Washington (CNN) -- The good news is that the chances an asteroid big enough to destroy a continent or all of civilization will hit Earth this year are only one in 20,000, a congressional panel learned Tuesday.
The bad news is the government needs to spend billions of dollars in coming years for new technology to prevent such a possible catastrophe, regardless of the low probability, experts told the House Science, Space and Technology Committee.
"The odds are very small, but the potential consequences of such an event are so large, it makes sense to take the risk seriously," contended John Holdren, who directs President Barack Obama's Office of Science and Technology Policy.
Asteroid 2012 DA14 made a record-close pass -- 17,100 miles -- by Earth on February 15. Most asteroids are made of rocks, but some are metal. They orbit mostly between Jupiter and Mars in the main asteroid belt. Scientists estimate there are tens of thousands of asteroids and when they get close to our planet, they are called near-Earth objects.
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Current efforts to detect and analyze possible space threats like the meteor that exploded over Russia last month, injuring more than 1,000 people and causing millions of dollars in damages, have made progress in identifying the threats, NASA Administrator Charles Bolden told the committee.
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He said scientists have identified 95% of asteroids more than a half-mile in diameter -- the kind that threaten human existence if they strike Earth, like the six-mile-wide one believed to have wiped out dinosaurs 65 million years ago -- and found none on a collision course with the planet.
However, the detection efforts have been less successful for smaller meteors still capable of causing major loss of life and damage, such as the one over Russia.
Only 10% of meteors more than 150 yards wide -- dubbed "potential city killers" by Holdren -- have been detected, meaning more than 10,000 are out there without our knowledge, he said.
If scientists detected a major asteroid headed for Earth now, it would take at least five years to develop an effective defense system to either alter its course or possibly destroy it, no matter how much money was spent, according to Holdren and Bolden.
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Government plans to bolster detection and mitigation capabilities include an infrared sensor that would orbit Venus, as well as a laser system or other method to deflect any threatening meteor away from Earth, they said.
"We really need to have space-borne assets," said Bolden of the infrared sensor that would cost more than $500 million.
Another NASA goal endorsed by Obama is to send an astronaut to an asteroid for the first time in history by 2025, a project that would cost $2 billion, he said.
Asked by panel members about the effects of forced spending cuts this year due to the inability of Congress to agree on fiscal issues, all the witnesses described heavy impacts.
"Just about my every working moment these days is consumed with this topic," Gen. William Shelton, commander of the U.S. Air Force Space Command, said about the spending cuts that took effect March 1. He added that "we are clearly less capable."
Bolden noted that NASA's budget for detecting Near Earth Objects has multiplied in recent years to reach more than $20 million in 2012. Now, he said, Congress needs to at least maintain such funding to prevent stagnation or, even worse, atrophy.
"This is really important and it has to be continuous," he said.
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This graphic shows Asteroid 2012 DA14's predicted path as it passes closest to Earth on February 15 at 2:24 p.m. ET. It will fly 17,200 miles (27,700 kilometers) above Earth's surface and inside the ring of weather and communications satellites. The asteroid is about 150 feet (45 meters) in diameter. It is heading toward Earth at 17,450 mph.
Another asteroid, Apophis, got a lot of attention from space scientists and the media when initial calculations indicated a small chance it could hit Earth in 2029 or 2036. NASA scientists have since ruled out an impact, but on April 13, 2029, Apophis, which is about the size of 3½ football fields, will make a close visit -- flying about 19,400 miles (31,300 kilometers) above Earth's surface. The images above were taken by the European Space Agency's Herschel Space Observatory in January 2013.
If you really want to know about asteroids, you need to see one up close. NASA did just that. A spacecraft called NEAR-Shoemaker, named in honor of planetary scientist Gene Shoemaker, was the first probe to touch down on an asteroid, landing on the asteroid Eros on February 12, 2001. This image was taken on February 14, 2000, just after the probe began orbiting Eros.
The first asteroid to be identified, 1 Ceres, was discovered January 1, 1801, by Giuseppe Piazzi in Palermo, Sicily. But is Ceres just another asteroid? Observations by NASA's Hubble Space Telescope show that Ceres has a lot in common with planets like Earth. It's almost round and it may have a lot of pure water ice beneath its surface. Ceres is about 606 by 565 miles (975 by 909 kilometers) in size and scientists say it may be more accurate to call it a mini-planet. NASA's Dawn spacecraft is on its way to Ceres to investigate. The spacecraft is 35 million miles (57 million kilometers) from Ceres and 179 million miles (288 million kilometers) from Earth. The photo on the left was taken by Keck Observatory, Mauna Kea, Hawaii. The image on the right was taken by the Hubble Space Telescope.
One big space rock got upgraded recently. This image of Vesta was taken by the Dawn spacecraft, which is on its way to Ceres. In 2012, scientists said data from the spacecraft show Vesta is more like a planet than an asteroid and so Vesta is now considered a protoplanet.
The three-mile long (4.8-kilometer) asteroid Toutatis flew about 4.3 million miles (6.9 million kilometers) from Earth on December 12, 2012. NASA scientists used radar images to make a short movie.
Asteroids have hit Earth many times. It's hard to get an exact count because erosion has wiped away much of the evidence. The mile-wide Meteor Crater in Arizona, seen above, was created by a small asteroid that hit about 50,000 years ago, NASA says. Other famous impact craters on Earth include Manicouagan in Quebec, Canada; Sudbury in Ontario, Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico.
NASA scientists say the impact of an asteroid or comet several hundred million years ago created the Aorounga crater in the Sahara Desert of northern Chad. The crater has a diameter of about 10.5 miles (17 kilometers). This image was taken by the Space Shuttle Endeavour in 1994.
In 1908 in Tunguska, Siberia, scientists theorize an asteroid flattened about 750 square miles (1,200 square kilometers) of forest in and around the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia.
What else is up there? Is anyone watching? NASA's Near-Earth Object Program is trying to track down all asteroids and comets that could threaten Earth. NASA says 9,672 near-Earth objects have been discovered as of February 5, 2013. Of these, 1,374 have been classified as Potentially Hazardous Asteroids, or objects that could one day threaten Earth.
One of the top asteroid-tracking scientists is Don Yeomans at the Jet Propulsion Laboratory, which is managed by the California Institute of Technology. Yeomans says every day, "Earth is pummeled by more than 100 tons of material that spewed off asteroids and comets." Fortunately, most of the asteroid trash is tiny and it burns up when it hits the atmosphere, creating meteors, or shooting stars. Yeomans says it's very rare for big chunks of space litter to hit Earth's surface. Those chunks are called meteorites.
Asteroids and comets are popular fodder for Earth-ending science fiction movies. Two of the biggest blockbusters came out in 1998: "Deep Impact" and "Armageddon." (Walt Disney Studios) Others include "Meteorites!" (1998), "Doomsday Rock" (1997), "Asteroid" (1997), "Meteor" (1979), and "A Fire in the Sky" (1978). Can you name others?
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