The Earth s magnetosphere

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1 The Earth s magnetosphere 1

2 Re-call: Earth s magnetosphere C. Russell, The solar wind interaction with the Earth s magnetosphere: Tutorial 2

3 Magnetospheres Term introduced by Thomas Gold in 1959 Not a sphere : solar wind deforms the shape of the magnetosphere Proper magnetospheres (objects with internal B) - Mercury, Earth, Jupiter, Saturn, Uranus, Neptun - magnetized moons (Ganymede) and asteroids (Gaspra?) Mercury Earth Solar wind-induced magnetospheres - Venus, Mars, comets Jupiter Venus Mars 3

4 Compare the sizes 4

5 Planetary magnetospheres 5

6 Solar system planets Terrestrial planets: Mercury Venus Earth Mars Recall: Pluto is no more a planet! Interiors of terrestrial planets are different very different magnetic fields Gas giants: Jupiter Saturn Uranus Neptune Gas giants are fast rotators (10 17 h) strong magnetic fields 6

7 IAU (International Astrophysical Union) defines (Dwarf planet: CERES, Pluto, Eris, Makemake and Haumea) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies". 7

8 Dwarf planets orbit around the Sun: Most of them are located in the Kuiper Belt (or Trans-Neptunian objects), a region of icy objects beyond the orbit of Neptune. Pluto is about 40 AU away from the Sun. Dwarf planet Ceres is in the main asteroid belt between Mars and Jupiter. Dwarf planets Pluto and Eris have thin atmospheres that expand when they come closer to the Sun and collapse as they move farther away. 8

9 Solar induced magnetospheres: - When planet lacks a magnetic field and its ionosphere separates the atmosphere from the solar wind and excludes the solar magnetic field. The solar wind interacts directly with the planetary ionosphere. Planets: Venus, Mars Comets Comets are cosmic snowballs of frozen gases, rock and dust. A comet warms up as it nears the sun and develops an atmosphere, or coma. The coma may be hundreds of thousands of kilometers in diameter. Comet C/2001 Q4 (NEAT) was taken at Kitt Peak National Observatory on 7 May

10 Ionopause = pressure balance between the solar wind dynamic pressure on the outside and the thermal pressure of the ionospheric ions and electrons on the inside. 10

11 Venus mass: kg (0.82 M E ) radius: 6051 km (0.95 R E ) orbit period: days No satellites rotates around its axis once per revolution around the Sun (243 d). No intrinsic magnetic field, but Dense, hot carbon dioxide atmosphere a dense ionosphere that interacts with the solar wind. Extreme case of the greenhouse effect Surface temperature ~500 C 11

12 Exploration of Venus Series of Mariner and Venera probes studied Venus 1960s -1980s Mariner 5, passed within 1.4 R V in 1967 solar wind of deflection around an 'obstacle' Venera 4 made magnetic measurements down to 200 km altitude, no planetary field Venera 9,10: no Earth-like magnetotail Pioneer Venus project 1978 Atmosphere and radar mapping of the surface + five probes entering the atmosphere Low altitude passes (~150 km) Venus intrinsic magnetic field < ~ 10-5 times that of Earth. Magellan Probe 1989: radar observations of the Venusian surface Venus Express, 2005: Polar orbit. Studies atmosphere, plasma environment, surface characteristics 12

13 An induced magnetosphere J Tail current is a result of the draping of the field lines always ^ B SW The ionospheric plasma forces the solar wind to flow around the planet No radiation belts, no magnetotail composed of fields of planetary origin Parts of the neutral atmosphere of Venus reach to the solar wind particles are ionized (EUV, charge-exchange) they become under the influence of E = V B solar wind picks-up these newly born ions (pick-up ions) the mass of solar wind increases (mass-loading) the flow slows down locally 13

14 Magnetosphere of Venus ASPERA-4 ionosheath 1.5 R V ionopause Few hundreds km Pressure balance between the incident solar wind dynamic pressure and ionospheric plasma pressure Currently ESA s Venus Express is making observations of Venus atmosphere and its interaction with the solar wind. One of its instruments is ASPERA-4, parts of which have been built in Finland 14

15 Escape of water V IMF B IMF O + H + Oxygen ions and protons are found to escape from the upper atmosphere of Venus in the same proportion as they exist in water H 2 O The escape takes place in the plasma wake, preferentiall in the sector which the induced electric field E = V x B points to Importance for the planets evolment? 15

