211
Planetary
Atmospheres
up to the escape energy of 2 eV, i. e., the hot oxygen Martian corona is formed
[Gröller et al. 2012; Krauss et al., 2012]. The transfer of energy from hot oxygen
atoms to thermal hydrogen atoms creates an additional nonthermal flux of atom‑
ic hydrogen escaping from the Martian atmosphere [Shematovich 2013].
The escape of hot O and C atoms from the present
Martian atmosphere during
low and high solar activity conditions has been studied with a Monte-Carlo mod‑
el. The results yield a total loss rate of hot oxygen of 2.3–2.9×10
25
s
‑1
. The total
loss rates of carbon are found to be 0.8 and 3.2×10
24
s
‑1
for low and high solar
activity, respectively. Depending on solar activity, the obtained carbon loss rates
are up to ~40 times higher than the CO
2
+
ion loss rate inferred from ASPERA-3/
Mars Express observations. Finally, collisional effects above the exobase reduce
the escape rates by about 20–30% with respect to a collisionless exosphere
[Gröller et al. 2014].
The effect of the weak magnetic field on the escape processes from Mars and
Venus is considered. The solar wind helium may be a significant source of neutral
helium in the Martian atmosphere. The precipitating particles also transfer mass,
energy, and momentum. To investigate the transport of He
2+
in the upper atmos‑
phere of Mars, the direct simulation Monte Carlo method to solve the kinetic
equation was applied. The calculated upward fluxes of He, He
+
, and He
2+
fluxes
are compared to ASPERA-3/Mars Express measurements. If the induced mag‑
netic field is ignored the precipitating He
2+
ions are not backscattered by the
Martian upper atmosphere. An assumed 20 nT horizontal magnetic field, a typi‑
cal field measured by Mars Global Surveyor results in 30%-40% of the energy
flux being backscattered. The induced magnetic field plays therefore a crucial
role in the transport of charged particles in the
upper atmosphere of Mars and
determines the energy deposition of the solar wind [Shematovich et al., 2013].
Isolated events of proton and alpha particle precipitation in the Venusian at‑
mosphere were recorded with the use of the ASPERA-4/Venus Express space‑
craft. Using a Monte Carlo simulation method for calculation of proton and alpha
particle precipitations in the Venusian atmosphere, reflected and upward particle
fluxes have been found. Only a vanishing fraction of protons and alpha particles
are backscattered to the Venusian exosphere when neglecting the induced mag‑
netic field and under conditions of low solar activity. Accounting for the induced
field drastically changes the situation: the backscattered by the atmosphere en‑
ergy fluxes increase up to 44% for the horizontal magnetic field B = 20 nT,
measured for Venus, for the case of precipitating protons, and up to 64%, for
alpha particles. The reflected energy fluxes increase to about 100% for both
protons and alpha particles as the field grows to 40 nT, i. e., the atmosphere is
protected against penetration of solar wind particles [Shematovich et al., 2014].
A number of other studies dedicated to dissipation of
planetary atmospheres,
including in-depth consideration of hydrodynamic escape were conducted
212
O. I. Korablev
[Lammer et al., 2011, 2012ab; Erkaev et al., 2013, 2014, 2015; Kislyakova et al.,
2013; Schaufelberger et al., 2012; Shematovich et al., 2014]
5.3. Other Issues on Comparative Studies
Actual state and perspectives of the observations of the planetary atmos‑
pheres in the ultraviolet range of wavelengths are discussed. The following hot
problems of the planetary astronomy in the UV wavelength range are formu‑
lated: (i) UV observations of hot coronas of the terrestrial planets; (ii) forma‑
tion and morphology of the rarefied H
2
O
‑
, O
2‑
and O‑dominant
atmospheres of
the icy satellites in the giant planet systems; formation and evolution of the
neutral gas clouds in the giant planet systems; (iii) studies of the extended
hydrogen coronae of the transit-exoplanets formed due to the stellar UV and
plasma wind forcing. The mathematical models such as the Monte Carlo mod‑
el for the electron, proton, and heavy-ion precipitation into the planetary at‑
mospheres were also discussed. Such models are currently used to calculate
the excitation rates of the atmospheric UV emissions and will be used for the
interpretation of the expected UV observations of the planetary atmospheres
with the space observatory World Space Observatory-Ultraviolet (WSO-UV)
[Shematovich 2011].
Imaging spectrometers are highly effective instruments for investigation of
planetary atmospheres. They deliver the information on both the compositional
and the spatial distribution, allowing simultaneous study of chemistry and dy‑
namics in the atmospheres of Venus and Mars. Recent results about the O
2
(a
1
g
—
X
3
Σ
g‑
) night and day glows, obtained by VIRTIS/Venus Express and OMEGA/
Mars Express respectively, the imaging spectrometers currently in orbit around
Venus and Mars [Migliorini et al., 2011].
6. Methods and Instruments
A number of investigation related to CO
2
atmospheres were conducted. A new
version of the CO
2
spectral line database CDSD-2013 is created [Tashkun, Pere‑
valov, 2011, 2013]. Experimental and theoretical studies of high-resolution CO2
spectrum in the ranges of 1.18, 1.10 and 0.87 µm, used for modeleing of Mars
and Venus spectra is conducted. CDSD parameters are updated [Petrova et al.,
2013]. New isotopologue linelists of HD
18
O, HD
17
O and HD
16
O in the wavenum‑
ber range 5600–12600 cm
‑1
for Venus atmosphere
studies are compiled
[Lavrentieva and Voronin 2013; Lavrentieva et al., 2014, 2015]. The parameters
of methane
lines broadening by CO
2
in the range of 5550–6140 cm
‑1
are meas‑
ured [Lyulin et al., 2014]. The analysis and identification of new isotopologue