CITIZEN SCIENTISTS DISCOVER EXOPLANET
NASA

Using data from the Kepler space telescope, citizen scientists have
discovered a planet roughly twice the size of the Earth located within its
star's habitable zone (the range of orbital distances where liquid water may
exist on the planet's surface). The new world, known as K2-288Bb, could be
rocky or could be a gas-rich planet similar to Neptune. Its size is rare
among exoplanets (planets beyond our Solar System). Located 226 light-years
away in the constellation Taurus, the planet lies in a stellar system known
as K2-288, which contains a pair of dim, cool M-type stars separated by
about 8.2 billion kilometres -- roughly six times the distance between
Saturn and the Sun. The brighter star is about half as massive and large as
the Sun, while its companion is about one-third the Sun's mass and size.
The new planet, K2-288Bb, orbits the smaller, dimmer star every 31.3 days.
Examining data from the fourth observing campaign of Kepler's K2 mission,
the team noticed two probable planetary transits in the system. But
scientists require a third transit before claiming the discovery of a
candidate planet, and there wasn't a third signal in the observations they
reviewed. As it turned out, though, the team wasn't actually analyzing all
of the data. In Kepler's K2 mode, which ran from 2014 to 2018, the space-
craft repositioned itself to point at a new patch of sky at the start
of each three-month observing campaign. Astronomers were initially
concerned that that repositioning would cause systematic errors in the
measurements. To deal with that, early versions of the software that was
used to prepare the data for planet-finding analysis simply ignored the
first few days of observations -- and that's where the initial transit was
hiding. As scientists learned how to correct for the systematic errors,
that trimming step was eliminated -- but the early K2 data had been clipped.
The re-processed data were posted directly to Exoplanet Explorers, a project
where the public searches Kepler's K2 observations to locate new transiting
planets. In 2017 May, volunteers noticed the third transit and began an
excited discussion about what was then thought to be an Earth-sized
candidate in the system, which caught the attention of the team. Estimated
to be about 1.9 times the Earth's size, K2-288Bb is half the size of
Neptune. That places it within a recently discovered category called the
Fulton gap, or radius gap. Among planets that orbit close to their stars,
there's a curious dearth of worlds between about 1.5 and two times the
Earth's size. That is likely to be a result of intense starlight breaking
up atmospheric molecules and eroding away the atmospheres of some planets
over time, leaving behind two populations. Since K2-288Bb's radius places
it in that gap, it may provide a case study of planetary evolution within
that size range.


TESS DISCOVERS ITS THIRD NEW PLANET
Massachusetts Institute of Technology

NASA's Transiting Exoplanet Survey Satellite, TESS, has discovered a third
small planet outside our Solar System. The new planet, named HD 21749b,
orbits a bright, nearby dwarf star about 53 light-years away, in the
constellation Reticulum, and appears to have the longest orbital period of
the three planets so far identified by TESS. HD 21749b journeys around its
star in a relatively leisurely 36 days, compared to the two other planets --
Pi Mensae b, a 'super-Earth' with a 6.3-day orbit, and LHS 3844b, a rocky
world that speeds around its star in just 11 hours. All three planets were
discovered in the first three months of TESS observations. The surface of
the new planet is probably at around 150 C -- relatively cool, given its
proximity to its star, which is almost as bright as the Sun. The planet
is about three times the size of the Earth. Surprisingly, it is also a
whopping 23 times as massive as Earth. But it is unlikely that the planet
is rocky and therefore habitable; it is more likely to be made of gas, of a
kind that is much denser than the atmospheres of either Neptune or Uranus.
Serendipitously, the researchers have also detected evidence of a second
planet, though not yet confirmed, in the same planetary system, with a
shorter, 7.8-day orbit. If it is confirmed as a planet, it could be the
first Earth-sized planet discovered by TESS. Since it was launched in 2018
April, TESS has been monitoring the sky, sector by sector, for momentary
dips in the light of about 200,000 nearby stars. Such dips are likely to
represent planets passing in front of the stars.

 
SUB-SATURN GIANT PLANETS ARE COMMON
W. M. Keck Observatory

Astronomers have found a new exoplanet that could alter the standing theory
of planet formation. With a mass that is between those of Neptune and
Saturn, and its location beyond the 'snow line' of its host star, an alien
world of that scale was supposed to be rare. Using the Near-Infrared
Camera, second generation (NIRC2) instrument on the 10-m Keck II telescope
on Mauna Kea, Hawaii, and the Wide-Field Camera 3 (WFC3) instrument on the
Hubble Space Telescope, the researchers took simultaneous high-resolution
images of the exoplanet, named OGLE-2012-BLG-0950Lb, allowing them to
determine its mass. They were surprised to find the mass come out right in
the middle of the predicted intermediate-giant-planet mass gap. In an
uncanny timing of events, another team of astronomers published a
statistical analysis at almost the same time showing that such sub-Saturn-
mass planets are not rare after all. OGLE-2012-BLG-0950Lb was among the
sub-Saturn planets in the statistical study; all were detected through
microlensing, the only method currently sensitive enough to detect planets
with less than Saturn's mass in Jupiter-like orbits. Microlensing arises as
a consequence of Einstein's general theory of relativity: the bending and
magnification of light near a massive object like a star, producing a
natural lens in the sky. In the case of OGLE-2012-BLG-0950Lb, the light
from a distant background star was magnified by OGLE-2012-BLG-0950L (the
exoplanet's host star) over the course of two months as it passed close to
perfect alignment in the sky with the background star. By carefully
analyzing the light during the alignment, an unexpected dimming with a
duration of about a day was observed, revealing the presence of
OGLE-2012-BLG-0950Lb by its own influence on the lensing.

