Editing Asteroid impact avoidance (section)

{{Short description|Methods to prevent destructive asteroid hits}}
{{Redirect|Planetary defense|defending against alien invasion in fiction|Alien invasion}}
{{Distinguish|Planetary protection}}
{{Further|Asteroid impact prediction}}
[[File:DART-impact-SAAO-Lesedi-Mookodi.gif|thumb|Kinetic impactors such as the one used by the [[Double Asteroid Redirection Test]] – its impact with the [[Minor-planet moon|asteroid moon]] [[Dimorphos]] photographed above – are one of many methods designed to alter the trajectory of an asteroid to prevent its potential collision with Earth.]]
[[File:Tunguska Ereignis-1.jpg|thumb|upright=1.4|Damage caused by the [[Tunguska event]]. The object was {{convert|50|-|80|m|ft|sp=us}} across and exploded {{convert|6|-|10|km|mi|abbr=on}} above the surface; its explosion flattened 80 million trees and shattered windows hundreds of kilometers away.]]

'''Asteroid impact avoidance''' encompasses the methods by which [[near-Earth object]]s (NEO) on a potential collision course with Earth could be diverted, preventing destructive [[impact event]]s. An impact by a sufficiently large [[asteroid]] or other NEOs would cause, depending on its impact location, massive [[tsunamis]] or multiple [[firestorm]]s, and an [[impact winter]] caused by the sunlight-blocking effect of large quantities of pulverized rock dust and other debris placed into the [[stratosphere]]. A collision 66 million years ago between the Earth and an object approximately {{convert|10|km|mi|0|abbr=off|sp=us}} wide is thought to have produced the [[Chicxulub crater]] and triggered the [[Cretaceous–Paleogene extinction event]] that is understood by the [[scientific community]] to have caused the extinction of all non-avian dinosaurs.

While the chances of a major collision are low in the near term, it is a near-[[Law of large numbers|certainty]] that one will happen eventually unless defensive measures are taken. Astronomical events—such as the [[Comet Shoemaker-Levy 9|Shoemaker-Levy 9 impacts on Jupiter]] and the [[Chelyabinsk meteor|2013 Chelyabinsk meteor]], along with the growing number of near-Earth objects discovered and catalogued on the [[Sentry Risk Table]]—have drawn renewed attention to such threats.{{cn|date=March 2025}} The popularity of the 2021 movie ''[[Don't Look Up]]'' helped to raise awareness of the possibility of avoiding [[Near Earth Object|NEOs]].<ref>{{Cite web|last=Powell|first=Corey S.|title=How prepared is Earth for an asteroid collision?|url=https://astronomy.com/news/2021/12/how-prepared-is-earth-for-an-asteroid-collision|url-status=live|access-date=2022-01-12|website=Astronomy |date=December 20, 2021 |language=en|archive-url=https://web.archive.org/web/20211220180825/https://astronomy.com/news/2021/12/how-prepared-is-earth-for-an-asteroid-collision |archive-date=2021-12-20 }}</ref> Awareness of the threat has grown rapidly during the past few decades, but much more needs to be accomplished before the human population can feel adequately protected from a potentially catastrophic asteroid impact.<ref>{{cite web |title=Planetary Defense Roadmap|url=https://www.cosmos.esa.int/documents/336356/336472/SMPAG-RP-001_4_0_Roadmap_2023-03-02.pdf/7a95c347-f749-1615-2b5f-5a89ef57f242?t=1692603843886|access-date=10 April 2025 }}</ref>

In 2016, a [[NASA]] scientist warned that the Earth is unprepared for such an event.<ref>{{cite news |url=https://www.theguardian.com/science/2016/dec/13/space-asteroid-comet-nasa-rocket |title=Earth woefully unprepared for surprise comet or asteroid, Nasa scientist warns |work=[[The Guardian]] |first=Alan |last=Yuhas |date=13 December 2016}}</ref> In April 2018, the [[B612 Foundation]] reported "It's 100 percent certain we'll be hit by a devastating asteroid, but we're not 100 percent sure when."<ref name="INQ-20180428">{{cite news |last=Homer |first=Aaron |title=Earth Will Be Hit By An Asteroid With 100 Percent Certainty, Says Space-Watching Group B612 |url=https://www.inquisitr.com/4881237/earth-will-be-hit-by-an-asteroid-with-100-percent-certainty-says-space-watching-group-b612/ |date=28 April 2018 |work=[[Inquisitr]] |access-date=28 April 2018 |archive-date=24 January 2020 |archive-url=https://web.archive.org/web/20200124092654/https://www.inquisitr.com/4881237/earth-will-be-hit-by-an-asteroid-with-100-percent-certainty-says-space-watching-group-b612/ |url-status=dead }}</ref> Also in 2018, [[physicist]] [[Stephen Hawking]], in his final book, ''[[Brief Answers to the Big Questions (book)|Brief Answers to the Big Questions]]'', considered an asteroid collision to be the biggest threat to the planet.<ref name="WP-20181015">{{cite news |last=Stanley-Becker |first=Isaac |title=Stephen Hawking feared race of 'superhumans' able to manipulate their own DNA |url=https://www.washingtonpost.com/news/morning-mix/wp/2018/10/15/stephen-hawking-feared-race-of-superhumans-able-to-manipulate-their-own-dna/ |date=15 October 2018 |newspaper=[[The Washington Post]] |access-date=15 October 2018 }}</ref><ref name="QZ-20181014">{{cite web |last=Haldevang |first=Max de |title=Stephen Hawking left us bold predictions on AI, superhumans, and aliens |url=https://qz.com/1423685/stephen-hawking-says-superhumans-will-take-over-ai-is-a-threat-and-humans-will-conquer-space/ |date=14 October 2018 |work=[[Quartz (publication)|Quartz]] |access-date=15 October 2018 }}</ref> 

