Magnetosphere of Jupiter By 1973 the magnetic moment was known within a factor of two, whereas the tilt was correctly estimated at about 10°. The modulation of Jupiter's DAM by Io (the so-called Io-DAM) was discovered in 1964, and allowed Jupiter's rotation period to be precisely determined. The definitive discovery of the Jovian magnetic field occurred in December 1973, when the Pioneer 10 spacecraft flew near the planet. 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
James Webb Space Telescope (or about $1 billion in 2006 constant dollars), but by the time it was sent into orbit in 1990, the cost was about four times that. In addition new instruments and servicing missions increased the cost to at least $9 billion by 2006. In contrast to other proposed observatories, most of which have already been canceled or put on hold, including Terrestrial Planet Finder (2011), Space Interferometry Mission (2010), International X-ray Observatory (2011), MAXIM (Microarcsecond X-ray Imaging Mission), SAFIR (Single Aperture Far-Infrared Observatory), SUVO (Space Ultraviolet-Visible Observatory), and the SPECS (Submillimeter Probe of the Evolution of Cosmic Structure), the JWST