ORGANISMS SURVIVE UNDER MARTIAN CONDITIONS
University of Arkansas
New research suggests that methanogens -- among the simplest and
oldest organisms on Earth -- could survive on Mars. Methanogens,
microorganisms in the domain Archaea, use hydrogen as their energy
source and carbon dioxide as their carbon source, to metabolize and
produce methane. Methanogens live in swamps and marshes, but can also
be found in the gut of cattle, termites and other herbivores as well
as in dead and decaying matter. Methanogens are anaerobic, and do not
require require oxygen. They do not require organic nutrients and are
non-photosynthetic, so they could exist in sub-surface environments
and therefore are good candidates for life on Mars. Researchers
subjected two species of methanogens, Methanothermobacter wolfeii and
Methanobacterium formicicum, to Martian conditions.
The species were tested for their ability to withstand Martian freeze-
thaw cycles that are below the organisms' ideal growth temperatures:
37 degrees Celsius for M. formicicum and 55 degrees Celsius for M.
wolfeii. The surface temperature on Mars varies widely, often ranging
between -90 and +27C over the Martian day. If any life were to exist
on Mars now, it would have to survive at least that temperature range.
The survival of the two methanogen species exposed to long-term
freeze/thaw cycles suggests that methanogens could potentially inhabit
the sub-surface of Mars. The two species were selected because one is
a hyperthermophile, meaning it thrives in hot temperatures, and the
other is a thermophile, which thrives in warm temperatures. The low
temperature on Mars inhibited their growth, but they survived. Once
they got back to a warm temperature, they were able to grow and
metabolize again. In 2004, scientists discovered methane in the
Martian atmosphere, and the question of the source arose. One
possibility could be methanogens.
ASTRONOMERS DISCOVER PLANETS ORBITING KAPTEYN'S STAR
RAS
An international team of scientists reports two new planets orbiting
Kapteyn's star, one of the oldest stars found near the Sun.
Discovered at the end of the 19th century by the Dutch astronomer
Jacobus Kapteyn, the star is the second-fastest-moving one in the sky
in angular terms (proper motion), and belongs to the Galactic halo, an
extended cloud of stars orbiting our galaxy. It is a red dwarf of
spectral type M1, having about a third of the mass of the Sun; it is
catalogued as HD 33793 and is in the southern constellation Pictor,
and at magnitude 8.85 it is easily seen in a small telescope.
The astronomers used the HARPS radial-velocity spectrometer at the ESO
La Silla observatory in Chile to measure tiny periodic changes in the
motion of the star and deduce the masses and orbital period of the
planetary bodies responsible for those changes. The planet Kapetyn b
is at least five times as massive as the Earth and orbits the star
every 48 days; it must be warm enough for liquid water to be present
on its surface. The second planet, Kapteyn c, is a more massive
super-Earth; its year lasts 121 days and astronomers think it is too
cold to have liquid water. At the moment, only a few properties of
the planets are known: approximate masses, orbital periods, and
distances from the star.
Typical planetary systems detected by the Kepler mission are hundreds
of light-years away. but, Kapteyn's star is the 25th-nearest star to
the Sun, 'only' 13 light years away. It is thought to have had an
unusual history, as it seems likely to have been born in a dwarf
galaxy absorbed and disrupted by the early Milky Way. The disruption
event put the star into a high-velocity halo orbit round our Galaxy.
The probable remnant core of the original dwarf galaxy is Omega
Centauri, an enigmatic globular cluster 16000 light-years away which
contains hundreds of thousands of similarly old stars. That sets the
most likely age of the planets at 11.5 billion years, which is 2.5
times the age of the Earth and 'only' 2 billion years younger than the
Universe itself (around 13.7 billion years).
