The Role of Amateur Astronomers in Documenting the Spatial Context and Time Evolution of the Jovian Atmosphere to Benefit the Juno Mission

Introduction

Many of Juno’s observations use external information to determine their context in space and time for the “snapshots” of usually very limited regions of the planet that it detects in its close approaches (“perijoves”, PJs).  This has been the role of the campaign of supporting observations from the professional community, but it has always been bolstered by the near-continuous observations made by the increasingly sophisticated cadre of the world-wide amateur network.  This year is one in which this role was particularly apparent.

 

Tracking Activity in Jupiter

Among the many areas of interest in Jupiter undergoing changes are the following.

   Great Red Spot (GRS).  Continuing activity follows on from remarkable interaction of small-scale anticyclones transported counter-clockwise inside the GRS Hollow throughout the spring and fall of 2019. These caused arcuate features, commonly called “flakes”, to appear on the western side of the GRS , which were likely to be material swept off the upper portions of the GRS itself [1]. JunoCam continued to record evidence of them during geocentric solar conjunction at PJ23, PJ24 & PJ25, and  the amateur community has continued to monitor them in early 2020.  We expect that this type of interaction will continue, as it is apparently tied to the secular longitudinal shrinkage of the GRS, with the results distinguishing between different models for the dynamical interactions involved [2,3].

   Equatorial Zone Disturbance.  The Equatorial Zone (EZ) was predicted to undergo a disturbance based on the cyclic nature of past events [4] with a major disruption of its bright visual and cold 5-µm appearance.  Although the disruption of its 5-µm appearance did not happen, the EZ darkened in blue and UV light, and there was an increase in the thickness or altitude of an upper-atmospheric haze [5]. The amateur-observation record shows that a darker shade of its visual appearance is still present as this coloration episode declines.  Juno scientists continue to be interested in the EZ to determine whether such events relate to changes in the remarkably deep-seated upwelling of air detected by the Juno Microwave Radiometer as a column of concentrated ammonia gas [6].  So we are interested in changes to the color, either a return to its normally bright appearance or a renewed darkening that might presage a true disruptive event that is simply “late”.

  Outbursts.  Two major outbursts of convective plumes were observed by JunoCam, one in the North Temperate Belt shortly before PJ2 [7] and another in the South Equatorial Belt near PJ4 [8,9] that was associated with lightning detections [10].  Such outbursts are of interest to Juno scientists. Hi-res amateur imaging also synergizes with JunoCam in characterizing smaller outbursts.  One notable example, discovered just before this writing by Foster [11], was recorded in detail by JunoCam at PJ27, showing some morphological similarities with the initial development stages of terrestrial tropical storms.

 

Overcoming COVID-19 Disruptions

For recent Juno orbits, low-latitude regions are observed at extremely oblique angles except during perijoves when off-Earth pointing of the spacecraft is adopted.  These are chosen carefully because they use up fuel that the Juno science team would like to reserve for an extension of the mission. A single orbit in 2020, chosen for such a turn at PJ26 on April 10, turned out to be in the middle of the COVID-19 pandemic when nearly all professional observatories scheduled to provide Juno support were shuttered. Except for two semi-automated observatories and Hubble Space Telescope, whose ground crew were deemed “essential”, it was the amateur community who provided the only information about Jovian variability during this time.   This was also true for PJ27 on June 2, when a few more professional observatories opened.

 

Future Prospects

We hope for continued support from the amateur community. Scientists on the Juno mission hope to persuade NASA to fund an extension; one candidate scenario could extend out to PJ70 in late 2025.  This would not only extend the time line for continued observations of atmospheric evolution but would take advantage of different types of observations not possible during the primary mission, due to orbital geometry.  We would hope observations by this community would continue to provide the continuity of atmospheric scrutiny from which we have benefitted so far.

 

References

 

[1] Foster et al. 2020.  The Great Red Spot in 2019 and its interaction with retrograding vortices as monitored by the amateur planetary imaging community. https://britastro.org/node/22552

[2] Sanchez-Lavega, et al. 2019. Jupiter’s Great Red spot threatened along 2019 by strong interactions with close anticyclones. Amer. Geophys. Union meeting. P44A-01.

[3] Marcus, et al. 2019. On the shedding of flakes by Jupiter’s Great Red Spot: It is not dying. Amer. Geophys. Union meeting. P13B-3505.

[4] Antuñano, et al. 2018.   Infrared characterisation of Jupiter's equatorial disturbance cycle.  Geophys. Res. Lett.  45, 10987-10995.

[5] Orton, et al. 2019. Juno and Juno-supporting observations of Jupiter’s 2018-2019 Equatorial Zone disturbance. EPSC-DPS2019-109.

[6] Li et al. 2017. The distribution of ammonia on Jupiter from a preliminary inversion of Juno microwave radiometer data. Geophys. Res. Lett. 44, 5317-5325.

[7] Sanchez-Lavega et al. 2017. A planetary-scale disturbance in the most intense Jovian atmospheric jet from JunoCam and ground-based observations. Geophys. Research Lett.  44, 4679-4686.

[8] de Pater et al. 2019. First ALMA millimeter wavelength maps of Jupiter, with a multi-wavelength study of convection. Astronomical Journal. 158, 139 (17pp).

[9] Wong, et al. 2020. High-resolution UV/optical/IR imaging of Jupiter in 2016-2019. Astrophys. J. Suppl. Ser. M. H. Wong, et al. 2020. High-resolution UV/optical/IR imaging of Jupiter in 2016-2019. Astrophys. J. Suppl. Ser. 247:58 (25 pp).

[10] Brown et al. 2018. First detection of lightning sferics from Jupiter reveals new insights into the global distribution of moist convection.  Nature 558, 87-90.

[11] Foster et al. 2020. A rare methane-bright outbreak in Jupiter’s South Temperate domain.  EPSC2020.