Comets are an extraordinary occurence on the night sky. Consisting of unprocessed material of the early solar system, they provide important indications of its formation. The European spacecraft Rosetta will rendezvous the comet 67P/Churyumov-Gerasimenko in may 2014 in order to make measurements concerning its physical and chemical properties, the structure of the nucleus and its interaction with the solar wind. Therefore, Rosetta will orbit the comet in a distance of a few kilometers. Additionally, the lander PHILEA will be deployed onto the nucleus to perform the first experiments on the surface of a comet. Together with Churyumov-Gerasimenko, the orbiter and the lander will approach the sun in summer 2015 investigating the comet's increasing activity as an "in-situ" measurement.
The IGEP participates in the Rosetta mission with an experiment both on the orbiter (RPC) as on the lander (ROMAP). That means, that both experiments were partly developped at the IGEP and that scientists at the IGEP are the PIs of the experiments.
The mission was launched on march 2, 2004 by an Ariane-5 launch vehicle from Kourou, French Guayana. During its long way to 67p/Churymov-Gerasimenko, Rosetta will swing-by the planet Mars and fly-by the asteroids 2867 Steins and 21 Lutetia and study them from greater distance.
Event | Nominal date |
---|---|
Launch | March 2004 |
First Earth gravity assist | March 2005 |
Mars gravity assist | February 2007 |
Second Earth gravity assist | November 2007 |
Asteroid Steins flyby | September 2008 |
Third Earth gravity assist | November 2009 |
Asteroid Lutetia flyby | July 2010 |
Enter hibernation | July 2011 |
Exit hibernation | January 2014 |
Rendezvous manoeuvre | May 2014 |
Start Global Mapping | August 2014 |
Lander Delivery | November 2014 |
Perihelion Passage | August 2015 |
End of Mission | December 2015 |
The mission was named after the "Rosetta Stone", found in 1799 in Egypt, which helped the linguists Champollion and Young for the first time to unravel the hieroglyphs. And just as this stone contributed in understanding the civilization of the ancient Egypt, the Rosetta space mission is intended to disclose the last secrets of the oldest inhabitants of our solar system: the comets. Consisting of precursor material of the solar system, comets material has hardly changed for the last 4,6 billion years. The study of comets offers therefore an unique possibility to look back in time and to explore the provenience of our solar system.
As comets have not yet been analyzed in-situ, many questions concerning their structure and composition still remain unanswered. Therefor, the scientific objectives of the Rosetta mission are the followings:
The interaction between the comet and the solar wind can be characterized by plasma properties as for example plasma waves plasmaboundaries. It depends on the solar wind intensity, on the comets outgassing rate increasing with its vicinity to the sun and its potentially intrinsic magnetic field. The magnetic properties of comets could hint at its own origin: Up to now, it is not yet well understood, how and why dust and ice stuck together to form comets. Magnetic attraction could possibly have contributed to this process. Hence, both the orbiter as the lander are equipped with a combined
plasma and magnetometer experiment (RPC onboard the orbiter and ROMAP onboard the Lander). To estimate the required instruments sensitivity, numerical simulations concerning the interactions between the solar wind plasma and the comets ionosphere were performed at the Institut for Theoretical Physics. They shed light on the plasmaphysical environment of the comets nucleus. Besides the electromagnetic field distribution also energy spectra of the involved ion species are computed by these simulations. According to these simulations, C-G has to be classified as a "weak comet", meaning that the qualitative conditions in the plasma environment are significantly different in comparison to the classical description of a strong comet. Therefore, the simulations provide precious assistance at the mission planning as well as at the interpretation of the measurement results.
Wissenschaftlerinnen und Wissenschaftler vom Institut für Geophysik und extraterrestrische Physik der Technischen Universität Braunschweig haben eine Videoanimation erstellt, die die Landung von Philae auf der Kometenoberfläche zeigt. Genutzt haben sie dafür die wissenschaftlichen Messdaten der beiden Braunschweiger Magnetometer "RPC-Mag" und "ROMAP" sowie weiterer Instrumente an Bord der Landeeinheit. Das internationale Forscherteam um Dr. Hans-Ulrich Auster, Dr. Ingo Richter und Prof. Dr. Karl-Heinz Glaßmeier stellte am 12. November 2014 mithilfe des Magnetometers "ROMAP" als erstes die ungeplante mehrmalige Landung auf dem Kometen 67P/Churyumov-Gerasimenko fest. Doch was die Wissenschaftlerinnen und Wissenschaftler damals anhand ihrer Messdaten ablesen konnten, machte ihr Kollege Philip Heinisch vom Braunschweiger Rosetta-Team zum ersten Jahrestag der Landung in einer Videoanimation sichtbar.
