NASA's new planetary defense system is online

To date, nearly 28,000 near-Earth asteroids (NEAs) have been found by telescopes that continuously scan the night sky, adding new discoveries at a rate of around 3,000 per year. But as larger and more advanced telescopes accelerate research over the next few years, a rapid increase in discoveries is expected. In anticipation of this increase, NASA astronomers have developed a next-generation impact monitoring algorithm called Sentry-II to better assess the probabilities of NEA impact.

Popular culture often depicts asteroids as objects chaotic that whizzes haphazardly around our solar system, changing course unpredictably and threatening our planet without warning. This is not the reality. Asteroids are extremely predictable celestial bodies that obey the laws of physics and follow knowable orbital paths around the Sun.

But at times, these paths can get very close to the position of the Earth and, due to small uncertainties in the positions. of asteroids, a future impact on Earth cannot be completely ruled out. Then, astronomers use sophisticated impact monitoring software to automatically calculate the risk of impact.

Operated by NASA's Jet Propulsion Laboratory in Southern California, the Center for Near Earth Object Studies (CNEOS) calculates each known NEA orbit, to improve impact risk assessments, in support of NASA's Planetary Defense Coordination Office (PDCO). CNEOS monitored the impact risk posed by NEAs with software called Sentry, developed by JPL in 2002.

But with Sentry-II, NASA has a tool that can quickly calculate impact probabilities for all known NEAs, including some special cases not captured by the original Sentry. Sentry-II reports the objects of greatest risk in the CNEOS sentinel table.



By systematically calculating the probabilities of impact in this new way, researchers have made the impact monitoring system more robust , allowing NASA to confidently assess all potential impacts with probabilities down to a few chances in 10 million.

"The fact that Sentry could not automatically handle the Yarkovsky effect was a limitation," said Davide Farnocchia , a JPL engineer who also helped develop Sentry-II. “Whenever we came across a special case, such as the asteroids Apophis and Bennu or 1950 DA, we had to do complex and time-consuming manual analyzes. With Sentry-II, we don't have to do that anymore. ”

Another problem with the original Sentry algorithm was that it sometimes couldn't accurately predict the probability of impact of asteroids undergoing extremely close encounters with Earth. The motion of these NEAs is significantly deflected by our planet's gravity, and post-encounter orbital uncertainties can increase dramatically. In these cases, the old guard's calculations may fail, requiring manual intervention. Sentry-II does not have this limitation.

The new algorithm models thousands of random points not limited by hypotheses about how the region of uncertainty may evolve; select random points throughout the entire region of uncertainty. The Sentry-II algorithm then asks what are the possible orbits within the entire region of uncertainty that could hit the Earth.

In this way, the orbital determination calculations are not modeled by assumptions predetermined on which portions of the region of uncertainty could lead to a possible impact. This allows Sentry-II to focus on lower probability impact scenarios, some of which Sentry may have missed.