Solar eruption ‘photobombed’ Mars encounter with Comet Siding Spring
September 21, 2017

European Planetary Science Congress 2017 Press Notice
Thursday, 21st September

Solar eruption ‘photobombed’ Mars encounter with Comet Siding Spring

When Comet C/2013 A1 (Siding Spring) passed just 140,000 kilometres from Mars on 19th October 2014, depositing a large amount of debris in the martian atmosphere, space agencies coordinated multiple spacecraft to witness the largest meteor shower in recorded history. It was a rare opportunity, as this kind of planetary event occurs only once every 100,000 years. However, scientists analysing the data have found that a very powerful Coronal Mass Ejection (CME) launched by the Sun also arrived at Mars 44 hours before the comet, creating significant disturbances in the martian upper atmosphere and complicating analysis of the data. Results describing the combined effects of the comet and the CME throughout the martian atmosphere are being presented in a special session at the European Planetary Science Congress (EPSC) 2017 in Riga on Thursday, 21st September.

Dr Beatriz Sanchez-Cano, of the University of Leicester and co-organiser of the session, explains: “Comet Siding Spring flew very close to Mars, at one third of the Earth-Moon distance. This is one of the most exciting planetary events that we’ll see in our lifetime. Mars was literally engulfed by the coma, the comet’s outer atmosphere, for several hours. However, a deeper analysis of the data shows that the comet’s interaction with Mars is much more difficult to understand than we expected because of the effects of a CME that hit Mars a few hours earlier. In addition, the encounter happened at the peak of the martian dust season. We need to understand the full context of the observations in order to separate out the real cometary effects on Mars.”

CMEs occur when magnetic field lines at the visible surface of the Sun become tangled and break, releasing large quantities of electrically charged particles into space. The interval before, during and after the Comet Siding Spring encounter with Mars was one of the most disturbed periods of the current solar cycle. The CME was launched from the largest sunspot group observed in the last 24 years and several additional solar flares were detected that would have impacted on Mars around this time.

Sanchez-Cano has investigated the interaction of the comet with energetic particles from the Sun, and the effects of the CME and cometary encounter on the martian atmosphere, using data from ESA’s Mars Express mission, NASA’s MAVEN and Mars Odyssey orbiters, and the Curiosity rover on the martian surface. Her results show clear signs of ‘showers’ of energetic oxygen ions and dust from the time that Mars was inside the coma up to 35 hours after comet’s closest approach. These ions, most likely from the comet, were accelerated by the highly active solar wind during the comet encounter and delivered into the martian atmosphere. This created an extra electrically-conducting layer (ionosphere) at a lower level than the planet’s usual ionosphere. None of those particles seem to have arrived at the martian surface as observed by the Curiosity rover, confirming that they were absorbed in the atmosphere.

Prof Mats Holmström, of the Swedish Institute of Space Physics, who will present the first results of the encounter from the Mars Express ASPERA-3 instrument, says: “Our data and modelling show that the upper layers of the martian atmosphere were disturbed by the passing comet. The precipitation from the comet was mainly water, either in the form of neutral molecules or broken down into ions through interactions with light. However, the ASPERA-3 results show that the amount of ionised water interacting with the martian atmosphere was much smaller than expected, compared to the amount of neutral water molecules and the charged particles from the solar wind. This means that there were less of the ions interacting with the upper atmosphere and more water molecules interacting at lower depths. We think that, because of the relatively large size and activity of the comet, the majority of ionised water was carried away by the solar wind rather than dropping down into Mars’s atmosphere.

Matteo Crismani, of the University of Colorado at Boulder, will present observations of the encounter from the MAVEN orbiter. These indicate that the meteor shower was the largest in recorded history, peaking at 30 meteors per second and lasting up to 3 hours. Dust grains from the comet, travelling at 200,000 kilometres per hour, entered Mars’s atmosphere with enough energy to melt and release their constituent atoms, such as magnesium and iron. Data from MAVEN’s Imaging UltraViolet Spectrograph (IUVS) enabled Crismani and colleagues to determine the composition these metallic species, how they evolved and how they moved through the martian atmosphere.


3D scenario of the encounter of comet Siding Spring with Mars, showing how different spacecraft at Mars coordinated observations. Credit: Marc Costa/European Space Agency. URL:


Still from animation showing encounter of Comet Siding Spring with Mars, showing the orientation of the comet’s tails and orbits of the spacecraft at Mars. Credit: Marc Costa/European Space Agency

An artist’s conception of the martian meteor shower due to Comet Siding Spring. The comet has passed the planet in this image, and is shown left and above the planet, heading towards the outer solar system. The planet’s atmosphere is exaggerated to highlight the presence of a coherent group of meteors due to the comet’s debris stream. Credit: Don Davis/IUVS Team

Hubble image of Comet Siding Spring before and after filtering, as captured by Wide Field Camera 3 on NASA’s Hubble Space Telescope. Credit: NASA, ESA, and J.-Y. Li (Planetary Science Institute)

Science Contacts

Dr Beatriz Sanchez-Cano
University of Leicester, UK

Prof Mats Holmström
Swedish Institute of Space Physics
Kiruna, Sweden

Matteo Crismani
University of Colorado, USA

Media Contacts

Anita Heward
EPSC 2017 Press Officer
+44 07756 034243

Livia Giacomini
EPSC 2017 Press Officer

Notes for Editors
EPSC 2017
The European Planetary Science Congress (EPSC) 2017 ( is taking place at the Radisson Blu Latvija in Riga, from Sunday 17 to Friday 22 September 2017. EPSC is the major European annual meeting on planetary science and in 2017 is hosted for the first time in the Baltic States. Around 800 scientists from Europe and around the world will attend the meeting and will give around 1,000 oral and poster presentations about the latest results on our own Solar System and planets orbiting other stars.
EPSC 2017 is organised by Europlanet and Copernicus Meetings. The Local Organising Committee is led by Baltics in Space, a not-for-profit organisation that is supporting 25 members centred around nine Baltic space facilities for the conference. The meeting is sponsored by Investment and Development Agency of Latvia, the Latvian Ministry of Education and Science, Latvijas Mobilais Telefons, Finnish Meteorological Institute, The Estonia-Latvia programme, The Representation of the European Commission in Latvia, the Planetary Science Institute, Latvijas Universitate and The Division for Planetary Sciences of the AAS.
Details of the Congress and a full schedule of EPSC 2017 scientific sessions and events can be found at the official website:

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The philosophy of the nonprofit organization, Baltics in Space, is to “Inventory, Identify, and Integrate” with a sprinkling of Inspiration to build a space product greater than the sum of its parts. The best resource in the space business is people. With an eye to strengthening the triple helix links (Industry, Education, Research), its planned outcomes are integrating Baltic-wide space events, compiling catalogs of skill-sets for prospective users and Baltic space project development with distributed teams and Baltic space education.