Editing Yarkovsky effect (section)

==Measurement==
The effect was first measured in 1991–2003 on the asteroid [[6489 Golevka]]. The asteroid drifted 15&nbsp;km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995, and 1999 from the [[Arecibo Observatory|Arecibo radio telescope]]).<ref>{{cite journal |last=Chesley |first=Steven R. |url=https://www.aldebaran.cz/bulletin/2004_15/golevka_science.pdf |title=Direct Detection of the Yarkovsky Effect via Radar Ranging to Asteroid 6489 Golevka |journal=[[Science (journal)|Science]] |volume=302 |issue=5651 |pages=1739–1742 |year=2003 |doi=10.1126/science.1091452 |pmid=14657492 |bibcode=2003Sci...302.1739C |s2cid=21091302 |display-authors=etal |access-date=2021-08-12 |archive-date=2021-08-12 |archive-url=https://web.archive.org/web/20210812022035/https://www.aldebaran.cz/bulletin/2004_15/golevka_science.pdf |url-status=live }}</ref>

Without direct measurement, it is very hard to predict the exact result of the Yarkovsky effect on a given asteroid's orbit. This is because the magnitude of the effect depends on many variables that are hard to determine from the limited observational information that is available. These include the exact shape of the asteroid, its orientation, and its [[albedo]]. Calculations are further complicated by the effects of shadowing and thermal "reillumination", whether caused by local craters or a possible overall concave shape. The Yarkovsky effect also competes with [[radiation pressure]], whose net effect may cause similar small long-term forces for bodies with albedo variations or non-spherical shapes.

As an example, even for the simple case of the pure seasonal Yarkovsky effect on a spherical body in a circular orbit with 90° [[obliquity]], semi-major axis changes could differ by as much as a factor of two between the case of a uniform albedo and the case of a strong north-south albedo asymmetry. Depending on the object's orbit and [[Rotation|spin axis]], the Yarkovsky change of the semi-major axis may be reversed simply by changing from a spherical to a non-spherical shape.

Despite these difficulties, using the Yarkovsky effect is one scenario under investigation to alter the course of potentially Earth-impacting [[near-Earth object|near-Earth asteroid]]s. Possible [[asteroid deflection strategies]] include "painting" the surface of the asteroid or focusing solar radiation onto the asteroid to alter the intensity of the Yarkovsky effect and so alter the orbit of the asteroid away from a collision with Earth.<ref>{{cite web |last1=Randall |first1=Keith |title=Asteroids No Match For Paint Gun, Says Prof |url=http://tamutimes.tamu.edu/2013/02/21/asteroids-no-match-for-paint-gun-says-prof/ |access-date=12 August 2021 |archive-url=https://web.archive.org/web/20130302134556/http://tamutimes.tamu.edu:80/2013/02/21/asteroids-no-match-for-paint-gun-says-prof/ |archive-date=2 March 2013 |date=21 February 2013 |url-status=dead }} [https://today.tamu.edu/2013/02/21/asteroids-no-match-for-paint-gun-says-prof/ Alternate link, with video] {{Webarchive|url=https://web.archive.org/web/20210812022037/https://today.tamu.edu/2013/02/21/asteroids-no-match-for-paint-gun-says-prof/ |date=2021-08-12 }}</ref> The [[OSIRIS-REx]] mission, launched in September 2016, studied the Yarkovsky effect on [[101955 Bennu|asteroid Bennu]].<ref>{{cite web| url = https://www.asteroidmission.org/qa/| title = OSIRIS-REx - Q & A| access-date = 2021-08-12| archive-date = 2021-08-12| archive-url = https://web.archive.org/web/20210812022036/https://www.asteroidmission.org/qa/| url-status = live}}</ref>

In 2020, astronomers confirmed Yarkovsky acceleration of the asteroid [[99942 Apophis]]. The findings are relevant to [[asteroid impact avoidance]] as 99942 Apophis was thought to have a very small chance of Earth impact in 2068, and the Yarkovsky effect was a significant source of prediction uncertainty.<ref>{{cite news |title=Infamous asteroid Apophis is accelerating {{!}} EarthSky.org |url=https://earthsky.org/space/asteroid-99942-apophis-encounters-2029-2036-2068 |access-date=10 November 2020 |work=earthsky.org |archive-date=2 May 2021 |archive-url=https://web.archive.org/web/20210502132009/https://earthsky.org/space/asteroid-99942-apophis-encounters-2029-2036-2068 |url-status=live }}</ref><ref>{{cite journal |last1=Tholen |first1=D. |last2=Farnocchia |first2=D. |title=Detection of Yarkovsky Acceleration of (99942) Apophis |journal=AAS/Division for Planetary Sciences Meeting Abstracts |date=1 October 2020 |volume=52 |issue=6 |pages=214.06 |bibcode=2020DPS....5221406T |url=https://aas.org/sites/default/files/2020-10/David_Tholen_DPS52.pdf |access-date=12 August 2021 |archive-date=12 August 2021 |archive-url=https://web.archive.org/web/20210812015900/https://aas.org/sites/default/files/2020-10/David_Tholen_DPS52.pdf |url-status=live }}</ref> In 2021, a multidisciplinary professional-amateur collaboration combined [[Gaia satellite]] and ground-based radar measurements with amateur stellar [[occultation]] observations to further refine 99942 Apophis's orbit and measure the Yarkovsky acceleration with high precision, to within 0.5%. With these data, astronomers were able to eliminate the possibility of a collision with the Earth for at least the next 100 years.<ref>{{cite web |title=Apophis' Yarkovsky Acceleration Improved Through Stellar Occultation |url=https://www.cosmos.esa.int/web/gaia/iow_20210329/ |website=www.cosmos.esa.int |access-date=12 August 2021 |date=26 March 2021 |archive-date=12 August 2021 |archive-url=https://web.archive.org/web/20210812140459/https://www.cosmos.esa.int/web/gaia/iow_20210329/ |url-status=live }}</ref>