HIDDEN SITES FOR HUMAN HABITATS ON MOON AND MARS
Europlanet Media Centre
Lava tubes --underground caves created by volcanic activity -- could
provide protected habitats large enough to house streets on Mars or
even towns on the Moon, according to research presented at the
European Planetary Science Congress (EPSC) 2017 in Riga. A further
study shows how the next generation of lunar orbiters will be able to
use radar to locate such structures under the Moon's surface. Lava
tubes can form in two ways. 'Overcrusted' tubes form when low-
viscosity lava flows fairly close to the surface, developing a hard
crust that thickens to create a roof above the moving lava stream.
When the eruptions end, the conduit is drained, leaving a tunnel a few
metres beneath the surface. 'Inflated' tubes are complex and deep
structures that form when lava is injected into existing fissures
between layers of rock or cavities from previous flows. The lava
expands and leaves a huge network of connected galleries as it forces
its way to the surface. Lava tubes are found in many volcanic areas
on Earth, including Lanzarote, Hawaii, Iceland, North Queensland in
Australia, Sicily, and the Galapagos islands. Underground networks of
tubes can span up to 65 kilometres. Space missions have also observed
chains of collapsed pits and 'skylights' on the Moon and Mars that
have been interpreted as evidence of lava tubes. Recently the NASA
GRAIL mission provided detailed gravity data for the Moon that
suggested the presence of enormous sub-surface voids related to lava
tubes below the lunar 'maria', plains of basalt formed in volcanic
eruptions early in the Moon's history. Scientists have also presented
a concept for a radar system specifically designed to detect lava
tubes on the Moon from orbit. The radar will probe beneath the lunar
surface with low-frequency electromagnetic waves and measure the
reflected signals. Such a radar instrument could determine accurately
the physical composition, size and shape of the caves and obtain a
global map of their locations. The studies show that a multi-
frequency sounding system is the best option for detecting lava tubes
of very different dimensions. The simulations show that lava tubes
have unique electromagnetic signatures, which can be detected from
orbit irrespective of their orientation with respect to the radar
movement direction. Therefore, an orbiter carrying such an instrument
could make a crucial step towards finding safe habitats on the Moon
for human colonisation.
MERCURY'S POLES ICIER THAN WAS THOUGHT
Brown University
The scorching-hot surface of Mercury may seem an unlikely place to
find ice, but research over the past 30 years has indicated that water
is frozen there, hidden away on crater floors that are permanently
shadowed from the Sun's blistering rays. Now, a new study suggests
that there could be much more ice on Mercury's surface than previously
thought. The study adds three new members to the list of craters
near Mercury's north pole that appear to harbour large surface ice
deposits. But in addition to those large deposits, the research also
shows evidence that smaller-scale deposits are scattered around
Mercury's north pole, both inside craters and in permanently shadowed
areas between craters. Those deposits may be small, but they could
add up to a lot of previously-unaccounted-for ice. The idea that
Mercury might have frozen water emerged in the 1990s, when Earth-based
radars detected highly reflective regions inside several craters near
Mercury's poles. The planet's axis does not have much tilt, so its
poles get little direct sunlight, and the floors of some craters get
no direct sunlight at all. Without an atmosphere to hold in any heat
from surrounding surfaces, temperatures in those eternal shadows have
been calculated to be plenty low enough for water ice to be stable.
That raised the possibility that the 'radar-bright' regions could be
ice. That idea got a boost after NASA's MESSENGER probe entered an
orbit around Mercury in 2011. The spacecraft detected neutron signals
from the planet's north pole that were consistent with water ice.
MARS ONCE HAD A DENSE ATMOSPHERE
Tokyo Institute of Technology
Exploration missions have suggested that Mars once had a warm climate,
which sustained oceans on its surface. To keep Mars warm requires a
dense atmosphere with a sufficient greenhouse effect, while at the
present day Mars has a thin atmosphere whose surface pressure is only
0.006 bar, resulting in the cold climate it has today. It has been a
big mystery as to when and how Mars lost its dense atmosphere. An old
meteorite has been known to contain a sample of the ancient Martian
atmosphere. The researchers simulated how the composition of the
Martian atmosphere might have changed throughout history under various
conditions. By comparing the results to the isotopic composition of
the trapped gas, the researchers revealed how dense the Martian
atmosphere was at the time that the gas became trapped in the
meteorite. The research team concluded that Mars had a dense
atmosphere 4 billion years ago. The surface air pressure at the time
was at least 0.5 bar and could have been much higher. Because Mars
had a magnetic field about 4 billion years ago but subsequently lost
it, the result suggests that stripping by the solar wind has been
responsible for transforming Mars from a warm wet world into a cold
desert one. NASA's MAVEN spacecraft is orbiting Mars to explore the
processes that removed the Martian atmosphere. The Japan Aerospace
Exploration Agency (JAXA) is also planning to observe the removal
processes by the Martian Moons eXploration (MMX) spacecraft. Those
missions may well reveal how the dense atmosphere predicted in this
study to have existed on ancient Mars was removed over time.
