Adrastea (moon)
{{Short description|Moon of Jupiter}}
{{For|the moon of Jupiter known by this name between 1955 and 1975|Ananke (moon)}}
{{For|the main-belt asteroid|239 Adrastea}}
{{Good article}}
{{Infobox planet
| name = Adrastea
| pronounced = {{IPAc-en|æ|d|r|ə|ˈ|s|t|iː|ə}}as "Adrastia" in Noah Webster (1884) A Practical Dictionary of the English Language
| adjectives = Adrastean {{IPAc-en|æ|d|r|ə|ˈ|s|t|iː|ə|n}}A.H. Clough (1905) Plutarch's lives: the translation called Dryden's, vol. 3, p. 238.
| named_after = Ἀδράστεια Adrasteia
| image = File:adrastea.jpg
| image_scale =
| caption = Image of Adrastea taken by Galileo spacecraft between November 1996 and June 1997
| discoverer =
{{plainlist |
- David C. Jewitt
- G. Edward Danielson
}}
| discovered = 8 July 1979
| mean_orbit_radius = {{val|129000|u=km}}{{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| eccentricity = {{val|0.0015}}{{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| period = {{val|0.29826|u=d}}
(7 h, 9.5 min){{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| avg_speed = 31.378 km/s{{efn|name=calculated}}
| inclination = 0.03°
(to Jupiter's equator){{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| satellite_of = Jupiter
| mean_radius = {{val|8.2|2.0|u=km}}{{sfn|Thomas Burns et al.|1998}}
| dimensions = 20 × 16 × 14 km{{sfn|Thomas Burns et al.|1998}}
| volume = {{val|p=≈ |2345|u=km3}}{{efn|name=calculated}}
| mass =
| density =
| surface_grav =
| escape_velocity =
| rotation = synchronous
| axial_tilt = zero{{sfn|Thomas Burns et al.|1998}}
| albedo = {{val|0.10|0.045}}{{sfn|Thomas Burns et al.|1998}}
| single_temperature = ≈ 122 K
}}
Adrastea ({{IPAc-en|æ|d|r|ə|ˈ|s|t|iː|ə}}), also known as {{nowrap|Jupiter XV}}, is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in photographs taken by Voyager 2 in 1979, making it the first natural satellite to be discovered from images taken by an interplanetary spacecraft, rather than through a telescope.{{sfn|IAUC 3454}} It was officially named after the mythological Adrasteia, foster mother of the Greek god Zeus—the equivalent of the Roman god Jupiter.{{sfn|IAUC 3872}}
Adrastea is one of the few moons in the Solar System known to orbit its planet in less than the length of that planet's day. It orbits at the edge of Jupiter's main ring and is thought to be the main contributor of material to the rings of Jupiter. Despite observations made in the 1990s by the Galileo spacecraft, very little is known about the moon's physical characteristics other than its size and the fact that it is tidally locked to Jupiter.
Discovery and observations
Adrastea was discovered by David C. Jewitt and G. Edward Danielson in Voyager 2 probe photographs taken on July 8, 1979, and received the designation {{nowrap|S/1979 J 1}}.{{sfn|IAUC 3454}}{{sfn|Jewitt Danielson et al.|1979}} Although it appeared only as a dot,{{sfn|Jewitt Danielson et al.|1979}} it was the first moon to be discovered by an interplanetary spacecraft. Soon after its discovery, two other of the inner moons of Jupiter (Thebe and Metis) were observed in the images taken a few months earlier by Voyager 1. The Galileo spacecraft was able to determine the moon's shape in 1998, but the images remain poor.{{sfn|Thomas Burns et al.|1998}} In 1983, Adrastea was officially named after the Greek nymph Adrastea, the daughter of Zeus and his lover Ananke.{{sfn|IAUC 3872}}
Although the Juno orbiter, which arrived at Jupiter in 2016, has a camera called JunoCam, it is almost entirely focused on observations of Jupiter itself. However, if all goes well, it should be able to capture some limited images of the moons Metis and Adrastea.[http://adsabs.harvard.edu/abs/2015AGUFM.P41B2066H JunoCam: Science and Outreach Opportunities with Juno] Hansen, C. J.; Orton, G. S. American Geophysical Union 12/2015
{{clear|left}}
Physical characteristics
Adrastea has an irregular shape and measures 20×16×14 km across.{{sfn|Thomas Burns et al.|1998}} A surface area estimate would be between 840 and 1,600 (~1,200) km2. This makes it the smallest of the four inner moons. The bulk, composition, and mass of Adrastea are not known, but assuming that its mean density is like that of Amalthea,{{sfn|Burns Simonelli et al.|2004}} around 0.86 g/cm3,{{sfn|Anderson Johnson et al.|2005}} its mass can be estimated at 2{{E-sp|15}} kg. Amalthea's density implies that the moon is composed of water ice with a porosity of 10–15%, and Adrastea may be similar.{{sfn|Anderson Johnson et al.|2005}}
