PLEASE NOTE:
*
CCNet 8/2002 - 11 January 2002
------------------------------
"Each spring we see a 60% ozone
depletion over the Antarctic and yet
no mass extinction. In a paper in
paleobiology in 1999 (Crises and
extinction in the fossil record - a role
for UV radiation?) I
explain that in fact the lack of
evidence for supernova-induced
extinctions is entirely consistent with
the observations that large-
scale depletions over the Antarctic do
not cause extinctions."
--Charles Cockell, British Antarctic Survey, 10 January 2002
"The widely accepted theory that
changes in Earth's orbit drive
cycles of glaciation can't account for
an early thawing of glaciers
from the next-to-last ice age, according
to research at the
University of Minnesota. The failure of
the Milankovitch theory,
also called orbital forcing, to predict
this thawing points to the
existence of other factors that can
override orbital forcing to
influence climate, the researchers
said."
--Deane Morrison, University of Minnesota, 10 January 2002
(1) GEOLOGIST HELPS NASA EXPLORE GIANT ASTEROIDS
Ron Baalke <baalke@jpl.nasa.gov>
(2) ASTEROID 1620 GEOGRAPHOS: PHYSICAL CHARACTERISTICS, A REVIEW.
Maximiliano Rocca <maxrocca@hotmail.com>
(3) THERE'S MORE TO ICE AGES THAN MAIN THEORY EXPLAINS
Andrew Yee <ayee@nova.astro.utoronto.ca>
(4) NEW REPORT: U.S. SPACE PROGRAM MAKES LEAST IMPORTANT PRIORITY
LIST
Space.com, 10 January 2002
(5) EARTH-LIKE PLANETS UNLIKELY TO FORM IN 47 UMa
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) TERMINATION OF CANADIAN SPACEGUARD PROGRAMME
Tom Gehrels <tgehrels@lpl.arizona.edu>
(7) BETTER ADVANCE NOTICE, WHAT WOULD IT TAKE?
Hermann Burchard <burchar@mail.math.okstate.edu>
(8) SUPERNOVAE ND UV RADIATION
Charles Cockell <csco@bas.ac.uk>
(10) NO NOVEL ABOUT IMPACTORS
Pavel Chichikov <fishhook@erols.com>
(11) BODE'S LAW AND THE DISCOVERY OF CERES
Michael Hoskin
===========
(1) GEOLOGIST HELPS NASA EXPLORE GIANT ASTEROIDS
>From Ron Baalke <baalke@jpl.nasa.gov>
http://pr.tennessee.edu/news/article.asp?id=1202
UT Geologist Helps NASA Explore Giant Asteroids
University of Tennessee
January 7, 2002
KNOXVILLE -- A University of Tennessee geologist is part of
NASA's
latest mission, which seeks to study the two largest known
asteroids in
the solar system.
Dr. Harry Y. "Hap" McSween has been named to NASA's
Dawn mission, which
launches in 2006 on a nine-year journey to orbit the asteroids
Vesta and
Ceres.
"These asteroids are two 'baby planets' that are very
different from
each other yet both contain tantalizing clues about the formation
of the
solar system," McSween said.
NASA will use special instruments to observe the two bodies
located in
the asteroid belt between Mars and Jupiter, McSween said.
Ceres, the largest asteroid, has a diameter of about 600 miles.
Scientists are intrigued by its primitive development, including
a
relatively unscathed surface, water-bearing minerals and possibly
a very
weak atmosphere and frost, McSween said.
Vesta is the brightest asteroid and the only one visible by the
naked
eye. Its average diameter is about 320 miles.
Vesta's surface is dry and has been resurfaced by lava flows,
McSween
said. Like the Earth's Moon, it has been hit many times by
smaller space
rocks, sending out meteorites at least five times in the last 50
million
years. McSween is among those scientists who have studied
meteorites
from these impacts.
During its journey through the asteroid belt, Dawn will
rendezvous with
Vesta and Ceres, orbiting from 500 miles to about 62 miles above
the
surface.
