Download Why is there weather on Uranus

Mission update
Why is there weather on Uranus?
Uranus is something of an
unknown quantity among the
giant planets of the outer solar
system; Voyager’s flyby in 1986
showed a virtually featureless bluegreen atmo­sphere, in contrast to
the turmoil of Jupiter and Saturn’s
less prominent weather bands.
High-resolution infrared data from
the Keck II telescope on Hawaii
have now revealed a complex
banded atmospheric structure.
The detail in the atmosphere
of Uranus was revealed by using
filters and stacking images to
reduce the signal-to-noise ratio.
The data revealed an asymmetric
circulation, with scalloped bands
around the equator and many
small, presumed convective,
features around the north pole.
The swarm of small cloud features
looks a little like features captured
by Cassini at Saturn’s south pole,
where they seem to be associated
with a polar vortex.
The big question posed by this
New Horizons in
dry run for Pluto
NASA’s New Horizons spacecraft,
now half way to Pluto, has been put
through its paces in a scripted runthrough of the close encounter with
the dwarf planet and its moons in
2015. The simulation proceeded as if
it were 14 July 2015 and was intended
to iron out any problems with the
complex sequences of commands that
will be required. While the software
had been tested on Earth, experience
suggested that problems might arise
when it was used in situ on the spacecraft. It was also useful to ensure that
there was sufficient time between
spacecraft manoeuvres to collect the
data. The simulation built on New
Horizons’ experience flying by Jupiter in 2007, and will in turn feed into
next year’s simulation of the nine-day
Pluto encounter.
http//pluto.jhuapl.edu
Dawn finds
fault with Vesta
In 2011, NASA’s Dawn spacecraft
found faults running across the surface of Vesta, arising from an impact
A&G • December 2012 • Vol. 53 News • Mission Update
Space Shorts
Sentinel for 2017 launch
The first privately funded deep
space mission, the Sentinel
Space Telescope intended
to provide early warning of
asteroids hazardous to Earth,
has undergone a successful
technical and management
review. The mission now has
the independent Sentinel Space
Science Review Team to provide
technical advice and assistance
to the B612 Foundation, which
is funding and building the
spacecraft, together with Ball
Aerospace.
http://www.b612foundation.org
LADEE gets ready
The sharpest, most detailed picture of Uranus to date, in infrared
wavelengths, achieved over two nights of observation in superb weather
conditions, reveals a surprisingly active atmosphere. The north pole of
Uranus (to the right) is characterized by a swarm of storm-like convective
features, and an unusual scalloped pattern of clouds encircles the
planet’s equator. (L Sromovsky, P Fry, H Hammel, I de Pater)
atmospheric activity is where does
the energy come form? Uranus’s
atmosphere comprises mainly
hydrogen, helium and methane
and the major weather systems
suggested by these data must be
at the south pole. They suggest that
Vesta has a layered interior.
Most similar linear features on
asteroids are simple V-shaped cracks.
Vesta’s troughs are bigger, more
systematically arranged, and have
flat floors, like extensional faultbounded troughs (grabens) on Earth.
The largest, Divalia Fossa, is bigger
than the Grand Canyon, at 465 km
long, 22 km wide and 5 km deep, on a
body one-seventh the diameter of the
Moon. Vesta’s troughs have flat valley floors, with a slight tilt towards
one side or the other – typical of grabens on Earth, where fault movement
extends the crust and drops down the
valley floor. The relative movement
implied by the grabens on Vesta is
thought to arise from a differentiated
interior; the different densities of
interior layers control the deformation, according to Debra Buczkowski
of the Johns Hopkins University
Applied Physics Laboratory in Laurel, Maryland. An alternative idea is
that the collision gave Vesta its unusually fast rotation, which in turn
caused extension, expressed at the
surface by grabens.
While it is not certain how these
troughs originated, they may provide
another line of evidence that Vesta
has more in common with a planet
driven by energy from the Sun.
Solar energy drives atmospheric
circulation on Earth, but Uranus is
30 times further away and sunlight
is therefore 900 times weaker.
http://www.news.wisc.edu/21179
than a typical asteroid. The proposed mechanism suggests a plastic
mantle; in addition, Dawn’s surface
mapping shows features that appear
to be formed by lava, suggesting that
this planet melted early in its history,
making a differentiated interior more
likely. Buczkowski and her team published their research in Geophysical
Research Letters.
http://bit.ly/RKFYmr
Vesta shows
signs of dynamo
Another sign that Vesta differentiated early in its history is remanent
magnetism discovered in an iron
meteorite from the asteroid, collected in the Allen Hills region of
Antarctica in 1981. The meteorite
is thought to have crystallized at a
time when the crustal rocks of Vesta
retained traces of its magnetic field,
generated in an iron core. The body
must then have differentiated early
in its history. This makes Vesta, at
around 500 km across, the smallest
body to have generated a dynamo.
