SPOTLESS SUN FOR THE FIRST TIME IN NEARLY A CENTURY
NASA
According to data from Mount Wilson Observatory, more than an entire
month has passed without the Sun showing a spot. The last time such an
event occurred was in 1913 June. Sunspot data have been collected
since 1749. The event may be significant, as many climatologists now
believe that solar magnetic activity -- which affects the number of
sunspots -- influences climate on the Earth.
When the Sun is active, it is not uncommon for sunspot numbers to be
100 or more in a single month. Every 11 years, activity slows, and
numbers briefly drop nearly to zero. Normally sunspots return very
quickly, as a new cycle begins. But this year -- which corresponds to
the start of Solar Cycle 24 -- the minimum has been extraordinarily
long and quiet, with the first seven months averaging a sunspot number
of only 3, August following with none at all. In the past 1000 years,
three previous such events (necessarily inferred from data more
oblique than actual sunspot counts) -- the Dalton, Maunder and Spörer
Minima -- have all been associated with rapid cooling, in one case
enough to be called a 'mini ice age'.
ROSETTA PROBE MAKES ASTEROID PASS
ESA
The Rosetta space probe, whose prime goal is to catch and orbit Comet
67P/Churyumov- Gerasimenko out near Jupiter in 2014, has observed the
4.6-km asteroid (2867) Steins. The probe passed it on September 5,
about 360 million km from the Earth,in the asteroid belt between the
orbits of Mars and Jupiter, at a distance of about 800 km and a
relative speed of 8.6 km/s. Rosetta will make another asteroid
rendezvous before reaching the comet, visiting Lutetia on 2010 June
10, but passing at the larger distance of 3000 km.
Only a few asteroids have so far been observed by spacecraft. They
have proved to be very different in shapes, sizes and compositions.
They are often referred to as 'rubble', because they represent
leftovers that were never incorporated into planets when the Solar
System formed 4.6 billion years ago. As with comets, they may contain
very primitive materials that have not undergone the constant
recycling experienced by, for example, Earth rocks. Once in orbit
around Comet Churyumov-Gerasimenko, whose nucleus is thought to be
about 4 km across, the craft will despatch a small lander called
Philae to the surface to study the object's chemistry. The mission
will then follow the comet as it moves in towards the Sun, monitoring
the changes that take place on the icy body.
NEW PARTIAL RINGS DISCOVERED AROUND SATURN
Space .com
The Cassini spacecraft has found two new, partial rings around Saturn
that each accompany a small moon, shedding light on what determines
whether a partial or complete ring forms with the moon. The partial
rings, called ring arcs, extend ahead of and behind the small
Saturnian moons Anthe and Methone in their orbits. Both Anthe and
Methone orbit Saturn in locations called resonances, where the gravity
of the nearby larger moon Mimas disturbs their orbits. Mimas produces
a regular gravitational impulse on each moon, which causes the moons
to skip forwards and backwards within an arc-shaped region along their
orbital paths.
Scientists believe that the faint ring arcs consist of material
knocked off the small moons by micrometeoroid impacts. The material
does not spread all the way around Saturn to form a complete ring
because the interactions of the moons with Mimas confine the material
to a narrow region along the moons' orbits. The recent Cassini images
were the first detection of arc material near Anthe; the Methone arc
was detected by Cassini previously. Cassini images have also shown
faint rings connected with other small moons within or near the
outskirts of Saturn's main ring system, such as Pan, Janus, Epimetheus
and Pallene. Cassini has also previously observed an arc in the G
ring, one of Saturn's faint complete rings.
NEARBY STAR APPEARS TO HAVE DENSER ANALOGUE OF KUIPER BELT
New Scientist
A ring of debris around a nearby star appears to be a much bigger
version of our Solar System's Kuiper belt, the region of ice-rich
objects beyond Neptune that is thought to be a reservoir of comets.
A team of astronomers used the orbiting Spitzer telescope and the
Gemini South telescope in Chile to study infrared light from the disc
around HD 181327, which lies about 150 light-years away. They saw
a peak in brightness at a wavelength of around 63 microns, which
is characteristic of water ice, evidence that the composition may be
similar to our Kuiper belt. The disc has a radius of about 12 billion
kilometres, roughly twice the size of the Kuiper belt. It is also
exceptionally bright, suggesting that it holds a lot of material -- so
the system may be swarming with comets.