The mission will determine these asteroids physical attributes
such as
shape, size, mass, craters and internal structure, and produce
data on
more complex properties such as composition, density and
magnetism,
McSween said.
McSween was a science team member of NASA's Mars Pathfinder, Mars
Global
Surveyor and Mars Odyssey missions. He also will be working on
the Mars
Exploration Rover mission in 2003.
An advisor to NASA and the National Research Council, McSween was
president of the Meteoritical Society and chaired the Planetary
Division
of the Geological Society of America. He won the Leonard medal,
the top
award in planetary science, in 2001.
Dawn's principal investigator is Dr. Christopher T. Russell of
the
University of California, Los Angeles. It is one of two missions
selected for funding from 26 NASA proposals in 2001. The second
is
Kepler, a spaceborne telescope which will look for earth-like
planets.
Information about Dawn is available at:
http://www.college.ucla.edu/dawn/
--
Contact: Dr. Harry Y. McSween (865-974-9805)
Mike
Bradley (865-974-5034)
===============
(2) ASTEROID 1620 GEOGRAPHOS: PHYSICAL CHARACTERISTICS, A REVIEW.
>From Maximiliano Rocca <maxrocca@hotmail.com>
Dear Benny:
Asteroid 1620 is in my opinion one of the most interesting NEAs.
With the possible exception of CERBERUS, this huge rock is one of
the
most elongated objects known in the Solar System.
Bellow you will find a review of its physical characteristics as
2001.
So far, this article remains unpublished.
thanks! Max
ASTEROID 1620 GEOGRAPHOS: PHYSICAL CHARACTERISTICS, A REVIEW.
INTRODUCTION.
Apollo asteroid 1620 Geographos ( 1951RA ) is one of the most
elongated
objects in the Solar System. It was discovered on Sept.
14th.,1951 by
Albert Wilson and Rudolph Minkowski at Palomar Observatory, USA,
as part
of the Palomar Observatory Sky Survey, wich photographed the
entire
Northern Hemisphere Sky. The survey was sponsored by the National
Geographic Society, hence the asteroid's name.
ORBIT
Semimajor axis = 1.24 A.U. , e = 0.355 , I = 13.3º
It is a Potentially Hazardous Asteroid (PHA).
SPACE MISSIONS
In the 1990s, the Departament of Defense's "Clementine"
space probe
mission was planned to do a flyby of this asteroid on Aug.
31st 1994.
Sadly, that mission was terminated.
ABSOLUTE VISUAL MAGNITUDE
Its absolute Magnitude ( H ) is 15.6
LIGHTCURVE AND COLOR
First observations of Lightcurve ( LC ) , brightness, colors and
polarization were made on an 8-month interval in 1969 from the
Catalina
Station Observatory, L.P.L., Arizona, USA.
Its albedo in blue light was found to be 0.16.
Colors don't changed appreciably with phase: B-V = 0.87 , U-B =
0.50.
Lightcurve had two distinct maxima and minima and the largest
amplitude
recorded was 2.03 magnitudes...record for an asteroid at that
time.
Its rotation (retrograde) was estimated in 5h. 13m. 23s.
Laboratory model experiments to reproduce the LC were made. The
best
fitting model gave as result a cylinder of 4.0 - 1.5 kms.
[1].
In 1993 and 1994, photometric CCD LCs were made at Ostrowik
Station of
Warsaw Univ. Observatory, Poland.
Using their observation astronomers found a retrograde sidereal
period
of 0.21763867 days for this asteroid and, by assuming a triaxial
ellipsoid model they obtained axial ratios of a/b = 2.6 and b/c =
1.1 for
its shape [2].
Using 8 LCs from 1969, 1983 and 1993/94 apparitions, the
physical
characteristics of Geographos were again derived.
