Editing Asteroid impact avoidance (section)

=== Kinetic impact ===
{{See also|Ramming|Deep Impact (spacecraft)|Lightweight Exo-Atmospheric Projectile|Double Asteroid Redirection Test|Hayabusa2}}
[[File:HRIV Impact.gif|thumb|The 2005 ''[[Deep Impact (spacecraft)|Deep Impact]]'' collision with the {{convert|8|by|5|km|0|spell=in|adj=on|sp=us}} comet [[Tempel 1]]. The impact flash and resulting [[ejecta]] are clearly visible. The impactor delivered 19 [[gigajoule]]s (the equivalent of 4.8 [[ton]]s of [[Trinitrotoluene|TNT]]) upon impact.<ref>{{Cite web|url=https://www.nasa.gov/mission_pages/deepimpact/spacecraft/impactor.html|archiveurl=https://web.archive.org/web/20160623220100/http://www.nasa.gov/mission_pages/deepimpact/spacecraft/impactor.html|url-status=dead|title=NASA - Deep Impact's Impactor|archivedate=June 23, 2016|website=www.nasa.gov}}</ref> Impact created a crater estimated to be about 150 meters in diameter.<ref>{{cite web |title=In Depth - Deep Impact (EPOXI) |url=https://solarsystem.nasa.gov/missions/deep-impact-epoxi/in-depth/ |website=NASA Solar System Exploration |access-date=11 October 2022}}</ref> The comet "returned to preimpact conditions only 6 days after the event".<ref>{{cite journal | doi = 10.1086/499301 | bibcode=2006AJ....131.1130S | volume=131 | issue=2 | title=Photometry and Imaging Results for Comet 9P/Tempel 1 and Deep Impact: Gas Production Rates, Postimpact Light Curves, and Ejecta Plume Morphology | year=2006 | journal=The Astronomical Journal | pages=1130–1137 | last1 = Schleicher | first1 = David G. | last2 = Barnes | first2 = Kate L. | last3 = Baugh | first3 = Nicole F.| s2cid=123344560 | doi-access= }}</ref>]]

The impact of a massive object, such as a spacecraft or even another near-Earth object, is another possible solution to a pending NEO impact. An object with a high mass close to the Earth could be sent out into a collision course with the asteroid, knocking it off course.

When the asteroid is still far from the Earth, a means of deflecting the asteroid is to directly alter its [[momentum]] by colliding a spacecraft with the asteroid.
[[File:Dart impact replay.webm|thumb|upright=1.2|Compiled timelapse of DART's final 5.5 minutes until impact]]
A [[NASA]] analysis of deflection alternatives, conducted in 2007, stated:

{{blockquote|Non-nuclear kinetic impactors are the [[Deep Impact (spacecraft)|most mature approach]] and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body.<ref name="nasa" />}}

This deviation method, which has been implemented by [[Double Asteroid Redirection Test|DART]] and, for a completely different purpose (analysis of the structure and composition of a comet), by NASA's [[Deep Impact (spacecraft)|Deep Impact]] space probe, involves launching a spacecraft against the [[Near-Earth object|near Earth object]]. The speed of the asteroid is modified due to the [[law of conservation of momentum]]:

{{Center|1=M{{Subscript|1}} x V{{Subscript|1}} + M{{Subscript|2}} x V{{Subscript|2}} = (M{{Subscript|1}} + M{{Subscript|2}}) x V{{Subscript|3}}}}

with V{{Subscript|1}} velocity of the spacecraft, V{{Subscript|2}} velocity of the celestial body before impact, and V{{Subscript|3}} the velocity after impact. M{{Subscript|1}} and M{{Subscript|2}} respective mass of the spacecraft and of the celestial body. Velocities are [[Vector space|vectors]] here.

The European Union's NEOShield-2 Mission<ref>{{cite web|url=http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|title=Kinetic impactor -|date=2016-08-29|access-date=2016-11-17|archive-date=2022-03-19|archive-url=https://web.archive.org/web/20220319000029/http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|url-status=dead}}</ref> is also primarily studying the Kinetic Impactor mitigation method. The principle of the kinetic impactor mitigation method is that the NEO or Asteroid is deflected following an impact from an impactor spacecraft. The principle of momentum transfer is used, as the impactor crashes into the NEO at a very high velocity of {{cvt|10|km/s|km/h mph||}} or more. The momentum of the impactor is transferred to the NEO, causing a change in velocity and therefore making it deviate from its course slightly.<ref>{{cite web|url = http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|title = NEOShield Project|publisher = European Union Consortium|date = 17 November 2016|access-date = 17 November 2016|archive-date = 19 March 2022|archive-url = https://web.archive.org/web/20220319000029/http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|url-status = dead}}</ref>

As of mid-2021, the modified [[AIDA (mission)|AIDA mission]] has been approved. The NASA [[Double Asteroid Redirection Test]] (''DART'') kinetic impactor spacecraft was launched in November 2021. The goal was to impact [[Dimorphos]] (nicknamed ''Didymoon''), the {{convert|180|m|adj=on|sp=us|}} [[minor-planet moon]] of near-Earth asteroid [[65803 Didymos]]. The impact occurred in September 2022 when Didymos is relatively close to Earth, allowing Earth-based telescopes and planetary radar to observe the event. The result of the impact will be to change the orbital velocity and hence orbital period of Dimorphos, by a large enough amount that it can be measured from Earth. This will show for the first time that it is possible to change the orbit of a small {{convert|200|m|adj=on|sp=us|}} asteroid, around the size most likely to require active mitigation in the future. The launch and use of the [[Double Asteroid Redirection Test]] system in March 2023 showed the world that asteroids could be safely redirected without the use of nuclear means. The second part of the [[AIDA (mission)|AIDA]] mission{{ndash}}the ESA [[Hera (spacecraft)|HERA]] spacecraft{{ndash}}has been approved by ESA member states in October 2019. It would reach the Didymos system in 2026 and measure both the mass of Dimorphos and the precise effect of the impact on that body, allowing much better extrapolation of the [[AIDA (mission)|AIDA]] mission to other targets.<ref>{{Cite web |title=NASA - NSSDCA - Spacecraft - Details |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=HERA |access-date=2022-10-12 |website=nssdc.gsfc.nasa.gov}}</ref>