Illustration par défaut

Hydrogen peroxide on Mars

1er juin 2004

An international team of astronomers, led by researchers from Paris Observatory, has just discovered hydrogen peroxide on Mars, with the NASA 3m telescope IRTF (InfraRed Telescope Facility) at Hawaii. Since the negative results announced by the Viking experiments regarding the search for organic molecules at the Martian surface, astronomers have always suspected the presence of hydrogen peroxide H2O2 in the Martian atmosphere. This strong oxidizer, product of the photochemistry of water and carbon dioxide, would be able to sterilize the Martian surface down to a depth of a few meters.

Still, until last summer, all attempts to detect H2O2 on Mars have been unsuccessful. Because of its very weak expected amount, the search for H2O2 requires high-resolution spectroscopy in the infrared or submillimeter range, which can be achieved only from the ground, using large telescopes. In February 2001, a team from Paris Observatory, using a high-resolution imaging spectrometer in the 8 microns range, built by the University of Texas and mounted at the 3-m IRTF (InfraRed Telescope Facility) at Mauna Kea (Hawaii), had obtained a stringent upper limit of the H2O2 abundance, lower than the photochemical predictions (Encrenaz et al., 2002).

Figure 1 Carte du rapport de mélange de H2O2 dans l’atmosphère de Mars (en unités de 10-8). Le point blanc indique le point sub-solaire. Cliquer sur l’image pour l’agrandir

This team, using again the same instrument in June 2003, has been able this time to detect the H2O2 molecule and to map it over the Martian disk (Encrenaz et al., 2003, 2004). Remarkably, the measured abundance (which corresponds to a mixing ratio of a few 10-8), is significantly larger than the upper limit inferred in 2002 (4 10-9), which shows evidence for strong seasonal variations. The H2O2 abundance and its spatial distribution, which exhibits a maximum in the morning side, around the sub-solar latitude, are this time in satisfactory agreement with the theoretical predictions, and, in particular, with the 3D simulations performed at the Laboratoire de Météorologie Dynamique. The amount of H2O2 inferred from the observations is also in good agreement with the global measurement, integrated over the Martian disk, achieved in the submillimeter range, in September 2003, by a team from the Space Science Institute in Boulder (Clancy et al., 2004). The nature of the seasonal cycle of H2O2 and its relation with the water cycle remain to be understood.

Encrenaz, T., T. K. Greathouse, B. Bézard, S. K. Atreya, A. S. Wong, M. J. Richter, M., and J. H. Lacy 2002. A stringent upper limit of the H2O2 abundance in the Martian atmosphere. Astron. Astrophys. 396, 1037-1044. Encrenaz, T., B. Bézard, T. K. Greathouse, J. H. Lacy, M. J. Richter, S. K. Atreya, and A. S. Wong 2003. Mars. IAUC 8254, Dec. 9, 2003. Encrenaz, Th., B. Bézard, T. K. Greathouse, M. J. Richter, J. H. Lacy, S. K. Atreya, A. S. Wong, S. Lebonnois, F. Lefèvre, F. Forget 2004. Hydrogen Peroxide on Mars : Evidence for Spatial and Seasonal Variations. Icarus, in press.

Contact

  • Thérèse Encrenaz
    Observatoire de Paris, LESIA
  • Bruno Bézard
    Observatoire de Paris, LESIA
Actualités