Sky and Telescope - June 2018 - 8

NEWS NOTES

Amazing Storms, Jet
Streams on Jupiter
NEW RESULTS PUBLISHED in the

March 8th 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
(2,500-mile-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 kilometers
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.

Cyclones surround Jupiter's north pole.

8

J U N E 2 018 * SK Y & TELESCOPE

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
favor a long-standing theory for 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.

COSMOLOGY

Signal from First Stars
Suggests Primordial Chill
A SIMPLE EXPERIMENT has

detected a signal from the very ﬁrst
stars. The observations may have
intriguing implications for the
nature of dark matter.
For years, astronomers have been
trying to map the early universe's
neutral hydrogen gas via its 21-cm
radio emission. In particular, they
want to see how the ﬁrst stars' highenergy radiation heated this gas,
ionizing bubbles that spread across
the infant universe. Detecting the
emission is difﬁcult, as it has been
redshifted to low radio frequencies
and is often swamped by foreground
signals. Nevertheless, several large
radio arrays are getting close to
detecting the emission signal.
Now, Judd Bowman (Arizona
State University) and colleagues
have turned the tables, using a
simple setup to ﬁnd early hydrogen
via absorption instead. Ultraviolet
light from the ﬁrst stars would have
altered the energy states of hydrogen atoms, knocking them out of
balance with the cosmic microwave
background (CMB). The hydrogen
could then make itself known not by
emitting 21-cm radio waves but by
absorbing them from the CMB.
The team used a detector called
the Experiment to Detect the Global
Epoch of Reionization Signature
(EDGES) in the radio-quiet Australian Outback. About the size of
a large desk, EDGES contains few
electronics and is extremely well
calibrated to lower frequencies. As
the team reports in the March 1st
Nature, EDGES successfully detected
hydrogen absorption by averaging the
signal across the sky. The subtle dip
in the radio spectrum is centered at
a frequency of 78 MHz and corresponds to an epoch just 180 million
years after the Big Bang.
But to scientists' surprise, the
absorption observed was deeper than
theory predicts, suggesting that the

N ASA / JPL- CA LTECH / SWRI / ASI / IN A F / JIR A M

SOLAR SYSTEM
https://www.is.gd/junosjupiter
Sky and Telescope - June 2018

Table of Contents for the Digital Edition of Sky and Telescope - June 2018
