Topic: Mid February Astronomy bulletin

[Clive]

METEORITE MAY REPRESENT BULK OF MARS' CRUST
Brown University

NWA 7034, a meteorite found a few years ago in the Moroccan desert, is
like no other rock ever found on Earth.  It has been shown to be a
4.4-billion-year-old piece of the crust of Mars and, according to a
new analysis, rocks just like it may cover vast swaths of Mars.  In a
new paper, scientists report that spectroscopic measurements of the
meteorite are a spot-on match with measurements from orbit of the
Martian dark plains, areas where the planet's coating of red dust is
thin and the rocks beneath are exposed.  The findings suggest that the
meteorite is representative of the 'bulk background' of rocks on the
Martian surface.  When scientists started analyzing the meteorite in
2011, they knew that they had something special.  Its chemical make-up
confirmed that it came from Mars, but it was unlike any other Martian
meteorite.  Previously, all the Martian rocks found on Earth were
classified as SNC meteorites (shergottites, nakhlites, or
chassignites).  They are mainly igneous rocks made of cooled volcanic
material, but the new object is a breccia, a mash-up of different rock
types welded together in a basaltic matrix.  It contains sedimentary
components that match the chemical make-up of rocks analyzed by the
Mars rovers.  Scientists concluded that it is a piece of Martian crust
-- the first such sample to be found on the Earth.

Scientists thought it might help to clear up a long-standing enigma:
spectra obtained from SNC meteorites never quite match remotely-sensed
spectra from the Martian surface.  So after acquiring a chip of the
meteorite, they used a variety of spectroscopic techniques to analyze
it.  The researchers say that the spectral match suggests that the
'dark plains' on Mars are dominated by brecciated rocks similar to the
new meteorite.  Because the dark plains are dust-poor regions, they
are thought to be representative of what lies beneath the red dust on
much of the rest of the planet.  The researchers claim that, in the
light of what is known about Mars, the idea that the surface would be
rich in such breccias makes sense.  Mars has more than 400,000 impact
craters more than 1 km in diameter.  Because brecciation is a natural
consequence of impacts, it is to be expected that material similar to
NWA 7034 has accumulated on Mars over time.  In other words, many of
the rocks on the surface of Mars are probably very similar to the
meteorite.


MERGING STARS DESTINED TO BECOME SUPERNOVA
ESO

Astronomers observing the planetary nebula Henize 2-428 have
identified a close pair of white-dwarf stars -- tiny, extremely dense
stellar remnants -- that have a total mass of about 1.8 times that of
the Sun.  It is the most massive such pair yet found, and when the two
stars merge, as they seem destined to do about 700 million years from
now, they will create a runaway thermonuclear explosion leading to a
Type Ia supernova.  The team that found the massive pair actually set
out with a different interest.  They wanted to find out how some stars
produce strangely shaped and asymmetric nebulae late in their careers.
One of the objects they studied was the unusual planetary nebula known
as Henize 2-428.  The team looked at the object's central star with
the Very Large Telescope, and found not just one but a pair of stars
at the heart of that strangely lopsided glowing cloud.  Further
observations, made with telescopes in the Canary Islands, allowed them
to determine the orbit of the two stars and to deduce their masses and
their separation.  They found that each of the stars has a mass
slightly less than that of the Sun and that they orbit one another
every four hours.  They are so close together that, according to
Einstein's theory of general relativity, they will get closer and
closer, spiralling in owing to loss of energy through the emission of
gravitational waves, before eventually merging into a single star that
will promptly explode.


NEARBY SUPERNOVA REMNANT HAS FROTHY INTERIOR
Harvard-Smithsonian Center for Astrophysics

Cassiopeia A, or Cas A for short, is one of the best-studied supernova
remnants in the Galaxy, but we do not know everything about it yet.
Astronomers have generated a new 3-D map of its interior.  They found
that the remnant includes a collection of about half a dozen great
cavities.  About 340 years ago a massive star exploded in the
constellation Cassiopeia.  As it blew itself apart, extremely hot and
radioactive matter rapidly streamed outward from the star's core,
mixing and churning debris.  The complex physics behind such
explosions is difficult to model.  However, by studying relatively
young supernova remnants like Cas A, astronomers can try to
investigate the processes that drive such titanic stellar explosions.

To make the 3-D map, astronomers examined Cas A in near-infrared
wavelengths with the Mayall 4-m telescope at Kitt Peak.  Spectroscopy
allowed them to measure expansion velocities of extremely faint
material in Cas A's interior, which provided the crucial third
dimension.  They found that the large interior cavities appear to be
connected to -- and nicely explain -- the previously observed large
rings of debris that make up the bright and easily seen outer shell of
Cas A.  The two best-defined cavities are 3 and 6 light-years in
diameter, and the entire arrangement has a structure like a Swiss
cheese.  The bubble-like cavities were probably created by plumes of
radioactive nickel generated during the stellar explosion.  Since the
nickel will decay to form iron, the astronomers think that Cas A's
interior cavities should be enriched with as much as a tenth of a
solar mass of iron.  Such enriched interior debris has not been
detected by previous observations, however, so next-generation
telescopes may be used to look for the 'missing' iron and confirm the
origin of the cavities.


