Killer asteroids are hiding in plain sight. A new tool helps spot them.
By Kenneth Chang
Ed Lu wants to save Earth from killer asteroids.
Or at least, if there is a big space rock streaking our way, Lu, a former NASA astronaut with a doctorate in applied physics, wants to find it before it hits us — hopefully with years of advance warning and a chance for humanity to deflect it.
Late last month, B612 Foundation, a nonprofit group that Lu helped found, announced the discovery of more than 100 asteroids. (The foundation’s name is a nod to Antoine de Saint-Exupéry’s children’s book “The Little Prince”: B612 is the home asteroid of the main character.)
That by itself is unremarkable. New asteroids are reported all the time by sky-watchers around the world. That includes amateurs with backyard telescopes and robotic surveys systematically scanning the night skies.
What is remarkable is that B612 did not build a new telescope or even make new observations with existing telescopes. Instead, researchers financed by B612 applied cutting-edge computational might to years-old images — 412,000 of them in the digital archives at the National Optical-Infrared Astronomy Research Laboratory, or NOIRLab — to sift asteroids out of the 68 billion dots of cosmic light captured in the images.
“This is the modern way of doing astronomy,” Lu said.
The research adds to the “planetary defense” efforts undertaken by NASA and other organizations around the world.
Today, of the estimated 25,000 near-Earth asteroids at least 460 feet in diameter, only about 40% of them have been found. The other 60% — about 15,000 space rocks, each with the potential of unleashing the energy equivalent to hundreds of million of tons of TNT in a collision with Earth — remain undetected.
B612 collaborated with Joachim Moeyens, a graduate student at the University of Washington, and his doctoral adviser, Mario Juric, a professor of astronomy. They and colleagues at the university’s Institute for Data Intensive Research in Astrophysics and Cosmology developed an algorithm that is able to examine astronomical imagery not only to identify those points of light that might be asteroids, but also to figure out which dots of light in images taken on different nights are actually the same asteroid.
In essence, the researchers developed a way to discover what has already been seen but not noticed.
Typically, asteroids are discovered when the same part of the sky is photographed multiple times during the course of one night. A swath of the night sky contains a multitude of points of light. Distant stars and galaxies remain in the same arrangement. But objects that are much closer, within the solar system, move quickly, and their positions shift over the course of the night.
Astronomers call a series of observations of a single moving object during a single night a “tracklet.” A tracklet provides an indication of the object’s motion, pointing astronomers to where they might look for it on another night. They can also search older images for the same object.
Many astronomical observations that are not part of systematic asteroid searches inevitably record asteroids, but only at a single time and place, not the multiple observations needed to put together tracklets.
The NOIRLab images, for example, were mainly taken by the Victor M. Blanco 4-Meter Telescope in Chile as part of a survey of almost one-eighth of the night sky to map the distribution of galaxies in the universe.
The additional specks of light were ignored because they were not what the astronomers were studying. “They’re just random data in just random images of the sky,” Lu said.
But for Moeyens and Juric, a single point of light that is not a star or a galaxy is a starting point for their algorithm, which they named Tracklet-less Heliocentric Orbit Recovery, or THOR.
The motion of an asteroid is precisely dictated by the law of gravity. THOR constructs a test orbit that corresponds to the observed point of light, assuming a certain distance and velocity. It then calculates where the asteroid would be on subsequent and previous nights. If a point of light shows up there in the data, that could be the same asteroid. If the algorithm can link together five or six observations across a few weeks, that is a promising candidate for an asteroid discovery.
So far, the scientists have sifted through about one-eighth of the data of a single month, September 2013, from the NOIRLab archives. THOR churned out 1,354 possible asteroids. Many of them were already in the catalog of asteroids maintained by the International Astronomical Union’s Minor Planet Center. Some of them had been previously observed, but only during one night and the tracklet was not enough to confidently determine an orbit.
The Minor Planet Center has confirmed 104 objects as new discoveries so far. The NOIRLab archive contains seven years of data, suggesting that there are tens of thousands of asteroids waiting to be found.
NASA is accelerating its planetary defense efforts. Its asteroid telescope, NEO Surveyor, is in the preliminary design stage, aiming for launch in 2026.
And later this year, its Double Asteroid Redirection Test mission will slam a projectile into a small asteroid and measure how much that changes the asteroid’s trajectory. China’s national space agency is working on a similar mission.
For B612, instead of wrangling a telescope project costing almost a half-billion dollars, it can contribute with less expensive research endeavors such as THOR. Last week, it announced that it had received $1.3 million of gifts to finance further work on cloud-based computational tools for asteroid science. It also received a grant from Tito’s Handmade Vodka that will match up to $1 million from other donors.
B612 and Lu are now not just trying to save the world. “We’re the answer to a trivia question of how vodka is related to asteroids,” he said.