The SOCIETY for POPULAR ASTRONOMY

The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 252 2008 September 14

Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is Britain's liveliest Astronomical society, with members all over the world. We accept subscription payments online using our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://tinyurl.com/kogyx

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.

The SPA Electronic News Bulletins are sponsored by the Open University.

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Bulletin compiled by Clive Down