Asteroid hunters have become increasingly good at their job. The discipline, which took a back seat in the early days of astronomy, has really come into its own as of late. Once the general public, probably spurred on by popular 1990s movies like Deep Impact and Armageddon, realized the potentially existential threat they posed, support for finding all asteroids that could be planet killers skyrocketed. At this point, astronomers think that most planet-killing asteroids have been found and have worked their way down to much smaller but still devastating impactors. And now they’ve reached a new milestone with over 30,000 Near Earth Asteroids (NEAs) officially discovered.
That milestone results from years of steady work identifying and tracking those objects. Better equipment has helped with that task – over 15,000 have been discovered in the last ten years alone. Given that the first NEA was discovered in the 1800s, that is a pretty impressive pickup in pace.
A new crop of improved instruments helps with that. The Catalina Sky Survey (CSS) is the most prolific, having been responsible for approximately 47% of all NEOs discovered. It continues to find a few new asteroids every week, but even so, it has dramatically improved its capabilities in recent years. In 2005, it found 310 new asteroids, whereas, in 2019, it found 1067.
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With those sensing capabilities, the CSS has been even more effective at finding smaller asteroids. Scientists are pretty sure they’ve found all the large space rocks that fit the definition of an NEA – i.e., that its orbit takes it at least within 1.3 AU of the Sun. “Large,” in this case, is quantified as a few kilometers in diameter – enough to cause an extinction-level event if it were to hit Earth.
More recently, CSS and its fellow asteroid hunters have been concentrating on smaller rocks on the order of a few hundred meters in diameter. Being much smaller, these are also much harder to detect as they aren’t as bright in the night sky as their larger cousins. While these could still cause significant damage if they were to impact Earth, none appear to be on an immediate collision course – at least for the next 100 years.
However, there are over 1,400 that have a “non-zero” chance of hitting Earth in the future. A team of planetary defenders (and asteroid hunters) employed by ESA stress that there isn’t any immediate danger, and we will have plenty of time to summon up a mission like the recently successful DART to push any threatening asteroid out of the way well before it causes any issues.
But if you’re still interested in learning which floating balls of rock and ice are most dangerous, ESA maintains an Asteroid Risk List that keeps track of their orbits and the chances they will impact Earth. Hopefully, that won’t be useful for anything other than to keep track of potential sites for asteroid mining.
However, even with all its improving technology and continually growing list of potential targets, there is still a chance that the planetary defenders at ESA and elsewhere missed one. Or there might be a long-period metallic comet with no tail that could literally come out of the black directly on a collision course. The only way we can eliminate that possibility is by continually monitoring the sky and, when necessary, by taking action. This 30,000 NEA milestone is another successful step on that journey.
ESA – 30 000 near-Earth asteroids discovered and rising
ESA – NEO Risk List
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Screenshot from a video visualizing Gaia’s search for stars.
Credit – ESA