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physicallove
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do all planets have magnetospheres?
Why does Venus lack a magnetic field? Francis Nimmo
Venus and Earth have similar radii and estimated bulk compositions, and both have an iron core that is at least partially liquid. However, despite these similarities, Venus lacks an appreciable dipolar magnetic field. Here I examine the hypothesis that this absence is due to Venus's also lacking plate tectonics for the past 0.5 b.y. The generation of a global magnetic field requires core convection, which in turn requires extraction of heat from the core into the overlying mantle. Plate tectonics cools Earth's mantle; on the basis of elastic thickness estimates and convection models, it is argued here that the mantle temperature on Venus is currently increasing. This heating will reduce the heat flux out of the core to zero over 1 b.y., halting core convection and magnetic field generation. If plate tectonics was operating on Venus prior to ca. 0.5 Ga, a magnetic field may also have existed. On Earth, the geodynamo may be a consequence of plate tectonics; this connection between near-surface processes and core magnetism may also be relevant to the generation of magnetic fields on Mars, Mercury, and Ganymede.
The New Solar System, 4th Edition by J. Beatth, C. Peterson, A Chaikin
As Voyager approached Uranus in January 1986, we wondered if our experiences with symmetric magnetic environments of Earth, Jupiter, and Saturn would true for a planet that is quite literally spinning on its side. (My comment in relationship to Uranus’ orbit about the sun.)
An empirical relationship that relates angular momentum and magnetic moments, the “Bode’s law” of planetary magnetism, suggested that the magnetic moment of Uranus would be about one-tenth of Saturn.
We knew that the rotational axis of Uranus would lie, in early 1986, within 8 degrees of the planet-Sun line. If Uranus’s magnetic and rotational axis were nearly parallel, as is the case for other magnetized planets, (my comment in planets in the solar system), one pole would be pointed almost directly at the Sun and the a very unusual magnetospheric shape would be expected.
The planet’s magnetic moment is nearly the same strength as that predicted, but orientation is very different from our expectations. Uranus’ magnetic axis is tilted at huge 59 degrees from Uranus’s rotational axis and offset from the planet’s center.
Figure 18
The magnetic fields of Uranus and Neptune are remarkably – and unexpectedly – alike. The large offset from centre means that the field strength … It also means that the fields source cannot lie in the cores but rather must in a turbulent liquid mantle where dynamo driving convection can be substained.
Can the Earth’s Dynamo Run on Heat Alone?
Is the geodynamo process intrinsically unstable?
Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal' state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30,000 to 100,000 kyr; it may not therefore be as stable as we thought.
Recent studies suggest that the Earth's magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the field from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998). One of us (Gubbins 1999) has suggested that this is evidence of a rapid natural timescale (500 yr) in the outer core, and that the magnetic field is usually prevented from reversing completely by the longer diffusion time of the inner core (2 to 5 kyr). This raises a number of important but difficult questions for geodynamo theory. How can the geomagnetic field change so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geodynamo process intrinsically unstable?
A magnetosphere is an invisible magnetic field that surrounds a planet and protects it from harmful solar winds and radiation.
A planet's magnetosphere is formed by the rotation and convection of its liquid iron core. This creates a magnetic field that extends into space and forms a protective shield around the planet.
No, the size and strength of a planet's magnetosphere can vary greatly. Factors such as the size and composition of the planet, as well as its distance from the sun, can affect the size of its magnetosphere.
No, not all planets have magnetospheres. Smaller bodies like asteroids and comets do not have enough internal heat or liquid metal to generate a magnetic field. However, all of the planets in our solar system have magnetospheres.
A planet's magnetosphere plays a crucial role in protecting its atmosphere and surface from the harsh solar winds and radiation. Without a strong magnetosphere, a planet's atmosphere can be stripped away, making it less hospitable for life as we know it.