16 Mars The most Earth-like planet, but smaller mass: kg (0.11 M E ) radius: 3400 km (0.53 R E ) orbit period: 24.6 days Satellites: Phobos and Deimos Thin atmosphere ionosphere not enough magnetofluid in the core to sustain a dynamo Remanent magnetism found by NASA s Mars Global Surveyor Solar wind interacts mostly with the ionosphere 16

17 Exploration of Mars Dozens of spacecraft, including orbiters, landers, and rovers, have been sent to Mars by the Soviet Union, US, Europe, and Japan Mars curse nearly 2/3 of the missions have failed First flyby by Mariner 4 in 1964 First probes to land on surface: Mars 2&3 launched in 1971 (lost contact within seconds of landing) Viking 1&2 launched 1975: orbits and Landers: mapped the surface Mars Global Surveyor, Mars Pathfinder, Phoenix Mars lander, Mars Odyssey orbited, Mars Express Orbiter (Beagle 2 lander failed descent), Mars Exploration Rovers (Spirit and Opportunity), Mars Reconnaissance Orbiter 17

18 Martian magnetosphere Bow shock: ~1.5 R M first indication of the weakness of the magnetic field: Mariner 4 flyby in 1965 (at closest approach 3.9 R M no indication of earth-like dipole field) However: shock-like disturbance in the solar wind 18

19 Martian magnetosphere Magnetic fields in the wake of Mars are determined by the interplanetary field orientation Dipole moment 10-4 the Earth s Magnetotail relatively somewhat wider than that of Venus Phobos-2 observations of solar wind Mars interaction in

20 Intrinsic magnetospheres (proper magnetospheres): Different sizes, different dynamics For the magnetized planets, those with intrinsic magnetic fields, the obstacle to the solar wind is the planetary magnetic field and the size of the magnetosphere is governed by the relative strengths of the magnetic field and the solar wind at the planet. 20

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22 The semi-theoretical shapes of some planetary bow shocks. Length scales have been normalised to the standoff nose distances R BS of the corresponding planetary bow shocks. In this representation the sizes of the planetary bodies are inverted. Jupiter shrinks to a point at the origin while the small planets Mars and Venus become grossly oversized. Mercury is not included here. 22

23 Some typical empirical values for solar wind parameters at different distances from the Sun: 23

24 Mercury The magnetic field is about 1.1% as strong as Earth s magnetic field. It is much weaker than Earth's magnetic field (about 1/100 its magnitude) according to Mariner 10 data, the magnetic field is still strong enough to deflect solar wind, inducing a magnetosphere. 24

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28 Not proven, but: recent data from the Galileo orbiter indicate that Io might have its own magnetic field. Io has an extremely thin atmosphere made up mostly of sulfur dioxide. 28

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31 Saturn A fast rotating gas giant mass: kg (95.2 ME) radius: km (9.4 RE) rot. per: 10 h 39 min dipole axis almost along rotation axis (incl. 27º) magnetic field at equator: 21 mt New moons being found: June 2006: 35 moons given names Pioneer 11, 1979: low-res images of the planet, studied the rings Voyager flybys, 1980, 1981: high-res images of Saturn, rings and satellites NASA/ESA Cassini/Huygens came to Saturn in 2004: Huygens landed on Titan on Jan 14, 2005 Cassini continues observations of the Saturnian system. 31

32 Titan Second largest moon in the solar system radius 2570 km (larger than Mercury) nitrogen atmosphere at surface p =1.5 atm Large hydrocarbon lakes Titan does not have a magnetic field It has an ionosphere that moves subsonically through the magnetic field of Saturn (a unique space plasma feature!) 32

33 Kronian magnetosphere Very simple structure Saturn s «Kronian No tilt to the rotation axis Bow shock: R S Dipole moment 580 times larger than the Earth s 33

34 Kronian radiation belts and auroras Rings and moons absorb radiation belt particles 34

35 Uranus and Neptune Uranus Rot. period 17 h 14 min Radius km Mass kg Rot. axis 97.9º Dipole axis from rotation axis 59º B at equator 23 mt Neptune Rot. period 16 h 06 min Radius km Mass kg Rot. axis 28.8º Dipole axis from rotation axis 47º B at equator 14 mt 35

36 Complicated dynamics Note the dependence on the phase of the orbit around the Sun: During the period of 83.7 years the rotation axis is Sun-aligned twice and perpendicular to the Sun-Uranus axis twice Splitting and rejoining of the plasma sheet in 8 hours (half day) 36

Solar System Fact Sheet

Solar System Fact Sheet (Source: http://solarsystem.nasa.gov; http://solarviews.com) The Solar System Categories Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Rocky or Gas Rocky Rocky Rocky Rocky