New results on gas giant’s atmosphere published in Science

Cassini and Saturn
Credits: Lamy et al., Science, 2018

On September 15, 2017, NASA’s spacecraft Cassini ended its mission by performing a series of 22 diving orbits between the rings and ionosphere of the giant planet Saturn. Since then scientists, including several from the Swedish Institute of Space Physics (IRF), have been analyzing this unique data set and their first results will be published in Science on 5 October. IRF in Uppsala built the Langmuir Probe (LP) on board Cassini. It is part of the Radio and the Plasma Wave Science instrument package (RPWS) which made the measurements.

Michiko Morooka at IRF is one of the scientists who has contributed to the new research results.
"The atmosphere of the gas giant Saturn is much more complicated than we previously believed. It has a different sort of ionosphere which is controlled by heavy electrically charged particles," says Michiko Morooka.

Measurements in the auroral zone of Saturn
In one of the studies the scientists use Cassini's measurements of planetary radio emission from Saturn. The radio emissions are created by the energetic particles that cause the aurora in the atmosphere. Similar radio emissions can be observed above the Earth. The study found out that the source region was in a low plasma density region. This condition seems to be time variable and may be related to the planet's rotation.

Heavy and complex organic compounds
Two other studies showed a remarkable connection between the rings and the atmosphere of Saturn. The high energy particle instrument MIMI (Magnetic IMaging Instrument) detected 1-3 nm sized dust grains both near the D-ring and in the ionosphere, indicating that the ring particles collide with Saturn’s upper atmosphere and then fall to the planet.

Ring material has long been thought to enter Saturn’s atmosphere and modify the chemistry of atmosphere and ionosphere but careful analysis of the data set revealed that the composition of Saturn’s ionosphere is more complicated than scientists had expected. Saturn’s upper atmosphere consists of complex heavy organic compounds including Methane (CH4), Ammonia (NH3) and water (H2O), and some of them are in the form of a cluster molecule.

"Cassini has also found a complex and heavy organic atmosphere at Saturn's moon Titan, but in different material. Scientists must now develop a new atmospheric model for Saturn," says scientist Michiko Morooka, IRF. "That mechanism may help answer a fundamental question, how stars evolved from gas in space."

Jan-Erik Wahlund, Scientist, Swedish Institute of Space Physics (IRF) in Uppsala
+46 18 4715946

Michiko Morooka, Scientist, Swedish Institute of Space Physics (IRF) in Uppsala
+46 18 471 5921

Lina Hadid, Scientist, Swedish Institute of Space Physics (IRF) in Uppsala
+46 18 471 59 34

The articles:

The low frequency source of Saturn’s Kilometric Radiation
L. Lamy, P. Zarka, B. Cecconi, R. Prangé, W. S. Kurth, G. Hospodarsky, A. Persoon, M. Morooka, J.-W. Wahlund, G. J. Hunt, Science (2018)

Chemical Interactions between Saturn’s Atmosphere and Rings
J. H. Waite, Jr., R. Perryman, M. Perry, K. Miller, J. Bell, T. E. Cravens, C. R. Glein, J. Grimes, M. Hedman, J. Cuzzi, T. Brockwell, B. Teolis, L. Moore, D. Mitchell, A. Persoon, W. S. Kurth, J-E. Wahlund, M. Morooka, L. Hadid, S. Chocron, J. Walker, A. Nagy, R. Yelle, S. Ledvina, R. Johnson, W. Tseng, O. J. Tucker, W.-H., Ip, Science (2018)

D-Ring Dust Falling into Saturn’s Equatorial Upper Atmosphere
D.G. Mitchell, M. E. Perry, D. C. Hamilton, J. H. Westlake, P. Kollmann, H. T. Smith, J. F. Carbary, J. H. Waite, Jr., R. Perryman, H.-W. Hsu, J.-E. Wahlund, M. W. Morooka, L. Z. Hadid, A. M. Persoon, and W. S. Kurth, Science (2018)

Other links:

Atmospheric composition

Press release from NASA

The Swedish Institute of Space Physics (IRF) is a governmental research institute which conducts research and postgraduate education in atmospheric physics, space physics and space technology. Measurements are made in the atmosphere, ionosphere, magnetosphere and around other planets with the help of ground-based equipment (including radar), stratospheric balloons and satellites. IRF was established (as Kiruna Geophysical Observatory) in 1957 and its first satellite instrument was launched in 1968. The head office is in Kiruna (geographic coordinates 67.84° N, 20.41° E) and IRF also has offices in Umeå, Uppsala and Lund.

Institutet för rymdfysik, IRF, är ett statligt forskningsinstitut under Utbildningsdepartementet. IRF bedriver grundforskning och forskarutbildning i rymdfysik, atmosfärsfysik och rymdteknik. Mätningar görs i atmosfären, jonosfären, magnetosfären och runt andra planeter med hjälp av ballonger, markbaserad utrustning (bl a radar) och satelliter. För närvarande har IRF instrument ombord på satelliter i bana runt tre planeter, jorden, Mars och Saturnus. IRF har ca 100 anställda och bedriver verksamhet i Kiruna (huvudkontoret), Umeå, Uppsala och Lund.