possible infrared aurorae on jupiter

ICARUS 44, 667--675 (1980)

Possible Infrared Aurorae on Jupiter

J O H N C A L D W E L L 1

Department of Earth and Space Sciences, State University of New York, Stony Brook, New York 11794

A. T. T O K U N A G A 2

Institute for Astronomy, University of Hawaii, Honolulu, Ha wafi 90822

A N D

F. C. G I L L E T T

Kitt Peak National Observatory 3, Tucson, Arizona 85726

Received August 4, 1980; revised November 14, 1980

We have observed infrared brightenings near the poles of Jupiter at 8 /zm in early 1980. We suspect they are nonthermal in origin. These brightenings are apparently related to the auroral zones which are determined by the magnetic mapping of the magnetotail onto the atmosphere, rather than by the Io flux tube. They were present in both hemispheres in January, present only in the north in February, and probably absent in the south in March. When visible, they were only seen in the hemisphere where the auroral zone was oriented toward the Earth and absent otherwise.

I. INTRODUCTION

Photometry of Jupiter in the wavelength range near 8/xm, which is in the wing of the very intense v4 fundamental of methane (CH4), provides information about the Jo- vian stratosphere, at and above the 10- mbar-pressure level. Such data have previously been interpreted as thermal emission, with at most small departures from local thermodynamic equilibrium (Orton, 1977).

For example, we have suggested that an observed nor th-south asymmetry on Jupi-

1 Visiting Astronomer at the Infrared Telescope Facility which is operated by the University of Hawaii under contract from the National Aeronautics and Space Administration.

2 Visiting Astronomer, Kitt Peak National Observa- tory, and Staff Astronomer at the Infrared Telescope Facility.

3 Operated for the National Science Foundation by the Association of Universities for Research in As- tronomy, Inc.

ter at this wavelength is due to a seasonal variation in the Jovian stratospheric temperature, caused by its small but finite obliquity (Caldwell et al., 1979). We have further claimed that small infrared features at intermediate latitudes, which correlate with visual belt-zone structure, can be un- derstood in terms of enhanced stratospheric heating over latitudes where the tropospheric cloud heights are higher than average, resulting in more backscattering of sunlight to the stratosphere (Cess et al., 1980).

In the present paper, we present new data on Jupiter at 8 tzm, obtained by the N A S A 3-m Infrared Telescope Facility (IRTF) at Mauna Kea and the Mayall 4-m telescope at the Kitt Peak National Obser- vatory, from January to March 1980. These data reveal a previously unreported phenomenon: infrared brightenings near both poles, confined to different longitudes in each hemisphere. The brightenings were

667 0019-1035/80/120667-09502.00/0 Copyright ~) 19~0 by Academic Press, Inc.

All rights of reproduction in any form reserved.

N APERTURE -,~ M- S

66

p r e s e n t in b o t h h e m i s p h e r e s in ea r ly Janu- a ry 1980; p r e s e n t in the nor th b u t no t in the sou th in ea r ly F e b r u a r y ; and a b s e n t a t l eas t in the sou th in ea r ly M a r c h .

T h e t ime sca le o f this c h a n g e in s t ra to- sphe r i c p r o p e r t i e s is m u c h less than ex- p e c t e d as a s ta t ic , t he rma l r e s p o n s e to changing in so l a t i on (Ca ldwe l l et al., 1979). T w o e x p l a n a t i o n s a p p e a r to b e c o n c e p t u - a l ly p o s s i b l e to us: d y n a m i c a l effects and a u r o r a l ( non the rma l ) effects . O u r da t a do no t d i s t ingu i sh b e t w e e n t h e s e poss ib i l i t i e s , bu t w e po in t ou t s eve ra l i n t e re s t ing f ea tu re s of the la t te r .

