Geology of Mercury
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The geology of Mercury is the scientific study of the surface, crust, and interior of the planet Mercury. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geology. In planetary science, the term geology is used in its broadest sense to mean the study of the solid parts of planets and moons. The term incorporates aspects of geophysics, geochemistry, mineralogy, geodesy, and cartography.[1]
Historically, Mercury has been the least understood of all the
Mercury's surface is dominated by
Mercury's density implies a solid iron-rich core that accounts for about 60% of its volume (75% of its radius).[10] Mercury's magnetic equator is shifted nearly 20% of the planet's radius towards the north, the largest ratio of all planets.[11] This shift suggests there being one or more iron-rich molten layers surrounding the core producing a dynamo effect similar to that of Earth. Additionally, the offset magnetic dipole may result in uneven surface weathering by the solar wind, knocking more surface particles up into the southern exosphere and transporting them for deposit in the north. Scientists are gathering telemetry to determine if such is the case.[11]
After having completed the first solar day of its mission in September 2011, more than 99% of Mercury's surface had been mapped by NASA's MESSENGER probe in both color and monochrome with such detail that scientists' understanding of Mercury's geology has significantly surpassed the level achieved following the Mariner 10 flybys of the 1970s.[7]
Difficulties in exploration
Reaching Mercury from Earth poses significant technical challenges, because the planet orbits so much closer to the Sun than does the Earth. A Mercury-bound spacecraft launched from Earth must travel 91 million kilometers into the Sun's gravitational potential well.[12] Starting from the Earth's orbital speed of 30 km/s, the change in velocity (delta-v) the spacecraft must make to enter into a Hohmann transfer orbit that passes near Mercury is large compared to other planetary missions. The potential energy liberated by moving down the Sun's potential well becomes kinetic energy; requiring another large delta-v to do anything other than rapidly pass by Mercury. In order to land safely or enter a stable orbit the spacecraft must rely entirely on rocket motors because Mercury has negligible atmosphere. A direct trip to Mercury actually requires more rocket fuel than that required to escape the Solar System completely. As a result, only two space probes, Mariner 10 and MESSENGER, both by NASA, have visited Mercury so far.
Furthermore, the space environment near Mercury is demanding, posing the double dangers to spacecraft of intense
Historically, a second obstacle has been that Mercury's
Earth-based observations are made difficult by Mercury's constant proximity to the Sun. This has several consequences:
- Whenever the sky is dark enough for viewing through telescopes, Mercury is always already near the horizon, where viewing conditions are poor anyway due to atmospheric factors.
- The Hubble Space Telescope and other space observatories are usually prevented from pointing close to the Sun for safety reasons (Erroneously pointing such sensitive instruments at the Sun is likely to cause permanent damage).
Mercury's geological history
Like the Earth, Moon and
After the formation of Mercury along with the rest of the
Since then, the main surface processes have been intermittent impacts.
Timeline
Time unit: millions of years
Surface features
Mercury's surface is overall similar in appearance to that of the Moon, with extensive mare-like plains and heavily cratered terrains similar to the lunar highlands and made locally by accumulations of pyroclastic deposits.[6]
Topography |
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Impact basins and craters
Craters on Mercury range in diameter from small bowl-shaped craters to
The largest known crater is the enormous
Overall about 15 impact basins have been identified on the imaged part of Mercury. Other notable basins include the 400 km wide, multi-ring,
As on the Moon, fresh craters on Mercury show prominent bright ray systems. These are made by ejected debris, which tend to be brighter while they remain relatively fresh because of a lesser amount of space weathering than the surrounding older terrain.
Pit-floor craters
Some impact craters on Mercury have non-circular, irregularly shaped depressions or pits on their floors. Such craters have been termed pit-floor craters, and
Plains
There are two geologically distinct plains units on Mercury:[14][19]
- Intercrater plains are the oldest visible surface,[14] predating the heavily cratered terrain. They are gently rolling or hilly and occur in the regions between larger craters. The intercrater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km in diameter.[19] It is not clear whether they are of volcanic or impact origin.[19]The intercrater plains are distributed roughly uniformly over the entire surface of the planet.