What is unique about the microlensing method is its sensitivity to
sub-Saturn planets like OGLE-2012-BLG-0950Lb that orbit beyond the 'snow
line' of their host stars. The snow line, or frost line, is the distance in
a young solar system, (a.k.a. a protoplanetary disc) at which it is cold
enough for water to condense into ice. At and beyond the snow line there is
a dramatic increase in the amount of solid material needed for planet
formation. According to the core accretion theory, the solids are thought
to build up into planetary cores first through chemical and then gravita-
tional processes. A key process of the core-accretion theory is called
'runaway gas' accretion. Giant planets are thought to start their formation
process by collecting a core mass of about 10 times the Earth's mass in rock
and ice. At that stage, a slow accretion of hydrogen and helium gas begins
until the mass has doubled. Then, the accretion of hydrogen and helium is
expected to speed up exponentially in a runaway gas-accretion process. That
process stops when the supply is exhausted. If the supply of gas is stopped
before runaway accretion stops, we get 'failed Jupiter' planets with masses
of 10-20 Earth-masses (like Neptune). The runaway gas-accretion scenario of
the core-accretion theory predicts that planets like OGLE-2012-BLG-0950Lb
are expected to be rare. At 39 times the mass of the Earth, planets that
size are thought to be continuing through a stage of rapid growth, ending in
a much more massive planet. This new result suggests that the runaway-
growth scenario may need revision. The discovery has not only called into
question an established theory, it was made using a new technique that will
be a key part of NASA's next big planet-finding mission, the Wide-Field
Infra-Red Survey Telescope (WFIRST), which is scheduled to be launched into
orbit in the mid-2020s.


A GALAXY WITHOUT NEIGHBOURS
University of Michigan

Researchers have long known that the Milky Way has about 10 smaller
satellite galaxies surrounding it, each with at least a million stars, and
up to more than a billion, such as the Magellanic Clouds. Now, with
the Subaru telescope, astronomers can observe galaxies five or ten times the
distance from the Milky Way, such as M94. They can then use the physics of
how satellite galaxies form around the Milky Way to predict how many
satellite galaxies a similar-sized galaxy such as M94 may have. When
astronomers examined M94, they expected to find a similar number of
satellite galaxies. However, they detected just two galaxies near M94, with
very few stars each. The results have implications for the current
understanding of how galaxies form -- which is in much larger haloes of dark
matter. Those halos of dark matter surrounding galaxies have immense
gravitational force, and can pull in gas from their immediate vicinity.
Large galaxies like the Milky Way generally form in haloes of about the same
mass. But smaller satellite galaxies, which form in smaller 'subhaloes' are
not nearly so dependable. The production rate of high-mass stars in such
satellite galaxies actually modulates their growth. If, for example, the
nascent satellite galaxy forms too many high-mass stars at one time, their
eventual supernova explosions might expel all its gas and halt all further
growth. But astronomers are unsure at what size halo such 'scatter' in
galaxy formation becomes important. M94 indicates that galaxy formation in
intermediate-sized dark haloes may be much more uncertain than previously
thought. To observe the number of satellite dwarf galaxies around M94, the
researchers took a composite image of the large galaxy. The image covered
about 12 square degrees of the night sky. That kind of image includes
layers and layers of 'noise', including cosmic rays and scattered light,
which make faint dwarf galaxies difficult to detect. To make sure they
weren't missing satellite galaxies, the team engineered artificial galaxies
back into the image and recovered them using the same methods as for real
satellites. With that technique, the researchers confirmed that there were
no more than two galaxies around M94.


X-RAY PULSE DETECTED NEAR EVENT HORIZON
Massachusetts Institute of Technology

On 2014 Nov. 22, astronomers observed a rare event in the night sky: a
supermassive black hole at the centre of a galaxy, nearly 300 million light
years away, ripping apart a passing star. The event, known as a tidal-
disruption flare, for the black hole's massive tidal pull that tears a star
apart, created a burst of X-ray activity near the centre of the galaxy.
Since then, many observatories have trained their sights on the event, in
the hope of learning more about how black holes feed. Now researchers have
pored through data from multiple telescopes' observations of the event, and
discovered a curiously intense, stable, and periodic pulse, or signal, of
X-rays, across all datasets. The signal appears to emanate from an area
very close to the black hole's event horizon -- the point beyond which
material is swallowed inescapably by the black hole. The signal appears
periodically to brighten and fade every 131 seconds, and persisted over at
least 450 days. The researchers believe that whatever is emitting the
periodic signal must be orbiting the black hole, just outside the event
horizon, near the Innermost Stable Circular Orbit, or ISCO -- the smallest
orbit in which a particle can safely travel around a black hole. Given the
signal's stable proximity to the black hole, and the black hole's mass,
which researchers previously estimated to be about 1 million times that of
the Sun, the team has calculated that the black hole is spinning at about
half the speed of light. The findings are the first demonstration of a
tidal-disruption flare being used to estimate a black hole's spin. Most
supermassive black holes are dormant and do not usually emit much in the
way of X-ray radiation. Only occasionally will they release a burst of
activity, such as when stars get close enough for black holes to devour
them. Such tidal-disruption flares can be used to estimate the spin of
supermassive black holes -- a characteristic that has been, up until now,
incredibly tricky to pin down. Events where black holes shred stars that
come too close to them could help us map out the spins of several super-
massive black holes that are dormant and otherwise hidden at the centres of
galaxies. That could ultimately help us understand how galaxies evolved
over cosmic time.

