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Another Popular Astronomy Note. More will follow.
DAWN MISSION TO CERES EXTENDED
NASA
NASA has authorized a second extension of the Dawn mission at Ceres, the
largest object in the asteroid belt between Mars and Jupiter. During
this extension, the spacecraft, which has been orbiting Ceres since 2015
March, will descend to lower altitudes than ever before. The spacecraft
will continue at Ceres for the remainder of its investigation and will
remain in a stable orbit indefinitely after its hydrazine fuel runs out.
The Dawn flight team is studying ways to manoeuvre Dawn into a new
elliptical orbit, which may take the spacecraft to less than 200 km from
the surface of Ceres at closest approach. Previously, Dawn's lowest
altitude was 385 km. A priority of the second Ceres mission extension
is collecting data with Dawn's gamma-ray and neutron spectrometer,
which measures the number and energy of gamma rays and neutrons. That
information is important for understanding the composition of Ceres'
uppermost layer and how much ice it contains. The spacecraft will also
take visible-light images of Ceres' surface with its camera, as well as
measurements of Ceres' mineralogy with its visible and infrared mapping
spectrometer.
The extended mission additionally allows Dawn to be in orbit while Ceres
goes through perihelion, its closest approach to the Sun, which will
occur in 2018 April. At closer proximity to the Sun, more ice on Ceres'
surface may turn to water vapour, which may in turn contribute to the
weak transient atmosphere detected by ESA's Herschel space observatory
before Dawn's arrival. Building on Dawn's findings, the team has
hypothesized that water vapour may be produced in part from energetic
particles from the Sun interacting with ice at shallow depths in Ceres'
surface. Scientists will combine data from ground-based observatories
with Dawn's observations to study these phenomena further as Ceres
approaches perihelion.
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Popular Astronomy Note: Electronic News Bulletin No. 456 2017 November 5
FRESH FINDINGS FROM CASSINI
NASA
The Cassini spacecraft ended its journey on Sept. 15 with an intentional
plunge into the atmosphere of Saturn, but analysis continues on the
mountain of data the spacecraft sent during its long 'life'. The
spacecraft's Ion and Neutral Mass Spectrometer (INMS) returned a lot
of direct measurements of the components in Saturn's upper atmosphere,
which stretches almost to the rings. From those observations, the team
sees evidence that molecules from the rings are raining down onto the
atmosphere. That influx of material from the rings was expected, but
INMS data show hints of ingredients more complex than just water, which
makes up the bulk of the rings' composition. In particular, the
instrument detected methane, a volatile molecule that scientists would
not expect to be abundant in the rings or found so high in Saturn's
atmosphere.
Chief among the questions that scientists hope to answer by using data
from Cassini is the age and origin of the rings. Theoretical modelling
has shown that, without forces to confine them, the rings would spread
out over hundreds of millions of years -- much younger than Saturn
itself. Such spreading happens because faster-moving particles that
orbit closer to Saturn occasionally collide with slower particles on
slightly farther-out orbits. When that happens, some momentum from the
faster particles is transferred to the slower particles, speeding the
latter up in their orbit and causing them to move farther out. The
inverse happens to the faster, inner particles. Previous research had
shown that gravitational tugs from the moon Mimas are solely responsible
for halting the outward spread of Saturn's B ring -- that ring's outer
edge is defined by the dark region known as the Cassini Division. Ring
scientists had thought that the small moon Janus was responsible for
confining the outer edge of the A ring, but a new modelling study shows
that the A ring's outward creep is kept in check by a confederation of
moons, including Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus and
Mimas.
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Thanks, DW. There are so many new findings. I had to google Ceres and Dawn.
