Author Topic: THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 475 2018 Sept 2  (Read 37 times)

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THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 475 2018 Sept 2
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is arguably Britain's liveliest astronomical
society, with members all over the world. We accept subscription
payments online at our secure site and can take credit and debit
cards. You can join or renew via a secure server or just see how
much we have to offer by visiting http://www.popastro.com/
 
STUDY SHOWS EARTH'S INGREDIENTS ARE NORMAL
Goldschmidt Conference

The Earth's building blocks seem to be built from 'pretty normal'
ingredients, according to researchers working with the world's most powerful
telescopes. Scientists have measured the compositions of 18 different
planetary systems from up to 456 light-years away and compared them to ours,
and found that many elements are present in similar proportions to those
found on Earth. This is amongst the largest examinations to measure the
general composition of materials in other planetary systems, and begins to
allow scientists to draw more general conclusions on how they are forged,
and what that might mean for finding Earth-like bodies elsewhere. The first
planets orbiting other stars were not found until 1992 (the first one was
orbiting a pulsar); since then scientists have been trying to understand
whether some of the stars and planets are similar to our own Solar System.
It is difficult to examine remote planets directly; the nearby star tends to
overwhelm any electromagnetic signal, such as light or radio waves. Because
of that, the team decided to look at how the planetary building blocks
affect signals from white-dwarf stars. Those are stars which have burnt up
most of their hydrogen and helium, and shrunk to be very small and dense --
it is anticipated that our Sun will become a white dwarf in around 5 billion
years. White dwarfs' atmospheres are composed of either hydrogen or helium,
which give out a pretty clear and clean spectroscopic signal. However, as
the star cools, it begins to pull in material from the planets, asteroids,
comets and so on which had been orbiting it, with some forming a dust disk,
a little like the rings of Saturn. As that material approaches the star, it
changes how we see the star. The change is measurable because it influences
the star's spectroscopic signal, and allows us to identify the type and even
the quantity of material surrounding the white dwarf. Such measurements can
be extremely sensitive, allowing bodies as small as an asteroid to be
detected.
The team took measurements with spectrographs on the Keck telescope in
Hawaii, the world's largest optical and infrared telescope, and on the
Hubble Space Telescope. In that study, the team focused on the sample of
white dwarfs with dust disks. Astronomers were able to measure the calcium,
magnesium, and silicon content in most of those stars, and a few additional
elements in some of them. They may also have found water in one of the
systems, but have not yet quantified it: it is likely that there will be a
lot of water in some of those objects. For example, the team previously
identified one star system, 170 light-years away in the constellation
Bootes, which was rich in carbon, nitrogen and water, giving a composition
similar to that of Halley's Comet. In general, though, their composition
looks very similar to that of the Earth. That would mean that the chemical
elements, the building blocks of the Earth, are common in other planetary
systems. From what can be seen, in terms of the presence and proportion of
those elements, we are normal, pretty normal. And that means that we can
probably expect to find Earth-like planets elsewhere in our Galaxy. This
work is still on-going and the recent data release from the Gaia satellite,
which so far has characterized 1.7 billion stars, has revolutionized the
field. That means that we will understand the white dwarfs a lot better.
The team hopes to determine the chemical compositions of extra-solar
planetary material to a much higher precision.

STEVE IS NOT AN AURORA
Spaceweather.com

A new type of aurora nicknamed 'STEVE' may not be an aurora at all,
according to a group of researchers who combined satellite data with
ground-based imagery during a geomagnetic storm to investigate how STEVE is
formed. The main conclusion is that STEVE is not an aurora. STEVE is a
purple ribbon of light that amateur astronomers in Canada have been
photographing for decades, belatedly catching the attention of the
scientific community in 2016. It doesn't look exactly like an aurora, but
it often appears alongside aurorae during geomagnetic storms. Is it an
aurora -- or not? That's what the team wanted to find out. Aurorae appear
when energetic particles from space rain down on the Earth's atmosphere
during geomagnetic storms. If STEVE is an aurora, they reasoned, it should
form in much the same way. On 2008 March 28, STEVE appeared over eastern
Canada just as NOAA's Polar Orbiting Environmental Satellite 17 (POES-17)
passed overhead. The satellite, which can measure the rain of charged
particles that causes aurorae, went directly above the purple ribbon. The
team looked carefully at the old data and found ... no rain at all. The
results verify that that STEVE event is clearly distinct from the aurora
borealis since it is characterized by the absence of particle precipitation.
Interestingly, its skyglow could be generated by a new and fundamentally
different mechanism in the Earth's ionosphere. Another study has shown that
STEVE appears most often in spring and autumn. With the next equinox only a
month away, new opportunities to study STEVE are just around the corner.

