JUPITER HAS AN EXTRA MAGNETIC POLE
Spaceweather.com
When NASA's Juno spacecraft reached Jupiter in 2016, planetary scientists
were eager to learn more about the giant planet's magnetic field. Juno would
fly over both of Jupiter's poles, skimming just 4000 km above the cloud tops
for measurements at point-blank range. Now a team of researchers has
announced that Jupiter's magnetic field is different from all other known
planetary magnetic fields. The best way to appreciate its strangeness is by
comparison with the Earth's. Our planet has two well-defined magnetic poles
-- one in each hemisphere. This is normal. Jupiter's southern hemisphere
looks normal, too. It has a single magnetic pole located near the planet's
spin axis. Jupiter's northern hemisphere, however, is different. The north
magnetic pole is smeared into a swirl, which some writers have likened to a
'ponytail'. And there is a second south pole located near the equator. The
researchers have dubbed that extra pole 'The Great Blue Spot' because it
appears blue in their false-colour images of magnetic polarity. The
scientists consider the possibility that we are catching Jupiter in the
middle of a magnetic reversal -- an unsettled situation with temporary poles
popping up in strange places. However, they favour the idea that Jupiter's
inner magnetic dynamo is simply unlike that of other planets. Deep within
Jupiter, they posit, liquid metallic hydrogen mixes with partially dissolved
rock and ice to create strange electrical currents, giving rise to an
equally strange magnetic field. More clues could be in the offing, as Juno
continues to orbit Jupiter until 2021. Changes to Jupiter's magnetic
structure, for instance, might reveal that a reversal is under way or,
conversely, that the extra pole is stable.
WATER FOUND ON JUPITER
NASA/Goddard Space Flight Center
For centuries, scientists have worked to understand the makeup of Jupiter.
It's no wonder: that planet is the biggest one in the Solar System by far,
and chemically, the closest relative to the Sun. Understanding Jupiter is a
key to learning more about how the Solar System formed, and even about how
other solar systems develop. But one critical question has bedevilled
astronomers for generations: Is there water deep in Jupiter's atmosphere,
and if so, how much? By looking with ground-based telescopes at wavelengths
sensitive to thermal radiation leaking from the depths of Jupiter's
persistent storm, the Great Red Spot, they detected the chemical signatures
of water above the planet's deepest clouds. The pressure of the water, the
researchers concluded, combined with their measurements of another oxygen-
bearing gas, carbon monoxide, imply that Jupiter has 2 to 9 times more
oxygen than the Sun. This finding supports theoretical and computer-
simulation models that have predicted abundant water (H2O) on Jupiter made
of oxygen (O) tied up with molecular hydrogen (H2). The revelation was
stirring, given that the team's experiment could easily have failed. The
Great Red Spot is full of dense clouds, which makes it hard for electromag-
netic energy to escape and teach astronomers anything about the chemistry
within. New spectroscopic technology and sheer curiosity gave the team a
boost in peering deep inside Jupiter, which has an atmosphere thousands of
miles deep. The data the team collected will supplement the information the
Juno spacecraft is gathering as it circles the planet from pole to pole once
every 53 days. Among other things, Juno is looking for water with its own
infrared spectrometer and with a microwave radiometer that can probe deeper
than anyone has seen -- to 100 bars, or 100 times the atmospheric pressure
at Earth's surface. (Altitude on Jupiter is measured in bars, which
represent atmospheric pressure, since the planet has not got a surface,
like the Earth, from which to measure elevation.) If Juno returns similar
water findings, thereby backing the ground-based technique, it could open a
new window into solving the water problem.
