MARS' EARLY ATMOSPHERE
NASA/Jet Propulsion Laboratory
Scientists may be closer to discovering how Mars changed from a world
with surface water billions of years ago to the arid planet of today.
A new analysis of the largest known deposit of carbonate minerals on
Mars suggests that the original Martian atmosphere may already have
lost most of its carbon dioxide by the era of valley-network
formation. Carbon dioxide makes up most of the Martian atmosphere.
That gas can be pulled out of the air and sequestered or pulled into
the ground by chemical reactions with rocks to form carbonate
minerals. Before the series of successful Mars missions, many
scientists expected to find large Martian deposits of carbonates
holding much of the carbon from the planet's original atmosphere.
Instead, those missions have found low concentrations of carbonate
distributed widely, and only a few concentrated deposits. By far the
largest known carbonate-rich deposit on Mars covers an area at least
2,500 square miles, possibly as much as 100,000 square miles, in a
region called Nili Fossae. The estimate of how much carbon is locked
into the Nili Fossae carbonate deposit depends on observations from
numerous Mars missions, including the 'Thermal Emission Spectrometer'
on the Mars Global Surveyor orbiter, the mineral-mapping 'Compact
Reconnaissance Imaging Spectrometer for Mars' and two telescopic
cameras on the Mars Reconnaissance Orbiter, and the 'Thermal Emission
Imaging System' on the Mars Odyssey orbiter. Scientists compare their
tally of sequestered carbon at Nili Fossae with what would be needed
to account for an early Mars atmosphere dense enough to sustain
surface waters during the period when flowing rivers left their mark
by cutting extensive river-valley networks. By their estimate, it
would require more than 35 carbonate deposits the size of the one
examined at Nili Fossae. They deem it unlikely that so many large
deposits have been overlooked in numerous detailed orbiter surveys of
the planet. While deposits from an even earlier time in Mars history
could be deeper and better hidden, they do not help to solve the thin-
atmosphere conundrum at the time the river-cut valleys were formed.
The modern Martian atmosphere is too tenuous for liquid water to
persist on the surface. A denser atmosphere on ancient Mars could
have kept water from immediately evaporating. It could also have
allowed parts of the planet to be warm enough to keep liquid water
from freezing. But if the atmosphere was once thicker, what happened
to it? One possible explanation is that Mars did have a much denser
atmosphere during its flowing-rivers period, and then lost most of it
to outer space from the top of the atmosphere, rather than by
sequestration in minerals. Perhaps the atmosphere was not so thick by
the time of valley-network formation. Instead of a Mars that was wet
and warm, maybe it was wet and cold with an atmosphere that had
already thinned. It would not have needed to have been very warm for
the valleys to form. In most locations, there could have been snow
and ice instead of rain. It would only have needed temperatures to
rise above the freezing point occasionally to get ice and snow to thaw
and give flowing water, and that does not require very much atmosphere.
The Curiosity Mars rover mission has found evidence of ancient top-of-
atmosphere loss, from the modern Mars atmosphere's isotopic carbon
ratio. Uncertainty remains about how much of that loss occurred
before the period of valley formation; much may have happened earlier.
The MAVEN orbiter, examining the outer atmosphere of Mars since late
2014, may help reduce the uncertainty.
PLUTO PROBE'S NEXT TARGET
BBC News
The New Horizons spacecraft has a new target to aim for following its
historic flyby of Pluto. It is called 2014 MU69, and was one of two
comet-like objects that were under consideration by scientists working
on the mission. The US space agency will now carry out a review of
the plan before officially approving the mission's extension. New
Horizons carried out its flyby of Pluto in July, approaching within
12,500 km of the surface. The spacecraft obtained detailed images and
other data not only of Pluto, but also of its moons, Charon, Styx,
Nix, Kerberos and Hydra. The new target is about a thousand million
miles beyond Pluto. It is about 45 km across and is thought to be one
of the type of building blocks from which bigger objects such as Pluto
were formed. Such objects form a region of the outer Solar System
called the Kuiper Belt, containing a deep-frozen sample of what our
neighbourhood was like when it formed 4.6 billion years ago. The
spacecraft carries enough hydrazine fuel for another fly-by, and
scientists say it could continue operating into the late 2020s or
beyond. 2014 MU69 costs less fuel to reach than other candidate
targets, leaving more fuel for the fly-by, for ancillary science, and
greater fuel reserves to protect against the unforeseen. In summer
2014, the Hubble telescope discovered five icy objects, later narrowed
to two, within New Horizons' flight path. In late October and early
November, the spacecraft will perform a series of engine burns to set
its course towards 2014 MU69 for an encounter currently set for 2019
January 1.
