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Detection of the forbidden SO a(1) Delta -> X-3 Sigma(-) rovibronic transition on Io at 1.7 mu m

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Published copy (DOI)


  • I de Pater
  • H Roe
  • J R Graham
  • D F Strobel
  • P Bernath


Publication details

DatePublished - Mar 2002
Issue number1
Number of pages6
Pages (from-to)296-301
Original languageEnglish


We report the discovery of the forbidden electronic a(1)Delta --> X(3)Sigma(-) transition of the SO radical on Io at 1.7 mum with the W. M. Keck II telescope on 24 September 1999 (UT), while the satellite was eclipsed by Jupiter. The shape of the SO emission band suggests a rotational temperature of similar to1000 K; i.e., the gas is extremely hot. We interpret the observed emission rate of similar to2 x 10(17) photons s(-1) to be caused by SO molecules in the excited a I A state being directly ejected from the vent at a thermodynamic quenching temperature of similar to1500 K, assuming a SO/SO2 abundance ratio of similar to0.1 and a total venting rate of similar to10(31) molecules s(-1) (Strobel and Wolven 2001, Astrophys. Space Sci. 277, 1-17). The shape of our complete (1.6-2.5 mum) spectrum suggests that the volcano Loki contains a small (similar to2 km(2)) hot spot at 960+/-12 K, as well as a larger (similar to50 km(2)) area at 640+/-5 K. (C) 2002 Elsevier Science (USA).

    Research areas

  • Io, infrared observations, volcanism, atmosphere composition, atmosphere structure, MOLECULAR-OXYGEN, SULFUR MONOXIDE, SO2 ATMOSPHERE, PLASMA TORUS, TELESCOPE, STARS

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