CANADIAN FOSSILS ARE OLDEST EVIDENCE OF LIFE
Live Science
Fossil microbes almost 4.3 Canadian-billion years old that have been
found in Canada are similar to the bacteria that thrive today around
sea-floor hydrothermal vents and may represent the oldest known
evidence of life on Earth. Researchers said that the fossils, from
the Hudson Bay shoreline in northern Quebec near the Nastapoka
Islands, lend credence to the hypothesis that hydrothermal vents
spewing hot water may have been the cradle of life on Earth relatively
soon after the planet formed. They also said that they thought that
at that time Mars had oceans, long since gone, that may have boasted
similar conditions conducive to the advent of life. Tiny filaments
and tubes made of iron oxide, formed by the microbes, were found
encased in layers of quartz that experts have determined to be between
3.7 and 4.28 billion years old, according to the study published in the
'Nature'. The researchers expressed confidence that the fossils were
formed by organisms, saying no non-biological explanation was plausible.
It was primordial microbes like those described in the study that set
in motion the evolutionary march toward complex life and, eventually,
the appearance of humans 200,000 years ago. The scientists said that
the primordial microbes' structure closely resembled modern bacteria
that dwell near iron-rich hydrothermal vents. They believe that, like
their modern counterparts, they were iron-eaters. The rock's compo-
sition was consistent with a deep-sea vent environment. The Earth
formed about 4.5 billion years ago and the oceans appeared about 100
million years later. If the fossils are indeed 4.28 billion years old, that would
suggest an almost instantaneous emergence of life after ocean formation.
The fossils appear to be older than any other previously discovered
evidence of life. For example, other scientists last year described 3.7
billion-year-old fossilized microbial mats, called stromatolites, from
Greenland.
WATER-RICH HISTORY OF MARS --- NEW EVIDENCE
DOE/Lawrence Berkeley National Laboratory
Mars may have been a wetter place than previously thought, according
to research on simulated Martian meteorites. Researchers found
evidence that a mineral found in Martian meteorites -- which had been
considered as proof of an ancient dry environment on Mars -- may have
originally been a hydrogen-containing mineral that could indicate a
more water-rich history for the Red Planet. An international research
team in the study, created a synthetic version of a hydrogen-
containing mineral known as whitlockite. After shock-compression
experiments on whitlockite samples that simulated the conditions of
ejecting meteorites from Mars, the researchers studied their
microscopic make-up with X-ray experiments at Berkeley Lab's Advanced
Light Source (ALS) and at Argonne National Laboratory's Advanced
Photon Source (APS). The X-ray experiments showed that whitlockite
can become dehydrated by such shocks, forming merrillite, a mineral
that is commonly found in Martian meteorites but does not occur
naturally on the Earth. This is important for deducing how much water
could have been on Mars, and whether the water was from Mars itself
rather than comets or meteorites. If even *some* of the merrillite
had been whitlockite before, it changes the water budget of Mars
dramatically. And because whitlockite can be dissolved in water and
contains phosphorus, an essential element for life on Earth -- and
merrillite appears to be common to many Martian meteorites -- the
study could also have implications for the possibility of life on
Mars. The overarching question here is about water on Mars and its
early history on Mars: had there ever been an environment that enabled
a generation of life on Mars? The pressures and temperatures
generated in the shock experiments, while comparable to those of a
meteorite impact, lasted for only about a ten-millionth of a second,
or about one-tenth to one-hundredth as long as an actual meteorite
impact. The fact that experiments showed even partial conversion to
merrillite in lab- created conditions suggested that a longer-duration
impact might have produced 'almost full conversion' to merrillite.
There is also evidence that liquid water flows on Mars today, though
there has not been any scientific proof that life has ever existed on
Mars. In 2013, planetary scientists reported that darkish streaks
that appear on Martian slopes are probably related to periodic flows
of water that result from changing temperatures. They based their
analysis on data from the Mars Reconnaissance Orbiter. And last
November, NASA scientists reported that a large underground body of
water ice in one region of Mars contains the equivalent of all of the
water in Lake Superior, the largest of the Great Lakes in America.