A GREEN COMET APPROACHES THE EARTH
Spaceweather.com

Comet 21P/Giacobini-Zinner is approaching the Earth. On Sept. 10, it will
be 0.39 AU (58 million km) from our planet and almost bright enough to see
with the naked eye. Already it is an easy target for amateur telescopes.
The comet is relatively small -- its nucleus is barely more than a mile in
diameter -- but it is bright and active, and a frequent visitor to the
inner Solar System as it orbits the Sun once every 6.6 years. On Sept. 10,
21P/Giacobini-Zinner will not only be near the Earth, but also at peri-
helion, its closest approach to the Sun. Solar heating will make it
shine like a star of 6th to 7th magnitude, just below the threshold of
naked-eye visibility but well within the range of common binoculars.
21P/Giacobini-Zinner is the parent of the annual Draconid meteor shower, a
bursty display that typically peaks on Oct. 8. Will the shower be extra
good this year? Draconid outbursts do tend to occur in years near the
comet's close approach to the Sun. However, not every close approach brings
a meteor shower. Forecasters say that there are no known Draconid debris
streams squarely crossing the Earth's path this year, so we will have to
wait and see.

ICE CONFIRMED AT MOON'S POLES
NASA/Jet Propulsion Laboratory

A team of scientists has directly observed definitive evidence of water ice
on the Moon's surface, in the darkest and coldest parts of the Moon's polar
regions. The ice deposits are patchily distributed and could possibly be
ancient. At the southern pole, most of the ice is concentrated in craters,
while the northern pole's ice is more widely, but sparsely, spread. A team
of scientists used data from NASA's Moon Mineralogy Mapper (M3) instrument
to identify three specific signatures that definitively prove that there is
water-ice on the surface of the Moon. M3, aboard the Chandrayaan-1 space-
craft, launched in 2008 by the Indian Space Research Organization, was
equipped to confirm the presence of solid ice on the Moon. It collected
data that not only picked up the reflective properties we would expect from
ice, but by infrared spectroscopy it could differentiate between liquid
water or vapour and solid ice. Most of the newfound water ice lies in the
shadows of craters near the poles, where the temperature never reaches above
minus 157 Centigrade. Because of the very small tilt of the Moon's rotation
axis, sunlight never reaches those regions. Previous observations indirect-
ly found possible signs of surface ice at the lunar south pole, but they
could have been explained by other phenomena, such as unusually reflective
lunar soil. With enough ice sitting at the surface -- within the top few
millimetres -- water would possibly be accessible as a resource for future
expeditions to explore and even stay on the Moon, and potentially easier to
access than the water detected beneath the Moon's surface.

INSIGHT PASSES HALFWAY POINT TO MARS
NASA

NASA's InSight spacecraft, en route to a Nov. 26 landing on Mars, passed the
halfway mark on Aug. 6. All of its instruments have been tested and are
working well. The spacecraft has covered 300 million kilometres since its
launch. It will touch down in Mars' Elysium Planitia region, where it will
be the first mission to study the planet's deep interior. InSight stands
for Interior Exploration using Seismic Investigations, Geodesy and Heat
Transport. The InSight team is using the time before the spacecraft's
arrival at Mars not only to plan and practise for that critical day,
but also to activate and check spacecraft sub-systems vital to cruise,
landing and surface operations, including the highly sensitive scientific
instruments. InSight's seismometer, which will be used to detect quakes on
Mars, received a clean bill of health on July 19. The SEIS instrument
(Seismic Experiment for Interior Structure) is a six-sensor seismometer
combining two types of sensors to measure ground motions over a wide range
of frequencies. It will give scientists a window into Mars' internal
activity.

