In 2005, Congress assigned NASA the task of locating 90 percent of all near-Earth asteroids big enough to cause significant damage if they hit us by 2020.

Only about 10% of these asteroids have been spotted so far

On Monday, a new NASA audit concluded that the agency is nowhere near meeting this goal.

According to NASA inspector general Paul Martin, only about 10 percent of these asteroids have been spotted so far, despite a tenfold increase in funding since 2009 for the program responsible. For the audit, the agency confirmed it will not reach the 90 percent goal.

Last week, a relatively small asteroid passed extremely close to Earth — ten times as close as the moon, and as close as some of our communications satellites. We had about one week of warning between when astronomers spotted it and when it arrived.

If this had been a slightly larger asteroid headed for Earth, we'd still be dealing with the consequences. This report is yet another sign that we're still not taking the proper precautions to deal with the threat of asteroids.

The scale of the asteroid threat

When most people consider asteroid impacts, they think of the enormous, 10-kilometer wide one that hit Earth some 65 million years ago and likely led to the extinction of the dinosaurs.

The good news is that scientists have located more than 90 percent of the huge near-Earth asteroids capable of causing a global catastrophe — those a kilometer wide or larger. None of them, thankfully, are on track to hit us.

But the bad news is that mid-sized asteroids (those that are a few hundred meters wide) hit Earth much more regularly, can also cause significant damage, and we've still only spotted a small percentage of them. Specifically, NASA is tasked with locating 90 percent of those larger than 140 meters wide.

The goal is 90 percent, not 100 percent, partly because the baseline total is an estimate to begin with — scientists can't know how many asteroids they don't know about, so they have to calculate how many do exist based on their knowledge about the general distribution of asteroids in the solar system. Additionally, as asteroids are spotted, locating the final ten percent gets harder and harder as easier-to-see ones are eliminated — so 90 percent is a reasonable short-term start to mapping all potentially dangerous objects.

Regardless, the new report says NASA has only identified an estimated ten percent of them. To get an idea of how much damage a mid-sized asteroid might cause, consider the Tunguska event: a 30 to 60 meter-wide asteroid that exploded in a remote corner of Siberia in 1908.

When this occurred, this modest asteroid discharged an amount of energy one thousand times greater than the atomic bomb dropped on Hiroshima, scientists estimate. It knocked down some 80 million trees over a roughly 830 square mile area.

In human terms, impacts of this magnitude are relatively rare: they're estimated to occur every few centuries. But this still means that, given enough time, they will occur. And smaller impacts that also cause damage — like the 18 meter-wide asteroid that blew up over Chelyabinsk, Russia last year, injuring about 1,000 people due to broken windows — are even more common.

If we want to stick around for thousands of years as a species, investing more in asteroid detection and deflection programs is a relatively cheap insurance policy that will inevitably save lives.

How we could defend ourselves from asteroids

The first step to protect ourselves from asteroids is seeing them, and to an extent, Congress has recognized the importance of this goal. The Near-Earth Object Program, charged with meeting the 90 percent goal, has seen its funding increase from $4 million to $40 million since 2009.

The new report blames a lack of coordination and structure, not funding, for the failure to meet the goal, and recommends a reorganization of the program, with better oversight and tracking of grants to outside astronomers and telescopes.

However, there's also a broader hardware problem: all of the telescopes currently used to spot asteroids are on Earth, but the best way to see smaller ones is to use telescopes in space, because they don't have to deal with interference from the atmosphere and the sun's glare.

NASA has proposed launching one of these, called NEOCam, and a private organization called the B612 Foundation is currently raising $450 million for a complementary mission, called Sentinel, that would survey a different area of the sky.

If both these missions happen, they'd dramatically increase our ability to spot mid-sized asteroids that pose a threat and give us enough time to actually do something. But the NASA mission is still just a proposal — one that is reportedly short on money — and the B612 mission is also short of its fundraising goal.

If we did spot an asteroid heading our way, we don't currently have any proven means of stopping it. The simplest way would probably be sending a craft crashing into the asteroid, nudging it off its path enough so that it'd miss Earth. The UN has proposed designing and testing a network of small probes that would be capable of doing so, but it's still waiting on the necessary funding from various national space agencies, with an estimated price tag of about $2.5 billion.

That might sound like a lot. But the cost of doing nothing could be infinitely larger. Not long ago, the B612 Foundation produced this map: what it would look like if the 1908 Tunguska asteroid landed squarely in Washington, DC.

Odds are, an asteroid of this size will never land in Washington, DC. But when thinking about this issue, the important thing to remember is that, given enough time, it will happen again somewhere on the planet.

Asteroid impacts are the rare natural disasters that we can plan for and prevent, if we commit the necessary time and resources. If we fail to do so and suffer the consequences, we'll only have ourselves to blame.

Further reading: What are your odds of being hit by an asteroid?

Correction: This article previously referred to the Tunguska asteroid hitting the ground, instead of vaporizing in the atmosphere.