SUPERMASSIVE BLACK HOLES IN NEAREST QUASAR
University of Oklahoma
Astrophysicists using observations from the Hubble telescope have
found two super-massive black holes in Markarian 231, the quasar
nearest to us. The discovery of *two* black holes -- of unequal
masses -- is evidence of a binary black hole and may suggest that
super-massive black holes assemble their masses through violent
mergers. The observers looked at ultraviolet radiation emitted from
the centre of Mrk 231; then they applied a model that they developed
to the spectrum of the galaxy and recognized the existence of the
binary black hole. The observation not only shows the existence of a
close binary black hole in Mrk 231, but also paves a way to search for
other binary black holes from the nature of their ultraviolet light
emission. The denizens of the Universe, such as giant galaxies and
clusters of galaxies, grow by the merging of smaller systems into
larger ones, and binary black holes are natural consequences of
mergers of galaxies. Eventually, the two black holes discovered in
Mrk 231 will collide and merge to form a quasar with a super-massive
black hole.
CLUES TO STAR BIRTH IN NEIGHBOURING GALAXY
Space Telescope Science Institute (STScI)
In a survey of Hubble images of 2,753 young, blue star clusters in the
Andromeda galaxy (M31), astronomers have found that M31 and our own
Galaxy have similar percentages of newborn stars in terms of mass.
From the distribution of stellar masses within a cluster (the 'Initial
Mass Function' or IMF), scientists are more likely to be able to
interpret the light from distant galaxies and understand the formation
history of the stars. The intensive survey, assembled from 414 mosaic
photographs taken by Hubble of M31, was a collaboration between
astronomers and 'citizen scientists', volunteers who provided
invaluable help in analyzing the mountain of data from Hubble.
Measuring the IMF was the primary driver behind Hubble's survey,
called the 'Panchromatic Hubble Andromeda Treasury' (PHAT). Nearly
8,000 images of 117 million stars in the galaxy's disc were obtained
from viewing Andromeda in near-ultra-violet, visible, and near-
infrared wavelengths. Stars are born when a cloud of molecular
hydrogen, dust, and trace elements collapses. The cloud fragments
into knots of material that each precipitate hundreds of stars. The
stars are not all created equally: their masses can range from 1/12th
to 200 solar masses. Until now, astronomers have only had IMF
measurements made in the local stellar neighbourhood within our own
Galaxy, but the M31 survey has offered a good sampling of star
clusters that are all at approximately the same distance of about 2.5
million light-years. The survey is diverse because the clusters are
scattered across M31; they vary in mass by factors of 10, and they
range in age from 4 million to 24 million years.
To the researchers' surprise, the IMF was very similar among all the
clusters surveyed. Nature apparently cooks up stars with a consistent
distribution from massive blue supergiants to small red dwarfs.
