JUNO SPACECRAFT OBSERVES JUPITER'S GREAT RED SPOT
NASA
Data collected by the Juno spacecraft during its first pass over Jupiter's
Great Red Spot in 2017 July indicate that that iconic feature penetrates
well below the clouds. Other revelations from the mission include that
Jupiter has two previously uncharted radiation zones.
Jupiter's Great Red Spot is a giant oval, in Jupiter's southern hemisphere,
of crimson-coloured clouds that race counterclockwise around the oval's
perimeter, with wind speeds greater than those in any storm on Earth.
Measuring 16,000 kilometres as of 2017 April 3, the Great Red Spot is 1.3
times as wide as the Earth. The future of the Great Red Spot is still very
much up for debate. While the storm has been monitored since 1830, it has
possibly existed for more than 350 years. In the 19th century, the Great
Red Spot was well over two Earths wide, but in modern times, it has appeared
to be diminishing in size, as measured by spacecraft and Earth-based telescopes.
At the time that NASA's Voyagers 1 and 2 sped by Jupiter on their way to Saturn
and beyond, in 1979, the Great Red Spot was twice the Earth's diameter. Today,
measurements by Earth-based telescopes indicate that the oval that Juno flew
over has diminished in width by one-third and height by one-eighth since Voyager
times.
Juno also has detected a new radiation zone, just above the planet's
atmosphere, near the equator. The zone includes energetic hydrogen,
oxygen and sulphur ions moving at almost light speed. The new zone
was identified by the Jupiter Energetic Particle Detector Instrument (JEDI)
investigation. The particles are believed to be derived from energetic neutral
atoms in the gas around the moons Io and Europa. The neutral atoms
then become ions as their electrons are stripped away by interaction with
the upper atmosphere of Jupiter. Juno also found signatures of a high-
energy heavy-ion population within the inner edges of Jupiter's relativistic-
electron radiation belt -- a region dominated by electrons moving close to
the speed of light. The signatures are observed during Juno's high-
latitude encounters with the electron belt, in regions never explored by
previous spacecraft. The origin and exact species of those particles is
not yet understood. Juno's Stellar Reference Unit (SRU-1) star camera
detects the signatures of that population as extremely-high-noise
signatures in images collected by the mission's radiation-monitoring
investigation.
Juno was launched on 2011 August 5 from Cape Canaveral, and arrived
in orbit around Jupiter on 2016 July 4. It is in an elongated orbit, and to
date has completed nine passes over Jupiter.
VOYAGER 1 FIRES UP THRUSTERS AFTER 37 YEARS
NASA
If you tried to start a car that's been sitting in a garage for decades, you
might well expect the engine to fail to respond. But a set of thrusters on
the Voyager 1 spacecraft successfully fired up after 37 years without use.
Voyager 1, NASA's farthest and fastest spacecraft, is the only man-made
object in interstellar space, the environment between the stars. The space-
craft, which has been flying for 40 years, relies on small thrusters to
orient itself so that it can communicate with the Earth.
The thrusters fire in tiny pulses, or puffs, lasting mere milliseconds,
to rotate the spacecraft slightly so that its antenna continues to point
at our planet. Now, the Voyager team is able to use a set of four backup
thrusters, dormant since 1980. The thrusters will be able to extend the
life of the Voyager 1 spacecraft by two or three years. Since 2014,
engineers have noticed that the thrusters Voyager 1 has been using to orient
itself, called 'attitude-control thrusters', have been degrading. Over
time, the thrusters require more puffs to produce the same amount of energy.
In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and
important moons of each. The thruster test went so well that the team will
probably do a similar test on the thrusters of Voyager 2, a twin of Voyager 1.
The attitude-control thrusters currently used for Voyager 2 are not yet as
degraded as Voyager 1's, however. Voyager 2 is also on course to enter
interstellar space, probably within the next few years.
INFANT STARS FOUND NEAR MILKY WAY BLACK HOLE
National Radio Astronomy Observatory
At the centre of our Galaxy, in the immediate vicinity of its supermassive
black hole, is a region wracked by powerful tidal forces and bathed in
intense ultraviolet light and X-ray radiation. Those harsh conditions,
astronomers surmise, do not favour star formation, especially of low-mass
stars like the Sun. Surprisingly, new observations from the Atacama Large
Millimetre/submillimetre Array (ALMA) suggest otherwise. ALMA has revealed
the telltale signs of eleven low-mass stars forming perilously close -- within
three light-years -- to the Milky Way's supermassive black hole,
known to astronomers as Sagittarius A* (Sgr A*). At that distance, tidal
forces driven by the supermassive black hole should be energetic enough to
rip apart clouds of dust and gas before they can form stars. The presence
of the newly discovered proto-stars (the formative stage between a dense
cloud of gas and a young, shining star) suggests that the conditions
necessary to produce low-mass stars may exist even in one of the most
turbulent regions of our Galaxy and possibly in similar locales throughout
the Universe. The ALMA data also suggest that the proto-stars are about
6,000 years old. The team of researchers identified the proto-stars by
seeing the classic 'double lobes' of material that bracket each of them.
