EVIDENCE FOR ORGANIC MATERIAL ON CERES
NASA
The Dawn mission has found evidence for organic material on Ceres,
a 'dwarf planet' and the largest body in the main asteroid belt
between Mars and Jupiter. Scientists using the spacecraft's 'visible
and infrared mapping spectrometer' (VIR) detected the material in and
around a northern-hemisphere crater called Ernutet. Organic molecules
are interesting to scientists because they are necessary, though not
sufficient, components of life on Earth. The discovery adds to the
growing list of bodies in the Solar System where organics have been
found. Organic compounds have been found in certain meteorites as
well as inferred from telescopic observations of several asteroids.
Ceres shares many commonalities with meteorites rich in water and
organics -- in particular, a meteorite group called carbonaceous
chondrites. This discovery further strengthens the connection between
Ceres, those meteorites and their parent bodies. Data support the
idea that the organic materials are native to Ceres. The carbonates
and clays previously identified on Ceres provide evidence for chemical
activity in the presence of water and heat. That raises the
possibility that the organics were similarly processed in a warm
water-rich environment.
The organics discovery adds to Ceres' attributes associated with
ingredients and conditions for life in the distant past. Previous
studies have found hydrated minerals, carbonates, water ice, and
ammoniated clays that must have been altered by water. Salts and
sodium carbonate, such as those found in the bright areas of Occator
Crater, are also thought to have been carried to the surface by
liquid. The discovery adds to our understanding of the possible
origins of water and organics on Earth. The VIR instrument was able
to detect and map the locations of the material because of its
special signature in near-infrared light. The organic materials on
Ceres are mainly located in an area covering approximately 1,000
square kilometres. The signature of organics is very clear on the
floor of Ernutet Crater, on its southern rim and in an area just
outside the crater to the southwest. Another large area with
well-defined signatures is found across the northwest part of the
crater rim and ejecta. Having completed nearly two years of
observations in orbit at Ceres, Dawn has now made its way to a new
altitude of around 20,000 km, about the height of GPS satellites above
the Earth, and to a different orbital plane. This will put Dawn in a
position to study Ceres in a new geometry. In late spring, Dawn will
view Ceres with the Sun directly behind the spacecraft, such that
Ceres will appear brighter than before, and perhaps reveal more clues
about its nature.
WEB SITE LETS PUBLIC SEARCH FOR NEW WORLDS IN SOLAR SYSTEM
Science Daily
NASA is inviting the public to help search for possible undiscovered
worlds in the outer reaches of our Solar System and in neighbouring
interstellar space. A new web site, called Backyard Worlds: Planet 9,
lets everyone participate in the search by viewing brief movies made
from images captured by NASA's Wide-field Infrared Survey Explorer
(WISE) mission. The movies highlight objects that have gradually
moved across the sky. It is just over four light-years from
Neptune to Proxima Centauri (the nearest star after the Sun), and much
of that vast territory is unexplored. Because there is so little
sunlight, even large objects in that region barely shine in visible
light. But by looking in the infrared, WISE may have imaged objects
we otherwise would have missed. WISE scanned the entire sky between
2010 and 2011, producing the most comprehensive survey at mid-infrared
wavelengths currently available. With the completion of its primary
mission, WISE was shut down in 2011. It was then reactivated in 2013
and given a new mission assisting NASA's efforts to identify
potentially hazardous near-Earth objects (NEOs), which are asteroids
and comets on orbits that bring them into the vicinity of the Earth's
orbit. The mission was re-named the Near-Earth Object Wide-field
Infrared Survey Explorer (NEOWISE). The new web site uses the data to
search for unknown objects in and beyond the Solar System. In 2016,
astronomers at Caltech, in Pasadena, California, showed that several
distant Solar-System objects possessed orbital features indicating
that they were affected by the gravity of an as-yet-undetected planet,
which the researchers nicknamed 'Planet Nine'. If Planet Nine -- also
known as Planet X -- exists and is as bright as some predictions, it
could show up in WISE data. The search also may discover more-distant
objects like brown dwarfs, sometimes called failed stars, in nearby
interstellar space.
