Sentry (monitoring system)

Asteroid 2020 VV risk corridor for the obsolete virtual impactor of 12 October 2033.

Sentry is an automated impact prediction system started in 2002 and operated by the Center for Near Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ years.[1] Whenever a potential impact is detected, it will be analyzed and the results immediately published by CNEOS.[1] However, alerts do not imply certainty about future impacts, as the small amounts of optical data that can trigger an alert are not enough to conclusively identify an impact years in the future.[2] In contrast, eliminating an entry on the risk page is a negative prediction (a prediction of where it will not be).[2]

Scientists warn against worrying about the possibility of impact with an object based on only a few weeks of optical data that show a possible Earth encounter years from now.[2] Sometimes, it cannot even be said for certain what side of the Sun such an object will be at the time of the listed virtual impactor date.[2] For example, even though 2005 ED224 had a 1-in-500,000 chance of impacting Earth on 11 March 2023, its most likely position at that date was farther away than the Sun.[3] Most objects in the Sentry Risk Table have an observation arc of less than 14 days, making their positions highly uncertain, and have not been observed for years.

There are 1620 near-Earth asteroids listed in the risk table and 37,736 virtual impact dates, so for each asteroid in the risk table, there is an average of about 23 virtual impact dates. Only about 19 objects in the table are large enough, with a diameter greater than about 140 meters, to be considered potentially hazardous objects. The average size of an object on the default page of Sentry is 120 meters, with an average impact probability of about 1 in 500. More eccentric orbits (such as 2015 RD36) that extend to nearly the orbit of Jupiter can make atmospheric entry at velocities of ~40 km/s (25 mi/s).[4]

  1. ^ a b Cite error: The named reference risk-table was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Giorgini was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference NEODyS2023 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference velocity was invoked but never defined (see the help page).