Lick
Observatory, Mt.Hamilton, California
W.
M. Keck Observatory,
Hawaii
|
|
|
|
|
Lick
Observatory, Mt.Hamilton, California
|
W.
M. Keck Observatory,
Hawaii
|
Record-breaking Storm Activity on Uranus in 2014
See Full Press Release from the Keck Observatory The first images that triggered the amateur observing campaign were reported on the Keck observatory's website.
In spite of an expected decline in convective activity following the 2007 equinox of Uranus, large storms were detected on the planet with the near-infrared camera NIRC2, coupled to the adaptive optics system, on the 10-m W.M. Keck telescope on UT 5 and 6 August 2014. All storms were on Uranus's northern hemisphere, including the brightest storm ever seen in this planet at 2.2 micron, reflecting 30% as much light as the rest of the planet at this wavelength. The storm was at a planetocentric latitude of ~15deg N and reached altitudes of ~330 mbar, well above the regular uppermost cloud layer (methane-ice) in the atmosphere. A cloud feature at a latitude of 32 deg N, that was deeper in the atmosphere (near ~2 bar), was later seen by amateur astronomers, as well in our HST ToO program (see below). The images in Fig. 1 also show the first detection of a long-awaited haze over the north polar region. Several images from our paper are shown below. (I. de Pater, L.A., Sromovsky, P.M.Fry, H.B. Hammel, C. Baranec, K. Sayanagi, 2015. Record-breaking Storm Activity on Uranus in 2014. Icarus, 252, 121-128.)
Fig. 1. Images of Uranus at H (1.6 micron) and K' band (2.2 micron) obtained with the 10-m Keck telescope on UT 5 and 6 August 2014 (top and middle row); the bottom row shows H band images taken on UT 17 and 20 August 2014. Note the extremely large storm system (labeled Br) on 6 August. Seven other large features are indicated as well. A feature seen in H band on the southern hemisphere on 5 August is marked with an arrow and the symbol S1. Numerous other features are also visible in the H band images when suitably enhanced. A longitude-latitude (planetocentric) grid has been superposed on the K' band images with a grid interval of 30deg.
Fig. 2. Color composite images of Features 1, 2 and Br, projected on a rectangular grid. The K' band image, sensitive to the highest altitudes, is shown in red; H band, sensitive to the deepest levels, is shown in blue, and CH4S in green. The boxes A-D for Feature 1, and A-F for Br indicate the areas where cloud altitudes were determined (Table 1 in de Pater et al., 2015). Feature E is the same as Feature 4 in Fig. 1.
Upon issuing an alert through the International Outer Planets Watch, the amateur community responded with an extensive observation campaign. By early October several amateur astronomers had reported the detection of a bright cloud feature on the planet's disk, using telescopes varying in size from 14-inch up to the 1-m telescope at Pic-du-Midi and broadband filters spanning ~650-850 nm range. The top images were taken on Sept. 19 and Oct. 2, and show the dramatic appearance of a bright storm on a planet that normally displays only a diffuse bright polar region. (Courtesy of amateur astronomer Anthony Wesley, Murrumbateman, Australia.) The bottom image is an animation showing the bright spot as Uranus rotated over a two-hour period on Oct. 4, 2014. These images were taken at the Pic du Midi telescope in the French Pyrenees. (Courtesy of Marc Delcroix and F. Colas (S2P))
The amateur observations were used to trigger our Target of Opportunity (ToO) program on HST (GO13712, PI: K. Sayanagi). These observations were carried out on UT 14 October 2014. Left: An image taken at 845 nm (845M band), where the contrast of features on Uranus's disk is large. The image on the right shows a 3-color composite; the image has been rotated such that Uramus's north pole is up. The highest levels in the atmosphere are probed in the FQ889N filter (red); the deepest levels in the atmosphere are probed in the FQ937N filter (blue); the Q658N filter probes intermediate altitudes (green). Feature 2, with its extended streamer, is visible just north of the center of the disk. At this time it looks like a complex feature, visible in all filters, i.e., it appears to extend from the deep atmosphere to the highest layers in the atmosphere. Rather than just Feature 2, however, we see instead the chance appearance of both Features 1 and 2 at nearly the same longitude; Feature 1, being higher in the atmosphere (Fig. 1), gives the complex feature the red color near 35deg N. Feature 2's extended streamer is visible only in the blue (FQ937N filter). The triplet of features near 17deg N is most likely connected to feature Br in Fig. 1.
See Full Press Release from UC Berkeley
