Date: Fri, 6 Oct 2000 21:05:55 +0100 (BST) From: John Rogers Subject: Jupiter: Interim Report Hi, As Cassini appears to be embarking on a Voyager-style movie marathon for Jupiter, here is a quick update on what has been observed on the planet in the last few months. As always, more details are available from Hans-Joerg or Damian or myself if required. Looking forward to this encounter! -- John. (IJW - See images in Current Images.) ************** JUPITER IN 2000/01: SECOND INTERIM REPORT, PART 1: GENERAL APPEARANCE OF THE PLANET IN MULTISPECTRAL IMAGES, 2000 JULY-SEPT. A good set of multispectral images has now been produced, largely due to Tomio Akutsu, from UV to near-IR (including methane), plus thermal IR (4.8 micron, by courtesy of Dr. Glenn Orton). Isao Miyazaki is taking no images from Sep. to Dec. as he is away on an official trip, but other observers are ably filling the gap. Wavebands used are: -- UV (~360 nm; Akutsu; Aug.1 & 28 [lo-res], Sep.14). Limited resolution because the planet is dark in this waveband. Generally like an extreme violet picture with GRS and NEB as the darkest features, zones bright. -- Visible colours (~400-700 nm; Akutsu, Cidadao, Miyazaki, Moore, Parker, Peach, et al.; June--Sep.). Data include whole-planet sets by Miyazaki on July 16-21 and Aug.14-19, and by others on Aug.25, and maps by Iga et al. on July 16-22 and Aug.24-25. No major abnormalities at present. Pale yellowish tint in SEBZ and EZ(N), though the exact shade must be sensitive to the image-processing -- I-band (~820 nm; Akutsu; July 16--Sep.21). Generally like an extreme red picture, with belts of lowish contrast, but the 'dark bluish' patches of EZs and EZn are very dark. -- Methane (893 nm; Akutsu, Miyazaki; June 25--Sep.21). Limited resolution because the planet is dark in this waveband. Brightest features are always the polar hoods, GRS, STB white ovals (now BA), and EZ. Belts are always dark, including portions that are visibly faint such as SEBZ. -- Thermal IR (4.8 micron; many thanks to Glenn Orton for providing these maps, Aug,21 & 28). Generally a negative of the visible picture, showing bright where the cloud layers are broken. Here is a brief summary of interesting global features in these wavebands. STropZ: A bright zone as usual from UV to IR, except for the fragmentary S. Trop. Band p. the GRS; in UV, this is unresolved but specially dusky. GRS: -- UV: Darkest feature on the planet, along with NEB. -- Visible: As usual, an orange oval (orange colour mainly in a dark central condensation), with a grey-brown oval rim, mostly detached from the SEB; and a darker grey outer rim that varies and sometimes seems to carry material anticlockwise, from a dark spot at f. end onto the sector of S.Trop.Band p. the GRS. -- I-band: Bright, with dark outer rim. -- Methane: Solidly bright oval, as usual. -- Thermal IR: Dark, with bright rim representing the outer rim and RSH, as usual. SEB: -- UV: Dark belt. -- Visible: SEB(S) is very dark, dull brown. The SEBZ, which has developed since March, is bright and appears less yellowish than before in most images. There is a long bluish northerly SEB(C) sector p. the RSH, and elsewhere a grey-brown SEB(N) which is weak and disturbed (see below). -- I-band: Most of SEB resembles the visible picture, but SEB(N) is faint or absent along ths stormy sector. -- Methane: Whole SEB is dark, inc. probable SEBs jetstream spots. SEBZ (both main SEBZ and post-GRS disturbance) must be quite dark or it would be seen, although not fully resolved. -- Thermal IR: SEB(S) is very bright, inc. probable jetstream spots. SEBZ totally dark. SEB(N) fragmentary. SEBn/EZ(S): The disturbance now covers more than half the circumference. The main complex has been invisible in visible and I-band since it passed the GRS in late July, but still is a striking 'step-up' in methane*. Multispectral images show that the stormy sector p. it has lost most of its cloud decks both high and deep, although the EZ(S) is still a normal zone f. the main complex. -- UV (lo-res): Bright (Sep.14) -- Visible: The disturbance, with bright spots and bluish spots or streaks as last apparition, now covers more than half the circumference. The main complex was invisible in August, apart from some deflection of the EB, but reappeared as a bright rift as it passed the GRS on Sep.19. F. the main complex, EZ(S) is still bright white tho with small spots. -- I-band: SEB(N) is faint but the visibly bluish streaks and spots are very dark in I-band -- even up to 250 deg. p. the main complex -- a striking picture (always, but esp. July 31 & Sep.1; & hi-res on Aug.28 when the spots are seen breaking out p. RSH although ~160 deg. p. the main complex). -- Methane: Stormy sector is all dark -- remarkable given that much of this zone is still visibly bright! Even the main rift, when present, is dark in methane. F. it, there is a sharp 'step-up' marking the main complex, f. which the undisturbed EZ(S) is bright as usual for a short distance. -- Thermal IR: Stormy sector is filled with many bright streaks, like a belt. Elsewhere, mostly dark as usual. EB/EZ(N): The EB and festoons seem less prominent and a