Topic: Late December Astronomy Bulletin

[Clive]

A CHRISTMAS COMET?
By Jonathan Shanklin, SPA Comet Section Director

There is a chance that Christmas will bring with it a binocular comet
that could even become visible to the naked eye in the evening sky.
Terry Lovejoy, from Queensland, Australia, discovered comet 2014 Q2 on
August 16 with a CCD camera on his 0.2-m Schmidt-Cassegrain. Initially
of 15th magnitude, the comet has brightened quite rapidly on its way
to perihelion at 1.3 AU at the end of January. Currently visible from
the Southern Hemisphere as a 7th-magnitude object, it is moving
northwards and may become visible low down in the south just before
midnight on Christmas Eve. It continues to move northwards, and by
early January the comet will be visible in the early evening. It
should be at its brightest in mid-January and could remain visible in
binoculars until well into March. It is unlikely to show much of a
tail, but one of a degree or so in length might be seen with
binoculars. Interesting observing opportunities include the early
hours of December 29 when the comet is very close to M79, mid-January
when it is close to the Pleiades, and February 2 when it passes
between M 34 and NGC 752. There is a finding chart on the SPA web
pages. Making a sketch is a good way to train the eye to see faint
features in astronomical objects, and those of a diffuse comet tail
are often particularly subtle. Spend some time getting fully
dark-adapted, then try looking a little bit away from the comet, but
keeping it in your field of view. That technique of 'averted vision'
sometimes allows you to see faint objects that cannot be seen when
looked at directly. Do send me your observations, which could include
magnitude estimates, drawings, written descriptions or images.


BARRAGE OF SMALL IMPACTS ERASED THE EARTH'S PRIMORDIAL ATMOSPHERE
Massachusetts Institute of Technology

Today's atmosphere may bear little trace of its primordial self.
Geochemical evidence suggests that Earth's atmosphere may have been
completely obliterated at least twice since its formation more than
4 billion years ago. However, it is not known what could have driven
such dramatic losses. Now researchers have suggested that a relent-
less blitz of small space rocks, or planetesimals, may have bombarded
the Earth about the time that the Moon was formed, kicking up clouds
of gas with enough force permanently to eject small portions of the
atmosphere into space. Tens of thousands of such small impacts could
jettison the Earth's entire primordial atmosphere. Such impacts may
also have blasted other planets, and even peeled away the atmospheres
of Venus and Mars. In fact, the researchers found that small planet-
esimals may be much more effective than giant impactors in driving
atmospheric loss. According to their calculations, it would take a
giant impact -- almost as massive as the Earth slamming into itself --
to disperse most of the atmosphere. But taken together, many small
impacts would have the same effect, with a tiny fraction of the mass.
Understanding the drivers of the Earth's ancient atmosphere may help
scientists to identify the conditions that encouraged life to form.
The new finding sets a very different initial state for the early
Earth's atmosphere and a new starting point for trying to understand
what was the composition of the atmosphere, and what were the
conditions for developing life.


WATER VAPOUR ON ROSETTA'S COMET SIGNIFICANTLY DIFFERENT
ESA

The measurements were made in the month following the spacecraft's
arrival at Comet 67P/Churyumov-Gerasimenko on August 6. It is one of
the most anticipated early results of the mission, because the origin
of the Earth's water is still an open question. One of the leading
hypotheses on the Earth's formation is that it was so hot when it
formed 4.6 billion years ago that any original water content should
have boiled off. But, today, two-thirds of the surface is covered in
water -- where did it come from? In this picture, it must have been
delivered after the Earth had cooled down, most likely from comets and
asteroids. The relative contribution of each class of object is,
however, still debated. The key to determining where the water
originated is in the proportion of deuterium -- a form of hydrogen
with an additional neutron -- to normal hydrogen. That proportion is
an important indicator of the formation and early evolution of the
Solar System, with theoretical simulations showing that it should
change with distance from the Sun and with time in the first few
million years. One key goal is to compare the value for different
kinds of object with that measured on the Earth, in order to estimate
how much each type of object may have contributed.

