THE MOON ONCE HAD AN ATMOSPHERE
Lunar and Planetary Institute
A new study shows that an atmosphere was produced around the ancient
Moon, 3 to 4 (US-)billion years ago, when intense volcanic eruptions
spewed gases above the surface faster than they could escape to space.
When one looks at the Moon, dark surfaces of volcanic basalt can easily
be seen to fill large impact basins. Those seas of basalt, known as
maria, erupted while the interior of the Moon was still hot and
generating magmatic plumes that sometimes breached the surface and
flowed for hundreds of kilometres. Analyses of Apollo samples indicate
that those magmas carried gas components, such as carbon monoxide, the
ingredients for water, sulphur, and other volatile species. In new
work, astronomers have calculated the amounts of gases that rose from
the erupting lavas as they flowed over the surface and showed that those
gases accumulated around the Moon to form a transient atmosphere. The
atmosphere was thickest during the peak in volcanic activity about 3.5
billion years ago and, when created, would have persisted for about 70
million years before being lost to space.
The two largest pulses of gases were produced when lava seas filled the
Serenitatis and Imbrium basins about 3.8 and 3.5 billion years ago,
respectively. The margins of those lava seas were explored by astro-
nauts on the Apollo 15 and 17 missions, who collected samples that not
only provided the ages of the eruptions, but also contained evidence of
the gases produced from the erupting lavas. This new picture of the
Moon has important implications for future exploration. The analysis of
Needham and Kring quantifies a source of volatiles that may have been
trapped from the atmosphere into cold, permanently shadowed regions near
the lunar poles and, thus, may provide a source of ice suitable for a
sustained lunar exploration program. Volatiles trapped in icy deposits
could provide air and fuel for astronauts conducting lunar-surface
operations and, potentially, for missions beyond the Moon.
MARS STUDY YIELDS CLUES TO POSSIBLE CRADLE OF LIFE
NASA
The discovery of evidence for ancient sea-floor hydrothermal deposits
on Mars identifies an area on the planet that may offer clues about
the origin of life on Earth. A recent report examines observations by
NASA's Mars Reconnaissance Orbiter (MRO) of massive deposits in a basin
in the southern hemisphere of Mars. The authors interpret the data as
evidence that those deposits were formed by heated water from a volcan-
ically active part of the planet's crust entering the bottom of a large
sea long ago. Mars today has neither standing water nor volcanic
activity. Researchers estimate an age of about 3.7 billion years for
the Martian deposits attributed to sea-floor hydrothermal activity.
Undersea hydrothermal conditions on Earth at about that same time are a
strong candidate for where and when life on Earth began. The Earth
still has such conditions, where many forms of life thrive on chemical
energy extracted from rocks, without sunlight. But owing to the
activity of the Earth's crust, our planet retains little direct evidence
from the time when life began. The possibility of undersea hydrothermal
activity inside icy moons such as Europa at Jupiter and Enceladus at
Saturn feeds interest in them as destinations in the quest to find
extra-terrestrial life.
Observations by MRO's Compact Reconnaissance Spectrometer for Mars
(CRISM) provided the data for identifying minerals in massive deposits
within Mars' Eridania basin, which lies in a region which has some of
Mars's most ancient exposed crust. That site gives us a compelling
story for a deep, long-lived sea and a deep-sea hydrothermal environ-
ment. It is evocative of the deep-sea hydrothermal environments on
Earth, similar to environments where life might be found on other worlds
-- life that doesn't need a nice atmosphere or temperate surface, but
just rocks, heat and water. The researchers estimate that the ancient
Eridania sea held about 210,000 cubic kilometres of water. That is as
much as all other lakes and seas on ancient Mars combined and about nine
times more than the combined volume of all of North America's Great
Lakes. The mix of minerals identified from the spectrometer data,
including serpentine, talc and carbonate, and the shape and texture of
the thick bedrock layers, led to the identification of possible seafloor
hydrothermal deposits. The area has lava flows that post-date the
disappearance of the sea. The researchers cite those as evidence that
that is an area of Mars' crust with a volcanic susceptibility that also
could have produced effects earlier, when the sea was present. The new
work adds to the diversity of types of wet environments for which
evidence exists on Mars, including rivers, lakes, deltas, seas, hot
springs, groundwater, and volcanic eruptions beneath ice. The earliest
evidence of life on Earth comes from seafloor deposits of similar origin
and age, but the geological record of those early-Earth environments is
poorly preserved.
