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CNES project in-situ dating of Martian rocks

Project Presentation :

Mars is one of the most exciting scientific topics of XXIst century. The many space missions that have followed since the 70’s brought massive amounts of data and information on the geology, the magnetic field, atmosphere ... but no mission could provide up to present accurate dating. Currently planetary scientists assess the age of the surface using the methods of counting craters, validated method for the Moon through levies that have been made. However, unlike the Moon, no Martian rock has been collected and reported on Earth (although it is envisaged for the mission « Mars Sample Return » that could be launched in 2020-2022).

It is in this context that project is. An experience of dating of Martian rock in situ is essential to clarify the knowledge and to constrain models on the history of the Red Planet.

To date the rocks, several methods exist. We will use the K-Ar method by measuring LIBS (K) & MS (Ar) (Laser-induced breakdown spectroscopy (for potassium) & Mass Spectrometer (for argon)). This method was chosen because it is the most realistic on Mars, the others being from other more expensive in energy and time of measure per sample.

In addition, LIBS used in this experiment will be based on technologies and know-how of the team that designed the instrument ChemCam which equip the Mars Science Laboratory rover.

Mars has rocks that are conducive to the K-Ar method, since some areas are covered by basaltic lava flows. Here are three of the largest volcanic provinces on Mars:

  • Tharsis, which has a dozen volcanic massifs such as Olympus Mons, Mons Ascraeus, Uranius Tolus, Ceranius Tolus, Tharsis and Alba Tolus Mons
  • Elysium Planitia with volcanoes of Elysium Mons, Albor Tholus and Hecate Mons.
  • Syrtis Major with caldera of Nili Patera and Meroe Patera.

On Mars, there are more than twenty major volcanoes identified (including the largest in the Solar System) which is added a number of buildings more discreet. The great basalt plains that stretch on this planet will be sites relevant to the achievement of dating experience.

Glossary Martian: Mons [1], Patera [2], Tolus [3]

The experience:

In the laboratory IDES we are developing a prototype that will aim to validate the laboratory stage. This is the first instrumental realization of the project. It is intended to show that in laboratory conditions, this experiment gives results whose we know the reproducibility and error. If these results are compelling, other models (Field, miniaturized, spatial, etc ...) will be made then tested. If all these steps are successful the final model will go on Mars.

The main difficulties are numerous at the prototype stage of laboratory since we have to make a new experience. In this case, it must involve all the different instruments, calibration and testing. We must also ensure that the whole system works, choose the right tools, good software, coding programs, ...

The prototype consists of:

  • a Nd: YAG laser
  • an optical emission spectrometer
  • a quadrupole (mass spectrometer)
  • vacuum pump
  • Automatic and manual valve
  • getter (gas purification)

Simplified protocol of the experience:

  • A sample is placed in a cell firing in which a high vacuum is created.
  • The laser shot on the sample in the ultraviolet
  • Plasma thus created is analyzed by the optical spectrometer (analysis of major elements and measurement of potassium)
  • Plasma releases the gas was contained in the dug by the laser
  • Gas is purified by the getter and brings in a set of valves to the quadrupole
  • Quadrupole measure the amount of argon present in the gas

Exemple of laser shot on a sample:

Example of detection of argon:

[1High relief in the form of isolated mountain or mountain range

[2Reliefs more or less spread resembling a saucer reversed, with crater and contour irregularly

[3Dome, cupola