Juno is the latest spacecraft tasked with finding water, probably in gas
form, on this giant gaseous planet. Water is a significant and abundant
molecule in our Solar System. It spawned life on Earth and now lubricates
many of its most essential processes, including weather. It is a critical
factor in Jupiter's turbulent weather, too, and in determining whether the
planet has a core made of rock and ice. Jupiter is thought to be the first
planet to have formed by siphoning the elements left over from the formation
of the Sun as our star coalesced from an amorphous nebula into the fiery
ball of gases we see today. A widely accepted theory until several decades
ago was that Jupiter was identical in composition to the Sun -- a ball of
hydrogen with a hint of helium -- all gas, no core. But evidence is mount-
ing that Jupiter has a core, possibly 10 times the Earth's mass. Spacecraft
that previously visited the planet found chemical evidence that it formed a
core of rock and water ice before it mixed with gases from the solar nebula
to make its atmosphere. The way Jupiter's gravity acts on Juno also
supports that theory. There's even lightning and thunder on the planet,
phenomena fuelled by moisture. The moons that orbit Jupiter are mostly
water ice, so the whole neighbourhood has plenty of water. Why wouldn't the
planet -- which is this huge gravity well, where everything falls into it --
be water rich, too? In its search for water, the team used radiation data
collected from the summit of Mauna Kea in Hawaii in 2017. They relied on
the most sensitive infrared telescope on Earth at the W.M. Keck Observatory,
and also on a new instrument that can detect a wider range of gases at the
NASA Infrared Telescope Facility. The idea was to analyze the light energy
emitted through Jupiter's clouds in order to identify the altitudes of its
cloud layers. That would help the scientists determine temperature and
other conditions that influence the types of gases that can survive in those
regions. Planetary-atmosphere experts expect that there are three cloud
layers on Jupiter: a lower layer made of water ice and liquid water, a
middle one made of ammonia and sulphur, and an upper layer made of ammonia.
To check that through ground-based observations, the team looked at wave-
lengths in the infrared range of light where most gases don't absorb heat,
allowing chemical signatures to leak out. Specifically, they analyzed the
absorption patterns of a form of methane gas. Because Jupiter is too warm
for methane to freeze, its abundance should not change from one place to
another on the planet. The team found evidence for the three cloud layers
in the Great Red Spot, supporting earlier models. The deepest cloud layer
is at 5 bars, the team concluded, right where the temperature reaches the
freezing point of water. The location of the water cloud, plus the amount
of carbon monoxide that the researchers identified on Jupiter, confirms that
Jupiter is rich in oxygen and, thus, water. The technique now needs to be
tested on other parts of Jupiter to get a full picture of global water
abundance, and the data squared with Juno's findings.
PLUTO SHOULD BE RECLASSIFIED AS A PLANET
University of Central Florida
In 2006, the International Astronomical Union established a definition of a
planet that required it to "clear" its orbit, or in other words, be the
largest gravitational force in its orbit. Since Neptune's gravity influences
its neighbouring planet Pluto, and Pluto shares its orbit with frozen gases
and objects in the Kuiper belt, that meant Pluto was out of planet status.
However, a new study reports that that standard for classifying planets is
not supported in the research literature. The study reviewed scientific
literature from the past 200 years and found only one publication -- from
1802 -- that used the clearing-orbit requirement to classify planets, and it
was based on since-disproved reasoning. Moons such as Saturn's Titan and
Jupiter's Europa have been routinely called planets by planetary scientists
since the time of Galileo. The IAU definition would mean that the funda-
mental object of planetary science, the planet, is supposed to be a defined
on the basis of a concept that nobody uses in their research. It would
leave out the second-most-complex, interesting planet in the Solar System.
We now have a list of well over 100 recent examples of planetary scientists
using the word planet in a way that violates the IAU definition, but they
are doing it because it is functionally useful. They didn't say what they
meant by clearing their orbit. If you take that literally, then there are
no planets, because no planet clears its orbit.
The study said that the literature review showed that the real division
between planets and other celestial bodies, such as asteroids, occurred in
the early 1950s when Gerard Kuiper published a paper that made the distinc-
tion based on how they were formed. However, even that reason is no longer
considered a factor that determines if a celestial body is a planet.
The IAU's definition is erroneous, since the literature review shows that
clearing of the orbit is not a standard that is used for distinguishing
asteroids from planets, as the IAU claimed when crafting the 2006 definition
of planets. Instead, the study recommends classifying a planet on the basis
of whether it is large enough for its gravity causes it to become spherical
in shape. Pluto, for instance, has an underground ocean, a multi-layer
atmosphere, organic compounds, evidence of ancient lakes and multiple moons,
he said. It is more dynamic than Mars. The only planet that has more
complex geology is the Earth.