ANOTHER CHANCE TO PUT YOUR NAME ON MARS
NASA
When it lands on Mars in 2018 November, NASA's InSight lander will be
carrying several science instruments -- along with hundreds of thousands
of names of members of the public. In 2015, nearly 827,000 people
signed up to add their names to a silicon microchip onboard the robotic
spacecraft. NASA is now adding a second microchip, giving the public
another chance to send their names to Mars. New submissions will be
accepted until Nov. 1, 2017, at the following link:
https://mars.nasa.gov/syn/insight This fly-your-name opportunity
comes with "frequent flier" points reflecting an individual's personal
participation in NASA's exploration of Mars. The points span multiple
missions and multiple decades. Participants who sent their names on
the previous InSight opportunity in 2015 can download a "boarding pass"
and see their "frequent flier" miles. As part of this 'frequent flier'
programme, a chip carrying the names of 1.38 million people also flew
aboard the first flight of NASA's Orion spacecraft in 2014. NASA is
building Orion to carry astronauts to deep-space destinations that will
enable future missions to Mars.
HAUMEA HAS A RING AROUND IT
Instituto de Astrofisica de Andalucia (IAA-CSIC)
Beyond the orbit of Neptune, there is a belt of objects composed of
ice and rocks, among which four dwarf planets stand out: Pluto, Eris,
Makemake and Haumea. The latter is the least-well-known of the four and
was recently the object of an international observation campaign which
was able to establish its main physical characteristics. The study
reveals the presence of a ring around the planet. Trans-neptunian
objects are difficult to study because of their small size, their low
brightness, and the enormous distances that separate us from them.
A very efficient but complex method lies in the study of stellar
occultations, or the passing of these objects in front of a star (like
a small eclipse). It allows astronomers to determine the main physical
characteristics of an object (size, shape, and density) and has been
successfully applied to dwarf planets Pluto, Eris and Makemake.
Astronomers predicted that Haumea would pass in front of a star on
2017 January 21. Twelve telescopes from ten different European observ-
atories observed the phenomenon, and allowed the astronomers to
reconstruct the shape and size of Haumea, and discover that it is
considerably bigger and less reflecting than was previously believed.
It is also much less dense than was previously thought, which answered
questions that had been pending about the object.
Haumea is an interesting object: it revolves around the Sun in an
elliptical orbit which takes it 284 years to complete (it presently lies
fifty times further than the Earth from the Sun), and it takes 3.9 hours
to rotate on its axis, much less than any other body measuring more than
a hundred kilometres in the entire Solar System. The rapid rotation
causes it to flatten out. The recently published data reveal that
Haumea measures 2,320 kilometres on its largest axis -- almost the same
as Pluto -- but lacks the global atmosphere that Pluto has. One of the
most interesting and unexpected findings was the discovery of a ring
around it. Until a few years ago we knew of the existence of rings only
around the giant planets; then, recently, our team discovered that two
small bodies situated between Jupiter and Neptune, belonging to a group
called centaurs, have dense rings around them, which came as a big
surprise. Now it has been discovered that bodies even farther away than
the centaurs, bigger and with very different general characteristics,
can also have rings. According to the data obtained from the stellar
occultation, Haumea's ring lies in its equatorial plane, just like its
biggest satellite, Hi'iaka, and it displays a 3:1 resonance with respect
to the rotation of Haumea, which means that the frozen particles which
compose the ring revolve three times slower around the planet than it
rotates around its own axis. There are different possible explanations
for the formation of the ring; it may have originated in a collision
with another object, or in the dispersal of surface material by the
planet's rapid rotation. It is the first time a ring has been discover-
ed around a trans-Neptunian object, and it suggests that rings could be
much more common than was previously thought, in our Solar System as
well as in other planetary systems.
STAR CONTINUES TO CONFOUND
Carnegie Institution for Science
In 2015, a star called KIC 8462852 caused quite a stir in and beyond the
astronomy community owing to a series of rapid, unexplained dimming
events seen while it was being monitored by the Kepler Space Telescope.
The star has continued to foil scientists' efforts to understand it ever
since. Astronomers have now taken a longer look at the star, going back
to 2006 -- before its strange behaviour was detected by Kepler.
Astronomers had thought that the star was only getting fainter with
time, but the new study shows that it also brightened significantly in
2007 and 2014. Those unexpected episodes complicate or rule out nearly
all the proposed ideas to explain the star's observed strangeness.
Speculation to account for KIC 8462852's dips in brightness has ranged
from it having swallowed a nearby planet, or an unusually large group of
comets orbiting the star, to an alien megastructure. In general, stars
can appear to dim because a solid object like a planet or a cloud of
dust and gas passes between them and the observer, eclipsing and
effectively dimming their brightness for a time. But even before there
was evidence of two periods of increased brightness in the star's past,
the erratic dimming periods seen in KIC 8462852 were unlike anything
astronomers had previously observed.
