ROSETTA'S COMET CONTAINS SOME OF THE INGREDIENTS FOR LIFE
University of Bern
Ingredients that were crucial for the origin of life on Earth,
including phosphorus and the simple amino-acid glycine, which are key
components of DNA and cell membranes, have been discovered in Comet
67P/Churyumov-Gerasimenko. The possibility that water and organic
molecules were brought to the early Earth through impacts of objects
like asteroids and comets has long been a subject of debate. While
Rosetta's ROSINA instrument already showed a significant difference in
composition between the water on Comet 67P and that on Earth, the same
instrument has now shown that even if comets did not play as big a
role in delivering water as was once thought, they certainly had the
potential to deliver the ingredients of life. While more than 140
different molecules have already been identified in the interstellar
medium, amino-acids could not be traced. However, hints of the amino-
acid glycine, a biologically important organic compound commonly found
in proteins, were found during the Stardust mission that flew by Comet
Wild 2 in 2004, but terrestrial contamination of the collected dust
samples during the analysis could not be ruled out. Now, for the
first time, repeated detections at a comet have been confirmed by
Rosetta in Comet 67P's fuzzy atmosphere, or coma. The first detection
was made in 2014 October, while most measurements were taken during
the perihelion in 2015 August -- the closest point to the Sun along
the comet's orbit, when the outgassing was strongest. This is the
first unambiguous detection of glycine in the thin atmosphere of a
comet.
Glycine is very hard to detect, owing to its non-reactive nature: it
sublimates at slightly below 150°C, so little is released as gas from
the comet's surface or sub-surface owing to the low temperatures
there. Scientists see a strong correlation of glycine with dust,
suggesting that it is probably released from the grains' icy mantles
once they have warmed up in the coma, perhaps together with other
volatiles. At the same time, the researchers also detected the
organic molecules methylamine and ethylamine, which are precursors to
forming glycine. Alone among amino-acids, glycine has been shown to
be able to form without liquid water. The simultaneous presence of
methylamine and ethylamine, and the correlation between dust and
glycine, also hints at how the glycine was formed. Another exciting
detection that ROSINA has made for the first time at a comet is that
of phosphorus, an element found in all living organisms and in the
structural frameworks of DNA and RNA. The multitude of organic
molecules already identified by ROSINA, now joined by glycine and
phosphorus, suggests that comets have the potential to deliver
molecules important for prebiotic chemistry. Demonstrating that
comets are reservoirs of primitive material in the Solar System, and
vessels that could have transported vital ingredients to the Earth, is
one of the goals of the Rosetta mission.
RADAR FINDS ICE-AGE RECORD IN MARS'S POLAR CAP
NASA
After 10 years in orbit, the Mars Reconnaissance Orbiter and its six
instruments are still in excellent order. Scientists using radar data
from it have found a record of the most recent Martian ice age
recorded in the planet's north-polar ice cap. The new results agree
with previous models that indicated that a glacial period ended about
400,000 years ago, as well as predictions about how much ice would
have been accumulated at the poles since then. The results help to
refine models of Mars's past and future climate by allowing scientists
to determine how ice moves between the poles and mid-latitudes, and in
what quantities. Mars has bright icy polar caps that are easily seen
in telescopes on Earth. A seasonal cover of carbon-dioxide ice and
snow is observed to advance and retreat over the poles during the
Martian year. During summer time in the planet's north, the remaining
northern polar cap is all water ice; the southern cap is water ice as
well, but remains covered by a relatively thin layer of carbon-dioxide
ice even in southern summertime. But Mars also undergoes variations
in its tilt and the shape of its orbit over hundreds of thousands of
years. The changes cause substantial shifts in the planet's climate,
including ice ages. The Earth has similar, but less variable, phases
called Milankovitch cycles.
Scientists use data from MRO's 'Shallow Sub-surface Radar' (SHARAD) to
produce images called radargrams that are like vertical slices through
the layers of ice and dust that comprise the Martian polar ice
deposits. For the new study, researchers analyzed hundreds of such
images to look for variations in the layer properties. They identified
in the ice a boundary that extends across the entire north-polar cap.
