Abstract
AbstractWe discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding‐Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov‐Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO‐A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110–111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
Highlights
Voyager 2 was near 111 astronomical units (AU) traveling roughly in the same direction as New Horizons, and we investigate whether the interplanetary coronal mass ejection (ICME) was observed by this spacecraft in late March 2016
If a shock is not observed at comet 67P, it could be for two reasons: the leading edge of the ICME disturbance has already interacted with the high-speed stream and no longer has a clear shock, or the possible shock at Mars was an artifact of the natural variation of the data
We have analyzed the journey of an ICME and its respective passages past STEREO-A, Mars, comet 67P, and Saturn, which were clearly identified
Summary
The study presented here was motivated by the analysis of Mars Express data acquired during the flyby of the Siding Spring comet on 19 October 2014 [e.g., Svedhem et al, 2014; Gurnett et al, 2015]. The originality of the present study resides in the good alignment of many spacecraft in the solar system with the direction of the ICME, allowing a comparison between observational data and propagation models. This gives us the opportunity to provide further insight into ICME propagation at large distances, such as the evolution of its magnetic structure or its speed profile. FDs generated by the passage of the ICME introduced above are identified at Mars, comet 67P, Saturn, and Voyager 2 Comparison of their characteristics provides valuable information on the evolution of the ICME with heliocentric distance and its interaction with the solar wind
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