Near-infrared monitoring of Io and detection of a violent outburst on 29 August 2013

We present initial data from our campaign to monitor Io in the near-infrared, beginning in August 2013, using 3.8-μm adaptive optics imaging at Gemini N and 2-5 μm disk-integrated spectroscopy at NASA's IRTF. Conducted during 2013-2014, these observations are coincident with the ISAS/JAXA EXCEED mission's continuous monitoring of the Io plasma torus and will enable the speculated effects of volcanic outgassing on the torus to be observed directly, in addition to enabling an assessment of the frequency and properties of large-scale outbursts. On 29 August 2013 we detected a powerful eruption (designated 201308C) on Io at 223.5 ± 2.6°W, 29.1 ± 1.8°N. Emitting between 15 and >25 TW, this event is one of the most powerful eruptions ever seen on Io and falls into the rare "outburst" class. This was the third eruption of this type seen on Io in August 2013, an unprecedented occurrence. Also unprecedented was the charting of the decay in thermal emission over the subsequent days and weeks. Modeling of the outburst spectrum places a lower bound of 1200-1300 K on the eruption temperature, and is suggestive of temperatures 1900 K or higher, typically associated with ultramafic lava composition. The eruption is likely a highly energetic, high-volume lava fountain event.