Portal:Jupiter/Theory

From Wikiversity
Jump to navigation Jump to search
Selected Theory


Radiative dynamos

This is a diagram of the dynamo within Jupiter producing its axisymmetric dipole magnetic field. Credit: Robert MacDowall, Planetary Magnetospheres Laboratory, Code 695, GSFC, NASA.

"The interior of Jupiter is the seat of a strong dynamo that produces a surface magnetic field in the equatorial region with an intensity of ~ 4 Gauss. This strong magnetic field and Jupiter’s fast rotation (rotation period ~ 9 h 55 min) create a unique magnetosphere in the solar system which is known for its immense size (average subsolar magnetopause distance 45-100 RJ where 1 RJ = 71492 km is the radius of Jupiter) and fast rotation [...]. Jupiter’s magnetosphere differs from most other magnetospheres in the fact that it derives much of its plasma internally from Jupiter’s moon Io. The heavy plasma, consisting principally of various charge states of S and O, inflates the magnetosphere from the combined actions of centrifugal force and thermal pressure."[1]

In "the absence of an internal heavy plasma, the dipole field would balance the average dynamic pressure of the solar wind (0.08 nPa) at a distance of ~ 42 RJ in the subsolar region [...] the observed average magnetopause location of ~ 75 RJ [...] The heavy plasma is also responsible for generating an azimuthal current exceeding 160 MA in the equatorial region of Jupiter’s magnetosphere where it is confined to a thin current sheet (half thickness ~ 2 RJ in the dawn sector)."[1]

"The energization of plasma by various electrical fields as it diffuses inwards is responsible for the creation of radiation belts in the inner magnetosphere of Jupiter. It is believed that the radial diffusion is driven by the ionospheric dynamo fields produced by winds in Jupiter’s atmosphere"[1]

"In situ and remote observations of Io and its surroundings from Voyager showed that Io is the main source of plasma in Jupiter’s magnetosphere [...] "[1]

"It is estimated that upward of 6 × 1029 amu/s (~ 1 ton/s) of plasma mass is added to the magnetosphere by Io. The picked-up plasma consists mostly of various charged states of S and O and populates a torus region extending from a radial distance of ~ 5.2 RJ to ~ 10 RJ."[1]

"The next most important source of plasma in Jupiter’s magnetosphere is the solar wind whose source strength can be estimated by a consideration of the solar wind mass flux incident on Jupiter’s magnetopause and the fractional amount that makes it into the magnetosphere (< 1%). Such a calculation suggests that the solar wind source strength is < 100 kg/s (Hill et al. 1983) considerably lower than the Io source. Nevertheless, the number density of protons (as opposed to the mass density) may be comparable to the iogenic plasma number density in the middle and outer magnetospheres where the solar wind may be able to gain access to the magnetosphere."[1]

"The escape of ions (mainly H+ and H2+ ) from the ionosphere of Jupiter provides the next significant source of plasma in Jupiter’s magnetosphere. The ionospheric plasma escapes along field lines when the gravity of Jupiter is not able to contain the hot plasma (~ 10 eV and above). The escape however is not uniform and depends on the local photoelectron density, the temperature variations of the ionosphere with the solar zenith angle, other factors such as the auroral precipitation of ions and electrons and the ionospheric heating from Pedersen currents. In situ measurements show that in Io’s torus, protons contribute to less than 20% of total ion number density and constitute < 1% of mass suggesting that the ionosphere is not a major source of plasma in Jupiter’s magnetosphere. [The] ionospheric source strength [is] in the range of ~ 20 kg/s."[1]

The "surface sputtering of the three icy satellites by jovian plasma provides the last significant source of plasma in Jupiter’s magnetosphere. Because the icy moons lack extended atmospheres and the fluxes of the incident plasma are low at the locations of these moons, the total pickup of plasma from these satellites is estimated to be less than 20 kg/s based on the plasma sputtering rates provided".[1]

"Other minor constituents found in the torus [...] were Na+ (with an abundance of < 5%) and molecular ions SO+ and SO2+ (both with abundances of < 1% of the total). The average mass of a torus ion is ~ 20 and the average fractional charge on an ion is ~ 1.2 [...]. The bulk velocity of the plasma was found to be ~ 75 km/s, close to the corotational value."[1]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Krishan K. Khurana, Margaret G. Kivelson, Vytenis M. Vasyliunas, Norbert Krupp, Joachim Woch, Andreas Lagg, Barry H. Mauk, and William S. Kurth (2004). Bagenal, F.; Dowling, T.E.; McKinnon, W.B., ed. The Configuration of Jupiter’s Magnetosphere, In: Jupiter: The Planet, Satellites and Magnetosphere (PDF). Cambridge University Press. p. 24. ISBN 0-521-81808-7. Retrieved 2014-03-29.CS1 maint: Multiple names: authors list (link)



Planetary sciences

This is a schematic of Jupiter's magnetosphere and the components influenced by Io (near the center of the image). Credit: John Spencer.

