Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/JPLNEWS1/0457.PR

Text File | 1993-04-21 | 6KB | 110 lines

OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.  TELEPHONE [phone]

FOR RELEASE:  AM's, Sunday, October 8, 1967

            MARINER V TO PROBE VENUS ATMOSPHERE, HEAT
          PASADENA, California--Venus, the cloud-shrouded mystery
planet, may yield some of her secrets in mid-October to Mariner V
experimenters at Caltech's Jet Propulsion Laboratory and several
allied installations.
          Scientists and engineers involved in the Mariner Venus
Project of the National Aeronautics and Space Administration hope
instruments aboard the spacecraft will record more exact data on
the sister planet's atmosphere, ionosphere, temperatures and per-
haps even surface qualities.  Several of the project's seven plan-
ned experiments have been specially designed to probe Venus close-up.
          To measure the density of the Venusian atmosphere an
S-band radio occultation experiment will be performed by a group
of scientists headed by Dr. Arvydas Kliore of JPL.
          They will study changes in the Mariner's radio signal
before and after the spacecraft passes behind the planet.  Mariner
V is scheduled to fly within 2,500 miles of Venus on October 19.
The occultation experiment is similar to one performed by Mariner
IV in its 1964-5 flight past Mars.
          In the case of Mars, the occultation (radio-signal
disruption) studies showed the Martian atmosphere to be only one-
tenth as thick as previously assumed.
          Since then, radar-beam experiments conducted at JPL's
Goldstone, California, tracking station indicate that Venus' sur-

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face is not smooth and may have similar promontories and
depressions.
          With extreme luck, the close-in measurements of the
Venus atmospheric density might be used to determine something
about the planet's surface.  However, the expected high density of
the Venus atmosphere--probably 40 miles deep beneath the opaque
cloud tops--may nullify efforts to make such deductions on this
flight.
          Dr. Kliore believes, though, that if the cloud mixture
is uniform, it may be possible to learn the composition, pressure,
density and lower elevation temperatures of the atmosphere.  At
least, his group hopes to obtain basic data for a density-altitude
profile of the Venusian atmosphere and ionosphere.
          The Venus atmosphere has been estimated at up to 8,000
miles high, with a pressure perhaps five to several hundred times
heavier than Earth's atmosphere.
          Temperature and components of the planet's upper
atmosphere could be determined by another experiment using three
ultraviolet photometers.  These instruments are designed
specifically to detect hydrogen and oxygen atoms.
          A scientific team led by Dr. Charles A. Barth of the
University of Colorado will conduct this test.  By measuring the
amount of ultraviolet light radiated by the upper atmosphere,
these photometers should supply information on atmospheric
components from several thousand miles altitude down to the top
of the clouds.

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          Carbon dioxide, nitrogen, neon, helium and perhaps
argon are believed present in the Venus atmosphere.  The chances
of finding hydrogen and oxygen are rated good.
          From the 1962 flight of Mariner II, scientists
calculated Venus cloud-top temperatures at from -30 to -70
degrees Fahrenheit.  At the base of the cloud layer, heat may be
higher than 200 degrees.  Temperatures on the planet's surface
were estimated as high as 800 degrees.  However, these readings
were obtained from a spacecraft which flew no closer than within
21,600 miles of Venus.
          A dual-frequency radio occulations experiment to study
the planet's ionosphere will be conducted by Prof. Von R. Eshleman
at Stanford University.  Signals of two different frequencies will
be beamed from the 150-foot diameter antenna at Palo Alto, Cali-
fornia.  The effect of both the Venus ionosphere and atmosphere
on the signals received by Mariner then will be studied.  The
changes observed could reveal the altitude, thickness and day-
night variation of the ionosphere, the electrified layer high in
the planet's atmosphere.
          Dr. John D. Anderson of JPL will compare the NASA-JPL
Deep Space Network tracking data with that of the 1962 Mariner
mission to refine the estimated masses of Venus and the Moon and
to determine more accurate orbits for Earth and Venus.
          Throughout the flight, the network will receive data
indicating very precisely the position of the spacecraft relative
to the Earth, and in October it will observe the change of path
caused by Venus' attraction.

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          Venus, roughly 95 percent the size of Earth, has a mass
about 82 per cent of ours.  Its distance at Mariner V encounter
on October 19 will be 49.5 million miles.
          In sum, the scientific findings of Mariner V could
contribute some leading answers--not final, of course, but
helpful--to the interesting questions:
          How much is our sister planet really like Earth?
          What chance is there of finding life on Venus via robot
landers?
          And, ultimately, would there be any point in sending a
manned spacecraft to Venus in the distant future?

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