with the mission NASA’s DART recently managed to deflect an asteroid From its course, you might think that our planet is tidy when it comes to defense against incoming asteroids. But there are plenty of asteroids out there, and searching for potentially dangerous asteroids is ongoing work.
According to European Space Agency (ESA), there is now more than 30,000 known near-Earth asteroids in our solar system. A near-Earth asteroid is defined as one that approaches Earth at some point in its orbit, as many asteroids have highly elliptical orbits that bring them closer to the sun at some times than others. Astronomers use a measurement called the Astronomical Unit (AU), which is the distance between the Sun and Earth, and near-Earth asteroids are those within 1.3 AU of the Sun.
Not all near-Earth asteroids are a threat to the planet, as many are small enough to burn up in Earth’s atmosphere, while others travel in a way that doesn’t intersect with Earth’s orbit. If an asteroid is larger than 460 feet in diameter and has crossed Earth’s orbit, it is classified as a potentially hazardous object and will be monitored by astronomers.
But to decide which asteroids are potentially dangerous, they must first be identified, and that’s no easy task. Tools like ESA’s Gaia, a space observatory tasked with mapping all the stars in the Milky Way, can help by providing information about background stars seen when looking for asteroids.
“Thanks to Gaia, we know more about the stars in the galaxy that act as the backdrop for asteroid observations,” explained Tineke Roegiers, community support for the Gaia mission, in a release. “The positions of the asteroids are obtained against these background stars, so the better one knows where the stars are, the more precisely the orbits of the asteroids can be calculated.”
Once an asteroid has been detected, it needs to be observed several times to determine its orbit and see if it is approaching Earth. “Of course, any asteroid discovered near Earth qualifies as a near-Earth asteroid, but many are far from home,” said Marco Micheli, an astronomer at ESA’s Near-Earth Object Coordination Centre. “New objects are observed over time, their movements are studied and, with just a handful of data points from different nights, their future positions can be predicted. Depending on the number and quality of observations, this may extend decades, even hundreds of years into the future.”
If you feel like you’re hearing more about dangerous asteroids today than you used to, it may seem like the threat from the skies is growing, but in fact, we’ve gotten a lot better at detecting them.
“The good news is that more than half of the near-Earth asteroids known today were discovered in the last six years, showing how much our view of asteroids is improving,” said Richard Moissl, head of planetary defense at the ESA. “As this new milestone of 30,000 detections shows, and as new telescopes and detection methods are built, it is only a matter of time until we have found them all.”