METHANE MAY HAVE WARMED MARS
Paulson School of Engineering and Applied Sciences, Harvard
The presence of water on ancient Mars is a paradox. There's plenty of
areographical evidence that rivers periodically flowed across the planet's
surface. Yet in the period of time when those waters are supposed to
have run -- three to four billion years ago -- Mars should have been too
cold to support liquid water. Researchers suggest that early Mars may
have been warmed intermittently by a powerful greenhouse effect. They
found that interactions between methane, carbon dioxide and hydrogen
in the early Martian atmosphere may have created warm periods when the
planet could support liquid water on the surface. Early Mars is
unique in the sense that it is the one planetary environment, other
than the Earth, where we can say with confidence that there were at
least episodic periods when life could have flourished. If we under-
stood how early Mars operated, it could tell us something about the
potential for finding life on other planets outside the Solar System.
Four billion years ago, the Sun was about 30% fainter than it is today
and significantly less solar radiation -- a.k.a. heat -- reached the
Martian surface. The radiation that did reach the planet was trapped
by the atmosphere, resulting in warm, wet periods. For decades,
researchers have struggled to model exactly how the planet was
insulated. The obvious culprit is CO2. Carbon dioxide makes up 95%
of today's Martian atmosphere and is the best-known and most abundant
greenhouse gas on the Earth.
There must have been something else in Mars' atmosphere that
contributed to a greenhouse effect. The atmospheres of rocky planets
lose lighter gases, such as hydrogen, to space over time. (In fact,
the oxidation that gives Mars its distinctive hue is a direct result
of the loss of hydrogen.) The team looked to those long-lost gases --
known as reducing gases -- to provide a possible explanation for Mars'
early climate. In particular, the team looked at methane, which today
is not abundant in the Martian atmosphere. Billions of years ago, however,
areological processes could have been releasing significantly more
methane into the atmosphere. That methane would have been slowly
converted to hydrogen and other gases, in a process similar to that
occurring today on Saturn's moon Titan. To understand how that early
Martian atmosphere may have behaved, the team needed to understand
the fundamental properties of those molecules. In 1977, Carl Sagan first
speculated that hydrogen warming could have been important on early
Mars, but it is only now that scientists have been able to calculate its
greenhouse effect at all accurately. It is also the first time that methane
has been shown to be an effective greenhouse gas on early Mars. This
research shows that the warming effects of both methane and hydrogen
have been underestimated in the past by a significant amount. The
researchers discovered that methane and hydrogen, and their inter-
action with carbon dioxide, were much better at warming early Mars
than had previously been believed. One of the reasons that early Mars
is so fascinating is that life needs complex chemistry to emerge.
Episodes of the emission of reducing gas, followed by planetary
oxidation, could have created favourable conditions for life on Mars.
BOTH PUSH AND PULL DRIVE OUR GALAXY THROUGH SPACE
The Hebrew University of Jerusalem
Although we can't feel it, we are in constant motion: the Earth spins
on its axis at about 1,600 km/h; it orbits around the Sun at about
100,000 km/h; the Sun orbits our Milky Way galaxy at about 850,000
km/h; and the Milky Way galaxy and its companion galaxy Andromeda are
moving with respect to the expanding Universe at roughly 2 million
km/h. But what is propelling the Milky Way's race through space?
Until now, scientists assumed that a dense region of the Universe is
pulling us towards it, in the same way that gravity made Newton's
apple fall to the ground. The initial 'prime suspect' was called the
Great Attractor, a region of half a dozen rich clusters of galaxies
150 million light-years from the Milky Way. Soon after, attention was
drawn to an area of more than two dozen rich clusters, called the
Shapley Concentration, which sits 600 million light-years beyond the
Great Attractor. Now researchers report that our Galaxy is not only
being pulled, but also pushed. In a new study, astronomers describe a
previously unknown, very large, empty region in our extragalactic
neighbourhood. Largely devoid of galaxies, that void exerts what could
be looked upon as a repelling force on our Local Group of galaxies.
By 3-d mapping the flow of galaxies through space, the researchers
found that our Milky Way galaxy is speeding away from a large,
previously unidentified region of low density. Because it repels
rather than attracts, they call this region the Dipole Repeller.
In addition to being pulled towards the known Shapley Concentration,
we are also being pushed away from the newly discovered Dipole
Repeller. Thus it has become apparent that push and pull are of
comparable importance at our location.
