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Tuesday, 28 September 2010

SPA ENB No. 295

       Electronic News Bulletin No. 295     2010 September 26
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
at 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
By Richard Bailey, SPA Solar Section Director
The Solar Section Monthly Reports, with many pictures sent in by
Section members, can be viewed by going to the SPA home page, then to
the Solar Section link.  On the left-hand side of it is the list of
Reports, the latest being for 2010 August.  There are two pages of
pictures on the most recent Reports.  I upload my Monthly Section
Reports as soon as possible after the end of each month.
By Alastair McBeath, SPA Meteor Section Director
An exciting development over the summer has been the creation of an
all-sky fireball camera system for southeastern Britain, run by the
University of Hertfordshire.  At present, it has four operational
stations, at Bayfordbury and Hemel Hempstead (both in Herts), Niton
(Isle of Wight) and Cromer (Norfolk).  The Bayfordbury Observatory
camera has been running on a trial basis since 2009 October, and among
its captures were several single-station Perseid fireballs in 2010
August.  However, the first multi-site recording of a fireball was from
three of the four stations soon after they had all become active, on
September 5-6.  (A computer fault lost the data from the Hemel
Hempstead system, unfortunately including details on the meteor's
velocity and duration.)  The fireball occurred at 00:39 UT, and
information calculated from the triangulated trail indicated the
meteor passed on an ESE-WNW track (the trail heading was towards
azimuth 275°), starting at 103 km altitude nearly above Chelmsford in
Essex, and ending at 81 km altitude almost above Hertford, just 9 km
ENE of the Bayfordbury camera.  The trail length was 46 km, descending
at an angle to the horizontal of 29° (data kindly provided by
Hertfordshire University analyst David Campbell).  There are links to
the three images and more information about the Hertfordshire
University camera system on the SPA's General Chat Forum topic at:
David Campbell also reported that the meteor had been imaged by the
Cambridge University Institute of Astronomy's all-sky camera
( and another elsewhere operated by Paul
Beesken.  The trail was recorded too by Klaas Jobse at Oostkapelle in
the Netherlands (see: ).
Many congratulations go to all involved!
By Alastair McBeath, SPA Meteor Section Director
Fresh results arriving since ENB 294 appeared have helped fill some of
the gaps in the SPA's coverage of this favourite shower, with over
3500 Perseids now reported.  Zenithal Hourly Rates (ZHRs) on August
12-13 have suggested a peak of ~100 +/- 10 around 22h-23h UT, but they
apparently dropped to ~70 +/- 5 from 00h-02h, before picking up again
to ~90 +/- 5 from 03h-06h, declining generally thereafter.  The
International Meteor Organization's (IMO's) findings, based on many
more data, have remained similar to those noted last time, however
(see: ), so it is uncertain how
accurate the features in the SPA analysis may have been.
I carried out my usual analysis of the Perseid radio results just
before the International Meteor Conference at Armagh (September
16-19), drawing on reports from the near-peak period as presented in
Radio Meteor Observation Bulletin 205 for 2010 August (see: for details of all the observers and their
equipment).  Three datasets from North America and 12 from Europe were
deemed sufficiently complete, accurate and free from interference to
be fully analysed. The main findings were as follows.
1) The better Perseid activity probably happened from ~17h UT
on August 12 to ~17h on August 13, although this was not strongly
confirmed beyond 11h on the 13th.
2) The main Perseid peak probably occurred between 01h and 11h UT
on August 13. There may have been two phases within that interval,
one around 02h-05h UT, the other from 08h-10h, but the possibility
that that was influenced by radiant geometry could not be ruled out.
3) There was evidence for a possible early peak on August 12,
between 17 and 19h UT, especially 18h-19h, in some datasets from
both Europe (where the circumpolar Perseid radiant was near its
lowest for the day) and North America (from where the radiant
geometry was much more favourable).  However, that potential
event seemed weaker than the main maximum activity on August 13,
and may have been less rich in brighter meteors (events producing
longer-duration radio echoes).