Unlike more distant objects, those in or closer to the Solar System
appear to move across the sky at different rates. The best way to
discover them is through a systematic search of moving objects in WISE
images. While parts of this search can be done by computers, machines
are often overwhelmed by image artifacts, especially in crowded parts
of the sky. Those include brightness spikes associated with star
images and blurry blobs caused by light scattered inside WISE's
instruments. Planet 9 relies on human eyes because we easily
recognize the important moving objects while ignoring the artifacts.
It is a 21st-century version of the technique that astronomer Clyde
Tombaugh used to find Pluto in 1930. On the web site, people around
the world can work their way through millions of 'flipbooks', which
are brief animations showing how small patches of the sky changed over
several years. Moving objects flagged by participants will be priori-
tized by the science team for follow-up observations by professional
astronomers. Participants will share credit for their discoveries in
any scientific publications that result from the project. Planet 9 is
potentially a once-in-a-century discovery, and it is exciting to think
that it could be observed first by a citizen scientist.
SPITZER TELESCOPE FINDS SEVEN EARTH-SIZE PLANETS
NASA/Jet Propulsion Laboratory
The Spitzer Space Telescope has revealed the first known system of
seven Earth-size planets around a single star. Three of the planets
are firmly located in the habitable zone, the area around the parent
star where a rocky planet is most likely to have liquid water. The
exo-planet system is 40 light-years away in the constellation of
Aquarius and called TRAPPIST-1, named for The Transiting Planets and
Planetesimals Small Telescope (TRAPPIST) in Chile. In 2016 May,
researchers using TRAPPIST announced that they had discovered three
planets in the system. Assisted by several ground-based telescopes,
including ESO's Very Large Telescope, Spitzer confirmed the existence
of two of the planets and discovered five additional ones, increasing
the number of known planets in the system to seven. Using Spitzer
data, the team precisely measured the sizes of the seven planets and
made initial estimates of the masses of six of them, allowing their
densities to be estimated. On the basis of their densities, all of
the TRAPPIST-1 planets are likely to be rocky. Further observations
will not only help determine whether they are rich in water, but also
possibly reveal whether any could have liquid water on their surfaces.
The mass of the seventh and farthest planet has not yet been estimated
-- scientists believe it could be an icy, 'snowball-like' object --
but further observations are needed.
In contrast to the Sun, the TRAPPIST-1 star -- classified as an
ultra-cool dwarf -- is so cool that liquid water could survive on
planets orbiting very close to it, closer than is possible on planets
in the Solar System. All seven of the TRAPPIST-1 planetary orbits are
closer to their host star than Mercury is to the Sun. The closest one
orbits the star at a distance of only 0.01 AU, and the most distant
one at 0.06 AU. The planets are also very close to one another. If a
person were standing on the surface of one of the planets, he could
gaze up and potentially see the geological features or clouds of
neighbouring ones, which would sometimes appear larger than the Moon
in our sky. The planets are likely to be tidally locked to their
star, which means that the same side of the planet is always facing
the star, therefore each side has either perpetual day or night. That
could mean that they have weather patterns totally unlike those on the
Earth, such as strong winds blowing from the day side to the night
side, and extreme temperature changes.
ASTRONOMERS FIND 100 NEW PLANETS
Carnegie Institution for Science
An international team of astronomers has released the largest-ever
compilation of exo-planet-detecting observations made by the radial-
velocity method. They demonstrated how the observations can be used
to hunt for planets by detecting more than 100 potential exo-planets,
including one orbiting the fourth-closest star to the Solar System,
which is about 8.1 light-years away. The radial-velocity method is
one of the most successful techniques for finding and confirming
planets. It takes advantage of the fact that in addition to a planet
being influenced by the gravity of the star it orbits, the planet's
gravity also affects the star. Astronomers are able to use
sophisticated tools to detect the tiny wobble the planet induces as
its gravity acts on the star. The virtual mountain of data released
to the public in the paper was gathered as part of a 20-year radial-
velocity planet-hunting programme that uses a spectrometer called
HIRES, mounted on the 10-m Keck-I telescope of the Keck Observatory
on Mauna Kea in Hawaii. The compilation includes almost 61,000
individual measurements made of more than 1,600 stars. By making the
data public, the team is offering unprecedented access to one of the
best exo-planet searches in the world. HIRES was not specifically
optimized to do that type of work, but has turned out to be a work-
horse instrument for the field.
