Biomarker on Callisto

Ozone (O₃), regarded as a biomarker, has been observed on the icy satellites Ganymede [1a], Dione and Rhea [1b]. Presence of O₃ on the icy surfaces of Ganymede, Rhea and Dione are due to energetic processing of oxygen-bearing molecules. Laboratory experiments had shown efficient synthesis of O₃ in oxygen-bearing molecules such as CO_x, SO_x and NO_x. Most of the experiments used InfraRed (IR) spectroscopy to detect O₃ [2a]. However, unambiguous O₃ detection in planetary objects using IR signatures is difficult due to the presence of silicates. Therefore, the Hartley band of O₃, 220 – 310 nm, was used to find O₃ presence on icy surfaces [2b]. 

Apart from the three satellites of the outer Solar System, there may be other satellites that might harbour O₃. UltraViolet (UV) spectrum of Callisto recorded by the HST was reported to show spectral signatures of SO₂ [3]. Based on this observation, the irradiation experiments simulating SO₂ ices on Callisto revealed the coexistence of SO₂ and O₃. The spectral signatures in the UV were found to extend from 220 – 310 nm with a broad peak 255 – 285 nm, clear indication of O₃ embedded in the SO₂ ice matrix. Here we will present the detailed analysis that suggests the presence of O₃ on Callisto.  

 

References:

[1] Noll et al. [a] (1996) Science, 273, 341. & [b] (1997) Nature, 388, 45.

[2] Sivaraman et al. [a] (2007)  ApJ, 669, 1414. & [b] (2014) Chem Phy Lett, 603, 33.

[3] Noll et al. (1997) GRL, 24, 1139.