The risk of an asteroid rending civilization into bits is a favorite scenario in disaster movies, but it has been none too popular with the United States government. Eleven years ago, Congress tasked NASA with detecting, tracking, and classifying large asteroids and comets that pose a threat to Earth; these are generically termed near earth objects, or NEOs. Since then, save for a small grant, NASA has funded the project on its own. Now Congress has created new goals for the program and requested that they be achieved by 2020. The National Research Committee has put out an interim report on the NEO project, and it indicates that very little progress has been made since 2005, primarily due to a lack of funding.

Congress kicked off the NEO-tracking project in 1998, requiring that NASA's equipment be able to locate and identify at least 90 percent of all NEOs one kilometer in diameter or larger. Congress selected this size as the lower bound because it is the smallest size that might be globally catastrophic if it ran into Earth. To guarantee a catastrophe, an asteroid would have to be even larger, perhaps 1.5 to 2 kilometers. On impact, an asteroid of this size would create a fireball the size of a continent and a crater fifteen times the asteroid's diameter; if it hits the ocean, there would be an enormous tsunami.

Congress awarded NASA a $1.6 million grant in 1999 to put towards the NEO discovery program. Unfortunately, this was the only funding Congress gave to NASA to pursue this goal; nonetheless, NASA continued the project on its own, and has since successfully achieved the objective of a 90 percent track rate for 1km NEOs. The problem now, the NRC report asserts, is that we shouldn't be satisfied with this.

What NASA has accomplished so far will largely enable us to at least attempt to prevent any impacts that would ultimately cause the majority of humans that survive the initial blow to die of starvation. However, asteroids smaller than 1km in diameter are not sufficiently less disastrous than their larger counterparts that we can happily ignore them.

For example, the NRC report states that the body that caused the 1908 Tunguska explosion and destroyed 2,000 square kilometers of Siberian forest was only 30-40 meters in diameter. This realization is what led Congress to change its mind and decide that NASA should track even smaller asteroids. The new goal: track 90 percent of NEOs 140 meters or larger in diameter by 2020.

The NRC report primarily takes issue with the lack of action on this goal from anyone involved: Congress has not volunteered funding for their mandate, and NASA has not allotted any of their budget to it, either. The equipment currently in use to track NEOs can easily see the 1km monsters, but it's not sensitive enough to track the 140m asteroids. As a result, if a Tunguska-sized body were headed for Earth today, its arrival would probably be a complete surprise.

Of course, the Tunguska explosion is the only collision of this sort in recorded history, suggesting that threatening bodies that cross Earth's path are fortunately rare. Considering this, and the fact that the most disastrous varieties of asteroids are fairly well covered, danger is probably not imminent.

However, Congress is not doing its own deadline any favors by squaring off with NASA over funding. The committee that produced the interim report has been asked to focus in particular with evaluating whether the established NEO discovery goals should be modified. The report is decidedly in favor of tracking the smallest asteroids possible, given that even small NEOs have significant potential for destruction. But for the NEO program to move forward toward any goal, Congress will have to pay up.