ASTRONOMERS FIND NEW TYPE OF PLANET
Harvard-Smithsonian Center for Astrophysics
Astronomers have discovered a new type of planet -- a massive rocky
one. It is called Kepler-10c and circles a Sun-like star once every
45 days. It is about 560 light-years from us in the constellation
Draco. It was discovered by the Kepler spacecraft, which finds
planets by looking for stars that show periodic dimmings when planets
pass in front of them. From the amount of dimming, astronomers can
estimate a planet's size. However, Kepler can not tell whether a
planet is rocky or gassy. Kepler-10c was known to have a diameter of
about 18,000 miles, 2.3 times as large as the Earth. That suggested
that it fell into a category of planets known as mini-Neptunes, which
have thick, gaseous envelopes. However, the team used the HARPS-North
instrument on the Telescopio Nazionale Galileo (TNG) in the Canary
Islands to measure the mass of Kepler-10c, and found it to be 17 times
as much as the Earth -- far more than expected. It must have a dense
composition of rocks and/or other solids. Theorists have a hard time
explaining how such a large, rocky planet could develop -- they
believed that such a planet could not form because anything so massive
would accrete hydrogen as it grew and become a Jupiter-like gas giant.
The system also hosts a 3-Earth-mass 'lava world', Kepler-10b, in a
remarkably fast 20-hour orbit.
STELLAR BEHEMOTH SELF-DESTRUCTS IN TYPE IIb SUPERNOVA
DOE/Lawrence Berkeley National Laboratory
Our Sun may seem pretty impressive: a third of a million times as
massive as the Earth, it accounts for 99.86% of the Solar System's
total mass. Yet in comparison with some other stars, it's a
lightweight. The real cosmic behemoths are Wolf-Rayet stars, which
are more than 20 times as massive as the Sun and at least five times
as hot. Because such stars are relatively rare and often obscured,
scientists do not know much about how they form, 'live' and 'die'.
But they are learning, thanks to a new sky survey called the
intermediate Palomar Transient Factory (iPTF), to observe fleeting
cosmic events such as supernovae. For the first time, scientists have
direct confirmation that a Wolf-Rayet star -- 360 million light-years
away in the constellation Bootes -- died in a violent explosion known
as a Type IIb supernova. Using the iPTF pipeline, researchers at
Israel's Weizmann Institute of Science observed supernova SN 2013cu
within hours of its explosion. They then triggered ground- and
space-based telescopes to observe the event approximately 5.7 hours
and 15 hours after it self-destructed. Those observations are
providing valuable insights into the life and death of the progenitor
Wolf-Rayet. For the first time, we can say that that type of Wolf-
Rayet star leads to that kind of supernova.
Some super-massive stars become Wolf-Rayets in the final stages of
their lives. Scientists find such stars interesting because they
enrich galaxies with the heavy chemical elements that could
potentially become the building blocks for planets and life.
Astronomers are gradually determining which kinds of stars explode,
and why, and what kinds of elements they produce. The Wolf-Rayet
phase occurs before the supernova. As nuclear fusion slows, the heavy
elements forged in the star's core are mixed to the surface and set
off powerful winds. The winds shed a tremendous amount of material
into space and obscure the star from prying telescopes on Earth. When
a Wolf-Rayet star goes supernova, the explosion typically overtakes
the stellar wind and all information about the progenitor star is
gone. Astronomers were lucky with SN 2013cu -- they caught the
supernova before it overtook the wind. Shortly after the star
exploded, an ultraviolet flash from the shock wave heated and lit up
the wind. The conditions that were observed at that moment were very
similar to what was there before the supernova. Before the supernova
debris overtook the wind, the iPTF team observed its spectrum with the
Keck telescope in Hawaii and saw the telltale signs of a Wolf-Rayet
star. When the team performed follow-up observations nine hours later
with the Swift satellite, the supernova was still hot and strongly
emitting in the ultraviolet. In the following days, iPTF collaborators
rallied telescopes around the world to watch the supernova shell
crash into material that had previously been ejected from the star.
As the days went by, the researchers were able to classify SN 2013cu
as a Type IIb supernova because of the weak hydrogen signatures and
strong helium features in the spectra that appeared after the
supernova cooled.
With the largest telescopes it might be possible to get a spectrum of
a Wolf-Rayet star in the nearest galaxies to the Milky Way, perhaps
4 million light-years away. SN 2013cu is 360 million light years away
-- further by almost factor of 100. It was because the researchers
caught the supernova early -- when the ultraviolet flash lit up the
progenitor's stellar wind -- that they were able to obtain spectra.
