Callisto (moon)
Callisto is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei and named after Kallisto.[1] It is the second largest moon orbiting Jupiter, after Ganymede, and the third largest moon in the Solar System.[4]
| File:Callisto - July 8 1979 (38926064465).jpg | |||||||||
| Discovery | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Discovered by | Galileo Galilei | ||||||||
| Discovery date | 7 January 1610[1] | ||||||||
| Designations | |||||||||
| Jupiter IV | |||||||||
| Adjectives | Callistoan, Callistonian | ||||||||
| Orbital characteristics | |||||||||
| Periapsis | 1869000 km[a] | ||||||||
| Apoapsis | 1897000 km[b] | ||||||||
| 1 882 700 km | |||||||||
| Eccentricity | 0.0074 | ||||||||
| 16.6890184 d | |||||||||
Average orbital speed | 8.204 km/s | ||||||||
| Inclination | 2.017° (to the ecliptic) 0.192° (to local Laplace planes) | ||||||||
| Satellite of | Jupiter | ||||||||
| Physical characteristics | |||||||||
Mean radius | 2410.3±1.5 km (0.378 Earths)> | ||||||||
| 7.30×107 km2 (0.143 Earths)[c] | |||||||||
| Volume | 5.9×1010 km3 (0.0541 Earths)[d] | ||||||||
| Mass | (1.075938±0.000137)×1023 kg (0.018 Earths) | ||||||||
Mean density | 1.8344±0.0034 g/cm3 | ||||||||
| 1.235 m/s2 (0.126 g)[e] | |||||||||
| 0.359±0.005[2] (estimate) | |||||||||
| 2.440 km/s[f] | |||||||||
| synchronous | |||||||||
| zero | |||||||||
| Albedo | 0.22 (geometric) | ||||||||
| |||||||||
| 5.65 (opposition)[3] | |||||||||
| Atmosphere | |||||||||
Surface pressure | 7.5 picobar (7.5×10−10 kPa, 7.4019×10−12 atm) | ||||||||
| Composition by volume | ≈ 4×108 molecules/cm3 carbon dioxide; up to 2×1010 molecules/cm3 molecular oxygen(O2) | ||||||||
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Callisto is almost the same size as the planet Mercury, being 99% the diameter of the planet, but is much less massive. Of the four Galilean moons of Jupiter, Callisto is the farthest out, with an orbital radius of about 1,880,000 kilometres. It does not form part of the orbital resonance that affects three inner Galilean satellites, Io, Europa and Ganymede.[5] Like the Earth's Moon, Callisto rotates synchronously with its orbital period. This means that one side is always turned toward Jupiter, while the other side never sees the face of the planet. Callisto's surface is less affected by Jupiter's magnetosphere than the seven moons nearer the planet.[6]
Callisto has about equal amounts of rock and ices, with an average density of about 1.83 g/cm³. Chemical compounds on the surface include water ice, carbon dioxide, silicates, and organics. The Galileo spacecraft made investigations of the moon, and revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water more than 100 kilometers deep.[7][8]
The surface of Callisto is heavily cratered and extremely old. The surface does not show any sign of processes occurring below the surface such as plate tectonics, earthquakes or volcanoes, and is thought to have evolved mainly under the influence of meteorite impacts.[9] Notable surface features include multi-ring structures, impact craters in different shapes, and chains of craters (known as catenae) and associated scarps, ridges and deposits.[9] On a smaller scale, the surface is varied. It is made up of frost on hill tops, surrounded by a smooth blanket of dark material in valleys. This is thought to result from the degradation of small landforms, caused by sublimation. This is supported by the few small impact craters, and the presence of numerous small knobs which are thought to be their remains.[10] The absolute ages of the landforms are not known.
Callisto is surrounded by an extremely thin atmosphere made out of carbon dioxide and probably oxygen molecules. There is also a rather intense ionosphere.[11] An ocean is thought to exist within Callisto. This may mean that life might exist. However, this is less likely than on nearby Europa.[12]
Various space probes from Pioneers 10–11 to Galileo and Cassini−Huygens have studied the moon. Callisto is considered the most suitable place for humans to settle for future exploration of the Jovian system.[13]
Callisto (moon) Media
- 001221 Cassini Jupiter & Europa & Callisto.jpg
Callisto (bottom left), Jupiter (top right) and Europa (below and left of Jupiter's Great Red Spot) as viewed by Cassini–Huygens
- PIA00844 NIMS spectra.gif
Near-IR spectra of dark cratered plains (red) and the Asgard impact structure (blue), showing the presence of more water ice (absorption bands from 1 to 2 μm) and less rocky material within Asgard.
- Callisto diagram.svg
Model of Callisto's internal structure showing a surface ice layer, a possible liquid water layer, and an ice–rock interior
- Cratered plains PIA00745.jpg
Galileo image of cratered plains, illustrating the pervasive local smoothing of Callisto's surface
- Callisto Har PIA01054.jpg
Impact crater Hár with a central dome. Chains of secondary craters from formation of the more recent crater Tindr at upper right crosscut the terrain.
- Valhalla crater on Callisto.jpg
Voyager 1 image of Valhalla, a multi-ring impact structure 3,800 km in diameter
- Landslides and knobs PIA01095.jpg
Two landslides 3–3.5 km long are visible on the right sides of the floors of the two large craters on the right.
- Callisto field.svg
Induced magnetic field around Callisto
References
Notes
- ↑ Periapsis is derived from the semimajor axis (a) and eccentricity (e): [math]\displaystyle{ a(1-e) }[/math].
- ↑ Apoapsis is derived from the semimajor axis (a) and eccentricity (e): [math]\displaystyle{ a(1+e) }[/math].
- ↑ Surface area derived from the radius (r): [math]\displaystyle{ 4\pi r^2 }[/math].
- ↑ Volume derived from the radius (r): [math]\displaystyle{ \frac{4}{3}\pi r^3 }[/math].
- ↑ Surface gravity derived from the mass (m), the gravitational constant (G) and the radius (r): [math]\displaystyle{ \frac{Gm}{r^2} }[/math].
- ↑ Escape velocity derived from the mass (m), the gravitational constant (G) and the radius (r): [math]\displaystyle{ \textstyle\sqrt{\frac{2Gm}{r}} }[/math].
Footnotes
- ↑ 1.0 1.1 Galilei, G.; Sidereus Nuncius Archived 2009-08-23 at the Wayback Machine (March 13, 1610)
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ "Classic Satellites of the Solar System". Observatorio ARVAL. Archived from the original on 25 August 2011. Retrieved 13 July 2007.
- ↑ Cox, Brian; Cohen, Andrew (2010). Wonders of the Solar System. HarperCollins. p. 231. ISBN 9780007386901.
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ 9.0 9.1 Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Trautman, Pat; Bethke, Kristen (2003). "Revolutionary concepts for human outer planet exploration (HOPE)" (PDF). NASA. Archived from the original (PDF) on 2012-01-19. Retrieved 2007-12-13.