Comets in particular retain evidence of the early Solar System: they
harbour material left over from the proto-planetary disc out of which
the planets formed, and therefore should reflect the primordial
composition of their places of origin. But thanks to the dynamics of
the early Solar System, that is not a straightforward process.
Long-period comets that hail from the distant Oort cloud originally
formed in the Uranus-Neptune region, far enough from the Sun that
water-ice could survive. They were later scattered to the Solar
System's far outer reaches as a result of gravitational interactions
with the gas-giant planets as they settled in their orbits. Converse-
ly, Jupiter-family comets like Rosetta's comet were thought to have
formed further out, in the Kuiper Belt beyond Neptune. Occasionally,
bodies are disrupted from that location and sent towards the inner
Solar System, where their orbits are controlled by the gravitational
influence of Jupiter. Indeed, Rosetta's comet now travels around the
Sun between the orbits of the Earth and Mars at its closest and just
beyond Jupiter at its furthest, with a period of about 6.5 years.

Previous measurements of the deuterium/hydrogen (D/H) ratio in other
comets have shown a wide range of values. Of the 11 comets for which
measurements have been made, it is only the Jupiter-family Comet
103P/Hartley 2 that was found to match the composition of the Earth's
water, in observations made by the Herschel mission in 2011. Meteor-
ites originally hailing from asteroids in the Asteroid Belt also match
the composition of terrestrial water. Thus, despite the fact that
asteroids have a much lower overall water content, impacts by a large
number of them could still have provided the water in the oceans. It
is against that backdrop that Rosetta's investigations are important.
Interestingly, the D/H ratio measured by the 'Rosetta Orbiter
Spectrometer for Ion and Neutral Analysis' (ROSINA), is more than
three times greater than for the Earth's oceans and for its Jupiter-
family sibling, Comet Hartley 2. It is even higher than has been
measured for any Oort-cloud comet as well. That surprising finding
could indicate a diverse origin for the Jupiter-family comets --
perhaps they formed over a wider range of distances in the young Solar
System than was previously thought. The finding also rules out the
idea that Jupiter-family comets contain solely Earth-ocean-like water,
and offers credence to models that place more emphasis on asteroids as
the main source of water for the Earth's oceans.


TWO STARS SO CLOSE THAT THEY WILL MERGE INTO SUPER-MASSIVE STAR
ASOCIACION RUVID

Most of the stars in our Galaxy have been formed in binary or multiple
systems, some of which are eclipsing. One of those is MY Camelopard-
alis (MY Cam). Observations from Calar Alto Observatory indicate that
MY Cam is the most massive binary star observed, and its components,
two stars of spectral type O (blue, very hot and bright), 38 and 32
times the Sun's mass, are still on the main sequence and are very
close to one another, with an orbital period less than 1.2 days, the
shortest orbital period known for such a pair. That indicates that
the binary was formed virtually as it is now: the stars were almost in
contact at the time when they were formed. The expected development
is the merger of the components into a single object of over 60 solar
masses before either of them has time to evolve significantly, in line
with some theoretical models that suggest that most massive stars are
formed by merging less-massive stars.

Stars which, like the Sun, move alone in the Galaxy with only
planetary systems are a minority; most stars are tied by gravity to
one or more companion stars. In particular, stars that have masses
equivalent to many Suns usually appear in company. Recent studies
suggest that such high-mass stars, that are much larger and hotter
than the Sun, form parts of systems with at least one other companion
of comparable mass. A particularly striking example is MY Cam, the
brightest star in the open cluster 'Alicante 1', which was recently
identified as a small stellar nursery by researchers at the University
of Alicante. Although it has been known for over 50 years that MY Cam
is a high-mass star, it was only ten years ago that it was recognised
as an eclipsing binary. Eclipses allow us to discover many of the
characteristics of the component stars. Astrophysicists obtained a
large number of spectra of MY Cam with the FOCES spectrograph, which
operated for many years on the 2.2-m telescope at Calar Alto. As well
as measuring the velocities with which the stars moved in their
orbits, the observers could determine the fundamental properties of
the stars, such as their surface temperatures and sizes. Amateur
astronomers helped in determining the light-curve of the system.
Analysis of those data has shown that MY Cam is a truly exceptional
system. The components appear to be extremely young stars, formed in
the past two million years.