Theoretical models of tidal-disruption flares show that when a black hole
shreds a star apart, some of that star's material may stay outside the event
horizon, circling, at least temporarily, in a stable orbit such as the ISCO,
and giving off periodic flashes of X-rays before ultimately being fed by the
black hole. The periodicity of the X-ray flashes thus encodes key
information about the size of the ISCO, which itself is dictated by how fast
the black hole is spinning. Astronomers thought that if they could see such
regular flashes very close to a black hole that had undergone a recent tidal
disruption event, those signals could give them an idea of how fast the
black hole was spinning. They focused their search on ASASSN-14li, the
tidal-disruption event that astronomers identified in 2014 November, using
the ground-based All-Sky Automated Survey for SuperNovae (ASASSN). The
team looked through archived datasets from three observatories that collected
X-ray measurements of the event since its discovery: the European Space
Agency's XMM-Newton space observatory, and NASA's space-based Chandra
and Swift observatories. On the basis of the properties of the signal, and the
mass and size of the black hole, the team estimated that the black hole is
spinning at at least half the speed of light. Once the team discovered the
periodic signal, it was up to the theorists to find an explanation for what
may have generated it. The team came up with various scenarios, but the one
that seems the most likely to generate such a strong, regular X-ray flare
involves not just a black hole shredding a passing star, but also a smaller
white-dwarf star, orbiting close to the black hole. Such a white dwarf may
have been circling the supermassive black hole, at ISCO -- the innermost
stable circular orbit -- for some time. Alone, it would not have been
enough to emit any sort of detectable radiation. For all intents and
purposes, the white dwarf would have been invisible to telescopes as it
circled the relatively inactive, spinning black hole. Sometime around 2014
Nov. 22, a second star passed close enough to the system that the black hole
tore it apart in a tidal-disruption flare that emitted an enormous amount of
X-ray radiation, in the form of hot, shredded stellar material. As the
black hole pulled that material inward, some of the stellar debris fell into
the black hole, while some remained just outside, in the innermost stable
orbit -- the very same orbit in which the white dwarf circled. As the white
dwarf came in contact with that hot stellar material, it probably dragged it
along as a luminous overcoat of sorts, illuminating the white dwarf in an
intense amount of X-rays each time it circled the black hole, every 131
seconds. The scientists admit that such a scenario would be incredibly rare
and would last only for several hundred years at most -- a blink of an eye
on the cosmic scale. The chances of detecting such a scenario would be
exceedingly slim. Estimating spins of several black holes from the
beginning of time to now would be valuable in terms of estimating whether
there is a relationship between the spin and the age of black holes.


BIRTH OF BLACK HOLE OR NEUTRON STAR
NASA

A brief and unusual flash observed in the night sky on 2018 June 16 puzzled
astronomers and astrophysicists across the globe. The event -- called
AT2018cow and nicknamed 'the Cow' after the coincidental final letters in
its official name -- is unlike any celestial outburst ever seen before,
prompting multiple theories about its source. Over three days, the Cow
produced a sudden explosion of light at least 10 times brighter than a
typical supernova, and then it faded over the next few months. The unusual
event occurred inside or near a star-forming galaxy known as CGCG 137-068,
located about 200 million light-years away in the constellation Hercules.
The object was first observed by the Asteroid Terrestrial-impact Last Alert
System telescope in Hawaii. So exactly what is the Cow? Using data from
multiple NASA missions, including the Neil Gehrels Swift Observatory and the
Nuclear Spectroscopic Telescope Array (NuSTAR), two groups are publishing
papers that provide possible explanations for the Cow's origins. One paper
argues that the Cow is a monster black hole shredding a passing star. The
second paper hypothesizes that it is a supernova that gave birth to a black
hole or a neutron star. One potential explanation of the Cow is that a star
has been ripped apart in what astronomers call a 'tidal disruption event'.
Just as the Moon's gravity causes Earth's oceans to bulge, creating tides, a
black hole has a similar but more powerful effect on an approaching star,
ultimately breaking it apart into a stream of gas. The tail of the gas
stream is flung out of the system, but the leading edge swings back round
the black hole, collides with itself and creates an elliptical cloud of
material. According to one research team using data spanning from infrared
radiation to gamma rays from Swift and other observatories, that transform-
ation best explains the Cow's behaviour.

