FRAGMENT PROBABLY FROM THE EARTH'S FORMATION RETURNS
ESO
Astronomers have found a unique object that appears to be made of
inner-Solar-System material from the time of the Earth's formation,
which has been preserved in the Oort Cloud far from the Sun for
thousands of millions of years. Observations with the Very Large
Telescope, and the Canada-France-Hawaii Telescope, show that C/2014 S3
(PANSTARRS) is the first object to be discovered on a long-period
cometary orbit that has the characteristics of a pristine inner-Solar-
System asteroid. It may provide important clues as to how the Solar
System formed. Observations indicate that it is an ancient rocky
body, rather than a contemporary asteroid that strayed out. As such,
it is one of the potential building blocks of the rocky planets, such
as the Earth, that was expelled from the inner Solar System and
preserved in the deep freeze of the Oort Cloud for thousands of
millions of years. C/2014 S3 (PANSTARRS) was originally identified by
the Pan-STARRS1 telescope as a weakly active comet a little over twice
as far from the Sun as the Earth. Its current long orbital period
(around 860 years) suggests that its source was in the Oort Cloud, and
it was nudged comparatively recently into an orbit that brings it
closer to the Sun. The team immediately noticed that C/2014 S3 was
unusual, as it does not have the characteristic tail that most long-
period comets have when they approach so close to the Sun. As a
result, it has been dubbed a Manx comet, after the tailless cat.
Within weeks of its discovery, the team obtained spectra of the very
faint object with the Very Large Telescope in Chile.
Study of the light reflected by C/2014 S3 indicates that it is typical
of asteroids known as S-type, which are usually found in the inner
asteroid main belt. It does not look like typical comets, which are
believed to form in the outer Solar System and are icy rather than
rocky. It appears that the material has undergone very little
processing, indicating that it has been deep-frozen for a very long
time. The very weak comet-like activity associated with C/2014 S3,
which is consistent with the sublimation of water ice, is about a
million times lower than is exhibited by active long-period comets at
similar distances from the Sun. Astronomers conclude that the object
is probably made of fresh inner-Solar-System material that has been
stored in the Oort Cloud and is now making its way back into the inner
Solar System. Various theoretical models are able to reproduce much
of the structure that we see in the Solar System. An important
difference between the models is what they predict about the objects
that make up the Oort Cloud. Different models predict significantly
different ratios of icy to rocky objects. This first discovery of a
rocky object from the Oort Cloud therefore initiates a potentially
important test of the different predictions of the models. The
authors estimate that observations of 50--100 such Manx comets will be
needed to distinguish between the current models, so it promises to be
a long time before such a study can throw much light on the origins of
the Solar System.
CLUES ABOUT VOLCANOES UNDER ICE ON ANCIENT MARS
NASA
New evidence from the Mars Reconnaissance Orbiter, which has been
circling Mars since 2006, suggests that volcanoes erupted beneath an
ice sheet thousands of millions of years ago, far from any ice sheet
on Mars today. The research on the volcanoes indicates that there was
extensive ice on ancient Mars. It also adds information about an
environment combining heat and moisture, which could have provided
favourable conditions for microbial life. Researchers used the
orbiter's mineral-mapping spectrometer to investigate surface
composition in an oddly textured region of southern Mars called
Sisyphi Montes. The region is studded with flat-topped mountains.
Other researchers previously noted those domes' similarity in shape to
volcanoes on Earth that erupted underneath ice. When a volcano begins
erupting beneath a sheet of ice on Earth, the rapidly generated steam
typically leads to explosions that punch through the ice and propel
ash high into the sky. For example, the 2010 eruption of ice-covered
Eyjafjallajokull in Iceland lofted ash that disrupted air travel
across Europe for about a week. Characteristic minerals resulting
from such sub-glacial vulcanism on Earth include zeolites, sulphates
and clays. Those are just what the new research has detected at some
flat-topped mountains in the Sisyphi Montes region examined with the
spacecraft's 'imaging spectrometer', which has a resolution of about
18 metres per pixel. The Sisyphi Montes region extends from about 55
to 75 degrees south latitude. Some of the sites that have shapes and
compositions consistent with volcanic eruptions beneath an ice sheet
are about 1,600 kilometres from the current south-polar ice cap of
Mars. The cap now has a diameter of about 350 kilometres.
