Protecting Earth from asteroids
Asteroid impacts with Earth are a near-certainty, scientists say. The question is: What, if anything, should we do to track asteroids and protect Earth from them?
Last week, a meteorite reportedly crashed through the roof of a doctor's office in Virginia. No one was hurt when, traveling at some 200 miles per hour, a half-pound space rock smashed into an examination room, breaking into pieces on the concrete floor. But the incident highlighted the not-insignificant threat posed by asteroids and ice balls from space.
The consequences of a sufficiently large asteroid or comet strike could be catastrophic, which is why you're reading this in a blog about the environment:. Depending on size, an amount of energy equivalent to tens of thousands and even many millions of nuclear bombs would be released on impact. Such a strike could be disastrous not just for civilization, but for the planet's entire web of life.
If it landed in the ocean, the impact would send walls of water in all directions, inundating continental margins. If it struck land, it could ignite continent-wide fires.
And while the destruction would be immediate around the strike zone, the problems would likely become global in the aftermath: Dust injected into the atmosphere could block sunlight. Photosynthetic organisms would stop growing. Everything else that depended on them would suffer the consequences of a reduced food supply. Mass starvation would ensue.
The last asteroid strike on this scale is widely thought to have contributed to the dinosaurs' end 65 million years ago. The asteroid, which left a 110-mile-wide crater off Mexico's Yucatan Peninsula, was only six miles in diameter, roughly the size of Manhattan Island. But three-quarters of life on Earth disappeared.
Scientists generally agree that asteroid impacts in the future are a near-certainty – smaller ones more often, larger and much more catastrophic ones less often. Scientists think that asteroids like the one that ended the dinosaurs' reign hit Earth every 100 million years or so.
That's why, in 2005, Congress mandated that NASA should try to detect 90 percent of near earth objects (NEOs) with a diameter of more 140 meters or more by 2020. Asteroids of this size hit earth roughly every 30,000 years.
Before that, in 1998, Congress asked that NASA find 90 percent of all NEOs measuring more than 1 kilometer in diameter within 10 years. These hit with less regularity, but could cause substantially more damage.
Late last week, the National Research Council released a progress report that found that NASA has been quite good at locating and tracking objects larger than 1 km in diameter. But, due to insufficient funding — only $4 million yearly for tracking NEOs — NASA wouldn't meet the goals set out by Congress in 2005.
"The current near-Earth object surveys cannot meet the goals of the 2005 George E. Brown, Jr. Near-Earth Object Survey Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020," the report states. Then the authors lay out a few options for getting the job done:
If completion of the survey as close to the original 2020 deadline as possible is considered most important, a space mission conducted in concert with observations using a suitable ground-based telescope and selected by peer-reviewed competition is the best approach. This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.
If cost conservation is deemed most important, the use of a large ground-based telescope is the best approach. Under this option, the survey could not be completed by the original 2020 deadline, but could be completed before 2030. To achieve the intended cost effectiveness, the funding to construct the telescope must come largely on the basis of non-NEO programs.
The report also calls on the US to lead the formation of an international body to monitor and deal with NEO threats.
According to experts cited by Space.com, NASA needs an additional $1 billion in funding over the next 15 years to attain its goal of cataloguing all potentially threatening asteroids. As of today, NASA's Near Earth Object Program is aware of and tracking 6,691 objects.
NASA estimates that every few million years, an asteroid comes along that could threaten civilization. Every 2,000 years, a football field-size meteor hits Earth, causing significant damage to the immediate area. Anything smaller than 25 meters will likely burn up in Earth's atmosphere.
But in 1908, something — probably a comet — exploded over the Siberia. It flattened 2,000 square kilometers (772 square miles) of forest in a largely uninhabited region.
Scientists assumed that the object was some 70 meters across. But new research indicates it might have been just 30 to 50 meters wide. And it still caused extensive damage. Objects of this size are thought to arrive every 300 years.
Because of the newfound importance of this size class, and relatively short interval at which they arrive, the authors of the report recommend that "surveys should attempt to detect as many 30- to 50-meter objects as possible."
Illustrating just how difficult asteroids are to detect, last week New Scientist reported that a 10-meter asteroid passed quite close to Earth — about one-third the distance between Earth and the moon. We noticed it only when it was three days out, far too late to head it off had it been on a collision course with Earth.
In October, an asteroid of similar size detonated over Indonesia, creating a fireball visible from the ground. Last July, an amateur Australian astronomer noticed that something had smashed into Jupiter. No one predicted it.
The good news: Our NEO detection abilities are improving. Last week, the recently launched Wide-Field Infrared Survey Explorer, which is scanning the heavens at infrared wavelengths, discovered its first near-Earth asteroid, a 1 km rock some 98 million miles away. It poses no threat to Earth — at least not on its current orbit.
Even if we saw an object headed our way with enough lead time, what could we do? The National Research Council report lists four approaches:
1. Get out of the way — evacuate of the soon-to-be-impacted area.
2. Use a "slow push" or "slow pull" exerted by spacecraft to nudge the asteroid off a collision course with Earth.
3. Fly something directly into the asteroid to change its path.
4. Detonating a nuclear device on or near the asteroid to either destroy it or move it off-course.
But for large meteors, such as the one that took out the dinosaurs, the authors acknowledge that there's currently no "feasible defense." Which doesn’t mean we can’t develop one.
The authors conclude their executive summary with an interesting discussion on the probability of catastrophes like this, and what — if anything — to do about it. The discussion echoes some arguments in the global warming debate — namely, that allocating resources now toward heading off potential catastrophes is, even if they're unlikely, a good investment if the catastrophes in question are costly enough.
[T]he committee points out a current estimate of the long-term average annual human fatality rate from impactors: slightly under 100. At first blush, one is inclined to dismiss this rate as trivial in the general scheme of things. However, one must also consider the extreme damage that could be inflicted by a single impact; this presents the classic problem of the conflict between extremely important and extremely rare. The committee considers work on this problem as insurance, with the premiums devoted wholly towards preventing the tragedy. The question then is: What is a reasonable expenditure on annual premiums?
The authors then outline three funding scenarios — $10 million, $50 million, and $250 million. The first option wouldn't be enough to achieve NASA's goals as currently state. The second option would, however. In the third scenario, NASA could achieve its goals and also provide for a space mission and real-life testing of NEO mitigation strategies.
Policymakers, the authors say, must decide which is best.