Editing Albedo feature (section)

{{short description|Region of a planet's surface which contrasts in brightness to its surroundings}}
[[File:Mars télescope.jpg|thumb|250px|A telescopic view of [[Mars]] at [[planetary phase|full phase]], featuring its [[classical albedo features on Mars|prominent maria]] and south [[Martian polar ice caps|polar ice cap]]]]

In [[planetary geology]], an '''albedo feature''' is a large area on the surface of a [[planet]] (or other [[Solar System]] body) which shows a contrast in brightness or darkness ([[albedo]]) with adjacent areas.

Historically, albedo features were the first (and usually only) features to be seen and named on [[Mars]] and [[Mercury (planet)|Mercury]].  Early classical maps (such as those of [[Giovanni Schiaparelli|Schiaparelli]]<ref>[[Willy Ley|Ley, Willy]] and [[Wernher von Braun|von Braun, Wernher]] ''The Exploration of Mars'' New York:1956 The Viking Press Pages 70–71 Schiaparelli's original map of Mars</ref> and [[Eugène Antoniadi|Antoniadi]]<ref>[https://history.nasa.gov/SP-423/p15a.htm Antoniadi's map of Mercury]</ref>) showed only albedo features, and it was not until the arrival of [[space probe]]s that other surface features such as [[Impact crater|crater]]s could be seen.

On bodies other than Mars and Mercury, an albedo feature is sometimes called a regio.

On bodies with a very thick atmosphere like [[Venus]] or [[Titan (moon)|Titan]], permanent albedo features cannot be seen using ordinary optical telescopes because the surface is not visible, and only clouds and other transient atmospheric phenomena are seen. The ''[[Cassini–Huygens]]'' probe observed [[List of geological features on Titan#Albedo features|multiple albedo features]] on Titan after its arrival in [[Saturn]]'s orbit in 2004.

The first albedo feature ever seen on another planet was [[Syrtis Major Planum]] on Mars in the 17th century.<ref>{{cite book| title=Mapping Mars: Science, Imagination, and the Birth of a World| first=Oliver| last=Morton| publisher=Picador USA| location=New York| year=2002| isbn=0-312-24551-3| pages=[https://archive.org/details/mappingmarsscien00mort_0/page/14 14]–15| url-access=registration| url=https://archive.org/details/mappingmarsscien00mort_0}}</ref><ref>{{cite web|url=http://www.uapress.arizona.edu/onlinebks/mars/chap02.htm|title=The Planet Mars: A History of Observation and Discovery - Chapter 2: Pioneers|author=William Sheehan|accessdate=2015-01-05|archive-date=2012-04-26|archive-url=https://web.archive.org/web/20120426163500/http://www.uapress.arizona.edu/onlinebks/MARS/CHAP02.HTM|url-status=dead}}</ref>

Today, thanks to space probes, very high-resolution images of surface features on Mars and Mercury are available, and the classical nomenclature based on albedo features has fallen somewhat into disuse, although it is still used for Earth-based observing of Mars by [[amateur astronomy|amateur astronomer]]s.

However, for some Solar System bodies (such as [[Pluto]] prior to the ''[[New Horizons]]'' mission), the best available images show only albedo features.  These images were usually taken by the [[Hubble Space Telescope]] or by ground-based telescopes using [[adaptive optics]].

[[Cydonia Mensae]] on Mars is an example of an albedo feature.