SUN'S CORE ROTATES FOUR TIMES FASTER THAN SURFACE
University of California - Los Angeles
The Sun's core rotates nearly four times faster than its surface,
according to new findings by an international team of astronomers.
Scientists had assumed that the core rotates at about the same speed
as the surface. The most likely explanation is that the core rotation
is left over from the period when the Sun formed, some 4.6 billion
(U.S. billion, = 10 to the 9, throughout this Bulletin) years ago.
The rotation of the solar core may give us a clue as to how the Sun
formed. After the Sun formed, the solar wind probably slowed down
the rotation of the outer layers. The rotation might also affect
sunspots, which also rotate. Sunspots can be enormous; a single
sunspot can be larger than the Earth. The researchers studied surface
acoustic waves in the Sun's atmosphere, some of which penetrate to the
Sun's core, where they interact with gravity waves that have a slosh-
ing motion similar to how water would move in a half-filled tanker
lorry driven on a winding mountain road. From those observations,
they detected the sloshing motions of the solar core. By carefully
measuring the acoustic waves, the researchers determined precisely
the time it takes an acoustic wave to travel from the surface to the
centre of the Sun and back again. That travel time turned out to be
influenced slightly by the sloshing motion of the gravity waves.
The researchers identified the sloshing motion and made the calcula-
tions using 16 years of observations from an instrument called GOLF
(Global Oscillations at Low Frequency) on a spacecraft called SoHO
(the Solar and Heliospheric Observatory) -- a joint project of ESA
and NASA. The method was developed by researchers at the Observatoire
de la Cote d'Azur in Nice. The idea that the solar core could be
rotating more rapidly than the surface has been considered for more
than 20 years, but has never before been measured. The core of the
Sun differs from its surface in another way as well. The core has a
temperature of approximately 15.7 million degrees Kelvin, whereas the
surface is `only' 5,800 Kelvin.
COMPLEX CHEMISTRY IN TITAN'S ATMOSPHERE
National Radio Astronomy Observatory
Saturn's largest moon, Titan, is one of our Solar System's most
intriguing and Earth-like bodies. It is nearly as large as Mars and
has a hazy atmosphere made up mostly of nitrogen with a smattering of
organic (i.e. carbon-based) molecules, including methane (CH4) and
ethane (C2H6). Planetary scientists theorize that that chemical
make-up is similar to the Earth's primordial atmosphere. The con-
ditions on Titan, however, are not conducive to the formation of life
as we know it; it is simply too cold. At ten times the distance from
the Earth to the Sun, Titan is so cold that liquid methane rains onto
its solid icy surface, forming rivers, lakes, and seas. The pools of
hydrocarbons, however, create a unique environment that may help
molecules of vinyl cyanide (C2H3CN) link together to form membranes,
features resembling the lipid-based cell membranes of living organisms
on Earth. Astronomers using archival data from the Atacama Large
Millimeter/submillimeter Array (ALMA), which were collected over
a series of observations from February to May 2014, have found
compelling evidence that molecules of vinyl cyanide are indeed
present on Titan in significant quantities. By reviewing the archival
data, astronomers found three distinct signals -- spikes in the
millimetre-wavelength spectrum -- that correspond to vinyl cyanide.
Those telltale signatures originated at least 200 kilometres above
the surface of Titan.
Titan's atmosphere is a veritable chemical factory, harnessing the
light of the Sun and the energy from fast-moving particles that orbit
around Saturn to convert simple organic molecules into larger, more
complex chemicals. As our knowledge of Titan's chemistry grows, it
becomes increasingly apparent that complex molecules arise naturally
in environments similar to those that existed on the early Earth, but
there are important differences. For example, Titan is much colder
than the Earth ever was at any period in its history. The temperature
on Titan averages about 95°K, so water at its surface remains frozen.
Geological evidence also suggests that the early Earth had high
concentrations of carbon dioxide (CO2); Titan does not. The Earth's
rocky surface was also frenetically active, with extensive vulcanism
and routine asteroid impacts, which would have affected the evolution
of our atmosphere. In comparison, Titan's icy crust appears quite
docile. The team is looking for new and more complex organic
chemicals as well as studying Titan's atmospheric circulation
patterns. In the future, higher-resolution studies will shed more
light on that intriguing satellite, and possibly give us new insights
into Titan's potential for prebiotic chemistry.
