Astronomers at the University of Massachusetts will be observing the effects of the impacts of the fragments of comet SL-9 using a 256 × 256 NICMOS3 infrared camera (NICMASS) at the 0.4m Whately Observatory. This page will be updated with recent results.
Our main objective is to monitor the changes in the appearance of Jupiter at a wavelength of 2.26 µm. At visible wavelengths, light from the Sun can pass through Jupiter's upper atmosphere, reflect off of cloud particles, and emerge again through the upper atmosphere to be seen by a distant observer. At certain wavelengths in the infrared, particularly between 2.2 and 2.4 µm, methane and molecular hydrogen in Jupiter's atmosphere strongly absorb the incident sunlight -- long before it can penetrate through the atmosphere to reflect off of the clouds. As a result, Jupiter reflects virtually no sunlight at certain near-infrared wavelengths, making it appear nearly pitch-black to an observer working at these wavelengths. Our expectation is that the impacts of the fragments of comet SL-9 will stir particles high enough into the atmosphere so that sunlight can reflect off of them before being absorbed. Jupiter may develop a bright spot near the impact site that will be spread around the planet as a belt by the global winds.
If you click here you will see a spectrum of Jupiter spanning the wavelength range from 2.0 to 2.5 µm. The spectrum illustrates why the planet appears so dark when observed at 2.30 µm. This spectrum was obtained in by Phil Nicholson and Mike Skrutskie in 1985 using a single channel InSb grating spectrometer at Cornell University's 0.6m Hartung-Boothroyd observatory near Ithaca, New York.
The images below compare the appearance of Jupiter at 1.64 µm (a wavelength where you can see reflected sunlight from the clouds) and at 2.26 µm (a wavelength where the planet appears dark due to absorption of sunlight by methane molecules). The images are shown scaled to their true relative brightness. When these images were obtained with the NICMASS camera (by Phil Nicholson (Cornell), Mike Meyer (UMASS), and Guy Worthey (Michigan)) at the 2.4m Hiltner Telescope at Michigan-Dartmouth-MIT observatories, the satellite Io was in transit across the disk of Jupiter. Io is a good reflector of sunlight at both 1.64 µm and 2.26 µm and provides yet another reference point to see how dark Jupiter itself appears at these wavelengths. Note that the shadow of Io is visible on the cloudtops of Jupiter in the leftmost image. You can click on either image to see it at full scale.
If you click on the 1.64 µm image of Jupiter below you will see the results of observations taken at the Whately Observatory on July 13, 1994 UT at wavelengths of 1.64 µm, 2.12 µm, 2.16 µm, and 2.23 - 2.29 µm. These observations were obtained so that we have reference images of Jupiter before its atmosphere is disturbed by the impacts.
Observations from the Whately Observatory in Western Massachusetts with the NICMASS Infrared camera have detected atmospheric features induced by impact "A". Observing in a 2.23-2.29µm filter (deep in the methane band) at 00:20 UT we see a bright spot at the impact latitude about to disappear over the West limb. The spot is about 10 times fainter than Io (which just emerged from behind the planet). The feature was still visible at 01:34UT. Observers were Mike Skrutskie and Sven Aas from the University of Massachusetts.
Additional information: At 1:50 UT the impact site was no longer visible, having rotated over the limb. Unfortunately we cannot provide a more accurate timing as it was cloudy between 01:38UT (the last observation where we could see the feature) and 01:50UT.
Click on the above image to see the results of the impact of fragment "A" observed with the NICMASS camera at Whately Observatory through a 2.23 - 2.29 µm filter at 01:31UT on July 17. The impact region is the small detached dot on the lower right (southwest) portion of the planet. The bright satellite to the left is Io. Io appeared about 50 times brighter than the impact zone when this image was taken. The rotation of Jupiter carried the impact zone over the limb shortly after this image was taken.
Observations of the impact of fragment "B" at Whately Observatory were clouded out. Of course it became crystal clear after Jupiter set below the trees....
At fragment "F" impact time it is raining at the Whately Observatory. Given the forecast, observations are unlikely before Tuesday.
The skies cleared miraculously at sunset tonight (Monday). Humidity is about 100% (it's like Keck last night -- with oxygen). We are imaging in a variety of bands (2.23-2.29, 2.12, and 1.64 µm). Able to see 4 impact sites at 00:40UT in the 2.23-2.29µm band. "H" fragment site is quite prominent in all bands going over the limb. Clouds came in after about 1 hour of observing. Added images at 1.28, 2.16, and 2.24 µm. All wavelengths listed individually are through a 1% filter.
The images above were obtained on July 19 UT at the 0.4m Whately Observatory using the NICMASS infrared camera. Four impact sites are visible in the 2.23 - 2.29 µm image taken at 00:43UT (shown individually with a color stretch in the left image above). From east (left) to west the sites are C, A, E/F, and H. Site "H" is just disappearing over the western limb. The planet rotated to carry the "H" site out of view in the subsequent images. The observers were Mike Skrutskie and Sven Aas from the University of Massachusetts.
