Atmosphere and Water Loss from Early Mars Under Extreme Solar Wind and Extreme Ultraviolet Conditions

Abstract

The upper limits of the ion pickup and cold ion outflow loss rates from the early martian atmosphere shortly after the Sun arrived at the Zero-Age-Main-Sequence (ZAMS) were investigated. We applied a comprehensive 3-D multi-species magnetohydrodynamic (MHD) model to an early martian CO(2)-rich atmosphere, which was assumed to have been exposed to a solar XUV [X-ray and extreme ultraviolet (EUV)] flux that was 100 times higher than today and a solar wind that was about 300 times denser. We also assumed the late onset of a planetary magnetic dynamo, so that Mars had no strong intrinsic magnetic field at that early period. We found that, due to such extreme solar wind-atmosphere interaction, a strong magnetic field of about approximately 4000 nT was induced in the entire dayside ionosphere, which could efficiently protect the upper atmosphere from sputtering loss. A planetary obstacle ( approximately ionopause) was formed at an altitude of about 1000 km above the surface due to the drag force and the mass loading by newly created ions in the highly extended upper atmosphere. We obtained an O(+) loss rate by the ion pickup process, which takes place above the ionopause, of about 1.5 x 10(28) ions/s during the first < or =150 million years, which is about 10(4) times greater than today and corresponds to a water loss equivalent to a global martian ocean with a depth of approximately 8 m. Consequently, even if the magnetic protection due to the expected early martian magnetic dynamo is neglected, ion pickup and sputtering were most likely not the dominant loss processes for the planet's initial atmosphere and water inventory. However, it appears that the cold ion outflow into the martian tail, due to the transfer of momentum from the solar wind to the ionospheric plasma, could have removed a global ocean with a depth of 10-70 m during the first < or =150 million years after the Sun arrived at the ZAMS.

Variability of solar/stellar activity and magnetic field and its influence on planetary atmosphere evolution

“…Although the formation of magnetospheres and possible locations of a magnetopause are not well known for such planets, expanded atmospheres of "super-Earths" could have been subject to stellar wind erosion. However, one should note that previous studies focused either on thermal effects and escape (e.g., Tian et al, 2008aTian et al, , 2009Tian, 2009) or on non-thermal processes (e.g., Kulikov et al, 2006Kulikov et al, , 2007Terada et al, 2009;Lichtenegger et al, 2010) although both processes are strongly coupled and should not be separately studied. As illustrated in Fig.…”

Geophysical and Atmospheric Evolution of Habitable Planets

“…Ø weak magnetic protection that results in increased high energetic particle impact (Grießmeier et al, 2005(Grießmeier et al, , 2009) and Ø enhanced atmospheric erosion processes due to stellar winds and coronal mass ejection Lammer et al, 2007Lammer et al, , 2009aTerada et al, 2009).…”

“…These newly generated planetary ions are accelerated to higher altitudes and energies by the interplanetary electric field and gradually guided by the solar, or stellar, wind plasma flow around the planetary obstacle, where they can be removed from the planet (e.g., Spreiter and Stahara, 1980;Lundin et al, 1989Lundin et al, , 1990Lundin et al, , 2004Lichtenegger and Dubinin, 1998;Biernat et al, 2001;Terada et al, 2002Terada et al, , 2009Lammer et al, 2003c;Liu et al, 2009). Figure 13 shows the atmospheric erosion of a planet with the size and mass of Mars for present times (1 EUV) and 3.5 Gyr ago, where the EUV flux of a Sun-like star is about 6 times larger than at present.…”

The Sun and stars as the primary energy input in planetary atmospheres

“…Relevant processes include the loss of atmospheric constituents to space (basically molecules and H, He, C, N and O ions) and the balance with the incorporation in the Martian soil via weathering processes. Recent sophisticated studies based on 2D and 3D modeling (Lammer et al 2003a;Donahue 2004;Terada et al 2009) suggest that the loss of volatiles from Mars could amount to a global water ocean with a depth of several tens of meters. This is in agreement with the inference from the water-related features visible on the Martian surface as shown by the images of the Mars Global Surveyor (Carr & Head 2003).…”