Ceres:
https://en.wikipedia.org/wiki/Ceres_(dwarf_planet)
Dawn:
(old article)
http://earthsky.org/space/dawn-at-ce...stery-features
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The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 456 2017 November 5
ASTEROID VISITS FROM BEYOND SOLAR SYSTEM
NASA
A small, recently discovered asteroid -- or perhaps a comet -- appears
to have originated from outside the Solar System, coming from somewhere
else in our Galaxy. If so, it would be the first 'interstellar object'
to be observed and confirmed by astronomers. The unusual object -- for
now designated A/2017 U1 -- is less than 400 metres in diameter and is
moving remarkably fast. Astronomers are using telescopes around the
world and in space to observe this notable object, in an effort to learn
about the origin and possibly composition of the object. A/2017 U1 was
discovered on October 19 by the University of Hawaii's Pan-STARRS 1
telescope during the course of its nightly search for near-Earth objects.
Astronomers immediately realized that it was an unusual object. Its
motion could not be explained as either a normal Solar-System asteroid
orbit or a comet orbit. Combined data from follow-up images taken at
the ESA telescope on Tenerife proved that the object came from outside
the Solar System. It is the most extreme orbit that NASA scientists
have ever seen. The object is moving extremely fast, and on such a
trajectory that we can say with confidence that it is on its way out of
the Solar System and will not come back. The team plotted the object's
current trajectory and even looked into its future. A/2017 U1 came from
the direction of the constellation Lyra, cruising through interstellar
space at a brisk 25.5 km/s.
The object approached the Solar System from almost directly 'above' the
ecliptic, the approximate plane in space where the planets and most
asteroids orbit the Sun, so it did not have close encounters with any
of the major planets during its plunge toward the Sun. On Sept. 2, the
small body crossed under the ecliptic plane just inside Mercury's orbit
and then made its closest approach to the Sun on Sept. 9; answering to
the Sun's gravity, it made a hairpin turn under our Solar System,
passing under the Earth's orbit on Oct. 14 at a distance of about 24
million kilometres -- about 60 times the distance to the Moon. It has
now shot back up above the plane of the planets and, travelling at
44 km/s with respect to the Sun, is speeding toward the constellation
Pegasus. Astronomers have long suspected that such objects should
exist, because during the process of planet formation a lot of material
should be ejected from planetary systems. What is surprising is that we
have never seen interstellar objects pass through before. Since this is
the first object of its type ever discovered, rules for naming such
objects will need to be established by the International Astronomical
Union.
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The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 456 2017 November 5
AMATEUR DETECTS COMET ORBITING DISTANT STAR
RAS
A 'citizen scientist' was the first to detect tell-tale signs that a
comet was orbiting a distant star monitored by the Kepler space
observatory. The discovery marks the first time that the presence of an
object as small as a comet has been inferred by observing dips in the
intensity of light from a star. Such dips usually signal crossings of
planets or other objects in front of the star, which briefly block a
small fraction of its light. In this case things were different: the
researchers were able to pick out the comet's tail, a trail of gas and
dust, which blocked about 0.1 per cent of the star's light as the comet
streaked by. The data came from the Kepler space telescope, a stellar
observatory that was launched in 2009. For four years, the spacecraft
monitored about 200,000 stars for dips in brightness caused by transit-
ing exoplanets. To date, the mission has identified and confirmed more
than 2,400 exoplanets, mostly orbiting stars in the constellation
Cygnus, with the help of automated algorithms that quickly sift through
the data, looking for the characteristic dips. The smallest exoplanets
detected thus far measure about one-third the diameter of the Earth.
Comets, in comparison, are only the size of a small city at their
largest, making them much more difficult to detect. But on March 18
this year Thomas Jacobs, an amateur astronomer who makes it his hobby to
comb through Kepler's data, was able to pick out several curious light
patterns amid the noise. Jacobs is part of the 'Planet Hunters'
citizen-scientist project established by Yale University, which enlists
amateur astronomers in the search for exoplanets. The idea was that the
human eye might be able to notice things that a computer would miss.
Astronomers could name 10 types of objects that those people have found
in the Kepler data but that algorithms could not find, because of the
pattern-recognition capability of the human eye. During the search, the
amateur observed three unusual dips in the light coming from KIC
3542116, a faint star located 800 light-years away - he flagged the
events and alerted a professional astronomer with whom he had collab-
orated in the past to interpret his findings. A further three transits
were subsequently found. The asymmetry in the light curves resembled
disintegrating planets, with long trails of debris that would continue
to block a bit of light as the planet moves away from the star.
