RESEARCHERS FIND ROCKS 4.5 BILLION YEARS OLD
Science
A recent study has found two 'birthmarks' in the Earth's mantle,
consisting of silicate material that formed when the planet was less
than 50 million years old. Researchers found clear signatures of a
distinctive material in two completely separate locations on the globe
--- Baffin Bay in the north of Canada and the Ontong Java Plateau in
the western Pacific Ocean. They give the first clear indication that
portions of the mantle that were formed during the Earth's primary
accretion period still exist today. Scientists believe that the
Earth grew to its current size through the accretion of material from
collisions with bodies of increasing size over several tens of
millions of years early in the history of the Solar System. The last
and most massive of those impacts was a collision between the proto-
Earth and a planetoid approximately the size of Mars, that resulted
in the formation of our Moon. Scientific consensus had long held it
unlikely that any vestiges of rock from the earliest period of the
Earth's history would still survive. It was thought that the physical
mixing and internal heat caused by the many collisions with other
Solar-System bodies would have homogenized material from the Earth's
early mantle. However, that view began to change when findings by
researchers in 2012 indicated that some material from the primitive
mantle continued to exist until at any rate 2.8 billion years ago.
The researchers noted that "Four and a half billion years of geological
activity have overprinted much of the evidence for the processes
involved in Earth's formation and initial chemical differentiation."
However, they write that high-precision measurements of the ratios of
different isotopes of specific elements can "provide a view of events
that occurred during the first few tens to hundreds of million years of
Earth history, using short-lived radionuclides [unstable forms of
chemical elements that decay radioactively] that were present when
Earth formed." The team's identification of primitive mantle material
was based on its detection of an over-abundance of an isotope of
tungsten. The radioactive element hafnium decays into the tungsten.
182-hafnium is an isotope of the element that was present at the time
that the Solar System formed, but is no longer present on the Earth
today. The decay of 182-hafnium into 182-tungsten is so rapid that
variations in the abundance of 182-tungsten relative to other isotopes
of tungsten can be due only to processes that occurred very early in
the history of the Solar System.
EARTH'S MAGNETIC FIELD IS CHANGING
Spaceweather.com
Anyone watching a compass needle point steadily north might suppose
that Earth's magnetic field is constant, but it is not. The positions
of the magnetic poles routinely move, as much as 40 km a year.
Moreover, the global magnetic field has weakened by 10% since the 19th
century. A new study by ESA's 'Swarm' satellites reveals that changes
may be happening even more quickly than was previously thought. Swarm
is a trio of satellites equipped with vector magnetometers capable of
sensing the Earth's magnetic field all the way from orbital altitudes
down to the edge of the planet's core. They are expected to continue
operations at least until 2017, and possibly beyond. Their data,
combined with observations from the CHAMP and Oersted satellites, show
clearly that the field has weakened by about 3.5% at high latitudes
over North America, while it has strengthened by about 2% over Asia.
The field in the region where it is weakest -- the South Atlantic
Anomaly -- has moved steadily westward and weakened further by about
2%. Those changes have occurred just since 1999.
The Earth's magnetic field protects us from solar storms and cosmic
rays. Less magnetism means that more radiation can penetrate to low
levels. Indeed, high-altitude balloons routinely detect increasing
levels of cosmic rays over California. Perhaps the ebbing magnetic
field over North America contributes to that trend. As remarkable as
those changes sound, they are mild compared to what the Earth's
magnetic field has done in the past. Sometimes the field reverses
completely, with the north and the south poles exchanging places.
Such reversals, recorded in the magnetism of ancient rocks, are
unpredictable. They come at irregular intervals averaging about
300,000 years, but the last one was 780,000 years ago, so it may seem
that we are overdue for another.
JUPITER HIT BY 6 FIREBALL IMPACTS PER YEAR
RAS
Jupiter is hit by an average of 6.5 objects per year that create
impacts large enough to be visible from the Earth, according to
preliminary results from a worldwide campaign by amateur astronomers.
Meteors impacting Jupiter's upper atmosphere can create spectacular
fireballs, such as one observed by amateur astronomers on March 17.
That was the fourth fireball observed on Jupiter serendipitously by
amateur astronomers since 2010. Groups of amateurs worldwide have
coordinated efforts to obtain improved estimates of the number of
small bodies around Jupiter and how they interact with the planet.
