8 AUSTRALIAN SKY & TELESCOPE May | June 2018
NASA / JPL-CALTECH / SWRI / ASI / INAF / JIRAM A13 AND TRIAND:© T. MUELLER / NASA / JPL-CALTECHAmazingstorms,jetstreamsonJupiter
Cyclones surround Jupiter’s north pole.NEW RESULTS PUBLISHED in the March
8 issue of Nature show us the latest looks
at Jupiter from NASA’s Juno spacecraft,
revealing details of the giant planet’s
atmosphere.
In a visually stunning result, Alberto
Adriani (INAF Institute for Astrophysics and
Space Planetology, Italy) and colleagues
report the discovery of two sets of
cyclones at the planet’s poles.
The complex at Jupiter’s north pole has
a central, 4,000-km-wide cyclone, with a
ring of eight, regularly spaced storms of
similar size around it. At the south pole,
a central cyclone sits in the middle of an
imperfect pentagon of five others, each
between 5,600 to 7,000 km wide, or about
half of Earth’s diameter.
The individual storms rotate every 27
to 60 hours at hundreds of kilometres per
hour. It’s possible they drift around the
central cyclones, but Juno observed little
change over 7 months. The team doesn’t
know why the patterns remain stationary.
It’s also still unclear whether the cyclones
formed at the poles or migrated there from
elsewhere.
Additional work shows that the planet’s
jet streams reach some 3,000 km down, far
deeper than many scientists expected. For
comparison, Jupiter’s weather layer — the
part where sunlight is absorbed and clouds
form — is only about 100 km deep. Deep
jet streams favour a long-standing theoryfor Jupiter’s atmosphere, in which the jet
streams form a series of nested cylinders,
like a roll of toilet paper that’s been carved
into a sphere (but fewer layers). Each
latitude band corresponds to a different
layer in the nest, with higher latitudes
corresponding to deeper cylinders.
In the region dominated by the jet
streams, the planet rotates differentially,
turning more quickly at its equator than at
its poles. But below the deep jet-stream
layer, the planet appears to rotate more
like a solid ball, which means the cylinder
scenario may need some modification.
More results are forthcoming, including
about widespread lightning, predominantly
in the northern hemisphere. Still, questions
linger — such as how deep the Great Red
Spot goes — and await additional data.
■ CAMILLE M. CARLISLE- For more results and images, visit
https://is.gd/junosjupiter
Moreover, TriAnd and A13 have
similar abundances to each other,
implying a common birthplace — even
though they’re separated by 30,
light-years.
Bergemann and colleagues simulated
a possible origin scenario. The
Sagittarius dwarf galaxy, now stretched
into a thin stream that wraps around
the Milky Way, careened into our
galaxy several billion years ago. Such
an interaction would have disrupted
the Milky Way’s disk and sent swirls
of stars above and below the galactic
plane. ■ MONICA YOUNGNEWS NOTESSunATr iA ndThe A13 and TriAnd clouds are in the outer galaxy,
roughly 15,000 light-years above and below the
galactic plane, respectively.Dwarf galaxy evicted
Milky Way starsMOST STELLAR STREAMS in the Milky
Way’s halo are ghosts of dwarf galaxies
past, long ago torn into shreds after
encounters with our more massive galaxy.
Now, new research that appeared online
February 26 in the journal Nature shows
that some of these stars might not be
dwarf remnants at all — they might have
come from the Milky Way’s own disk.
Maria Bergemann (Max Planck
Institute for Astronomy, Germany)
and colleagues studied 14 stars in two
halo populations, known as A13 and
Triangulum-Andromeda (TriAnd),
using the Keck I telescope in Hawai‘i
and the Very Large Telescope in Chile.
After collecting the stellar spectra, the
astronomers measured the abundances
of elements heavier than hydrogen and
helium. Unlike most of the stellar halo,
these stars are rich in heavy elements,
more akin to stars in the galaxy’s disk.