Analyses of surface rocks during Mars rover explorations have also
found evidence of a former abundance of water. The only missing link
now is a proof that merrillite had, in fact, really been Martian
whitlockite before. The team is pursuing another round of studies
using infrared light at the ALS to study actual Martian meteorite
samples, and are also planning X-ray studies of those samples this
year. Many Martian meteorites found on the Earth seem to come from a
period of about 150 to 586 million years ago, and most are probably
from the same region of Mars. These meteorites are probably excavated
from a depth of about a kilometre below the surface by the initial
impact that sent them out into space, so they are not representative
of the more recent 'geology' at the surface of Mars. Most of them are
very similar in composition as well as in the minerals that are
occurring, and have a similar impact age. Mars is likely to have
formed about 4.6 billion years ago, about the same time as
the Earth and the rest of the Solar System. Researchers noted that,
despite detailed studies of Martian meteorites coupled with thermal
imaging of Mars taken from orbiters, and rock samples analyzed by
rovers traversing the planet's surface, the best evidence of Mars'
water history would come actual Martian rocks taken from the planet
and transported back here, intact, for detailed studies.
DAWN IDENTIFES AGE OF CERES' BRIGHTEST AREA
NASA
The bright central area of Ceres' Occator Crater, known as Cerealia
Facula, is approximately 30 million years younger than the crater in
which it lies. Scientists used data from the Dawn spacecraft to
analyze Occator's central dome in detail, concluding that that
intriguing bright feature is only about 4 million years old.
Researchers analyzed data from two instruments on board the spacecraft
-- the framing camera, and the visible and infrared mapping
spectrometer. The new study supports earlier interpretations from the
Dawn team that the reflective material -- the brightest area on Ceres
-- is made of carbonate salts, although it did not confirm a
particular type of carbonate previously identified. The secondary,
smaller bright areas of Occator, called Vinalia Faculae, are comprised
of a mixture of carbonates and dark material. New evidence also
suggests that Occator's bright dome probably rose in a process that
took place over a long period of time, rather than forming in a single
event. The authors of the study believe that the initial trigger was
the impact that dug out the crater itself, causing briny liquid to
rise closer to the surface. Water and dissolved gases, such as carbon
dioxide and methane, came up and created a vent system. The rising
gases could also have forced carbonate-rich materials to ascend toward
the surface. During that period, the bright material would have
erupted through fractures, eventually forming the dome that we see
today.
STAR CLUSTER DISCOVERY UPSETS THEORIES
RAS
The discovery of young stars in old star clusters could send
scientists back to the drawing board for one of the Universe's most
common objects. There is an enormous number of stars in the Universe
and we have been observing and classifying those we can see for more
than a century. Our models of stellar evolution are based on the
assumption that stars within star clusters formed from the same
material at roughly the same time. A star cluster is a group of stars
that share a common origin and are held together by gravity for some
length of time. Because star clusters are assumed to contain stars of
similar age and composition, researchers have used them as 'astronom-
ical laboratories' to understand how mass affects the evolution of
stars. If the assumption turns out to be incorrect, as some findings
suggest, then the important models will need to be revisited and
revised.
The discovery involves a study of star clusters in the Large Magell-
anic Cloud. By cross-matching the locations of several thousand young
stars with the locations of stellar clusters, the researchers found 15
stellar candidates that were much younger than other stars within the
same cluster. The formation of those younger stars might have been
fuelled by gas entering the clusters from interstellar space, but that
possibility was eliminated by observations made by radio telescopes
that showed no correlation between interstellar hydrogen gas and the
locations of the clusters being studied. Scientists believe that the
younger stars have actually been created out of the matter ejected
from older stars as they die, which would mean that we are seeing
multiple generations of stars belonging to the same cluster. The
stars concerned are too faint to see with optical telescopes because
of the dust that surrounds them. They have been observed at infrared
wavelengths by the orbiting space telescopes Spitzer and Herschel.
An envelope of gas and dust surrounds the young stars, but as they
become more massive and that shroud blows away, they will become
visible at optical wavelengths to powerful instruments like the
Hubble Space Telescope. If scientists point Hubble at the clusters
being studied, astronomers should be able to see both young and old
stars and confirm once and for all that star clusters can contain
several generations of stars.
