The program used by NASA's Jet Propulsion Laboratory (JPL) to assess potentially hazardous asteroids was recently updated to account for the effect of sunlight on orbits, among other improvements.

Despite decades of rigorous investigation, there are no imminent known space rock risks to Earth, astronomers continue to examine the heavens just in case. Sentry-II, a new impact monitoring algorithm, replaces software that has been in use for 20 years.

The newer Sentry-II, like its predecessor Sentry, will scan a table of potentially hazardous asteroids with known orbits generated by JPL's Center for Near Earth Object Studies.

Sentry-II will continue to calculate for at least the next decade, notifying the objects with the most dangerous orbits to Earth. (Another system called Scout evaluates asteroids whose orbits are only partially known.)

However, Sentry-II features a significant improvement that will improve the accuracy of its assessments: the Yarkovsky effect will be taken into account.

When sunlight is absorbed by the asteroid's surface and re-emitted as heat, the Yarkovsky effect occurs. This heat release has a modest but profound effect on an asteroid's route through space — and could affect the asteroid's chances of colliding with Earth.

The Yarkovsky effect has been known by astronomers for decades, but it was only lately that computer tools developed powerful enough to handle evaluating it on big datasets. According to JPL, Sentry-II will allow the agency to assess probable consequences with probability as low as a few chances in a million.

"The fact that Sentry couldn't automatically handle the Yarkovsky effect was a limitation," Davide Farnocchia, a JPL navigation engineer who also helped develop Sentry-II, said in a statement.

Because the initial Sentry system lacked Yarkovsky calculations, astrophysicists had to perform manual assessments every time they came across a "special case" asteroid, according to Farnocchia. One of the more well-known cases was asteroid Apophis, which required manual assessment for the Yarkovsky effect in order to determine the likelihood of an asteroid collision in 2068. Fortunately, NASA found last year that Apophis' passage in 2068 will be harmless.

The earlier method also had a flaw in that it couldn't always forecast the likelihood of asteroids swinging dangerously near to Earth colliding. According to NASA, Sentry-II provides for a more rigorous set of computations that takes into consideration the major impact of Earth's gravity in such situations.

Sentry-II also makes less assumptions about which orbits are the most likely for an asteroid to take, allowing the program to uncover low-probability impact scenarios that its predecessor could have missed.

According to NASA, Sentry-II will come into its own as larger and more capable survey telescopes become available during the following decade. Near-Earth asteroids number almost 28,000, and observatories are discovering new ones at a pace of roughly 3,000 per year, according to NASA. As the decade progresses, the rate of discovery will pick up.

Among the new observatories will be the Near-Earth Object (NEO) Surveyor mission, which is set to launch in 2026 and will be the first dedicated spacecraft to look for asteroids. Within a decade of its launch, NEO Surveyor is projected to find 90% of near-Earth asteroids with a diameter of 460 feet (140 meters).

The Vera C. Rubin Observatory, based in Chile, is another widely anticipated asteroid-hunting observatory. Rubin, formerly known as the Large Synoptic Survey Telescope, is set to launch in July 2023. Rubin was financed by the National Science Foundation of the United States to look for possibly hazardous asteroids by scanning at the same area of the sky hourly and looking for objects that changed location.

On December 1, 2021, a research outlining Sentry-II was published in the Astronomical Journal.