Interstellar Dust Measured In Situ by Ulysses

Impacts of interstellar dust (ISD) grains on the Ulysses spacecraft allowed for the first successful in situ measurement of ISD (Grün et al. 1993).

Long-term measurements of ISD with Ulysses and comparisons with numerical simulations (Landgraf 1998; Sterken et al. 2015) have since revealed previously unknown details of ISD. For example, Krüger et al. (2015) have analysed the ISD mass distribution in the Solar System and inferred the gas-to-dust mass ratio in the local interstellar medium (LISM), while Strub et al. (2015) have investigated the ISD time-variability due to the solar magnetic cycle and observed a change in the ISD flow direction in 2005–2006.

Ulysses’ orbit was highly inclined with respect to the Solar System’s ecliptic plane (Wenzel et al. 1992), in which interplanetary dust particles (IDPs) are predominant (e.g. Grün et al. 1997).

The spacecraft’s orbital plane was oriented almost perpendicular to the inflow direction of ISD. Because zodiacal dust predominantly moves on prograde orbits, it can be easily distinguished from ISD during the majority of Ulysses’ orbit. Only close to the spacecraft’s perihelion did the direction of motion of ISD coincide with the direction of motion of particles on prograde orbits (Strub et al. 2015).

Interstellar dust measured in situ by Ulysses: New aspects of the particle size distribution and its modulation by the heliosheath, Astronomy & Astrophysics (open access)

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