Magnetosphere of Jupiter - Exploration After 1970

Exploration After 1970

As of 2009 a total of eight spacecraft have flown around Jupiter and all have contributed to the present knowledge of the Jovian magnetosphere. The first space probe to reach Jupiter was Pioneer 10 in December 1973, which passed within 2.9 R_j from the center of the planet. Its twin Pioneer 11 visited Jupiter a year later, traveling along a highly inclined trajectory and approaching the planet as close as 1.6 R_j.

Pioneer provided the best coverage available of the inner magnetic field. The level of radiation at Jupiter was ten times more powerful than Pioneer's designers had predicted, leading to fears that the probe would not survive; however, with a few minor glitches, it managed to pass through the radiation belts, saved in large part by the fact that Jupiter's magnetosphere had "wobbled" slightly upward at that point, moving away from the spacecraft. However, Pioneer 11 did lose most images of Io, as the radiation had caused its imaging photo polarimeter to receive a number of spurious commands. The subsequent and far more technologically advanced Voyager spacecraft had to be redesigned to cope with the massive radiation levels.

Voyagers 1 and 2 arrived to Jupiter in 1979–1980 and traveled almost in its equatorial plane. Voyager 1, which passed within 5 R_j from the planet's center, was first to encounter the Io plasma torus. Voyager 2 passed within 10 R_j and discovered the current sheet in the equatorial plane. The next probe to approach Jupiter was Ulysses in 1992, which investigated the planet's polar magnetosphere.

The Galileo spacecraft, which orbited Jupiter from 1995 to 2003, provided a comprehensive coverage of Jupiter's magnetic field near the equatorial plane at distances up to 100 R_j. The regions studied included the magnetotail and the dawn and dusk sectors of the magnetosphere. While Galileo successfully survived in the harsh radiation environment of Jupiter, it still experienced a few technical problems. In particular, the spacecraft's gyroscopes often exhibited increased errors. Several times electrical arcs occurred between rotating and non-rotating parts of the spacecraft, causing it to enter safe mode, which led to total loss of the data from the 16th, 18th and 33rd orbits. The radiation also caused phase shifts in Galileo's ultra-stable quartz oscillator.

When the Cassini spacecraft flew by Jupiter in 2000, it conducted coordinated measurements with Galileo. The last spacecraft to visit Jupiter was New Horizons in 2007, which carried out a unique investigation of the Jovian magnetotail, traveling as far as 2500 R_j along its length. The coverage of Jupiter's magnetosphere remains much poorer than for Earth's magnetic field. Future missions (Juno, for instance) are important to further understand the Jovian magnetosphere's dynamics.

In 2003, NASA conducted a conceptual study called "Human Outer Planets Exploration" (HOPE) regarding the future human exploration of the outer solar system. The possibility was mooted of building a surface base on Callisto, because of the low radiation levels at the moon's distance from Jupiter and its geological stability. Callisto is the only one of Jupiter's Galilean satellites for which human exploration is feasible. The levels of ionizing radiation on Io, Europa and Ganymede are inimical to human life, and adequate protective measures have yet to be devised.