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NASA installs a new and improved algorithm to better track near-Earth asteroids

Nearly 20 year-old software used to protect humanity gets an upgrade

NASA has upgraded its near-Earth asteroid monitoring algorithm to model hazardous space rocks more accurately after nearly two decades, it announced on Tuesday.

The new system, dubbed Sentry-II, is more powerful than its predecessor, Sentry. Astronomers working at the space agency's Center for Near Earth Object Studies can now automatically calculate thermal influences that nudge an asteroid’s orbit, potentially sending it hurtling towards our home planet.

The so-called Yarkovsky effect describes the subtle and gradual change of motion when asteroids are heated by the Sun’s light. When asteroids spin, one side of its surface exposed to the star gets heated. As it continues to rotate, the hot region enters shade and cools down. Infrared energy is radiated outwards; the photons carry momentum and impart a tiny thrust on the asteroid. Over long periods of time, these small kicks can change their paths and knock them out of their original orbit.

Although NASA’s old Sentry system could adjust orbital calculations for an asteroid by considering the gravitational effects of the Sun and planets as it whizzed around space, it couldn’t take other external factors into account like the Yarkovsky effect.

“The fact that Sentry couldn’t automatically handle the Yarkovsky effect was a limitation,” Davide Farnocchia, a navigation engineer at JPL who also helped develop Sentry-II, said. “Every time we came across a special case – like asteroids Apophis, Bennu, or 1950 DA – we had to do complex and time-consuming manual analyses. With Sentry-II, we don’t have to do that anymore.”

When a new object is discovered by astronomers, its coordinates are logged in a database. The data is then fed into NASA’s Sentry system to figure out the asteroid’s orbit, there is some uncertainty and the algorithm calculates a range of possible paths.

Scientists can work out if the space rock might come uncomfortably close to Earth in the future by tracing its possible orbits over time. The level of uncertainty, however, is based on assumptions.

Sentry-II employs new techniques, described in a paper published in the Astrophysical Journal earlier this month (here’s the free pre-print version [PDF]), to calculate impact properties. Instead of starting from assumptions, the new algorithm “models thousands of random points” within a large region to take uncertainty into account.

“Sentry-II’s algorithm then asks: What are the possible orbits within the entire region of uncertainty that could hit Earth?,” NASA explained. “This way, the orbital determination calculations aren’t shaped by predetermined assumptions about which portions of the uncertainty region might lead to a possible impact. This allows Sentry-II to zero in on more very low probability impact scenarios, some of which Sentry may have missed.”

NASA reckons it’ll find more of these edge cases as more asteroids are spotted using new telescopes, like the upcoming space-based NEO Surveyor and the Vera C. Rubin Observatory in Chile.

The original Sentry system developed in 2002 was capable of estimating the impact probability of asteroids over the next 100 years in under an hour. The new Sentry-II algorithm is able to do this too, Javier Roa Vicens, lead author of the aforementioned paper, told El Reg. “It’s pretty much the same for Sentry-II: it also analyzes close approaches in the next 100 years and runs in less than an hour, on average.”

Sentry-II, however, is more robust and can find low impact risk probabilities missed by the older Sentry system. The new algorithm is written in a mixture of low-level code in Fortran and Python, as well as Perl for its higher-level interfaces, we’re told. ®

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