However, such disintegrating planets orbit their star, transiting
repeatedly. In contrast, no such periodic pattern had been observed in
the transits identified. The only kind of body that could do the same
thing and not repeat is one that probably gets destroyed in the end. In
other words, instead of repeatedly orbiting the star, the objects must
have transited, then ultimately flown too close to the star, and
vaporised. The only thing that fits the bill, and has a small enough
mass to be destroyed, is a comet.
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Interesting links, DW! Now comes an astronomical crime story!
The brown dwarf that killed its brother
"How do you kill a star? Apparently, all it takes is a nearby companion, astronomers have found. After spotting a system consisting of a low-mass white dwarf (a stellar remnant from a star 0.5-8 times the Sun’s mass) and a “failed star” or brown dwarf, a Brazilian team of astronomers determined that the white dwarf was the result of a normal star’s “premature death” brought about by its tiny companion.
The work, published September 21 in the Monthly Notices of the Royal Astronomical Society, explores a low-mass binary system consisting of a 0.2-0.3-solar-mass white dwarf, and a 34-46-Jupiter-mass brown dwarf. Located in the constellation Perseus, this binary once held a normal, Sun-like star and a small substellar object, perhaps a brown dwarf (depending on its initial mass). But as the normal star began to swell into a red giant , the smaller object was engulfed — and instead of being destroyed, it triggered a massive ejection of material from the red giant that killed it instead."
http://www.astronomy.com/news/2017/1...-dwarf-brother
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https://www.universetoday.com/137778...illions-years/
This is hardly surprising, but I look forward to the more detailed study of Enceladus in the decade or so to come. I won't be around then, but the thought is nice.
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I was going to write about this, but Danik beat me to it... Five spaces too short I am told!
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Sorry, DW! Anyway, its the dialogue that matters.
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Quote:
Originally Posted by
Dreamwoven
"Proxima Centauri, in addition to being the closest star system to our own, is also the home of the closest exoplanet to Earth. The existence of this planet, Proxima b, was first announced in August of 2016 and then confirmed later that month. The news was met with a great deal of excitement, and a fair of skepticism, as numerous studies followed t were dedicated to determining if this planet could in fact be habitable.
Another important question has been whether or not Proxima Centauri could have any more objects orbiting it. According to a recent study by an international team of astronomers, Proxima Centauri is also home to a belt of cold dust and debris that is similar to the Main Asteroid Belt and Kuiper Belt in our Solar System. The existence of this dusty belt could indicate the presence of more planets in this star system."
https://www.universetoday.com/137783...-even-planets/
They are so desperately after habitable planets that they are going to find something soon, which they think habitable. Anyway, I am sorry in advance for whoever is going to undego thr test of living on those celestial bodies. Back after breakfast to read the other links.
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I am going to try out starting a discussion of what we already know of Enceladus, the icy moon of Saturn, and one of the moons of Jupiter, Europa. I provide some links for discussion: NASA is planning to do a special study of these moon using a new probe, to see if this moon's oceans may contain life, because of the plumes of water breaking through Enceladus' icy surface. The Europa clipper probe is being planned for the 2020s. These links provide some of the background.
https://www.jpl.nasa.gov/news/news.php?feature=6942
https://www.nasa.gov/europa
https://www.nasa.gov/topics/solarsystem/index.html
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Great, DW. Before we start the discussion itself I will try to sum up some of the research trends I observed in the links we posted lately in order not to get lost with so many discoveries.
I have noticed three major trends:
-The first one is a general exploration of the celestial realm that exists beyond the solar system. Recent expeditions and more powerfull instruments have led to astonishing discoveries.The former all dominating solar system appears now as a small? part of a bigger mostly unknown whole.
-Another major focus is the interaction between celestial bodies, specially in regard of originating or destructing each other. I think this concern is related to the query how the earth itself was created and how easily it could be destructed by another celestial body.
-Last but certainly not least there is an intense interest in the study of the constitution of celestial bodies and their atmosphere. The foremost interest is this obsessive search for an habitable planet.