Those cosmic hourglass-like shapes signal the early stages of star
formation. Molecules, like carbon monoxide (CO), in the lobes glow
brightly in millimetre-wavelength light, which ALMA can observe with
remarkable precision and sensitivity. Proto-stars form from interstellar
clouds of dust and gas. Dense pockets of material in the clouds collapse
under their own gravity and grow by accumulating more and more star-forming
gas from their parent clouds. A portion of the infalling material, however, never
makes it onto the surface of the star. Instead, it is ejected as a pair of high-velocity
jets from the proto-star's north and south poles. Extremely turbulent environments
can disrupt the normal procession of material onto a proto-star, while intense radiation --
from massive nearby stars and supermassive black holes -- can blast away the
parent cloud, thwarting the formation of all but the most massive of stars.
The Milky Way's Galactic Centre, with its 4-million-solar-mass black hole,
is located approximately 26,000 light-years from us in the direction of the
constellation Sagittarius. Vast stores of interstellar dust obscure that
region, hiding it from optical telescopes. Radio waves, however, including
the millimetre and submillimetre light that ALMA sees, are able to penetrate
the dust, giving radio astronomers a clearer picture of the dynamics and
content of that hostile environment. Previous ALMA observations of the
region surrounding Sgr A* revealed multiple massive infant stars that are
estimated to be about 6 million years old. Those objects, known as
proplyds, are common features in more placid star-forming regions, like the
Orion Nebula. Though the Galactic Centre is a challenging environment for
star formation, it is possible for particularly dense cores of hydrogen gas
to cross the necessary threshold and forge new stars. For that to occur,
outside forces would have to compress the gas clouds near the centre of the
Galaxy to overcome the violent nature of the region and allow gravity to
take over and form stars. Astronomers speculate that high-velocity gas
clouds could aid in star formation as they force their way through the
interstellar medium. It is also possible that jets from the black hole
itself could be ploughing into the surrounding gas clouds, compressing
material and triggering the burst of star formation.
WATERLESS EXOPLANET HAS SMOTHERING STRATOSPHERE
NASA
Astronomers have found evidence that the oversized exoplanet WASP-18b is
wrapped in a smothering stratosphere loaded with carbon monoxide and devoid
of water. The findings come from a new analysis of observations made by the
Hubble and Spitzer space telescopes. The formation of a stratosphere layer in
a planet's atmosphere is attributed to 'sunscreen'-like molecules, which absorb
ultraviolet (UV) and visible radiation coming from the star and then release that
energy as heat. The new study suggests that the 'hot Jupiter' WASP-18b, a
massive planet that orbits very close to its host star, has an unusual composition,
and the formation of that planet might have been quite different from that of Jupiter
and gas giants in other planetary systems. On the Earth, ozone absorbs UV in
the stratosphere, protecting our world from a lot of the Sun's harmful radiation.
For the handful of exo-planets with stratospheres, the absorber is typically
thought to be a molecule such as titanium oxide, a close relative of titanium
dioxide, used on Earth as a paint pigment and sunscreen ingredient. The
researchers looked at data collected for WASP-18b, located 325 light-years
from the Earth, as part of a survey to find exo-planets with stratospheres.
The heavyweight planet, which has the mass of 10 Jupiters, has been observed
repeatedly, allowing astronomers to accumulate a relatively large trove of data.
The studyanalyzed five eclipses from archived Hubble data and two from Spitzer.
From the light emitted by the planet's atmosphere at infrared wavelengths, it is
possible to identify the spectral fingerprints of water and some other important
molecules. The analysis revealed WASP-18b's peculiar fingerprint, which does
not resemble that of any exo-planet examined so far. To decide which molecules
were most likely to match it, the team carried out extensive computer modelling.
The findings indicate that WASP-18b has hot carbon monoxide in the stratosphere
and cooler carbon monoxide in the layer of the atmosphere below (the troposphere).
The team determined that by detecting two types of carbon monoxide signatures,
an absorption signature at a wavelength of about 1.6 microns and an emission
signature at about 4.5 microns. This is the first time that researchers have detected
both types of signature for a single type of molecule in an exo-planet's atmosphere.
In theory, another possible fit for the observations is carbon dioxide, which has a
similar fingerprint. The researchers ruled that out because if there were enough
oxygen available to form carbon dioxide, the atmosphere should also have some
water vapour. To produce the spectral fingerprints seen by the team, the upper
atmosphere of WASP-18b would have to be loaded with carbon monoxide.
