Tracking a solar eruption through the Solar System
Date: 15 August 2017
Copyright: ESA
Animation visualising the propagation of a coronal mass ejection leaving the Sun on 14 October 2014 and highlighting the speed at which it reached various spacecraft over the following days, weeks and months (not to scale).
The spacecraft detected various properties of the coronal mass ejection, between them including images, an enhancement of the magnetic field strength, increases in the solar wind speed, and decreases in the influx of the galactic cosmic rays.
In the inner Solar System data was collected ESA's Venus Express and by NASA's Stereo-A, at Mars by ESA's Mars Express, NASA's Mars Odyssey and Maven orbiters and its Curiosity rover, and at Comet 67P/Churyumov–Gerasimenko by Rosetta. In the outer Solar System, the NASA/ESA/ASI Cassini spacecraft felt the effects, and although inconclusive, hints of the CME were also seen at NASA's New Horizons and Voyager-2.
The speed of the CME leaving the Sun was estimated to be around a maximum of 1000 km/s. The effects were felt at Venus Express (inferred from housekeeping data) in the morning of 16 October, and at Stereo-A in the evening. The next day, it arrived at Mars, with the speed measured by the Energetic Neutral Atoms Analyser (ASPERA-3) on Mars Express. The decrease in speed was slightly lower at the Mars side as the CME was riding on a high-speed solar wind stream, compared with a quicker decrease on the Venus side. At Rosetta the speed was derived from the analysis of ion counts recorded by the Ion Composition Analyser of the Rosetta Plasma Consortium package. At Saturn, the speed could not be measured directly, but rather the 500 km/s is estimated from modelling. The speed at New Horizons corresponds to solar wind speeds observed in a window around the estimated arrival time.