EARTH STOPS HIGH-ENERGY NEUTRINOS
Penn State
For the first time, an experiment has measured the Earth's ability to
absorb neutrinos -- the smaller-than-an-atom particles that zoom
throughout space and through us by the billions every second at nearly
the speed of light. The experiment was achieved with the IceCube
detector, an array of 5,160 basketball-sized sensors frozen deep within
a cubic kilometre of very clear ice near the South Pole. The first
detections of extremely-high-energy neutrinos were made by IceCube in
2013, but a question remained as to whether any kind of matter could
truly stop a neutrino's journey through space. Astronomers knew that
lower-energy neutrinos pass through just about anything, but although
they had expected higher-energy neutrinos to be different, no previous
experiments had been able to demonstrate convincingly that higher-energy
neutrinos could be stopped by anything. The results are based on one
year of data from about 10,800 neutrino-related interactions. This
new discovery with IceCube is an interesting addition to our deepening
understanding of how the Universe works. It also is a little bit of a
disappointment for those who hope for an experiment that will reveal
something that cannot be explained by the current Standard Model of
Particle Physics. The results of this Ice Cube study are fully consis-
tent with that model -- the reigning theory that for the past half-
century has described all the physical forces in the universe except
gravity.
Neutrinos were first formed at the beginning of the Universe, and they
continue to be produced by stars throughout space and by nuclear
reactors on Earth. IceCube's sensors do not directly observe neutrinos,
but instead measure flashes of blue light, known as Cherenkov radiation,
emitted after a series of interactions involving fast-moving charged
particles that are created when neutrinos interact with the ice. By
measuring the light patterns from those interactions in or near the
detector array, IceCube can estimate the neutrinos' energies and
directions of travel. The scientists found that the neutrinos that had
to travel the furthest through the Earth were less likely to reach the
detector. Most of the neutrinos selected for this study had more than
a million times as much energy as those produced by more familiar
sources, like the Sun or nuclear power plants. The analysis also
included a small number of astrophysical neutrinos, which are produced
outside the Earth's atmosphere, from cosmic accelerators unidentified to
date, perhaps associated with supermassive black holes. In addition to
providing the first measurement of the Earth's absorption of neutrinos,
the analysis shows that IceCube's scientific reach extends beyond its
core focus on particle-physics discoveries and the emerging field of
neutrino astronomy into the fields of planetary science and nuclear
physics. This analysis is also of interest to geophysicists who would
like to use neutrinos to image the Earth's interior in order to explore
the boundary between the Earth's solid inner core and its liquid outer
core. Physicists now hope to repeat the study using an expanded, multi-
year analysis of data from the full 86-string IceCube array, and to look
at higher ranges of neutrino energies for any hints of new physics
beyond the Standard Model.
MARS WATER WAS JUST SAND AND DUST AVALANCHES
NASA
In 2015 September, scientists mistakenly announced that Mars had liquid
water flowing on its surface. Now, a team of scientists from the U.S.
Geological Survey has reinterpreted the findings and says that the
surface features are, in fact, likely to be avalanches of sand and dust.
The study re-examined the original data from NASA that looked at the
Recurring Slope Lineae, or RSL. That area is a narrow, sloping surface
where the features appear to be darker than the rest of their
surroundings. They were found to fade and reappear at regular
intervals, returning during the warmest time of the year. When the
streaks were first discovered, scientists believed that they had
convincing evidence that appeared to confirm that water -- albeit briny
-- is flowing today on the surface of Mars. The announcement generated
huge excitement at the time -- the implications of such a finding
increased the likelihood that life once existed, and could still exist,
on Mars.
The latest findings dash such hopes. Scientists thought of RSL as
possible liquid-water flows, but now say the slopes are more like what
we expect for dry sand. The new understanding of RSL supports other
evidence that shows that Mars today is very dry. Findings showed that
the RSL slopes are similar to those in areas where the movement of sand
dunes causes such features to appear. The scientists say that water is
highly unlikely to be responsible -- the amount of water required does
not correspond to what the data are showing. Also, they say that it is
highly unlikely that water is only produced at the top of slopes -- it
should appear on lower slopes too. The findings do not rule out the
possibility of liquid water on Mars or that it could play a role in the
movement of dust and sand -- potentially initiating the avalanches that
the scientists suggest are responsible for the features.