STRUCTURALLY 'INSIDE OUT' PLANETARY NEBULA DISCOVERED
The University of Hong Kong

Astronomers have discovered the unusual evolution of the central star of a
planetary nebula in our Milky Way. That discovery sheds light on the future
evolution, and more importantly, the ultimate fate of the Sun. The research
team believes that the inverted ionization structure of the nebula is the
result of the central star undergoing a 'born-again' event, ejecting
material from its surface and creating a shock that excites the nebular
material. Planetary nebulae are ionized clouds of gas formed by the
hydrogen-rich envelopes ejected at late evolutionary stages of low- and
intermediate-mass stars. As such stars age, they typically strip their
outer layers, forming a 'wind'. As the star transitions from its red-giant
phase to become a white dwarf, it becomes hotter, and starts ionizing the
material in the surrounding wind. That causes the gaseous material closer
to the star to become highly ionized, while the material further out is less
so. Studying the planetary nebula HuBi 1 (17,000 light-years away and
nearly 5 billion years ahead of our Solar System in evolution), however,
the team found the reverse: HuBi 1's inner regions are less ionized, while
the outer regions are more so. Analysing the central star, with the
participation of theoretical astrophysicists, the authors found that it
is surprisingly cool and metal-rich, and has evolved from a low-mass
progenitor star which had a mass 1.1 times that of the Sun. The authors
suggest that the inner nebula was excited by the passage of a shock wave
caused by the star ejecting matter unusually late in its evolution. The
stellar material cooled to form circumstellar dust, obscuring the star; that
would explain why the central star's optical brightness has diminished
rapidly over the past 50 years. In the absence of ionizing photons from the
central star, the outer nebula has begun recombining -- becoming neutral.
The authors conclude that, as HuBi 1 was roughly the same mass as the Sun,
this finding may provide a glimpse of a potential future for our Solar
System.
The discovery resolves a long-lasting question regarding the evolutionary
path of metal-rich central stars of planetary nebulae. The team has been
using the Nordic Optical Telescope to observe the evolution of HuBi 1 since
2014, and was among the first astrophysicists to discover its inverted
ionization structure. After noting that structure and the unusual nature of
HuBi 1's central star, the observers collaborated with theoretical astro-
physicists in an effort to find the reasons for what they had observed.
They came to realize that they had caught HuBi 1 at the exact time when its
central star underwent a brief 'born-again' process to become a hydrogen-
poor [WC] and metal-rich star, which is very rare in white-dwarf stars'
evolution. The findings suggest that the Sun may also experience a 'born-
again' process while it is dying, about 5000 million years from now; but
long before that event the Earth will be engulfed by the Sun when it expands
into a red giant and nothing living will survive.

WATER WORLDS ARE COMMON
Goldschmidt Conference

Scientists have shown that water is likely to be a major component of those
exoplanets (planets orbiting other stars) which are between two and four
times the size of the Earth. That has implications for the search for life
in our Galaxy. The 1992 discovery of exoplanets orbiting other stars has
sparked interest in understanding the compositions of those planets, to
determine, among other goals, whether they are suitable for the development
of life. Now a new evaluation of data from the exoplanet-hunting Kepler
Space Telescope and the Gaia mission indicates that many of the known
planets may contain as much as 50% water. That is very much more than the
Earth's 0.02% (by weight) water content. Scientists have found that many of
the 4000 confirmed or candidate exoplanets discovered so far fall into two
size categories: those with the planetary radii averaging around 1.5 times
that of the Earth, and those averaging around 2.5 Earth radii. Now a group
of scientists, after analyzing the exoplanets with mass measurements and
recent radius measurements from the Gaia satellite, has developed a model
of their internal structure. The group has looked at how mass relates to
radius, and developed a model which might explain the relationship. The
model indicates that those exoplanets which have radii of around 1.5 Earth
radii tend to be rocky planets (of typically five times the mass of the
Earth), while those with radii of about 2.5 Earth radii (with masses around
ten times that of the Earth) are probably water worlds.
Their water is not as is commonly found here on Earth. Their surface
temperatures are expected to be in the 200- to 500-degree Celsius range.
Their surfaces may be shrouded in a water-vapour-dominated atmosphere, with
a liquid water layer underneath. Deeper down, one would expect to find the
that the water transforms into high-pressure ices before one reaches the
solid rocky core. The beauty of the model is that it explains just how
composition relates to the known facts about such planets. The data
indicate that about 35% of all known exoplanets which are bigger than the
Earth should be water-rich. Those water worlds probably formed in ways
similar to the giant-planet cores (Jupiter, Saturn, Uranus, Neptune) which
we find in our own Solar System. The newly-launched TESS mission is
expected to find many more of them, with the help of ground-based spectro-
scopic follow-up.