Roger Fu and Benjamin Weiss of
Earth, Atmospheric and Planetary
Sciences (EAPS) at MIT, together
with other researchers at MIT
NASA’s Lunar Atmosphere and
Dust Environment Explorer
(LADEE), a robotic mission to
the Moon to gather detailed
information about the lunar
atmosphere, and surface
environment, has come closer
to its 2013 launch and now
has all instruments installed.
LADEE carries an Ultraviolet and
Visible Light Spectrometer and
a Neutral Mass Spectrometer
to examine the tenuous lunar
atmosphere, and the Lunar Dust
Experiment to analyse lunar
dust in the atmosphere. LADEE
will also carry a technology
demonstration payload, the
Lunar Laser Communications
Demonstration, which uses
lasers instead of radio waves to
achieve broadband speeds to
communicate with Earth.
http://1.usa.gov/Uc81kW
Global observatory
The Las Cumbres Observatory
Global Telescope now has
three robotic 1 m telescopes at
Cerro Tololo Inter-American
Observatory in Chile. These are
part of the planned network
of 15 similar telescopes
around the world, plus the
two 2 m Faulkes Telescopes;
the next three will go to the
South African Astronomical
Observatory, then two to Siding
Spring Observatory, Australia.
The Scottish Universities
Physics Alliance, specifically
St Andrews University, has
had a science partnership
with the observatory over the
past seven years, focusing on
exoplanet identification and
characterization with the Faulkes
Telescopes. This will continue
and other science partnerships
are anticipated.
http://lcogt.net
6.7
News • Mission Update
and the University of California at
Berkeley, assessed the oldest component of magnetism preserved in
the iron mineral of a 1 g fragment
of ALH A81001, and dated the formation of the minerals at 3.7 billion years old, based on the decay
of potassium in its minerals. While
the team is not the first to work on
the palaeomagnetism of this meteorite, it was able to determine that
the rock gained its field as it cooled
relatively slowly (by examining
individual crystals within it). This
makes impact-related magnetization unlikely.
Radiometric dating also suggests
that planets and bodies such as Vesta
formed within about 10 million years
of the formation of the solar disc. Fu
and Weiss believe that a dynamo
formed early on, in the liquid iron
core of Vesta, and probably magnetized the surface within the first
100 million years of the asteroid’s
history. The field persisted in the
surface rocks over billions of years,
so that when ALH A81001 formed
3.7 billion years ago, it would have
also become magnetized by cooling
and crystallizing in fields from the
surrounding magnetized crust. The
team published its work in Science.
http://bit.ly/RAIGyh
Water water
everywhere
ESA’s Herschel space observatory
has discovered enough water vapour
to fill Earth’s oceans more than 2000
times over, in a gas and dust cloud
that is on the verge of collapsing into
a new Sun-like star – the first detection of water vapour in a molecular
cloud on the verge of star formation.
The water has been found in a cold
pre-stellar core in the constellation
of Taurus known as Lynds 1544.
The water vapour is thought to originate from icy dust grains, released
by high-energy cosmic rays passing
through the cloud. “To produce that
amount of vapour, there must be a
lot of water ice in the cloud, more
than three million frozen Earth
oceans’ worth,” said Paola Caselli
of the University of Leeds, UK, lead
author of the paper reporting the
results in Astrophysical Journal
Letters. “Before our observations,
the understanding was that all the
water was frozen onto dust grains
because it was too cold to be in the
gas phase and so we could not measure it. Now we will need to review
our understanding of the chemical
processes in this dense region and,
in particular, the importance of cosmic rays to maintain some amount of
water vapour.”
