NASA is not doing enough to complete a mandated search for Earth-threatening asteroids and comets because the space agency is not receiving enough money for the problem, according to a National Research Council report.
In a report released Friday, scientists said Congress and the administration have not requested or appropriated funding to complete a survey mandated in the NASA Authorization Act of 2005.
Called the George E. Brown, Jr., Near-Earth Object Survey, the detection program was tasked with discovering 90 percent of Near-Earth Objects, or NEOs, larger than 140 meters, or 459 feet, by 2020. NEOs of that size would have regional or continental affects if they struck Earth.
“You have this conflict between having a very small probability of anything bad happening, versus a terrific impact if there is a bad event,” said Irwin Shapiro, chairman of the NEO committee from the Harvard-Smithsonian Center for Astrophysics.
Congress asked the National Research Council in 2008 to determine the best way to achieve the George Brown survey.
“If there were really a credible threat, money would flow like water, but it may be too late if we don’t do anything preparing ahead of time,” Shapiro told Spaceflight Now in a Friday interview.
NASA currently spends about $4 million per year searching for NEOs, but accomplishing the George Brown survey by the 2020 deadline is now unattainable.
“To complete the George Brown survey, you’re probably talking about something like $50 million a year, at least to complete it in a reasonable time scale,” said Michael A’Hearn, the research committee’s vice chairman and an astronomy professor at the University of Maryland, College Park.
Knowing where threatening objects are and developing viable mitigation strategies is like buying insurance on your house, Shapiro said.
With current technologies, it may take up to a century to find the bulk of the 140-meter class asteroids, according to scientists.
“There’s no way to do it by 2020 now because there’s been no funding for it since it was mandated,” A’Hearn said.
NASA is close to completing the Spaceguard project, another legislative mandate to find 90 percent of NEOs larger than 1 kilometer, or about 3,300 feet, in diameter. Such objects are large enough to have global affects if they impact Earth.
More than 6,700 NEOs have been discovered to date, including more than 800 objects greater than 1 kilometer in size, according to a NASA Web site.
A’Hearn said there are no known large objects that pose a credible threat to Earth within the next century, but there are plenty of smaller asteroids that still have not been detected.
“If we were to discover one that is about to hit us, we wouldn’t know what to do. In that sense, no one is doing enough,” A’Hearn said in an interview Friday.
The committee proposed two alternatives, one option that would relatively quickly detect NEOs larger than 140 meters, and another that limits costs but delays the survey.
“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 is the best approach,” the report said. “This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.”
A’Hearn said infrared telescopes tailored for asteroid and comet surveys have been proposed to be launched into Earth orbit or a solar orbit near Venus, but none have been selected by NASA.
“There’s nothing in the pipeline,” A’Hearn said.
The WISE telescope launched by NASA in December is capable of detecting new asteroids, but it won’t come close to fulfilling the Brown survey requirements, according to A’Hearn.
A cheaper option would be to utilize a large ground-based telescope such as the Large Survey Synoptic Telescope, a U.S.-led observatory to be built in Chile.
“It would detect all moving objects in the solar systme, as well as transient objects in outer space,” Shapiro said.
When the LSST facility begins observations around 2016, it could single-handedly complete the George Brown survey. But it would cost about $125 million to modify the telescope for NEO detections, according to Shapiro.
In its report, the panel analyzed hypothetical funding levels of $10 million, $50 million and $250 million annually.
While $10 million would be insufficient to significantly improve NEO observations, greater funding would permit NASA to accomplish the George Brown survey, albeit up to 10 years late.
$50 million per year is enough funding to mount an observation campaign with a ground-based telescope, and the $250 million funding level would allow NASA to develop a spacecraft to detect NEOs, or even pay for missions to demonstrate deflecting asteroids.
“Whether you try to do it in space quickly, or on the ground somewhat more slowly, is a question of political will,” A’Hearn said.
Shapiro’s team also recommended searching for objects as small as 30 meters, or about 100 feet. An object about that size was the culprit of the Tunguska event in 1908, which leveled a sizable chunk of the Siberian wilderness.
“As we get down to these smaller objects, late discoveries are going to become more common,” A’Hearn said.
Congress also requested the National Research Council study mitigation techniques that could be employed after an object is found heading for Earth.
Scientists say a major part of the problem is that asteroid impacts are not part of the U.S. defense framework.
Congress asked the White House science and technology department what federal agency would be in charge of handling such a catastrophe, but A’Hearn said the government may analyze Friday’s report before making a decision.
NASA, the military and homeland security agencies would likely play key roles in such an event, but international cooperation would be imperative.
The council’s researchers cited four types of mitigation, including civil defense, slow efforts to change an object’s orbit, a kinetic impactor, and a nuclear detonation.
Civil defense, encompassing evacuations and sheltering, would be the best method of dealing with a small object or an impact with little warning.
“If it’s small one, where civil defense is adequate, say evacuate the state of Louisiana, in principle a couple of months would be plenty,” A’Hearn said. “In practice, we had trouble evacuating New Orleans, let alone a larger area.”
A kinetic impactor was demonstrated during NASA’s Deep Impact mission to comet Tempel 1 in 2005. A’Hearn was the principal investigator for Deep Impact.
“The kinetic impact is relatively ready to deploy,” A’Hearn said. “That’s because we have done impacts before. We know we will need to improve the targeting compared to the Deep Impact mission to deal with much smaller objects.”
Deliberate propulsive techniques to slowly push an object off its trajectory toward Earth are impractical with current technologies. A nuclear explosion would be a last resort, although it would be the only way to guard against the most massive NEOs, the committee wrote.
It would take up to a decade, and maybe longer, to adequately design, build and launch a spacecraft to deflect an incoming asteroid or comet, according to A’Hearn.
“We don’t even know how big a thing we need to send out there to divert a given NEO,” A’Hearn said.
But scientists must first detect an object before employing any defense measures.
“Unexpected ones we might typically get with a year or two warning,”
A’Hearn said. “The smaller ones, where we have very incomplete knowledge, with our present facilities, we would find most of them only at the very last minute.”
In October 2008, astronomers for the first time discovered a space rock on course for Earth just 20 hours before impact.
Luckily, the asteroid was small, estimated to be between 7 to 16 feet across.
“That’s a one-day warning,” A’Hearn said. “We could not have done anything to prevent it, but it wasn’t big enough to worry about anyway.”
The small meteorite exploded in an airburst more than 20 miles above Sudan, causing no harm or damage.
“This is the only natural disaster that we have the opportunity and know how to guard against,” Shapiro said. “We can’t predict earthquakes, we don’t know how to predict hurricanes very accurately, but here’s something where we do know how to find out what’s going on and even prevent it, in most cases.”
Stephen Clark
Spaceflight Now