GALAXY CLUSTER HIDING IN PLAIN SIGHT
Massachusetts Institute of Technology

MIT scientists have uncovered a sprawling new galaxy cluster hiding in plain
sight. The cluster, which is 2.4 billion light-years away, is made up of
hundreds of individual galaxies and surrounds an extremely active super-
massive black hole, or quasar. The central quasar is called PKS1353-341 and
is intensely bright -- so bright that for decades astronomers observing it
in the night sky have assumed that the quasar was quite alone in its corner
of the Universe, shining out as a solitary light source from the centre of a
single galaxy. The researchers estimate that the cluster has a mass of
about 690 times 10 to the 12 Suns. Our Milky Way galaxy, for comparison,
weighs in at around 400,000 million solar masses. The team also calculates
that the quasar at the centre of the cluster is 46 billion times brighter
than the Sun. Its extreme luminosity is probably the result of a temporary
feeding frenzy: as an immense disk of material swirls around the quasar, big
chunks of matter from the disk are falling in and feeding it, causing the
black hole to radiate huge amounts of energy out as light. That might be a
short-lived phase that clusters go through, where the central black hole has
a quick meal, gets bright, and then fades away again. Some astronomers
believe that the discovery of the hidden cluster inplies there may be other
similar galaxy clusters hiding behind extremely bright objects that
astronomers have mis-catalogued as single light sources. The researchers
are now looking for more hidden galaxy clusters, which could be important
clues to estimating how much matter there is in the Universe and how fast
the Universe is expanding.
In 2012, the team discovered the Phoenix cluster, one of the most massive
and luminous galaxy clusters in the Universe. The mystery was why that
cluster, which was so intensely bright and in a region of the sky that is
easily observable, had not been found before. It is because astronomers had
preconceived notions of what a cluster should look like. For the most part,
astronomers have assumed that galaxy clusters look 'fluffy', giving a very
diffuse signal in the X-ray band, unlike brighter, point-like sources, which
have been interpreted as extremely active quasars or black holes. The
images are either all points, or fluffs; the points are black holes that are
accreting gas and glowing as the gas spirals in, and the fluffs are great
million-light-year balls of hot gas that we call clusters. The Phoenix
discovery proved that galaxy clusters could indeed host immensely active
black holes, prompting astronomers to wonder whether there could be other
'nearby' galaxy clusters that were simply misidentified. To answer that
question, the researchers set up a survey named CHiPS, for Clusters Hiding
in Plain Sight, which was designed to re-evaluate X-ray images taken in the
past. For every point source that was previously identified, the
researchers noted the coordinates and then studied them more directly with
the Magellan Telescope, a powerful optical telescope in Chile. If they
observed a higher-than-expected number of galaxies surrounding the point
source (a sign that the gas may stem from a cluster of galaxies), the
researchers looked at the source again, using NASA's space-based Chandra
X-Ray Observatory, to identify an extended, diffuse source around the main
point source. Some 90% of the sources turned out to not be clusters. The
team plans to comb through more X-ray data in search of galaxy clusters that
might have been missed the first time.

SOME OF THE OLDEST GALAXIES IN UNIVERSE
Durham University

Astronomers from the Institute for Computational Cosmology at Durham
University and the Harvard-Smithsonian Center for Astrophysics have found
evidence that the faintest satellite galaxies orbiting our own Milky Way
galaxy are amongst the very first galaxies that formed in the Universe.
Scientists working on that research have described the finding as "hugely
exciting". The research group's findings suggest that galaxies including
Segue-1, Bootes I, Tucana II and Ursa Major I are in fact some of the first
galaxies ever formed, thought to be over 13 billion years old. When the
Universe was about 380,000 years old, the very first atoms formed. They
were atoms of hydrogen, the simplest element in the Periodic Table. Those
atoms collected into clouds and began to cool gradually and settle into the
small clumps or 'haloes' of dark matter that emerged from the Big Bang.
That cooling phase, known as the 'Cosmic dark ages', lasted about 100
million years. Eventually, the gas that had cooled inside the haloes
became unstable and began to form stars -- these objects are the very first
galaxies ever to have formed. With the formation of the first galaxies, the
Universe burst into light, bringing the cosmic dark ages to an end.
The team identified two populations of satellite galaxies orbiting the Milky
Way. The first was a very faint population consisting of the galaxies that
formed during the 'cosmic dark ages'. The second was a slightly brighter
population consisting of galaxies that formed hundreds of millions of years
later, once the hydrogen that had been ionized by the intense ultraviolet
radiation emitted by the first stars was able to cool into more massive dark
matter haloes. Remarkably, the team found that a model of galaxy formation
that it had developed previously agreed perfectly with the data, allowing it
to infer the formation times of the satellite galaxies. The finding
supports the current model for the evolution of the Universe, the 'Lambda-
cold-dark-matter model' in which the elementary particles that make up the
dark matter drive cosmic evolution. The intense ultraviolet radiation
emitted by the first galaxies destroyed the remaining hydrogen atoms by
ionizing them (knocking out their electrons), making it difficult for that
gas to cool and form new stars. The process of galaxy formation ground to a
halt and no new galaxies were able to form for the next billion years or so.
Eventually, the haloes of dark matter became so massive that even ionized
gas was able to cool. Galaxy formation resumed, culminating in the formation
of spectacular bright galaxies like our own Milky Way. A decade ago, the
faintest galaxies in the vicinity of the Milky Way would have gone under the
radar. With the increasing sensitivity of present and future galaxy counts,
a whole new trove of the tiniest galaxies has come to light, allowing us to
test theoretical models in new regimes.

