that we leave in the rest of the solar system? The answers hinge on how humanity chooses to ascribe value to things like life, the natural world, and the unknown potential and desires of of future generations.

Current constraints

We can鈥檛 yet travel around the solar system picking up after ourselves. But we can minimize what we leave behind, scientists say. Some probes, like NASA鈥檚 Stardust mission to sample a comet鈥檚 dust, can return to Earth at the end of an exploration.聽For more far-flung missions, scientists have sent spacecraft to a fiery end in a planet鈥檚 atmosphere, as they did at the end of the Cassini mission in September.

When we make the decision to protect a place from our mission leftovers, it highlights what we consider to be worth preserving.聽Current international planetary protection policies place a high priority on preserving places where there might be life.

Guidelines set in the Outer Space Treaty of 1967 direct signatories to minimize contamination of potentially life-bearing worlds. Although these international guidelines are not binding, NASA鈥檚 policy aligns with them and scientists are expected to incorporate detailed planetary protection plans into end-of-mission plans for places where there might be life or habitable worlds.

That was the case with NASA鈥檚 Galileo mission to Jupiter, says John Rummel, a former聽NASA Planetary Protection Officer聽who is now a senior scientist at the SETI Institute. When the probe began to show signs of falling apart, mission scientists worried that they could soon lose control of its trajectory. That possibility was particularly troubling given scientists鈥� growing suspicion that Jupiter鈥檚 moon Europa could be habitable. Furthermore, modeling suggested that Galileo might even be jostled out of Jupiter鈥檚 orbit by other satellites if left to its own devices.

鈥淒o you really want to have 36 pounds of plutonium wandering around on its own? Everybody agreed that that was probably not a good idea,鈥澛燚r. Rummel says. So he and fellow mission scientists directed Galileo to crash into Jupiter鈥檚 atmosphere where it burned up. That plan spared the potentially habitable Europa.

Beyond life

But does responsible stewardship of our solar system only extend to places where life can thrive?

鈥淲e should be in the business of protecting what you might call the integrity of these places,鈥� says Tony Milligan, a professor of philosophy and ethics at King鈥檚 College London. 鈥淭here鈥檚 something about the uniqueness and the history of these places which makes them worthy of our consideration.鈥�

For some, the potential for scientific discovery adds inherent value to every spec of the universe. For others, the intrinsic beauty of heavenly bodies makes them equally worthy of protection as any canyon or river on Earth. And others still, associate an abstract sense of wrongness when it comes to destruction of nature, here or elsewhere.

鈥淭here is an argument to be made for the intrinsic value of nature, that rocks and rivers, whether on Earth or on Mars, have an intrinsic value to them and that there should be some degree of regard for that value,鈥� says Margaret McLean, director of bioethics at the Markkula Center for Applied Ethics at Santa Clara University.

Dr. Milligan points to a thought experiment frequently used by environmental ethicists known as the last man argument. Envision that the last human alive decides to level Mars鈥� Olympus Mons, the tallest mountain in the solar system, he says. Although it wouldn鈥檛 harm humans or any other lifeforms, most people react poorly to that idea. 鈥淚t just looks as if they鈥檙e doing something wrong,鈥� he says.

But mining dead space rocks for resources has also been seen as a way to clean up our own planet while sustaining a ballooning and advancing human population on Earth. 鈥淎 lot of people are all for solar system mining if it鈥檒l shut down the mine around the corner that is leaching materials into the river,鈥� Rummel says. And if we can extract resources without upsetting the balance of another planetary environment, 鈥淚鈥檓 all for it,鈥� he says.

So how, then, do we decide what to prioritize?

One generation鈥檚 trash ...

鈥淗ow we value things is a sliding scale,鈥� says Dr. McLean.聽鈥淲e have a greater obligation to another human being than we do to a rock.鈥�

That obligation extends to future generations. But how do we know what they will value?

Today, much of society places value in the pristine nature of wilderness. One could argue that a similar kind of wilderness experience applies to, say, the Valles Marineris canyon system on Mars. Future generations might want to hike in a pristine Martian canyon system.

Or they might actually value our space trash, 鈥渙ne era鈥檚 debris can be another era鈥檚 historic object,鈥� Milligan says. The stuff we鈥檝e left on the moon and are leaving on Mars may be seen by future generations as valuable monuments to human achievement worthy of protecting, too.

Or perhaps they, too, might want to mine ores and other resources found in space, and if we plunder it all right away, what will be left for them?

So what do we do?

When exploring, 鈥渓eaving no trace is impossible,鈥� says Margaret Race, a senior research scientist in planetary protection at the SETI Institute. 鈥淚f you really want to have it be pristine, just don鈥檛 go.鈥�

And space policy discussions make the assumption that we鈥檙e going to explore outer space.

So 鈥渨hat we鈥檙e asked to do is to balance the risk with the benefit that we may gain, and to do so in a way that minimizes the risk,鈥� McLean says. And, she says, the interdisciplinary planetary protection dialogues that governments and scientists already engage in are good conduits for finding that balance.

鈥淕oing slowly and going carefully makes a whole lot more sense than rushing into something and wishing you had done it later,鈥� Rummel says. 鈥淭he bottom line is that we have only one chance to move out into the solar system in an appropriate manner.鈥�

Still, 鈥渨e鈥檙e not going blind into this,鈥� McLean says. Space may be unchartered territory, but we have past experiences pushing into new frontiers here on Earth to draw from.聽鈥淲e are explorers, but we need to take the lessons that we鈥檝e learned from our last place of experience with us as we explore.鈥