Now as the survey moves into its third decade, the team members have
decided on a new stategy. With so many data at hand and a limited
amount of time, they recognized that more exo-planets might be found
if they shared their catalogue with the astronomical community.
But the team is not just giving everyone the keys to its exo-planet
finder; it is also undertaking a sophisticated statistical analysis of
the large data set to try to identify the periodic signals that are
most likely to be planets. Even with the most stringent criteria,
they found over 100 new likely planet candidates. One of them is
around a star called GJ 411, also known as Lalande 21185. It is the
fourth-closest star to the Sun and has only about 40% of the mass
of the Sun. The planet has a very short orbital period of just under
10 days, so it is by no means an Earth twin. However, the inferred
planet, GJ 411 b, continues a trend that has been seen in the overall
population of detected exo-planets: the smallest planets are found
around the smallest stars.
BRIGHTEST AND FARTHEST KNOWN PULSAR
ESA
Astronomers using the XMM-Newton orbiting telescope have found a
pulsar that is a thousand times brighter than was previously thought
possible. The pulsar is also the most distant of its kind ever
detected, with its light travelling 50 million light-years before
being detected by XMM-Newton. Pulsars are spinning, magnetized
neutron stars that sweep regular pulses of radiation across the cosmos
in two symmetrical beams. If suitably aligned with the Earth such
beams are like lighthouse beacons appearing to flash on and off as the
source rotates. Pulsars were once massive stars that exploded as
powerful supernovae at the ends of their natural lives, before
becoming small and extraordinarily dense stellar corpses. The newly
discovered one, an X-ray source, is the most luminous of its type
detected to date: it is 10 times brighter than the previous record-
holder. In one second it emits the same amount of energy as is
released by the Sun in 3.5 years. [A roundabout way of saying that it
is 100 million times brighter. -- ED] XMM-Newton observed the object
several times in the last 13 years; the discovery was a result of a
systematic search for pulsars in the data archive --- its 1.13-second
periodic pulses giving it away.
Previously, it was believed that only black holes at least 10 times
more massive than the Sun feeding off their stellar companions could
achieve such extraordinary luminosities, but the rapid and regular
pulsations of this source are the fingerprints of neutron stars and
clearly distinguish them from black holes. Archival data from NuStar
also revealed that the pulsar's spin rate has changed over time, from
1.43 s per rotation in 2003 to 1.13 s in 2014. The same relative
acceleration in the Earth's rotation would shorten a day by five hours
in the same time span. Only a neutron star is compact enough to keep
itself together while rotating so fast. Although it is not unusual
for the rotation rate of a neutron star to change, the high rate of
change in this case is likely to be linked to the object rapidly
consuming mass from a companion. The scientists think that there must
be a strong, complex magnetic field close to its surface, such that
accretion onto the neutron-star surface is still possible while still
generating the high luminosity.
GIANT RADIO GALAXY DISOVERED
Phys.org
An international team of astronomers reports the discovery of a new
giant radio galaxy (GRG) associated with the galaxy triplet known as
UGC 9555. The newly discovered galaxy turns out to be one of the
largest GRGs so far detected. Located some 820 million light-years
away, UGC 9555 is a part of a larger group of galaxies designated
MSPM 02158. The team has analyzed the data available in the LOFAR
Multifrequency Snapshot Sky Survey (MSSS). The images obtained as a
part of that survey allowed the scientists to distinguish a new giant
radio galaxy. It has not received any official designation yet, but
it has a projected linear size of 8.34 million light-years, making it
one of the largest GRGs known to date.
Currently, with a projected size of approximately 16 million light-
years, an object designated J1420-0545 holds the title of the largest
giant radio galaxy discovered so far. However, the available LOFAR
MSSS of the new GRG and archival radio data are still insufficient to
determine its classification. Radio sources are divided into two
classes: Fanaroff & Riley Class I (FRI) and Class II (FRII). The
researchers concluded that the luminosity suggests that the new object
is a borderline case between FRI and FRII, although the large size and
therefore old age contributes to a decreased luminosity. They hope
that further data gathered from a deep LOFAR observation will clearly
classify the properties of this GRG.