FAILED DWARF GALAXY SURVIVES GALACTIC COLLISION
National Radio Astronomy Observatory
A high-velocity hydrogen cloud hurtling toward the Milky Way appears
to be encased in a shell of dark matter, according to a new analysis.
Astronomers believe that without its protective shell, the high-
velocity cloud known as the Smith Cloud would have disintegrated long
ago when it first collided with the disc of our Galaxy. If confirmed
by further observations, a halo of dark matter could mean that the
Smith Cloud is actually a failed dwarf galaxy, an object that has all
the right stuff to form a true galaxy, just not enough to produce
stars. The Smith Cloud is fast, quite extensive, and close enough to
study in detail. It is also a bit of a mystery; such an object ought
not to survive a trip through the Milky Way, but all the evidence
points to the conclusion that it did. Previous studies of the Smith
Cloud indicated that it first passed through our Galaxy many millions
of years ago. By re-examining and carefully modelling the cloud,
astronomers now believe that the Smith Cloud contains and is actually
wrapped in a substantial halo of dark matter -- the gravitationally
significant yet invisible stuff that in recent years has been
suggested to make up about 80% of all the matter in the Universe. It
is all the extra dark matter that seems to have enabled the cloud to
survive the disc crossing.
The Milky Way has hundreds of high-velocity clouds, which are made up
primarily of hydrogen gas that is too rarefied to form stars in any
detectable amount. The only way to observe those objects is with
radio telescopes which can detect the faint emission of neutral
hydrogen. If it were visible to the naked eye, the Smith Cloud would
cover almost as much of the sky as the constellation Orion. Most
high-velocity clouds share a common origin with the Milky Way, either
as the leftover building blocks of galaxy formation or as clumps of
material launched by supernovae in the disc of the Galaxy. A rare
few, however, are interlopers from further off in space with their own
distinct pedigree. A halo of dark matter would strengthen the case
for the Smith Cloud being one of those exceptions. Currently, the
Smith Cloud is about 8,000 light-years away from the disc of our
Galaxy. It is moving towards the Milky Way at more than 250 km/s
and is predicted to impact again in approximately 30 million years.
[Note by editor: those numbers are not self-consistent. At 250 km/s,
8000 light-years would take less than 10 million years.] If confirmed
to have a lot of dark matter, the cloud would in effect be a failed galaxy.
Such a discovery would begin to indicate the lower limit to how small a
galaxy could be.
VERY DISTANT GALAXY CLUSTER CONFIRMED
Carnegie Institution
The structures and star populations of massive galaxies appear to
change as they age, but much about how those galaxies formed and
evolved remains unknown. Many of the oldest and most massive galaxies
are in clusters. Galaxy clusters in the early Universe are thought to
be the key to understanding the life-cycles of old galaxies, but to
date astronomers have located only a handful of such rare, distant
structures. New research has confirmed the presence of an unusually
distant cluster, JKCS 041, and observations of it make it one of the
best-studied structures from the early Universe. Astronomers began
studying JKCS 041 in 2006, but it has taken a long time to determine
its distance. The team took spectra with the Hubble telescope, and
found 19 galaxies at the same distance of 9.9 billion light-years,
evidently members of a cluster. A previous study with the Chandra
X-ray observatory discovered X-ray emissions from the location of
JKCS 041; the X-rays must originate from hot gas in the cluster.
Today the largest and oldest galaxies are found in clusters, but it is
not known when and why the giant galaxies stopped forming new stars
and became dormant, or quiescent. Looking back to a time when the
galaxies in JKCS 041 were only 1 billion years old, the team found
that most had already entered a quiescent phase. Because JKCS 041 is
the most-distant known cluster of its size, it gives astronomers the
best opportunity to study old galaxies in detail. Even after massive
galaxies enter their quiescent phase, they continue to increase in
overall size. That is thought to occur as they collide and merge with
one another. Early clusters have been suspected to be prime locations
for collisions, but to the team's surprise it found that the galaxies
in JKCS 041 were growing at only about the same rate as non-cluster
galaxies.
Topic: Early June Astronomy Bulletin (Read 1880 times)