EARLY OPAQUE UNIVERSE LINKED TO GALAXY SCARCITY
University of California - Riverside

A team of astronomers has made a surprising discovery: 12.5 billion years
ago, the most opaque place in the Universe contained relatively little
matter. It has long been known that the Universe is filled with a web-like
network of dark matter and gas. That 'cosmic web' accounts for most of the
matter in the Universe, whereas galaxies like our own Milky Way make up only
a small fraction. Today, the gas between galaxies is almost totally
transparent because it is kept ionized -- electrons detached from their
atoms -- by a bath of energetic ultraviolet radiation. Over a decade ago,
astronomers noticed that in the very distant past -- roughly 12.5 billion
years ago, or about 1 billion years after the Big Bang -- the gas in deep
space was not only highly opaque to ultraviolet light, but its transparency
varied widely from place to place, obscuring much of the light emitted by
distant galaxies. Then a few years ago, a team at the University of
Cambridge found that those differences in opacity were so large that either
the amount of gas itself, or more likely the radiation in which it is
immersed, must vary substantially from place to place. Today, we live in a
fairly homogeneous Universe. If you look in any direction you find, on
average, roughly the same number of galaxies and similar properties for the
gas between galaxies, the so-called intergalactic gas. At that early time,
however, the gas in deep space looked very different from one region of the
Universe to another. To find out what created the differences, astronomers
used one of the largest telescopes in the world, the Subaru telescope on the
summit of Mauna Kea in Hawaii. Using its powerful camera, the team looked
for galaxies in a vast region, roughly 300 million light-years in size,
where they knew the intergalactic gas was extremely opaque.
For the cosmic web, more opacity normally means more gas, and hence more
galaxies. But the team found the opposite: the region contained far fewer
galaxies than average. Because the gas in deep space is kept transparent by
the ultraviolet light from galaxies, fewer galaxies nearby might make it
murkier. Normally it does not matter how many galaxies are nearby; the
ultraviolet light that keeps the gas in deep space transparent often comes
from galaxies that are extremely far away. At that very early time, it
looks as if the UV light could not travel very far, so a patch of the
Universe with few galaxies in it would look much darker than one with plenty
of galaxies around. That discovery may eventually shed light on another
phase in cosmic history. In the first billion years after the Big Bang,
ultraviolet light from the first galaxies filled the Universe and
permanently transformed the gas in deep space. Astronomers believe that
that occurred earlier in regions with more galaxies, so the large fluctua-
tions in intergalactic radiation may be a relic of that patchy process, and
could offer clues to how and when it occurred. By studying both galaxies
and the gas in deep space, astronomers hope to get closer to understanding
how the intergalactic ecosystem took shape in the early Universe.