Other astronomers think that the shredded star was a white dwarf -- a hot,
roughly Earth-sized stellar remnant marking the final state of stars like
our Sun. They also calculated that the black hole's mass ranges from
100,000 to 1 million times the Sun's, almost as large as the central black
hole of its host galaxy. It is unusual to see black holes of that scale
outside the centre of a galaxy, but it is possible that the Cow occurred in
a nearby satellite galaxy or a globular star cluster whose older stellar
populations could have a higher proportion of white dwarfs than average
galaxies. A third team of scientists was able to gather data on the Cow
over an even broader range of wavelengths, spanning from radio waves to
gamma rays. On the basis of those observations, the team suggests that a
supernova could be the source of the Cow. When a massive star dies, it
explodes as a supernova and leaves behind either a black hole or an
incredibly dense neutron star. The Cow could represent the birth of one
such stellar remnant. The team used high-energy X-ray data to show that the
Cow has characteristics similar to a compact body like a black hole or
neutron star consuming material. But on the basis of what we saw in other
wavelengths, we think that this was a special case and that we may have
observed -- for the first time -- the creation of a compact body in real
time. The team analyzed data from multiple observatories, including NASA's
NuSTAR, ESA's XMM-Newton and INTEGRAL satellites, and the National
Science Foundation's Very Large Array. The team proposes that the bright
optical and ultraviolet flash from the Cow signalled a supernova and that
the X-ray emissions that followed shortly after the outburst arose from gas
radiating energy as it fell onto a compact object. Typically, a supernova's
expanding debris cloud blocks any light from the compact object at the
centre of the blast. Because of the X-ray emissions, astronomers suggest
that the original star in this scenario may have been relatively low in mass,
producing a comparatively thinner debris cloud through which X-rays from
the central source could escape. If we are seeing the birth of a compact object
in real time, this could be the start of a new chapter in our understanding
of stellar evolution.


DARK MATTER ON THE MOVE
RAS

Scientists have found evidence that dark matter can be heated up and moved
around, as a result of star formation in galaxies. The findings provide the
first observational evidence for the effect known as 'dark matter heating',
and give new clues as to what makes up dark matter. In the new work,
scientists set out to hunt for evidence for dark matter at the centres of
nearby dwarf galaxies. Dwarf galaxies are small, faint galaxies that are
typically found orbiting larger galaxies like our own Milky Way. Dark
matter is thought to make up most of the mass of the Universe. However,
since it does not interact with light in the same way as normal matter, it
can only be observed through its gravitational effects. The key to studying
it may however lie in how stars are formed in these galaxies. When stars
form, strong winds can push gas and dust away from the heart of the galaxy.
As a result, the galaxy's centre has less mass, which affects how much
gravity is felt by the remaining dark matter. With less gravitational
attraction, the dark matter gains energy and migrates away from the centre,
an effect called 'dark matter heating'. The team of astrophysicists
measured the amount of dark matter at the centres of 16 dwarf galaxies with
very different star-formation histories. They found that galaxies that
stopped forming stars long ago had higher dark-matter densities at their
centres than those that are still forming stars today. That supports the
theory that the older galaxies had less dark-matter heating. The findings
provide a new constraint on dark-matter models: dark matter must be able to
form dwarf galaxies that exhibit a range of central densities, and those
densities must relate to the amount of star formation. The team hopes to
expand on that work by measuring the central dark-matter density in a larger
sample of dwarfs, pushing to even fainter galaxies, and testing a wider
range of dark-matter models.


RADIO SIGNALS FROM DEEP SPACE
BBC Science

Astronomers have revealed details of mysterious signals emanating from a
distant galaxy, picked up by a telescope in Canada. The precise nature and
origin of the blasts of radio waves is unknown. Among the 13 bursts of fast
radio waves, known as FRBs, was a very unusual repeating signal, coming from
the same source about 1.5 billion light-years away. Such an event has only
been reported once before, by a different telescope. The CHIME observatory,
located in British Columbia's Okanagan Valley, consists of four 100-metre
semi-cylindrical antennae, which scan the entire northern sky each day. The
telescope only got up and running last year, detecting 13 of the radio
bursts almost immediately, including the repeater. FRBs are short, bright
flashes of radio waves, which appear to be coming from almost halfway across
the Universe. So far, scientists have detected about 60 single fast radio
bursts and two that repeat. They believe there could be as many as a
thousand FRBs in the sky every day. There are a number of theories about
what could be causing them. They include a neutron star with a very strong
magnetic field that is spinning very rapidly or two neutron stars merging
together.


GALAXY ZOOMS IN ON BEGINNING OF TIME
Association of Universities for Research in Astronomy (AURA)

Observations from Gemini Observatory identify a key fingerprint of an
extremely distant quasar, allowing astronomers to sample light emitted from
the dawn of time. Astronomers happened upon this deep glimpse into space
and time thanks to an unremarkable foreground galaxy acting as a
gravitational lens, which magnified the quasar's ancient light. The Gemini
observations provide critical pieces of the puzzle in confirming the object
as the brightest-appearing quasar so early in the history of the Universe,
raising hopes that more sources like it will be found. Before the cosmos
reached its billionth birthday, some of the very first cosmic light began
a long journey through the expanding Universe. One particular beam of
light, from a quasar, serendipitously passed near an intervening galaxy,
whose gravity bent and magnified the quasar's light and refocused it in our
direction, allowing telescopes like Gemini North to probe the quasar in
great detail. The Gemini observations provided key pieces of the puzzle by
filling a critical hole in the data. The Gemini North telescope on Mauna
Kea, Hawaii, utilized the Gemini Near-InfraRed Spectrograph (GNIRS) to
dissect a significant swath of the infrared part of the light's spectrum.
The Gemini data contained the tell-tale signature of magnesium which is
critical for determining how far back in time we are looking. The Gemini
observations also led to a determination of the mass of the black hole
powering the quasar. When astronomers combined the Gemini data with
observations from multiple observatories on Mauna Kea, the Hubble Space
Telescope, and other observatories around the world, they were able to paint
a complete picture of the quasar and the intervening galaxy. That picture
reveals that the quasar is located extremely far back in time and space --
shortly after what is known as the Epoch of Reionization -- when the very
first light emerged from the Big Bang. This is one of the first sources to
shine as the Universe emerged from the cosmic dark ages. Before then, no
stars, quasars, or galaxies had been formed, until objects like this
appeared like candles in the dark.

