Ulysses Status Report - October 2003
Regarding the possible extension of spacecraft operations beyond September 2004, positiverecommendations have been given by the Solar System Working Group at its meeting on 23 April, and by the NASA Sun-Earth Connections (SEC) Senior Review Panel in its final report issued on 5 August. The SSWG in its recommendation noted that the scientific case for a further extension was strong; the Senior Review Panel recommended that Ulysses should be funded through its return to the north solar pole in 2008.
On 5 November, Ulysses will be at a radial distance of 5.23 AU from the Sun, and heliographic latitude 5.5° north of the solar equator, on its way to aphelion.
Operations and Archive
All science operations during the reporting period have been nominal. The ESA Ulysses archive Information regarding the data archive may be obtained from the Ulysses Data System Coordinator, Dr. C. Tranquille (Cecil.Tranquilleesa.int).
Interstellar dust, which enters the heliosphere with the same velocity as neutral interstellar gas, was detected first by Ulysses. The incoming flux is expected to remain constant but, once inside the heliosphere, the dust particles are subject to forces exerted by the sun's gravitational field, solar radiation pressure and, since the dust is electrically charged, the heliospheric magnetic field (HMF). Gravity and radiation pressure affect the more massive grains, but the motion of low-mass interstellar dust is dominated by the magnetic force.
Theory indicates that changes in the HMF causes a solar cycle variation in the dust distribution. The dust is deflected toward higher latitudes (defocused) when the polar cap field is outward in the north hemisphere and the dust is deflected equator-ward (focused), when the north polarity is inward. The modulation also depends on the inclination of the HCS. Recent measurements by the DUST experiment on board Ulysses have confirmed that the flux does indeed change significantly with the solar cycle. In 1996, near minimum, the interstellar grains began a slow decrease that continued until near maximum (2000) when the flux levelled off and began to increase. The Ulysses DUST team has developed a model that includes changes in the field polarity and the inclination of the solar dipole, and which reproduces the observations and allows an estimate to be made of the relative contribution of grains of different masses. The model predicts a steady increase in the flux of interstellar dust in the inner heliosphere to occur as a result of the recent reversal of the Sun's magnetic polarity.