The Solar System at Radio Wavelengths 71 7
planets, 17.24±0.01 hours for Uranus and 16.11±0.02
hours for Neptune. The upper bound to the frequency of
the emissions is determined by (and indicative of) the plan-
ets’ surface magnetic field strength.
From Uranus, we have also received impulsive bursts,
similar to the SED events of Saturn, which are referred
to as UED or Uranus electrostatic discharge events. They
were fewer in number and less intensive than the SEDs.
If these emissions are caused by lightning, the lower fre-
quency cutoff suggests peak ionospheric electron densities
on the day side of∼ 6 × 105 cm−^3. In addition to the broad-
band emissions, both planets also emit trapped continuum
and narrowband radiation.
4. Future of Ground-Based Radio Astronomy
for Solar System Research
This chapter highlighted the value of radio observations
for planetary atmospheres (composition, dynamics), sur-
face composition and structure, comets (parent molecules,
source of material, outgassing), and magnetospheres (mag-
netic field configurations, particle distributions). Momen-
tarily, many exciting projects are not quite doable with
existing telescopes. The prospects for the future, however,
when new large arrays come on-line, are spectacular. Plane-
tary science may be advanced in significant ways with these
arrays.
At millimeter wavelengths, the BIMA and Owens Valley
Radio Observatory (OVRO) arrays are combined (and
expanded) into the Combined Array for Research in
Millimeter-wave Astronomy (CARMA), located at Cedar
Flat in eastern California, at∼8000 ft altitude. The At-
acama Large Millimeter Array (ALMA) is being built in
Chili, jointly by the United States, Canada, Europe, and
Chili. The Smithsonian Submillimeter Array (SMA) is al-
ready in existence, and has produced interesting scientific
results; in this chapter we highlighted some of its results
on Titan. At longer wavelengths, the Allan Telescope Ar-
ray (ATA), operating at∼0.5–∼10 GHz, is being built in
California by the SETI institute and UC Berkeley, with
funding from Paul Allan. Several low-frequency arrays are
either under construction (the Low Frequency Array LO-
FAR in the Netherlands) or being planned, while the ulti-
mate Square Kilometer Array (SKA) is under discussion in
many countries.
These new arrays open up a wealth of potential obser-
vations for planetary research, in all areas. For example,
several millimeter telescopes observed the apparition of
comet Hale–Bopp, with fantastic results, as described in
Section 2.7. ALMA will enable detection of hundreds of
asteroids, “bare” cometary nuclei, emissions from molecu-
lar “jets” from comets at high spatial and time resolution,
Io’s volcanic plumes, Titan’s hydrocarbon chemistry, and
“proto-Jupiters” in nearby stellar systems. We expect, be-
sides simple detection experiments, to actually carry out
scientific research in these areas, such as to determine
the mass and chemical composition of protoplanets. SKA
will improve maps at centimeter wavelengths by orders
of magnitude; it will enable mapping thermal emissions
from giant planets in minutes of time and obtain maps of
Jupiter’s synchrotron emission at many wavelengths quasi-
simultaneously. At lower frequencies, below 40 MHz, ar-
rays such as LOFAR will allow, for the first time, mapping
of Jupiter’s decametric emissions, and pinpoint its sources
with high accuracy.Bibliography
Berge, G. L., and Gulkis, S. (1976). Earth based radio
observations of Jupiter: Millimeter to meter wavelengths. In
“Jupiter” (T. Gehrels, ed.), pp. 621–692, Univ. Arizona Press,
Tucson.
Butler, B. J., Campbell, D. B., de Pater, I., and Gary, D. E.
(2004). Solar system science with SKA.New Astronomy Reviews,
48 (11–12), 1511–1535.
Carr, T. D., Desch, M. D., and Alexander, J. K. (1983). Phe-
nomenology of magnetospheric radio emissions. In “Physics of the
Jovian Magnetosphere” (A. J. Dessler, ed.), pp. 226–284. Cam-
bridge Univ. Press, Cambridge, United Kingdom.
Crovisier, J., and Schloerb, F. P. (1991). The study of comets
at radio wavelengths. In “Comets in the Post-Halley Era” (R. L.
Newburn and J. Rahe, eds.); a book as a result from an international
meeting on Comets in the Post-Halley Era, Bamberg, April 24–28,
1989, 149–174.
de Pater, I., Schulz, M., and Brecht, S. H. (1997). Synchrotron
evidence for Amalthea’s influence on Jupiter’s electron radiation
belt.J. Geoph. Res. 102 (A10), 22,043–22,064.
de Pater, I., Butler, B., Green, D. A., Strom, R., Millan, R.,
Klein, M. J., Bird, M. K., Funke, O., Neidhofer, J., Maddalena, R.,
Sault, R. J., Kesteven, M., Smits, D. P., and Hunstead, R. (2003).
Jupiter’s radio spectrum from 74 MHz up to 8 GHz.Icarus 163 ,
434–448.
Desch, M. D., Kaiser, M. L., Zarka, P., Lecacheux, A., LeBlanc,
Y., Aubier, M., and Ortega-Molina, A. (1991). Uranus as a radio
source. In “Uranus” (J. T. Bergstrahl, A. D. Miner, and M. S.
Matthews, eds.), pp. 894–925. Univ. Arizona Press, Tucson.
Gulkis, S., and de Pater, I. (2002). Radio astronomy, planetary.
In “Encyclopedia of Physical Science and Technology,” vol., 13,
3rd Ed., pp. 687–712. Academic Press.
Harrington, J., de Pater, I., Brecht, S. H., Deming, D., Mead-
ows, V. S., Zahnle, K., and Nicholson, P. D. (2004). Lessons
from Shoemaker–Levy 9 about Jupiter and planetary impacts. In
“Jupiter: Planet, Satellites & Magnetosphere” (F. Bagenal, T. E.
Dowling, and W. McKinnon, eds.), pp. 158–184. Cambridge Univ.
Press, Cambridge, United Kingdom.
Kaiser, M. L., Desch, M. D., Kurth, W. S., Lecacheux, A.,
Genova, F., Pederson, B. M., and Evans, D. R. (1984). Saturn as