MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
Contact: Martha Heil (818) 354-0850
FOR IMMEDIATE RELEASEOctober 26, 2000
RECIPE FOR NEPTUNE REVEALED BY SCIENTISTS
What do you get if you mix together one part helium and
five-and-a-half parts hydrogen, add a dash of methane, heat to 60
Kelvins (-351 degrees F) and let sit for over four billion years?
If you made a large enough batch of these mixed gases, you might
get the planet Neptune.
One of a broad range of objectives of the European Space
Agency's Infrared Space Observatory was to observe Neptune from
1995 to 1998, to find out the ratio of hydrogen to helium, two
gases known to make up almost all of the planet's thick
atmosphere. Dr. Glenn Orton, senior research scientist at NASA's
Jet Propulsion Laboratory, Pasadena, Calif., analyzed data from
the spaceborne observatory's long wavelength spectrometer, which
measures how elements reflect or absorb long wavelengths of
light, and from the short wavelength spectrometer, which does the
same for short wavelengths of light.
Neptune seems to be generating some of its own heat, Orton
said. Data from the two spectrometers imply that Neptune is
radiating heat at about 60 Kelvins (-351 degrees Fahrenheit.)
Scientists would expect Neptune to be only about 46.6 Kelvins
(-375 degrees Fahrenheit), if its only source of heat were
sunlight. According to Orton, it can be deduced from this that
Neptune must have an internal heat source.
The long wavelength spectrometer also looked at how much
hydrogen and how much helium make up Neptune. It discovered that
the planet is made up of about 83 percent hydrogen, 15 percent
helium and two percent methane. This is the latest in a series of
evaluations of composition data from the gas planets, Jupiter,
Saturn, Uranus and Neptune, which have increasingly shown that
their makeup is very close to the amounts of hydrogen and helium
in the sun.
The first spacecraft to determine the main composition of
any of the outer planets was Pioneer, which studied Jupiter and
Saturn, and more substantial data were taken by the twin Voyager
spacecraft. Recent revision of the Jupiter and Saturn data has
led scientists to reexamine the data from all the outer planets
and has revealed that the gas giant planets' main compositions
are almost identical to that of the Sun. This means that helium
hasn't sunk to the center of the planet, as some models had
suggested, but has stayed mixed in the atmosphere.
Orton was joined in his studies by Dr. Martin Burgdorf, ISO
Data Centre, Astrophysics Division, European Space Agency,
Villafranca, Spain; Dr. Gary Davis, University of Saskatchewan,
Saskatoon, Canada; Dr. Bruce Swinyard, Rutherford Appleton
Laboratory, Chilton, United Kingdom; Dr. Sunil Sidher and Dr.
Matt Griffin, Queen Mary and Westfield College, London, United
Kingdom; and Dr. Helmut Feuchtgruber, MPI Extraterrestrische
Physik, Garching, Germany. The Infrared Space Observatory was
operational between 1995 and 1998.