The image at right represents "[t]he Jovian magnetosphere [magnetic field lines in blue], including the Io flux tube [in green], Jovian aurorae, the sodium cloud [in yellow], and sulfur torus [in red]."[1]

"Io may be considered to be a unipolar generator which develops an emf [electromotive force] of 7 x 105 volts across its radial diameter (as seen from a coordinate frame fixed to Jupiter)."[2]

"This voltage difference is transmitted along the magnetic flux tube which passes through Io. ... The current [in the flux tube] must be carried by keV electrons which are electrostatically accelerated at Io and at the top of Jupiter's ionosphere."[2]

"Io's high density (4.1 g cm-3) suggests a silicate composition. A reasonable guess for its electrical conductivity might be the conductivity of the Earth's upper mantle, 5 x 10-5 ohm-1 cm-1 (Bullard 1967)."[2]

As "a conducting body [transverses] a magnetic field [it] produces an induced electric field. ... The Jupiter-Io system ... operates as a unipolar inductor" ... Such unipolar inductors may be driven by electrical power, develop hotspots, and the "source of heating [may be] sufficient to account for the observed X-ray luminosity".[3]

"The electrical surroundings of Io provide another energy source which has been estimated to be comparable with that of the [gravitational] tides (7). A current of 5 x 106 A is ... shunted across flux tubes of the Jovian field by the presence of Io (7-9)."[4]

"[W]hen the currents [through Io] are large enough to cause ohmic heating ... currents ... contract down to narrow paths which can be kept hot, and along which the conductivity is high. Tidal heating [ensures] that the interior of Io has a very low eletrical resistance, causing a negligible extra amount of heat to be deposited by this current. ... [T]he outermost layers, kept cool by radiation into space [present] a large resistance and [result in] a concentration of the current into hotspots ... rock resistivity [and] contact resistance ... contribute to generate high temperatures on the surface. [These are the] conditions of electric arcs [that can produce] temperatures up to ionization levels ... several thousand kelvins".[4]

"[T]he outbursts ... seen [on the surface may also be] the result of the large current ... flowing in and out of the domain of Io ... Most current spots are likely to be volcanic calderas, either provided by tectonic events within Io or generated by the current heating itself. ... [A]s in any electric arc, very high temperatures are generated, and the locally evaporated materials ... are ... turned into gas hot enough to expand at a speed of 1 km/s."[4]

References

  1. John Spencer (November 2000). John Spencer's Astronomical Visualizations. Boulder, Colorado USA: University of Colorado. Retrieved 2013-04-05.
  2. 2.0 2.1 2.2 Peter Goldreich and Donald Lynden-Bell (April 1969). "Io, a jovian unipolar inductor". The Astrophysical Journal 156 (04): 59-78. doi:10.1086/149947. 
  3. Kinwah Wu, Mark Cropper, Gavin Ramsay, and Kazuhiro Sekiguchi (March 2002). "An electrically powered binary star?". Monthly Notices of the Royal Astronomical Society 321 (1): 221-7. doi:10.1046/j.1365-8711.2002.05190.x. 
  4. 4.0 4.1 4.2 Thomas Gold (November 1979). "Electrical Origin of the Outbursts on Io". Science 206 (4422): 1071-3. doi:10.1126/science.206.4422.1071. 



Astrognosy

Diagram is of Jupiter, its interior, surface features, rings, and inner moons. Credit: Kelvinsong.

The model for the interior of Jupiter suggests the occurrence of such materials as metallic hydrogen.




Coronal clouds

Because of an eccentricity of 0.048, the distance from Jupiter and the Sun varies by 75 million km between perihelion and aphelion, or the nearest and most distant points of the planet along the orbital path respectively.

"Favorable oppositions occur when Jupiter is passing through perihelion, an event that occurs once per orbit. As Jupiter approached perihelion in March 2011, there was a favorable opposition in September 2010.[1]

It's orbital period is 4,332.59 d (11.8618 y).