The foreground galaxy that enhances our view of the quasar is especially
dim, which is extremely fortuitous. If that galaxy were much brighter,
astronomers would not have been able to differentiate it from the quasar.
The intense brilliance of the quasar, known as J0439+1634, also suggests
that it is fuelled by a supermassive black hole at the heart of a young
forming galaxy. The broad appearance of the magnesium fingerprint captured
by Gemini also allowed astronomers to measure the mass of the quasar's
supermassive black hole at 700 million times that of the Sun. The
supermassive black hole is most likely surrounded by a sizeable flattened
disc of dust and gas. That torus of matter -- known as an accretion disc --
most likely continually spirals inward to feed the black hole powerhouse.
Observations at sub-millimetre wavelengths with the James Clerk Maxwell
Telescope on Mauna Kea suggest that the black hole is not only accreting gas
but may be triggering star birth at a prodigious rate -- which appears to be
up to 10,000 stars per year; for comparison, our Milky Way Galaxy makes one
star per year. However, because of the boosting effect of gravitational
lensing, the actual rate of star formation could be much lower. Quasars are
extremely energetic sources powered by huge black holes thought to have
resided in the very first galaxies to form in the Universe. Because of
their brightness and distance, quasars provide a unique glimpse into the
conditions in the early Universe. This quasar has a redshift of 6.51, which
translates to a distance of 12.8 billion light-years, and appears to
shine with a combined light of about 600 million million Suns, boosted by
the gravitational lensing magnification. The foreground galaxy which bent
the quasar's light is about half that distance away, at a mere 6 billion
light-years from us. The first follow-up spectroscopic observations,
conducted with the Multi-Mirror Telescope in Arizona, confirmed the object
as a high-redshift quasar. Subsequent observations with the Gemini North
and Keck I telescopes in Hawaii confirmed the MMT's finding, and led to
Gemini's detection of the crucial magnesium fingerprint -- the key to
nailing down the quasar's fantastic distance. However, the foreground
lensing galaxy and the quasar appear so close that it is impossible to
separate them with images taken from the ground owing to blurring by the
Earth's atmosphere. It took the Hubble Space Telescope to reveal that the
quasar image is split into three components by a faint lensing galaxy.
The quasar is ripe for future scrutiny. Astronomers also plan to use the
Atacama Large Millimetre/submillimetre Array, and eventually the James
Webb Space Telescope, to look within 150 light-years of the black hole and
directly detect the influence of the gravity from the black hole on gas
motion and star formation in its vicinity. Any future discoveries of very
distant quasars like J0439+1634 will continue to teach astronomers about the
chemical environment and the growth of massive black holes in the early
Universe.

Oh, so that's why I've had to reset the fonts in all my document templates.

Thank you, Microsh*t. 

Having fought it off as long as possible, the Oct update has finally landed on my W10 laptop.  The upgrade seems to have gone OK (I went out for the day and left it to it), but why does it have to reset all the fonts?  Very annoying! 

I bet that gave her the hump.

OSIRIS-REx CONFIRMS WATER ON ASTEROID
NASA
 
Early data from the Origins, Spectral Interpretation, Resource
Identification, Security-Regolith Explorer (OSIRIS-REx) mission revealed
water locked inside Bennu.  Data collected by the probe's two spectrometers,
OVIRS and OTES, revealed the presence of hydroxyls, molecules featuring
bonded oxygen and hydrogen atoms.  Scientists believe that those hydroxyl
groups exist across the asteroid in water-bearing clay minerals, suggesting
that, at some point, Bennu's rocky surface interacted with water.
OSIRIS-REx arrived at its asteroid target earlier this month.  Shortly after
its rendezvous, the probe's instruments began surveying the asteroid.  In
addition to studying the chemical composition of Bennu's surface, the
spacecraft's instruments are helping scientists map the asteroid's shape and
contours.  OSIRIS-REx's surveying efforts will continue for the next year.
Over the next several months, the probe will execute a series of fly-bys to
get a closer look at some of Bennu's features.  The spacecraft will swoop by
the asteroid's equator and poles.  Some of the approaches will put the probe
within 4.4 miles of the asteroid's surface.  With each fly-by, the maps of
Bennu will become more detailed.  Scientists will also use OSIRIS-REx's
observations to refine estimates of the asteroid's mass and spin rate.  The
new data will help scientists to understand better how asteroids form and
evolve.  Updated maps will also help OSIRIS-REx to perfect its orbit around
the asteroid, as well as to identify points of interest.  The data will also
help scientists choose where OSIRIS-REx will reach down with its robotic arm
and scoop up regolith -- rocks and dust -- from Bennu's surface.  The
earliest observations show that Bennu has a balanced mix of heavily
bouldered regions and relatively smooth areas.  The third New Frontiers
planetary science mission (following Juno and New Horizons), OSIRIS-REx is
expected to return to Earth with a collected specimen in 2023 September.