NANOSAT FLEET PROPOSED TO VISIT 300 ASTEROIDS
European Planetary Science Congress
A fleet of tiny spacecraft could visit over 300 asteroids in just
over three years, according to a mission study led by the Finnish
Meteorological Institute. The Asteroid Touring Nanosat Fleet concept
comprises 50 spacecraft propelled by innovative electric solar wind
sails (E-sails) and equipped with instruments to take images and
collect spectroscopic data on the composition of the asteroids. Each
nanosat would visit six or seven asteroids before returning to Earth
to deliver the data. In the mission scenario, the nanosats fly by
their target asteroids at a range of around 1000 kilometres. Each
nanosat carries a 4-centimetre telescope capable of imaging the
surface of asteroids with a resolution of 100 metres or better. An
infrared spectrometer analyses spectral signatures in light reflected
or emitted by the asteroid to determine its mineralogy. The instru-
ments can be pointed at the target by the use of two internal reaction
wheels inside the nanosats. E-sails make use of the solar wind -- a
stream of electrically charged particles emitted from the Sun -- to
generate efficient propulsion without the need for any propellent.
Thrust is generated by the slow rotation of a tether, attached at one
end to a main spacecraft carrying an electron emitter and a high-
voltage source and at the other to a small remote unit. The spinning
tether completes a rotation in about 50 minutes, tracing out a broad,
shallow cone around a centre of mass close to the main spacecraft.
By altering its orientation in relation to the solar wind, the nanosat
can change thrust and direction.
FARTHEST ACTIVE INBOUND COMET YET SEEN
NASA
The Hubble space telescope has photographed the most distant active
inbound comet ever seen, currently beyond the orbit of Saturn.
Slightly warmed by the remote Sun, it has already begun to develop an
80,000-mile-wide coma, enveloping a tiny, solid nucleus of frozen gas
and dust. The observations represent the earliest signs of activity
ever seen from a comet entering the Solar System's planetary zone for
the first time. The comet, called C/2017 K2 (PANSTARRS) or 'K2', has
been travelling for millions of years from its home in the frigid
outer reaches of the Solar System, where the temperature is about
minus 262 degrees Centigrade. The comet's orbit indicates that it
came from the Oort Cloud, a spherical region almost a light-year in
diameter and thought to contain hundreds of billions of comets.
Comets are the icy leftovers from the formation of the Solar System
4.6 billion years ago and therefore pristine in icy composition.
The Hubble observations of K2's coma suggest that sunlight is heating
frozen volatile gases -- such as oxygen, nitrogen, carbon dioxide, and
carbon monoxide -- that coat the comet's frigid surface. Those icy
volatiles lift off from the comet and release dust, forming the coma.
Past studies of the composition of comets near the Sun have revealed
the same mixture of volatile ices. The volatiles are spread all
through K2, and in the beginning, billions of years ago, they were
probably all through every comet presently in the Oort Cloud. But the
volatiles on the surface are the ones that absorb the heat from the
Sun, so, in a sense, the comet is shedding its outer skin. Most
comets are discovered much closer to the Sun, near Jupiter's orbit, so
by the time we see them, the surface volatiles have already been baked
off. That is why astronomers think that K2 is the most primitive
comet ever seen.
K2 was discovered in 2017 May by the Panoramic Survey Telescope and
Rapid Response System (Pan-STARRS) in Hawaii, a survey project of
NASA's Near-Earth Object Observations Program. Hubble revealed the
extent of the coma and also helped to estimate the size of the nucleus
-- less than 12 miles across -- though the tenuous coma is 10 Earth
diameters across. That vast coma must have formed when the comet was
even further away from the Sun. Digging through archival images,
astronomers uncovered views of K2 and its fuzzy coma taken in 2013 by
the Canada-France-Hawaii Telescope (CFHT) in Hawaii. But the object
was then so faint that no one noticed it. It is likely that the comet
has been continuously active for at least four years. In the CFHT
data, K2 had a coma already, when it was at 2 billion miles from the
Sun, between the orbits of Uranus and Neptune. As it approaches the
Sun, it is getting warmer and warmer, and the activity is ramping up.
