PLEASE NOTE:


*

CCNet DIGEST, 22 April 1999
---------------------------

     QUOTE OF THE DAY

     "The people who carved this moon map were the first scientists,"
     says Dr Stooke. "They knew a great deal about the motion of the
     moon. They were not primitive at all." (BBC Online News, 22 April)



(1) COMMENTS ON POTENTIALLY HAZARDOUS ASTEROID 1999 AN10
    BY PAUL CHODAS (NASA, NEO PROGRAM OFFICE)

(2) ASTEROID RESEARCHER DISCOVERS PREHISTORIC MOON MAP
    BBC ONLINE NETWORK, 22 April

(3) ICE-RINKS IN HELL: WAS THE ICE ON MERCURY DEPOSITED BY GIANT
    IMPACTS?
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) LEONID ARTICLE
    Rob McNaught <rmn@aaocbn.aao.gov.au>

(5) TWO WORLDS - ONE SUN
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(6) APRIL'S LYRID METEOR SHOWERS
    NASA Science News <expressnews@sslab.msfc.nasa.gov>


============
(1) COMMENTS ON POTENTIALLY HAZARDOUS ASTEROID 1999 AN10
    BY PAUL CHODAS (NASA, NEO PROGRAM OFFICE)

[as posted by Ron Baalke <baalke@ssd.jpl.nasa.gov>

Comments on Potentially Hazardous Asteroid 1999 AN10

Asteroid 1999 AN10 made the news recently because, according to a group
of researchers in Italy, there is a remote possibility that it could
collide with the Earth in the year 2039.  Writing in a scientific paper
submitted for publication, researchers Andrea Milani, Steven R. Chesley
and Giovanni B. Valsecchi say that the chance of a collision in 2039 is
exceedingly small, only about one in a billion, but they add that the
asteroid's orbit will remain threateningly close to the Earth's orbit
for many centuries to come. 
 
Although the threat posed by 1999 AN10 must certainly be taken 
seriously, the probability of impact for this object is so miniscule
that the authors of the paper felt no great urgency to inform the press
of the new calculations, and the other NEO scientists reviewing the
paper agreed with this policy. To put it into perspective, consider
that the probability of 1999 AN10 impacting in 2039 is tens of
thousands of times *less* than the probability of an undiscovered
asteroid of equivalent size hitting the Earth during the same 40-year
period.  Furthermore, in just a few months, 1999 AN10 will be observed
again, as it moves back into the nighttime sky, and the new data will,
in all likelihood, completely eliminate the possibility of impact in
2039. Researchers should then be able to start examining the
possibility of impacts after 2039.
 
As it turned out, the Milani et al. paper was publicized not by the
authors, but by a third party who found it accidentally on one of the
author's web pages; the authors were not even consulted before their
results were publicized.  An internet debate ensued on such issues as
why the results had not been made public, and whether or not the paper
had been peer-reviewed to ensure accuracy. The reasons for not making
the results public have already been described: basically, there was no
great urgency to publicize a one-in-a-billion-chance impact 40 years
from now, when even that remote a possibility will likely disappear in
a few months. 
 
On the issue of peer review, Milani and his colleagues followed a
commendable course. The authors distributed their paper to qualified
experts more than a week before placing the paper on their web page,
seeking confirmation of their results.  Our group at JPL examined the
paper and saw no major flaws. We have also confirmed the existence of
the impact scenario for 2039, and we confirm that the probability of
impact in 2039 is about one in a billion.
 
Paul W. Chodas
Research Scientist
NEO Program Office
April 21, 1999

=================
(2) ASTEROID RESEARCHER DISCOVERS PREHISTORIC MOON MAP

From the BBC ONLINE NETWORK, 22 April
http://news.bbc.co.uk/hi/english/sci/tech/newsid_325000/325290.stm

PREHISTORIC MOON MAP UNEARTHED

By BBC News Online Science Editor Dr David  Whitehouse

A map of the Moon 10 times older than anything known before has been
found carved into stone at one of Ireland's most ancient and mysterious
Neolithic sites.

