The European Space Agency (ESA) has started a technical investigation into the Planetary Fourier Spectrometer (PFS) on board Mars Express, after a problem developed in the instrument a few months ago.

Vibration effects -- induced by spacecraft activities -- have been suggested as a cause for the observed behaviour. However no source has yet been identified and other causes internal to the instrument cannot be fully ruled out.

In order to establish the exact cause of the problem, ESA's Mars Express team is setting up an investigations board involving experts from the Mission Science Working Team, ESA, industry and the Italian Space Agency (ASI).

This could lead to resuming scientific observations using modified procedures but, until all existing data and a number of additional measurements currently being planned have been examined, it is too early to draw a conclusion on the operational status of the PFS instrument.

The PFS instrument has performed without any such problems for almost two years, following the launch of Mars Express in June 2003. In this period, the instrument has provided much new information on the global composition and movement of the Martian atmosphere.

Even if it is found that PFS is no longer fully functional, it is only one element in the scientific package on board Mars Express. The other six instruments (HRSC, OMEGA, ASPERA, SPICAM, MARSIS, MaRS) are all currently working well and are providing new insights into the Red Planet and its evolution. These remaining instruments will continue the scientific success of the Mars Express mission.