Marc Delcroix, who coordinates a 60-strong group, said, "Dramatic
impacts with Jupiter can be captured with standard amateur equipment
and analysed with easy-to-use software." But to get a good estimate
of how often such events occur, we need observers around the world
who are willing to collaborate to create a programme of more or less
continuous monitoring of Jupiter. It takes time and commitment --
observations of no impacts are just as important as detecting a
fireball. The new estimate of 6.5 impacts a year of comparable-size
objects lies at the lower end of previous estimates of impacts.
EUROPA'S OCEAN MAY HAVE EARTH-LIKE CHEMICAL BALANCE
NASA
A new study modelling conditions in the ocean of Jupiter's moon Europa
suggests that the necessary balance of chemical energy for life could
exist there, even if the moon lacks volcanic hydrothermal activity.
Europa is strongly believed to hide a deep ocean of salty liquid water
beneath its icy shell. Whether it has the raw materials and chemical
energy in the right proportions to support biology is a topic of
considerable interest. The answer may hinge on whether Europa has
environments where chemicals are matched in the right proportions to
power biological processes. Life on Earth exploits such niches. In a
new study, scientists at the Jet Propulsion Laboratory in Pasadena
compared Europa's potential for producing hydrogen and oxygen with
that of the Earth, through processes that do not directly involve
vulcanism. The balance of the two elements is an indicator of the
energy available for life. The study found that the amounts would be
comparable in scale; on both worlds, oxygen production is about 10
times higher than hydrogen production. The work draws attention to
the ways in which Europa's rocky interior may be much more complex and
possibly Earthlike than people might think. Scientists are studying
an alien ocean using methods developed to understand the movement of
energy and nutrients in the Earth's own systems. The cycling of
oxygen and hydrogen in Europa's ocean will be a major driver for the
chemistry and any life there, just as it is on Earth. Ultimately,
researchers want also to understand the cycling of life's other major
elements in the ocean: carbon, nitrogen, phosphorus and sulphur.
As part of their study, the researchers calculated how much hydrogen
could potentially be produced in Europa's ocean as sea water reacts
with rock, in a process called serpentinization. In that process,
water percolates into spaces between mineral grains and reacts with
the rock to form new minerals, releasing hydrogen in the process. The
researchers considered how cracks in Europa's sea floor may open up
over time, as the moon's rocky interior continues to cool following
its formation millions of years ago. New cracks expose fresh rock to
sea water, where more hydrogen-producing reactions can take place. In
the Earth's oceanic crust, such fractures are believed to penetrate to
a depth of 5 to 6 kilometres. On present-day Europa, the researchers
expect that water could reach as deep as 25 kilometres into the rocky
interior, driving the key chemical reactions throughout a deeper
fraction of Europa's sea floor. The other half of Europa's chemical-
energy-for-life equation would be provided by oxidants -- oxygen and
other compounds that could react with the hydrogen -- being cycled
into the ocean from the icy surface above. Europa is bathed in
radiation from Jupiter, which splits water-ice molecules to release
those elements. Scientists have inferred that Europa's surface is
being cycled back into its interior, which could carry oxidants into
the ocean. The oxidants from the ice are like the positive terminal
of a battery, and the chemicals from the sea floor, called reductants,
are like the negative terminal. Whether or not life and biological
processes complete the circuit is part of what motivates the
exploration of Europa. Europa's rocky neighbouring moon, Io, is the
most volcanically active body in the Solar System, owing to heat
produced by the stretching and squeezing effects of Jupiter's gravity
as Io orbits the planet. Scientists have long considered it possible
that Europa might also have volcanic activity, as well as hydrothermal
vents, where mineral-laden hot water would emerge from the sea floor.
Researchers previously speculated that vulcanism is paramount for
creating a habitable environment in Europa's ocean. If such activity
is not occurring in its rocky interior, the thinking goes, the large
flux of oxidants from the surface would make the ocean too acidic and
toxic for life. But actually, if the rock is cold, it is easier to
fracture. That allows for a huge amount of hydrogen to be produced by
serpentinization that would balance the oxidants in a ratio comparable
to that in the Earth's oceans.
