On the morning of October 19, 2018 astronomers at the Catalina Sky Survey in Arizona detected and named asteroid 2018 UA. A short time later, traveling at 50,760 Km/hour 2018 UA passed at a distance of 7,300 – 15,350 kilometers. For perspective, television satellites orbit at more than 35,000 kilometers. 2018 UA became the 4th closest asteroid approach in recorded history.
Earth was never in danger, at 3-6 meters in diameter 2018 UA would disintegrate on contact with our atmosphere. At worst a meteoric fireball visible in the light of day might herald 2018 UA’s fiery demise. As it was, 90 minutes separated 2018 UA from initial discovery to near earth cosmic footnote. 90 minutes is worth pondering.
Asteroids are sneaky, cosmic debris ricochets at will. Without prediction, apology or reason, asteroids can appear with very little warning.
In 1998 NASA established NEO, the Near Earth Objects Observation program, administered by JPL ( NASA Jet Propulsion Laboratory). In 2016 NASA launched PDCO ( Planetary Defense Coordination Office ), consequently NEO inherited the moniker CNEOS, (Center For Near Earth Object Studies ) .From NASA Jet Propulsion Laboratory –
The first and most important step in assessing the impact risk of an asteroid or comet is to determine whether any given object’s orbit will cross Earth’s orbit — and then how close it will actually get to our planet. JPL was determining high-precision orbits for a few NEOs even before NASA launched its NEO Observations Program, and has since upgraded its orbit models to provide the most accurate assessment available for asteroid positions and orbits.
Observatories around the world take digital images of the sky to detect moving points of light (the asteroid or comet) over days, weeks, months (and even decades!), and then report the positions of these moving objects relative to the static background of stars to the Minor Planet Center. See “How a Speck of Light Becomes an Asteroid”.The CNEOS scientists then use all this observation data to more precisely calculate an NEO’s orbit and predict its motion forward in time for many years, looking for close approaches and potential impacts to the Earth, its Moon, and other planets.
A CNEOS system called “Sentry” searches ahead for all potential future Earth impact possibilities over the next hundred years — for every known NEO. Sentry’s impact monitoring runs continually using the latest CNEOS generated orbit models, and the results are stored online.In most cases so far, the probabilities of any potential impacts are extremely small, and in other cases, the objects themselves are so small — less than 20 meters in size, or nearly 66 feet — that they would almost certainly disintegrate even if they did enter Earth’s atmosphere.
“If Sentry finds potential impacts for an object, we add it to our online ‘impact risk’ table, and asteroid observers can then prioritize that object for further observation,” said Steve Chesley of JPL, a member of the CNEOS team who was the main developer of the Sentry system. “The more measurements made of the object’s position over time, the better we can predict its future path.”
“In most cases, the new measurements mean the object can be removed from the risk list because the uncertainties in the orbital path are reduced and the possibility of impact is ruled out,” Chesley said.
More recently, CNEOS also developed a system called Scout to provide more immediate and automatic trajectory analyses for the most recently discovered objects, even before independent observatories confirm their discovery. Operating around the clock, the Scout system not only notifies observers of the highest priority objects to observe at any given time, it also immediately alerts the Planetary Defense Coordination Office of any possible imminent impacts within the next few hours or days.A recent example is the Scout-predicted impact of the small asteroid 2018 LA over Botswana, Africa.
In the span of 90 minutes 2018 UA went from discovery to fourth closest asteroid approach in recorded history.