Philae – a high-tech cube with an edge length of roughly one metre – is the name of the landing craft in the Rosetta Mission. Its main purpose is to conduct on the ground analysis of the comet material, probably the most primeval and oldest material found anywhere in the Solar System. The analysis is designed to focus in particular on element and isotope distribution, organic molecules, minerals and ice. The main purpose of analysing the structure and properties of the comet core is to determine the surface properties, the physical characteristics of the comet core and the structure of its layers, alongside the global internal structure. Furthermore, observations will zero in on and examine the repercussions of temporal variations, prompted by the day/night cycle and the emergence of the comet’s tail as it approaches the Sun.
Almost all of the flanks on the landing craft are fitted with solar power cells that on average can generate around eight watts of electrical energy for the scientific experiments. Energy is a scarce and valuable resource on a comet, as the available sunlight in this distant location, so far from the Sun, is barely a tenth of what it would be on Earth. So the landing craft is fitted with additional primary and secondary batteries to store the energy, and is also a divided into warm and cold areas; the heated zones are used to improve the performance of the experiments, while the cold zones are merely fitted with insulating foil to protect against the permanently harsh external environment (minus 50 degrees Celsius to minus 170 degrees Celsius).
The 10 instruments on board the lander:
APX is a spectrometer used to analyse the elemental composition of material found directly on the comet's surface.
Principal Investigator (PI): Göstar Klingelhöfer, Johannes Gutenberg University, Mainz, Germany.
CIVA (Comet Infrared and Visible Analyser)
CIVA consists of the panorama camera system seen here, used to analyse the landing site, and microscopes to represent and provide spectroscopy of the material samples from the comet's surface acquired using the drill SD2.
Principal Investigator (PI): Jean-Pierre Bibring, Institut d'Astrophysique Spatiale, Université Paris Sud, Orsay, France.
CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission)
CONSERT is a radio wave probe used for tomography of the comet core using interaction with the orbiter.
Principal Investigator (PI): Wlodek Kofman, Institut de Planétologie et d'Astrophysique de Grenoble, Grenoble, France.
COSAC (Cometary Sampling and Composition)
COSAC is deployed to identify the elementary, isotopic and chemical composition of the frozen components on the comet’s surface and down to a depth of around 30 centimetres. The instrument contains a mass spectrometer and a gas chromatograph and will analyse the organic components (for instance amino acids, if found) in particular.
Principal Investigator (PI): Fred Goesmann, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.
MUPUS (Multi-Purpose Sensors for Surface and Subsurface Science)
MUPUS uses an array of sensors to measure the surface temperature and temperature profiles close to the surface, also the thermal conductivity of the surface material and the solidity of the comet’s material. The most important scientific objectives with which MUPUS is charged are to determine the thermal and mechanical properties found in the outer layers of a comet and to identify the energy balance on the comet's surface and outer layers. The results acquired using this instrument should help achieve better understanding of cometary activity and may permit statements on the original nature of material. It also contributes to the cosmo-chemical experiments that the Philae landing craft will perform.
Principal Investigator (PI): Tilman Spohn, Institute of Planetary Research, German Aerospace Center, Berlin, Germany.
Co-Investigators: Matthias Grott, Jörg Knollenberg, Ekkehard Kührt, Institute of Planetary Research, German Aerospace Center, Berlin, Deutschland.
PTOLEMY is a mass spectrometer with upstream gas chromatograph to analyse the isotopic composition of drilled specimens.
Principal Investigator (PI): Ian Wright, Open University, Milton Keynes, UK.
ROLIS (Rosetta Lander Imaging System)
ROLIS is one of two camera systems on board the Rosetta landing craft Philae. ROLIS will use a miniaturised CCD camera to shoot high spatial resolution images of the landing site on the comet as Philae descends from the orbiter. After landing, ROLIS will focus on a distance of 30 centimetres to take images of the comet’s surface beneath the landing craft. A lamp fitted with four monochromatic light emitting diodes in a spectral range of 470, 530, 600 and 4870 nanometres will permit multispectral images. The system will also shoot pictures of the point where the drilled samples are taken and the areas designated for analysis by the alpha X-Ray spectrometer (APXS). This will provide pictures of the immediate environment for comparison with measurements conducted in the in-situ analyser. The drill hole will be inspected once drilling is complete to study its morphology and to look for signs of different layers (stratification). The landing craft is able to rotate and to take stereo image pairs, hence facilitating cartography and the identification of surface structures.
Principal Investigator (PI): Stefano Mottola, Institute of Planetary Research, German Aerospace Center, Berlin, Germany.
Co-Investigators: Gerhard Hahn, Ralf Jaumann, Gabriele Arnold, Institute of Planetary Research, German Aerospace Center, Berlin, Germany.
ROMAP (Rosetta Lander Magnetometer and Plasmamonitor)
ROMAP determines the comet's magnetic field and its plasma environment.
Principal Investigator (PI): Hans-Ulrich Auster, Technische Universität, Braunschweig, Germany; István Apáthy, KFKI, Budapest, Hungary.
SD2 (Sample, Drill and Distribution)
SD2 is a drilling mechanism to acquire samples from a depth of up to 30 centimetres.
Principal Investigator (PI): Amalia Ercoli-Finzi, Politecnico di Milano, Milan, Italy.
SESAME (Surface Electric Sounding and Acoustic Monitoring Experiment)
SESAME is equipped with sensors to measure the acoustic and dielectric properties of the comet core and its structure close to the surface, along with a particle impact monitor. SESAME consists of the instruments CASSE, DIM and PP.
The instrument CASSE (Cometary Acoustic Surface Sounding Experiment) will use acoustic methodologies to analyse the structure of the material found beneath the comet's surface. It offers two means of measurement: one passive, which, like a seismometer, listens in on the comet, and one active, which is similar to an echo sounder and probes the surface layers.
The Dust Impact Monitor (DIM) registers the signals caused by the impact of cometary dust and ice particles on the sensor cube. The measurements can determine the number, mass and velocity of the particles.
The Permittivity Probe (PP) instrument determines the water ice content in the cometary surface layers and its change over time. To do this PP uses quadrupole technology in which two electrodes connected with an alternating current generator induce variable current in the comet’s soil.
Principal Investigator (PI): Klaus Seidensticker, Institute of Planetary Research, German Aerospace Center, Berlin, Germany; István Apáthy, KFKI , Budapest, Hungary.
Co-Investigators: H.-H. Fischer, Martin Knapmeyer, Institute of Planetary Research, German Aerospace Center, Berlin, Germany.