High spectral (0.27 nm) and spatial (40-60 km/pixel) resolution
HST/STIS observations obtained during the Venus Express Mission
provided the first (and only) direct and simultaneous record of the
latitude and local time distribution of Venus’ 70-80 km SO and SO2
(collectively SOx) gas density. (Jessup et al. 2015)
The HST observations show for the first time that at ~77±3 km
altitude the latitude distribution of the SO2 and SO gas species is
directly correlated; this behavior is opposite to what is expected if
the SOx balance is determined solely by photolysis.
This means Venus’ sulfur
reservoir must be abundant
enough to react with O and
actively reproduce SO2 and SO
on the same chemical time
scales; thus, Venus’ SOx balance
must involve chemical pathways
HST retrieved SO2 and SO gas densities
increase and decrease simultaneously
additional to SOx photolysis
Venus’ H2SO4 clouds reflect over 75% of incoming solar radiation and
trap heat between the clouds and the surface. Although H2SO4 is
formed from SOx photolysis products, no photochemical model has ever
replicated the observed H2SO 4 formation rate . The new HST data
provide a clear empirical constraint that must be met by combined
photochemical +microphysical models used to study Venus’ sulfur cycle
and H2SO4 formation process. Developing these new models (Jessup et al.
in preparation) should ultimately lead to an advancement in our ability to
model and interpret the relationship between Venus’ sulfur chemistry
cycle, H2SO4 cloud formation and climate evolution.
Sulfur Chemistry Cycle:
.
Jessup et al., 2015 doi:10.1016/j.icarus.2015.05.027; this work was sponsored by NASA, ESA and STScI.
Photolysis of SO2 SO, S, O
Kinetic reaction with photolysis
componentsO2, SO2, SO3
H2SO4 is formed from kinetic
reaction of SO3+H2SO4
Venus’ H2SO4 formation cannot be
understood independent of the
sulfur chemistry cycle
altitude, km
Incoming Solar Radiation
Strongly Reflected
80
H2SO4 Clouds T=250 K
50
0
Lower Atmosphere T= 400 K
Near Surface T= 735 K