Tracking a solar eruption through the Solar System

Ten spacecraft, from ESA’s Venus Express to NASA’s Voyager-2, felt the effect of a solar eruption as it washed through the Solar System while three other satellites watched, providing a unique perspective on this space weather event.

Scientists working on ESA’s Mars Express, including researchers from our Department of Physics and Astronomy, were looking forward to investigating the effects of the close encounter of Comet Siding Spring on the Red Planet’s atmosphere on 19 October 2014, but instead they found what turned out to be the imprint of a solar event.

While this made the analysis of any comet-related effects far more complex than anticipated, it triggered one of the largest collaborative efforts to trace the journey of an interplanetary ‘coronal mass ejection’ – a CME – from the Sun to the far reaches of the outer Solar System.

Although Earth itself was not in the firing line, a number of Sun-watching satellites near Earth – ESA’s Proba-2, the ESA/NASA SOHO and NASA’s Solar Dynamics Observatory – had witnessed a powerful solar eruption a few days earlier, on 14 October.

NASA’s Stereo-A not only captured images of the other side of the Sun with respect to Earth, but also collected in situ information as the CME rushed passed.

Thanks to the fortuitous locations of other satellites lying in the direction of the CME’s travel, unambiguous detections were made by three Mars orbiters – ESA’s Mars Express, NASA’s Maven and Mars Odyssey – and NASA’s Curiosity Rover operating on the Red Planet’s surface, ESA’s Rosetta at Comet 67P/Churyumov–Gerasimenko, and the international Cassini mission at Saturn.

ESA image
Source: ESA; The location of various spacecraft during the Sun’s coronal mass ejection (CME) on 14 October 2014.

A number of researchers from our Department of Physics and Astronomy were involved in analysing observations made at Mercury, Mars, Comet 67P/Churyumov-Gerasimenko and Saturn, all made by many different spacecraft, which demonstrates the breadth of interest of the University’s work. 

The original observations at Mars were being studied by the Leicester team because the CME passed by that planet at the time of an encounter with another comet, Siding Spring, and the effects of the CME need to be clearly understood in order to work out how the comet interacted with Mars and its atmosphere.

Professor Mark Lester said: “When we worked out the time the CME left the Sun and tracked its passage to Mars, we realised that there may be other observations elsewhere which could help us with the study. The fortuitous alignment of planets and hence spacecraft has really helped with this study.”

This is an unusual set of circumstances, Professor Lester suggests, where the researchers have been able to track the remnants of this large explosion of plasma from the sun across the solar system.

“These Coronal Mass Ejections, as they are called, can be very disruptive at Earth where they can cause significant disturbances to space and ground technologies, while also creating large and dynamic displays of the aurora, possibly even over the UK.  Understanding their effects not only at Earth but elsewhere in the solar system is therefore really important,” he added.