4) While generally in line with the IMO's Perseid visual results,
the ZHR ~130, short-lived peak found around 17:00-17:30 UT on
August 12 was not well confirmed, either in its apparent strength or
As always, grateful thanks and praise go to all our contributors.
By Alastair McBeath, SPA Meteor Section Director
New details on the June Boötids have appeared recently in the German
Arbeitskreis Meteore journal "Meteoros" (Vol. 13, No. 8).  IMO Video
Commission Director Sirko Molau presented these as part of his June
video-meteor review.  The European video cameras detected increased
Boötid activity from the usual radiant on June 23-24.  However, the
activity was barely one-third that of the concurrent sporadics, and
the shower's video-rate seemed near to or below the level that can be
usefully detected visually.  That may be why there were both negative
and weak positive visual reports that night (see ENBs 291 & 292, at
The IMO's journal WGN will publish an English-language version of the
video findings shortly.
The recent discovery of water on the Moon may have an impact on future
plans for Moon-based astronomy.  Space scientists from the Chinese
Academy of Sciences have calculated that the scattering caused by
molecules vaporised in sunlight could distort certain observations
from telescopes mounted on the Moon.  The research has particular
implications for the Chinese lunar lander, Chang'E-3, which is planned
to be launched in 2013.  An ultraviolet astronomical telescope will be
installed on the lander, which will operate on the sunlit surface of
the Moon, powered by solar panels.  At certain ultraviolet
wavelengths, hydroxyl molecules cause a particular kind of scattering
where photons are absorbed and rapidly re-emitted.
The Moon's potential as a site for astronomical observatories has been
discussed since the era of the Space Race.  Moon-based telescopes
could have several advantages over telescopes on Earth, including a
cloudless sky and low seismic activity.  The far side of the Moon
could be an ideal site for radio astronomy, being permanently shielded
from interference from the Earth.  Radio observations would not be
affected by plausible hydroxyl levels.
The origin of the Martian satellites Phobos and Deimos is a
long-standing puzzle.  It has been proposed that both moons may be
asteroids that were captured by Mars' gravity.  Spectra of Phobos at
visible and near-infrared wavelengths have been considered to be
analogous to those of carbonaceous-chondrite meteorites, commonly
associated with asteroids dominant in the middle part of the asteroid
belt, but recent thermal-infrared observations show poor agreement
with any class of chondritic meteorite.  They instead argue in favour
of in-situ formation, by re-accretion of rocky debris lofted into
orbit round Mars by a large impact.  Two quasi-independent
compositional analyses of thermal-infrared spectra, from the Mars
Express and Mars Global Surveyor missions, yield very similar
conclusions.  The re-accretion picture is strengthened by the
measurements of Phobos's high porosity from the radio-science
experiment on Mars Express.
Astronomers detected for the first time a type of mineral called
phyllosilicates on the surface of Phobos, particularly in the areas
northeast of Stickney, its largest impact crater.  That is intriguing,
as it implies the interaction of silicate materials with liquid water
on the parent body prior to incorporation into Phobos.  Alternatively
phyllosilicates may have formed in situ, but that would mean that
Phobos required sufficient internal heating to enable liquid water to
remain stable.  More detailed mapping, in-situ measurements from a
lander, or sample return would ideally help to settle the issue.
Other observations appear to match the types of minerals identified on
the surface of Mars. Thus, the derived composition on Phobos appears
more closely related to Mars than to objects elsewhere in the Solar
System.  The asteroid-capture proposals also have difficulty in
explaining the current near-circular and near-equatorial orbits of
both Martian moons.
