Space law, says David Koplow of Georgetown University Law Centre, Washington DC, is based on the principle of strict liability.
“The concept is that space activities are hazardous and therefore the harm should not fall on an innocent bystander,” Koplow says.
Another problem stems from the fact that only a few countries have the technological ability to deflect an incoming asteroid, and there is, at present, no international authority tasked with making sure everyone else is represented in the decision-making process.
In fact, says Cordula Steinkogler, a space law expert at the University of Vienna, Austria, current treaties don’t even require nations to share information about such hazards, let alone act to protect each other.
She notes, however, that the United Nationscharterdoes establish a “very general” duty for them to act toward solving international problems that affect economic, social, cultural, educational, and health wellbeing.
Failure to share information can be more than just an inconvenience.
To start with, says Petr Boháček, of Charles University in Prague in the Czech Republic, it could make countries wonder if, instead of international cooperation, the rule is actually everyone for themselves.
The nation-state concept of sovereignty, he adds, dates back several hundred years.
“I’m not sure how many concepts from the seventeenth century you use in your decision-making,” he says, “but making decisions for planetary defence based on this dinosaur method of decision-making may not be the best choice.”
Another problem is that the nation hit by an asteroid might see it as an attack by a foe, and retaliate.
“[It] could look like the damage of a nuclear attack,” says Seth Baum, executive director of the Global Catastrophic Risk Institute, a US-based think tank, “so the prospect [of] a counterattack seems like something worth taking very seriously.”
Ironically, the risk of this is probably inversely proportional to the size of asteroid.
Smaller ones, like the one that in 2013 exploded high aboveChelyabinsk，俄罗斯很难预测，俄罗斯的力量约为470千座TNT。
To the extent we can see something like that coming in, Baum says, it would be good to alert militaries around the world of its approach, just to make sure they don’t mistake it for a nuclear attack.
But the biggest worry is about the use ofnuclear weapons与传入的小行星抗衡。
At the moment, there are several methods for diverting a bolide from its collision course, if it is spotted far enough in advance.
One is to hit it with a fast-moving rocket, just hard enough to nudge it into missing us.
There’s just one problem: under the terms of theOuter Space Treaty1967年，禁止使用核装置。尽管有可能修改条约（或在紧急情况下使联合国安理会覆盖该条约），但绝不是Gimme。
In part, says Koplow, the prohibition against using nuclear devices in space is based on the desire to prevent a nuclear arms race above the atmosphere, and the concern that carving out an exception might open the floodgates for military deployments.
But there is also a potential effect on efforts for nuclear disarmament and non-proliferation.
“And”, Boháček adds, “the non-proliferation regime is based on the assumption that you do not need nuclear weapons for national survival.”
If one country used them to divert an asteroid, he says, that “would send a signal that they are necessary”.
Also relevant, Baum says, is the “nuclear taboo” – an “informal but nonetheless very powerful” stigma against using nuclear devices for any purpose, even peaceful ones.
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