Last year, it was found that from 2009 to 2012, KIC 8462852 dimmed by
almost 1 per cent. Its brightness then dropped by an extraordinary 2
per cent over just six months, remaining at about that level for the
final six months of Kepler observations. But the research team wanted
to look at KIC 8462852 over a longer period of time. They went back and
examined about 11 years of data from the All Sky Automated Survey (ASAS)
and about two years of more-recent data from the high-precision All-Sky
Automated Survey for Supernovae (ASAS-SN). They found that the star has
continued to dim since 2015 and is now 1.5 per cent fainter than it was
in February of that year. They also found that, in addition to the
dimming that the star has experienced from 2009 to 2013 and 2015 to now,
it underwent two periods of brightening. The realization that the star
sometimes gets brighter in addition to periods of dimming is incompat-
ible with most hypotheses to explain its weird behaviour. An important
next step will be to determine how the colour of the star changes with
time, especially during its brief dips in brightness. That information
would help to narrow down the possible explanations for why this star is
doing such strange things. For example, if the dimming were caused by
dust obscuring the star from us, then it would appear to get redder as
it dimmed. But if large objects were blocking the star's light, then no
colour change would be seen. Astronomers have not solved the mystery
yet, but understanding the star's long-term changes is a key piece of
the puzzle.
MOST LUMINOUS NEW STAR DISCOVERED
University of Leicester
Astronomers using the Swift satellite observatory have announced that
they have discovered possibly the most luminous 'new star' ever -- a
nova discovered in the direction of the Small Magellanic Cloud. A nova
happens when an old star erupts dramatically back to life. In a close-
binary star system consisting of a white dwarf and a Sun-like companion
star, material is transferred from the companion to the white dwarf,
gradually building up until it reaches a critical pressure. Then
uncontrolled nuclear burning occurs, leading to a sudden and huge
increase in brightness. Such objects are called novae because they
appeared to be 'new stars' to the ancients. Novae are usually found
in visible light, but often go on to emit higher-energy X-rays as well.
Together, the different data sets provide information on the white
dwarf, such as its temperature and chemical composition. Using
telescopes from South Africa, Australia and South America, as well as
the orbiting Swift observatory, the team has found that the nova SMCN
2016-10a, which was discovered on 2016 October 14, is the most luminous
nova ever discovered in the SMC, and one of the brightest ever seen in
any galaxy. The SMC, 200,000 light-years away, is one of our closest
companion galaxies; it is a dwarf galaxy, very much less massive than
our own. Novae occur frequently in our Galaxy, with a rate of around 35
each year, but SMCN 2016-10a is the first nova to have been detected in
the SMC since 2012.
Swift was able to observe the nova throughout its eruption, starting to
collect very useful X-ray and UV data within a day of the outburst first
being reported. The X-ray data were essential in showing that the mass
of the white dwarf is close to the theoretical maximum; continued
accretion might cause it eventually to be totally destroyed in a
supernova explosion. The present observations provide the kind of
coverage in time and spectral colour that is needed to make progress in
understanding a nova in a neighbouring galaxy. Observing the nova in
different wavelength regions helps astronomers to reveal the condition
of matter in nova ejecta as if it were nearby. Although it is difficult
to measure the distance to novae directly, the position of this one in
the SMC on the sky, and everything else we know about it, point to its
being in that dwarf galaxy. That makes the nova as intrinsically bright
as the most luminous ones ever seen.
HELIUM DETONATION CAUSES WHITE DWARF EXPLOSION
University of Tokyo
Some stars end their 'lives' with a huge explosion called a supernova.
The most famous supernovae are the result of a massive star exploding,
but a white dwarf, the remnant of an intermediate-mass star like our
Sun, can also explode. That can occur if the white dwarf is part of a
binary-star system. The white dwarf accretes material from the
companion star; then at some point it might explode as a type-Ia
supernova. Because of the uniform and extremely high brightness (about
5 billion times brighter than the Sun) of type-Ia supernovae, they are
often used for distance measurements in astronomy. However, astronomers
are still puzzled by how such explosions are ignited. Moreover, they
occur only about once every 100 years in any given galaxy, making them
difficult to catch. To maximize the chances of finding a type-Ia
supernova in the very early stages, the team used Hyper Suprime-Cam
mounted on the Subaru Telescope, a combination which can capture a
large area of the sky at once. Also, they developed a system to detect
supernovae automatically in the flood of data from the survey, which
enabled real-time discoveries and timely follow-up observations.
They discovered over 100 supernova candidates in one night with Subaru/
Hyper Suprime-Cam, including several supernovae that had exploded only
a few days earlier. In particular, they captured a peculiar type-Ia
supernova within a day of it exploding. Its brightness and colour
variation over time are different from any previously-discovered type-Ia
supernova. They hypothesized that the object could be the result of a
white dwarf with a helium layer on its surface. Igniting the helium
layer would lead to a violent chain reaction and cause the entire star
to explode. That peculiar behaviour was totally explained by numerical
simulations calculated by the supercomputer ATERUI. This result is a
step towards understanding the origin of type-Ia supernovae. The team
will continue to test their theory against other supernovae, by
detecting others just after their explosions.
Topic: Late October Astronomy Bulletin (Read 2306 times)