coloration event may be beginning. -- UV (lo-res): Slightly shaded -- darker than other zones, consistent with the visible colour, but not nearly as dark as in 1989/90 when UV darkening preceded visible colour. NEBs projections not resolved but presumably not dark. -- Visible: The EB and festoons, which were still prominent in June, are perhaps less so now; festoons are less regular, and are embedded in a dull, slightly 'reddish' shading over the whole latitude band. It appears feebly yellowish-brown (fawn) in most images. (It is only slightly shaded in Cidadao's blue images, tho his filter is broad-band.) -- I-band: The dark NEBs patches and festoons or veils show up especially dark. -- Methane: Very bright as usual; EB and festoons not visible. NEBs dark patches are similar in methane and visible, in contrast to pre-1999 years. (So the picture is the same as last apparition.) -- Thermal IR: EB not visible away from the EZ(S) stormy sector. NEBs 'hot spots' (coinciding with visibly dark bluish patches on NEBs) are conspicuous as usual. NEB: Some sectors are now broadened into the canonical NTropZ; the confusing activity of last apparition seems to have constituted a slow 'broadening event' but (so far) it has only gone to completion in some sectors. The broadened sector is genuinely belt-like at all wavelengths. There may also have been some concomitant reddening of the NEB. -- UV: NEB is the darkest belt, consistent with visible reddening. -- Visible: NEB is the reddest belt. -- I-band: A very spotty belt. -- Methane: Very dark belt, inc. the broadened sector. -- Thermal IR: Bright as usual; the broadened sector is broad and spotty. NTropZ: Essentially a normal white zone. -- UV: Patchy but mostly fairly clear, like other zones. -- Visible: Mostly white. Only a few images hint at creamy tint on some sectors. -- I-band: Bright. -- Methane: Dusky, with darker sectors associated with NEBn barges. -- Thermal IR: Dark as usual. John Rogers Jupiter Section Director, British Astronomical Association. 2000 Sep.22 *************************** SECOND INTERIM REPORT (PART 2: INDIVIDUAL FEATURES) Most spots have persisted since the 1999/2000 apparition, so I won't comment further. They are nicely tracked on Hans-Joerg Mettig's JUPOS charts. Here are notes on some of the newer developments. STB: Oval BA: Oval BA is large and coherent, though not always entirely oval. It is gradually acquiring a dark rim. Its drift is still not stable. The much smaller AWO f. it is now quite conspicuous and approaching it. The EZ(S)/SEBn disturbance: The disturbance now covers more than half the circumference, with bluish streaks increasing in prominence with increasing longitude up to the 'main complex' at the f. end. Often there has been a large dark blue streak in EZ(S) a short distance p. the main complex, e.g. in late July/early August around L1 ~ 190. The main complex disappeared visually after it passed the GRS in late July, but remarkably it has remained distinct as a step-up in methane images ever since April (DL1 = +40.6 deg/mth frm June to August, more like +29 deg/mth in Sept.).The main rift was seen breaking out again as it passed the GRS, in images by Damian Peach on Sep.18, Tomio Akutsu on Sep.19, and Ed Grafton on Sep.20. But Akutsu's images from Sep.21 showed that the rift rapidly faded againand was barely perceptible as it drew ahead of the GRS, altho the methane 'step-up' was still present tho indistinct, and there was a very methane-dark patch on its p. side. NEB: The NEB continues to show interesting evolution this apparition, and the attached set of images [WSZSet2b.jpg] shows a particularly interesting sector around the long-lived prograding white spot Z. Features include: >> White spot Z (L2 ~ 230, L3 ~ 170): a white oval that has existed since 1997 and has always had a faster drift than the other NEBn features. Iteliminates other spots preceding it, and new spots are created following it. In July, Damian Peach pointed out that it was approaching another white oval in the same latitude. The latter oval disappeared or merged with w.s.Z around Aug.10. [Damian or I can send further sets of images if required.] >> Dark barges at L2 ~ 205, 240, 270. The barge at 240 was created after w.s.Z passed that longitude, and has rapidly faded again in Sept. (There are also some very dark barges at other longitudes.) >> A prograding dark spot on N.Trop.Band p. the barge at L2 ~ 205. >> The broadened sector of NEB has a distinct p. end here, around L2 ~ 240, just f. w.s.Z. The broadened sector extends up to L2 ~ 330 (fully broadened to the north) or to L2 ~ 60 (weaker). In Sept. the region around w.s.Z itself also appears to have darkened slightly, so w.s.Z appears as a brilliant 'porthole'. At other longitudes there are also wisps of N.Trop.Band so the broadening, which has been sputtering on since last apparition, may be proceeding further. NNTB: An isolated, very dark, reddish-brown bar has been conspicuous at L2 ~ 0. However, Antonio Cidadao reports that it seems to have broken up rapidly between Sep.26 and Oct.3. John Rogers Jupiter Section Director, British Astronomical Association. 2000 Oct.6