 
EVIDENCE FOR CARBON-RICH SURFACE ON CERES
Southwest Research Institute

Astronomers have concluded that the surface of dwarf planet Ceres is rich in
organic matter.  Data from the Dawn spacecraft indicate that Ceres's surface
may contain several times the concentration of carbon that is present in the
most carbon-rich primitive meteorites found on Earth.  Ceres is believed to
have originated about 4.6 billion years ago at the dawn of our Solar System.
Dawn data previously revealed the presence of water and other volatiles,
such as ammonium derived from ammonia, and now a high concentration of
carbon.  That chemistry suggests that Ceres formed in a cold environment,
perhaps outside the orbit of Jupiter.  An ensuing shake-up in the orbits of
the large planets would have pushed Ceres to its current location in the
main asteroid belt, between the orbits of Mars and Jupiter.  Geophysical,
compositional and collisional models based on Dawn data revealed that Ceres'
partially differentiated interior has been altered by fluid processes.
Dawn's Visible and Infrared Mapping Spectrometer has shown that the overall
low albedo of Ceres' surface is a combination of rock--water interaction
products such as phyllosilicates and carbonates and a significant amount of
spectrally neutral darkening agents, such as magnetite, an iron oxide.
Because Dawn's Gamma Ray and Neutron Detector limits magnetite to only
a few per cent by mass, the data point to the presence of an additional darkening
agent, probably amorphous carbon.  Interestingly, specific organic compounds
have also been detected near a 31-mile-wide impact crater named Ernutet,
giving further support to the notion of widespread presence of organics in
Ceres' shallow subsurface.  The new study also finds that 50-60 per cent of
Ceres' upper crust may have a composition similar to that of primitive
carbonaceous chondrite meteorites. That material is compatible with contam-
ination from infalling carbonaceous asteroids, a possibility supported by
Ceres' battered surface.


THE MYSTERY OF ULTIMA THULE
Spaceweather.com

When NASA's New Horizons spacecraft flew past Pluto three years ago, mission
scientists watching the first close-up images were shocked.  Despite being
stuck in the deep freeze of the Solar System 6 billion km from the Sun,
Pluto was not the frozen world that many expected it to be.  It was alive
with mountain ranges, windswept dunes, bladed terrain and much more.  In one
quick fly-by, New Horizons turned planetary science on its head.  New
Horizons is now less than 2 weeks away from a new world even less known than
Pluto.  Its name is 'Ultima Thule' (2014 MU69), which means means 'beyond
the borders of the known world'.  Indeed, the little space rock is
profoundly unknown.  Located almost a billion kilometres farther from the
Sun than Pluto, Ultima Thule has never been much more than a faint speck of
light in telescopes.  It inhabits the distant Kuiper Belt.  On New Year's
Eve and New Year's Day, New Horizons will swoop three times closer to Ultima
Thule than it flew past Pluto in July 2015, shattering previous records for
the most distant body explored by a spacecraft.  First images will be posted
on a web site set up by the New Horizons' team: SeeUltimaThuleNow.com . 

We already know one thing about Ultima Thule.  Its shape is elongated and
strange.  In 2017, astronomers watched a distant star pass behind Ultima
Thule.  Starlight winked in and out in a pattern suggesting two lobes with
diameters of 20 and 18 km, respectively.  Ultima Thule could be a small
binary system.  Ultima Thule is 100 times smaller than Pluto, but its
scientific value is incalculable.  From everything we know, it was formed
4.5 or 4.6 billion years ago, 4 billion miles from the Sun.  It has been
remained at that enormous distance from the Sun, at a temperature of nearly
absolute zero, ever since, so it probably represents the best sample of the
ancient solar nebula ever studied.


MOST-DISTANT SOLAR-SYSTEM OBJECT OBSERVED
Carnegie Institution for Science
 
A team of astronomers has discovered the most-distant body ever observed in
our Solar System.  It is the first known Solar-System object that has been
detected at a distance that is more than 100 times farther than the Earth is
from the Sun.  The new object has been given the provisional designation
2018 VG18.  2018 VG18, nicknamed 'Farout' by the discovery team for its
extremely distant location, is at about 120 astronomical units (AU).  The
second-most-distant observed Solar-System object is Eris, at about 96 AU.
Pluto is currently at about 34 AU, making 2018 VG18 more than three and a
half times more distant than the Solar System's most-famous dwarf planet.
2018 VG18 was discovered as part of the team's continuing search for
extremely distant Solar-System objects, including the suspected Planet X,
which is sometimes also called Planet 9.  In October, the same group of
researchers announced the discovery of another distant Solar-System object,
called 2015 TG387 and nicknamed 'The Goblin' because it was first seen near
Halloween.  The Goblin was discovered at about 80 AU and has an orbit that
is consistent with its being influenced by an unseen Super-Earth-sized
Planet X on the Solar System's very distant fringes.  The existence of a
ninth major planet at the fringes of the Solar System was first proposed by
that same research team in 2014 when they discovered 2012 VP113, nicknamed
Biden, which is currently near 84 AU.

