Topic: Early January Astronomy Bulletin

[Clive]

DETECTION OF BORON ON MARS
Los Alamos National Laboratory

Data from NASA's Curiosity rover reveal that boron has been identified
for the first time on the surface of Mars, indicating that groundwater
offering the potential for long-term habitability existed on Mars in
the distant past.  If the boron that was found in calcium-sulphate
mineral veins on Mars is analogous to what we see on Earth, it would
indicate that the groundwater of ancient Mars that formed the veins
would have been at 0 to 60 degrees Celsius and neutral-to-alkaline pH. 
The temperature, pH, and dissolved mineral content of the groundwater
could make it habitable.  The boron was identified by the rover's
laser-shooting 'Chemistry and Camera' ('Chem Cam') instrument.  Boron
is associated on Earth with arid sites where much water has evaporated
away.  However, the environmental implications of the boron found by
Curiosity are still open to debate.  Scientists are considering at
least two possibilities for the source of the boron that ground water
left in the veins.  It could be that the drying out of part of Gale
lake resulted in a boron-containing deposit in an overlying layer, not
yet reached by Curiosity.  Some of the material from that layer could
later have been carried by groundwater down into fractures in the
rocks.  Or perhaps changes in the chemistry of clay-bearing deposits
and groundwater affected how boron was picked up and dropped off
within the local sediments.

The discovery of boron is only one of several recent findings related
to the composition of Martian rocks.  Curiosity is climbing a layered
Martian mountain and finding rock-composition evidence of how ancient
lakes and wet underground environments changed, thousands of millions
of years ago, in ways that affected their favourability for microbial
life.  As the rover has progressed uphill, compositions trend toward
more clay and more boron.  Those and other variations can tell us
about conditions under which sediments were initially deposited and
about how later groundwater moving through the accumulated layers
altered and transported ingredients.  Groundwater and chemicals
dissolved in it that appeared later on Mars left their effects most
clearly in mineral veins that filled cracks in older layered rock.
But they also affected the composition of the rock matrix surrounding
the veins, and the fluid was in turn affected by the rock.  Whether
life has ever existed on Mars is still unknown.  No compelling
evidence for it has been found.  When Curiosity landed in Mars' Gale
Crater in 2012 the mission's main goal was to determine whether the
area ever offered an environment favourable for microbes.  Four recent
drilling sites, from 'Oudam' this past June to 'Sebina' in October,
are spaced about 25 metres apart in elevation.  Their uphill pattern
allows the scientific team to sample progressively younger layers that
reveal Mount Sharp's ancient environmental history.  Variations in
those minerals and elements indicate a dynamic system.  They interact
with groundwater as well as surface water.  The water influences the
chemistry of the clays, but the composition of the water also changes.
We are seeing chemical complexity indicating a long, interactive
history with the water.  The more complicated the chemistry is, the
better it is for habitability.  The boron and clay underline the
mobility of elements and electrons, and that is good for life.
 

WHERE IS THE ICE ON CERES?
NASA

At first glance, Ceres, the largest body in the main asteroid belt,
does not look icy.  Images from the Dawn spacecraft have revealed a
dark, heavily cratered world whose brightest area is made of highly
reflective salts -- not ice.  But newly published studies from Dawn
scientists show two distinct lines of evidence for ice at or near the
surface.  Those studies support the idea that ice separated from rock
early in Ceres' history, forming an ice-rich crustal layer, and that
ice has remained near the surface over the history of the Solar
System.  Water ice on other planetary bodies is important because it
is an essential ingredient for life as we know it.  By finding bodies
that were water-rich in the distant past, we may discover clues as to
where life may have existed in the early Solar System.  Ceres'
uppermost surface is rich in hydrogen, with higher concentrations at
mid-to-high latitudes -- consistent with broad expanses of water ice.
On Ceres, ice is not just localized to a few craters.  It is every-
where, and nearer to the surface at higher latitudes.  Researchers
used the GRaND instrument to determine the concentrations of hydrogen,
iron and potassium in the uppermost metre of Ceres.  GRaND measures
the number and energy of gamma rays and neutrons emanating from Ceres.
Neutrons are produced as Galactic cosmic rays interact with Ceres'
surface.  Some neutrons get absorbed into the surface, while others
escape.  Since hydrogen slows down neutrons, it is associated with
fewer neutrons escaping.  On Ceres, hydrogen is likely to be in the
form of frozen water.