But curiously, the Hubble images do not show any tail flowing from K2.
The absence of such a feature indicates that the particles lifting off
the comet are too large for radiation pressure from the Sun to sweep
them back into a tail. Astronomers will have plenty of time to
conduct detailed studies of K2. For the next five years, the comet
will continue its journey into the inner Solar System before it
reaches its closest approach to the Sun in 2022 just beyond Mars'
orbit. The James Webb space telescope, an infrared observatory
scheduled to be launched in 2018, could measure the heat from the
nucleus, which would give astronomers a more accurate estimate of its
size.
HUBBLE OBSERVES PITCH BLACK PLANET
ESA/Hubble Information Centre
Astronomers have discovered that the well-studied exoplanet WASP-12b
reflects almost no light, making it appear essentially pitch black.
That discovery sheds new light on the atmospheric composition
of the planet and also refutes previous hypotheses about WASP-12b's
atmosphere. The results are also in stark contrast to observations of
another similarly-sized exoplanet. The results are surprising, as
the measured albedo of WASP-12b is 0.064 at most. That is an
extremely low value, making the planet darker than fresh asphalt!
It makes WASP-12b two times less reflective than our Moon, which has
an albedo of 0.12. The low albedo shows that we still have a lot to
learn about WASP-12b and other similar exoplanets. WASP-12b orbits
the Sun-like star WASP-12A, about 1400 light-years away, and since its
discovery in 2008 it has become one of the best-studied exoplanets.
With a radius almost twice that of Jupiter and a year of just over one
Earth day, WASP-12b is categorised as a 'hot Jupiter'. Because it is
so close to its parent star, the gravitational pull of the star has
stretched WASP-12b into an egg shape, and its heat has raised the
surface temperature of the daylight side to 2600 degrees Celsius.
The high temperature is also the most likely explanation for
WASP-12b's low albedo. There are other hot Jupiters that have been
found to be remarkably black, but they are much cooler than WASP-12b.
For those planets, it is suggested that things like clouds and alkali
metals are the reason for the absorption of light, but those don't
work for WASP-12b because it is so incredibly hot. The daylight side
of WASP-12b is so hot that clouds cannot form and alkali metals are
ionized. It is even hot enough to break up hydrogen molecules into
atomic hydrogen, which causes the atmosphere to act more like the
atmosphere of a low-mass star than like a planetary atmosphere. That
leads to the low albedo of the exoplanet. To measure the albedo of
WASP-12b the scientists observed the exoplanet in 2016 October during
an eclipse, when the planet was near full phase and passed behind its
host star for a time. That is the best method to determine the albedo
of an exoplanet, as it involves directly measuring the amount of light
being reflected. However, that technique requires a precision ten
times greater than traditional transit observations. Using Hubble's
Space Telescope Imaging Spectrograph, the scientists were able to
measure the albedo of WASP-12b at several different wavelengths.
WASP-12b is only the second planet to have spectrally resolved albedo
measurements, the first being HD 189733b, another hot Jupiter. The
data allowed scientists to determine whether the planet reflects more
light towards the blue or the red end of the spectrum. While the
results for HD 189733b suggest that the exoplanet has a deep blue
colour, WASP-12b, on the other hand, is not reflecting light at any
wavelength. WASP-12b does, however, emit light because of its high
temperature, giving it a red hue similar to hot glowing metal.
IS MILKY WAY AN 'OUTLIER GALAXY'?
Yale University
The most-studied galaxy in the universe -- the Milky Way -- might not
be as "typical" as previously thought, according to a new study. The
Milky Way, which is home to the Earth and solar system, is host to
several dozen smaller galaxy satellites. Those smaller galaxies orbit
around the Milky Way and are useful in understanding the Milky Way
itself. Early results from the Satellites Around Galactic Analogs
(SAGA) survey indicate that the Milky Way's satellites are much more
tranquil than other systems of comparable luminosity and environment.
Many satellites of those 'sibling' galaxies are actively pumping out
new stars, but the researchers found that the Milky Way's satellites
are mostly inert. That is significant, according to the researchers,
because many models for what we know about the universe rely on
galaxies behaving in a fashion similar to the Milky Way. The SAGA
survey began five years ago with a goal of studying the satellite
galaxies around 100 Milky Way siblings. Thus far it has studied eight
other Milky Way sibling systems, which the researchers say is too
small a sample to come to any definitive conclusions. SAGA expects
to study 25 Milky Way siblings in the next two years.