No surface details of Adrastea are known, due to the low resolution of available images.{{sfn|Thomas Burns et al.|1998}}
Orbit
Adrastea is the smallest and second-closest member of the inner Jovian satellite family. It orbits Jupiter at 70,200 mph at a radius of about {{Convert|129,000|km|mi|abbr=on|sp=us|sigfig=1}} (1.806 Jupiter radii) at the exterior edge of the planet's main ring.{{sfn|Burns Simonelli et al.|2004}} Its orbit has a very small eccentricity of around 0.0015 and an inclination relative to Jupiter's equator of 0.03°, respectively.{{sfn|Burns Simonelli et al.|2004}}
Due to tidal locking, Adrastea rotates synchronously with its orbital period, keeping one face always looking toward the planet. Its long axis is aligned towards Jupiter, this being the lowest energy configuration.{{sfn|Thomas Burns et al.|1998}}
The orbit of Adrastea lies inside Jupiter's synchronous orbit radius (as does Metis's), and as a result, tidal forces are slowly causing its orbit to decay so that it will one day impact Jupiter. If its density is similar to Amalthea's then its orbit would actually lie within the fluid Roche limit. However, since it is not breaking up, it must still lie outside its rigid Roche limit.{{sfn|Burns Simonelli et al.|2004}}
Relationship with Jupiter's rings
Adrastea is the largest contributor to material in Jupiter's rings. This appears to consist primarily of material that is ejected from the surfaces of Jupiter's four small inner satellites by meteorite impacts. It is easy for the impact ejecta to be lost from these satellites into space. This is due to the satellites' low density and their surfaces lying close to the edge of their Hill spheres.{{sfn|Burns Simonelli et al.|2004}}
It seems that Adrastea is the most copious source of this ring material, as evidenced by the densest ring (the main ring) being located at and within Adrastea's orbit.{{sfn|Burns Showalter et al.|1999}} More precisely, the orbit of Adrastea lies near the outer edge of Jupiter's main ring.{{sfn|Ockert-Bell Burns et al.|1999}} The exact extent of visible ring material depends on the phase angle of the images: in forward-scattered light Adrastea is firmly outside the main ring,{{sfn|Ockert-Bell Burns et al.|1999}} but in back-scattered light (which reveals much bigger particles) there appears to also be a narrow ringlet outside Adrastea's orbit.{{sfn|Burns Simonelli et al.|2004}}
Notes
{{notes
| notes =
{{efn
| name = calculated
| Calculated on the basis of other parameters.
}}
}}
References
{{reflist|20em}}
Cited sources
- {{cite journal| doi = 10.1126/science.1110422| last1 = Anderson | first1 = J. D.| last2 = Johnson | first2 = T. V.| last3 = Schubert | first3 = G.| last4 = Asmar | first4 = S.| last5 = Jacobson | first5 = R. A.| last6 = Johnston | first6 = D.| last7 = Lau | first7 = E. L.| last8 = Lewis | first8 = G.| last9 = Moore | first9 = W. B.| date = 27 May 2005| last10 = Taylor | first10 = A.| last11 = Thomas | first11 = P. C.| last12 = Weinwurm | first12 = G.| title = Amalthea's Density is Less Than That of Water| journal = Science| volume = 308| issue = 5726| pages = 1291–1293| pmid = 15919987| bibcode = 2005Sci...308.1291A| s2cid = 924257 | ref = {{sfnRef|Anderson Johnson et al.|2005}}}}
- {{cite journal| doi = 10.1126/science.284.5417.1146| last1 = Burns| first1 = Joseph A.| last2 = Showalter| first2 = Mark R.| last3 = Hamilton| first3 = Douglas P.| last4 = Nicholson| first4 = Philip D.| last5 = de Pater| first5 = Imke| last6 = Ockert-Bell| first6 = Maureen E.| last7 = Thomas| first7 = Peter C.| date = 14 May 1999| title = The Formation of Jupiter's Faint Rings| journal = Science| volume = 284| issue = 5417| pages = 1146–1150| pmid = 10325220| bibcode = 1999Sci...284.1146B| ref = {{sfnRef|Burns Showalter et al.|1999}}}}
- {{cite encyclopedia
| last1 = Burns
| first1 = Joseph A.
| last2 = Simonelli
| first2 = Damon P.
| last3 = Showalter
| first3 = Mark R.