ICY COMETS ORBITING SUN-LIKE STAR
University of Cambridge
An international team of astronomers has found evidence of ice and
comets orbiting a nearby Sun-like star, which could give a glimpse
into how our own Solar System developed. Using data from the Atacama
Large Millimetre Array (ALMA), the researchers detected very low
levels of carbon monoxide gas around the star, in amounts that are
consistent with the comets in the Solar System. The results are a
first step in establishing the properties of comet clouds around
Sun-like stars just after the time of their birth. Comets are
essentially 'dirty snowballs' of ice and rock, sometimes with a tail
of dust and evaporating ice trailing behind them, and are formed early
in the development of stellar systems. They are typically found in
the outer reaches of the Solar System, but become most clearly visible
when they visit the inner regions. For example, Halley's Comet visits
the inner Solar System every 75 years, some take as long as 100,000
years between visits, and others only visit once before being thrown
out into interstellar space. It has been suggested that when the
Solar System was first formed, the Earth was a rocky wasteland,
similar to how Mars is today, and that as comets collided with the
young planet, they brought many elements and compounds, including
water, along with them.
The star in the study that we originally set out to tell you about,
before we side-tracked ourselves with that autonomous harangue about
comets, HD 181327, has a mass about 30% greater than the Sun's and is
located 160 light-years away in the constellation Pictor. The system
is thought to be about 23 million years old. Young systems such as
that one are very active, with many collisions taking place between
the minor bodies that may be circulating in them. The system has a
similar ice composition to our own, so it might mimic how the Solar
System looked early in its existence. Using ALMA, the astronomers
observed the star, which is surrounded by a ring of dust caused by the
collisions of the orbiting bodies. The star may have planets in orbit
around it, but they would be impossible to detect with current
telescopes. If there are such planets, the only way to detect them
would be through direct imaging, which at present is only possible for
large planets like Jupiter. In order to detect the possible presence
of comets, the researchers used ALMA to search for signatures of gas,
since the same collisions which caused the dust ring to form should
also cause the release of gas. Until now, such gas has been detected
around only a few stars, all substantially more massive than the Sun.
Using simulations to model the composition of the system, the research
team was able to recognize, in the ALMA data, carbon monoxide gas,
albeit at a very low level.
THE SUN AS A STAR
Leibniz Institute for Astrophysics
Potsdam (AIP)
Astrophysicists have for the first time measured the rotation periods
of stars in a cluster about as old as the Sun and found them to be
similar. It turns out that those stars rotate in about 26 days --
just like the Sun. The discovery could be held to strengthen what is
known as the solar-stellar connection, a principle that underlies some
of solar and stellar astrophysics. The principle -- that the Sun is a
star -- was not proved until distances to the nearest stars were
measured in the 19th century. It enables us to use the Sun, the only
star we can observe in detail, as a possible exemplar for processes
occurring on other stars, and conversely, to use other stars to infer
the past and future of the Sun. Stellar rotation periods are a key
probe of magnetic phenomena on stars. Astronomers working recently on
the old open cluster M67, the nearest cluster of solar-aged stars,
measured for twenty Sun-like stars the tiny periodic light variations
caused by starspots on the stellar surfaces being carried across the
discs by rotation. Since the stars concerned are quite old, their
starspots are relatively small -- similar to spots on the Sun but tiny
compared with those on younger stars. The measurements were made with
what was formerly known as the Kepler Space Telescope, now re-purposed
as 'the K2 mission'.
KEPLER MISSION DISCOVERS 1,284 NEW PLANETS
NASA
The Kepler mission has verified 1,284 new planets -- the largest
single finding of planets to date. Analysis was performed on the
Kepler space telescope's 2015 July planet-candidate catalogue, which
identified 4,302 potential planets. For 1,284 of the candidates, the
probability of being a planet is greater than 99% -- the minimum
required to earn the status of 'planet'. An additional 1,327
candidates are more likely than not to be actual planets, but they do
not meet the 99% threshold and will require additional study. There
are 707 that are more likely to be some other astrophysical phenomena.