EXPOLANET FOUND VERY CLOSE TO STAR
Universite de Montreal
Wolf 503b, an exoplanet twice the size of the Earth, has been discovered
by an international team of researchers using data from the Kepler Space
Telescope. Wolf 503b is about 145 light-years from the Earth in the Virgo
constellation; it orbits its star every six days and is thus very close to
it, about 10 times closer than Mercury is to the Sun. The team identified
distinct, periodic dips such as appear in the light-curve of a star when a
planet passes in front of it. In order to characterize better the system of
which Wolf 503b is part, the astronomers first obtained a spectrum of the
host star at the NASA Infrared Telescope Facility. That confirmed that the
star is an old 'orange dwarf', slightly less luminous than the Sun but about
twice as old, and allowed precise determinations of the radii both of the
star and its companion. To confirm that the companion was indeed a planet
and to avoid making a false positive identification, the team obtained
adaptive-optics measurements from Palomar Observatory and also examined
archival data. With those, they were able to confirm that there were no
binary stars in the background and that the star did not have another, more
massive, companion that could be interpreted as a transiting planet. Wolf
503b is interesting, first, because of its size. Thanks to the Kepler
telescope, we know that most of the planets in the Milky Way that orbit
close to their stars are about as big as Wolf 503b, somewhere between the
the sizes of the Earth and Neptune (which is four times bigger than the
Earth). Since there is nothing like them in the Solar System, astronomers
wonder whether these planets are small and rocky 'super-Earths' or gaseous
mini versions of Neptune. One recent discovery also shows that there are
significantly fewer planets that are between 1.5 and 2 times the size of the
Earth than those either smaller or larger than that. In their study of the
discovery, published in 2017, the researchers say that that gap, called the
Fulton gap, could be what distinguishes the two types of planets from one
another.
Wolf 503b is one of the only planets with a radius near the gap that has a
star that is bright enough to be accessible to more detailed study that will
constrain its true nature better. The second reason for interest in the
Wolf 503b system is that the star is relatively close to the Earth, and is
bright. One of the possible follow-up studies for bright stars is the
measurement of their radial velocities to determine the masses of the
planets in orbit around them. A more massive planet will have a greater
gravitational influence on its star, and the variation in line-of-sight
velocity of the star over time will be greater. The mass, together with the
radius determined by Kepler's observations, gives the bulk density of the
planet, which in turn may tell us something about its composition. For
example, at its radius, if the planet has a composition similar to that of
the Earth, it would have to be about 14 times ithe Earth's mass. If, like
Neptune, it has an atmosphere rich in gas or volatiles, it would be
approximately half as massive. Because of its brightness, Wolf 503 will
also be a prime target for the upcoming James Webb Space Telescope.
Using a technique called transit spectroscopy, it will be possible to study the
chemical content of the planet's atmosphere, and to detect the presence of
molecules like hydrogen and water. That is crucial to determine whether its
atmosphere is similar to that of the Earth, or that of Neptune, or entirely
different from the atmospheres of planets in the Solar System. Similar
observations can not be made of most planets found by Kepler, because their
host stars are usually much fainter. As a result, the bulk densities and
atmospheric compositions of most exoplanets are still unknown.
LITTLE STAR SHEDS LIGHT ON YOUNG PLANETS
University of Tokyo
The star IRAS 15398-3359) is small, young and relatively cool. Its dimin-
utive stature means that the weak light that it shines with can't even reach
us through a cloud of gas and dust that surrounds it. But that does not
stop inquisitive minds from exploring the unknown. In 2013, astronomers
used the Atacama Large Millimetre/sub-millimetre Array (ALMA) in Chile to
observe the star in sub-millimetre wavelengths, as that kind of light can
penetrate the dust cloud. Analysis revealed some interesting nebulous
structures, despite the images the astronomers worked from being difficult
to comprehend. The model describes a dense disc of material that consists
of gas and dust from the cloud that surrounds the star. Such a disc has not
previously been seen around such a young star. The disc is a precursor to a
protoplanetary disc, which is far denser still and eventually becomes a
planetary system in orbit around a star. Astronomers can't say for sure
that this particular disc will coalesce into a new planetary system. The
dust cloud may be pushed away by stellar winds or it might all fall into the
star itself. What is exciting is how quickly that might happen. The star
is small, at around 0.7 per cent of the mass of the Sun, on the basis of
observations of the mass of the surrounding cloud. It could grow to as
large as 20 per cent in just a few tens of thousands of years, a blink of
the eye on the cosmic scale. The observations and resultant model were only
possible thanks to advances in radio astronomy with observatories such as
ALMA. The team was lucky that we see the disc practically edge-on, so the
starlight ALMA sees passes through enough of the gas and dust of the disc to
divulge important characteristics of it.