| last4 = Hamilton
| first4 = Douglas P.
| last5 = Porco
| first5 = Carolyn C.
| last6 = Throop
| first6 = Henry
| last7 = Esposito
| first7 = Larry W.
| year = 2004
| pages = 241–262
| title = Jupiter's Ring-Moon System
| encyclopedia = Jupiter: The Planet, Satellites and Magnetosphere
| publisher = Cambridge University Press
| editor1-last = Bagenal
| editor1-first = Fran
| editor2-last = Dowling
| editor2-first = Timothy E.
| editor3-last = McKinnon
| editor3-first = William B.
| url = http://www.astro.umd.edu/~hamilton/research/preprints/BurSimSho03.pdf
| bibcode = 2004jpsm.book..241B
| isbn = 978-0-521-81808-7
| ref = {{sfnRef|Burns Simonelli et al.|2004}}
}}
- {{cite journal
| last1 = Evans
| first1 = M. W.
| last2 = Porco
| first2 = C. C.
| last3 = Hamilton
| first3 = D. P.
| date=September 2002
| title = The Orbits of Metis and Adrastea: The Origin and Significance of their Inclinations
| journal = Bulletin of the American Astronomical Society
| volume = 34
| pages = 883
| bibcode = 2002DPS....34.2403E
| ref = {{sfnRef|Evans Porco et al.|2002}}
}}
- {{cite journal| doi = 10.1126/science.206.4421.951| last1 = Jewitt| first1 = David C.| last2 = Danielson| first2 = G. Edward| last3 = Synnott| first3 = Stephen P.| date = November 23, 1979| title = Discovery of a New Jupiter Satellite| journal = Science| volume = 206| issue = 4421| pages = 951| pmid = 17733911| bibcode = 1979Sci...206..951J| s2cid = 6391249| ref = {{sfnRef|Jewitt Danielson et al.|1979}}}}
- {{cite journal
|last=Marsden
|first=Brian G.
|date=February 25, 1980
|title=Editorial Notice
|journal=IAU Circular
|volume=3454
|url=http://www.cbat.eps.harvard.edu/iauc/03400/03454.html
|access-date=2012-03-28
|ref={{sfnRef|IAUC 3454}}
|url-status=dead
|archive-url=https://web.archive.org/web/20110725035158/http://www.cbat.eps.harvard.edu/iauc/03400/03454.html
|archive-date=2011-07-25
}} (discovery)
- {{cite journal
| last = Marsden
| first = Brian G.
| date = September 30, 1983
| title = Satellites of Jupiter and Saturn
| journal = IAU Circular
| volume = 3872
| url = http://www.cbat.eps.harvard.edu/iauc/03800/03872.html
| access-date = 2012-03-28
| ref = {{sfnRef|IAUC 3872}}
}} (naming the moon)
- {{cite journal| doi = 10.1006/icar.1998.6072| last1 = Ockert-Bell | first1 = M. E.| last2 = Burns | first2 = J. A.| last3 = Daubar | first3 = I. J.| last4 = Thomas | first4 = P. C.| last5 = Veverka | first5 = J.| last6 = Belton | first6 = M. J. S.| last7 = Klaasen | first7 = K. P.| date = 1 April 1999| title = The Structure of Jupiter's Ring System as Revealed by the Galileo Imaging Experiment| journal = Icarus| volume = 138| issue = 2| pages = 188–213| bibcode = 1999Icar..138..188O| ref = {{sfnRef|Ockert-Bell Burns et al.|1999}}| doi-access = free}}
- {{cite journal| doi = 10.1006/icar.1998.5976| last1 = Thomas | first1 = P. C.| last2 = Burns | first2 = J. A.| last3 = Rossier | first3 = L.| last4 = Simonelli | first4 = D.| last5 = Veverka | first5 = J.| last6 = Chapman | first6 = C. R.| last7 = Klaasen | first7 = K.| last8 = Johnson | first8 = T. V.| last9 = Belton | first9 = M. J. S.| author10 = Galileo Solid State Imaging Team| date =September 1998| title = The Small Inner Satellites of Jupiter| journal = Icarus| volume = 135| issue = 1| pages = 360–371| bibcode = 1998Icar..135..360T| ref = {{sfnRef|Thomas Burns et al.|1998}}| doi-access = free}}
External links
- [https://web.archive.org/web/20130317224600/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Adrastea Adrastea Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
{{Spoken Wikipedia|date=2021-03-01|En-Adrastea (moon)-article.ogg}}{{Moons of Jupiter}}
{{DEFAULTSORT:Adrastea (Moon)}}
Category:Discoveries by David C. Jewitt