A spat over the search for killer asteroids
More than 14,000 known asteroids zip through Earth’s neighborhood. They will all miss Earth in the coming decades.
But hundreds of thousands more have not yet been discovered, and whether any of those are on course to slam into our planet, no one knows. So finding and tracking all the asteroids that could cross Earth’s path would allow officials to issue warnings and potentially provide time to deflect dangerous ones.
The community of scientists contemplating such doomsday possibilities is small and usually cordial — at least it was until Nathan P. Myhrvold barged in. Once the chief technologist at Microsoft, Myhrvold moved on to other endeavors like a six-volume, 2,438-page compendium of cooking knowledge that has been celebrated by chefs. (A sequel, about baking, is in the works.)
He has also become a statistics scold of scientists. His latest target is NASA, in a squabble over data from the Wide-field Infrared Survey Explorer spacecraft.
WISE, launched in 2009, snapped images of three-quarters of a billion stars, galaxies and other celestial objects, including the heat emissions of asteroids. An offshoot called Neowise used the heat data to calculate the size and reflectivity of 158,000 asteroids.
Myhrvold contends that the Neowise analysis is deeply flawed. “The bad news is it’s all basically wrong,” he said. “Unfortunately for a lot of it, it’s never going to be as accurate as they had hoped.”
He submitted his own analysis of the Neowise results to the journal Icarus.
Myhrvold is not arguing that NASA has overlooked dangers from the known asteroids. But he does question whether scientists know as much as they think they do.
He has also zeroed in on a proposed space-based telescope with a price tag of more than $500 million, the Near-Earth Object Camera, or Neocam, a project headed by some of the same scientists whose work he is second-guessing.
Most of the millions of asteroids are found between the orbits of Mars and Jupiter, but some dip closer to the sun. There is no doubt that some will hit Earth someday.
The bigger the asteroid, the greater the potential cataclysm. The reflectivity of the surface — what astronomers call albedo — tells how easily it can be detected.
“From the practical perspective of finding asteroids,” Myhrvold said, “it’s really important that we know the distribution of diameters and the distribution of albedos.”
According to NASA’s scientists, the estimates of asteroid diameters made by Neowise are often within 10 percent of the actual size. But Myhrvold says the uncertainties are much greater, more than 100 percent in many cases.
Space agency officials disagree. “He’s a very smart man,” said Lindley Johnson, who oversees NASA’s efforts to protect the planet from space rocks. “But that doesn’t make him an expert in everything.”
Other scientists say that Myhrvold’s criticisms have merit.
“I do think he’s performed a really very useful service,” said Alan W. Harris, a senior research scientist at the Space Science Institute, “to do the error analysis more carefully and alert people that you shouldn’t just take some of the data out of the WISE table and just assume they’re gospel.”
But even if Myhrvold is correct, Harris said the Neowise data “has good enough validity to be useful for most purposes.”
Myhrvold was drawn into asteroids research when the B612 Foundation, a nonprofit organization that advocates planetary defense efforts, asked him to contribute money for Sentinel, a privately financed $450-million, asteroid-finding spacecraft.
“What they didn’t know is that I had been interested in killer asteroids for a long time,” Myhrvold said. After all, an asteroid slamming into Earth is believed to have brought the age of dinosaurs to an end 66 million years ago.
But Myhrvold learned of several other efforts, including NASA’s Neocam, which would cost about $500 million (plus the rocket to launch it), and the Large Synoptic Survey Telescope, a ground-based observatory already under construction in Chile.
Each group offered computer simulations of how many unseen asteroids would be spotted, making different assumptions.
In a paper published in March in The Publications of the Astronomical Society of the Pacific, Myhrvold took a simpler approach to provide an apples-toapples comparison. He looked at the volume of space that each telescope could observe, then calculated what fraction of unseen asteroids would pass through that space.
“I thought it all looked quite reasonable,” said Steven R. Chesley, a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Nathan definitely brings a fresh approach.”
In writing the paper published in March, Myhrvold talked with people working on the different projects, including Amy Mainzer, the principal investigator for Neocam and Neowise.
Myhrvold said that Mainzer argued that a ground-based telescope could not detect asteroids within Earth’s orbit because they would be too close to the horizon.
That seemed strange to Myhrvold, because even amateurs can easily spot celestial objects far inside Earth’s orbit like Venus, 26 million miles closer to the sun than Earth.
Myhrvold said Mainzer responded that large telescopes were not designed to point that close to the ground. But the one in Chile is, he noted.
Chesley of NASA is coordinating a more detailed analysis of the telescope’s asteroid-finding prowess, with preliminary findings expected in late summer.
In recent presentations, NASA officials have portrayed Neocam more as a complement than a competitor. “It’s a team sport,” Johnson said. “There isn’t any one system that is going to provide us all the data we need.”
NASA declined to make Mainzer available for an interview. Responding to written questions, she said the Neowise team stood behind the findings and that the results had been validated by independent observations and other researchers.