NEW HORIZONS' NEXT TARGET
NASA
Could the next flyby target for NASA's New Horizons spacecraft
actually be two targets? New Horizons scientists look to answer that
question as they sort through new data gathered on the distant Kuiper-
Belt object (KBO) 2014 MU69, which the spacecraft will fly past on
2019 Jan. 1. That flyby will be the most distant in the history of
space exploration, a (US-)billion miles beyond Pluto. The ancient
KBO, which is more than 6.5 billion kilometres away, passed in front
of a star on 2017 July 17. A number of telescopes deployed by the New
Horizons team in a remote part of Patagonia were in the right place at
the right time to catch the fleeting occultation, and were able to
capture important data to help mission planners refine the spacecraft
trajectory and understand the size, shape, orbit and environment
around MU69.
On the basis of those new occultation observations, team members say
that MU69 may not be not a lone spherical object, but suspect it could
be an `extreme prolate spheroid', or even a binary pair. The odd
shape has scientists thinking that two bodies may be orbiting very
close together or even touching (a system known as a close or contact
binary), or perhaps they are observing a single body with a large
chunk taken out of it. The size of MU69 or its components also can be
determined from the data. It appears to be no more than 30 km long,
(or, if it is binary, each component is about 15-20 km in diameter).
The July 17 stellar occultation event that gathered the data was the
third of a historic set of three ambitious occultation observations
for New Horizons. The team used data from the Hubble telescope and
the Gaia satellite to calculate whereabouts the shadow of MU69 would
fall on the Earth's surface.
ATMOSPHERE MIGHT NOT SURVIVE PROXIMA b's ORBIT
NASA/Goddard Space Flight Center
At only four light-years away, Proxima b is our closest known extra-
solar neighbour. However, owing to the fact that it has not been seen
crossing in front of its host star, the exoplanet eludes the usual
method for learning about its atmosphere. Instead, scientists must
rely on models to understand whether it is habitable. One computer
model considered what would happen if the Earth orbited Proxima
Centauri, our nearest stellar neighbour and Proxima b's host star, in
an orbit analogous to that of Proxima b. The study suggests that the
Earth's atmosphere would not survive in close proximity to the violent
red dwarf. Just because Proxima b's orbit is in the habitable zone,
which is the distance from its host star where water could pool on a
planet's surface, does not mean that it is habitable. It does not
take into account, for example, whether water actually exists on the
planet, or whether an atmosphere could survive in that orbit.
Atmospheres are also essential for life as we know it: having the
right atmosphere allows for climate regulation, the maintenance of a
water-friendly surface pressure, shielding from hazardous space
weather, and the housing of life's chemical building blocks. The
computer model used the Earth's atmosphere, magnetic field and gravity
as proxies for Proxima b's. It also calculated how much radiation
Proxima Centauri produces on average, on the basis of observations
from the Chandra X-ray Observatory. With those data, the model
simulates how the host star's intense radiation and frequent flaring
affect the exoplanet's atmosphere. An active red dwarf star like
Proxima Centauri strips away atmosphere when high-energy extreme-UV
radiation ionizes atmospheric gases, knocking off electrons and
producing a lot of electrically charged particles. In that process,
the newly formed electrons gain enough energy that they can readily
escape the planet's gravity and race out of the atmosphere. Opposite
charges attract, so as more negatively charged electrons leave the
atmosphere, they create a powerful charge separation that pulls
positively charged ions along with them, out into space.
In Proxima Centauri's habitable zone, Proxima b encounters bouts of
extreme ultraviolet radiation hundreds of times greater than the Earth
does from the Sun. That radiation generates enough energy to strip
away not just the lightest molecules -- hydrogen -- but also, over
time, heavier elements such as oxygen and nitrogen. The model shows
that Proxima Centauri's powerful radiation drains the Earth-like
atmosphere as much as 10,000 times faster than happens at the Earth.