Several ways of avoiding an asteroid impact have been described.<ref name="SPC-20190502">{{cite news |last=Wall |first=Mike |title=A Killer Asteroid Is Coming — We Don't Know When (So Let's Be Ready), Bill Nye Says  |url=https://www.space.com/killer-asteroids-warning-bill-nye.html |date=2 May 2019|work=[[Space.com]] |access-date=2 May 2019 }}</ref> There are two primary ways: to modify the trajectory of the object so that it does not collide with the Earth, or to modify the object by breaking it up so that the resulting fragments do not collide with the Earth or their
smaller size reduces the subsequent hazard posed to the Earth.<ref>{{cite web |title=Space Mission Planning Advisory Group Work Plan|url=https://www.cosmos.esa.int/documents/336356/336472/SMPAG-PL-002_2_0_Workplan_2019_09-01+%283%29.pdf/a117c9aa-27c1-788c-7d30-513fb7c06367?t=1590414041069|access-date=10 April 2025 }}</ref>

Nonetheless, in March 2019, scientists reported that asteroids may be much more difficult to destroy than thought earlier.<ref name="PHYS-20190304">{{cite news |author=Johns Hopkins University
 |title=Asteroids are stronger, harder to destroy than previously thought |url=https://phys.org/news/2019-03-asteroids-stronger-harder-previously-thought.html
 |date=4 March 2019 |work=[[Phys.org]] |access-date=4 March 2019 |author-link=Johns Hopkins University }}</ref><ref name="ICRS-20190315">{{cite journal |last1=El Mir |first1=Charles |last2=Ramesh |first2=KT |last3=Richardson |first3=Derek C. |title=A new hybrid framework for simulating hypervelocity asteroid impacts and gravitational reaccumulation |date=15 March 2019 |journal=[[Icarus (journal)|Icarus]] |volume=321 |pages=1013–1025 |doi=10.1016/j.icarus.2018.12.032 |bibcode=2019Icar..321.1013E |s2cid=127119234 }}</ref> An asteroid may reassemble itself due to gravity after being disrupted.<ref name="NYT-20190308">{{cite news |last=Andrews |first=Robin George |title=If We Blow Up an Asteroid, It Might Put Itself Back Together{{Snd}} Despite what Hollywood tells us, stopping an asteroid from creating an extinction-level event by blowing it up may not work. |url=https://www.nytimes.com/2019/03/08/science/asteroids-nuclear-weapons.html |date=8 March 2019 |work=[[The New York Times]] |access-date=9 March 2019 }}</ref> In May 2021, NASA astronomers reported that 5 to 10 years of preparation may be needed to avoid a [[Sentry (monitoring system)|virtual impactor]] based on a simulated exercise conducted by the 2021 Planetary Defense Conference.<ref name="BUS-20210512">{{cite news |last1=McFall-Johnsen |first1=Morgan |last2=Woodward |first2=Aylin |title=A NASA simulation revealed that 6 months' warning isn't enough to stop an asteroid from hitting Earth. We'd need 5 to 10 years.|url=https://www.businessinsider.com/nasa-asteroid-simulation-reveals-need-years-of-warning-2021-5 |date=12 May 2021 |work=[[Business Insider]] |accessdate=14 May 2021 }}</ref><ref name="SPC-20210501">{{cite news |last=Bartels |first=Meghan |title=How did you spend your week? NASA pretended to crash an asteroid into Earth. |url=https://www.space.com/planetary-defense-asteroid-impact-scenario-exercise-2021 |date=1 May 2021 |work=[[Space.com]] |accessdate=14 May 2021 }}</ref><ref name="NASA-20210430">{{cite news |last1=Chodas |first1=Paul |last2=Khudikyan |first2=Shakeh |last3=Chamberlin |first3=Alan |title=Planetary Defense Conference Exercise - 2021 Planetary Defense Conference (virtually) in Vienna, Austria, April 26–April 30, 2021. |url=https://cneos.jpl.nasa.gov/pd/cs/pdc21/ |date=30 April 2021 |work=[[NASA]] |accessdate=14 May 2021 }}</ref>

In 2022, NASA spacecraft [[Double Asteroid Redirection Test|DART]] impacted [[Dimorphos]], reducing the minor-planet moon's orbital period by 32 minutes. This mission constitutes the [[Timeline of space exploration|first successful attempt]] at asteroid deflection.<ref name=":2">{{Cite web |last=Bardan |first=Roxana |date=2022-10-11 |title=NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space |url=http://www.nasa.gov/press-release/nasa-confirms-dart-mission-impact-changed-asteroid-s-motion-in-space |access-date=2022-12-08 |website=NASA}}</ref> In 2027, China plans to launch a deflection mission to the near-Earth object [[2015 XF261]], with the impact estimated to occur in April 2029. <ref name=":3">{{Cite web |last=Foust |first=Jeff |date=2024-07-16 |title=China reschedules planetary defense mission for 2027 launch |url=https://spacenews.com/china-reschedules-planetary-defense-mission-for-2027-launch/ |access-date=2025-05-31 |website=SpaceNews |language=en-US}}</ref>