2015 TG387 and 2012 VP113 never get close enough to the Solar System's giant
planets, like Neptune and Jupiter, to have significant gravitational
interactions with them.  That means that those extremely distant objects can
be probes of what is happening in the Solar System's outer reaches.  The
team does not know 2018 VG18's orbit very well yet, so it has not been able
to determine if it shows signs of being shaped by Planet X.  2018 VG18 is
much more distant and slower-moving than any other observed Solar-System
object, so it will take a few years to determine its orbit fully.  But it
was found in a similar location in the sky to the other known extreme Solar
System objects, suggesting that it might have the same type of orbit that
most of them do.  The orbital similarities shown by many of the known small,
distant Solar-System bodies was the catalyst for the original assertion that
there is a distant, massive planet at several hundred AU shepherding those
smaller objects.  All that we currently know about 2018 VG18 is its extreme
distance from the Sun, its approximate diameter, and its colour.  Because
2018 VG18 is so distant, it orbits very slowly, probably taking more than
1,000 years to take one trip around the Sun.  The discovery images of 2018
VG18 were taken by the Japanese Subaru 8-m telescope on Mauna Kea in
Hawaii on 2018 November 10.  Once 2018 VG18 was found, it needed to
be re-observed to confirm its very distant nature.  (It takes multiple nights
of observing to determine an object's distance.)  2018 VG18 was seen for
the second time in early December at the Magellan telescope at Las Campanas
Observatory in Chile.  The Magellan observations confirmed that 2018 VG18
is at around 120 AU, making it the first Solar-System object observed beyond
100 AU.  Its brightness suggests that it is about 500 km in diameter.  It has a
pinkish hue, a colour generally associated with ice-rich objects.


WHERE DID ALL THE NEPTUNES GO? 
Universite de Geneve

"But where did the hot Neptunes go?"  That is a question astronomers have
been asking for a long time, faced with the mysterious absence of planets
the size of Neptune very close to their stars.  A team of researchers has
just discovered that one such planet is losing its atmosphere at a frantic
pace.  That observation strengthens the theory that hot Neptunes have lost
much of their atmospheres and turned into smaller planets called
super-Earths, which are much more numerous.  Fishermen would be puzzled if
they netted only big and little fish, but few medium-sized fish.  That is
similar to what happens to astronomers hunting exoplanets.  They found a
large number of hot planets the size of Jupiter and numerous others a little
larger than the Earth (called super-Earths, whose diameters do not exceed
1.5 times that of the Earth), but no planets close to their star the size of
Neptune.  The mysterious 'desert' of hot Neptunes suggests two explanations:
either such worlds are rare, or that they were plentiful at one time, but
have since disappeared.  A few years ago, UNIGE astronomers using NASA's
Hubble Space Telescope discovered that a warm Neptune on the edge of the
desert, GJ 436b, was losing hydrogen from its atmosphere.  The loss is not
enough to threaten the atmosphere of GJ 436b, but suggested that Neptunes
receiving more energy from their star could evolve more dramatically.  That
has just been confirmed by the same astronomers, members of the national
research centre PlanetS.  They observed with Hubble that another warm
Neptune at the edge of the desert, named GJ 3470b, is losing its hydrogen
100 times faster than GJ 436b.  The two planets reside about 3.7 million
kilometres from their star, one-tenth the distance between Mercury and the
Sun, but the star hosting GJ 3470b is much younger and energetic.  The team
estimates that GJ 3470b has already lost more than a third of its mass.
Observing the evaporation of two warm Neptunes is encouraging, but team
members know that they need to study more of them to confirm their
predictions.  Unfortunately, the hydrogen that escapes from these planets
cannot be detected if they are more than 150 light-years from Earth
(GJ 3470b is 97 light-years away), because hydrogen is then hidden by
interstellar gas.  Researchers thus plan to use Hubble to look for other
traces of atmospheric escape, because hydrogen could drag upwards heavier
elements such as carbon.  The solution could also come from helium, whose
infrared radiation is not blocked by the interstellar medium.
 

DID SUPERNOVAE KILL OFF LARGE OCEAN ANIMALS?
University of Kansas
 
About 2.6 million years ago, an oddly bright light arrived in the pre-
historic sky and lingered there for weeks or months.  It was a supernova
some 150 light-years away.  Within a few hundred years, long after the
strange light in the sky had dwindled, a tsunami of cosmic energy from that
same shattering star explosion could have reached our planet and pummelled
the atmosphere, touching off climate change and triggering mass extinctions
of large ocean animals, including a shark species that was the size of a
school bus.  Recent papers revealing ancient seabed deposits of iron-60
isotopes provided the compelling evidence of the timing and distance of
supernovae.  Because iron-60 is radioactive, if it had formed with the Earth
it would be long gone by now.  So it had to have been rained down on us.
There is some debate about whether there was only one supernova really
nearby or a whole chain of them.  Studies of iron-60 residue reveal that
there is a huge spike 2.6 million years ago, but there is excess scattered
clear back 10 million years.  According to astronomers, other evidence for a
series of supernovae is found in the very architecture of the local
Universe.  We have the Local Bubble in the interstellar medium and we are
right on its edge.  It is a giant region about 300 light-years long.  It is
basically very hot, very low-density gas -- nearly all the gas clouds have
been swept out of it.  The best way to manufacture a bubble like that is a
number of supernovae that blow it bigger and bigger, and that seems to fit
well with idea of a chain.  Calculations are based on the idea that one
supernova that goes off, and its energy sweeps by Earth, and it's over. 
But with the Local Bubble, the cosmic rays bounce off the sides and the
cosmic-ray bath would last 10,000 to 100,000 years.  That way, one could
imagine a whole series of these things feeding more and more cosmic rays
into the Local Bubble and giving us cosmic rays for millions of years.

