Topic: Late August Astronomy Bulletin

[Clive]

COMET ISON TO PASS BY MARS
NASA

On October 1, Comet C/2012 S1 (ISON) will pass within 0.07 AU of
Mars, about six times closer than it will ever come to the Earth.
Mars rovers and satellites will get a close-up view.  It is uncertain
whether Curiosity will be able to see the comet from the surface of
Mars -- that depends on how much ISON brightens between now and then.
The Mars Reconnaissance Orbiter is equipped with a powerful half-metre
telescope named HiRISE that is more than capable of detecting the
comet's atmosphere and tail.  The Mars fly-by comes at a key time in
Comet ISON's journey.  It will just have crossed the 'frost line', a
place just outside the orbit of Mars where solar heating is enough to
start vaporizing frozen water.  The volatiles in a comet are 80% to
90% water ice and at present almost all the water is still frozen, and
the outgassing we see in ISON is driven by carbon dioxide and other
lesser constituents.  Probably only isolated patches of the comet's
nucleus are active.  When ISON crosses the frost line, the whole comet
could erupt in geysers of gas.  The amount of outgassing at Mars will
give researchers clues to the size of ISON's nucleus, which is hidden
from view deep within the comet's dusty atmosphere.  If ISON's nucleus
is much bigger than 0.5 km, it will probably survive its close
encounter with the Sun and might become one of the most spectacular
comets for many years.


EXOPLANET ORBITS STAR IN 8.5 HOURS
Massachusetts Institute of Technology

Researchers have discovered an Earth-sized exoplanet named Kepler 78b
that orbits its host star in a mere 8.5 hours -- one of the shortest
planetary orbital periods so far detected.  The planet is extremely
close to its star -- its orbital radius is only about three times the
radius of the star -- and its surface temperature may be as high as
3000 K; the outer layer of the planet is probably completely melted,
forming a massive, roiling ocean of lava.  What is most exciting to
the scientists is that they were able to detect light emitted by the
planet -- the first time that researchers have been able to do so for
an exoplanet as small as Kepler 78b.  That light, when observed with
larger telescopes, may give some information about the planet's
surface composition and reflective properties.  Kepler 78b is so close
to its star that scientists hope to measure its gravitational
influence on the star.  Such information would allow an estimate to be
made of the planet's mass, which could make Kepler 78b the first
Earth-sized planet outside our own Solar System whose mass would be
known.  The star around which Kepler 78b orbits is probably relatively
young, as it rotates more than twice as fast as the Sun -- an
indication that it has not had as much time to slow down.


A MAGNETAR AT THE HEART OF THE MILKY WAY
Max-Planck-Gesellschaft

Astronomers have discovered a magnetar -- a pulsar with an extremely
strong magnetic field -- at the centre of the Milky Way.  It enables
researchers to investigate the immediate vicinity of the black hole at
the heart of the Galaxy.  The team has been able to measure the
strength of the magnetic field around that central object (called
Sagittarius A*, or Sgr A* for short) and was able to show that the
field controls the inflow of mass into the black hole, also explaining
the X-ray emissions.  Pulsars are extremely precise cosmic clocks, and
the one now found to be orbiting the super-massive black hole at the
centre of the Milky Way should enable measurements to be made of the
properties of space and time around that object and comparisons to be
made with Einstein's theory of General Relativity.  Shortly after the
discoveries, first by the Swift telescope of a flaring X-ray source in
the direction of the Galactic centre, and then by the NuSTAR telescope
of pulsations with a period of 3.76 seconds, a radio follow-up
programme was started with the 100-m dish pf the Effelsberg radio
observatory in Germany.

The pulsar, called PSR J1745-2900 according to its position, belongs
to a sub-group called magnetars, which are pulsars with extremely high
magnetic fields, of the order of 10 to the power 14 times stronger
than the Earth's field.  The emission from such objects is known to be
highly polarized.  Measurements of the rotation, caused by an external
magnetic field, in the plane of polarization (the Faraday effect) can
be used to infer the strength of that field along the line of sight to
the pulsar.  The black hole at the centre of the Galaxy is gradually
swallowing material from its surroundings (mainly hot ionized gas).
The field strength in the gas has not been known until now, and is an
important parameter influencing the structure and dynamics of the
accretion flow, helping or even hindering the process.  The new pulsar
has allowed measurements of the strength of the field at the beginning
of the accretion flow onto the hole, indicating that there is indeed a
large-scale and strong field.  Understanding the accretion of gas
should help astronomers to understand more generally the properties of
Sgr A*.


