More than 1,000 people were injured last February in Chelyabinsk, Russia, when a meteor exploded over the city. The collision shattered windows and pelted startled residents with shards of glass and debris. In the aftermath, the world was transfixed by extraordinary videos of the huge fireball as it streaked across the sky. Many wondered, why on earth did no one see it coming?
"The odds of asteroid impacts are much higher than people realize," said Ed Lu, a former astronaut and chief executive officer of the B612 Foundation, which searches for asteroids that could potentially hit the Earth and cause human devastation. He said that there is a 30 percent chance of a city-destroying asteroid hitting the Earth in the next 100 years.
The primary source of meteors like the one that exploded over Russia is the asteroid belt between the orbits of Jupiter and Mars. The gravitational pull of giant Jupiter causes space debris to collide repeatedly, breaking into smaller and smaller fragments that became asteroids.
Jupiter interacts with these asteroids gravitationally, periodically throwing them out of their orbit and sending them further out into the reaches of the solar system. Or they can be tossed inward, toward the sun and Earth. These projectiles are the asteroids that pose a threat to Earth.
It's only recently that scientists even knew the scope of the threat posed by asteroids. "Fifty years ago, scientists, when they looked at the moon, they thought those craters were volcanic," said James Green, director of planetary science at NASA. Now, common knowledge holds that most of the craters on the moon were caused by asteroids. If they can hit the moon, they can hit the Earth, too.
But how will we know where the asteroids are in space? That's a question that has plagued scientists for a generation. Computer models were able to give estimates of how many asteroids were out there and with what frequency they were likely to hit the Earth. But simulations can't always tell us where actual asteroids are, nor when they will show up. Unlike stars or planets, asteroids are incredibly difficult to see-most look like dark lumps of rock or metal set against the shadowy backdrop of space.
In 1998, NASA began searching for potentially dangerous "near-Earth objects" such as asteroids and comets. The agency identified more than 90 percent of objects that are larger than one kilometer, and at least 90 percent of debris that spans more than 140 meters. Luckily, the trajectories of those asteroids aren't due to menace Earth for another 200 years.
The hunt is now on for smaller asteroids that can still cause immense amounts of damage. So far, scientists have found only a fraction of the city-destroying asteroids that are larger than 40 meters. There are estimated to be about 1 million of them in our area of the solar system.
One of those caused the Tunguska event in 1908. An asteroid approximately 37 meters in diameter exploded over the Siberian Wilderness, leveling more than 1,000 square miles of forest, an area larger than Washington, D.C., or New York. The recent Chelyabinsk meteor, by comparison, was only 17 meters in diameter and still caused considerable damage.
The likelihood of one of these city-killing asteroids actually hitting a city is low (most of the Earth is covered by oceans, not major metropolitan areas) but the effects could be devastating regardless. If an asteroid of that size did hit the ocean, it would certainly have the potential to cause a tsunami, but scientists are still trying to create accurate models for such an event.
To try to prevent such an incident, the nonprofit B612 Foundation is currently raising $450 million to send the Sentinel Space Telescope to orbit. Designed to search for asteroids, the telescope will be positioned in a way that mirrors Venus' orbit. The launch is planned for 2017-18.
The Sentinel is an infrared telescope that will search for heat signatures of asteroids, instead of relying on the faint reflections of sunlight cast off an asteroid's surface. Once in place, the telescope should be capable of locating nearly all of the million or so asteroids within range of Earth. By mapping their trajectories, scientists will be able to figure out which asteroids are capable of doing damage to the Earth.
"We're going to have far and away the most capable telescope in the world, and that's because it has been optimized for finding asteroids," Lu said.
Lu compares the need for these asteroid-detecting programs to the need for hurricane preparedness in cities like New Orleans.
City leaders and the Army Corps of Engineers once claimed that it was unnecessary to fix levees for 100-year floods. Then Hurricane Katrina struck.
In the same way, we need to prepare now for an asteroid event. "A hurricane is really child's play compared to an asteroid impact," Lu said. "You can't just hope for the best every year."
In August, NASA announced plans to reactivate the Wide-field Infrared Survey Explorer and take up the hunt for asteroids. While not as specialized as the proposed Sentinel, the WISE telescope has already had asteroid-hunting success as part of a project called NEOWISE. The telescope was originally built to create a map of the night sky but has since been tasked with finding near-Earth objects. The NEOWISE mission ended in 2011. In the next mission, NASA hopes the telescope will locate 150 more near-Earth objects.
NASA also announced the Asteroid Grand Challenge. The agency hopes this program will be an interdisciplinary venture that brings together private businesses, amateur astronomers, space agencies and universities around the world to tackle the threat of asteroids.
"This is one of the only natural disasters that we have the ability to solve. We have the ability to prove that we are smarter than the dinosaurs," said Jason Kessler of NASA's Office of the Chief Technologist.
Kessler hopes to inspire people around the world by merging two topics that are almost universally beloved in science classrooms: dinosaurs and space.
"This is a marrying of the two. We can prove that we are smarter than the dinosaurs, and take our fate into our own hands," Kessler said. "They (the dinosaurs) didn't have the technology to defend themselves from planetary threats of this nature." j
NASA's ASTEROID RETRIEVAL MISSION
The NASA plan to lasso an asteroid might seem to be a punchline to a space cowboy joke, but the people at work on the program are serious about it.
"The president has set an objective that Mars is our ultimate destination, and asteroids are along that path," said James Green, NASA's director of planetary science.
Instead of hunting one down in the asteroid belt, the plan would be to find an asteroid in near-Earth orbit, target it and bring it between the Earth and the moon. It would be located and harnessed initially by an unmanned spacecraft. Once securely in place between the Earth and the moon, astronauts would be sent up to visit the asteroid, taking samples and bringing them back to Earth. The exercise might seem frivolous, but the astronauts would be practicing with technologies and developing skills essential to any future Mars missions, when explorers would have to rely on resources gathered from asteroids or the surface of Mars.
Budget decisions made by Congress this summer have stymied work on NASA's Asteroid Retrieval Mission.
The House Appropriations committee, concerned about the feasibility and cost of such a mission, called the proposed mission "premature" and refused to include any budget increases associated with the mission. They recommended that NASA "complete further concept studies, pursue the support of Congress through the authorization process and line up support from potential international partners before seeking new resources to carry out the mission."
This article is excerpted from USA TODAY's special publication NASA's Future in Space, available on newsstands or atnasa.usatoday.com.
Copyright 2013 USATODAY.com
