Forschung Aktuell

 Science Service
Nr. 1, September 2000

TU Berlin Science Service of the TU Berlin
Nr. 1 / September 2000

Astrophysics
Simulating the Jupiter phenomenon

The spectacular impacts of the Shoemaker-Levy 9 comet in the atmosphere of Jupiter in 1994 fascinated scientists and the general public alike. Researchers at the Technical University (TU) Berlin have now simulated the physical and chemical effects on the ringed planet in the laboratory and can use this to draw conclusions about its atmosphere.

In July 1994, scientists and hobby astronomers were turning their telescopes to the southern skies, where many were able to witness for the first time the collision of extraterrestrial bodies. The spectacle was provided by the Shoemaker-Levy 9 comet, fragments of which collided into the planet Jupiter at more than 60 kilometres per second, or 50-times the speed of sound. The tremendous energy released by the impacts was equivalent to many hundreds of nuclear weapons. More than 20 pieces of the comet created balls of fire and gas each larger than the Earth. The impact of Shoemaker-Levy 9 left visible traces of the collision on Jupiter, which is 300-times the size of Earth, and has produced considerable alterations.

A research project at the Technische Universität (TU) Berlin has set itself the goal of analysing and simulating the chemical processes in the shock waves generated by the impacts on the planet. "We have been able to simulate in the laboratory the process of degeneration and formation of molecules which were initiated by the enormous impact forces", explained physicist Dr. Dietrich Ewert, commenting on the results of this project, which has been funded by the DFG (German Research Society) and was carried out in cooperation with RFTH Aachen.

Initial data was provided by a probe from the Galileo spacecraft that entered the atmosphere of Jupiter on 7 December 1995, allowing measurement of molecule concentrations there for the first time. The results of the mission showed the existence after the collision of millions of tonnes of hydrogen cyanide.

The formation of these molecules can be simulated in the laboratory. The scientists used an eight-metre-long shock-wave pipe to reproduce the thermochemical processes. Helium was pumped into the high-pressure zone of the pipe where it was contained by an aluminium membrane. The high pressure of the gas finally broke the membrane and a shock-wave moved through the low pressure section of the pipe, which contained a mixture of ammonia, methane and water vapour. These substances are typical for the atmosphere on Jupiter. As in the wake of the comet's impact, they were compressed and heated by the shock-wave in the simulation, which resulted in chemical reactions. Despite the very high temperatures, stable new molecules were formed which could be identified by analysing the microwave signals emitted. The successful experiment and the identification of hydrogen cyanide will now enable the researchers to draw conclusions about the nature of Jupiter's atmosphere.

Since the hydrogen cyanide was formed in the experiments in a "dry" gas, the Berlin scientists have shown that the atmosphere of Jupiter contains much less water than at first thought. Final proof of this was finally provided by the Galileo probe.

The research of events such as the collision of two celestial bodies seems to have grown in importance in recent times. As a result of improved methods of observation, astronomers are discovering more and more "Near-Earth Objects". Already some 800 asteroids and comets have been identified that under certain circumstances may enter into the earth's atmosphere. American researchers writing in the scientific journal Nature estimate that there are some 700 "Near-Earth Objects" with a diameter of more than 1 kilometre which could lead to global climate changes, but the actual figure could be twice as large.

Database

Contact: Dr. Dietrich Ewert and Prof. Erwin Sedlmayr, Technische Universität Berlin, Institute of Astronomy and Astrophysics, Prof. Dr. Dieter Zimmermann, E-Mail: dz@kalium.physik.tu-berlin.de, Tel.: +49 30 314-25108, Fax: +49 30 314-23018
Special field: Astronomy and Astrophysics
Research project: Shock wave experiments to simulate the comet impact of Shoemaker-Levy 9 on Jupiter and theoretical modelling
Address: Str. d. 17 Juni 135, 10623 Berlin, Germany, Tel +49 30 314-23736, E-mail:sedlmayr@physik.tu-berlin.de

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