Seit der Landung war der Rosetta-Orbiter auf der Suche nach dem genauen Standort von Philae auf der Kometenoberfläche. Unter anderem mithilfe der rekonstruierten Flugbahn des Landers gelang es dem OSIRIS-Team am 5. September 2016 auf einer hochaufgelösten Fotografie Philae wieder zu finden.
Since August, 6 2014 Rosetta is in orbit around the comet 67P/Churyumov-Gerasimenko. On the November, 12 the Rosetta mission reached one of its highlights when the lander Philae was separated from the orbiter to land on the comet's surface. Both the magnetometer on board the orbiter (RPC-Mag) as well as the magnetometer on board the lander (ROMAP) recorded the different events on this day.
The separation of the lander left a clear signature in the magnetic field data at 08:35 UTC recorded by the orbiter magnetometer. The lander creates his own magnetic field which is superimposed on the background magnetic field. As this influence disappears after separation it can be seen as a clear jump in the data. In the same way the lander magnetometer is also influenced by the orbiter's presence and a similar jump can be seen in the magnetic field data obtained by the lander instrument.
The instrument ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) is located at the end of a boom. During the journey to the comet the boom was retracted to the lander body. After separation this boom deployed and the magnetometer changed its position relative to Philae's body. This was recorded and confirmed by the magnetometer at 08:56 UTC.
After seven hours of decent Philae arrived at the desired landing site at 15:34 UTC. There the lander rebounced and floated above the comet's surface for another two hours. The comet's gravity pulled Philae back to the ground and the lander touched the surface for the second time at 17:25. Once again it bounced back into space and stayed on the ground after the third landing at 17:31. With each ground contact the landing gear of Philae was moving while adapting to the ground. These movements have been detected by ROMAP and every single touchdown left specific signatures in the data (left figure).
With the help of appropriate analyses methods the measured events can be seen more clearly in the data. In the right figure the second and third touchdown are shown after a method called EMD (Empirical Mode Decomposition) was applied to the data. The EMD is a numerical procedure to find and separate the intrinsic modes of a time series.
ROMAP (ROsetta Lander MAgnetometer and Plasma Monitor) consists of the Rosetta Lander-Magnetometer (ROLAND) and the Lander Plasma Monitor (SPM). The Fluxgate-Magnetometer, designed and built lead-managed by the Institute for Geophysics und extraterrestrial Physics, is situated in zhe center of the experiment. It consists of two entwined ringcores plus pick-up coils and Helmholtz coils for each sensor axis. With a weight of less than 40 g it can perform measurements betweenn +/- 2000nT with a resolution of 10 pT. The IWF (Graz) and the MPE Garching joined the development and construction of the magnetometer and its electronics.
Parameter | |
---|---|
Sensor mass | 35 g |
Sensor volume | 523 cm³ |
Electronics mass | 150 g |
Resolution | 10 pT |
Dynamic range | 4000nT |
Sensor noise (@1Hz) | 10pT/(Hz)1/2 |
Bandwidth | 0 - 32Hz |
Sample rate | [1; 64] vecs/s |
Power (incl. plasmamonitor) | 1 W |
Temperature range | -160 ... +120C |
Time of operation | ~ weeks |
The plasma monitor, a cooperation between KFKI (Budapest),MPS (Katlenburg-Lindau) and IKI (Moskau), measures the electron and ion distribution in a wide energy range. Furthermore, a Penning sensor and a Pirani sensor for pressure measurements are available (10-8-10-3mbar respectively 10-3-10mbar). The electronics for both experiments are located inside the lander, the sensors, except for the pressure sensors,are mounted on a small boom.
The Orbiter-Magnetometer is part of the Rosetta Plasma Consortium (RPC) and was developped in a close cooperation with the Imperial College (London). The instrument consists of two identical fluxgate sensors mounted on a 1.5 m long boom outside the spacecraft andan electronics box placed inside the orbiter.The sensor has beeen designed and manufactured in lead-management by Prof. Dr. Karl-Heinz Glaßmeier at the IGEP in Braunschweig. The development of the electronics was a teamwork with the IWF in Graz.
On Sunday, 25th february 2007, Rosetta flew by Mars performing a gravityt assist manoeuvre. Rosetta passed by the red planet's surface in a distance of some hundred kilometers. This close approach was a good opportunity to switch on the lander experiment ROMAP in order to calibrate its magnetometer. Additionally, the data set taken during the flyby provides an insight into the plasma environment around Mars.
All components of ROMAP worked satisfyingly during the flyby. In the magnetogramm plotted above, one can follow Rosettas itinerary around Mars: its approach through the solar wind and the crossing of the bowshock and he tail.
See also ESA article about Rosettas flyby.
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