"It is shown that starting with the alignment of Venus with Jupiter at perihelion position, these two planets will perfectly align at Jupiter's perihelion after every 23.7 years".[2]

"The tidal forces hypothesis for solar cycles has been proposed by Wood (1972) and others. Table 2 below shows the relative tidal forces of the planets on the sun. Jupiter, Venus, Earth and Mercury are called the "tidal planets" because they are the most significant. According to Wood, the especially good alignments of J-V-E with the sun which occur about every 11 years are the cause of the sunspot cycle. He has shown that the sunspot cycle is synchronous with the alignments, and J. Schove's data for 1500 year of sunspot maxima supports the 11.07 year J-V-E period average."[3]

"Both the 11.86 year Jupiter tropical period (time between perihelion's or closest approaches to the sun and the 9.93 year J-S alignment periods are found in sunspot spectral analysis. Unfortunately direct calculations of the tidal forces of all planets does not support the occurrence of the dominant 11.07 year cycle. Instead, the 11.86 year period of Jupiter's perihelion dominates the results. This has caused problems for several researchers in this field."[3]

The coronal cloud around Jupiter is exactly opposite to that around the Sun. At the Sun there are polar coronal holes, whereas at Jupiter the coronal cloud is most prevalent over the magnetic poles.

References

  1. Horizons output. Favorable Appearances by Jupiter. Retrieved 2008-01-02. (Horizons)
  2. S.D. Verma (1986). K. B. Bhatnagar, ed. Influence of Planetary Motion and Radial Alignment of Planets on Sun, In: Space Dynamics and Celestial Mechanics. 127. Springer Netherlands. pp. 143–54. doi:10.1007/978-94-009-4732-0_13. ISBN 978-94-010-8603-5. Retrieved 2013-07-07.
  3. 3.0 3.1 Ray Tomes (February 1990). Towards a Unified Theory of Cycles. Cycles Research Institute. pp. 21. http://cyclesresearchinstitute.org/cycles-general/tomes_unified_cycles.pdf. Retrieved 2013-07-07. 



Jupiter systems

"A definite color gradient is observed [in the small inner satellites of Jupiter], with the satellites closer to Jupiter being redder: the mean violet/green ratio (0.42/0.56 μm) decreases from Thebe to Metis. This ratio also is lower for the trailing sides of Thebe and Amalthea than for their leading sides."[1]

References

  1. P.C. Thomas, J.A. Burns, L. Rossier, D. Simonelli, J. Veverka, C.R. Chapman, K. Klaasen, T.V. Johnson, M.J.S. Belton, Galileo Solid State Imaging Team (September 1998). "The Small Inner Satellites of Jupiter". Icarus 135 (1): 360-71. doi:10.1006/icar.1998.5976. http://www.sciencedirect.com/science/article/pii/S0019103598959760. Retrieved 2012-06-01. 



Sun-Jupiter binary

The Sun-Jupiter binary may serve to establish an upper limit for interstellar cometary capture when three bodies are extremely unequal in mass, such as the Sun, Jupiter, and a third body (potential comet) at a large distance from the binary.[1] The basic problem with a capture scenario even from passage through “a cloud of some 10 million years, or from a medium enveloping the solar system, is the low relative velocity [~0.5 km s-1] required between the solar system and the cometary medium.”[2] The capture of interstellar comets by Saturn, Uranus, and Neptune together cause about as many captures as Jupiter alone.[2]

In a mechanism of chaos assisted capture (CAC), particles such as comets or those of sizes in the range of the irregular moons of Jupiter become entangled in chaotic layers which temporarily “extend the lifetimes of [these] particles within the Hill sphere, thereby providing the breathing space necessary for relatively weak dissipative forces (eg gas-drag) to effect permanent capture.”[3] These objects of the Sun-Jupiter binary system may localize near Jupiter and become satellites, specifically the irregular moons.[3]

References

  1. MJ Valtonen (February 1983). "On the capture of comets into the Solar System". The Observatory 103 (2): 1-4. 
  2. 2.0 2.1 M. J. Valtonen; K. A. Innanen (April 1982). "The capture of interstellar comets". The Astrophysical Journal 255 (4): 307-15. doi:10.1086/159830. 
  3. 3.0 3.1 Sergey A. Astakhov and David Farrelly (November 2004). "Capture and escape in the elliptic restricted three?body problem". Monthly Notices of the Royal Astronomical Society 354 (4): 971-9. doi:10.1111/j.1365-2966.2004.08280.x. http://arxiv.org/pdf/astro-ph/0408271. Retrieved 2012-03-12.