SUPERNOVAE CLUE TO STELLAR EVOLUTION
National Institutes of Natural Sciences
At the end of its life, a red supergiant star explodes as a hydrogen-rich
supernova. By comparing observational results to simulation models, an
international research team found that in many cases the explosion takes
place inside a thick cloud of circumstellar matter shrouding the star. That
result completely changes our understanding of the last stage of stellar
evolution. The research team used the Blanco Telescope to find 26 super-
novae coming from red supergiants. Their goal was to study the shock
breakout, a brief flash of light preceding the main supernova explosion.
But they could not find any signs of that phenomenon. On the other hand, 24
of the supernovae brightened faster than expected. To solve that mystery,
astronomers simulated 518 models of supernova brightness variations and
compared them with the observational results. The team found that models
with a layer of circumstellar matter about 10% of the mass of the Sun
surrounding the supernovae matched the observations well. The circumstellar
matter hides the shock breakout, trapping its light. The subsequent
collision between the supernova ejecta and the circumstellar matter creates
a strong shock wave that produces extra light, causing it to brighten more
quickly. Near the end of its life, some mechanism in the star's interior
must cause it to shed mass that then forms a layer around the star. We do
not yet have a clear idea of the mechanism causing such mass loss; further
study is needed. That will also be important in revealing the supernova
explosion mechanism and the origin of the diversity in supernovae.
CONFIRMATION OF SUPER-FAST JET FROM STAR MERGER
National Radio Astronomy Observatory
Precise measurement using a continent-wide collection of National Science
Foundation (NSF) radio telescopes has revealed that a narrow jet of
particles moving at nearly the speed of light broke out into interstellar
space after a pair of neutron stars merged in a galaxy 130 million light-
years away. The merger, which occurred in 2017 August, sent gravitational
waves rippling through space. It was the first event ever to be detected
both by gravitational waves and electromagnetic waves, including gamma rays,
X-rays, visible light, and radio waves. The aftermath of the merger, called
GW170817, was observed by orbiting and ground-based telescopes around the
world. Scientists watched as the characteristics of the received waves
changed with time, and used the changes as clues to reveal the nature of the
phenomena that followed the merger. One question that stood out, even
months after the merger, was whether or not the event had produced a narrow,
fast-moving jet of material that made its way into interstellar space. That
was important, because such jets are required to produce the type of gamma-
ray bursts that theorists had said should be caused by the merger of
neutron-star pairs. The answer came when astronomers used a combination of
the NSF's Very Long Baseline Array (VLBA), the Karl G. Jansky Very Large
Array (VLA), and the Robert C. Byrd Green Bank Telescope (GBT) and discovered
that a region of radio emission from the merger had moved, and the motion was
so fast that only a jet could explain its speed. They measured an
apparent motion that is four times faster than light. That illusion, called
superluminal motion, results when the jet is pointed nearly towards the
Earth and the material in the jet is moving close to the speed of light.
The astronomers observed the object 75 days after the merger, then again 230
days after. The jet is likely to be very narrow, at most 5 degrees wide,
and was pointed only 20 degrees away from the Earth's direction. To match
the observations, the material in the jet has to be blasting outwards at
over 97% of the speed of light.
The scenario that emerges is that the initial merger of the two super-dense
neutron stars caused an explosion that propelled a spherical shell of debris
outward. The neutron stars collapsed into a black hole whose powerful
gravity began pulling material towards it. That material formed a rapidly-
spinning disc that generated a pair of jets moving outwards from its poles.