- Smooth plains are widespread flat areas resembling the lunar maria, which fill depressions of various sizes. Notably, they fill a wide ring surrounding the Caloris Basin. An appreciable difference to the lunar maria is that the smooth plains of Mercury have the same albedo as the older intercrater plains. Despite a lack of unequivocally volcanic features, their localisation and lobate-shaped colour units strongly support a volcanic origin. All the Mercurian smooth plains formed significantly later than the Caloris basin, as evidenced by appreciably smaller crater densities than on the Caloris ejecta blanket.[14]
The floor of the
Tectonic features
One unusual feature of the planet's surface is the numerous compression folds which crisscross the plains. It is thought that as the planet's interior cooled, it contracted and its surface began to deform. The folds can be seen on top of other features, such as craters and smoother plains, indicating that they are more recent.
Faculae
Faculae on Mercury are bright areas often surrounding irregular depressions. They are generally interpreted to be pyroclastic in nature.[22] The faculae on Mercury are all named using words in different languages meaning snake.
Terminology
Non-crater surface features are given the following names:
- Albedo features – areas of markedly different reflectivity
- List of ridges on Mercury)
- Montes — mountains (see List of mountains on Mercury)
- List of plains on Mercury)
- List of scarps on Mercury)
- List of valleys on Mercury)
High-albedo polar patches and possible presence of ice
The first radar observations of Mercury were carried out by the
Radar maps of the surface of the planet were made using the Arecibo radiotelescope. The survey was conducted with 420 kW UHF band (2.4 GHz) radio waves which allowed for a 15 km resolution. This study not only confirmed the existence of the zones of high reflectivity and depolarization, but also found a number of new areas (bringing the total to 20) and was even able to survey the poles. It has been postulated that surface ice may be responsible for these high luminosity levels, as the silicate rocks that compose most of the surface of Mercury have exactly the opposite effect on luminosity.
In spite of its proximity to the Sun, Mercury may have surface ice, since temperatures near the poles are constantly below freezing point: On the polar plains, the temperature does not rise above −106 °C. Craters at Mercury's higher latitudes (discovered by radar surveys from Earth as well) may be deep enough to shield the ice from direct sunlight. Inside the craters, where there is no solar light, temperatures fall to −171 °C.[23]
Despite
At the South Pole, the location of a large zone of high reflectivity coincides with the location of the Chao Meng-Fu crater, and other small craters containing reflective areas have also been identified. At the North Pole, a number of craters smaller than Chao-Meng Fu have these reflective properties.
The strength of the radar reflections seen on Mercury are small compared to that which would occur with pure ice. This may be due to powder deposition that does not cover the surface of the crater completely or other causes, e.g. a thin overlying surface layer. However, the evidence for ice on Mercury is not definitive. The anomalous reflective properties could also be due to the existence of deposits of
Possible origin of ice
Mercury is not unique in having craters that stand in permanent shadow; at the south pole of Earth's
Mercury |
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Water ice (yellow) at Mercury's north polar region
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Mercury's biological history
Habitability
There may be scientific support, based on studies reported in March 2020, for considering that parts of the planet Mercury may have been
See also
- Atmosphere of Mercury – Composition and properties of the atmosphere of the innermost planet of the Solar System
- List of craters on Mercury
- List of geological features on Mercury
References
- ISBN 0-412-05181-8.
- ^ Strom, R.G. in “Geology of the Terrestrial Planets,” M.H. Carr, Ed., Special Paper 469, NASA Scientific and Technical Information Branch:Washington D.C., 1984, p. 13. https://www.lpi.usra.edu/publications/books/geologyTerraPlanets/
- ^ MESSENGER website. Johns Hopkins Applied Physics Laboratory. https://messenger.jhuapl.edu/Explore/images/impressions/messenger-byTheNumbers-lg.jpg
- ^ "Solar System Exploration: Mercury". NASA. Archived from the original on 21 July 2011. Retrieved 17 February 2012.