BLACK HOLE COLLISION DETECTED
National Science Foundation
In August, detectors on two continents recorded gravitational-wave
signals from a pair of black holes colliding. That discovery is the
first observation of gravitational waves by three different detectors,
marking a new era of greater insights and improved localization of
cosmic events now available through globally networked gravitational-
wave observatories. The collision was observed on Aug. 14 at 10:30:43
UTC by two Laser Interferometer Gravitational-Wave Observatory (LIGO)
detectors located in Louisiana and Washington, and the Virgo detector
located in Italy. The collision is designated GW170814. The detected
gravitational waves -- ripples in space and time -- were emitted
during the final moments of the merger of two black holes, one with a
mass about 31 times that of our Sun, the other about 25 times the mass
of the Sun. The event, located about 1.8 billion light-years away,
resulted in a spinning black hole with about 53 times the mass of our
Sun -- that means about three solar masses were converted into
gravitational-wave energy during the coalescence. When an event is
detected by a three-detector network, the area in the sky likely to
contain the source shrinks significantly, improving distance accuracy.
The sky region for GW170814 has a size of only 60 square degrees, more
than 10 times smaller than the size using data available from the two
LIGO interferometers alone. Being able to identify a smaller search
region is important, because many compact-object mergers -- for
example those involving neutron stars -- are expected to produce
broadband electromagnetic emissions in addition to gravitational
waves. The precise pointing information enabled 25 partner facilities
to perform follow-up observations based on the LIGO-Virgo detection,
but no counterpart was identified -- as expected for black holes.
COSMIC RAYS FROM A DISTANT GALAXY
Michigan Technological University
Astronomers have definitively answered the question of whether cosmic
particles emanate from outside the Milky Way Galaxy. Studying the
distribution of the cosmic-ray arrival directions is the first step in
determining where extragalactic particles originate. The collabor-
ating scientists were able to make their recordings using the largest
cosmic-ray observatory ever built, the Pierre Auger Observatory in
Argentina, which involves more than 400 scientists from 18 countries.
Scientists are now considerably closer to solving the mystery of where
and how those extraordinary particles are created, a question of great
interest to astrophysicists. Cosmic rays are the nuclei of elements
from hydrogen to iron. Studying them gives scientists a way to study
matter from outside our solar system -- and now, outside our galaxy.
Cosmic rays help us to understand the composition of galaxies and the
processes that occur to accelerate the nuclei to nearly the speed of
light. By studying cosmic rays, scientists may come to understand
what mechanisms create the nuclei. Astronomer Carl Sagan once said,
"The nitrogen in our DNA, the calcium in our teeth, the iron in our
blood, the carbon in our apple pies, were made in the interiors of
collapsing stars. We are made of starstuff." To put it simply,
understanding cosmic rays and where they originate can help us to
answer fundamental questions about the origins of the Universe, our
galaxy and ourselves.
It is extremely rare for cosmic rays with energies greater than two
joules to reach the Earth; the rate of their arrival at the top of
the atmosphere is only about one per square kilometre per year, the
equivalent to one cosmic ray hitting an area the size of a soccer
field about once per century. A joule is a measure of energy; one
joule is equivalent to one 3,600th of a watt-hour. When a single
cosmic-ray particle hits the Earth's atmosphere, that energy is
deposited within a few millionths of a second. Such rare particles
are detectable because they create showers of electrons, photons and
muons through successive interactions with the nuclei in the
atmosphere. The showers spread out, sweeping through the atmosphere
at the speed of light in a disc-like structure, like a giant
dinner-plate, several kilometres in diameter. They contain more than
10 billion particles. At the Pierre Auger Observatory, cosmic rays
are detected by measuring the Cherenkov light -- electromagnetic
radiation emitted by charged particles passing through a medium, such
as water, at greater than the phase velocity of light in that medium.
The team measures the Cherenkov light produced in a detector, which is
a large plastic structure that contains 12 tons of water. They pick
up a signal in a few detectors within an array of 1,600 detectors.
The detectors are spread over 3,000 square kilometres in western
Argentina. The times of arrival of the particles at the detectors,
measured with GPS receivers, are used to determine the direction from
which the particles came within approximately one degree.
By studying the distribution of the arrival directions of more than
30,000 cosmic particles, the Auger Collaboration has discovered an
anisotropy, which is the difference in the rate of cosmic-ray arrivals
depending on which direction you look. That means that the cosmic
rays do not come uniformly from all directions; there is a direction
from which the rate is highest. The anisotropy is significant at
5.2 standard deviations (a chance of about one in five million) in
a direction where the distribution of galaxies is relatively high.