CASSINI EXPLORES METHANE SEA ON TITAN
NASA
A new study finds that a large sea on Saturn's moon Titan is composed
mostly of pure liquid methane, independently confirming an earlier
result. The sea bed may be covered in a sludge of carbon- and
nitrogen-rich material, and its shores may be surrounded by wetlands.
Of the hundreds of moons in the Solar System, Titan is the only one
with a dense atmosphere and large liquid reservoirs on its surface,
making it in some ways more like a terrestrial planet. Both the Earth
and Titan have nitrogen-dominated atmospheres -- over 95% nitrogen in
Titan's case. However, unlike the Earth, Titan has very little
oxygen; the rest of the atmosphere is mostly methane and trace amounts
of other gases, including ethane. At the frigid temperatures found at
Saturn's distance from the Sun, the methane and ethane can exist on
the surface in liquid form. For that reason, scientists had long
speculated about the possible existence of hydrocarbon lakes and seas
on Titan, and data from the Cassini-Huygens mission do not disappoint.
Since arriving in the Saturn system in 2004, the Cassini spacecraft
has revealed that more than 1.6 million square kilometres of Titan's
surface -- almost 2% of the total -- are covered in liquid. There are
three large seas, all located close to the moon's north pole,
surrounded by numerous of smaller lakes in the northern hemisphere.
Just one large lake has been found in the southern hemisphere. The
exact composition of those liquid reservoirs remained elusive until
2014, when the Cassini radar instrument was first used to show that
Ligeia Mare, the second-largest sea on Titan and bigger than any of
the American Great Lakes, is methane-rich. The new study is based on
data collected with Cassini's radar instrument during fly-bys of Titan
between 2007 and 2015.
During a 2013 experiment, the radar instrument detected echoes from
the sea floor and inferred the depth of the sea along Cassini's track
over Ligeia Mare -- the first-ever detection of the bottom of an
extra-terrestrial sea. The scientists were surprised to find depths
in the sea as great as 160 metres at the deepest point along the radar
track. In the atmosphere of Titan, nitrogen and methane react to
produce a wide variety of organic materials. Scientists believe that
the heaviest materials fall to the surface. They think that when
those compounds reach the sea, either by falling directly from the
air, by rain or through Titan's rivers, some are dissolved in the
liquid methane. Insoluble compounds, such as nitriles and benzene,
sink to the sea floor. The study also found that the shoreline around
Ligeia Mare may be porous and flooded with liquid hydrocarbons. The
data span a period running from local winter to spring, and the
scientists expected that -- as on Earth -- the surrounding solid
ground would warm more rapidly than the sea. However, Cassini's
measurements did not show any significant difference between the sea's
temperature and that of the shore over that time interval. That
suggests that the terrain surrounding the lakes and seas is wet with
liquid hydrocarbons, which would make them warm up and cool down much
like the sea itself.
LARGEST UN-NAMED OBJECT IN THE SOLAR SYSTEM
NASA
With the exception of Ceres, which is in the main asteroid belt
between Mars and Jupiter, all 'dwarf planets' in the Solar System are
in the depths beyond Neptune. They are far from the Earth, small
and cold, which makes them difficult to observe, even with large
telescopes. So it is little wonder that astronomers discovered most
of them only in the past decade or so. Pluto, the largest of the
dwarf planets, is a prime example of such elusiveness. Before the New
Horizons spacecraft visited it in 2015, Pluto had appeared as little
more than a slightly fuzzy star, even to the Space Telescope. Given
the inherent challenges in trying to observe such far-flung planets,
astronomers often need to combine data from a variety of sources just
to derive basic information about their properties. Recently, a group
of astronomers did that by combining data from two space observatories
to reveal something surprising: a dwarf planet named 2007 OR10 is
significantly larger than was previously thought. The results put
2007 OR10 as the largest un-named planet in the Solar System and the
third-largest of the current roster of about half a dozen dwarf
planets. The study also found that the object is quite dark and is
rotating more slowly than almost any other body orbiting the Sun
(Mercury, Venus and Pluto excepted), taking close to 45 hours to
complete its daily spin.