Model amplitudes were calculated by integrating different
scattering
laws over the triaxial ellipsoid surface for the same viewing and
illumination geometries as in the real observations. As result,
sidereal
period of 0.21763866 days and a triaxial ellipsoid with shape
ratios a/b =
2.5 and b/c = 1.1 were obtained [3].
In 1996, photometric observations of 93 LCs taken in 1993/94
apparition
were presented and, in combination with previously published
data, a new
model of Geographos was derived.
Sidereal period ( retrograde ) = 5.2233640 Hours.
Ellipsoidal axial ratios : a/b = 2.58 and b/c = 1.00.
A large number of observatories around the world were involved in
that
project. After analysis of the data, they obtained the best fit
between
the LCs and a triaxial model by the use of an ellipsoid cut by a
plane in
one side. That was the first surface "feature "
reported to be on
Geographos from LCs studies.
Mean color indices obtained were:
U-B = 0.45 , B-V = 0.855 , V-R = 0.475 , R-I = 0.32 , [ 4 ].
So far, it is not possible to say whether Geographos is a rubble
pile or
a monolithic rock.
REF.:
[1]: Dunlap J.L. : Astron. J. 79 ( 2 ) : 324-332, 1974.
[2]: Michalowski T. el al. : Acta Astronomica 444 : 223-226,
1994.
[3]: Kwiatkowski T. : Astron. Astrophys. 294 : 274-277, 1995.
[5]: Magnusson P. & 46 collegues : Icarus 123 : 227-244,
1996.
COMPOSITION
Observations and studies of visible ( 0.33 to 0.96 micrometers
wavelengths ) reflectance spetra of Near Earth Asteroids,
including
Geographos, were published in the late '70s and early '80s.,
[1,2].
According to their spectra a mineralogical interpretation was
done after
laboratory comparison experiments with mineral species and
meteorite
types. The spectrum of Geographos was found to be consistent with
minerals expected to occur at the core/mantle boundary of a
differentiated parent body. The precense of mafic silicate
minerals on it
was then stated: Geographos was found to be an S-type asteroid.
Its
spectrum has a linear UltraViolet ( UV ) absorption edge between
0.40 and
0.76 micrometers. The presence of a broad asymmetric 1.0
micrometers band
would support the precense of significant Olivine mineral on its
surface.
More recently, by CCD ( 0.54 to 0.98 micrometers ) spectra
obtained
with Catalina Station reflector, USA, a more precise
classification was
presented.
Geographos is an S-Type , S II- SIII subtypes of Gaffey,
asteroid.
Surface mineral assemblage appears to be a metallic ( Fe-Ni ) and
Pyroxene/Olivine mixture, [3].
No significant color variations across its surface were detected.
REF.:
[1]: Chapman C.R. et al. : Icarus 25 : 104-130, 1975.
[2]: McFadden L.A., Gaffey M .J. and McCord T.B.: Icarus 59:
25-40,
1984.
[3]: Hicks M.D. et al. : Icarus 113: 456-459, 1995.
RADIOMETRY
>From 10 micrometers infrared photometry , thermal models were
used to
derive the corresponding radiometric albedo and diameter of this
asteroid.
Geographos diameter was estimated to be 2.7 kilometers by this
method.
Albedo = 0.19.[ 1 ].
REF.:
[1]: Veeder G.J. et al.: Astron. J. 97 ( 4 ) : 1211-1219, 1989.
RADAR STUDIES
Radar measurements and studies of Geographos during its August
1994's
close encounter (0.034 A.U.) with the Earth were made from
Goldstone
Observatory, USA. The 70-m anthenna was used to run radar
experiments
from August through September '94.They yielded over 400
delay-Doppler
images (resolution about 80 meters) of Geographos. Tha
astronomers
estimated its radar albedo as 0.13. Geographos was found to be a
very
elongated object : 5.0 X 2.0 X 2.1 kilometers. That geometric
model was
developed using both radar and LCs data.
Sidereal period ( retrograde ) was estimated in 5.2233270 Hours.