It has been identified by Dr Philip Stooke of the University of Western
Ontario in Canada. He spends most of his time preparing maps of
asteroids based on spacecraft observations, but he has also prepared
detailed maps of the Moon.

What puzzled him greatly was that there was no recorded map of the moon
older than about 500 years. "I simply could not believe this," he told
BBC News Online. "I felt there just had to be an older map somewhere."

Prehistoric tombs

So he began looking in old manuscripts and history books as well as the
records of excavations of the Neolithic sites of the British Isles.

Then he found one. It took the eye of an expert to see it for what it
was. It was carved into a rock in one of Ireland's most remarkable
prehistoric tombs at Knowth, County Meath.

"I was amazed when I saw it. Place the markings over a picture of the
full Moon and you will see that they line up. It is without doubt a map
of the Moon, the most ancient one ever found," said Dr Stooke.

"It's all there in the carving. You can see the overall pattern of the
lunar features from features such as Mare Humorun through to Mare
Crisium."

Before this discovery, the oldest map of the Moon was by Leonardo da
Vinci, drawn about 1505. The Knowth map is 10 times older.

Knowth is already a major focus of research into understanding
prehistoric man. Now it will become one of the most important
scientific sites in the world.

"The people who carved this moon map were the first scientists," says
Dr Stooke. "They knew a great deal about the motion of the moon. They
were not primitive at all."

The passage tomb at Knowth is estimated to be about 5,000 years old. It
was obviously built by men who had a sophisticated understanding of the
motions of the Sun, Moon and stars.

It is known that many stone circles and ancient tombs are aligned with
the Sun but less attention has been paid to possible lunar alignments.
This is despite the fact that at certain times the Moon can rise or set
at any location on the horizon that the Sun can.

Series of arcs

Investigations at Knowth almost 20 years ago showed that at certain
times moonlight could shine down the eastern passage of the tomb.

Remarkably, the moonlight would also fall on the Neolithic lunar map.

During excavations, the stone in question was named Orthostat 47. Its
right-hand section contains a series of arcs.

The circular limb of the moon is not included in the carving. Dr Stooke
believes that it may have been drawn on the rock with chalk or with
coloured paint.

Copyright 1999, BBC

============
(3) ICE-RINKS IN HELL: WAS THE ICE ON MERCURY DEPOSITED BY GIANT
    IMPACTS?

From Andrew Yee <ayee@nova.astro.utoronto.ca>

Please note that this article is copyrighted.
 
[http://helix.nature.com/nsu/990422/990422-10.html]
 
Ice-rinks in Hell
By HENRY GEE
 
The temperature on Mercury, the closest of the planets to the Sun, can
get as high as 700 K (427 °C): yet there are persistent reports of ice
at its poles. But where did this ice come from? This difficult question
is tackled by Julianne I. Moses of the Lunar and Planetary Institute,
Houston, Texas and colleagues in a report in the journal Icarus. Their
conclusion is that the water on Mercury was probably delivered by the
impact of water-rich asteroids or comets: however, their study, which
used model simulations, was hampered by our ignorance both of Mercury
and the population of 'Sun-grazing' asteroids and comets. It could be
that the only way to solve the problem definitively is to travel to
Mercury and see.
 
The prize could be worth the trip. Mercury could have a thousand times
as much ice in its polar regions than our Moon, whose deposits of ice
were revealed by the recent Lunar Prospector mission. Ice on the Moon
is likely to be well-mixed with dust, but the ice on Mercury is
probably much cleaner -- true ice-rinks in Hell. Despite the presence
of sunshine bright enough to melt the most obdurate ice-cream cone in
seconds, there are places on Mercury in permanent shadow, where
temperatures could plummet below the temperatures of around 110 K
(minus 163 °C) required to ensure the stability of ice for the duration
of the history of the Solar System.
 