For their research, the scientists used the re-purposed planet-hunting
Kepler space telescope -- its mission now known as K2 -- along with
the archival data from the infrared Herschel space observatory. The
revised measurement of the planet's diameter, 1,535 km, is about 100
km greater than that of the next-largest dwarf planet, Makemake, or
about one-third smaller than Pluto. Another dwarf planet, named
Haumea, has an oblong shape that is larger along its long axis than
2007 OR10, but its overall volume is smaller. Like its predecessor
mission, K2 searches for the change in brightness of distant objects.
A tiny dip in the brightness of a star can be the signature of a
planet transiting, in front. Much closer to home, K2 also watches
small Solar-System bodies such as comets, asteroids, moons and dwarf
planets. Because of its sensitivity to small changes in brightness,
Kepler is an excellent instrument for observing the brightnesses of
distant Solar-System objects and how they change as they rotate.
THREE POTENTIALLY HABITABLE PLANETS
ESO
Astronomers using the TRAPPIST telescope at the La Silla Observatory
have discovered three planets orbiting a cool dwarf star just 40
light-years away. The planets have sizes and temperatures similar to
those of Venus and the Earth and are the best places found so far to
search for life outside the Solar System. They are the first planets
to be discovered around such a tiny and dim star. The team found that
the star faded slightly at regular intervals, indicating that several
objects were passing between it and us. Detailed analysis showed that
three planets with sizes similar to that of the Earth were present.
TRAPPIST-1 is much cooler and redder than the Sun and barely larger
than Jupiter. Such stars are both very common in the Milky Way and
very long-lived, but this is the first time that planets have been
found around one of them. Despite being so 'close' to the Earth, the
star is too dim and too red to be seen with the naked eye or even
visually with a large amateur telescope. It lies in the constellation
Aquarius. Astronomers will search for signs of life by studying the
effect that the atmosphere of a transiting planet has on the light
reaching the Earth. For Earth-sized planets orbiting most stars, that
tiny effect is swamped by the brilliance of the star light. Only for
the case of faint, red, very cool dwarf stars like TRAPPIST-1 is that
effect liable to be big enough to be detected.
Follow-up observations with larger telescopes, including the HAWK-I
instrument on the 8-m Very Large Telescope in Chile, have shown that
the planets orbiting TRAPPIST-1 have sizes very similar to that of the
Earth. Two of the planets have orbital periods of about 1.5 days and
2.4 days respectively, and the third has a much less well determined
period in the range 4.5 to 73 days. With such short orbital periods,
the planets are very much closer to their star than the Earth is to
the Sun. The structure of that planetary system is much more similar
in scale to the system of Jupiter's moons than to that of the Solar
System. Although they orbit very close to their host star, the inner
two planets receive only four times and twice, respectively, the
amount of radiation received by the Earth, because their star is much
fainter than the Sun. That still puts them closer to their star than
the 'habitable zone' for that system, although it remains possible
that they possess habitable regions on their surfaces. The third,
outer, planet's orbit is not yet known, but the object probably
receives less radiation than the Earth does, though perhaps still
enough to lie within the habitable zone. Thanks to several giant
telescopes currently under construction, including E-ELT and the Webb
space telescope due for launch in 2018, we should soon be able to
study the atmospheric composition of those planets and to explore them
first for water, then for traces of biological activity. That would
be a considerable step in the search for life elsewhere in the
Universe.
This work opens up a new direction for exo-planet hunting, as around
15% of the stars near to the Sun are very cool dwarf stars, and it
also serves to highlight that the search for exo-planets is now
entering the realm of potentially habitable cousins of the Earth.