The asteroid's surface was found to be homogeneous and displayed
modest
roughness at centimeter to meter scales. Seven main surface
features were
identified in the delay-Doppler images. They included several
possible
impact craters. The most prominent large-scale feature found was
a bend
near 90º E longitude. Two protuberances at the asteroid's
ends may be
related to impact ejecta removal and deposition under the low
gravity
field of Geographos. , [1,2,3].
REF.:
[1]: Ostro S.J. et al. : Nature 375 : 474-477, 1995.
[2]: Ostro S.J. et al. : Icarus 121 : 46-60 , 1996.
[3]: Hudson R.S. and Ostro S.J. : Icarus 140 : 369-378, 1999.
===============
(3) THERE'S MORE TO ICE AGES THAN MAIN THEORY EXPLAINS
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
University of Minnesota
Contact:
Christina Gallup, Geological Sciences Dept., University of
Minnesota
(218) 726-8984
Deane Morrison, University News Service
(612) 624-2346
Embargoed by Science until 2 p.m. EST Thursday, Jan. 10
THERE'S MORE TO ICE AGES THAN MAIN THEORY EXPLAINS
MINNEAPOLIS / ST. PAUL -- The widely accepted theory that changes
in
Earth's orbit drive cycles of glaciation can't account for an
early
thawing of glaciers from the next-to-last ice age, according to
research at the University of Minnesota. The failure of the
Milankovitch theory, also called orbital forcing, to predict this
thawing points to the existence of other factors that can
override
orbital forcing to influence climate, the researchers said. The
work
will be published in the Jan. 11 issue of Science.
Relying on extensive examinations of fossil corals, the
researchers
have tracked sea level changes and volumes of glacial ice, said
lead
author Christina Gallup, an assistant professor of geology at the
University of Minnesota-Duluth. Because sea levels fall when
glaciers
build up and rise during glacial melting, the elevation at which
corals grow depends partly on the glacial cycle. The Minnesota
team
has dated many ancient corals from Barbados beaches and
determined
when they grew and at what elevation with respect to current sea
level. They have used their findings to compare glacial cycles to
cycles in Earth's orbit, which, according to the theory of
Serbian
scientist Milutin Milankovitch (1879-1958), provide the impetus
for
ice buildup and melting.
"All previous coral data are in accord with
Milankovitch," said Gallup.
"Scientists have followed ice ages as far back as three
million years
and always found frequencies in the marine record of glaciations
that
are the same as the frequencies of variation in Earth's orbit.
"In this study, we did a more thorough sampling of the coral
terrace
built during the interglacial [between ice ages] period that
occurred
between 130,000 and 120,000 years ago. We found corals whose age
and
position indicated that during the transition to that
interglacial,
sea level rose too early to be consistent with Milankovitch. This
exception tells us something. It implies that other things can
override orbital forcing of glacial cycles."
The Milankovitch theory says that summer heating at high northern
latitudes drives the melting of glaciers, Gallup explained. At
latitude 65 degrees north, changes in Earth's orbit would have
caused
summer heating to reach a minimum at about 140,000 years ago and
increase to a peak at 129,000 years ago. The theory predicts that
most
of the melting would occur after the halfway point, that is,
134,000
years ago and later. But the corals from Barbados indicate that
sea
level was quite high -- within 20 percent of its all-time high --
136,000 years ago. Therefore, much melting must have occurred
thousands of years before the halfway point.
The early melting of glaciers could have been due to one or more
factors, said Gallup. Scientists have theorized that when ice
sheets
get heavy enough, they depress the land beneath them and sink.
They
encounter warmer air at lower elevations, they have less area
that's
accumulating snow and ice, and sometimes, seawater flows under
their
bottom layers and helps melt them further. Also, the height of an
ice
age probably experiences the biggest amounts of floating sea ice.
This hinders evaporation of water, shutting off the supply of
moisture that fuels snowfalls at high latitudes.