NEW EXAMPLE OF RARE TYPE OF GALAXY
National Radio Astronomy Observatory

With the help of citizen scientists, a team of astronomers has found
an important new example of a rare type of galaxy that may yield
insight on how galaxies developed in the early Universe. The new
discovery technique promises to find many more examples of this
unusual type of galaxy. The galaxy concerned, named J1649+2635,
nearly 800 million light-years away, is a spiral galaxy, but with
prominent jets of sub-atomic particles propelled outward from its core
at nearly the speed of light. Spiral galaxies are not supposed to
have such large jets: conventional wisdom is that such jets come only
from elliptical galaxies. J1649+2635 is only the fourth jet-emitting
spiral galaxy discovered so far. The first was found in 2003, when
astronomers combined a radio-telescope image from the Very Large Array
(VLA) and a visible-light image of the same object from the Hubble
telescope. The second was revealed in 2011 by images from the Sloan
Digital Sky Survey and the VLA, and the third, found earlier this
year, also was discovered by combining radio and visible-light images.

Astronomers realized that, to throw light on how such jets can be
produced by the 'wrong' kind of galaxy, they needed to find more of
them. To do that, they looked for help in the form of large
collections of images from both radio and optical telescopes, and the
hands-on assistance of volunteer 'citizen scientists'. The volunteers
are participants in an on-line project called the Galaxy Zoo, in which
they look at images from the visible-light Sloan Digital Sky Survey
and classify the galaxies as spiral, elliptical, or other types. Each
galaxy image is inspected by multiple volunteers to improvee accuracy
in classification. So far, Galaxy Zoo participants have classified
some 700,000 galaxies. Astronomers used a specially well-classified
sub-set of more than 65,000 galaxies, for which 95% of those viewing
each galaxy's image agreed on the classification. About 35,000 of
those are spiral galaxies. J1649+2635 had been classified by 31
Galaxy Zoo volunteers, 30 of whom agreed that it is a spiral. Next,
the astronomers cross-matched the visible-light spirals with galaxies
in a catalogue that combines data from the VLA Sky Survey and the
'Faint Images of the Radio Sky at 20 cm' survey, both done with the
VLA. The cross-matching showed that J1649+2635 is both a spiral
galaxy and has powerful twin radio jets. This is the first time that
a galaxy was first identified as a spiral, then subsequently found to
have large radio jets. Jets such as those seen coming from J1649+2635
are propelled by the gravitational energy of a super-massive black
hole at the core of the galaxy. Material pulled toward the black hole
forms a rapidly-rotating disc, and particles are accelerated outwards
along the poles of the disc. The collision that is presumed to form
an elliptical galaxy disrupts gas in the merging galaxies and provides
'fuel' for the disc and acceleration mechanism. That same disruption,
however, is expected to destroy any spiral structure as the galaxies
merge into one. J1649+2635 is unusual not only because of its jets,
but also because it is the first example of a 'grand design' spiral
galaxy with a large halo of visible-light emission surrounding it.


ATOMIC HYDROGEN GAS DETECTED IN DISTANT GALAXIES
RAS

Using the world's largest radio telescope at Arecibo, astronomers have
detected the faint signal emitted by atomic hydrogen gas in nearly 40
galaxies three billion light-years away, breaking the previous record
distance by 500 million light-years. In doing so, the scientists
found galaxies with huge reservoirs of hydrogen gas, each galaxy
containing between 20 and 80 billion times the mass of the Sun in
atomic gas. Such galaxies are rare, but may have been more common in
the past, when the Universe was younger. Atomic hydrogen gas is the
material out of which new stars are formed, so it is a crucial thing
to study if we are to understand how galaxies form and evolve. Owing
to the limitations of current instruments, astronomers still know very
little about the gas content of galaxies beyond our 'local' neighbour-
hood. Detecting atomic-hydrogen emission from distant galaxies is
very challenging because the signals are not only weak, but they
appear at radio frequencies that are used by communication devices and
radars, which generate signals billions of times stronger than the
cosmic ones.