PLUTO IS COLDER THAN EXPECTED
University of California - Santa Cruz
The gas composition of a planet's atmosphere generally determines how
much heat gets trapped in the atmosphere. For the dwarf planet Pluto,
however, the predicted temperature based on the composition of its
atmosphere was much higher than actual measurements taken by the New
Horizons spacecraft in 2015. A new study proposes a novel cooling
mechanism controlled by haze particles to account for Pluto's frigid
atmosphere. The cooling mechanism involves the absorption of heat by
the haze particles, which then emit infrared radiation, cooling the
atmosphere by radiating energy into space. The result is an atmospheric
temperature of about minus 203 degrees Celsius instead of the predicted
minus 173 Celsius. The excess infrared radiation from haze particles
in Pluto's atmosphere should be detectable by the James Webb Space
Telescope, allowing confirmation of the hypothesis after the telescope's
planned launch in 2019. Extensive layers of atmospheric haze can be
seen in images of Pluto taken by New Horizons. The haze results from
chemical reactions in the upper atmosphere, where ultraviolet radiation
from the Sun ionizes nitrogen and methane, which react to form tiny
hydrocarbon particles tens of nanometres in diameter. As those tiny
particles sink down through the atmosphere, they stick together to form
aggregates that grow larger as they descend, eventually settling onto
the surface. The researchers are interested in studying the effects of
haze particles on the atmospheric energy balance of other planetary
bodies, such as Neptune's moon Triton and Saturn's moon Titan. Their
findings may also be relevant to investigations of exoplanets with hazy
atmospheres.
FIRST INTERSTELLAR ASTEROID IS NOTHING LIKE SEEN BEFORE
ESO
On 2017 October 19 the Pan-STARRS 1 telescope in Hawaii observed a
faint point of light moving across the sky. It looked initially like a
typical fast-moving small asteroid, but additional observations over
the next couple of days allowed its orbit to be computed fairly
accurately. The orbit calculations revealed beyond any doubt that
that body did not originate from inside the Solar System, like all
other asteroids or comets ever observed, but instead had come from
interstellar space. Although it was originally classified as a comet,
observations from ESO and elsewhere revealed no signs of cometary
activity after it passed closest to the Sun in 2017 September. The
object was re-classified as an interstellar asteroid and named
1I/2017 U1 (`Oumuamua). ESO's Very Large Telescope was immediately
called into action to measure the object's orbit, brightness and colour
more accurately than smaller telescopes could achieve. Speed was vital
as `Oumuamua was rapidly fading as it headed away from the Sun and past
the Earth's orbit, on its way out of the Solar System. There were more
surprises to come. Combining the images from the FORS instrument on the
VLT through four different filters with those of other large telescopes,
the team of astronomers found that `Oumuamua varies dramatically in
brightness by a factor of ten as it spins on its axis every 7.3 hours.
That unusually large variation in brightness means that the object is
highly elongated, about ten times as long as it is wide, with a complex,
convoluted shape. They also found that it has a dark red colour,
similar to objects in the outer Solar System, and confirmed that it
is completely inert, without the faintest hint of dust around it.
Those properties suggest that `Oumuamua is dense, possibly rocky or with
high metal content, lacks significant amounts of water or ice, and that
its surface is now dark and reddened owing to the effects of irradiation
from cosmic rays over millions of years. It is estimated to be at least
400 metres long. Preliminary orbital calculations suggested that the
object has come from the approximate present direction of Vega. However,
it has taken it so long for it to make the journey to the Solar System,
even though it has been travelling at a speed of about 26 km/s (95,000
km/h), that Vega was not near that position when the asteroid was there
about 300,000 years ago. `Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System. Astronomers estimate that interstellar asteroids similar to `Oumuamua pass through the inner Solar System about once a year, but they are faint and hard to spot and so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, were made powerful enough to have a chance of discovering them. Astronomers are continuing to observe this unique object and hope to pin down more accurately where it came from and where it is going next on its tour of the Galaxy.
EXOPLANET 55 CANCRI e LIKELY TO HAVE ATMOSPHERE
NASA/JPL
Twice as big as the Earth, the super-Earth 55 Cancri e was thought to
have lava flows on its surface. The planet is very close to its star,
and the same side of the planet always faces the star, so the planet has
permanent day and night sides. On the basis of a 2016 study using data
from the Spitzer Space Telescope, scientists speculated that lava would
flow freely in lakes on the starlit side and become hardened on the face
in perpetual darkness. The lava on the day side would reflect radiation
from the star, contributing to the overall observed temperature of the
planet. Now, a deeper analysis of the same Spitzer data finds that the
planet probably has an atmosphere whose ingredients could be similar to
those of the Earth's atmosphere, but thicker. Scientists have said that
lava lakes directly exposed to space without an atmosphere would create
local hot spots of high temperatures, so they are not the best expla-
nation for the Spitzer observations. Using an improved model of how
energy would flow throughout the planet and radiate back into space,
researchers find that the night side of the planet is not as cool as
previously thought. Even the 'cool' side is still quite toasty by
Earthly standards, at an average of 1,300 to 1,400 Celsius, and the
hot side averages 2,300 Celsius. The difference between the hot and
cold sides would be more extreme if there were no atmosphere.