Compared to other hot Jupiters, the planet's atmosphere would probably contain
300 times more 'metals', i.e. elements heavier than hydrogen and helium. That
extremely high metallicity would indicate that WASP-18b might have accumulated
greater amounts of solid ices during its formation than Jupiter, suggesting that it
may not have formed in the same way as other hot Jupiters.
PROPER MOTIONS MEASURED FOR STARS OUTSIDE THE MILKY WAY
University of Groningen
By combining data from the Hubble Space Telescope and the Gaia mission,
astronomers have been able to measure the proper motions of 15 stars in the
Sculptor galaxy, the first such measurement of stars in a small galaxy
outside the Milky Way. Analysis shows an unexpected preference in the
direction of movement, which suggests that the standard theoretical models
used to describe the motion of stars and dark matter haloes in other
galaxies might be invalid. Astronomers have long been able to measure the
movement of stars in our line of sight (i.e. the movement towards or away
from us) by measuring the redshift, which is caused by the Doppler effect.
However, measuring the movement in the plane of the sky, known as the
proper motion, is much more difficult. To detect that, you need multiple
precise measurements of a star's position over the course of several years.
The immense distances involved mean that many stars in our Galaxy move
very little across the sky when seen from Earth. For stars outside the Galaxy,
this movement is even less. The European Gaia mission, which is currently
under way, was designed to measure the exact location of more than one
billion stars, mostly in our own Galaxy. But Gaia also measures star positions
in nearby galaxies, and for some of those stars, astronomers also have their
location as measured by the Hubble Space Telescope, some 12 years ago.
Astronomers set out to combine the two data sets. That is not an easy task,
as the two missions measure the location in different ways. The team
managed to combine the data by using background galaxies which did not
change position in the 12 years. They were of course very careful to
minimize systematic errors, and out of 120 stars in the Sculptor Galaxy that
were measured by both Hubble and Gaia they found extremely accurate
paired observations for 15. Next, they determined how the stars move in
that small galaxy, which is quantified by the anisotropy parameter. If it is
high, the stars have very elongated trajectories, and if it is very small, they
have circular orbits. Knowing that allows astronomers to pin down the
properties of the dark-matter halo in which the galaxy is embedded. But
the measured value was very surprising, as the standard models did not
allow it. That means that some of the assumptions on which the models
are based must be wrong. So far, it has only been possible to test models
by using the line-of-sight movement. That seemed fine, but now, with proper
motion, the standard models are breaking down. One possible explanation is
that the models assume all stars to belong to a single population. But we know
that Sculptor is complex, with at least two stellar populations (one more compact
and one more extended). There is a model that includes that and does
predict the anisotropy which the team observed, as long as most of the stars
measured belong to the more compact population. The movement of stars
depends mostly on the invisible dark-matter halo around a galaxy. That is
why it is so important to determine the anisotropy parameter, because it can
be used to pin down the distribution of dark matter in a galaxy, which in
turn depends on the nature of dark matter itself. The present results show
that by using the Gaia data, combined with other data sets, we can measure
the proper motions of stars in galaxies outside the Milky Way and thus
improve the models which describe how dark matter is distributed in those
other galaxies. A second major result is a more precise measurement of the
orbit of the Sculptor Galaxy around the Milky Way. That orbit is much
bigger than expected. Previously, it was believed that the current
spheroidal shape of Sculptor was in part the result of some close passages,
but the measurements show that that is not the case.
SEARCH FOR LIFE ON OTHER PLANETS MAY BE MORE DIFFICULT THAN EXPECTED
RAS
New simulations show that the search for life on other planets may well be
more difficult than has previously been supposed. A new study indicates that
unusual air-flow patterns could hide atmospheric components from telescopic
observations, with direct consequences for formulating the optimal strategy for
searching for (oxygen-producing) life such as bacteria or plants on exo-planets.
Current hopes of detecting life on planets outside our own Solar System rest on
examining the planets' atmospheres to identify chemical compounds that may
be produced by living beings. Ozone, a variety of oxygen, is one such molecule,
and is seen as one of the possible tracers that may allow us to detect life on another
planet from afar. In the Earth's atmosphere, ozone forms a layer that protects us
from the Sun's harmful UV radiation. On an alien planet, ozone could be one piece
in the puzzle that indicates the presence of oxygen-producing bacteria or plants.