NEW DETAILS IN WHIRLPOOL GALAXY
Case Western Reserve University

Astronomers have discovered new features of a galaxy that has been
sketched and photographed for 170 years.  The researchers were able to
see faint plumes extending from the northeast and south of the nearby
spiral galaxy M51a, also called the 'Whirlpool Galaxy', by taking a
20-hour-exposure photograph.  The image also provides new details of
the linear northwest plume, which is nearly 120,000 light-years long,
and reveals a lack of stars in a portion of the southeast tail.  M51a
was the first galaxy whose spiral structure was recognized, when it
was identified and sketched by William Parsons, the Earl of Rosse, in
1845.  The whirlpool and its small companion, M51b, are about 31
million light years away, in the constellation of Canes Venatici.  The
images were taken from the Burrell Schmidt telescope at Kitt Peak in
2010 and 2012.  The team aimed the telescope at M51 on moonless nights
and exposed its digital camera to the light from the galaxy at
20-minute intervals, recalibrating in between.  For a total of 10
hours, light was filtered to reveal younger stars; for another 10
hours it was filtered to reveal older stars.  The two exposures were
merged to create the final image.

The northwest plume was seen in the 1970s, but the technology provided
limited detail.  The astronomers found that it is dominated by older,
redder stars and has little gas, found in small patches.  Owing to the
age of the stars and the extreme length of the plume, they suggest
that the plume was created by the interaction of an outer disc of M51
with another galaxy 200 million years or more ago.  The southern plume
is an oddity.  It has no morphological similarities to the surrounding
parts of M51, and no gas.  The plume has comparatively few stars and,
therefore, mass, and little total light.  One possibility, the
researchers suggest, is that the plume could be the remnant of a third
satellite or body in the M51 system.  The northeast plume has about
the same total light as the southern one and may be an extension of
the north side of the galaxy, but that is impossible to tell.  Other
researchers discovered the southeastern gas tail in 1990 and assumed
that it was pulled out during an interaction with another galaxy.
The new, deeper view still found no stars.  That is unusual for such a
tail, but it provides a clear test for future interaction models.  The
astronomers are now devising other ways to look at M51, particularly
to gather more detail about the faint plumes.  The northwest plume is
bright enough that it may be a good candidate for further study with
the Hubble telescope.


STARS ARE YOUNGER THAN PREVIOUSLY THOUGHT
Sissa Medialab

The latest data release from the Planck satellite consortium reveals
a surprise: star formation in the Universe may be more recent than
previously indicated by the analysis of Planck's predecessor, the WMAP
satellite.  Thanks to new maps of cosmic background radiation (in
particular, those containing 'polarization anisotropies' of radiation)
scientists have found that the 're-ionization' process could be more
recent than was estimated until now.  Re-ionization is one of the most
important processes in cosmology, as it is associated with star
formation, which cosmologists date back to after the 'dark ages' of
the Universe, when there was still no star light. The WMAP satellite,
launched in 2001, had given an initial estimate of the period when the
process may have taken place.  The discovery, which still requires
validation by the measurements that Planck is still able to provide
and that will be published in about a year's time, is associated with
the publication of maps of polarized cosmic background radiation (the
first light in the Universe produced by the Big Bang).  WMAP was the
first satellite to attempt to provide such a map, but today new Planck
data suggest that re-ionization may have occurred approximately 550
million years after the Big Bang, i.e., 100 million years later than
WMAP had estimated.  According to Planck's observations, stars may be
younger than believed, in keeping with other independent astrophysical
indicators, and that finding may have major consequences for our
attempts to understand the dark components of the Universe.


GRAVITATIONAL WAVES AND COSMIC INFLATION REMAIN ELUSIVE
NASA/Jet Propulsion Laboratory

A joint analysis of data from the Planck space mission and the ground-
based experiment BICEP2 has found no conclusive evidence of gravita-
tional waves from the birth of the Universe, despite earlier reports
of a possible detection.  The collaboration between the teams has
resulted in the most precise knowledge yet of what signals from the
ancient gravitational waves should look like, aiding future searches.
Planck and BICEP/Keck [Keck, in this item, does not refer to the large
telescopes in Hawaii, but to an array of small telescopes set up at
the South Pole. - ED] were both designed to measure relic radiation
emitted by the Universe shortly after its birth 13.8 billion years
ago.  An extraordinary source of information about the Universe's
history lies in that 'fossil' radiation, called the cosmic microwave
background (CMB).  Planck mapped the CMB over the entire sky from
space, while BICEP/Keck focused on one patch of sky over the South
Pole.  In 2014 March, astronomers presented intriguing data from the
BICEP2/Keck experiments, finding what appeared to be a possible signal
from the Universe when it was just born.  If the signal were indeed
from the early cosmos, then it would have confirmed the presence of
ancient gravitational waves.  It is hypothesized that those waves were
generated by an explosive and very rapid period of growth in the
Universe, called inflation, which took place when the Universe was
only a tiny of a fraction of a second old.  Specifically, the
BICEP/Keck experiments found evidence for a 'curly' pattern of
polarized light called B-modes.  Those patterns would have been
imprinted on the CMB light as the gravitational waves slightly
squeezed and stretched the fabric of space.  Polarization describes a
particular property of light.  Usually, the electric and magnetic
fields carried by light vibrate in all orientations equally, but when
they vibrate preferentially in a certain direction, the light is
polarized.