Researchers say that the atmosphere of the extraordinary planet could
contain nitrogen, water and even oxygen -- molecules found in *our*
atmosphere, too -- but with much higher temperatures throughout. The
density of the planet is also similar to that of the Earth, suggesting
that it, too, is rocky. The intense heat from the host star would be
far too great to support life, however, and could not allow liquid
water. Spitzer observed 55 Cancri e between 2013 June 15 and July 15,
using a camera specially designed for viewing infrared light, which is
an indicator of heat energy. By comparing changes in brightness
observed by Spitzer to energy-flow models, researchers realized that an
atmosphere with volatile materials could best explain the temperatures.
There are many open questions about 55 Cancri e, especially why the
atmosphere has not been stripped away from the planet, given the
perilous radiation environment of the star. Understanding that planet
could help us address larger questions about the evolution of rocky
planets.
SPACE DUST MAY TRANSPORT LIFE BETWEEN WORLDS
University of Edinburgh
Fast-moving flows of interplanetary dust that continually bombard our
planet's atmosphere could deliver tiny organisms from far-off worlds, or
send Earth-based organisms to other planets, according to new research.
The dust streams could collide with biological particles in the Earth's
atmosphere with enough energy to knock them into space. Such an event
could enable bacteria and other forms of life to make their way from one
planet in the Solar System to another and perhaps beyond. The finding
suggests that large asteroid impacts may not be the sole mechanism by
which life could transfer between planets, as was previously thought.
The research calculated how powerful flows of space dust -- which can
move at up to 70 km/s -- could collide with particles in our atmospheric
system. It found that small particles existing at 150 km or higher
above the Earth's surface could be knocked beyond retrieval by the
Earth's gravity by space dust and eventually reach other planets. The
same mechanism could enable the exchange of atmospheric particles
between distant planets. Some bacteria, plants and small animals called
tardigrades are known to be able to survive in space, so it is possible
that such organisms -- if present in the Earth's upper atmosphere --
might collide with fast-moving space dust and withstand a journey to
another planet. The proposition that space-dust collisions could propel
organisms over enormous distances between planets raises some exciting
prospects of how life and the atmospheres of planets originated. The
streaming of fast space dust is found throughout planetary systems and
could be a common factor in proliferating life.
NEARBY STARS AMONG OLDEST IN GALAXY
Georgia State University
Astronomers have discovered some of the oldest stars in our Milky Way
galaxy by determining their locations and velocities. A bit like humans,
stars have a life span: birth, youth, adulthood, seniority and death.
The study focussed on certain old stars, those known as cool subdwarfs,
that are much older and cooler than the Sun. The oldest stars are about
six to nine billion years old. They are found in the Galaxy's halo,
a roughly spherical component of the Galaxy that formed first, in which
old stars move in orbits that are highly elongated and tilted. Younger
stars in the Milky Way revolve together within the Galaxy's disc in
roughly circular orbits. In the reported study, astronomers conducted a
census of the solar neighbourhood to identify how many young, adult and
old stars are present. They targeted stars out to a distance of 200
light-years, which is relatively nearby in relation to a galaxy that is
more than 100,000 light-years across. That is further than the tradi-
tional horizon for the region of space that is referred to as 'the solar
neighborhood', which is about 80 light-years in radius. The astronomers
first observed the stars over many years with the 0.9-m telescope at
CTIO in the foothills of the Chilean Andes. They measured the stars'
positions and were able to determine their motions across the sky, their
distances and whether or not each star had an unseen companion orbiting
it. The team's work increased the known population of old stars in our
solar neighbourhood by 25%. Among the new sub-dwarfs, the researchers
discovered two old binary stars, even though older stars are typically
found to be alone, rather than in pairs.
The team also outlined two methods to identify such rare old stars. One
method uses stars' locations in the Hertzsprung-Russell (H-R) diagram.
