Sky and Telescope - November 2017 - 54

NOVEMBER 2017 OBSERVING
Exploring the Solar System

RESULTS FROM JUNO
º NASA's Juno spacecraft has been
sending back amazing images of
Jupiter's ever-changing cloudtops.
But its primary mission is to study
the planet's magnetosphere and
the high-energy particles trapped
inside it. By carefully tracking the
spacecraft, scientists are also
mapping Jupiter's gravity ﬁeld and
using that knowledge to probe
the structure of its interior and the
character of its core.

N O V E M B E R 2 0 17 * S K Y & T E L E S C O P E

January 26, 2016 (17.65 microns)

April 26, 2017 (0.889 micron)

p Although not obvious in visible-light images, a large-scale wave pattern persisted over the NEB
for most of 2017. Compare the right image, which uses a methane absorption band to accentuate
high-altitude detail, and the view made at 17.65 microns, which shows hot spots in the cloud deck.

You Call the Shots
Since JunoCam is intended primarily
for public outreach, its imaging targets
are being chosen by public vote. At the
JunoCam website, amateur astronomers
have been uploading their images of
Jupiter, which the camera team uses to
make up-to-date maps. Then the public
gets not only to nominate "points of
interest" but also to vote for the features that the spacecraft will image at
the next perijove.
JunoCam makes images from wideangle scans of the clouds directly below
the spacecraft, which swoops close in,
3,500 km in altitude, at each perijove.
So targets can be selected by latitude but
not by longitude, because the location
of a particular candidate "spot" depends
on its often-variable drift in longitude.
The amateur group JUPOS produces
maps (found at jupos.org) that track
all of the giant planet's atmospheric
features as they drift east or west, and
the author also produces a predictive
map, to give the best possible estimate
of which features will be observable at
any given perijove pass.
Also, because JunoCam views the
planet at such close range, it is important to put its images into a wider context using amateur images of the track

taken close to the time of perijove. Several observers have made special efforts
to obtain these, notably Clyde Foster
in South Africa. Such images can show
precisely how the dramatic cloudscapes
seen by Juno ﬁt into the ever-changing
patterns that we can see from Earth.
JunoCam has obtained striking
close-ups of several major features,
including a pale but persistent cyclonic
storm called the "STB Specter," which
revealed superb circulation patterns.
Close-ups have also covered long-lived
anticyclonic ovals at latitudes ranging
from 41°S (nicknamed the "String of
Pearls") to 41°N and on July 11th, most
dramatically of all, the Great Red Spot.
All the images, with preliminary
processing by the camera team and
with more advanced reﬁnement by
members of the public, can be viewed
on the JunoCam website. It's well worth
a visit - both to admire the striking
cloud patterns found on Jupiter and to
appreciate the rewarding results that
such professional-amateur collaboration
can achieve.
¢ Veteran planetary observer JOHN
ROGERS has served as Jupiter Section
director for the British Astronomical Association since 1987.

G LENN ORTON / SUBA RU TELESCOPE; CHRISTOPHER GO

these waves been so conspicuous, and
that likewise occurred during a NEB
broadening event. They are striking in
both amateur and professional infrared
images. A team led by Leigh Fletcher
(University of Leicester, UK) ﬁnds that
the wave pattern is inﬂuenced by heat:
The reﬂective haze looks thinner where
the air is warmer. Perhaps some aspect
of the disturbance in the "weather
layer" of Jupiter's clouds generates the
wave pattern seen in the overlying haze.
In any case, the waves remained prominent during 2017, and tracking them
using both amateur and professional
images should help us to understand
how they arise and propagate.
Meanwhile, the South Equatorial
Belt (SEB) has not shown cyclic, planetwide changes recently, but long-running
convective storm activity has waxed and
waned in more localized parts of it.
As with the planet's other major
cloud belts, the SEB remained largely
quiet throughout 2016, with only lowlevel convective activity in its usual
location just west of the Great Red Spot
(GRS). However, these storms have
become much more extensive since
February, and a new batch of similar
storms appeared well away from the
GRS last December 29th. So by mid2017 the SEB was intensely disturbed
around most of its length.

http://www.jupos.org

Sky and Telescope - November 2017

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