•! •! •! •! - •!

2 5 10

1962 1973

1 16

1961 1983

1978

1 2

1984

1989

2003

Discovery of the high temperature of Venus

•! There have been apparently contradictory observations: –! The brightness temperatures of Venus as seen from the Earth at infrared

wavelengths (8-13 µm) are between 234 and 240K. –! In 1956, centimeter wavelength radio emission from Venus was detected

with the 50-ft reflector of the Naval Research Laboratory. The derived brightness temperature of the integrated disk of Venus was approximately 600°K.

Infrared spectra of Venus taken by Venera 15 (Zasova et al., 1999)

Sagan (1960)

Marov (1978)

Venera-4 Descent Module (1967)

Downward solar flux

Marov (1978)

Radiative-convective equilibrium temperature profile

Pollack et al. (1980)

•! Solar energy flux reaching the Venus surface (17W/m2) is much less than that of the Earth (168W/m2).

•! Greenhouse effect of massive CO2 and small amount of H2O explains the high temperature.

cloud

Marov (1978)

D/H ratio measurement by Pioneer Venus neutral mass spectrometer

Venus : D/H = 0.016

Earth : D/H = 0.00015

Donahue (1982)

Pioneer Venus

!!!

!

Polarization of sunlight reflected by Venus

Refractive index = 1.44 !consistent with H2SO4-H2O

solution Effective radius ~ 1 µm

Hansen & Hovenier (1974)

Microphysical properties •! H2SO4-H2O droplets with radii r < 5 µm •! Smallest mode (including sub-cloud haze) might be

condensation nuclei whose composition is unknown. •! Size distribution is variable.

Pioneer Venus LCPS (54 km)

0.1 1 10 Diameter (µm)

Mode 1 Mode 2

Mode 3

Venera-13 Lander

Cl ? S ? P ?

Small particles (r ~ 1 µm)

Large particles (r ~ 4 µm)

Vertical structure of Venus cloud

Sulfur-rich atmosphere: origin of H2SO4 ?

Bertaux et al. (1996)

SO2 measurements by Vega landers

Ground-based observations of cloud-related gaseous species

Pollack et al., Icarus 103, 1, 1993

Retrieved vertical profiles

Pollack et al., Icarus 103, 1, 1993

60km

!

!!

H2SO4 vapor profiles

Equator by Mariner 10

0 5 (ppm) 0 5 10 15 (ppm)

40 km

50 km

67oN by Magellan

by Pioneer Venus

50 km

40 km

Equator

High lat.

Jenkins & Steffes (1991) Kolodner & Steffes (1998)

•! 48 58km

•! 58 70km

•! 48 58km

(dT/dz) !d

Baker et al.(1999)

cloud

SO2, H2O

Earth’s stratospheric aerosol lifecycle

Hamill et al. (1997)

•! CO2

SO2

•! 0.8

•! Venus Express >90 km SO, SO2

!"#$%&'(&#)*&+,-.,/ 01))2&'(&#)*&+,--3/

45,

665,

SO, SO2 profiles above cloud observed by Venus Express solar occultations (Belyaev et al. 2011)

•! Enhancement at high altitudes cannot be explained by traditional photochemical models.

SO: black SO2: blue

Artificial H2SO4 source added above 90 km:(Zhang et al. 2012)

Transport of cloud particles to the upper atmosphere by winds ? ! Open question

Pioneer Venus (365 nm)

•! <320nm SO2

•! >320nm

Crisp (1986)Ekonomov et al. (1984)

UV absorption coefficient based on Venera probe measurements

•! Is lightening in a dry atmosphere possible ?

Radio wave generation by lightning discharges ?

Russell et al. (2008)

•! CO2 •!

-

CaSiO3 + CO2 "! CaCO3 + SiO2

( 1998)

(Hashimoto & Abe, 2005

Variability of SO2 above cloudsBelyaev et al. (2008)

Volcanic eruptions ? Change of atmospheric dynamics ?

Massive eruptions several hundred million years ago ?

Wrinkle ridges may have been formed by thermal stress caused by a sporadic enhancement of greenhouse effect (H2O?) in the past.

Radar image of Venus surface by NASA’s Magellan spacecraft

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(Kouyama et al. 2013)