The old stars are found below the sequence of dwarf stars in the H-R
diagram, hence the name 'sub-dwarfs'. Astronomers then looked at one
particular characteristic of known subdwarf stars -- how fast they move
across the sky. The research showed that if a star has a tangential
velocity greater than 200 km/s, it has to be old. So on the basis of
their movements in our Galaxy, it can be possible to decide whether a
star is an old subdwarf or not. In general, the older a star is, the
faster it moves. The team applied the tangential-velocity cut-off and
compared stars in the sub-dwarf region of the H-R diagram to other
existing stellar data-bases, and identified an additional 29 previously
unrecognized old-star candidates. In 2018, results from the Gaia
mission, which is measuring accurate positions and distances for
millions of stars in the Milky Way, will make finding older stars much
easier for astronomers. Determining the distances of stars is now very
labour-intensive and requires a lot of telescope time and patience.
Because the Gaia mission will provide a much larger sample size, the
limited sample of sub-dwarfs will grow, and the rarest of those rare
stars -- binary sub-dwarfs -- will be revealed.
DO DARK MATTER AND DARK ENERGY REALLY EXIST?
Universite de Geneve
For close on a century, researchers have hypothesized that the Universe
contains matter that can not be directly observed, known as 'dark
matter'. They have also posited the existence of a 'dark energy' that
is more powerful than gravitational attraction. Those two hypotheses,
it has been argued, account for the movement of stars in galaxies and
for the accelerating expansion of the Universe respectively. But --
according to a researcher at the University of Geneva -- those concepts
may not be valid: the phenomena that they are supposed to describe can
be demonstrated without them. The research exploits a new theoretical
model based on the scale invariance of the empty space, potentially
solving two of astronomy's greatest problems. In 1933, the Swiss
astronomer Fritz Zwicky claimed that there was substantially more matter
in the Universe than we can actually see. Astronomers called that
unknown matter 'dark matter', a concept that was to take on yet more
importance in the 1970s, when the US astronomer Vera Rubin called on
it to explain the movements and speed of the stars. Scientists have
subsequently devoted considerable resources to identifying dark matter
-- in space, on the ground and even at CERN -- but without success. In
1998 a second problem arose: a team of Australian and US astrophysicists
discovered the acceleration of the expansion of the Universe, earning
them after some delay the Nobel Prize for physics in 2011. However, in
spite of much effort, no theory or observation has been able to define
the black energy that is allegedly stronger than Newton's gravitational
attraction. In short, dark matter and dark energy are two problems that
have stumped astronomersfor over 80 years and 20 years respectively.
The way we represent the Universe and its history are described by
Einstein's equations of general relativity, Newton's universal gravita-
tion and quantum mechanics. The model-consensus at present is that of a
big bang followed by an expansion. In that model, there is a starting
hypothesis that seems not to have been taken into account. That is the
scale invariance of the empty space; in other words, the empty space and
its properties do not change following a dilation or contraction. The
empty space plays a primordial role in Einstein's equations as it
operates in a quantity known as the 'cosmological constant', and the
resulting Universe model depends on it. On the basis of that hypothesis,
researchers are now re-examining the model of the Universe, pointing out
that the scale invariance of the empty space is also present in the
fundamental theory of electromagnetism.
When the researchers carried out cosmological tests on the new model,
they found that it matched the observations. They also found that the
model predicts the accelerated expansion of the Universe without having
to factor in any particle or dark energy. In short, it appears that
dark energy may not actually exist, since the acceleration of the
expansion is contained in the equations of the physics. In a second
stage, astronomers focussed on Newton's law, a special case of the
equations of general relativity. The law is also slightly modified when
the model incorporates the new hypothesis. Indeed, it contains a very
small outward acceleration term, which is particularly significant at
low densities. The amended law, when applied to clusters of galaxies,
leads to masses of clusters in line with that of visible matter
(contrary to what Zwicky argued in 1933): that means that no dark matter
is needed to explain the high speeds of the galaxies in the clusters.
A second test demonstrated that the law also predicts the high speeds
reached by the stars in the outer regions of galaxies (as Rubin had
observed), without having to turn to dark matter to describe them.
Finally, a third test looked at the dispersion of the speeds of the
stars oscillating around the plane of the Milky Way. That dispersion,
which increases with the age of the relevant stars, can be explained
very well by the invariant empty space hypothesis, while there was
previously no agreement on the origin of that effect.
Topic: Early December Astronomy Bulletin (Read 1812 times)