To understand how the process can vary, the scientists looked at two
other factors that exacerbate atmospheric loss. First, they
considered the temperature of the neutral atmosphere, called the
thermosphere. They found that, as the thermosphere heats with more
stellar radiation, atmospheric escape increases. The scientists also
considered the size of the region over which atmospheric escape
happens, the polar cap. Planets are most sensitive to magnetic
effects at their magnetic poles. When magnetic field lines at the
poles are closed, the polar cap is limited and charged particles
remain trapped near the planet. On the other hand, greater escape
occurs when magnetic field lines are open, providing a one-way route
out into space. The scientists show that with the highest thermo-
sphere temperatures and a completely open magnetic field, Proxima b
could lose an amount equal to the whole of the Earth's atmosphere in
100 million years -- which is only a small fraction of Proxima b's
4 billion years thus far. When the scientists assumed the lowest
temperatures and a closed magnetic field, that much mass escapes
over 2 billion years. Red dwarfs like Proxima Centauri or the
TRAPPIST-1 star are often the target of exoplanet hunts, because
they are the coolest, smallest and most common stars in the Galaxy.
Because they are cooler and dimmer, planets have to be in small
orbits for liquid water to be present. But unless the atmospheric
loss is counteracted by some other process -- such as a massive amount
of volcanic activity or comet bombardment -- such close proximity is
not promising for an atmosphere's survival or sustainability.
MILKY WAY'S ORIGINS ARE NOT WHAT THEY SEEM
RAS
In a first-of-its-kind analysis, Northwestern University astrophys-
icists have discovered that, contrary to previous supposition, up to
half of the matter in our Milky Way galaxy may have come from distant
galaxies. As a result, each one of us may be made in part from
extragalactic matter. Using supercomputer simulations, the research
team found a major and unexpected new mode for how galaxies, including
our own Milky Way, acquired their matter: intergalactic transfer.
The simulations show that supernova explosions eject copious amounts
of gas from galaxies, which causes atoms to be transported from one
galaxy to another by powerful galactic winds. Intergalactic transfer
is a newly identified phenomenon, which simulations indicate could
be critical for understanding how galaxies evolve. Galaxies are far
apart from each other, so even though galactic winds propagate at
several hundred km/s, this process occurred over several billion
years. The research group had developed sophisticated numerical
simulations that produced realistic 3D models of galaxies, following a
galaxy's formation from just after the Big Bang to the present day.
It then developed state-of-the-art algorithms to mine that wealth of
data and quantify how galaxies acquire matter from the Universe.
By tracking in detail the complex flows of matter in the simulations,
the research team found that gas flows from smaller galaxies to larger
galaxies, such as the Milky Way, where the gas forms stars. Such
transfer of mass through galactic winds can account for up to 50% of
matter in the larger galaxies. In a galaxy, stars are bound together:
a large collection of stars orbits a common centre of mass. After the
Big Bang 14 billion years ago, the Universe was filled with a uniform
gas -- no stars, no galaxies. But there were tiny perturbations in
the gas, and they started to grow by force of gravity, eventually
forming stars and galaxies. After galaxies formed, each had its own
identity. The findings open a new line of research in understanding
galaxy formation, the researchers say, and the prediction of inter-
galactic transfer can now be tested. The Northwestern team plans to
collaborate with observational astronomers who are working with the
Hubble telescope and ground-based observatories to test the simulation
predictions.
DAWN OF THE COSMOS
Arizona State University
Astronomers have discovered 23 young galaxies, seen as they were 800
million years after the Big Bang. Long ago, about 300,000 years after
the Big Bang, the Universe was dark. There were no stars or galaxies,
and the Universe was filled with neutral hydrogen gas. In the next
half-billion years or so the first galaxies and stars appeared. Their
energetic radiation ionized their surroundings, illuminating and
transforming the Universe. That dramatic transformation, known as
re-ionization, occurred some time in the interval between 300 million
years and one billion years after the Big Bang. Astronomers are
trying to pinpoint that milestone more precisely, and the galaxies
found in this study help in that determination. Before re-ionization,
the galaxies were very hard to see, because their light is scattered
by inter-galactic gas, like a car's headlights in fog. As enough
galaxies turn on and 'burn off the fog' they become easier to see.
By doing so, they help to provide a diagnostic to see how much of the
'fog' remains at any time in the early Universe. To detect such
galaxies, astronomers have been using the Dark Energy Camera (DECam),
a powerful new instrument installed at the 4-m Blanco Telescope at
CTIO in northern Chile.