A third factor was suggested by Robert Johnson, a geologist at
the
University of Minnesota-Twin Cities. Normally, as one moves from
tropical to polar latitudes, there is a strong gradient in the
amount of solar radiation received. But if this gradient and its
accompanying temperature contrasts should weaken, then there will
be
a lesser energy gradient to drive moisture northward.
"Bob found that there was a minimum in this gradient 140,000
years
ago," said Gallup. "This would contribute to glaciers
deflating. They
also could have been starved by sea ice and destabilized by
sinking."
Gallup's colleagues in the study were University of
Minnesota-Twin
Cities geology professor Lawrence Edwards and postdoctoral fellow
Hai
Cheng, along with Fred Taylor, a faculty member at the University
of
Texas at Austin. The work was supported by the National Science
Foundation.
------------
MODERATOR'S NOTE: For an alternative explanation of the causes
and
termination of Ice Ages see, CCNet-ESSAY: ON THE CAUSE OF
ICE-AGES, By
Fred Hoyle and Chandra Wickramasinghe
http://abob.libs.uga.edu/bobk/ccc/ce120799.html
================
(4) NEW REPORT: U.S. SPACE PROGRAM MAKES LEAST IMPORTANT PRIORITY
LIST
>From Space.com, 10 January 2002
http://www.space.com/news/brookings_study_020110.html
By Leonard David
Senior Space Writer
BOULDER, COLORADO -- A new report on what the federal government
should
consider top priorities has placed the nation's space program at
near
rock bottom of a low priority list.
The Brookings Institute, an influential Washington, D.C. think
tank that
studies economics, foreign policy and government, did the study.
The
assessment -- Government's 50 Greatest Priorities of the Next
Half-Century -- is based on a survey of 550 historians, political
scientists, sociologists, and economists carried out from July
through
October 2001.
The sampling of experts believe arms control, increasing health
care
access for poor Americans, and improving kindergarten through
12th grade
education should be among the federal government's top priorities
during
the coming decades.
These same academics generally agreed as well on the federal
government's ten least important priorities for the future.
Fourth down on that least important list, tied with support
veterans
readjustment and training, is "promote space
exploration."
Different futures
Paul Light, vice president and director of Governmental Studies
at the
Brookings Institution authored the report.
Those surveyed have led to a social top-ten list of priorities
for the
federal government:
1. Increase Arms Control and Disarmament
2. Increase Health-Care Access for Low-Income Americans
3. Expand and Protect the Right to Vote
4. Promote Financial Security in Retirement
5. Provide Assistance for the Working Poor
6. Tie: Improve Air Quality and (7) Increase Health Care Access
for
Older Americans
8. Improve Elementary and Secondary Education
9. Reduce Workplace Discrimination
10. Strengthen the National Defense
According to Light, whether the priorities pinpointed in the
survey will
become the federal government's greatest achievements during the
next
half-century depends largely on a choice between two very
different
futures.
"The first future," Light said, "is one in which
the nation's leaders
are able to maintain the bipartisan spirit that marks so much of
government's past achievement." A second future, he added,
"is one in
which Congress and presidents worry so much about their
reelections and
popularity that they demand immediate success or none at all,
young
Americans continue to avoid government service for fear of
dead-end
careers and bureaucratic red-tape, and the nation's leaders
continue to
demean government and its civic partners for not being able to do
more
with less and less."
In addition to ranking the future endeavors that should be top
priorities, respondents were also asked which of the greatest
endeavors
of the last 50 years the federal government should continue to
pursue.
The highest percentage of those surveyed indicated the federal
government should continue to work toward improving air quality.
Also,
reducing disease and ensuring safe food and drinking water should
continue to be high on the federal government's agenda.
On the federal government's ten least important priorities for
the
future, promoting space exploration was listed along with:
Improve Government Performance
Reduce Dependency Among Welfare Recipients
Strengthen the Nation's Highway System
Help Victims of Disaster
Devolve Responsibility to the States
Increase Market Competition
Reduce Illegal Drug Use
Support Veterans Readjustment and Training
Expand Home Ownership
Stabilize Agricultural Prices.