The radio-science team has used the Doppler shifts in the frequency of
the spacecraft's transmissions to determine the perturbations of the
craft's trajectory by the gravitational attraction of Phobos, and
hence the satellite's mass.  The resulting estimate of Phobos' density
is 1.86 ± 0.02 g/cm3 -- significantly lower than the density of
meteoritic material associated with asteroids.  It is held to imply a
sponge-like structure, with voids making up 25-45% in Phobos's
interior.  High porosity seems anyway to be required in order to
absorb the energy of the large impact that generated Stickney crater
without destroying the body.  A highly porous interior of Phobos
supports the idea of formation by re-accretion of rocky material in
orbit round Mars.  In that process, modelling suggests that the
largest blocks re-accrete first because of their larger mass, forming
a core with large boulders.  Then the smaller debris re-accrete but do
not fill the gaps left between the large blocks because of the low
self-gravity of the small body in formation.  Finally, a relatively
smooth surface of finely-divided material masks the voids inside the
Harvard-Smithsonian CfA
Beyond the orbit of Neptune are countless icy rocks known as trans-
Neptunian objects (TNOs).  Four of the biggest, including Pluto, are
classified as dwarf planets.  The region also has many comets, such as
Halley's Comet.  TNOs are small and receive little sunlight, so they
are faint and difficult to detect.  Now, astronomers searching the
data archives of the Hubble telescope have added 14 new ones to the
catalogue, and their method promises to turn up many more.  As TNOs
slowly orbit the Sun, they move against the starry background,
appearing as streaks in time-exposure photographs.  The team developed
software to analyze hundreds of Hubble images looking for such
streaks.  After promising candidates were flagged, the scientists
themselves examined the images to try to confirm or refute each
Most TNOs are located near the ecliptic, so the team searched within
5° of the ecliptic to increase the chance of success.  They found 14
objects, including one binary pair.  All were very faint, most being
between magnitudes 25 and 27.  According to estimates based on their
distances and magnitudes, the new-found TNOs range from 40 to 100
kilometres across.  The initial study examined only one-third of a
square degree of the sky, so hundreds more TNOs may well be
discoverable in the rest of the Hubble archives.
A new golden age of sailing may be about to begin -- in space.  Future
missions to explore the outer planets could employ fleets of
'data clippers', manoeuvrable spacecraft equipped with solar sails, to
ship vast quantities of scientific data back to the Earth.  The
technology could be ready in time to support mid-term missions to the
moons of Jupiter and Saturn.  Space-rated flash memories will soon be
able to store the huge quantities of data needed for the global
mapping of planetary bodies at high resolution.  But a full
high-resolution map of, say, Europa or Titan would take several
decades to download from orbiters of current designs.  Downloading
data is a major design driver for interplanetary missions, and
scientists believe that data clippers would be an efficient way of
overcoming the bottleneck.  They have carried out a preliminary
assessment for a data-clipper mission.  The concept is for a clipper
to fly close to a planetary orbiter, upload its data and then pass
close to the Earth, at which point terabytes of data could be
downloaded to a ground station.  A fleet of data clippers cruising
around the Solar System could provide support for an entire suite of
planetary missions.
Scientists have looked at the challenges of a data-clipper mission and
think that it could be ready for a launch in the late 2020s.  Recent
advances in technology mean that spacecraft propelled by solar sails,
which use radiation pressure from photons emitted by the Sun, or
electric sails, which harness the momentum of the solar wind, can now
be envisaged for mid-term missions.  The Japanese Space Agency, JAXA,
is currently testing a solar-sail mission, IKAROS.  Using the Sun as a
propulsion source has the considerable advantage of requiring no
propellant on board.  As long as the hardware does not age too much
and the spacecraft is manoeuvrable, the duration of the mission can be
very long.  The use of data clippers could lead to a valuable
down-sizing of exploration missions and lower ground-operation costs.
The orbiting spacecraft would still download some samples of their
data directly to Earth to enable real-time discoveries and interactive
mission operations.  But the bulk of the data is less urgent and is
often processed by scientists much later, so data clippers could
provide an economical delivery service from the outer Solar System,
over and over again.
Bulletin compiled by Clive Down
(c) 2010 the Society for Popular Astronomy
Good Clear Skies
Colin James Watling
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)

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