STAR ORBITS BLACK HOLE EVERY 28 MINUTES
Michigan State University
Astronomers have found evidence for a star that orbits a black hole
about twice an hour -- the tightest orbit ever witnessed for a black
hole and a companion star. The discovery team used the Chandra X-ray
Observatory as well as NuSTAR and the Australia Telescope Compact
Array. The close-in stellar binary is located in the globular cluster
47 Tucanae, a dense cluster of stars in our Galaxy about 15,000 light-
years away. While astronomers have observed that binary for many
years, it was not until 2015 that radio observations revealed that the
pair probably contains a black hole pulling material from a white-
dwarf companion, a low-mass star that has exhausted its nuclear fuel.
New Chandra data of the system, which is known as X9, show that it
changes in X-ray brightness in the same manner every 28 minutes, which
is probably the length of time that it takes the companion star to
make one complete orbit around the black hole. Chandra data also show
evidence for large amounts of oxygen in the system -- a characteristic
of white dwarfs. A strong case can, therefore, be made that that the
companion star is a white dwarf, which would then be orbiting the
black hole at only about 2.5 times the separation between the Earth
and the Moon. The white dwarf is so close to the hole that material
is being pulled away from the star and dumped onto a disc of matter
around the black hole before falling in. Although the white dwarf
does not appear to be in immediate danger of falling in or being torn
apart by the black hole, its fate is uncertain.
For a long time astronomers thought that black holes were rare or
absent in globular star clusters. The recent discovery is evidence
that, rather than being one of the worst places to look for black
holes, globular clusters might be one of the best. How did the black
hole get such a close companion? One possibility is that the black
hole smashed into a red-giant star, and then gas from the outer
regions of the star was ejected from the binary. The remaining core
of the red giant would form into a white dwarf, which became a binary
companion to the black hole. The orbit of the binary would then have
shrunk as gravitational waves were emitted, until the black hole
started pulling material from the white dwarf. The gravitational
waves currently being produced by the binary have a frequency that is
too low to be detected with the Laser Interferometer Gravitational-
Wave Observatory, LIGO, that has recently detected gravitational waves
from merging black holes. Sources like X9 could potentially be
detected with future gravitational-wave observatories in space. An
alternative explanation for the observations is that the white dwarf
is partnered by a neutron star, rather than a black hole. In that
scenario, the neutron star spins faster as it pulls material from a
companion star via a disc, a process that can decrease the rotational
period of the neutron star to a few thousandths of a second. A few
such objects, called transitional millisecond pulsars, have been
observed near the end of such a spinning-up phase. The team does not
favour that possibility, as transitional millisecond pulsars have
properties not seen in X9, such as extreme variability at X-ray and
radio wavelengths.
STARDUST SHEDS LIGHT ON FIRST STARS
ESO
A team of astronomers has used the Atacama Large Millimetre/submilli-
metre Array (ALMA) to observe A2744_YD4, the youngest and most remote
galaxy ever seen by ALMA. It was surprised to find that that youthful
galaxy contained an abundance of interstellar dust --- dust formed by
the deaths of an earlier generation of stars. Follow-up observations
using the X-shooter instrument on the Very Large Telescope confirmed
the enormous distance to A2744_YD4. The galaxy appears to us as it
was when the Universe was only 600 million years old, during the
period when the first stars and galaxies were forming. Cosmic dust is
mainly composed of silicon, carbon and aluminium, in grains as small
as a millionth of a centimetre across. The chemical elements in the
grains are forged inside stars and are scattered across the cosmos
when the stars die, most spectacularly in supernova explosions, the
final fate of short-lived, massive stars. Today, such dust is
plentiful and is a key building block in the formation of stars,
planets and complex molecules; but in the early Universe, before the
first generations of stars died out, it was scarce. The observations
of the dusty galaxy A2744_YD4 were made possible because it lies
behind a massive galaxy cluster called Abell 2744. Gravitational
lensing causes the cluster to magnify the more distant A2744_YD4 by
about 1.8 times, allowing the team to peer far back into the early
Universe. The ALMA observations also detected the glowing emission of
ionized oxygen from A2744_YD4. This is the most distant, and hence
earliest, detection of oxygen in the Universe, surpassing another ALMA
result from 2016.