II. THE DATA

N o r t h - s o u t h dr i f t s cans w e r e m a d e o f Jup i t e r dur ing the n ights J a n u a r y 4 - 6 , 1980; F e b r u a r y 2 -4 ; and M a r c h 2. T h e cen t r a l w a v e l e n g t h and b a n d p a s s e s o f the o b s e r v a - t ions w e r e h0 = 7 . 9 / z m , Ah = 0.6 /zm for the I R T F o b s e r v a t i o n s and h0 = 7 . 9 / z m , AX -- 0.2 /zm for the K P N O o b s e r v a t i o n s . A to ta l o f 14 scans at 8 /xm a re i n c l u d e d in this r e p o r t , 6 f rom J a n u a r y , 7 f r o m F e b r u a r y , and 1 f rom M a r c h . Dur ing the d i s c o v e r y run in J a n u a r y , the s cans w e r e i n t e r l e a v e d wi th o t h e r o b s e r v a t i o n s , b o t h o f Jup i te r and o f S a t u r n and its r ings ( T o k u n a g a et al. ,

TABLE I

Scan Mid-Time Date LCMm Telescope a Number (UT) (1980) (1965)

1 12:38 4 Jan. 168 3 m 2 10:52 5 Jan. 255 3 m 3 11:14 5 Jan. 268 3 m 4 11:06 6 Jan. 54 3 m 5 11:25 6 Jan. 66 3 m 6 16:26 6 Jan. 248 3 m 7 10:54 2 Feb. 154 4 m 8 9:24 3 Feb. 249 4 m 9 9:34 4 Feb. 47 4 m

10 9:46 4 Feb. 53 4 m 11 9:54 4 Feb. 56 4 m 12 10:07 4 Feb. 68 4 m 13 10:23 4 Feb. 73 4 m 14 7:55 2 Mar. 93 3 m

a 3 m = Infrared Telescope Facility, Mauna Kea, Hawaii; 4 m = Mayall Telescope, Kitt Peak National Observatory.

668 CALDWELL, TOKUNAGA, AND GILLETT

FIG. 1. North-south drift scans (numbers 1 to 6 from Table I) from the IRTF at Mauna Kea. (January 4-6, 1980, at 8/zm.)

1980). S ince the p o l a r b r igh ten ing p h e n o m - e n o n was no t a n t i c i p a t e d , our o b s e r v a t i o n s we re no t p l a n n e d to o p t i m i z e its inves t iga - t ion. H o w e v e r , we b e l i e v e tha t our resu l t s a re a d e q u a t e to e s t ab l i sh its rea l i ty .

T h e F e b r u a r y run was m o r e s y s t e m a t i c , cove r ing long i tudes d e t e r m i n e d to b e in ter - es t ing f rom the p r e v i o u s ser ies . Unfo r tu - na te ly , the M a r c h run was p l a gue d b o t h b y b a d w e a t h e r and b y e q u i p m e n t fa i lu res . N e v e r t h e l e s s , the l a t t e r two runs d id dem- o n s t r a t e a c h a n g e in the s o u t h e r n hemi- sphe re wi th r e s p e c t to the first run .

The de ta i l s o f . the o b s e r v a t i o n s a r e g iven in T a b l e I. T h e d a t a f rom J a n u a r y 1980, a r e p r e s e n t e d in F ig . 1. N o t e tha t a l though the scans a r e l i s t ed c h r o n o l o g i c a l l y in T a b l e I , t hey a r e o r d e r e d a c c o r d i n g to S y s t e m I I I (1965) cen t ra l m e r i d i a n long i tude (Sei- d e l m a n n and Div ine , 1977) in F ig . 1. In tha t f igure, the scans a re a l so c l u s t e r e d ve r t i c a l l y in t h ree g r o u p s , wi th L C M . I (1965) ~ 255 ° (3 scans ) , 168 ° (1 scan) , and 60 ° (2 scans) . The r e a s o n for this c lus te r ing will be d i s c u s s e d b e l o w .

In Fig . 1, ve r t i ca l a r r o w s m a r k the nor th and sou th l imbs . T y p i c a l e r r o r b a r s a re s h o w n for the t op scan . The a p e r t u r e d i a m e t e r is 2 a r c s e c , wh ich c o r r e s p o n d s to

IR AURORAE ON JUPITER 669

N S APERTURE --~ ~-

73

_N

/~ V-LCMllr(19651 = 249

FIG. 2. Scans 7 to 13, from the Mayall telescope at Kitt Peak. (February 2-4, 1980 at 8 ~m.)

two spatial steps in the photometry pro- gram. Although the data were recorded in discrete digital form, they have been joined by smooth curves, for clarity, in Fig. 1.