Apollo program ranked
Paradoxically, in a Brookings study done by Light in 2000,
Promote Space
Exploration was singled out as one of the government's greatest
endeavors in the past half century. That survey polled 450
historians
and political scientists to pick the 50 greatest endeavors of the
U.S.
government over the past 50 years.
Rebuilding Europe after World War II gained top billing.
Ranked as number 25 in the 50 top achievement list is government
action
to develop the technology for a lunar landing and further space
exploration, including a go-ahead in 1984 to support building a
permanently occupied space station.
"American plans for a lunar landing came together in 1961
when Congress
approved a substantial increase in appropriations to NASA. The
agency's
budget almost doubled from fiscal year 1961 to fiscal year
1962," the
Brookings 2000 study notes.
"Specific authorizations within the package included $160
million for
the Apollo space flight and exploration program, the initiative
charged
with making moon exploration a reality, as well as $159.8 million
specifically earmarked for lunar and planetary exploration.
Appropriations doubled again for fiscal year 1963 and reached a
high
point of $5.25 billion before tapering off in the late 1960s.
These huge
outlays were rewarded when the United States put the first humans
on the
moon in 1969," the study explains.
Copyright 2002, Space.com
===============
(5) EARTH-LIKE PLANETS UNLIKELY TO FORM IN 47 UMa
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
University of California-Santa Cruz
Media Contacts:
Tim Stephens, UC Santa Cruz
(831) 459-2495; stephens@cats.ucsc.edu
Kathleen Burton, NASA Ames
(650) 604-1731; kburton@mail.arc.nasa.gov
For Immediate Release: January 7, 2002
Analyzing a planetary system that closely resembles our solar
system,
astronomers find habitable worlds are unlikely
SANTA CRUZ, CA -- Of all the extrasolar planetary systems
detected by
astronomers in recent years, the star 47 Ursae Majoris and its
known
companions, two Jupiter-sized planets, is the one that most
closely
resembles our own solar system. Computer simulations now show,
however,
that Earth-sized planets are unlikely to form in the so-called
"habitable zone" of 47 Ursae Majoris (47 UMa).
The new findings are being reported at the American Astronomical
Society meeting in Washington, D.C., by Gregory Laughlin, an
assistant
professor of astronomy and astrophysics at the University of
California, Santa Cruz; John Chambers of NASA Ames Research
Center;
and Debra Fischer of the University of California, Berkeley.
Planet hunters have detected nearly 80 planets orbiting nearby
stars, but most of them have elongated, or "eccentric,"
orbits.
The two planets around 47 UMa, which is located in the Big Dipper
constellation, have nearly circular orbits, like those of Earth
and
other planets in our solar system. Their orbits are farther from
the
star than Mars is from the Sun, but closer than Jupiter.
The striking similarity between the pair of planets orbiting 47
UMa
and the Jupiter-Saturn pair in our solar system led Laughlin,
Chambers,
and Fischer to investigate whether smaller, Earth-sized planets
could
have formed and survived in the habitable zone around 47 UMa. The
habitable zone is the region surrounding a star where liquid
water
could exist on the surface of a planet -- a region roughly
equivalent
to the space between the orbits of Venus and Mars in the solar
system.
Earth-like (or "terrestrial") planets are too small to
be detected
with present-day planet hunting techniques.
The researchers performed a large set of computer simulations and
found
that Earth-sized planets have a very hard time forming in 47
UMa's
habitable zone. The combined gravitational forces of the two
large
outer planets conspire to prevent Earth-sized planets from
building up
in orbits where temperatures are clement, Laughlin said.
"Our simulations suggest that terrestrial planets can
readily form
around 47 UMa in orbits that are roughly half the size of Earth's
orbit," he said. "Out in the habitable zone, an
Earth-sized planet can
survive in a stable orbit, but it is very hard to see how such a
planet
could be assembled."