EXTRAGALACTIC SOURCE OF HIGH-ENERGY NEUTRINOS
Julius-Maximilians-Universitet Wurzburg
Nearly 10 billion years ago in a galaxy known as PKS B1424-418, a
dramatic explosion occurred. Light from the blast began arriving at
the Earth in 2012. Now, an international team of astronomers has
shown that a record-breaking neutrino seen at about the same time
probably originated in the same event. Neutrinos are the fastest,
lightest, most unsociable and least understood fundamental particles,
and scientists are only just now capable of detecting high-energy ones
arriving from deep space. The present work provides the first
plausible association between a single extragalactic object and one
such cosmic neutrino. Although neutrinos are supposed to outnumber by
far all the atoms in the Universe, they rarely interact with matter,
which makes detecting them quite a challenge. But that same property
lets neutrinos make a fast exit from places where light cannot easily
escape, such as the core of a collapsing star, and travel across the
Universe almost completely unimpeded. Neutrinos can provide
information about processes and environments that are simply not
accessible through a study of light alone. Recently, the IceCube
Neutrino Observatory at the South Pole found the first evidence for a
flux of extra-terrestrial neutrinos. To date, the scientific team of
IceCube Neutrino has announced about a hundred very-high-energy
neutrinos. On 2012 December 4, IceCube detected a neutrino with an
energy exceeding 2 x 10 to the 15 electron volts (2 PeV). To put that
in perspective, it is more than 10 to the 12 times greater than the
energy of a dental X-ray packed into a single particle thought to
possess less than a millionth of the mass of an electron. That was
the highest-energy neutrino ever detected at the time and still ranks
second. Where did it come from? The best IceCube position narrowed
the source only to a patch of the southern sky about 32 degrees
across.
Starting in the summer of 2012, the Fermi satellite witnessed a
dramatic brightening of PKS B1424-418, an active galaxy classified as
a gamma-ray blazar. An active galaxy is an otherwise typical galaxy
with a compact and unusually bright core. The excess luminosity of
the central region is produced by matter falling toward a supermassive
black hole having millions of times the mass of our Sun. As it
approaches the black hole, some of the material becomes channelled
into particle jets moving outward in opposite directions at nearly the
speed of light. In blazars one of the jets happens to point almost
directly towards us. During the year-long outburst, PKS B1424-418
shone between 15 and 30 times brighter in gamma rays than its average
before the eruption. The blazar is located within the high-energy-
neutrino source region, but then so are many other active galaxies
detected by Fermi. The scientists searching for the neutrino source
then turned to data from a long-term observing programme named TANAMI.
Since 2007, TANAMI has routinely monitored nearly 100 active galaxies
in the southern sky, including many flaring sources detected by Fermi.
Three radio observations between 2011 and 2013 cover the period of the
Fermi outburst. They reveal that the core of the galaxy's jet had
been brightening by about four times. No other galaxy observed by
TANAMI over the duration of the programme has exhibited such a
dramatic change. Within their jets, blazars are capable of
accelerating protons to relativistic energies. Interactions of such
protons with light in the central regions of the blazar can create
pions. When the pions decay, both gamma rays and neutrinos are
produced. Researchers combed through the field where the neutrino
must have originated, looking for astrophysical objects capable of
producing high-energy particles and light. There was a 'eureka'
moment when they realized that the most dramatic outburst ever seen
in a blazar happened in just the right place at just the right time.
The team suggests that the PKS B1424-418 outburst and the energetic
neutrino are linked, calculating only a 5% probability that the two
events occurred independently. Using data from the Fermi, Swift and
WISE satellites, the LBA and other facilities, the researchers
determined how the energy of the eruption was distributed across the
electromagnetic spectrum and showed that it was sufficiently powerful
to produce a neutrino at PeV energies. Taking into account all of the
observations, the researchers consider the blazar to be the prime
suspect as the origin of the neutrino.
Topic: Mid May Astronomy Bulletin (Read 1645 times)