Figure 2 similarly shows the data from February. In each case, two scans were coadded by the telescope data system com- puter before plotting. The aperture for these scans was 2.6 arcsec. The scans are clustered according to LCMm (1965) analo- gously to those in Fig. 1, with one, one, and five scans in the corresponding respective groups. Figure 3 shows the single scan from March, compared to scans from previous runs that are close in LCMIII (1965). The higher systematic noise during the March run is apparent f rom the errors bars, which are twice as large, and from the nature of the data.

III. DISCUSSION

The reason for grouping the scans according to central meridian longitude is apparent f rom Fig. 1. The scans near LCMm (1965) ~ 255 ° are all qualitatively similar to each other, including numbers 2 (255 °) and 6 (248°), which were obtained 29.5 hr apart, with qualitatively different

but repeatable scans, numbers 4 (54 °) and 5 (66 °) between them.

The group at LCMm (1965) ~ 255 ° is typical of scans of Jupiter at 8 tzm that we have obtained in recent seasons. For example, compare them with Fig. 1 of Caldwell et al. (1979) or with Fig. 1 of Cess et al. (1980). The asymmetry between the two polar limbs has previously been ascribed to seasonal stratospheric temperature differences (Caldwell et al., 1979). However , the structure at midlatitudes has changed somewhat in the past year.

At LCMm = 168 °, the northern limb is relatively enhanced with respect to the rest of the scan along Jupiter ' s central meridian, and such an effect does not occur for any other scan in the January run. For this scan, the southern limb is essentially the least bright part of the planet. However , near LCMm = 60 °, the northern limb is only slightly brighter than the equator, and the southern limb has become the brightest part of the planet.

Similarly in Fig. 2 scan number 7 [LCMm (1965) = 154 °] f rom February 2, 1980, ex- hibits a north polar enhancement with respect to all o ther scans during that run. Scan 7 is very similar to scan I ( 168 °) in Fig. 1. Note, however , that five attempts to reobserve the south polar brightening in the range from LCM.I = 50 to 70 ° in February

N S

Fro. 3. Scans from three runs (at 8 ~m): January and March 1980 at Manna Kea; February 1980 at Kitt Peak.


z

N

FIG. 4. Average of the six scans from Fig. 1, except that the north polar brightening of scan 1 and the south polar brightenings of scans 4 and 5 have been exempted from the average and plotted here as broken lines.

were all definitely negative. Scans 9-13 all have their southern limbs less bright than their equators , and are distinctly different f rom scans 4 and 5, obtained at similar longitudes.

Scan 14 [LCMIH (1965) = 93 °] in Fig. 3 also appears to be significantly different f rom other scans ~25 ° different in longitude. Although the data are noisy, its south pole is definitely less bright than the equator.

The polar limb brightenings are further defined in Fig. 4, where the six scans f rom Fig. 1 are combined at midlatitudes to give a quasi-longitudinally averaged Jovian nor th - sou th scan, but where the north limb enhancement of scan 1 [LCMI. (1965) =

168 °] and the south limb enhancements of scans 4 and 5 (54 °, 66 °) are exempted from the average of the other scans, and shown as b roken lines.

It is of interest to note that the magnitude of each polar enhancement is comparable to that of the equatorial brightening in Fig. 4. We have previously suggested that midlatitude features may be the stratospheric thermal response to t ropospheric cloud structure (Cess et al . , 1980). There- fore, it is possible that we are seeing at the poles yet another thermal s t ratospheric response. We have previously es t imated that the static radiative time constant for the appropriate levels of the Jovian stratosphere is ~-5 Ear th years (Caldwell e t a / . , 1979). Therefore , if these polar brightenings are thermal, their variability f rom month to month strongly suggests that there is a dynamical process occurring, and not just a static response to varying insolation or other parameters .

Howeve r , it is also possible that we are seeing a nonthermal phenomenon in the upper Jovian a tmosphere . This possibility will be explored in the next section.