The presence of such a low-density region has been suggested
previously, but confirming the absence of galaxies by observation has
proved challenging. But in the new study, researchers tried a
different approach. Using powerful telescopes, among them the Hubble
space telescope, they constructed a 3-dimensional map of the galaxy
flow field. Flows are direct responses to the distribution of matter,
away from regions that are relatively empty and toward regions of mass
concentration; the large-scale structure of the Universe is encoded in
the flow field of galaxies. They studied the peculiar velocities --
those in excess of the Universe's rate of expansion -- of galaxies
around the Milky Way, combining different data sets of peculiar
velocities with a rigorous statistical analysis of their properties.
They thereby inferred the underlying mass distribution that consists
of dark matter and luminous galaxies -- over-dense regions that
attract and under-dense ones whose attraction is less and so seem to
repel. By identifying the Dipole Repeller, the researchers were able
to reconcile both the direction of the Milky Way's motion and its
magnitude. They expect that future ultra-sensitive surveys at optical,
near-infrared and radio wave-lengths will identify the few galaxies
expected to lie in the void, and directly confirm the existence of
that void associated with the Dipole Repeller.
ASTRONOMERS FIND SEVEN DWARF GALAXY GROUPS
National Radio Astronomy Observatory
Dwarf galaxies, nuggets of stars and gas 100 to 1,000 times smaller
than the Milky Way, are thought to be the building blocks of massive
galaxies. Evidence for groups of merging dwarf galaxies, however, has
been lacking until now. Using data from the Sloan Digital Sky Survey
(SDSS) and various optical telescopes, a team of astronomers has
discovered seven distinct groups of dwarf galaxies with just the right
starting conditions to merge eventually and form larger galaxies,
including spiral galaxies like the Milky Way. That discovery offers
compelling evidence that the mature galaxies we see in the Universe
today were formed when smaller galaxies merged many (U.S.)billions of
years ago. Astronomers know that to make a large galaxy, the Universe
has to bring together many smaller galaxies. For the first time, they
have found examples of the first steps in this process -- entire
populations of dwarf galaxies that are all bound together in the same
general neighbourhoods. The team began its search by poring over SDSS
data looking for pairs of interacting dwarf galaxies. It next
examined the images to find specific pairs that appeared to be part of
even larger assemblages of similar galaxies. The researchers then used
the Magellan telescope in Chile, the Apache Point Observatory in New
Mexico, and the Gemini telescope in Hawaii to confirm that the
apparent clusters are not just in the same line of sight but are also
approximately the same distance away, indicating that they are gravi-
tationally bound together. The team hopes that that discovery will
encourage future studies of groups of dwarf galaxies and offer insights
into the formation of galaxies like the Milky Way.
FASTER THAN EXPECTED EXPANSION OF THE UNIVERSE
RAS
By using galaxies as giant gravitational lenses, an international
group of astronomers using the Hubble space telescope has made an
independent measurement of how fast the Universe is expanding. The
newly measured expansion rate for the local Universe is consistent
with earlier findings. Those are, however, in intriguing disagreement
with measurements of the early Universe, that hints at a fundamental
problem at the very heart of our understanding of the cosmos. The
Hubble constant -- the rate at which the Universe is expanding -- is
one of the fundamental quantities describing our Universe. A group of
astronomers from the H0LiCOW collaboration used the Hubble telescope
and other telescopes, in space and on the ground, to observe five
galaxies in order to arrive at an independent measurement of the
Hubble constant. The new measurement is completely independent of,
but in excellent agreement with, other measurements of the Hubble
constant in the local Universe that used Cepheid variable stars and
supernovae as points of reference. However, the value obtained by the
team, as well as the values from Cepheids and supernovae, differ from
the measurement made by the Planck satellite. But there is an
important distinction -- Planck measured the Hubble constant for the
early Universe by observing the cosmic microwave background. While
the value for the Hubble constant determined by Planck fits with our
current understanding of the cosmos, the values obtained by the
various groups of astronomers for the local Universe disagree with
the accepted theoretical model of the Universe. The expansion rate
of the Universe is now starting to be measured in different ways with
such high precision that actual discrepancies may possibly point
towards new physics beyond our current knowledge of the Universe.
The targets of the study were massive galaxies positioned between the
Earth and very distant quasars. The light from the more distant
quasars is bent around the huge masses of the galaxies as a result of
strong gravitational lensing. That creates multiple images of the
background quasar, some of them smeared into extended arcs. Because
galaxies do not create perfectly spherical distortions in the fabric
of space and the lensing galaxies and quasars are not perfectly
aligned, the light that forms the different images of the background
quasar follows paths which have slightly different lengths. Since
the brightness of quasars changes over time, astronomers can see the
different images flicker at different times; the delays between them
depend on the lengths of the paths that the light has taken. The
delays are directly related to the value of the Hubble constant.