At 22:17UT on July 19 UT we observed the beginning of the fragment "L" flash. Within 13 minutes the emission from the impact site saturated our NICMOS3 array through a 1% filter at 2.29µm with an 0.6s integration time. By 22:40 the spot had faded to be twice as bright as Io. At 23:00 the impact site was similar in appearance to site "K" through a 2.23 -- 2.29µm filter. We continued observing the development of site "L" at the usual set of wavelengths until Jupiter set below the trees.
The images above show a time sequence of the "L" impact observed through a 2.23 -- 2.29µm filter in daylight with the NICMASS camera at the 0.4m Whately Observatory. The sequence begins at the upper left and ends at the lower right. Each frame is an average of 10 0.6s exposures lasting 25 seconds in total. The sequence of mid-frame times is 22:15:43, 22:16:51, 22:17:35, 22:18:40, 22:19:40, 22:20:15, 22:21:12, 22:22:10, 22:23:10, 22:24:00, 22:24:53, 22:26:50. By frame 22:23:10 the brightness of the impact region matched that of Io. By the last frame in this sequence (just before the array saturated in the 2.23 - 2.29 filter) the impact region was 10 times brighter than Io. The bright spot to the right (west) of the "L" impact region is the "K" impact site. The region continued to brighten after 22:27, reaching a peak at 22:31. At peak brightness, observations through a 1% 2.29µm filter saturated as well, suggesting that the peak was at least 30 times brighter than Io. Click here to see a plot of the initial brightening in units of the brightness of Io. The uncertainty for the unsaturated points is 0.05.
The movie was constructed from 51 images taken over the course of 43 minutes. The 15 initial frames were taken through a 2.23 -- 2.29 µm filter. Saturation of the camera forced us to change to a 2.29 µm 1% filter (a dark spot appears in the middle of the impact flare due to saturation at this point). This change in filters is seen in the movie as an slight change in the brightness of the old "K" impact site as well as the near disappearance of any flux from the Jovian poles. The impact site continued to brighten significantly after switching filters -- a dark spot appears again in the middle of the region again due to saturation in this narrow filter. After 21 more frames were taken through this narrow filter we returned to the 2.23 -- 2.29 µm filter until the completion of the sequence. The data appear relatively noisy because they were obtained in daylight. The local time was about 6 p.m. Note how the rotation of the planet carries the "K" impact site across the disk. The separation between "K" and "L" appears to increase since "L" is near the limb and the projected motion due to rotation is small.
Whately Observatory did not detect any direct signature of the fragment "U" impact. Observations were made with the NICMASS infrared camera through a 2.23 - 2.29um filter during the interval 21:37UT to 22:30UT. We were observing in daylight, the fragment "K" impact site was coming up over the horizon, and fragment "U" is quite faint -- so the non-detection should not be surprising.
Click
on this image to see it at full scale.
On August 6-7 and 7-8 (UT) the NICMASS camera imaged Jupiter at 1.64µm (1%), 2.12µm (1%), and 2.23 - 2.29µm at the 0.4m Whately Telescope. The image above shows a mosaic of these images which provides full longitude coverage on Jupiter in all three bands. Each column in the mosaic contains images taken during about a 30 minute interval. There are two columns for each "night" of observation -- one set of images from the beginning of the night (actually during the afternoon) and one set of images from the end. The table below provides the corresponding UT times for each image. The impact sites are still quite distinct, although they have begun to spread in longitude. The table contains a listing site identifications visible from east to west in each set of images. Each distinct set of sites is separated by a ",". Combined sites are separated by a "/". In some cases sites that were separate in the center of the disk are combined due to foreshortening when near the limb. These identifications were derived by noting the longitude of the Great Red Spot at the beginning of August 6-7 UT.
August 6-7 UT August 7-8 UT
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1.64um | 23:20 UT 01:04 UT 22:48 UT 01:23 UT |
| |
2.12um | 23:08 01:22 22:35 01:11 |
| |
2.23- | 23:00 00:52 22:17 00:59 |
2.29um | |
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Sites | E/F, H, Q1, W/K/U, W/K/U, Q1/R/S/G, |
Visible | R/S/G C/A, E/F C/A/E L, W/K/U |
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The NICMASS camera will reside in Amherst until the Fall. We plan to continue infrared monitoring of the impact sites until Jupiter becomes inaccessible.
The images below show Jupiter as seen at 13:45UT on 01/14/1995 with the NICMASS infrared camera at the 2.4m Hiltner telescope of the Michigan-Dartmouth-MIT Observatories at Kitt Peak. Considerable structure is visible in the diffused debris from the impacts. These images were obtained through filters at 1.64um (1%), 2.12um (1%), and 2.23-2.29um. Observers were Mike Skrutskie and David Morris from the University of Massachusetts and Kester Allen from Amherst College.
Click here for a plethora of general information about the comet impacts.
skrutski@whately.phast.umass.edu
Last Update: 1/14/1995
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