- ^ "MESSENGER Team Presents New Mercury Findings". NASA. Archived from the original on 16 October 2011. Retrieved 16 February 2012.
- ^ .
- ^ a b "Orbital Observations of Mercury". Johns Hopkins University Applied Physics Lab. Archived from the original on 26 June 2015. Retrieved 16 February 2012.
- ^ "The MESSENGER Gamma-Ray Spectrometer: A window into the formation and early evolution of Mercury". Johns Hopkins University Applied Physics Lab. Archived from the original on 12 December 2012. Retrieved 18 February 2012.
- ^ a b "Evidence of Volcanism on Mercury: It's the Pits". Johns Hopkins University Applied Physics Lab. Archived from the original on 28 April 2014. Retrieved 16 February 2012.
- ^ "Mercury: The Key to Terrestrial Planet Evolution". Johns Hopkins University Applied Physics Lab. Archived from the original on 4 September 2014. Retrieved 18 February 2012.
- ^ a b "Mercury's Oddly Offset Magnetic Field". Johns Hopkins University Applied Physics Lab. Archived from the original on 12 December 2012. Retrieved 18 February 2012.
- ^ "Topic: 1.2.c Mercury missions | CosmoLearning Astronomy". CosmoLearning. Retrieved 24 July 2023.
- ^ "Mercury Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved 24 July 2023.
- ^ Bibcode:2001mses.conf..100S.
- ^ Shiga, David (30 January 2008). "Bizarre spider scar found on Mercury's surface". NewScientist.com news service.
- S2CID 121225801.
- ^ "Overlaying Color onto Praxiteles Crater". Johns Hopkins University Applied Physics Lab. Archived from the original on 26 June 2015. Retrieved 16 February 2012.
- ^ "A Newly Pictured Pit-Floor Crater". Johns Hopkins University Applied Physics Lab. Archived from the original on 26 June 2015. Retrieved 16 February 2012.
- ^ Bibcode:2001mses.conf..106W.
- .
- .
- ^ PYROCLASTIC DEPOSITS ON MERCURY DETECTED WITH MASCS/MESSENGER DATA: IDENTIFICATION THROUGH SPECTRAL CHARACTERIZATION AND PRINCIPAL COMPONENT ANALYSIS (PCA). By A. Galiano, F. Capaccioni, G. Filacchione, C. Carli. 53rd Lunar and Planetary Science Conference (2022).
- ^ "Ice on Mercury". National Space Science Data Center. Retrieved 16 February 2012.
- ^ Hall, Shannon (24 March 2020). "Life on the Planet Mercury? 'It's Not Completely Nuts' - A new explanation for the rocky world's jumbled landscape opens a possibility that it could have had ingredients for habitability". The New York Times. Retrieved 26 March 2020.
- PMID 32179758.
- Stardate, Guide to the Solar System. Publicación de la University of Texas at Austin McDonald Observatory
- Our Solar System, A Geologic Snapshot. NASA (NP-157). May 1992.
- Fotografía: Mercury. NASA (LG-1997-12478-HQ)
- This article draws heavily on the corresponding article in the Spanish-language Wikipedia, which was accessed in the version of 26 June 2005.
Original references for Spanish article
- Ciencias de la Tierra. Una Introducción a la Geología Física (Earth Sciences, an Introduction to Physical Geology), by Edward J. Tarbuck y Frederick K. Lutgens. Prentice Hall (1999).
- "Hielo en Mercurio" ("Ice on Mercury"). El Universo, Enciclopedia de la Astronomía y el Espacio ("The Universe, Encyclopedia of Astronomy and the Space"), Editorial Planeta-De Agostini, p. 141–145. Volume 5. (1997)
External links
- Mariner 10
- MESSENGER probe
- Mercury on Nineplanets.org
- USGS Geology of Mercury Retrieved 5 August 2007