One weighty decision that the world will need to make in 2010 is whether to support an idea raised by Anatoly Perminov, the head of the Russian space agency, Roscosmos, to launch an unmanned mission to redirect a large asteroid that might collide with Earth after 2030.
At more than 360 metres in diameter, the asteroid, Apophis, is a dozen times larger than the Tunguska space object (presumably a meteorite or comet) that devastated a large part of eastern Siberia a century ago. As far as can be determined, that object detonated on 30 June, 1908, with the power of a nuclear weapon, felling 80 million trees over 2,000 square kilometres.
According to Nasa, if Apophis hit the Earth, it could release more than 100,000 times the energy of the Tunguska event. Thousands of square kilometres could vaporise in the blast, but the whole Earth would suffer from the loss of sunlight and other effects of the dust released into the atmosphere.
This danger explains why a Russian analyst has called Apophis a “space terrorist.”
Current projections are that Apophis, which was discovered in 2004, will orbit near the Earth several times between 2029 and 2036. In October 2009, near-Earth object (NEO) trackers Steve Chesley and Paul Chodas, of Nasa, placed the odds of Apophis striking Earth in 2036 at about one in 233,000, lower than previous estimates.
But their forecast that it would come within 30,000 kilometres of our planet in 2029 (closer than the Moon) is more likely to please astronomers than international security experts. Some unknown comet or other space object could fly near enough to the asteroid in the next few decades to change its predicted path, perhaps in a way that redirects it towards Earth.
According to Mr Perminov, the proposals that Roscosmos is considering do not envision trying to destroy the asteroid, but rather to use the laws of physics to change its path. He says that if Roscosmos’s management decided to act, it would work with experts from Europe, the United States, China and other space powers.
Scientists have proposed various ways to deflect an asteroid. Some have suggested placing a large object nearby to change its trajectory through mutual gravitational attraction. Another method is to use mirrors, light, or painted colours to change the way the asteroid absorbs heat, which could also shift its direction. Others have suggested ramming a spacecraft or other object into the asteroid. A few scientists, and many science-fiction writers, have also speculated about using nuclear weapons to destroy or damage an asteroid, comet, meteor, or alien spacecraft heading towards the Earth. The Outer Space Treaty bans placing nuclear weapons in orbit, on celestial bodies, or stationing “such weapons in outer space in any other manner”, but may be interpreted to permit their one-time use.
The more practical problem is that even a nuclear explosion might not prove sufficiently powerful. Even if the nuclear warhead broke the asteroid into many small pieces, they could have time to re-combine into another large object. In addition, the space vehicle carrying the weapon might malfunction, and the nuclear warhead could land (and perhaps detonate) somewhere on Earth.
The safest approach might be to test several techniques on nearby asteroids before using them against Apophis. Unfortunately, it is estimated that “attacking” an asteroid would cost billions of dollars.
This raises the issue of who should pay for such a mission and, more fundamentally, who can authorise it. These global governance questions also apply to other worldwide threats, such as climate change.
In 2008, a report by space experts called for the United Nations Security Council to make the final decision about how to counter potential threats from near-Earth objects. The Security Council normally votes on issues that threaten international peace and security, but this method would allow only a small number of governments to decide Earth’s fate.
Since an asteroid collision could affect all of humanity, should not everyone have some say in the decision? Perhaps every country should vote in the UN General Assembly on how to proceed; the option receiving the most votes would prevail. Another option would be to allow every adult to vote directly in a global referendum for his or her preferred option.
An interesting issue would arise if some countries wanted to act, but others did not. Would Russia or a coalition of countries have the right to attempt to alter Apophis’s orbit without the approval of other states?
Mr Perminov’s proposal has raised important questions – both scientific and political. Whatever the dangers posed by Apophis, we would do well to start addressing them.