VISIBLE AND DARK MATTER KNOW ABOUT EACH OTHER
Case Western Reserve University
Research by a team of astronomers suggests that the distribution of
normal matter precisely determines gravitational acceleration in all
common types of galaxies. The team has shown that that radial
acceleration relationship exists in nearby high-mass elliptical and
low-mass spheroidal galaxies, adding to last year's discovery of the
relationship in spiral and irregular galaxies. That provides further
support for the idea that the relationship is tantamount to a new
natural law. It may demonstrate that there is a universal law for
galactic systems. That would be analogous to the Kepler law for
planetary systems, which does not care about the specific properties
of the planet: whether the planet is rocky like the Earth or gaseous
like Jupiter, the law applies. The researchers looked at 153 spiral
and irregular galaxies, 25 ellipticals and lenticulars, and 62 dwarf
spheroidals, and found that the observed acceleration tightly
correlates with the gravitational acceleration expected from visible
mass, whatever the type of galaxy. In other words, if astronomers
measure the distribution of normal matter, they know the rotation
curve, and vice versa. But it is still not clear what that
relationship means or what is its fundamental origin. Observed
deviations from the correlation are not related to any specific
galaxy property but completely random and consistent with measurement
errors, .
The tightness of the relationship is difficult to understand in terms
of dark matter as it is currently understood. It also challenges the
current understanding of galaxy formation and evolution, in which many
random processes such as galaxy mergers and interactions, inflows and
outflows of gas, star formation and supernovae, occur at the same
time. To make their discovery, researchers combined different tracers
of the centripetal acceleration found in different types of galaxies,
from which they made one-to-one comparisons. The kinematical tracers
were cold gas in spiral and irregular galaxies, stars or hot gas in
ellipticals and lenticulars, and individual giant stars in dwarf
spheroidals. The investigation included so-called ultra-faint dwarf
spheroidal galaxies, but owing to their faintness --- which makes
them hard to study --- the researchers can not confidently offer a
clear interpretation of the radial acceleration relation in those.
Nevertheless, the growing proof of the relationship, or natural law,
requires new thinking about dark matter and gravity. Within the
standard dark-matter paradigm, the law implies that the visible matter
and the dark matter must be tightly coupled in galaxies at a local
level and independently of global properties: they must 'know about
each other'. Within alternative models like modified gravity, the law
represents a key empirical constraint and may guide theoretical
physicists to build some appropriate mathematical extension of General
Relativity. The team's research so far has focused on galaxies in the
nearby Universe. The team plans to test the relationship in more
distant galaxies, just a few thousand million years after the Big
Bang. It is hoping to learn whether the same relationship holds
throughout the lifetime of the Universe.
NEURAL NETWORKS PROMISE SHARPEST EVER IMAGES
RAS
A telescope is normally limited by the size of the mirror or lens it
uses; its aperture sets a fundamental limit to its performance. Using
'neural nets', a form of artificial intelligence, a group of Swiss
researchers has now found a way to push past that limit, offering
scientists the prospect of the sharpest-ever images in optical
astronomy. A statistical concept known as the Nyquist sampling
theorem describes the resolution limit, and hence how much detail can
be seen. The Swiss authors use the latest in machine-learning
technology to challenge that limit. They teach a neural network, a
computational approach that simulates the neurons in a brain, what
galaxies look like, and then ask it to recover automatically a blurred
image and turn it into a sharp one. Just like a human being, the
neural net needs examples --- in this case a blurred and a sharp image
of the same galaxy --- to learn the technique. The system uses two
neural nets competing with one another, an emerging approach called a
'generative adversarial network', or GAN, popular with the machine-
learning research community. The whole teaching programme took just a
few hours on a high-performance computer.
The trained neural nets were able to recognize and reconstruct
features that the telescope could not resolve -- such as star-forming
regions, bars and dust lanes in galaxies. The scientists checked it
against the original high-resolution image to test its performance,
finding it better able to recover features than anything used to date,
including the 'deconvolution' approach used to improve the images made
in the early years of the Hubble space telescope. Researchers can
start by going back to sky surveys made with telescopes over many
years, see more detail than ever before, and for example learn more
about the structure of galaxies. There is no reason why the technique
cannot then be applied to the deepest images from Hubble, and from the
coming James Webb space telescope, to learn more about the earliest
structures in the Universe. The success of the project points to a
more 'data-driven' future for astrophysics in which information is
learnt automatically from data, instead of manually crafted physics
models. `
Topic: Early March Astronomy Bulletin (Read 2363 times)