But now researchers at the Max Planck Institute for Astronomy in Germany
have found that such tracers might be better hidden than we previously
thought. The team considered some of the nearest exo-planets that have the
potential to be Earth-like: Proxima b, which is orbiting the star nearest to
the Sun (Proxima Centauri), and the most promising of the TRAPPIST-1 family
of planets, TRAPPIST-1d. Those are examples of planets that orbit their host
star in 25 days or less, and as a side effect have one side permanently facing
their star and the other side permanently facing away. Modelling the flow of air
within the atmospheres of such planets, astronomers found that that unusual
day-night divide can have a marked effect on the distribution of ozone across
the atmosphere: at least for those planets, the major air flow may lead from the
poles to the equator, systematically trapping the ozone in the equatorial region.
Absence of traces of ozone in future observations does not have to mean that
there is no oxygen at all. It might be found in different places from where it is
found on Earth, or it might be very well hidden. Such unexpected atmospheric
structures may also have consequences for habitability, given that most of the
planet would not be protected against ultraviolet (UV) radiation. In principle, an
exo-planet with an ozone layer that covers only the equatorial region might still
be habitable. Proxima b and TRAPPIST-1d orbit red dwarfs, reddish stars that
emit very little harmful UV light to begin with. On the other hand, those stars
can be very temperamental, and prone to violent outbursts of harmful radiation
including UV. The combination of advances in modelling and much better data
from telescopes like the James Webb Space Telescope is likely to lead to
significant progress in this exciting field.
MILKY WAY ORBITS IN LOCAL SUPERCLUSTER
University of Hawaii at Manoa
A team of astronomers has produced the most detailed map ever of the orbits of
galaxies in our extended local neighbourhood, showing the past motions of almost
1,400 galaxies within 100 million light-years of the Milky Way. The team reconstructed
the galaxies' motions from 13 billion years in the past to the present day. The main
gravitational attractor in the mapped area is the Virgo Cluster, with 600 billion times
the mass of the Sun, 50 million light years from us. Over a thousand galaxies have
already fallen into the Virgo Cluster, while in the future all galaxies that are currently
within 40 million light years of the cluster will be captured. Our Milky Way galaxy lies
just outside the capture zone. However, the Milky Way and Andromeda galaxies, each
with 2 billion times the mass of the Sun, are destined to collide and merge in 5000
million years. For the first time, we are not only visualizing the detailed structure of
our Local Supercluster of galaxies but we are seeing how the structure developed over
the history of the Universe. An analogy is the study of the current geography of the Earth
from the movement of plate tectonics. Such dramatic merger events are only part of a
larger show. There are two over-arching flow patterns within this volume of the Universe.
All galaxies in one hemisphere of the region -- including our own Milky Way -- are
streaming towards a single flat sheet. In addition, essentially every galaxy over the
whole volume is flowing, as a leaf would in a river, towards gravitational attractors at far
greater distances.
MOST DISTANT BLACK HOLE YET DISCOVERED
NASA
Scientists have uncovered a rare relic from the early Universe: the furthest
known supermassive black hole. That matter-eating beast is 800 million
times the mass of our Sun and grew far larger than astronomers expected in
only 690 million years after the Big Bang, which challenges theories about
how black holes form. Astronomers combined data from NASA's Wide-field
Infrared Survey Explorer (WISE) with ground-based surveys to identify potential
distant objects to study, then followed up with Carnegie Observatories' Magellan
telescopes in Chile. For black holes to become so massive in the early Universe,
astronomers speculate that there must have been special conditions to allow
rapid growth -- but the underlying reason remains mysterious. The newly found
black hole is voraciously devouring material at the centre of a galaxy -- a phenomenon
called a quasar. This quasar is especially interesting because it comes from a time
when the Universe was just beginning to emerge from its dark ages. The discovery
will provide fundamental information about the Universe when it was only
5 per cent of its current age. Quasars are among the brightest and most
distant known celestial objects and are crucial to understanding the early
Universe. The Universe began in a hot soup of particles that rapidly spread
apart in a period called inflation. About 400,000 years after the Big Bang,
the particles cooled and coalesced into neutral hydrogen gas. But the
Universe stayed dark, without any luminous sources, until gravity condensed
matter into the first stars and galaxies. The energy released by the ancient
galaxies caused the neutral hydrogen to ionize, or lose an electron. The gas
has remained in that state ever since that time. Once the Universe became
re-ionzed, photons could travel freely throughout space. That is the point at
which the Universe became transparent to light. Much of the hydrogen surrounding
the newly discovered quasar is neutral. That means the quasar is not only the most
distant -- it is also the only example we have that can be seen before the Universe
became re-ionized. It has a redshift of 7.54, based on the detection of ionized carbon
emissions. That means that it took more than 13 billion years for the light from the quasar
to reach us. Scientists believe that the sky contains between 20 and 100 quasars as bright
and as distant as that one. Astronomers look forward to ESA's Euclid mission, and NASA's
Wide-field Infrared Survey Telescope (WFIRST) mission, to find more such distant objects.
Topic: Mid December Astronomy Bulletin (Read 1623 times)