Lick
Observatory, Mt.Hamilton, California
W.
M. Keck Observatory,
Hawaii
|
|
|
|
|
Lick
Observatory, Mt.Hamilton, California
|
W.
M. Keck Observatory,
Hawaii
|
Keck AO OBSERVATIONS OF JUPITER'S RED SPOTS
We observed the Great Red Spot and the red Oval BA with the Keck adaptive optics system on UT 21 July 2006, during a period they were passsing each other. We initially used the laser guidestar technique, but then switched to using Io for wavefront sensing, once it came close enough to Jupiter.
[Left]: A false-color composite near-infrared image of Jupiter and its moon Io, taken July 20 Hawaii time (July 21 UT) by the Keck II telescope on Mauna Kea using adaptive optics (AO) to sharpen the image.
Images taken in narrow band filters centered at 1.29 and 1.58 microns (shown in gold in this image) detect sunlight reflected off Jupiter's upper cloud deck - the same clouds that are seen in visible light. The narrow band image at 1.65 micron (shown in blue) shows sunlight reflected back from hazes lying just above these clouds The image was sharpened using the RegiStax software, developed by Cor Berrevoets.
The planet Jupiter is 143,000 km (90,000 miles) across. The Great Red Spot is about twice the diameter of Earth, while Red Spot Jr. has a diameter nearly equal to that of Earth. Resolution is about 0.1 arcseconds, or 370 kilometers (250 miles). The AO system used the satellite Io as its reference star. Io itself is visible in the upper right corner in the green, red and blue colors of the 1.29, 1.58 and 1.65 micron filters, respectively. The motion of the satellite with respect to Jupiter during the observing sequence is clearly seen. The fact that Io looks larger in the blue than in the other colors is an 'artefact' of the image processing. because Jupiter is much less bright in the methane band (1.65 filter), we had to `brighten' it relative to the other colors, which increased Io's apparent size.
Red Spot Jr., which is below the Great Red Spot, is not as bright, either because its clouds are thinner (lower optical depth) and thus reflect less light, or because the tops of the clouds are not as high as those of the larger spot. The red outline shows the approximate area covered by the 5-micron band mosaic shown on the right.
[Right]: A closeup of the two red spots through a 5-micron filter, which samples thermal radiation from deep in the cloud layer. Both spots appear dark because the clouds completely block heat emanating from lower elevations, though narrow regions around the spots that are devoid of clouds show leakage of heat into space. This 5-micron mosaic image reveals details in the cloud opacity not seen at the other wavelengths, and will help unravel the vertical structure of the spots.
Credit: Imke de Pater, Michael Wong (UC Berkeley); Al Conrad (Keck Observatory), and Chris Go (Cebu, Philippines)
Despite a typhoon, amateur astronomer Christopher Go of Cebu, Philippines, was able to obtain an optical image of Jupiter taken about two planet rotations (19+ hours) before the Keck images. The picture shows the two red spots and the moon Io (upper left edge) transiting the planet.
(Credit: Christopher Go 
