Mars is an unmagnetized planet with a thin layer of atmosphere compared to Earth. Due to the precipitation of energetic solar charged particles (mostly electrons) and the absorption of incoming solar radiation (EUV and X-rays), the neutral atmosphere of Mars becomes partially ionized forming the dayside ionosphere composed of ions and free electrons (Krasnopolsky, 2002;Němec et al., 2010). The dayside ionosphere is photochemically controlled below the exobase (about 220 km) (Mendillo et al., 2017). On the other hand, the nightside ionosphere is formed-apart from the impact ionization by precipitating energetic particles-due to the plasma transport from the dayside (

The raw exospheric composition data of Mars for the period September 2014 to October 2015 has been retrieved and analysed using the observations carried out by Mars Exospheric Neutral Composition Analyser (MENCA) payload on-board the Mars Orbiter Mission (MOM) launched by India on 5 November 2013. The state parameters viz. latitude, longitude, altitude and solar zenith angle coverage of the partial pressures of different exospheric constituents are determined and assigned to enrich the usefulness of data with orbit-wise assimilation particularly between 250 and 500 km altitude range of main interest. Apart from getting the results on mean individual orbits' partial pressure profiles during the northern winter, the variations of total as well as partial pressures are also studied with respect to the distribution of major atmospheric constituents and their dependence on solar activity. In particular, CO 2 and O variations are considered together for any differential effects due to photo-dissociation and photo-ionisation. The results on gradual reduction in densities due to the decreasing daily mean sunspot numbers and strong response of CO 2 and O pressures to solar energetic particle events like that of 24 December 2014 following a solar flare were discussed in this paper.

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Solar flares (SFs) are sudden brightening observed over the Sun's surface which is associated with a large energy release. Flares with burst of X-ray emission are normally followed by a mass ejection of electrons and ions from the solar atmosphere called Coronal Mass Ejections (CMEs). There is an evidence that solar magnetic field can change its configuration through reconnection and release energy, accelerating solar plasma causing SFs and CMEs. This study examines the SFs/CMEs data from SOHO and GOES satellites during the very low solar activity year of 2009 and moderately high solar activity of 2002.The results indicate that certain modifications in the existing mechanisms of generating SFs/CMEs would be necessary for developing more realistic forecast models affecting the space weather conditions.

<p>The Martian ionosphere, modulated by the solar wind from the topside and by remnant crustal magnetic fields close to the surface, possess unique structures different from Earth and Venus. Integrated observations by the plasma and magnetic field instruments onboard the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft show clear evidence of ionospheric plasma depletions, independent of seasonal variations at Mars. During such depletions, the plasma density of all ionospheric ion species is reduced by up to an order of magnitude and, at the same time, the electron temperature increases abruptly. An automated algorithm for the identification of such plasma depletions is developed. Altogether, as many as 580 events are identified in 8619 orbits available from October 2014 to May 2021. A statistical investigation of these events reveals that they are more prominent on the night side and occur at altitudes between 150 and 500 km. Considering the spacecraft velocity and the observed event durations, we suggest that the depletions are bubble-like structures, more elongated horizontally than vertically. A possible mechanism of their formation is discussed.</p>