ANCIENT QUASARS CONFIRM QUANTUM ENTANGLEMENT
Massachusetts Institute of Technology

Last year, physicists at MIT, the University of Vienna, and elsewhere
provided strong support for quantum entanglement, the seemingly far-out idea
that two particles, no matter how distant from each other in space and time,
can be inextricably linked, in a way that defies the rules of classical
physics. Take, for instance, two particles sitting on opposite edges of the
Universe. If they are truly entangled, then according to the theory of
quantum mechanics their physical properties should be related in such a way
that any measurement made on one particle should instantly convey
information about any future measurement outcome of the other particle --
correlations that Einstein sceptically saw as "spooky action at a distance".
In the 1960s, the physicist John Bell calculated a theoretical limit beyond
which such correlations must have a quantum, rather than a classical,
explanation. But what if such correlations were the result not of quantum
entanglement, but of some other hidden, classical explanation? Such
"what-ifs" are known to physicists as loopholes to tests of Bell's
inequality, the most stubborn of which is the 'freedom-of-choice' loophole:
the possibility that some hidden, classical variable may influence the
measurement that an experimenter chooses to perform on an entangled
particle, making the outcome look quantumly correlated when in fact it
isn't. Last February, the MIT team and their colleagues significantly
constrained the freedom-of-choice loophole, by using 600-year-old starlight
to decide what properties of two entangled photons to measure. Their
experiment proved that, if a classical mechanism caused the correlations
they observed, it would have to have been set in motion more than 600 years
ago, before the stars' light was first emitted and long before the actual
experiment was even conceived. Now, the same team has vastly extended the
case for quantum entanglement and further restricted the options for the
freedom-of-choice loophole. The researchers used distant quasars, one of
which emitted its light 7.8 billion years ago and the other 12.2 billion
years ago, to determine the measurements to be made on pairs of entangled
photons. They found correlations among more than 30,000 pairs of photons,
to a degree that far exceeded the limit that Bell originally calculated for
a classically based mechanism. If some conspiracy is happening to simulate
quantum mechanics by a mechanism that is actually classical, that mechanism
would have had to begin its operations -- somehow knowing exactly when,
where, and how this experiment was going to be done -- at least 7.8 billion
years ago. That seems incredibly implausible, so we have very strong
evidence that quantum mechanics is the right explanation. The Earth is
about 4.5 billion years old, so any alternative mechanism -- different from
quantum mechanics -- that might have produced our results by exploiting such
a loophole would have had to be in place long before even there was a planet
Earth, let alone an MIT. So we have pushed any alternative explanations
back to very early in cosmic history.

15 YEARS IN SPACE FOR SPITZER SPACE TELESCOPE
NASA

Initially scheduled for a minimum 2.5-year primary mission, NASA's Spitzer
Space Telescope has gone far beyond its expected lifetime -- and is still
going strong after 15 years. Launched into a solar orbit on 2003 Aug. 25,
Spitzer was the last of NASA's four Great Observatories to reach space. The
space telescope has illuminated some of the oldest galaxies in the Universe,
revealed a new ring around Saturn, and peered through shrouds of dust to
study newborn stars and black holes. Spitzer assisted in the discovery of
planets beyond our Solar System, including the detection of seven Earth-size
planets orbiting the star TRAPPIST-1, among other accomplishments. Spitzer
detects infrared light -- most often heat radiation emitted by warm objects.
Each of the four Great Observatories collects light in a different range of
wavelength. By combining their observations of various objects and regions,
scientists can gain a more complete picture of the Universe. Spitzer has
logged over 106,000 hours of observation time. Thousands of scientists
around the world have utilized Spitzer data in their studies, and Spitzer
data are cited in more than 8,000 published papers.
Spitzer's primary mission ended up lasting 5.5 years, during which time the
spacecraft operated in a 'cold phase', with a supply of liquid helium
cooling three onboard instruments to just above absolute zero. The cooling
system reduced excess heat from the instruments themselves that could
contaminate their observations. That gave Spitzer very high sensitivity for
'cold' objects. In 2009 July, after Spitzer's helium supply ran out, the
spacecraft entered a so-called 'warm phase'. Spitzer's main instrument,
called the Infrared Array Camera (IRAC), has four cameras, two of which
continue to operate in the warm phase with the same sensitivity that they
maintained during the cold phase. Spitzer orbits the Sun in an Earth-
trailing orbit (meaning it literally follows behind the Earth as the planet
orbits the Sun) and has continued to fall further and further behind the
Earth during its lifetime. This now poses a challenge for the spacecraft,
because while it is downloading data to Earth, its solar panels do not
directly face the Sun. As a result, Spitzer must use battery power during
data downloads. The batteries are then recharged between downloads. In
2016, Spitzer entered an extended mission dubbed 'Spitzer Beyond'. The
spacecraft is currently scheduled to continue operations till 2019 November,
more than 10 years after entering its warm phase.

Bulletin compiled by Clive Down
www.popastro.com


Geoff