While we track CMEs with a number of instruments, the sheer size of the solar system means that our observations are limited, and usually taken from a distance. However, scientists have recently used data from ten NASA and ESA spacecraft in the direct path of a CME to piece together an unprecedented portrait of how these solar storms move through space – in particular, narrowing down the changes in speed that happen as CMEs travel through the solar system beyond Earth's orbit.
On Oct. 14, 2014, a CME left the Sun, as measured by spacecraft that watch for CMEs from afar using an instrument called a coronagraph. From there, the CME washed over spacecraft throughout the inner solar system – including by Curiosity on Mars, near comet 67P/Churyumov-Gerasimenko, and out to Saturn. This wealth of data is a boon for scientists working on space science simulations. At NASA’s Goddard Space Flight Center in Greenbelt, Maryland, scientists work to validate, host, and improve such simulations, and this new information provides the most comprehensive look to date at how the speed of a CME evolves over time.
CMEs like this are common, especially when the Sun is in an active phase, as it was in 2014. This particular CME first caught scientists’ interest because of its interference with another set of observations: the interaction between Comet Siding Spring and the Martian atmosphere.
After scientists realized that comet 67P – and therefore ESA’s Rosetta spacecraft, then orbiting the comet – was lined up to be right in the path of the CME, too, they began hunting for other observations.
This added up to seven direct, confirmed detections of the CME. ESA’s Venus Express also measured the CME indirectly, and two additional NASA spacecraft had probable detections of the CME as well – a few months and then over a year after it burst from the Sun. New Horizons on its way to Pluto very likely observed this same CME in January 2015, and Voyager 2 on the edge of the heliosphere may have observed it in March 2016. But because of Voyager 2’s great distance from the Sun and New Horizon’s lack of a magnetometer – an instrument that measures magnetic fields – it’s not possible to say for certain if the particle changes detected by those spacecraft were caused by this particular CME.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0