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1993-04-21
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OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA. TELEPHONE 354-5011
FOR RELEASE AUGUST 22, 1968
PASADENA, Calif. -- The surface air pressure on the
planet Venus may be 75 or 100 times that on Earth--or four to five
times greater than the Venus pressure reported recently by Soviet
scientists--Jet Propulsion Laboratory researchers have revealed.
Dr. Arvydas J. Kliore and Dan L. Cain concluded in an
article for the Journal of Atmospheric Sciences that the Russian
Venera IV spacecraft either landed on a 15-mile-high Venusian
peak undetected by ground radar or stopped transmitting before it
reached the planet's solid surface.
Venera IV and the American spacecraft, Mariner V,
arrived at Venus one day apart last year after four-month flights
from Earth. The Russians reported a parachute landing on the
planet on October 18, 1967, 24 hours before Mariner V completed
its fly-by mission by crossing the Venus orbit at an altitude of
2540 miles.
The Soviet observations indicated a range of pressures
at Venus' surface from 17 to 20 times that on Earth's surface and
a maximum temperature of 520 degrees Fahrenheit.
Dr. Kliore was principal investigator and Cain a co-
investigator for the S-Band Occultation Experiment, one of seven
science experiments conducted by the National Aeronautics and
Space Administration's Mariner V spacecraft.
Precise radio tracking of Mariner V, the authors said,
enabled calculation of the position of the spacecraft's radio
-2-
beam, relative to the center of Venus, with an uncertainty of
about 200 yards at the point of closest approach.
The resulting Mariner profiles of temperature and
pressure, when superimposed with the data of the Russian Venera
IV, indicate that the Soviet probe penetrated to a radial distance
of about 3774 miles from the center of Venus. The Russians have
taken this point to be the surface of the planet.
The distance, however, is at variance with recent
Earth-based planetary radar studies. Analyses of data from four
powerful radar instruments in the United States and Puerto Rico
yielded a Venus radius of 3759 miles.
If the radar data is accurate, Venera IV made its final
measurements at an altitude of about 15 miles and reported
conditions far less extreme than those actually existing on the
surface.
Using the radar-determined radius as the solid surface
of Venus, the Venera IV measurements closely fit both the
pressure and temperature profiles expected at that altitude when
Mariner V data is projected to the surface. Venus surface
pressure, then, appears to be more than 75 Earth atmospheres and
surface temperature greater than 900 degrees F.
This is consistent also with temperature estimates
derived from passive radio astronomy and with the results of the
radiometer experiment conducted by Mariner II in 1962 when the
Venus surface temperture was found to be a surprisingly high 800
degrees F.
-3-
A pressure 75 times that of the Earth's atmosphere is
equivalent to the pressure experienced at an ocean depth of 2550
feet. The 900-degree temperature estimate exceeds the heat
required to melt lead and zinc.
The Kliore/Cain article appears in the current issue of
the Journal of Atmospheric Sciences, a publication of the American
Meteorological Society. The special issue, devoted entirely to
the Venusian atmosphere, contains reports from American and Soviet
authors and includes the Mariner V and Venera IV observations as
well as the radar and radio astronomy readings.
###
485-8/16/68