Above the boundary the layers accumulated very quickly and uniformly
in comparison with the layers below them. The layers in the upper few
hundred metres display features that indicate a period of erosion,
followed by a period of rapid accumulation that is still occurring
today. On Earth, ice ages take hold when the polar regions and high
latitudes become cooler than average for thousands of years, causing
glaciers to grow towards the mid-latitudes. In contrast, the Martian
variety occurs when -- as a result of the planet's increased tilt --
its poles become warmer than lower latitudes. During those periods,
the polar caps retreat and water vapour migrates towards the equator,
forming ground ice and glaciers at mid-latitudes. As the warm polar
period ends, polar ice begins accumulating again, while ice is lost
from mid-latitudes. Such retreat and re-growth of polar ice is
exactly what researchers see in the record revealed by the SHARAD
radar images. An increase in polar ice following a mid-latitude ice
age is also expected from climate models that show how ice moves
about according to variations in Mars's orbital characteristics,
especially its tilt. The models indicate that the last Martian ice
age ended about 400,000 years ago, as the poles began to cool
relatively to the equator. Models suggest that since then, the polar
deposits would have thickened by about 300 metres. The upper unit
reaches a maximum thickness of 320 metres across the polar cap, which
is equivalent to a 60-centimetre-thick global layer of ice. That is
much the same as model predictions that were made by other researchers
in 2003 and 2007.
WAS PLANET 9 ONCE AN EXO-PLANET?
Lund University
Through a computer-simulated study, astronomers at Lund University in
Sweden have shown that it is highly likely that the so-called Planet 9
(not Pluto, which is now considered too small to be a proper planet)
is an exo-planet. The theory is that the Sun, in its youth some 4.5
billion years ago, stole Planet 9 from its original star. An extra-
solar planet, or exo-planet, is by definition a planet located outside
the Solar System. Now it appears that that definition no longer
holds. Stars are born in clusters and often pass by one another. It
is during such encounters that a star can 'steal' one or more planets
from another star. That is probably what happened when the Sun
captured Planet 9. There is still no image of Planet 9, not even a
point of light. We do not know if it is made up of rock, ice, or gas.
All that we think we know is that its mass is probably around ten
times the mass of the Earth. It would require a lot more research
before it could be ascertained that Planet 9 is really an exo-planet
in the Solar System. If it is, it is the only exo-planet that we,
realistically, would be able to reach with a space probe.
NUMBER OF HABITABLE PLANETS COULD BE MORE LIMITED
RAS
New research has indicated that the number of planets capable of
harbouring life may be fewer than has been supposed, because their
atmospheres keep them too hot. When looking for planets that could
harbour life, scientists look for planets in the 'habitable zones'
around their stars -- at the right distance from the stars to allow
water to exist in liquid form. Traditionally, the search has focussed
on looking for planets orbiting stars like our Sun, such as the Earth.
However, recent research has turned to small planets orbiting very
close to M-type dwarfs, which are much smaller and dimmer than the
Sun. M dwarfs make up around 75% of all the stars in the Galaxy, and
recent discoveries have suggested that many of them host planets,
pushing the number of potentially habitable planets into the billions.
Last month, both the TRAPPIST and Kepler planet-hunting
telescopes announced the discovery of multiple near-Earth-sized
planets orbiting M-dwarf stars, some within the habitable zones. The
new research, from Imperial College London and the Institute for
Advanced Studies in Princeton, has found that, although they orbit
smaller and dimmer stars, many of the planets might still be too hot
to be habitable. The scientists suggest that some of the planets
might still be habitable, but only those with a smaller mass than the
Earth, comparable to Venus or Mars. It was previously assumed that
planets with masses similar to the Earth's would be habitable simply
because they were in the 'habitable zone'. However, when it was
considered how such planets evolve over billions of years, that
assumption was recognized not to be true. It was already known that
many of the planets are born with thick atmospheres of hydrogen and
helium, making up roughly 1% of the total planetary mass. In
comparison, the Earth's atmosphere makes up only a millionth of its
mass.
The greenhouse effect of such a thick atmosphere would make the
surface far too hot for water to exist as a liquid, rendering the
planets initially uninhabitable. However, it was thought that over
time, the strong X-ray and ultraviolet radiation from the parent M-
dwarf star would evaporate away most of the atmosphere, eventually
making the planets potentially habitable. The new analysis reveals
that that is not so. Instead, simulations show that thick hydrogen
and helium envelopes cannot escape the gravity of planets that are
similar to or more massive than the Earth, so many of them are likely
to retain their stifling atmospheres. However, all is not lost,
according to the researchers. While most of the M-dwarf planets that
are Earth-mass or more would retain thick atmospheres, smaller
planets, comparable to Mars, could still lose them to evaporation.
There are hints from recent exo-planet discoveries that relatively
puny planets may be even more common around red dwarfs than Earth-
mass or larger ones, in which case there may indeed be a bonanza of
potentially habitable planets around cool red stars. Ongoing ground
and space-based searches, and new space missions to be launched in the
near future, should provide a definite answer to that question, as
well as to other questions about the potential suitability of such
planets for life.