'NAKED EYE' GAMMA-RAY BURST WAS AIMED SQUARELY AT EARTH
RAS
The brightest explosion ever seen (in terms of absolute brightness or
candle-power) was observed in March this year. Now a team of
astronomers from around the world has combined data from various
satellites and observatories in an effort to explain what happened.
They show that the jet from a powerful stellar explosion in a galaxy
halfway across the Universe was aimed almost directly at Earth. The
event, called a Gamma-Ray Burst (GRB), was bright enough for human
eyes to see. GRBs are the Universe's most luminous explosions.
Early in the morning of March 19, the Swift satellite pinpointed
an extremely bright GRB and immediately sent out an alert to
observatories around the world. Two robotic cameras in Chile also
observed the brief flash. Within minutes many more telescopes were
observing, allowing the most detailed study of a bright GRB ever
undertaken, with data from gamma-ray to radio wavelengths.
The team of astronomers concludes that the extraordinary brightness of
the burst arose from a narrow jet that shot material directly towards
the Earth at 99.99995% of the speed of light. The data clearly reveal
the complexity of a GRB in which a narrow, ultra-fast jet is present
within a wider, slightly less fast jet. Astronomers normally detect
only the wide jet of a GRB as the inner jet is very narrow, equivalent
to not much more than 1/100th the angular size of the Full Moon. It
seems that to see a very bright GRB the narrow jet has to be pointing
precisely at the Earth. We would expect that to happen only about
once per decade. The GRB is thought to have been created when a
massive star ran out of nuclear fuel. The star's core collapsed to
form a black hole, driving powerful jets outwards. Such jets are
amongst the fastest flows of bulk matter in the cosmos, moving close
to the speed of light.
What makes that GRB unique is its extremely bright prompt optical
emission which coincides in time with the gamma-rays, and was recorded
with very high time resolution. The optical light and the gamma-rays
are produced by different emission mechanisms, but most likely came
from the same physical region, far from the progenitor star. The
optical burst would in principle have been visible to the naked eye,
although nobody is known actually to have seen it,
PHOENIX MISSION EXTENDED
University of Arizona
NASA has deemed the Phoenix Mars lander, having completed its 90-day
primary mission, to have sufficient power and experimental capacity
to continue operations until September 30. Phoenix has found the
presence of water-ice at its landing site, determined that the soil is
alkaline, and identified magnesium, sodium, potassium, chloride and
perchlorate in the soil. Chemical analyses continue even as Phoenix's
robotic arm reaches out for more samples. Meteorological instruments
have made daily atmospheric readings and have watched as the pressure
decreases, signalling a change in the season. At least one ice cloud
has been observed, and consistent wind patterns have been recorded
over the landing site.
Meanwhile, plans call for Phoenix to widen its deepest trench, about
18 cm deep, to scoop a fresh sample of soil for analysis in the
lander's 'wet chemistry laboratory'. The first attempt to collect the
sample, on August 26, got 2 to 3 cubic cm into the scoop, which was
judged to be not quite enough, so delivering the sample was deferred.
In coming days the team also plans to test a different method for
handling a sample rich in ice. Two such samples previously stuck to
the scoop.
CHINA SETS DATE FOR SPACE LAUNCH
BBC News
China will launch its third manned space mission in late September.
The Shenzhou VII flight will feature China's first 'space walk', which
will be broadcast live with cameras inside and outside the spacecraft.
Three 'yuhangyuan' (astronauts) will blast off on a Long-March II-F
rocket some time between September 25 and 30. In 2003, China became
only the third country in the world to send anyone into orbit. It
followed with a two-man mission in 2005. The Shenzhou spacecraft
closely resembles the Russian Soyuz capsules, but is substantially
larger. Unlike the Soyuz, it has an orbital module that is equipped
with its own propulsion, allowing autonomous flight. According to
reports, a small satellite will also be launched during the mission.
China launched an unmanned Moon probe last year about one month after
rival Japan blasted its own lunar orbiter into space.
Topic: Mid September Astronomy Bulletin (Read 2142 times)