The galaxy search using the Arizona-designed filter and DECam is part
of the ongoing `Lyman-Alpha Galaxies in the Epoch of Reionization'
project (LAGER). It is the largest uniformly selected sample that
goes far enough back in the history of the Universe to reach cosmic
dawn. The combination of the large survey size and sensitivity of
that survey enables astronomers to study galaxies that are common but
faint, as well as those that are bright but rare, at that early stage
in the Universe. The findings in the survey imply that a large
fraction of the first galaxies that ionized and illuminated the
Universe formed early, less than 800 million years after the Big Bang.
The next steps for the team will be to build on those results. They
plan to continue to search for distant star-forming galaxies over a
larger volume of the Universe and to investigate further the natures
of some of the first galaxies in the Universe.
VOYAGER SPACECRAFT'S 40 YEARS
NASA
Humanity's most distant and longest-lived spacecraft, Voyager 1 and 2,
achieve 40 years of operation this August and September. Despite
their vast distance, they continue to communicate with NASA daily.
Their story has not only informed generations of current and future
scientists and engineers, but also the Earth's culture, including
film, art and music. Each spacecraft carries a golden record of Earth
sounds, pictures and messages. Since the spacecraft could last
billions of years, those circular time capsules could one day be the
only traces of human civilization. The Voyagers have set numerous
records in their journeys. In 2012, Voyager 1, which was launched on
1977 Sept. 5, became the first spacecraft that could be claimed to
have entered interstellar space. Voyager 2, launched on 1977 Aug. 20,
is the only spacecraft to have flown by all four outer planets --
Jupiter, Saturn, Uranus and Neptune. The two spacecrafts' numerous
planetary encounters include discovering the first active volcanoes
beyond the Earth, on Jupiter's moon Io; hints of a subsurface ocean on
Jupiter's moon Europa; the most Earth-like atmosphere in the Solar
System, on Saturn's moon Titan; the jumbled-up, icy moon Miranda at
Uranus; and icy-cold geysers on Neptune's moon Triton. Though the
spacecraft have left the planets far behind -- and neither will come
remotely close to another star for 40,000 years -- the two probes
still send back observations about conditions where our Sun's
influence diminishes and interstellar space begins.
Voyager 1, now almost 13 billion miles from the Earth, travels through
interstellar space northward, out of the plane of the planets. The
probe has informed researchers that cosmic rays (atomic nuclei
accelerated to nearly the speed of light) are as much as four times
more abundant in interstellar space than in the vicinity of the Earth.
That means that the heliosphere, the bubble-like volume containing our
Solar System's planets and solar wind, effectively acts as a radiation
shield for the planets. Voyager 1 also hinted that the magnetic field
of the local interstellar medium is wrapped around the heliosphere.
Voyager 2, now almost 11 billion miles from the Earth, travels south
and is expected to enter interstellar space in the next few years.
The difference in the locations of the two Voyagers allows scientists
to compare already two regions of space where the heliosphere
interacts with the surrounding interstellar medium, using instruments
that measure charged particles, magnetic fields, low-frequency radio
waves and solar-wind plasma. Once Voyager 2 crosses into the inter-
stellar medium, the two spacecraft will be able to sample the medium
from two different locations simultaneously. The twin Voyagers have
been cosmic over-achievers, thanks to the foresight of mission
designers. By preparing for the radiation environment at Jupiter, the
harshest of all the planets in the Solar System, the spacecraft were
well equipped for their subsequent journeys. Both Voyagers carry
redundant systems that allow them to switch to backup systems
autonomously when necessary, as well as long-lasting power supplies.
Each Voyager has three radio-isotope thermoelectric generators,
devices that use the heat energy generated from the decay of
plutonium-238, which has a half-life of 88 years.
Because the Voyagers' power supplies decrease by four watts per year,
engineers are havng to learn how to operate the spacecraft under ever-
tighter power constraints. And to maximize the Voyagers' lifespans,
they also have to understand documents written decades earlier
describing commands and software, in addition to tapping the expertise
of former Voyager engineers. Team members estimate that they will
have to turn off the last scientific instrument by 2030. However,
even after the spacecraft go silent, they will continue on their
trajectories at about their present speed of some 48,000 kph,
completing an orbit of the Milky Way every 225 million years.
Topic: Mid August Astronomy Bulletin (Read 2465 times)