Solar Wind-Induced Atmospheric Erosion at Mars: First Results from ASPERA-3 on Mars Express

Abstract

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on board the Mars Express spacecraft found that solar wind plasma and accelerated ionospheric ions may be observed all the way down to the Mars Express pericenter of 270 kilometers above the dayside planetary surface. This is very deep in the ionosphere, implying direct exposure of the martian topside atmosphere to solar wind plasma forcing. The low-altitude penetration of solar wind plasma and the energization of ionospheric plasma may be due to solar wind irregularities or perturbations, to magnetic anomalies at Mars, or both.

Why an intrinsic magnetic field does not protect a planet against atmospheric escape

“…1b), an induced magnetosphere is formed (Russell 1993). Its outer boundary is called the induced magnetosphere boundary (IMB; Lundin et al 2004). The ionospheres of the unmagnetised planets are not magnetically connected to the solar wind, but the IMB is located closer to the planet than the magnetopause is to a magnetised planet.…”

“…The results are applied to the terrestrial planets, computing escape rates for hypothetical Venus-like, Earth-like, and Marslike planets that have the atmospheric properties these planets have today. Venus, Earth, and Mars are all rocky planets with atmospheres for which satellite-based measurements of atmospheric escape are available (e.g., Barabash et al 2007;Strangeway et al 2005;Lundin et al 2004). For present-day conditions, the escape rates we arrive at in this work are about 0.5 kg s −1 for Venus, 1.4 kg s −1 for Earth, and between 0.7 kg s −1 and 2.1 kg s −1 for Mars (Fig.…”

First ENA observations at Mars: ENA emissions from the martian upper atmosphere

“…The generated hydro-gen ENAs (solar wind ENAs) have the same energy as the solar wind protons. They can penetrate below the plasma boundary called the Induced Magnetosphere Boundary (IMB, see Lundin et al (2004)). When these solar wind ENAs reach the exobase, they experience elastic and inelastic collisions [Kallio and Barabash (2000)], and some of them are scattered back.…”

Modeling of Venus, Mars, and Titan

“…3(b) and 3(d)). Hybrid models also simulate the deposition of energy into the Martian atmosphere by precipitating solar wind plasma (Brecht 1997;Kallio and Janhunen 2001;Boesswetter et al 2004;Modolo et al 2005) as is evident in Mars Express observations (Lundin et al 2004;Dubinin et al 2006).…”

“…In addition, closer to the planet, a region of strong total magnetic field, reaching about 30 nT, is also shown (Fig. 3(a)) and corresponds to the Magnetic Pile-up Boundary (Bertucci et al 2003) or Induced Magnetospheric Boundary (Lundin et al 2004). The so-called Ion Composition Boundary (ICB), instead, indicates the transition from a region governed by solar wind plasma (Fig.…”