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To gain deeper insight into the cosmological model we have to access new independent and novel tracers of the early Universe, particle physics and structure formation such as the Cosmic Microwave Background (CMB) spectral distortions. These tiny departures of the average CMB energy spectrum from that of a perfect blackbody provide us with a fundamental probe of the cosmic thermal history.

With the FTS fOr CMB Spectral diStortIon expLoration (FOSSIL) surveying the sky from 30 to 2000 GHz we foresee the realisation of the essential improvements of COBE/FIRAS measurements by three orders of magnitude. FOSSIL will allow us to probe:

  • the early Universe physics and inflation
  • the black-hole formation scenarios
  • the nature of dark matter
  • the structure formation
  • the blackbody nature of the CMB

In addition, FOSSIL will allow us to:

  • probe recombination physics at last scattering
  • explore the end of the reionisation epoch
  • probe the dust-obscured star-formation history
  • realise breakthrough advances in our understanding of the diffuse Galactic components from the radio to the far infrared

The FOSSIL concept, proposed to the ESA M7 call by a consortium of more than 40 institutions in15 countries, builds on the heritage of COBE/FIRAS and on previous space-mission proposals (i.e., PIXIE and PRISTINE). It offers a unique opportunity to probe the thermal history of the Universe across time, providing guaranteed science results as well as a rich discovery potential for new physics.


  • Nabila Aghanim (
  • Bruno Maffei (
Project status: 
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