GIANT PLANET FOUND ORBITING VERY YOUNG STAR
Rice University
In contradiction to the long-standing idea that larger planets take
longer to form, astronomers have announced the discovery of a giant
planet in close orbit around a star so young that it still retains a
disc of circumstellar gas and dust. For decades, conventional wisdom
has held that large Jupiter-mass planets take a minimum of 10 million
years to form. That has been questioned over the past decade, and
many new ideas have been offered, but the fact is that we need to
identify a number of newly formed planets around young stars if we
hope to understand planet formation. The planet CI Tau b is at least
eight times larger than Jupiter and orbits a star only 2 million years
old about 450 light years from us in the constellation Taurus. The
Earth and the Sun are more than 4000 million years old, and while the
3,300-plus catalogue of exo-planets includes some older and some
younger than the Earth, the obstacles to finding planets around newly
formed stars are varied and daunting. There are few candidate stars
that are young enough, bright enough to view in sufficient detail with
existing telescopes, and which still retain the circumstellar discs of
gas and dust from which planets form. Stars that are so young also
are often active, with outbursts and dimmings, strong magnetic fields
and enormous starspots that can make it appear that planets exist
where they do not. CI Tau b orbits the star CI Tau once every nine
days. The planet was found by the radial-velocity method, that relies
on slight variations in the velocity of a star to detect the
gravitational pull exerted by nearby planets that are too faint to
observe directly. The discovery resulted from a survey begun in 2004
of 140 candidate stars in the star-forming region Taurus--Auriga.
The result demonstrates that a giant planet can form so rapidly that
the remnant gas and dust from which the young star formed, surrounding
the system in a disc, is still present. Giant-planet formation in the
inner part of the disc, where CI Tau b is located, will have a
profound impact on the region where smaller terrestrial planets are
also potentially forming. The team observed CI Tau dozens of times
with several large telescopes. Initial optical radial-velocity data
from McDonald Observatory confirmed that a planet might be present,
and the team added photometry measurements in both visible light and
the infrared to rule out the possibility that the optical signal
resulted from starspots or another masking phenomenon. The team has
examined about half of the young stars in the Taurus--Auriga survey
sample, and the data from several of them suggest that more planets
may be found. It is hoped that astronomers can find enough of them to
shed light on some of the nagging questions about planet formation,
for instance, the 'brown dwarf desert', an unexplained paucity of
objects that are larger than giant planets but smaller than stars. If
careful investigation reveals more brown dwarfs in short-period orbits
around young stars than around older ones, that would support the idea
that they tend to merge with their central stars within a few million
years of forming.
A NEW EINSTEIN RING
RAS
A team of astronomers has found an Einstein Ring, a rare image of a
distant galaxy lensed by gravity. In his General Theory of Relativity
published a century ago, Albert Einstein predicted that gravity would
distort the fabric of space-time, and that light would follow curved
paths as a result. Astronomers first observed that effect in 1919, by
measuring the positions of stars seen near the Sun during the total
solar eclipse of that year, and finding the predicted small shift
caused by the gravitational field. On a larger scale, light from
distant galaxies is bent by black holes and massive galaxies that lie
between them and the Earth. The intervening objects act as lenses,
creating arcs and 'Einstein rings' of light. The rings are
comparatively rare and usually appear as small features in the sky.
That makes them hard to see clearly, and most are observed with radio
telescopes, or with the Hubble telescope. Their rarity derives from
the huge distances involved, and the low probability of our Galaxy,
the lens galaxy and the distant galaxy being almost exactly in line.
The newly discovered ring lies in the direction of the constellation
Sculptor in the southern sky. It was found in archived images from
the Dark Energy Camera mounted on the Blanco 4-m telescope at CTIO in
Chile. The team named the ring 'Canarias', in homage to the work
carried out by astronomers on La Palma and Tenerife. Light arriving
at the Earth today left the Einstein ring 8 billion years ago, so we
see the ring as it was 5 billion years after the Big Bang. Despite
its small apparent size (4.5 arcseconds), it is larger than most of
the other rings found to date. Follow-up observations with the 10.4-m
Gran Telescopio Canarias confirms its distance and shows that the
intervening lens galaxy has a mass equivalent to about a million
million Suns.
CLUES TO BIRTH OF SUPER-MASSIVE BLACK HOLES
ESA/Hubble Information Centre
Astrophysicists have taken a major step forward in understanding how
super-massive black holes formed. Using data from Hubble and two
other space telescopes, Italian researchers have found the best
evidence yet for the seeds that ultimately grow into those cosmic
giants. For years astronomers have debated how the earliest
generation of super-massive black holes managed to form very quickly,
relatively speaking, after the Big Bang. Now, an Italian team has
identified two objects in the early Universe that seem to be the
origin of the early super-massive black holes. The two objects
represent the most promising black-hole seed candidates found so far.
The group used computer models and applied a new analysis method to
data from the Chandra X-ray observatory, the Hubble telescope and the
Spitzer space telescope to find the two objects. Both of them are
seen less than a billion years after the Big Bang and have an
initial mass of about 100,000 times that of the Sun. That new result
helps to explain why we see super-massive black holes less than a
billion years after the Big Bang.