FREE-FLOATING PLANETS MAY BE BORN FREE
Science Daily

It has been suggested that there is an enormous number of free-
floating planets (not attached to stars) in the Milky Way.  Until now
it has been supposed that they would have been ejected from normal
planetary systems.  But recent observations of dark cosmic clouds
suggest that some free-floating planets formed on their own.  A team
of astronomers from Sweden and Finland observed the Rosette Nebula, a
cloud of gas and dust 4600 light-years away in the constellation
Monoceros.  They collected observations at radio wavelengths with the
20-metre telescope at Onsala in Sweden, in sub-millimetre waves with
APEX in Chile, and in infrared light with the New Technology Telescope
(NTT) at La Silla in Chile.  The Rosette Nebula has more than a
hundred dark clouds known as globules.  By astronomical standards
they are small, with diameters less than 50 times the distance between
the Sun and Neptune.  Previously astronomers were able to estimate
that most of them are of planetary mass, less than 13 times Jupiter's
mass. Now there are much more reliable measures of mass and density
for many of the objects, and of their motion relative to their
environment.

The globules are dense and compact, and many of them have very dense
cores.  Many of them will collapse under their own gravity and form
free-floating planets.  The most massive of them can form brown
dwarfs, which are bodies with masses between those of planets and
stars.  The study shows that the clouds are moving outwards through
the Rosette Nebula at about 20 km/s.  It is thought that the clouds
have broken off the tall, dusty pillars of gas that were sculpted by
the intense radiation from young stars.  They have been accelerated
out from the centre of the nebula by radiation pressure from the hot
stars there.  During the history of the Milky Way, ever so many
nebulae like the Rosette have probably bloomed and faded away.  Each
would have had many globules, and any planets and brown dwarfs that
they formed must have been launched into the depths of the Milky Way.
There are so many of them that they could be a significant source of
the free-floating planets that have been discovered in recent years.


KEPLER TELESCOPE RETIRES FROM PLANET HUNTING
BBC NEWS

The Kepler space telescope has had to give up its prime planet-hunting
mission after engineers were unable to restore its pointing system.
The observatory lost the second of its four gyroscopes in May, and it
can no longer hold completely steady.  Kepler has so far confirmed 135
planets beyond our Solar System.  But it still has in its data base
more than 3,500 candidates that have yet to be fully investigated, and
the majority of them are expected to be confirmed as planets in due
course.

The 395m observatory was launched in 2009 March to try to find Earth-
sized planets orbiting their host stars in the so-called habitable
zone.  Kepler's method of detection has involved looking for the
minute dips in light, just fractions of a percent, as planets pass in
front of their stars.  The telescope has to be held absolutely still
during the observations -- something that needs a minimum of three
gyroscopes.  Kepler completed its prime mission last November, so it
has already worked beyond its minimum requirements.  But there is hope
that more science can be extracted from the spacecraft, with
suggestions that it be turned over to look for asteroids, comets and
exploding stars.  The US space agency, however, will have to decide
whether a lame Kepler merits further funding.  More planet-hunting
missions are in prospect in the coming years.  The European Space
Agency is to launch its Gaia observatory before the end of 2013.
Although its main goal is to map the positions of stars, it will do
that so precisely that it can be expected to discover thousands of
orbiting planets in the process.


NASA EULOGIZES SPITZER TELESCOPE -- 10 YEARS IN SPACE
NASA

Ten years after launch, the Spitzer space telescope, the last of the
four 'Great Space Observatories', warrants a celebration.  Spitzer's
infrared vision allowed it to see the far, cold and dusty parts of the
Universe.  Relatively close to home, the telescope observed Comet
Tempel 1, which was hit by the Deep Impact space craft in 2005.
Spitzer showed the composition of Tempel 1 to resemble that of solar
systems beyond our own.  It also surprised people by discovering the
largest of Saturn's rings.  That ring, a wispy band of ice and dust
particles, is very faint in visible light, but Spitzer's infrared
detectors were able to pick up the glow from its heat.  Spitzer was
the first telescope to detect light coming from a planet outside our
Solar System, a use that was not in the mission's original design.
With Spitzer's ongoing observations of such planets, astronomers have
been able to begin the study of exoplanet atmospheres.  Other
accomplishments of the mission include a census of forming stars in
nearby clouds, an improved map of the Milky Way's spiral-arm
structure, and, with Hubble, finding that the most distant galaxies
are more massive and mature than expected.

Spitzer, originally called the Space Infrared Telescope Facility, was
renamed after its launch (NASA having learnt from the initial Hubble
fiasco that it was tactless to attach people's names to spacecraft
until they had been successfully launched and proved properly
operational!) in honour of the late astronomer Lyman Spitzer.  Among
the first advocates of space telescopes, he began campaigning for them
as early as the 1940s.  His efforts also led to the development and
deployment of the Hubble telescope.  In anticipation of the Hubble
launch, NASA set up the 'Great Observatories' programme, four space
telescopes designed to cover a range of wavelengths: Hubble, Spitzer,
the Chandra X-ray observatory and the now-defunct Compton gamma-ray
observatory.  Spitzer ran out of the coolant needed for its longer-
wavelength instruments in 2009, and has not been so powerful since
then.