Editing Impact event (section)

===== Asteroid impact prediction =====
{{main|Asteroid impact prediction}}

[[File:2018 LA-orbit.png|thumb|250px|[[Orbit]] and positions of [[2018 LA]] and Earth, 30 days before impact. The diagram illustrates how orbit data can be used to predict impacts well in advance. Note that in this particular instance the asteroid's orbit was not known until a few hours before impact. The diagram was constructed afterwards for illustration.]]

In the late 20th and early 21st century scientists put in place measures to detect [[Near Earth object]]s, and predict the dates and times of [[asteroids]] impacting Earth, along with the locations at which they will impact. The [[International Astronomical Union]] [[Minor Planet Center]] (MPC) is the global clearing house for information on asteroid orbits. [[NASA]]'s [[Sentry (monitoring system)|Sentry System]] continually scans the MPC catalog of known asteroids, analyzing their orbits for any possible future impacts.<ref>{{YouTube|id=53Js-_vo3mo|title=How Does NASA Spot a Near-Earth Asteroid?}}</ref> Currently none are predicted (the single highest probability impact currently listed is ~7 m asteroid {{mpl|2010 RF|12}}, which is due to pass earth in September 2095 with only a 5% predicted chance of impacting).<ref>{{cite web|title=Sentry: Earth Impact Monitoring|url=https://cneos.jpl.nasa.gov/sentry/|website=Jet Propulsion Laboratory|publisher=NASA|access-date=25 August 2018}}</ref>

Currently prediction is mainly based on cataloging [[asteroids]] years before they are due to impact. This works well for larger asteroids (> 1 [[kilometre|km]] across) as they are easily seen from a long distance. Over 95% of them are already known and their [[orbit]]s have been measured, so any future impacts can be predicted long before they are on their final approach to Earth. Smaller objects are too faint to observe except when they come very close and so most cannot be observed before their final approach. Current mechanisms for detecting asteroids on final approach rely on wide-field ground based [[telescopes]], such as the ATLAS system. However, current telescopes only cover part of the Earth and even more importantly cannot detect asteroids on the day-side of the planet, which is why so few of the smaller asteroids that commonly impact Earth are detected during the few hours that they would be visible.<ref name="JPL-2017-SDT-Update">{{cite news
  |title      = Update to Determine the Feasibility of Enhancing the Search and Characterization of NEOs
  |work       = Near-Earth Object Science Definition Team Report 2017
  |publisher  = NASA
  |url        = https://www.nasa.gov/sites/default/files/atoms/files/2017_neo_sdt_final_e-version.pdf
  |access-date = 7 July 2018}}</ref>
So far only four impact events have been successfully predicted, all from innocuous 2–5 m diameter asteroids and detected a few hours in advance.

{{wide image|SmallAsteroidImpacts-Frequency-Bolide-20141114.jpg|500px|align-cap=center|Ground based telescopes can only detect objects approaching on the night-side of the planet, away from the [[Sun]]. Roughly half of impacts occur on the day-side of the planet.}}