Researchers found that, rather than a solid ice layer, there is likely
to be a porous mixture of rocky materials in which ice fills the pores.
The GRaND data show that the mixture is about 10% ice by weight.  That
result confirms predictions made nearly 30 years ago that ice can
survive for thousands of millions of years just beneath the surface of
Ceres.  The evidence strengthens the case for the presence of near-
surface ice on other main-belt asteroids.  Ceres' brightest area, in
the northern-hemisphere crater Occator, does not shine because of ice,
but rather because of highly reflective salts.  Occator's central
bright region, which includes a dome with fractures, has recently been
named Cerealia Facula.  The crater's cluster of less-reflective spots
to the east of the centre is called Vinalia Faculae.

Dawn began its 'extended mission' phase last July, and is currently in
an elliptical orbit more than 7,200 km from Ceres.  During the primary
mission, Dawn orbited and accomplished all of its original objectives
at Ceres and at the proto-planet Vesta, which the spacecraft visited
from 2011 July to 2012 September.


MOST OUTER PLANETS HAVE NEPTUNE MASS
NASA/Goddard Space Flight Center

A new statistical study of planets found by a technique called
gravitational microlensing suggests that Neptune-mass worlds are
likely to be the most common type of planet to form in the icy outer
realms of planetary systems.  The study provides the first indication
of the types of planets waiting to be found far from their host stars,
where scientists suspect planets form most efficiently.  Gravitational
microlensing occurs through the light-bending effects, predicted by
Einstein's general theory of relativity, of massive objects.  It occurs
when a foreground star, the lens, randomly aligns with a distant
background star, the source, as seen fromthe Earth.  As the lensing
star drifts along in its orbit around the galaxy, the alignment shifts
over days to weeks, changing the apparent brightness of the source.
The precise pattern of the changes offers clues about the nature of
the lensing star, including any planets it may host.  More than 50
exoplanets have been discovered through microlensing, compared to
thousands detected by other techniques, such as detecting the motion
or dimming of a host star caused by the presence of planets.  Because
the necessary alignments between stars are rare and occur randomly,
astronomers must monitor millions of stars for the tell-tale bright-
ness changes that signal a microlensing event.  However, microlensing
holds great potential.  It can detect planets hundreds of times more
distant than most other methods, allowing astronomers to investigate a
broad swath of our Milky Way galaxy.  The technique can locate exo-
planets of smaller masses and at greater distances from their host
stars, and it is sensitive enough to find planets floating through
the Galaxy on their own, not bound to stars.

The Kepler and K2 missions have been extraordinarily successful in
finding planets that dim their host stars, with more than 2,500
confirmed discoveries to date.  That technique is sensitive to
close-in planets but not to distant ones.  Microlensing surveys are
complementary, best probing the outer parts of planetary systems with
less sensitivity to planets closer to their stars.  Combining micro-
lensing with other techniques provides us with a clearer overall
picture of the planetary content of our Galaxy.  From 2007 to 2012,
the Microlensing Observations in Astrophysics (MOA) group, a
collaboration between researchers in Japan and New Zealand, issued
3,300 alerts informing the astronomical community about ongoing
microlensing events.  The team identified 1,474 well-observed
microlensing events, with 22 displaying clear planetary signals.
They include four planets that were never previously reported.  To
study the events in greater detail, the team included data from the
other major microlensing project operating over the same period, the
Optical Gravitational Lensing Experiment (OGLE), as well as additional
observations from other projects designed to follow up on MOA and OGLE
alerts.  From that information, the researchers determined the
frequency of planets as a function of the mass ratio of the planet and
star and the distance between them.  For a typical planet-hosting star
with about 60% of the Sun's mass, the typical microlensing planet has
between 10 and 40 times the Earth's mass.  For comparison, Neptune in
our own Solar System has a mass equivalent to 17 Earths.  The results
imply that cold Neptune-mass worlds are likely to be the most common
types of planets beyond the so-called snow line, the point where water
remained frozen during planetary formation.  In the Solar System, the
snow line is thought to have been located at about 2.7 times the
Earth's mean distance from the Sun, placing it in the middle of the
main asteroid belt today.


