Editing Poynting–Robertson effect (section)

=== Impact of the effect on dust orbits ===

Particles with <math>\beta \geq 0.5</math> have radiation pressure at least half as strong as gravity and will pass out of the Solar System on hyperbolic orbits if their initial velocities were Keplerian.<ref name="wyatt">{{Cite web | url = http://www.ast.cam.ac.uk/~wyatt/wyat06b.pdf | title = Theoretical Modeling of Debris Disk Structure | first = Mark | last = Wyatt | publisher = University of Cambridge | date = 2006 | access-date = 2014-07-16 | archive-date = 2014-07-27 | archive-url = https://web.archive.org/web/20140727004344/http://www.ast.cam.ac.uk/~wyatt/wyat06b.pdf | url-status = live }}</ref> 
For rocky dust particles, this corresponds to a diameter of less than 1&nbsp;[[μm]].<ref>{{Cite encyclopedia |title=Interplanetary dust particle (IDP) |encyclopedia=[[Britannica Online]] |url=https://www.britannica.com/topic/interplanetary-dust-particle |access-date=2017-02-17 |last=Flynn |first=George J. |date=2005-06-16 |archive-date=2017-02-17 |archive-url=https://web.archive.org/web/20170217224342/https://www.britannica.com/topic/interplanetary-dust-particle |url-status=live }}</ref>

Particles with <math>0.1 < \beta < 0.5</math> may spiral inwards or outwards, depending on their size and initial velocity vector; they tend to stay in eccentric orbits.

Particles with <math>\beta \approx 0.1</math> take around 10,000 years to spiral into the Sun from a [[circular orbit]] at 1&nbsp;[[Astronomical unit|AU]]. In this regime, inspiraling time and particle diameter are both roughly <math>\propto 1/\beta</math>.<ref name="inspiral">{{Cite journal |last1=Klačka |first1=J. |last2=Kocifaj |first2=M. |title=Times of inspiralling for interplanetary dust grains |journal=[[Monthly Notices of the Royal Astronomical Society]]|location=Oxford |date=27 October 2008 |volume=390 |issue=4 |pages=1491–1495 |quote=Sec. 4, Numerical results |doi=10.1111/j.1365-2966.2008.13801.x|bibcode=2008MNRAS.390.1491K |doi-access=free }}</ref>

If the initial grain velocity was not Keplerian, then circular or any confined orbit is possible for <math>\beta < 1</math>.

It has been theorized that the slowing down of the rotation of Sun's outer layer may be caused by a similar effect.<ref>{{Cite news |url=http://www.hawaii.edu/news/2016/12/12/giving-the-sun-a-brake/ |title=Giving the Sun a brake |date=2016-12-12 |newspaper=University of Hawai{{okina}}i System News |access-date=2017-02-17 |language=en-US |archive-date=2022-06-01 |archive-url=https://web.archive.org/web/20220601203813/http://www.hawaii.edu/news/2016/12/12/giving-the-sun-a-brake/ |url-status=live}}</ref><ref>{{cite journal | arxiv = 1612.00873 | title = Poynting-Robertson-like Drag at the Sun's Surface | first1 = Ian | last1 = Cunnyngham | first2 = Marcelo | last2 = Emilio | first3 = Jeff | last3 = Kuhn | first4 = Isabelle | last4 = Scholl | first5 = Rock | last5 = Bush | year = 2017 | journal = [[Physical Review Letters]] | volume = 118 | issue = 5 | page = 051102 | doi = 10.1103/PhysRevLett.118.051102 | pmid = 28211737 | bibcode = 2017PhRvL.118e1102C | s2cid = 206285189 }}</ref><ref>{{Cite journal |last=Wright |first=Katherine |date=2017-02-03 |title=Focus: Photons Brake the Sun |url=https://physics.aps.org/articles/v10/13 |journal=Physics |language=en-US |volume=10 |page=13 |doi=10.1103/Physics.10.13 |access-date=2017-02-17 |archive-date=2017-02-17 |archive-url=https://web.archive.org/web/20170217223800/https://physics.aps.org/articles/v10/13 |url-status=live|url-access=subscription }}</ref>