IV. THE MAGNETIC CONNECTION

Ness et a/ . (1979) have presented a model for the auroral zones on Jupiter, where the

180*

O*

18o"

0*

/

"NORTHERN" - - Io L SHELL FOOTPRINT "SOUTHERN"

(~ MAGNETIC DIPOLE AXIS

~ AURORAL ZONE

FiG. 5. The positions of the auroral zones, Io footprint and magnetic poles, taken directly from Ness et al. (1979). The arrows indicate longitudes for our January observations. Those arrows with double heads indicate infrared brightenings in the corresponding hemisphere. Note that the angular coordinate, which is System III (1965) longitude, is plotted in opposite senses for the two hemispheres.


magnetic field lines connect directly with the magnetospheric tail. Their Fig. 6 is reproduced here as Fig. 5, where we have added arrows to indicate the System III (1965) central meridian longitudes corresponding to the scans from January 4-6, 1980. The double-headed arrows depict longitudes where our scans indicate polar limb brightening in the appropriate hemisphere. The figure also shows the Io L shell footprint and the magnetic poles.

At the time of our observations, the Jovian rotational axis was nearly perpen- dicular to the direction of the Earth. The auroral zones of Ness et al. (1979) and the Io L shell footprints are offset from the rotational pole in approximately the same direction in the respective hemispheres. The correlation shown in Fig. 5 between the LCMs of our observations of excess polar infrared emission and the System III (1965) longitude of the auroral zone / Io footprint offset from the rotational pole is striking, although the number of examples is small.

Of the two types of regions on Jupiter, our observations suggest that it is the auroral zones rather than the Io footprints that are germane to the infrared brightenings. The equatorward extension of the northern hemisphere footprint near System III (1965) longitude 170 ° reaches zenographic latitude 47 °, approximately 5 arcsec, or 2.5 aperture diameters inside the polar limb. From Fig. 1, it appears that the northern peak emission of scan 1 at LCM.E (1965) = 168 ° is much closer to the limb than this. We therefore prefer to associate the brightenings with the smaller auroral zones, although we recognize that our spatial resolution is not quite good enough to preclude absolutely the larger footprints.

The preceding discussion refers to the region of the peak of the infrared excess emission. Our observations are ambiguous with respect to the possibility that the brightening may extend over a wide range of zenographic latitudes. From Fig. 4, it may be seen that scan 1 with the northern

excess does appear slightly brighter almost down to the equator. However , outside the peak emission in the south, the average of the two scans (4 and 5) showing the excess is slightly less bright than the overall average. These slight variations are actually similar to typical variations between scans at different longitudes, and may not be significant with respect to the distinct polar brightenings.

The brightenings have no apparent direct relation with the orbital position of Io. For example, scan 1 which showed a northern enhancement and " n o r m a l " southern appearance occurred at virtually the same orbital longitude of Io as scans 4 and 5, which showed southern enhancements and " n o r m a l " northern appearance. The former scan was made just before an eastern elongation o f l o , and the latter two were made 1.1 Ionian revolutions later, just after the following eastern elongation. If there were a mechanism by which Io triggered a polar brightening when it is near eastern elongation, we would expect it to be associ- ated with the large footprints and to be visible simultaneously in both hemispheres. As may be seen from Fig. 5, part of the footprint in each hemisphere is always visible from the Earth. Such a mechanism would not explain why there is no southern brightening in scan 1 (168 °) nor northern brightenings in scans 4 and 5 (54 °, 66°).

Another possibility is that it is the Sys- tem III (1965) longitude of Io which could be important in a hypothetical Io-controlled emission process. During the interval between scan 1 and scans 4 and 5 (46.6 hr), Io 's System III (1965) longitude has changed by -27 .793° /hr x 46.6 hr = - 1 2 9 5 ° = +145 ° . At the same time, the LCMIH (1965) has increased from 168 ° to - 6 0 °, that is, by - 2 5 2 °. These numbers do not suggest a causal relationship.

Fur thermore , the other observations of a northern enhancement , scan 7 [LCMm (1965) = 154 °] was made when Io was just past inferior conjunction. Since the LCMs of scans 1 and 7 are nearly the same, this


corresponds to a difference of - 130 ° in Io's System III longitude between times of northern enhancements.