Curiously, the brightest and most massive stars in the clusters are
25% less abundant than suggested by previous research. Astronomers
use the light from the brightest stars to estimate the masses of
distant star clusters and galaxies and to measure how rapidly the
clusters are forming stars. The new result suggests that mass
estimates in previous work were too low because they assumed that
there were too few faint, low-mass stars forming along with the
bright, massive stars. The evidence also implies that the early
Universe did not have as many heavy elements for making planets,
because there would be fewer supernovae from massive stars to
manufacture heavy elements for planet building. It is critical to
know the star-formation rate in the early Universe -- about 10 billion
years ago -- because that was the time when most of the Universe's
stars formed. The PHAT star-cluster catalogue, which forms the
foundation of the study, was assembled with the help of 30,000
volunteers who sifted through the thousands of images taken by Hubble
to search for star clusters. The Andromeda Project is one of the many
citizen-science efforts hosted by the Zooniverse organization. Over
the course of 25 days, the citizen-scientist volunteers submitted 1.82
million individual image classifications (based on how concentrated
the stars were, their shapes, and how well the stars stood out from
the background), which roughly represents 24 months of constant human
attention. Scientists used those classifications to identify a sample
of 2,753 star clusters, increasing the number of known clusters by a
factor of six in the PHAT survey region.
FARTHEST GALAXY EVER DETECTED
California Institute of Technology
A team of researchers that has spent years searching for the earliest
objects in the Universe now reports the detection of what may be the
most distant galaxy ever found. There is evidence for a galaxy called
EGS8p7 that is more than 13.2 billion years old. The Universe itself
is about 13.8 billion years old. Earlier this year, EGS8p7 had been
identified as a candidate for further investigation on the basis of
data gathered by the Hubble and Spitzer space telescopes. Using the
'multi-object spectrometer for infrared exploration' at the Keck
Observatory in Hawaii, the researchers determined its redshift from
the wavelength of the Lyman-alpha line, whose laboratory wavelength is
well down in the ultraviolet. A surprising aspect of the observation
is the detection of Lyman-alpha in a faint galaxy at a redshift of
8.68, corresponding to a time when the Universe has been thought to be
full of absorbing hydrogen clouds. Before the new discovery, the
farthest detected galaxy had a redshift of 7.73. One possible reason
why the object may be visible despite the hydrogen-absorbing clouds,
the researchers say, is that hydrogen re-ionization did not occur in a
uniform manner. Evidence from several observations indicates that the
re-ionization process was probably patchy. Some objects are so bright
that they form a bubble of ionized hydrogen, but the process is not
coherent in all directions. The galaxy EGS8p7 is unusually luminous,
and may be powered by a population of unusually hot stars, and have
special properties that enabled it to create a large bubble of ionized
hydrogen much earlier than would have been possible for more typical
galaxies at those times. Researchers are currently trying to estimate
more thoroughly the chances of finding that galaxy and seeing such
emission from it, and to understand whether they need to revise the
time-line of the re-ionization, which is one of the major questions
to answer in our understanding of the evolution of the Universe.
RUSSIA OFFICIALLY GOING BACK TO MOON
Tech Insider
Over 40 years have passed since human beings walked on the Moon, and
all of them were American. Russia has some grand plans to change that
as the US turns its attention to Mars. Roscosmos, the Russian space
agency, wants to set up a high-tech lunar base, complete with human
habitats, scientific and technical laboratories, a launching and
landing port for spacecraft, and even an astronomical observatory.
Roscosmos's concern with the Moon has a complicated past. During the
Apollo-era space race, the former Soviet Union landed robotic rovers
on the Moon -- but a series of rocket failures and explosions halted
progress on any man-carrying missions. Eventually, Roscosmos decided
that its Moon programme was not worth the money and the risk and shut
it down. But now Roscosmos is reviving that programme and thinking of
sending (but not in the near future) a robotic spacecraft, called Luna
25, to the Moon to do some scouting for a future lunar base. The
agency has announced that it will land Luna 25 at the Moon's south
pole in 2024. Engineers are already building the spacecraft, and the
finished product will carry eight cameras to help it navigate, take
pictures, and keep an eye on its drill tool as it digs into the lunar
surface. The Luna 25 spacecraft will run its electronics with a
battery fuelled by plutonium-238. Roscosmos isn't the only agency
thinking about a return to the Moon. ESA has already announced plans
for its own ambitious Moon colony.
Topic: Mid September Astronomy Bulletin (Read 1512 times)