The planet itself is an unlikely source of water. Mercury is very
dense, proportionately richer in metals such as iron than in the
silicate rocks that could be a source of water. It is possible that the
original rocky crust of Mercury was removed by impacts in the violent
early history of the Solar System -- impacts which could have expunged
Mercury's original inventory of water and other 'volatiles'.
 
Another source could be the constant rain of 'interplanetary dust
particles' (IDPs) that showers the planets (including the Earth) from
space. Over time, IDPs could have delivered sizeable amounts of water
to Mercury, but the resulting ice would have been far dirtier than
indicated by the bright spots of clear, reflective ice implied by radar
observations.
 
The most likely prospects are impacts by asteroids and comets. Comets
contain more ice than asteroids: the impact of a single, large comet
could deposit enough water on Mercury to account for the observations.
But cometary impacts are so energetic that most of the impactor would
be jetted back into space, and the gravity of small Mercury would not
be powerful enough to capture the débris.
 
This leaves the asteroids, and a subset of comets whose orbits are
dominated by the gravitational field of the giant planet Jupiter.
Sadly, we do not know enough about Sun-grazing asteroids and comets to
make good estimates of the rate at which such things would have struck
Mercury. The situation is complicated even further by the possibility
that some extinct and icy remnants of comets travel incognito,
disguised as asteroids -- it is often impossible to tell the difference
between the two. Whatever the source of the ice on Mercury, though,
Moses and colleagues claim that there is plenty of it.
 
© Macmillan Magazines Ltd 1999 - NATURE NEWS SERVICE

================
(4) LEONID ARTICLE

From Rob McNaught <rmn@aaocbn.aao.gov.au>

Hi Benny,

Thanks for mentioning the Leonid article, but there seems to have been 
a mixup somewhere. Your comment suggests that it is the whole article
that is presented. It is however just an abstract. The original article
is published in
 
The Astronomer, 1999 March, Vol 35, pp279-283
 
David Asher and I have an updated analysis of the time of Leonid maxima
and a model of the dust trail density, to be published in the next
issue of the IMO journal (WGN).  This is all based on David's upcoming
paper in MNRAS on the Leonid dust trails.
 
Cheers, Rob
 
Robert H. McNaught
rmn@aaocbn.aao.gov.au

=============
(5) TWO WORLDS - ONE SUN

From Andrew Yee <ayee@nova.astro.utoronto.ca>

News Service
Cornell University

Contact: David Brand
Office: (607) 255-3651   E-Mail: deb27@cornell.edu

Martian sundial designed for 2001 space mission is unveiled by Bill Nye
"The Science Guy"

ITHACA, N.Y. -- For the first time in history, humanity will send a
sundial to another planet. Inscribed with the motto "Two Worlds, One
Sun," the sundial will travel to Mars aboard NASA's Mars Surveyor 2001
lander.

Pictures of the sundial, taken by the lander's panoramic camera after
its arrival at Mars in January 2002, will reveal the passage of the
hours and seasons as the sun moves across the Martian sky. And the
sundial's central black, gray, and white rings and corner color tiles
will act as a calibration target -- a kind of test pattern -- to adjust
the brightness and tint of pictures taken by the camera.

In the process, the sundial could become one of the most photographed
objects ever sent to another world.

The sundial design team included Jon Lomberg, an artist and creative
consultant to the Mauna Kea Center for Astronomy Education, Hawaii;
Tyler Nordgren, an artist and astronomer at the U.S. Naval Observatory
in Flagstaff, Ariz.; sundial expert Woodruff Sullivan, professor of
astronomy at the University of Washington; Louis Friedman, executive
director of the Planetary Society; Cornell University astronomers
Steven Squyres and Jim Bell; and Bill Nye, the television writer and
host of the public television children's science program, "Bill Nye The
Science Guy."

"Our ancestors made astonishing discoveries about the nature of the
heavens and our place in it by closely watching the motion of shadows,"
said Nye, unveiling the sundial design at a press conference at Cornell
today (April 21). "Now, at the dawn of the next century, we can make
observations of new shadows, this time on another planet."