The swirly polarization pattern, reported by BICEP2, was also clearly
seen with new data from the Keck Array.  Searching for that unique
record of the very early Universe is as difficult as it is exciting,
since its subtle signal is hidden in the polarization of the CMB,
which itself represents only a feeble few per cent of the total light.
One of the trickiest aspects of identifying the primordial B-modes is
separating them from those that can be generated much closer to us by
interstellar dust in our Milky Way galaxy.  The Milky Way is pervaded
by a mixture of gas and dust shining at frequencies similar to those
of the CMB, and that closer, or foreground, emission affects the
observation of the oldest cosmic light.  Very careful data analysis is
needed to separate the foreground emission from that of the CMB.  The
BICEP2/Keck experiments collected data at a single microwave
frequency, making it difficult to separate the emissions coming from
the dust in the Milky Way and the CMB.  On the other hand, seven of
the Planck channels were also equipped with polarization-sensitive
detectors.  Some of those frequencies were chosen to make measurements
of dust in the Milky Way.  By careful analysis, those multi-frequency
data can be used to separate the various contributions of emissions.
The Planck and BICEP2/Keck teams joined forces, combining the space
satellite's ability to deal with foregrounds by means of observations
at several frequencies, with the greater sensitivity of the ground-
based experiments over limited areas of the sky.

The final results showed that most of the original BICEP2/Keck B-mode
signal, but not necessarily all of it, could be explained by dust in
the Milky Way.  As for signs of the Universe's inflationary period,
the question remains open.  The joint Planck/BICEP/Keck study sets an
upper limit on the amount of gravitational waves from inflation, which
might have been generated at the time but at a level too low to be
confirmed by the present analysis.  The new upper limit on the signal
due to gravitational waves agrees well with the upper limit obtained
earlier with Planck from the temperature fluctuations of the CMB. But
the gravitational-wave signal could still be there, and the search has
definitely not been abandoned.


UK 'TWINKLE' SATELLITE TO UNVEIL EXOPLANET ATMOSPHERES
RAS

UK scientists have announced plans for a small satellite, named
'Twinkle', that should give radical new insights into the chemistry,
formation and evolution of planets orbiting other stars.  The mission
should be launched within four years.  Nearly two thousand exo-planets
(orbiting stars other than the Sun) have been discovered to date, but
we know very little about them.  We can measure their mass, density
and distance from their star.  From that, we can deduce that that some
are freezing cold, some are so hot that they have molten surfaces,
some are balls of gas, like Jupiter, or small and rocky, like the
Earth.  When an exo-planet passes in front of the star that it orbits,
a tiny amount of starlight is filtered through the molecules and
clouds in the planet's atmosphere, if it has one.  Twinkle will
observe that light to see if it shows the characteristic spectral
signatures of gases such as water vapour or methane that might
be present on the planet.  Knowledge of the chemical composition of
exo-planet atmospheres is important for understanding whether a planet
was born in the orbit in which it is currently observed or whether it
has migrated from a different part of its planetary system.  The
make-up, evolution, chemistry and physical processes driving an
exo-planet's atmosphere are strongly affected by its distance from its
parent star.  The atmospheres of small, terrestrial-type planets may
have evolved quite dramatically from their initial composition.  The
loss of lighter molecules, impacts with other bodies such as comets or
asteroids, volcanic activity, or even life can significantly alter the
composition of primordial atmospheres.  Atmospheric composition is
therefore a tracer of an exo-planet's history as well as whether it
might be 'habitable'.

Twinkle will analyze at least 100 exo-planets in the Milky Way.  Its
infrared spectrograph will enable observations to be made of a wide
range of planet types including super-Earths (rocky planets 1-10 times
the mass of the Earth) and 'hot Jupiters' (gas giants orbiting very
close to their stars).  Some of the target planets are orbiting stars
similar to our Sun and some are orbiting cooler red dwarfs.  For the
largest planets orbiting bright stars, Twinkle is expected even to be
able to produce maps of clouds and temperature.  The spacecraft will
be built to operate for a minimum of three years, with the possibility
of an extension to five years or more. The mission will be funded
through a mixture of private and public sources.  With a total cost of
around £50 million, including launch, Twinkle is reckoned to be 10
times less expensive to build and operate than other astrophysical
spacecraft developed through international space-agency programmes.
The relatively moderate development time-scale and budget are made
possible through expertise already developed at UK institutions and
the use of off-the-shelf components.