Although that discovery clearly indicates an extragalactic origin for
the particles, the specific sources of the cosmic rays are still
unknown. The direction points to a broad area of sky rather than to
specific sources, because even such energetic particles are deflected
by a few tens of degrees in the magnetic field of our Galaxy. There
have been cosmic rays observed with even higher energy those used in
the Pierre Auger Collaboration study, some even with the kinetic
energy of a well-struck tennis ball. As the deflections of such
particles are expected to be smaller because of their higher energy,
the arrival directions should point closer to their birthplaces. Such
cosmic rays are even rarer, and further studies are under way to pin
down which extragalactic objects are the sources. Knowledge of the
nature of the particles will aid such identification, and continuing
work on this problem is targeted in the upgrade of the Auger
Observatory to be completed in 2018.
ALMA AND ROSETTA DETECT FREON-40 IN SPACE
ESO
Using data captured by ALMA in Chile and from the ROSINA instrument on
ESA's Rosetta mission, a team of astronomers has found faint traces of
the chemical compound Freon-40 -- (CH3Cl), also known as methyl
chloride and chloromethane, around both the infant star system IRAS
16293-2422, about 400 light-years away, and the famous comet
67P/Churyumov-Gerasimenko (67P/C-G) in our own Solar System. The new
ALMA observation is the first detection ever of a stable organohalogen
in interstellar space. Organohalogens consist of halogens, such as
chlorine and fluorine, bonded with carbon and sometimes other
elements. On Earth, such compounds are created by some biological
processes -- in organisms ranging from humans to fungi -- as well as
by industrial processes such as the production of dyes and medical
drugs. The new discovery of one such compound, Freon-40, in places
that must predate the origin of life, can be seen as a disappointment,
as earlier research had suggested that such molecules could indicate
the presence of life. Exoplanet research has gone beyond the point of
finding planets -- more than 3000 exoplanets are now known -- to
looking for chemical markers that might indicate the potential
presence of life. A vital step is determining which molecules could
indicate life, but establishing reliable markers remains a tricky
process. ALMA's discovery of organohalogens in the interstellar
medium also tells us something about the starting conditions for
organic chemistry on planets. Such chemistry is an important step
toward the origins of life. On the basis of this discovery, organo-
halogens are likely to be a constituent of the so-called 'primordial
soup', both on the young Earth and on nascent rocky exoplanets. That
suggests that astronomers may have viewed things round the wrong way;
rather than indicating the presence of existing life, organohalogens
may be an important element in the little-understood chemistry
involved in the origin of life.
Using ALMA, astronomers have previously found precursors to sugars
and amino acids around different stars. The additional discovery
of Freon-40 around Comet 67P/C-G strengthens the links between the
pre-biological chemistry of distant proto-stars and our own Solar
System. The astronomers also compared the relative amounts of
Freon-40 that contain different isotopes of chlorine in the infant
star system and the comet -- and found similar abundances. That
supports the idea that a young planetary system can inherit the
chemical composition of its parent star-forming cloud, and opens
the possibility that organohalogens could arrive on planets in young
systems during planet formation or via comet impacts. The results
shows that we still have more to learn about the formation of
organohalogens. Additional searches for organohalogens around other
proto-stars and comets need to be undertaken to help find the answer.
INVESTIGATION REVEALS RESTING PLACE OF SMART-1
RAS
Observations of the Moon have revealed the final resting place of the
European Space Agency's first lunar mission, SMART-1. The spacecraft
was sent to a controlled impact with the lunar surface 11 years ago.
Although an impact flash was imaged at the time by the Canada-France-
Hawaii Telescope on the dark side of the boundary between night and
day on the lunar surface, the exact location has not been identified
until now. Scientists say that SMART-1 had a hard, grazing and
bouncing landing at 2 km/s on the surface of the Moon. There were no
other spacecraft in orbit at the time to give a close-up view of the
impact, and finding the precise location became a 'cold case' for more
than 10 years. For this 'crash scene investigation', scientists used
all possible observational facts and computer models to identify the
exact site and have finally found the scars. The next step will be
to send a robotic investigator to examine the remains of the SMART-1
spacecraft body and 'wings' of the solar arrays. The location is
34°.262 south and 46°.193 west, consistent with the coordinates of
impact calculated initially. The SMART-1 impact site was discovered
from high-resolution images from NASA's Lunar Reconnaissance Orbiter
(LRO). The images show a linear gouge in the surface, about 4 metres
wide and 20 metres long, cutting across a small pre-existing crater.
At the far end, a faint fan of ejecta sprays out to the south.
Topic: Early October Astronomy Bulletin (Read 3090 times)