Appropriately for a science instrument involving Nye, the sundial
design evolved through suggestions and drawings from children across
the United States, solicited by Sheri Klug, director of Arizona State
University's Mars Education and Outreach Program.

The sundial will be 3 inches (about 8 centimeters ) square, and will
weigh just over 2 ounces (60 grams). Made of aluminum to minimize its
weight, the anodized metal surfaces will be black and gold. The
photometric surfaces, which will be used to calibrate the Mars lander's
color panoramic camera, called the Pancam, are made of a special
silicone rubber compound. Photo-etching and engraving will be used to
apply the lettering and the drawings to the face and side panels of the
sundial.

The central black, gray and white calibration rings are arranged to
represent the orbits of Mars and Earth, and red and blue dots show the
positions of the planets at the time of the landing in 2002. Portions
of the central shadow post are gold to represent the sun.

The sundial carries a message for future Martian explorers who may seek
it out, or who may find it by good fortune. The four gold side panels
around the sundial's base are engraved with the words:

"People launched this spacecraft from Earth in our year 2001. It
arrived on Mars in 2002. We built its instruments to study the Martian
environment and to look for signs of life. We used this post and these
patterns to adjust our cameras and as a sundial to reckon the passage
of time. The drawings and words represent the people of Earth. We sent
this craft in peace to learn about Mars' past and about our future. To
those who visit here, we wish a safe journey and the joy of discovery."

The Pancam is is one of four instruments being developed for the Mars
2001 lander under the leadership of Squyres, a Cornell professor of
astronomy, assisted by 20 researchers around the world, including Bell,
an assistant professor of astronomy, and a team of about 20 Cornell
undergraduates and staff. Together these instruments form the Athena
Precursor Experiment, or APEX, which will be a prelude to the Athena
Mars rover and sample return mission in 2003.

To help design the sundial, Arizona State's Klug sought the ideas of
schoolchildren. Announcements were made at a meeting of the National
Science Teachers Association in Seattle in 1998, and via several
international electronic mailing lists. Over 160 design concepts were
submitted from children across the country.

One idea suggested by children was that the sundial bear writing in
many languages, representing the diverse cultures of Earth. The face of
the sundial is engraved with the word "Mars" in Arabic, Bengali,
Braille, Chinese, Danish, English, French, German, Greek, Hawaiian,
Hebrew, Hindi, Inuktituk, Italian, Japanese, Korean, Lingala,
Malay-Indonesian, Portuguese, Russian, Spanish and Thai. Together these
languages are used by more than three quarters of Earth's population.
Also included are ancient Sumerian and Mayan. Mars figured prominently
in both the Sumerian and Mayan cultures.

Several children also suggested that stick-figure drawings be included,
representing the people of Earth. Artist Lomberg combined stick figures
drawn by children with other space-related motifs to create the series
of drawings that appear on the sundial's side panels. The aim of these
pictures is to capture the optimistic spirit of the text message,
combining a childlike sense of wonder with a vision of the human future
in space.

Once the spacecraft lands on Mars and the exact orientation of the
sundial can be determined, viewers will be able to tell local Martian
time from sundial images and a computer-generated overlay posted on the
World Wide Web. Mirrored segments along the outer ring of the sundial
will also reveal the color of the sky above the lander. Over the course
of a day, viewers on Earth will thus see the passage of time on Mars
recorded in the sweep of the shadow of the sundial's central post and
the changing colors of the Martian sky. The shadow will also reveal the
changing Martian seasons over the full duration of the mission.

=============
(6) APRIL'S LYRID METEOR SHOWERS

From NASA Science News <expressnews@sslab.msfc.nasa.gov>

NASA Space Science News for April 21, 1999
 
April's Lyrid Meteor Shower: The oldest known meteor shower peaks this
week on Thursday morning, breaking a 3 month lull in meteor activity.
FULL STORY at http://science.nasa.gov/newhome/headlines/ast21apr99_1.htm


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