Detection of the Forbidden SO a1Δ→X3Σ− Rovibronic Transition on Io at 1.7 μm

✍ Scribed by Imke de Pater; Henry Roe; James R. Graham; Darrell F. Strobel; Peter Bernath

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 259 KB
• Volume: 156
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.2001.6787

✦ Synopsis

We report the discovery of the forbidden electronic a 1 → X 3 - transition of the SO radical on Io at 1.7 µm 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 ∼1000 K; i.e., the gas is extremely hot. We interpret the observed emission rate of ∼2 × 10 27 photons s -1 to be caused by SO molecules in the excited a 1 state being directly ejected from the vent at a thermodynamic quenching temperature of ∼1500 K, assuming a SO/SO 2 abundance ratio of ∼0.1 and a total venting rate of ∼10 31 molecules s -1 (Strobel and Wolven 2001, Astrophys. Space Sci. 277, 1-17). The shape of our complete (1.6-2.5 µm) spectrum suggests that the volcano Loki contains a small (∼2 km 2 ) hot spot at 960 ± 12 K, as well as a larger (∼50 km 2 ) area at 640 ± 5 K.