The observations also revealed
that the water molecules are flowing
6.8
Remote sensing of active volcanoes – on Io
Current and potential future ground-based observations of Io. (Left): Detail visible with the current adaptive
optics system on the W M Keck telescope. (Middle): Simulation of results with a next-generation AO system
on the Keck (KNGAO). (Right): Simulation of detail expected with the Thirty Meter Telescope (TMT) and its
AO system NFIRAOS. The spatial resolution at the centre is respectively 140 km, 110 km and 35 km in H band
(1.6 μm). A and B mark two young eruptive centres that can be detected only with the TMT. KNGAO shows the
brightest eruption at A, but not that at B. The TMT will boost both angular resolution and sensitivity. (F Marchis)
Adaptive optics on 8–10 m
telescopes mean that groundbased researchers can monitor
volcanic activity on Jupiter’s moon
Io. Observations with the W M
Keck II 10 m telescope on Mauna
Kea, Hawaii, have provided planetary scientists with a nine-year
record of volcanic activity in Io,
one that will continue and improve
when the next generation of
ground-based telescopes becomes
available.
Io’s volcanic activity was discovered as Voyager 1 flew through the
jovian system in 1979. The Galileo
spacecraft orbited in the jovian
system from 1995 to 2003, observing more than 160 active volcanoes and a broad range of eruption
styles, but the data raised important questions about the nature of
this volcanism. Since 2003, a team
led by Franck Marchis of the Carl
Sagan Center of the SETI Institute
has been monitoring the volcanoes
thanks to adaptive optics, which
corrects for the blurring effects
of the atmosphere in real time.
They have used near-infrared
wavelengths to map the thermal
emission of the volcanoes, identifying energetic high-temperature
eruptions called outbursts, some
of which involve fire fountains,
and lower temperature eruptions
called effusions.
The overall pattern is of sporadic
activity at several volcanic centres.
For example, the volcano Tvashtar
erupted between 2006 and 2007,
as the New Horizons spacecraft
flew past on its way to Pluto. Older
observations from the Galileo
spacecraft and the Keck Observatory show that this volcano
previously displayed a similar fire
fountain eruption which started
in November 1999 and lasted
for 15 months. Similarly, Pillan,
an energetic eruption detected
with the Galileo spacecraft from
1996 to 1999, was sporadically
active again in August 2007. This
episodic behaviour suggests that
the magma chambers below the
towards the heart of the cloud where
a new star will probably form, indicating that gravitational collapse has
just started. A planetary system like
ours may be on the verge of forming
in L1544.
forms with variable proportions of
iron and magnesium. Magnesiumrich olivine is found in small and
primitive icy bodies like comets,
whereas iron-rich olivine is typically
found in large asteroids that have
undergone more heating and melting. Herschel detected the pristine
magnesium-rich variety in the Beta
Pictoris system at 15–45 au from the
star, where temperatures are around
85 K. Olivine condenses within about
10 au of the central star, so finding it
at these distances in the cold debris
disc suggests outward transport.
The Herschel team calculated that
olivine makes up 4% of the total
mass of dust at this distance, implying that the olivine was originally
bound up inside comets and released
http://bit.ly/PR8N5O
Olivine dust at
Beta Pictoris
ESA’s Herschel space observatory
has detected silicate dust similar to
that found in comets in the solar system, in the cool cloud of dust and gas
around the star Beta Pictoris, suggesting similarities between that disc
and our system in the distant past.
Olivine is a silicate mineral that
volcanoes are regularly recharged
after eruptions.
The monitoring of Io’s volcanic
activity will continue to build a
timeline of volcanic activity and
thermal emission variability,
which will be further complemented by data obtained by other
missions to the Jupiter system,
such as the ESA mission JUICE.
“The next giant leap in the field of
planetary astronomy is the arrival
of giant segmented mirror telescopes, such as the Thirty Meter
Telescope expected to be available
in 2021,” said Marchis, presenting
the research at the 2012 Division
of Planetary Science Meeting in
Reno, Nevada, in October. “It
will provide a spatial resolution
of 35 km in the near-infrared,
equivalent to the spatial resolution
of global observations taken by the
Galileo spacecraft. When pointed
at Io, these telescopes will offer the
equivalent of a spacecraft flyby of
the satellite.”
http://www.seti.org/node/1457
into space by collisions. Solar system comets 17P/Holmes and 73P/
Schwassmann-Wachmann 3 contain
2–10% magnesium-rich olivine, suggesting some sort of common processes in this disc and the early solar
system, despite their differences.
Earth lies at 1 au from our Sun
and the solar system’s Kuiper Belt
extends from the orbit of Neptune
at about 30 au out to 50 au from the
Sun. Beta Pictoris is over one-and-ahalf times the mass of the Sun, eight
times as bright, and its planetary
system architecture is different from
that of our own solar system today.
But these mineral grains suggest it
could eventually have a Kuiper Belt
of its own.
http://bit.ly/SN88S1
A&G • December 2012 • Vol. 53