As the event unfolded, the question became whether the jets would break out
of the shell of debris from the original explosion. Data from observations
indicated that a jet had interacted with the debris, forming a broad
'cocoon' of material expanding outward. Such a cocoon would expand more
slowly than a jet. The scientists said that the detection of a fast-moving
jet in GW170817 greatly strengthens the connection between neutron-star
mergers and short-duration gamma-ray bursts. They added that the jets need
to be pointed relatively accurately towards the Earth for the gamma-ray
burst to be detected. The merger event was important for a number of
reasons, and it continues to surprise astronomers with more information.
Jets are enigmatic phenomena seen in a number of environments, and now
these exquisite observations in the radio part of the electromagnetic spectrum
are providing fascinating insight into them, helping us to understand how they
work.
UNSTOPPABLE MONSTER IN EARLY UNIVERSE:
National Institutes of Natural Sciences
Astronomers have obtained the most detailed anatomy chart of a monster
galaxy located 12.4 billion light-years away. Using the Atacama Large
Millimetre/submillimetre Array (ALMA), the team revealed that the molecular
clouds in the galaxy are highly unstable, which leads to runaway star
formation. Monster galaxies are thought to be the ancestors of the huge
elliptical galaxies in today's Universe, therefore these findings pave the
way to understand the formation and evolution of such galaxies. Monster
galaxies, or starburst galaxies, form stars at a startling pace, 1000 times
higher than the star formation in our Galaxy. But why are they so active?
To tackle that problem, researchers need to know the environment around the
stellar nurseries. Drawing detailed maps of molecular clouds is an important
step to scout a cosmic monster. The team targeted a chimerical galaxy,
COSMOS-AzTEC-1. That galaxy was first discovered with the James Clerk
Maxwell Telescope in Hawaii, and later the Large Millimetre Telescope (LMT)
in Mexico found an enormous amount of carbon monoxide gas in the galaxy and
revealed its hidden starburst. The LMT observations also measured the
distance to the galaxy, and found that it is 12.4 US-billion light-years.
Researchers have found that COSMOS-AzTEC-1 is rich with the ingredients of
stars, but it was still difficult to figure out the nature of the cosmic gas
in the galaxy. The team utilized the high resolution and high sensitivity
of ALMA to observe this monster galaxy and obtain a detailed map of the
distribution and the motion of the gas. Thanks to the most extended ALMA
antenna configuration of 16 km, this is the highest-resolution molecular-gas
map of a distant monster galaxy ever made.
The team found that there are two distinct large clouds several thousand
light-years away from the centre. In most distant starburst galaxies, stars
are actively formed in the centre, so it is surprising to find off-centre
clouds. The astronomers further investigated the nature of the gas in
COSMOS-AzTEC-1 and found that the clouds throughout the galaxy are very
unstable, which is unusual. In a normal situation, the inward gravity and
outward pressure are balanced in the clouds. Once gravity overcomes
pressure, the gas cloud collapses and forms stars at a rapid pace. Then,
stars and supernova explosions at the end of the stellar life-cycle blast
out gases, which increase the outward pressure. As a result, the gravity
and pressure reach a balanced state and star formation continues at a
moderate pace. In that way star formation in galaxies is self-regulating.
But, in COSMOS-AzTEC-1, the pressure is far weaker than the gravity and hard
to balance. Therefore that galaxy shows runaway star formation and has
morphed into an unstoppable monster galaxy. The team estimated that the gas
in COSMOS-AzTEC-1 will be completely consumed in 100 million years, which is
10 times faster than in other star-forming galaxies. But why is the gas in
COSMOS-AzTEC-1 so unstable? Researchers have not got a definitive answer
yet, but galaxy merger is a possible cause. Galaxy collision may have
transported the gas efficiently into a small area and ignited intense star
formation. At this moment, however, astronomers have no evidence of any
merger in that galaxy. By observing other similar galaxies with ALMA,
astronomers hope to elucidate the relationship between galaxy mergers and
monster galaxies.
Topic: Mid September Astronomy Bulletin (Read 1308 times)