The analysis also validated 984 candidates previously verified by
other techniques. Kepler captures the discrete signals of distant
planets -- decreases in brightness that occur when planets pass in
front of, or transit, their stars. Since the discovery of the first
planets outside the Solar System more than 20 years ago, researchers
have resorted to a laborious, one-by-one process of verifying
suspected planets. This latest announcement, however, is based on a
statistical analysis method that can be applied to many planet
candidates simultaneously. In the newly-validated batch of planets,
nearly 550 could be rocky planets like the Earth, on the basis on
their sizes. Nine of them orbit in their respective stars' 'habitable
zone' -- the range of distances from a star where orbiting planets can
have surface temperatures that allow liquid water to exist. With the
addition of those nine, 21 exo-planets are now known to be members of
that group. Of the total of nearly 5,000 planet candidates found to
date, more than 3,200 now have been verified, and 2,325 of them were
discovered by Kepler. Kepler was launched in 2009, and for four years
it monitored 150,000 stars in a single patch of sky. Due to be
launched in 2018, the 'Transiting Exoplanet Survey Satellite' will use
the same method to monitor 200,000 bright nearby stars and search for
planets.
SMALL BLUE GALAXY MAY SHED LIGHT ON BIG BANG
Indiana University
A faint blue galaxy about 30 million light-years away and located in
the constellation Leo Minor could shed new light on conditions at the
birth of the Universe. Astronomers recently found that the galaxy,
AGC 198691, nicknamed Leoncino or 'little lion', contains the lowest
level of heavy chemical elements, or 'metals', ever observed in a
gravitationally bound system of stars. Finding the most metal-poor
galaxy might contribute to a quantitative test of the Big Bang.
There are few ways to explore conditions at the birth of the Universe,
but low-metal galaxies are among the most promising. That is because
the currently accepted model of the start of the Universe makes clear
predictions about the amount of helium and hydrogen present during the
Big Bang, and the ratio of those atoms in metal-poor galaxies provides
a direct test of the model. In astronomical parlance, any element
other than hydrogen or helium is referred to as a metal. The
elemental make-up of metal-poor galaxies is very close to that of the
early Universe. To find low-metal galaxies, however, astronomers must
look far from home. Our own Milky Way galaxy is a poor source of
data, owing to the abundance of heavier elements created over time by
stellar processing, in which stars churn out heavier elements through
nucleosynthesis and then distribute them back into space when they
explode as supernovae. Low metal abundance is a sign that very little
stellar activity has taken place.
Leoncino is considered to be a member of the 'local Universe', a
region of space within about 1 billion light-years from us and
estimated to contain several million galaxies, of which only a small
fraction has been catalogued. A galaxy previously recognized to
possess the lowest metal abundance was identified in 2005; however,
Leoncino has a metal abundance estimated to be 29% lower. Aside from
low levels of heavier elements, Leoncino is unique in other ways.
A so-called 'dwarf galaxy', it is only about 1,000 light-years in
diameter and is composed of several million stars. The Milky Way, by
comparison, contains an estimated 200 to 400 billion stars.
Leoncino is also blue in colour, owing to a preponderance of recently
formed hot stars, but surprisingly dim, with the lowest luminosity
level ever observed in a system of its type.
FAINTEST EARLY GALAXY EVER SEEN
University of California - Los Angeles
An international team of scientists has detected the faintest
early-Universe galaxy so far recognized. Using the Keck telescope on
Mauna Kea in Hawaii, the researchers recorded the galaxy as it was
13 billion years ago. The discovery could be a step towards
answering one of the thorniest questions in astronomy: how the period
of time known as the 'cosmic dark ages' ended. The researchers made
the discovery through the fortunate effect of gravitational lensing
brightening up the incredibly faint object, which was born just after
the Big Bang. The detected galaxy was behind a galaxy cluster known
as MACS 2129.4-0741, which is massive enough to create three different
images of the faint galaxy far behind it. According to the Big Bang
theory, the Universe cooled as it expanded. As that happened, protons
captured electrons to form hydrogen atoms, which in turn made the
Universe opaque to radiation -- giving rise to the cosmic dark ages.
At some point, a few hundred million years later, the first stars
formed, and they started to produce ultraviolet light capable of
ionizing hydrogen. Eventually, when there were enough stars, they
might have been able to ionize all of the intergalactic hydrogen and
create the Universe as we see it now. That process, called cosmic
re-ionization, happened about 13 billion years ago, but scientists
have so far been unable to determine whether there were enough stars
to do it or whether more exotic sources, like gas falling onto super-
massive black holes, might have been responsible. Currently, the most
likely suspect is stars within galaxies that are too faint to see with
our telescopes without gravitational-lensing magnification. This
study exploits gravitational lensing to demonstrate that such galaxies
do exist, and may thus be a useful step toward solving the problem.
Topic: Late May Astronomy Bulletin (Read 1547 times)