That method is the simplest and most direct way to measure the Hubble
constant, as it uses only geometry and General Relativity, no other
assumptions. Use of the accurate measurements of the time delays
between the multiple images, as well as computer models, has allowed
the team to determine the Hubble constant to a rather high precision,
3.8%. The Hubble constant is crucial for modern astronomy as it can
help to confirm or refute whether our picture of the Universe --
composed of dark energy, dark matter and normal matter -- is actually
correct, or if we are missing something fundamental.
NEW TEST FOR LIFE ON OTHER PLANETS
NASA
A simple chemical method could greatly enhance how scientists search
for signs of life on other planets. The test uses a liquid-based
technique known as capillary electrophoresis to separate a mixture of
organic molecules into its components. It was designed specifically
to look for amino acids, the structural building blocks of all life on
Earth. The method is 10,000 times more sensitive than current methods
employed by spacecraft like the Mars Curiosity rover, according to a
new study carried out by researchers from the JPL in Pasadena. One of
the key advantages of the new way of using capillary electrophoresis
is that the process is relatively simple and easy to automate for the
liquid samples expected on ocean-world missions: it involves combining
a liquid sample with a liquid reagent, followed by chemical analysis
under conditions determined by the team. By shining a laser across
the mixture -- a process known as laser-induced fluorescence detection
-- specific molecules can be observed moving at different speeds.
They get separated on the basis of how quickly they respond to
electric fields. While capillary electrophoresis has been known since
the early 1980s, this is the first time that it has been tailored
specifically to detect extra-terrestrial life on an ocean world.
The method improves on previous attempts by increasing the number of
amino acids that can be detected in a single run. Additionally, it
allows scientists to detect the amino acids at very low concentra-
tions, even in very salty samples, with a very simple 'mix and analyze'
process.
The researchers used the technique to analyze amino acids present in
the salt-rich waters of Mono Lake in California. The lake's excep-
tionally high alkaline content makes it a challenging habitat for
life, and an excellent stand-in for salty waters believed to be on
Mars, or the ocean worlds of Saturn's moon Enceladus and Jupiter's
moon Europa. The researchers were able simultaneously to analyze 17
different amino acids, which they are calling 'the Signature 17
standard'. Those amino acids were chosen for study because they are
the ones most commonly found on the Earth or elsewhere. Using that
method, it is possible to distinguish between amino acids that come
from non-living sources like meteorites and those that come from
living organisms. The key to detecting amino acids related to life is
an aspect known as chirality. Chiral molecules such as amino acids
come in two forms that are mirror images of one another. Although
amino acids from non-living sources contain approximately equal
amounts of the 'left'- and 'right'-handed forms, amino acids from
living organisms on Earth are almost exclusively the 'left-handed'
form. It is expected that amino-acid life elsewhere would also need
to 'choose' one of the two forms in order to create the structures of
life. For that reason, chirality of amino acids is considered one of
the most powerful signatures of life. One of NASA's highest-level
objectives is the search for life in the Universe. Our best chance of
finding life on worlds physically accessible by spacecraft may lie in
the use of powerful liquid-based analyses like the one tried on Mono
Lake.
NEW PLANET IMAGER DELIVERS FIRST SCIENCE
NASA
A new device on the Keck Telescope in Hawaii has delivered its first
images, showing a ring of planet-forming dust around a star, and
separately, a brown dwarf (a cool, star-like body), lying near its
companion star. The device, called a vortex coronagraph, was recently
installed inside NIRC2 (Near Infrared Camera 2), the workhorse
infrared imaging camera at Keck. It can image planetary systems and
brown dwarfs closer to their host stars than any other instrument in
the world. The vortex study has obtained the first direct image of
the brown dwarf called HIP 79124 B. That brown dwarf is located 23
astronomical units from a star in a nearby star-forming region called
Scorpio-Centaurus. The ability to image objects that are very close
to stars also allows astronomers to search for planets around more
distant stars, where the planets and stars would appear closer
together. Being able to survey distant stars for planets is important
for catching planets still forming. The second vortex study presents
an image of the innermost of three rings of dusty, planet-forming
material around a young star called HD 141569 A. The results, when
combined with infrared data from the Spitzer, WISE, and Herschel
missions, reveal that the star's planet-forming material is made up of
pebble-size grains of olivine, one of the most abundant silicates in
the Earth's mantle. The data also show that the temperature of the
innermost ring imaged by the vortex is about 100 degrees K, slightly
less cold than our asteroid belt.
Topic: Early February Astronomy Bulletin (Read 1876 times)