Energy deposition of pickup ions and heating of Titan's atmosphere

Michael, M.; Johnson, R. E.

doi:10.1016/j.pss.2005.08.001

Cited by 53 publications

(39 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From the scaled cross sections shown in Fig. 1 heating [14]. As mentioned above, the experimental determination of the Kinetic Energy Release (KER) in the fragmentation process is needed to model the dynamics of the atmosphere heating due to the post-collisional energy transfer of the fragments to the atmosphere.…”

Section: Single Electron Loss Of Variousmentioning

confidence: 99%

Projectile electron loss in nitrogen

Santos¹,

Melo²,

Sant’Anna³

et al. 2006

Braz. J. Phys.

View full text Add to dashboard Cite

The projectile electron loss channel plays an important role in modeling several processes connected to the penetration of swift ions in gases, such as radiation damage, energy loss, upper atmosphere studies, storage lifetimes of low-charge state heavy ions, etc. In this paper we have used recent measurements of projectile electron loss of He + ions in N 2 together with previous data for higher charged ions in order to shed light on the role played by the projectile electron loss in the heating and ionization of Titans atmosphere.

show abstract

Section: Single Electron Loss Of Variousmentioning

confidence: 99%

Projectile electron loss in nitrogen

Santos¹,

Melo²,

Sant’Anna³

et al. 2006

Braz. J. Phys.

View full text Add to dashboard Cite

show abstract

“…Direct simulation Monte Carlo (DSMC) models have been used to calculate the plasma-induced heating and loss at Titan (Shematovich et al 2003;Michael & Johnson 2005;Michael et al 2005a), referred to as atmospheric sputtering. Such simulations were also used to calibrate useful analytic models of atmospheric sputtering (Johnson 1994;Johnson et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Sputtering and heating of Titan's upper atmosphere

Johnson

2008

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

Titan is an important endpoint for understanding atmospheric evolution. Prior to Cassini's arrival at Saturn, modelling based on Voyager data indicated that the hydrogen escape rate was large (1-3!10 28 amu s K1), but the escape rates for carbon and nitrogen species were relatively small (5!10 26 amu s K1) and dominated by atmospheric sputtering. Recent analysis of the structure of Titan's thermosphere and corona attained from the Ion and Neutral Mass Spectrometer and the Huygens Atmospheric Structure Instrument on Cassini have led to substantially larger estimates of the loss rate for heavy species (0.3-5!10 28 amu s K1). At the largest rate suggested, a mass that is a significant fraction of the present atmosphere would have been lost to space in 4 Gyr; hence, understanding the nature of the processes driving escape is critical. The recent estimates of neutral escape are reviewed here, with particular emphasis on plasma-induced sputtering and heating. Whereas the loss of hydrogen is clearly indicated by the altitude dependence of the H 2 density, three different one-dimensional models were used to estimate the heavy-molecule loss rate using the Cassini data for atmospheric density versus altitude. The solar heating rate and the nitrogen density profile versus altitude were used in a fluid dynamic model to extract an average net upward flux below the exobase; the diffusion of methane through nitrogen was described below the exobase using a model that allowed for outward flow; and the coronal structure above the exobase was simulated by presuming that the observed atmospheric structure was due to solar-and plasma-induced hot particle production. In the latter, it was hypothesized that hot recoils from photochemistry or plasma-ion-induced heating were required. In the other two models, the upward flow extracted is driven by heat conduction from below, which is assumed to continue to act above the nominal exobase, producing a process referred to as 'slow hydrodynamic' escape. These models and the resulting loss rates are reviewed and compared. It is pointed out that preliminary estimates of the composition of the magnetospheric plasma at Titan's orbit appear to be inconsistent with the largest loss rates suggested for the heavy species, and the mean upward flow extracted in the one-dimensional models could be consistent with atmospheric loss by other mechanisms or with transport to other regions of Titan's atmosphere.

show abstract

“…Due to the lack of an own significant intrinsic magnetic field (Backes et al 2005), Lammer et al (1998) found that atmospheric sputtering by magnetospheric ions (protons and N + ions) becomes important during this time, heating the thermosphere by an amount of about 30 K. Under such conditions, they concluded that Titan's exospheric temperature may then reach or even exceed the critical temperature, at which diffusion-limited hydrodynamic escape of hydrogen atoms becomes important. However, Michael and Johnson (2005) also investigated 7 the energy deposition of pickup ions and found, contrary to Lammer et al (1998), a much lower increase in the exospheric temperature of only about 4 to 7 K caused by energy deposition of N + . With an escape parameter of Λ H = 1.77 one obtains a Jeans escape flux of…”

mentioning

confidence: 99%

Titan’s atomic hydrogen corona

Hedelt¹,

Ito²,

Keller³

et al. 2010

Icarus

View full text Add to dashboard Cite

Based on measurements performed by the Hydrogen Deuterium Absorption Cell (HDAC) aboard the Cassini orbiter, Titan's atomic hydrogen exosphere is investigated. Data obtained during the T9 encounter are used to infer the distribution of atomic hydrogen throughout Titan's exosphere, as well as the exospheric temperature.The measurements performed during the flyby are modeled by performing Monte Carlo radiative transfer calculations of solar Lyman-α radiation, which * Corresponding author, Tel. +33 557 776 127 ACCEPTED MANUSCRIPTis resonantly scattered on atomic hydrogen in Titan's exosphere. Two different atomic hydrogen distribution models are applied to determine the best fitting density profile. One model is a static model that uses the Chamberlain formalism to calculate the distribution of atomic hydrogen throughout the exosphere, whereas the second model is a particle model, which can also be applied to non-Maxwellian velocity distributions. The density distributions provided by both models are able to fit the measurements although both models differ at the exobase: Best fitting exobase atomic hydrogen densities of n H = (1.5 ± 0.5) · 10 4 cm −3 and n H = (7 ± 1) · 10 4 cm −3 were found using the density distribution provided by both models, respectively. This is based on the fact that during the encounter, HDAC was sensitive to altitudes above about 3,000 km, hence well above the exobase at about 1,500 km. Above 3,000 km, both models produce densities which are comparable, when taking into account the measurement uncertainty.The inferred exobase density using the Chamberlain profile is a factor of about 2.6 lower than the density obtained from Voyager 1 measurements and much lower than the values inferred from current photochemical models. However, when taking into account the higher solar activity during the Voyager flyby, this is consistent with the Voyager measurements. When using the density profile provided by the particle model, the best fitting exobase density is in perfect agreement with the densities inferred by current photochemical models.Furthermore, a best fitting exospheric temperature of atomic hydrogen in the range of T H = (150 − 175) ± 25 K was obtained when assuming an isothermal exosphere for the calculations. The required exospheric temperature depends on the density distribution chosen. This result is within the temperature range determined by different instruments aboard Cassini. The inferred temperature is close to the critical temperature for atomic hydrogen, above which it can escape hydrodynamically after it diffused through the heavier background gas.

show abstract

Energy deposition of pickup ions and heating of Titan's atmosphere

Cited by 53 publications

References 24 publications

Projectile electron loss in nitrogen

Projectile electron loss in nitrogen

Sputtering and heating of Titan's upper atmosphere

Titan’s atomic hydrogen corona

Contact Info

Product

Resources

About