There are two main theories to explain the formation of super-massive
black holes in the early Universe. One assumes that the seeds grow
out of black holes with masses of about ten to a hundred solar masses,
as expected for the collapse of a massive star. The black-hole seeds
then grow through mergers with other small black holes and by pulling
in gas from their surroundings. However, they would have to grow at a
remarkably high rate to reach the masses of super-massive black holes
already discovered to have formed in the first billion years of the
Universe. The new findings support another scenario where at least
some very massive black-hole seeds with 100,000 times the mass of the
Sun formed directly when a massive cloud of gas collapsed. In that
case the growth of the black holes would be jump-started, and would
proceed more quickly. Black-hole seeds are extremely hard to find,
and confirming their detection is very difficult. Even though both
black-hole seed candidates match the theoretical predictions, further
observations are needed to confirm their true nature. To distinguish
properly between the two formation theories, it will also be necessary
to find more candidates. The team plans to conduct follow-up
observations in X-rays and in the infrared range to check whether the
two objects have more of the properties expected for black-hole seeds.
Upcoming observatories, such as the James Webb space telescope and the
E-ELT, may be hoped to make a breakthrough in this field, by detecting
even smaller and more distant black holes.
UNIVERSE EXPANDING FASTER THAN EXPECTED
Space Telescope Science Institute (STScI)
Astronomers using the Hubble space telescope have discovered that the
Universe is expanding 5% to 9% faster than expected. That surprising
finding may be an important clue to understanding those mysterious
parts of the Universe that are said to make up 95% of everything and
do not emit light, such as 'dark energy', dark matter, and 'dark
radiation'. The team made the discovery by refining the Universe's
current expansion rate to unprecedented accuracy, reducing the formal
uncertainty to only 2.4%. It made the refinements by developing
innovative techniques that improved the precision of distance
measurements to far-away galaxies. Researchers looked for galaxies
containing both Cepheid variable stars and Type Ia supernovae.
Cepheid stars pulsate at rates that correspond to their true
brightnesses, which can be compared with their apparent brightnesses
as seen from here to determine their distances. Type Ia supernovae,
another commonly used cosmic yardstick, are exploding stars that flare
with the same brightness and are brilliant enough to be seen from very
long distances. By measuring about 2,400 Cepheid stars in 19 galaxies
and comparing the observed brightness of both types of stars, the
Hubble users determined their true brightness and calculated distances
to roughly 300 Type Ia supernovae in far-flung galaxies. The team
compared those distances with the expansion of space as measured by
the stretching of light from receding galaxies. Then the team used
the two values to calculate how fast the Universe expands with time,
or the Hubble constant.
The improved Hubble constant value is 73.2 km/s per megaparsec. (A
megaparsec is 3.26 million light-years.) The new value means that the
distance between cosmic objects will double in another 9.8 billion
years. That calibration presents a puzzle, however, because it does
not quite match the expansion rate found for the Universe from its
trajectory seen shortly after the Big Bang. Measurements of the
afterglow from the Big Bang by the Wilkinson Microwave Anisotropy
Probe (WMAP) and the Planck satellite mission yield predictions for
the Hubble constant that are 5% and 9% smaller, respectively. If we
know the initial amounts of stuff in the Universe, such as dark energy
and dark matter, and we have the physics correct, then we can go from
a measurement at the time shortly after the Big Bang and use that
understanding to predict how fast the Universe should be expanding
today. However, if the present discrepancy holds up, it suggests that
we may not have the right understanding, and it changes the value that
the Hubble constant should have today. Comparing the Universe's
expansion rate with WMAP, Planck, and Hubble is like building a
bridge. On the distant shore are the cosmic microwave background
observations of the early Universe. On the near shore are the
measurements made by Hubble. You start at the two ends, and you hope
to meet in the middle if all of your drawings and your measurements
are right. But now the two ends are not quite meeting in the middle
and we want to know why.
There are some possible explanations for the Universe's excessive
speed. One is that dark energy, already supposed to be accelerating
the Universe, may be shoving galaxies away from each other with even
greater -- or growing -- strength. Another idea is that the cosmos
contained in its early history a sub-atomic particle that travelled
close to the speed of light. Such speedy particles are collectively
referred to as 'dark radiation' and include previously known particles
like neutrinos. More energy from additional dark radiation could be
falsifying the best efforts to predict today's expansion rate from its
post-big-bang trajectory. The boost in acceleration could also mean
that dark matter possesses some weird, unexpected characteristics.
Dark matter is the backbone of the Universe upon which galaxies built
themselves up into the large-scale structures seen today. And
finally, the speedier Universe may be telling astronomers that
Einstein's theory of gravity is incomplete.
Topic: Mid June Astronomy Bulletin (Read 1687 times)