Note the remarkable correspondence with the NICMOS image taken six weeks later (below), at a shorter wavelength (but note that the image orientation is different).

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Keck I AO image of Io in H Band

Io is well known to be the most volcanically active body in the solar system. The surface of this moon-size satellite of Jupiter shows some dramatic features produced by the volcanic activity. Among the most impressive are the thermal emission called hot spots, creating rapid surface changes, plumes and volcanic features (caldera, volcanoes..).
On this impressive Keck I AO image, the high spatial resolution (estimated to 120 km) allows us to see a high number of details. The intensity contrast over the satellite surface is produced by the albedo variation of the surface component. On the eastern limb, close to the equator, two dark area correspond to Pele and Pillan. The Pillan area has known the largest surface change on Io, observed by Galileo probe. The dark features, due apparently to lava flows and detected by Galileo/SSI are clearly visible on this Keck AO image. Pele area also appears as dark on this H band image due to the low albedo of the deposit produced by its huge plume, previously detected on spatial data.
The circular dark area on the other limb of the satellite, reveals the Prometheus volcano. The largest dark area, located at the north pole, corresponds to the enigmatic Lei-Kung Fluctus region. This region is a very large, cool and stable lava flow area produced by an unknow volcano.
Bright areas on the disk may indicate the presence of deposit of sulphur dioxide in solid state (frost). Much smaller caldera, visible on the Voyager image, are also detected on this Keck data.
Note that we do not detect any obvious presence of outburst on the limb of the satellite as it has been once detected on the Io images taken during the Keck II AO science verification phase.

Locator Map - Voyager image of Area

ADONIS AO Image of Io showing 0012A (Tvashtar) eruption

Example of Io image after deconvolution and subtraction of the solar emission. The 0012A hot spot is clearly visible at the edge of the disc (right). Taken on December 16, 2000 at 140 GMT.

Locator Map - Deconvoluted Image

This is from http://astron.berkeley.edu/~fmarchis/Io_OA/Run2000/

Three data sets of Io (composed of 3 or 4 final processed images in L' band) were taken, for each of them we have a PSF data set. On the 5 hours of observation, wee can not only determine the center-to-limb variation of any bright hot spots, but we also increase the spatial coverage of our survey. After applying a deconvolution process (called MISTRAL, see Conan et al., SPIE, 4007, 913-924), we can identify several well-known hot spots. The brightest one on this side seems to correspond to Loki (309W, 13N). Furthermore, the emission is quite extended in direction of Daedalus and the center-to-limb variation do not follow a classical cos \Theta law. One basic interpretation could be the presence of another hot spot close to Loki which may contaminate the flux calculated. The flux estimated on the images with Loki nearest the central meridian indicates a vertical brightness of 85+/-10 GW/Sr/micron (similar the medium activity determined in September 1998).
Another important active area corresponds to the Janus-Kanehikili (J-K) group which approximately follows a cos \Theta law and is estimated to have a vertical brightness of 46+/-10 GW/Sr/micron.
We also isolated other possible sources of emission on the last data set (SEP longitude=3 \deg). Two eastern limb emissions correspond to Hi'Iaka and Gish Bar. Two unknown faint emissions are located on the internal disc: one at the NW (astronomical) of J-K (0011A) located at (27+/-10W, 20+/-7N) and another one (0011B?) close to the northern pole (55+/-15W, 58+/-15N). In our previous survey, this part of the Io surface has been poorly imaged (near-limb geometry). Therefore, it is not possible to compare and confirm the presence of such emissions. Sengen Patera area seems not to be active on our data (close-limb position).

Mercator Projection of the above images

Map of Io derived from the November (2 sets) and December (1 set) 2000 observations. The horizontal and vertical axis are west longitude and latitude. We have overplotted the persistent (green) and transient (yellow) hot spot locations detected by NIMS during the 10 first Galileo orbits (Lopes-Gautier et al., Icarus, 140, 243-264, 1999). The blue boxes correspond to the hot spot locations determined from our previous AO data (Marchis et al., submitted to JGR, 2000)