BIRTHPLACES OF MOST CURRENT STARS
National Radio Astronomy Observatory

Astronomers have used the Very Large Array (VLA) and the Atacama Large
Millimetre Array (ALMA) to look at distant galaxies seen as they were
some 10 thousand million years ago.  At that time, the Universe was
experiencing its peak rate of star formation.  Most stars in the
present Universe were born then.  We knew that galaxies in that era
were forming stars prolifically, but we did not know what those
galaxies looked like, because they were shrouded in so much dust that
almost no visible light escaped them.  Radio waves, unlike visible
light, can get through the dust.  However, in order to reveal the
details of such distant -- and faint -- galaxies, the astronomers had
to use the most sensitive radio telescopes.  The new observations,
from the VLA and ALMA, have answered long-standing questions about the
mechanisms that were responsible for the bulk of star formation in
those galaxies.  They found that intense star formation most
frequently occurred throughout the galaxies, whereas in present-day
galaxies with similar high star-formation rates it tends to occur in
much smaller regions.  The astronomers used the VLA and ALMA to study
galaxies in the Hubble Ultra-Deep Field, a small area of sky observed
since 2003 with the Hubble Space Telescope (HST).  The HST made very
long exposures of the area to detect galaxies in the far-distant
Universe, and numerous observing programmes with other telescopes have
followed up on the HST work.  The VLA showed where star formation was
occurring, and ALMA revealed the cold gas that is the fuel for star
formation.


SUPERCLUSTER OF GALAXIES NEAR MILKY WAY
Australian National University

Astronomers have found one of the Universe's biggest superclusters of
galaxies near the Milky Way.  The Vela supercluster, which had
previously gone undetected because it was hidden by stars and dust in
the Milky Way, is a huge mass that influenced the motion of our
Galaxy.  It is one of the biggest concentrations of galaxies in the
Universe -- possibly the biggest in the neighbourhood of our Galaxy,
but that will need to be confirmed by further study.  The gravity of
the Vela supercluster may explain the difference between the measured
motion of the Milky Way through space and the motion predicted from
the distribution of previously mapped galaxies.  The team used the
Anglo-Australian Telescope to measure distances for many galaxies to
confirm earlier suggestions that Vela is a supercluster.  It also
helped to estimate the supercluster's effect on the motion of the
Milky Way.  The research involved astronomers based in South Africa,
Australia and Europe.  Two new Australian surveys starting in 2017
will assess the size of the Vela supercluster.  The Taipan optical
survey will measure galaxy distances over a bigger area around Vela,
while the WALLABY radio survey will be able to see through the densest
parts of the Milky Way into the supercluster's heart.


LARGEST DIGITAL SURVEY OF VISIBLE UNIVERSE 
Queen's University Belfast

The largest-ever digital survey of the visible Universe, mapping
billions of stars and galaxies, has been publicly released.
The data have been made available by the international Pan-STARRS
project, which includes scientists from Queen's University Belfast,
who have claimed that it will lead to new discoveries about the
Universe.  Astronomers and cosmologists used a 1.8-m telescope at the
summit of Haleakala, on Maui, Hawaii, to image three-quarters of the
visible sky repeatedly over four years.  The Pan-STARRS1 Surveys
include 3 billion separate sources, including stars, galaxies, and
other objects, and are represented by two petabytes of computer data.
Pan-STARRS is hosted by the University of Hawaii Institute for
Astronomy, which is releasing the data alongside the Space Telescope
Science Institute in Baltimore.  The international collaboration also
includes Queen's University Belfast and the Universities of Durham and
Edinburgh, and is supported by NASA and the NSF.  The project has
found nearby asteroids in our Solar System, and also the most luminous
distant explosions in the Universe.  Pan-STARRS has already made
discoveries from Near Earth Objects and Kuiper-Belt objects in the
Solar System to lonely planets between the stars; it has mapped the
dust in three dimensions in our Galaxy and found new streams of stars;
and it has found new kinds of exploding stars and distant quasars in
the early Universe.  The roll-out of the survey data is being done in
two steps.  The current release is the 'Static Sky' which provides an
average value for the position, brightness and colour for objects seen
in the sky at individual moments in time.  In 2017, a second set of
data will be released including catalogues and images from each of the
individual snapshots that Pan-STARRS took of a given region of sky.
The data from the Pan-STARRS1 surveys will be available online at
panstarrs.stsci.edu  .