Measuring the atomic-hydrogen signal emitted by distant galaxies is
one of the main scientific drivers behind the billion-dollar Square
Kilometre Array (SKA) project, for which technology demonstrators like
the Australian SKA Pathfinder are under construction. The Arecibo
observations give astronomers a glimpse into the population of gas-
rich galaxies that will be routinely discovered by such instruments in
coming decades. The project started as an experiment to see at what
distances astronomers were able to detect the signal from atomic
hydrogen in galaxies. Not only were radio signals emitted by distant
galaxies detected, but their gas reservoirs turned out to be
unexpectedly large, about 10 times larger than the mass of hydrogen in
our Milky Way. Such a huge amount of gas will be able to support star
formation in those galaxies for several billion years into the future.


E-ELT CONSTRUCTION AGREED
ESO

The European Southern Observatory has budgeted for the construction
of the 'European Extremely Large Telescope' (E-ELT) in two phases.
Spending of around one billion euros has been authorised for the first
phase, which will cover the construction costs of a fully working
telescope with a suite of powerful instruments and with 'first light'
targeted in ten years' time. It should enable tremendous scientific
discoveries in the fields of exo-planets, the stellar composition of
nearby galaxies and the deep Universe. The largest ESO contract ever,
for the telescope dome and main structure, will be placed within the
next year. The E-ELT will be a 39-metre optical and infrared
telescope sited on Cerro Armazones in the Chilean Atacama Desert, 20
kilometres from the Very Large Telescope on Cerro Paranal. The
decision means that major industrial construction work for the E-ELT
is now funded and can proceed according to plan. There is already a
lot of progress in Chile on the summit of Armazones.

Telescope components that are not yet funded include parts of the
adaptive-optics system, some of the instrument work, the innermost
five rings of segments of the telescope's main mirror (210 mirror
segments) and a spare set of primary-mirror segments needed for more
efficient telescope operation in the future. The construction of those
components will be approved as additional funding becomes available,
including that expected from the incoming Member State, Brazil.


NEW HORIZONS WAKES UP ON PLUTO'S DOORSTEP
NASA

After a voyage of nearly nine years and three billion miles -- the
furthest any space mission has ever travelled to reach its primary
target -- the New Horizons spacecraft came out of hibernation on
Dec. 6 for its 2015 encounter with the Pluto system. Since launch in
2006, New Horizons has spent a total of 1873 days, about two-thirds
of its flight time, in hibernation. Its 18 separate hibernation
periods, from mid-2007 to late 2014, have ranged from 36 days to 202
days in length. The team used hibernation to save wear and tear on
spacecraft components and reduce the risk of system failures. The
New Horizons team will spend the next several weeks checking out the
spacecraft, making sure its systems and instruments are operating
properly. They will also continue to build and test the computer-
command sequences that will guide New Horizons through its flight to,
and reconnaissance of, the Pluto system. With a seven-instrument
payload that includes imaging infrared and ultraviolet spectrometers,
a compact multi-colour camera, a high-resolution telescopic camera,
two powerful particle spectrometers and a space-dust detector, New
Horizons will begin observing the Pluto system on Jan. 15. Closest
approach to Pluto will occur on July 14, but plenty of highlights are
expected before then, including, by mid- May, views of the Pluto
system better than any that the Hubble telescope can provide.


JAPAN LAUNCHES ASTEROID MISSION
NASA

On Dec. 3, the Japan Aerospace Exploration Agency (JAXA) successfully
launched its Hayabusa2 mission to rendezvous with an asteroid, land a
small probe plus three mini-rovers on its surface, and then return
samples to Earth. NASA and JAXA are cooperating on the science of the
mission and NASA will receive a portion of the Hayabusa2 sample in
exchange for providing Deep Space Network communications and
navigation support for the mission. Hayabusa2 builds on lessons
learned from JAXA's initial Hayabusa mission, which collected samples
from the asteroid Itokawa and returned them to the Earth in 2010.
Hayabusa2's target is an 870-m asteroid named 1999 JU3, one of the
C-type asteroids which are thought to contain more organic material
than other types. Scientists hope to improve understanding of how the
Solar System evolved by studying samples from such asteroids.