The European Space Agency (ESA) and Nasa are asking scientists to propose instruments for the first of two joint Mars missions, the ExoMars trace gas orbiter.

The ExoMars programme includes two missions to investigate the martian environment and its astrobiological issues, and to develop and demonstrate new technologies for planetary exploration.

The first mission will comprise an orbiter and an entry, descent and landing demonstrator. The second will include two rovers due for launch in 2016 and 2018, respectively.

The ESA will build the first spacecraft, the trace gas orbiter, and it will be launched by Nasa.

ESA has approved €850m ($1.2bn) for the Mars programme.