Astronomers at the University of Arizona are asking for the public’s help to scan through thousands of images of the night sky to search for undiscovered asteroids — some of which have the potential to collide with Earth.
Researchers conducting the Catalina Sky Survey, which is part of NASA’s search for near-Earth objects, have started an online project that allows anyone, including those with no experience, to examine telescopic images of the sky to spot undiscovered asteroids.
These flying rocks are leftover bits from the early solar system that weren’t incorporated into planets or moons, like ingredients left on the table after making a cake.
Most asteroids are in a belt between Mars and Jupiter, and can range in size from pebbles, to tens of metres to many kilometres in diameter. But gravitational interactions can throw them out of the asteroid belt into orbits that can cross the orbit of the Earth, posing a potentially serious threat if they hit our planet. Some astronomers have suggested this could be the source of the object that wiped out the non-avian dinosaurs 66 million years ago.
Fortunately, the big dinosaur killers are quite rare and relatively easy to spot at great distances. It’s the little ones we need to keep track of, because they are harder to spot, can show up without warning and still cause damage.
In 2013, a meteor only 20 metres across exploded in the upper atmosphere above the Russian town of Chelyabinsk, shattering windows and damaging buildings. As cities grow, they are becoming larger targets for these projectiles from space that can carry energy comparable to nuclear weapons.
Spotting new asteroids with the Catalina Survey involves up to five telescopes that take high-resolution images of a section of sky every few minutes. A computer program then compares the images to do a first pass to see if there are any moving light sources that could represent objects that have changed position. Stars trend to remain fixed in the sky, but asteroids move relatively quickly. In fact, the faster they move, the closer they are to us, and that is the group the astronomers are most interested in.
Unfortunately, the software is relatively non-discriminatory and will flag images that could just be twinkling stars or dust. Even a relatively untrained human is better at spotting objects and making judgments about them — that’s where the volunteers come in.
This new project is aimed at recruiting more humans to look at the flagged images for potential objects to decide if they look like asteroids. After enough citizen astronomers flag an object as relevant, it will be more closely examined by experts to determine their size, and orbit, and whether they’re ever likely to collide with Earth.
Through the Zooniverse, a public participation site, volunteers are given access to sets of four images to determine whether that object is an asteroid or a false detection.
More than 30,000 near-Earth asteroids have been identified, and about 1,400 are being monitored as having some (usually tiny) future risk of hitting Earth. Nearly half of these objects — around 14,400 — were discovered by the Catalina Sky Survey team.
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If one is heading our way, we do have the ability to alter its path. NASA’s DART mission demonstrated this in 2022, when it crashed a spacecraft into an asteroid and changed its orbit. A similar nudge could deflect an object heading towards us just enough so that it would miss the Earth.
But first we have to spot the potential threats, and see them early enough so we have time to mount a defence. The more eyes on the skies, the better.