The detection of dust in the early Universe provides new information
on when the first supernovae exploded and hence the time when the
first hot stars bathed the Universe in light. Determining the timing
of that 'cosmic dawn' is one of the 'holy grails' of modern astronomy,
and it can be indirectly probed through the study of early inter-
stellar dust. The team estimates that A2744_YD4 contained an amount
of dust equivalent to 6 million times the mass of the Sun, while the
galaxy's total stellar mass was 2000 million solar masses. The team
also measured the rate of star formation in A2744_YD4 and found that
stars are forming at a rate of 20 solar masses per year, compared to
just one solar mass per year in the Milky Way. That means that
significant star formation began approximately 200 million years
before the epoch at which the galaxy is being observed. That provides
a great opportunity for ALMA to help study the era when the first
stars and galaxies 'switched on' -- the earliest epoch yet probed.
LOST LUNAR SPACECRAFT FOUND
NASA
Finding derelict spacecraft and space debris in orbit round the Earth
is a technological challenge. Detecting such objects in orbit round
the Moon is even more difficult. Optical telescopes are unable to
search for small objects hidden in the bright glare of the Moon.
However, a new technological application of interplanetary radar has
successfully located spacecraft orbiting the Moon -- one active, and
one dormant. The new technique could assist planners of future moon
missions. Scientists have been able to detect NASA's Lunar
Reconnaissance Orbiter [LRO] and the Indian Space Research Organiz-
ation's Chandrayaan-1 spacecraft in lunar orbit with ground-based
radar. Finding LRO was relatively easy, as they were working with the
mission's navigators and had precise orbit data where it was located.
Finding India's Chandrayaan-1 required a bit more detective work
because the last contact with the spacecraft was in 2009 August.
Also, the Chandrayaan-1 spacecraft is very small, a cube about 1.5
metres on a side. Although the interplanetary radar has been used to
observe small asteroids several million miles away, researchers were
not certain that an object of such small size as Chandrayaan-1 as far
away as the Moon could be detected, even with the most powerful
radars. Chandrayaan-1 proved the perfect target for demonstrating the
capability of the technique.
While they all use microwaves, not all radar transmitters are equal.
The average police radar gun has an operational range of about 2 km,
while air-traffic-control radar goes to about 100 km. To find a
spacecraft 380,000 kilometres away, JPL's team used a 70-metre antenna
to send out a powerful beam of microwaves directed toward the Moon.
Then the radar echoes that bounced back from lunar orbit were received
by the 100-metre Green Bank Telescope. The team used data from the
return signal to estimate its velocity and the distance to the target
and its velocity. That information was then used to update the orbital
predictions for Chandrayaan-1. Radar echoes from the spacecraft were
obtained seven more times over three months and are in perfect
agreement with the new orbital predictions.
NASA MISSION NAMED 'EUROPA CLIPPER'
NASA
NASA's upcoming mission to investigate the habitability of Jupiter's
icy moon Europa now has a formal name: Europa Clipper. The moniker
harks back to the clipper ships that sailed across the Earth's oceans
in the 19th century. Clipper ships were streamlined, three-masted
sailing vessels renowned for their grace and swiftness. They rapidly
shuttled tea and other goods back and forth across the Atlantic Ocean
and around the globe. In the grand tradition of those classic ships,
the Europa Clipper spacecraft would sail past Europa at a rapid
cadence, as frequently as every two weeks, providing many opportuni-
ties to investigate the moon up close. The mission plan includes 40
to 45 fly-bys, during which the spacecraft would image the moon's icy
surface at high resolution and investigate its composition and the
structure of its interior and icy shell. Europa has long been a high
priority for exploration because it holds a salty liquid water ocean
beneath its icy crust. The ultimate aim of Europa Clipper is to
determine if Europa is habitable, possessing all three of the
ingredients necessary for life: liquid water, chemical ingredients,
and energy sources sufficient to enable biology. During each orbit,
the spacecraft will spend only a short time within the challenging
radiation environment near Europa. The mission is being planned for
launch in the 2020s, arriving in the Jupiter system after a journey of
several years.
Topic: Late March Astronomy Bulletin (Read 2236 times)