In summary, there is no indication in these data that the observations are related to Io. However, a much larger number of scans would clearly be useful to permit a more meaningful study of various parameters and it would be premature to exclude absolutely the possibility that the brightenings are somehow influenced by Io.

v. ENERGETICS AND PENETRATION

We estimate the energy involved in these peaks as follows. Six photometric observations of the central part of the equatorial zone of Jupiter were made from January 3- 5, 1980, with an average brightness of 11.9 ergs cm -z see -I /zm -1 sr-~. a Tau was used as a calibration standard. From Fig. 4, we estimate that the height of the excess at each pole above the average polar brightness is ~30% of the central brightness. Our bandpass, FWHM = 0.6 /xm, contains about one-half of the v4 band. Thus, if the emission to space goes to 2zr sr, and the projection factor for the emitting surface is ~cos 70 ° --~ ~, the energy required to produce our observed brightenings is ~9 ergs cm -2 see -1.

This requirement is not extreme by auroral standards. For example, it has been estimated that there are -100 ergs cm -z sec -1 deposited in the terrestrial high-alti- tude auroral zones (Kennel and Coroniti, 1977, p. 425). This is the same order of magnitude as the auroral energy sources for ultraviolet observations of Jovian aurorae from space (Atreya et al., 1977; Sandel et al., 1979).

As mentioned in Section I, CH4 is sufficiently opaque that thermal emission at 8/xm originates at and above the 10-mbar level, particularly toward the limb where the line of sight optical depth increases (Orton, 1977). The Voyager ultraviolet spectrometer experiment has demonstrated, at least for equatorial regions, that

measurable amounts of CH4 exist between the 1- and ~-mbar levels, although not at lower pressures (higher altitudes). Their some question whether in fact they can reach the levels where the CH4 exists. Hunten (1978) has discussed various as- pects of auroral electron penetration in the Jovian atmosphere.

We therefore must emphasize that we have not proved a link between our observations and auroral processes. The evidence is circumstantial, and a full explana- tion may involve processes not considered in this paper. results comes from an occultation of Regu- lus (a Leo) (Atreya et al., 1981).

If the auroral interpretation of our observations is correct, then the extra emission undoubtedly comes from the highest levels at which CH4 exists on Jupiter. Auroral electrons are not sufficiently energetic to penetrate significantly lower and there is

VI. COMPARISON WITH OTHER OBSERVATIONS OF JOVIAN AURORAE

There have been two positive observations of long-wavelength emission from Ju- piter that may have some relation to our work. Fox and Jennings (1977) observed what they called "possible Jovian methane emission" at 76.2 GHz, corresponding to a specific transition in the lowest vibrational state. They had no spatial resolution across the disk, but noted that their emission observation coincided with strong Jovian de- cametric activity. Their suggestion is consistent with ours, that CH4 can be excited nonthermally in the atmosphere of Jupiter.

Kostiuk et al. (1977) presented observations of emission from two lines of ammo- nia (NH3) at the north and south poles of Jupiter. They employed the superheterodyne technique with a COs laser. They suggested that their emissions were nonthermal because the line widths corresponded to T _< 100°K, whereas central intensities corresponded to T > 400°K. The latter is a lower limit only, because the small linewidth precluded broadening due


to Jupiter 's rotation. This in turn implied a very localized source, which underfilled their aperture.

Emission from NH 3 is surprising because it is depleted in the upper stratosphere by ultraviolet photodissociation (Combes et al., 1980). Therefore , the problems associ- ated with particle penetrat ion discussed in the previous section are orders of magnitude more severe against N H 3 than they are against CH 4. This further illustrates the difficulty in understanding the phenomenon completely.

There has also been at least one nonde- tection of CH 4 brightening published. Sin- ton et al. (1978) presented, among other data, a drift scan similar to ours from February 6, 1978, corresponding to a LCMm (1965) of 302 °. The absence of the brightening could be due to the longitude (see Fig. 5) or to lower solar activity at that time, or perhaps to other currently un- known reasons.

