Editing Gravitational lens (section)

==Solar gravitational lens==
{{Main|Solar gravitational lens}}
Albert Einstein predicted in 1936 that rays of light from the same direction that skirt the edges of the [[Sun]] would converge to a focal point approximately 542 [[astronomical unit|AU]] from the Sun.<ref>{{cite journal|author= Einstein, Albert|s2cid=38450435|title=Lens-Like Action of a Star by the Deviation of Light in the Gravitational Field|journal=Science|volume=84|date=1936|pages=506–507|bibcode = 1936Sci....84..506E |doi = 10.1126/science.84.2188.506|pmid=17769014|issue=2188}}</ref> Thus, a probe positioned at this distance (or greater) from the Sun could use the Sun as a gravitational lens for magnifying distant objects on the opposite side of the Sun.<ref>{{cite journal | last1 = Eshleman | first1 = Von R | year = 1979 | title = Gravitational lens of the sun: its potential for observations and communications over interstellar distances | journal = Science | volume = 205 | issue = 4411| pages = 1133–1135 | doi = 10.1126/science.205.4411.1133 | pmid = 17735051 | bibcode = 1979Sci...205.1133E | s2cid = 27692082 }}</ref> A probe's location could shift around as needed to select different targets relative to the Sun.

This distance is far beyond the progress and equipment capabilities of space probes such as ''[[Voyager 1]]'', and beyond the known planets and dwarf planets, though over thousands of years [[90377 Sedna]] will move farther away on its highly elliptical orbit.  The high gain for potentially detecting signals through this lens, such as microwaves at the 21-cm [[hydrogen line]], led to the suggestion by [[Frank Drake]] in the early days of [[SETI]] that a probe could be sent to this distance.  A multipurpose probe SETISAIL and later [[FOCAL (spacecraft)|FOCAL]] was proposed to the ESA in 1993, but is expected to be a difficult task.<ref name="Landis">Geoffrey A. Landis, [https://arxiv.org/abs/1604.06351 "Mission to the Gravitational Focus of the Sun: A Critical Analysis,"] ArXiv, paper 1604.06351, Cornell University, 21 Apr 2016 (downloaded 30 April 2016)</ref>  If a probe does pass 542 AU, magnification capabilities of the lens will continue to act at farther distances, as the rays that come to a focus at larger distances pass further away from the distortions of the Sun's corona.<ref>{{cite book|url=https://books.google.com/books?id=nGBhKDE1SFEC&pg=PA6|title=Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens|author=Claudio Maccone|date=2009|publisher=Springer|isbn=9783540729433}}</ref> A critique of the concept was given by Landis,<ref>Landis, Geoffrey A., “Mission to the Gravitational Focus of the Sun: A Critical Analysis,” paper AIAA-2017-1679, AIAA Science and Technology Forum and Exposition 2017, Grapevine TX, January 9–13, 2017. [https://arxiv.org/abs/1604.06351 Preprint] at arXiv.org (accessed 24 December 2016).</ref> who discussed issues including interference of the solar corona, the high magnification of the target, which will make the design of the mission focal plane difficult, and an analysis of the inherent [[spherical aberration]] of the lens.

In 2020, NASA physicist [[Slava Turyshev]] presented his idea of Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a [[Solar gravitational lens|Solar Gravitational Lens]] Mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution, enough to see surface features and signs of habitability.<ref>{{Cite web|last=Hall|first=Loura|date=2020-04-06|title=Direct Multipixel Imaging and Spectroscopy of an Exoplanet|url=http://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/Direct_Multipixel_Imaging_and_Spectroscopy_of_an_Exoplanet|access-date=2020-08-05|website=NASA}}</ref>