Abstract
AbstractThis paper is a phenomenological description of multispacecraft observations of energetic particles caused by the close flyby of comet C/2013 A1 Siding Spring with Mars on 19 October 2014. This is the first time that cometary energetic particles have been observed at Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN)‐solar energetic particle (SEP) and the Mars Odyssey‐High Energy Neutron Detector (HEND) instruments recorded evidence of precipitating particles, which are likely O+ pickup ions, during the ~10 hr that Mars was within the region of the comet's coma. O+ pickup ions were also detected several hours after, although whether their origin is the comet or space weather is not conclusive. We discuss the possible origin of those particles and also the cause of an additional shower of energetic particles that HEND observed between 22 and 35 hr after the comet's closest approach, which may be related to dust impacts from the comet's dust tail. An O+ pickup ion energy flux simulation is performed with representative solar wind and cometary conditions, together with a simulation of their energy deposition profile in the atmosphere of Mars. Results indicate that the O+ pickup ion fluxes observed by SEP were deposited in the ionosphere around 105 to 120 km altitude, and they are compared with precomet flyby estimations of cometary pickup ions. The comet's flyby deposited a significant fluence of energetic particles into Mars' upper atmosphere, at a similar level to a large space weather event.
Highlights
IntroductionPlain Language Summary Comet Siding Spring is a comet from the Oort cloud (a spherical shell of cometary bodies far beyond the solar system) that made a single flyby through the inner solar system in October 2014
Plain Language Summary Comet Siding Spring is a comet from the Oort cloud that made a single flyby through the inner solar system in October 2014
The dust activity of the coma was monitored for a year by Opitom et al (2016) and Li et al (2016) from telescopes observations, there are no current estimates of the actual amount of dust deposited into the Martian atmosphere
Summary
Plain Language Summary Comet Siding Spring is a comet from the Oort cloud (a spherical shell of cometary bodies far beyond the solar system) that made a single flyby through the inner solar system in October 2014. We analyze data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and the Mars Odyssey missions in order to understand how the Martian atmosphere reacts to such an unusual external event This is done through the study of energetic particles from the comet. As a close encounter of this type with Mars is predicted to occur only once in 100,000 years, this is likely the only opportunity for measurements associated with planetary/cometary encounters This unique event enables us to investigate the response of the Martian plasma system, as this may have implications for overall atmospheric evolution. The main goal of this work is to gain more knowledge about the energetic particle showers that rained over Mars during the comet Siding Spring flyby with the objective of determining the nature of the complex interaction between the solar wind during a highly active space weather interval, the comet, and Mars’ upper atmosphere. We define energetic particles as charged particles and photons with energy in the range of kiloelectron volts up to ~2 MeV
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