Observations of Jovian aurorae have also been made from space, both by Earth- orbiting ultraviolet spectrometers and by planetary flyby vehicles. Atreya et al. (1977) using the Earth-orbital Copernicus satellite detected brightness enhancements on Jupiter by Ly a, which they attributed to auroral emission from hot spots at the foot of the Io flux tube. They observed three cases of substantial enhancement , with LCMm (presumably of epoch 1957.0 rather than 1965) of 139, 259, and 154 ° . Their observations were made in August and Sep- tember 1976, about 3.5 years before ours.

Although their different coordinate system will introduce a slight systematic difference, their first and third observations are still quite close to our scans 1 (168 °) and 7 (154°). Interestingly, their observing geometry was artificially limited by the pointing constraints of the satellite, and they attributed the emission to the s o u t h e r n footprint, whereas our scans definitely have a northern enhancement . However , their slit spanned the diameter of Jupiter. By com- paring their Fig. la and our Fig. 5, it is

apparent that the northern auroral zone is also in their field of view. Therefore , their data do not literally exclude emission from the northern auroral zone.

Their "perp lex ing" positive observation at LCMm = 259 ° remains mysterious since neither auroral zone is favorably placed at this longitude. Fur thermore , our scans 2, 3, 6, and 8 at 225, 268, 248, and 249 ° respec- tively show no particular indication of enhancements.

Clark et al. (1980) observed Jovian aurorae with the International Ultraviolet Ex- plorer satellite. Their spatial resolution is several times lower than ours. However , they were able to infer that their observed emissions were, at least in some cases, diffuse in the eas t -wes t sense, but rather narrow in the nor th-south sense. They can- not distinguish between an auroral zone or a footprint source.

They also find that occasions with similar geometry do not always produce auroral emissions, much as our scans 9-13 are negative. In many respects , the findings of Clark et al. (1980) are therefore qualitatively consistent with ours.

The two Voyager spacecraft produced imaging and ultraviolet spectrophotometr ic evidence of aurorae on Jupiter. Smith et al. (1979) reported dark-side visual auroral observations by the Voyager 1 imaging experiment. The emission came from three auroral layers, 700, 1400, and 2300 km above the cloud tops, and was variable on a time scale of less than a minute. Their aurora was seen from the north pole to latitude +60 ° . Its relation to our data, if any, is not clear.

Broadfoot et al. (1979) reported auroral emission observed with the Voyager I ultraviolet spectrometer . They found the emission peaked away from the poles, near latitude 65 ° , suggesting to them that it origi- nated near the magnetic mapping of Io 's plasma torus onto the atmosphere. They found the northern aurora to be a factor of - 2 times brighter than the southern one.

Sandel et al. (1979) extended the Voy- ager UVS findings with Voyager 2 data.


They demonstrated that the auroral emission extends much farther from the poles than the auroral zones of Ness et al., which, as discussed in section IV, is a probable major difference between their results and ours.

However, since the energies of the pho- tons observed by the Voyager UVS and by us are separated by a factor of more than 50, these diverse conclusions are not con- tradictory. Several processes may be involved. Sandel et al. do not exclude a minor component poleward of the toms footprint.

They also found that by the time of the second Voyager encounter, the southern aurora had become - 40% brighter than their northern one. As may be seen in our Fig. 4, the infrared brightenings were of nearly the same peak intensity in both hemispheres.

We see, therefore, several examples of interesting differences between the various space observations and our ground-based infrared data. This leads us to suggest that more observations of this type would be useful.

VII. FUTURE OBSERVATIONS

Our present findings could be improved in several ways with more observations. In particular, the following would be useful:

(l) obtaining spectrally resolved observations near 8 p.m to determine if the emission is thermal or nonthermal;

(2) obtaining area scans similar to the ones in Figs. 1, 2, and 3 but at shorter wavelengths such as 3.3 /zm. If emission occurred there, it would be a conclusive demonstration of nonthermal origin. How- ever, failure to detect such emission could be due to an absence of sufficiently energetic (sic) particles at the locations on Jupi- ter where the brightenings reported here occur,

(3) increasing the number of observations, so that there is a better basis to decide what parameters, such as Io's loca- tion, influence the emission; and

(4) conducting observations from several observatories well separated in terrestrial longitude to improve temporal coverage of the phenomenon.