Whether or not there was one supernova or a series of them, the supernova
energy that spread layers of iron-60 all over the world also caused
penetrating particles called muons to shower the Earth, causing cancers and
mutations -- especially to larger animals.  The best description of a muon
would be a very heavy electron -- but muons are a couple of hundred times
more massive than electrons.  They are very penetrating.  Even normally,
there are lots of them passing through us.  Nearly all of them pass through
harmlessly, yet about one-fifth of our radiation dose comes by muons.  But
when the wave of cosmic rays hits, multiply those muons by a few hundred.
Only a small fraction of them will interact in any way, but when the number
is so large and their energy so high, you get increased mutations and cancer
-- those would be the main biological effects.  Scientists have estimated
that the cancer rate would go up about 50% for something the size of a human
-- and the bigger you are, the worse it is.  For an elephant or a whale, the
radiation dose is much larger.  A supernova 2.6 million years ago may be
related to a marine megafaunal extinction at the Pliocene-Pleistocene
boundary where 36 per cent of the genera were estimated to have become
extinct.  The extinction was concentrated in coastal waters, where larger
organisms would catch a greater radiation dose from the muons.  Indeed, one
of the extinctions that happened 2.6 million years ago was Megalodon, a
famously large and fierce marine animal inhabiting shallow waters.  Damage
from muons would extend down hundreds of metres into ocean waters, becoming
less severe at greater depths.  High-energy muons can reach deeper in the
oceans, being the more relevant agent of biological damage as depth
increases.


LARGE POPULATION OF YOUNG PLANETS 
University of Nevada, Las Vegas
 
Astronomers have catalogued nearly 4,000 exoplanets in orbit around distant
stars.  Though the discovery of those new-found worlds has taught us much,
there is still a great deal that we do not know about the birth of planets
and the precise cosmic recipes that spawn the wide array of planetary bodies
that we have already uncovered, including so-called hot Jupiters, massive
rocky worlds, icy dwarf planets, and -- hopefully some day soon -- distant
analogues of the Earth.  To help answer those and other intriguing
questions, a team of astronomers has conducted the first large-sample,
high-resolution survey of protoplanetary discs, the belts of dust and gas
around young stars.  Using the Atacama Large Millimetre/submillimetre Array
(ALMA) telescope, researchers have obtained high-resolution images of 20
nearby protoplanetary discs and given astronomers new insights into the
variety of features they contain and the speed with which planets can
emerge.  It appears that in other parts of our Milky Way there is
potentially a large population of young planets -- similar in mass to
Neptune or Jupiter -- in wide orbits, that are not detectable by other
current planet-searching techniques.  That implies that many extra-solar
systems may be similar to our Solar System in the sense that they also have
planets like Uranus and Neptune at the outer disc.

Understanding how the Earth was formed 4 billion years ago in our Solar
System is difficult because the Solar System finished the planet-formation
processes long ago.  On the other hand, we can observe young stars in other
parts of the Milky Way where young stars and young planets are currently
being assembled.  Since the young stars are far away from us, we need
powerful telescopes, like ALMA, to study those systems.  When stars are
young, they are surrounded by flat discs made of gas and dust.  Those discs,
called protoplanetary discs, are where young planets are born (that is also
why planetary orbits in the Solar System are coplanar, lying in a common
plane around our Sun).  It is very challenging, but, when we drop a pebble
into a pond, it will lead to ripples in the pond, which are more visible.
Similarly, when a young planet is present in its water pond (the proto-
planetary disc), it will excite waves too.  If the planet is massive enough,
the waves become a tsunami and cause damage to the disc, forming a gap along
the planet's orbit in the disc.  ALMA can detect tiny ripples and gaps in
protoplanetary discs.

 
FOSSIL FROM THE BIG BANG
W. M. Keck Observatory
 
A relic cloud of gas, orphaned after the Big Bang, has been discovered in
the distant Universe by astronomers using the world's most powerful optical
telescope, the W. M. Keck Observatory on Mauna Kea.  The discovery of such a
rare fossil offers new information about how the first galaxies in the
Universe formed.  Everywhere we look, the gas in the Universe is polluted by
waste heavy elements from exploding stars, but this particular cloud seems
pristine, unpolluted by stars even 1.5 billion years after the Big Bang.  If
it has any heavy elements at all, it must be less than 1/10,000th of the
proportion we see in the Sun.  That is extremely low; the most compelling
explanation is that it is a true relic of the Big Bang.  The team used two
of Keck Observatory's instruments -- the Echellette Spectrograph and Imager
(ESI) and the High-Resolution Echelle Spectrometer (HIRES) -- to observe the
spectrum of a quasar behind the gas cloud.  The quasar, which emits a bright
glow of material falling into a super-massive black hole, provides a light
source against which the spectral shadows of the hydrogen in the gas cloud
can be seen.  The team targeted quasars where previous researchers had only
seen shadows from hydrogen and not from heavy elements in lower-quality
spectra.  That allowed astronomers to discover such a rare fossil quickly
with the precious time on the Keck Observatory's twin telescopes.  The only
two other fossil clouds known were discovered in 2011.  The first two were
serendipitous discoveries but until now no one has discovered anything
similar -- they are clearly very rare and difficult to see.