ACKNOWLEDGMENTS

We are grateful to Dr. M. A. Forman for very helpful discussions, and we wish to thank our telescope operator at Mauna Kea, Mr. Ron Koehler, for working overtime to permit us to obtain scan 6 in this paper. J. C. received support from NASA Grant NSG 7320 and NSF Grant ENG 77-09124 during the course of this work.

REFERENCES

ATREYA, S. K., YUNG, Y. L., DONAHUE, Z. M., AND BARKER, E. S. (1977). Search for Jovian auroral hot spots. Astrophys. J. 218, L83-L87.

ATREYA, S. K., DONAHUE, T. M., AND FESTOU, M. C. (1981) Jupiter: Structure and composition of the upper atmosphere. Astrophys. J., in press.

BROADFOOT, A. L., et al. (1979). Extreme ultraviolet observations from Voyager I encounter with Jupi- ter. Science 204, 979-982.

CALDWELL, J., CESS, R. D., CARLSON, B. E., TO- KUNAGA, A. T., GILLETT, F. C., AND NOLT, I. G. (1979). Temporal characteristics of the Jovian atmosphere. Astrophys. J. 234, LI55-L158.

CESS, R. D., CARLSON, B. E., CALDWELL, J., NOLT, I. G., G1LLETT, F. C., AND TOKUNAGA, A. T. (1981). Latitudinal variations in the Jovian stratospheric temperature. Icarus, in press.

CLARKE, J. T., MOOS, H. W., ATREYA, S. K., AND LANE, A. L. (1980). Aurora on Jupiter observed from Earth orbit. Preprint; submitted for publica- tion.

COMBES, M., COURTIN, R., CALDWELL, J., EN- CRENAZ, Th., FRICKE, K. H., MOORE, V., OWEN, T., AND BUTTERWORTH, P. S. (1980). Vertical dis- tribution of NH3 in the upper Jovian atmosphere from IUE observations. Advances in Space Re- search, Vol. XXI. Pergamon Press, New York, in press.

FOX, K., AND JENNINGS, D. E. (1977). Possible Jovian methane emission at 76 GHz in coincidence with decameter activity. Astrophys. J. 216, L83-L84.

HUNTEN, D. M. (1978). Paper presented at Chapman Conference on Jovian Magnetospheric-Satellite In- teractions, University of California at Los Angeles, June 27-29, 1978.

KENNEL, C. F., AND CORONITI, F. V. (1977). Jupiter's magnetosphere. Annu. Rev. Astron. Astrophys. 15, 389-436.

KOSTIUK, T., MUMMA, M. J., HILLMAN, J. J., BUHL, D., BROWN, L. W. AND FARIS, J. L. (1977). NH 3

IR A U R O R A E O N J U P I T E R 675

Spectral line measurements on Earth and Jupiter using a 10 /zm superheterodyne receiver. Infrared Phys. 17,431-439.

NESS, N. F., Acur~A, M. H., LEPPING, R. P., BEHANNON, K. W., BURLAGA, L. F., AND NEUBAUER, F. M. (1979). Jupiter's magnetic tail. Nature 280, 799-802.

ORTON, G. S. (1977). Recovery of the mean Jovian temperature structure from inversion of spectrally resolved thermal radiance data. Icarus 32, 41-57.

SANDEL, B. R., et al. (1979). Extreme ultraviolet

observations from Voyager 2 encounter with Jupi- ter. Science 206, %2-966.

SEIDELMANN, P. K., AND DIVINE, N. (1977). Evalua- tion of Jupiter longitudes in System III (1%5). Geophys. Res. Lett. 4, 65-68.

SMITH, B. A., et al. (1979). The Jupiter system through the eyes of Voyager 1. Science 204, 951- 972.

TOKUNAGA, A. T., CALDWELL, J., AND NOLT, I. G. (1980). The 20 /xm brightness of the unilluminated side of Saturn's rings. Nature 287, 212-213.

possible infrared aurorae on jupiter

Documents