During the formation of a planetary system, terrestrial planets
such
as Earth or Mars are believed to form from successive collisions
of
small asteroid-sized bodies which stick together to form
progressively
larger bodies called "planetary embryos." This process
is known as
planetary accretion. It is likely that our solar system went
through
a such a phase, in which hundreds of moon-sized planetary embryos
emerged from numerous collisions among a much larger number of
small
precursor bodies, Laughlin said.
The researchers used a highly efficient computer program
developed by
Chambers to simulate the further development of planetary
accretion
from this stage. A typical calculation followed the long-term
evolution
of a swarm of 280 moon-sized planetary embryos in the presence of
the
two giant planets orbiting 47 UMa, and spanned a time frame of 50
million years near the beginning of 47 UMa's history. The
simulations
showed that embryos starting in the habitable zone tend to jostle
each
other into orbits where the gravitational tugs from the two outer
planets either fling the embryos from the system or drive them
into
the star itself. On the other hand, the embryos that started
inside the
habitable zone were always able to consolidate into several
Earth-sized
planets, all having an orbital period of half a year or less.
At the end of several simulations, a single tiny survivor was
left
in the habitable zone. In other simulations, the habitable zone
was
entirely cleared, Chambers said.
The survival of isolated remnant embryos in the habitable zone of
47 UMa suggests a possible parallel to the asteroid belt in our
own
solar system. Within the asteroid belt, many orbits are stable,
but
certain locations within the belt contain unstable
"resonances" where
objects experience rapid orbital instability. Planetary embryos
tend
to scatter each other into these unstable zones, leaving behind a
smattering of survivors -- the asteroids -- which are much
smaller
than the terrestrial planets.
"Because these two giant planets orbiting 47 UMa are more
than twice
as close to the star as Jupiter and Saturn are to the Sun, the 47
UMa
system looks like an overweight, scaled-down version of the solar
system. Any terrestrial planets or an analogue to the asteroid
belt
around 47 UMa would likely be about twice as close to the star as
well," Chambers said.
The researchers' assessment of habitable planet formation was
part of
a larger theoretical investigation of the two planets orbiting 47
UMa,
in which the team narrowed the range of possible orbital
configurations
that the planets might occupy. They also showed that the two
outer
planets have undergone very little orbital modification since
their
formation. The research was funded by the NASA Origins of Solar
Systems Program.
# # #
Editor's note: Reporters may contact Laughlin at (831) 459-3208
or
laughlin@ucolick.org;
Chambers at (650) 604-5514 or
john@mycenai.arc.nasa.gov;
and Fischer at (510) 643-8973 or
fischer@serpens.berkeley.edu
.
Images can be downloaded from the web at
http://www.ucsc.edu/news_events/download/
IMAGE CAPTIONS:
[Figure 1:
http://www.ucsc.edu/news_events/download/images/figure1-lg.jpg
(34KB)]
This figure shows the relative scale of the orbits of the two
planets
('b' and 'c') orbiting the star 47 Ursae Majoris. The sizes of
the
planets are not to scale with the size of the central star. The
habitable zone around 47 UMa is shown as a light blue band. For
comparison, the orbital radii of Venus, Earth and Mars are shown
as
dotted lines. A series of numerical simulations have shown that
any
terrestrial (Earth-size) planets in the 47 UMa system are likely
to
lie closer to the star than the habitable zone.
Credit: Gregory Laughlin
[Figure 2:
http://www.ucsc.edu/news_events/download/images/figure2-lg.jpg
(67KB)]
Six snapshots in time of a planetary accretion simulation showing
the
hypothetical development of terrestrial planets in the 47 UMa
system.
The simulation begins with 280 lunar-mass planetary embryos with
initial orbits lying between 0.4 and 2.0 astronomical units (an
astronomical unit is the distance from Earth to the sun). Embryos
are removed rapidly from much of this region as mutual
gravitational
perturbations scatter them into unstable resonances associated
with
the giant planets. The inner giant planet, 47 UMa 'b,' is seen at
the right of each panel. The outer giant planet, 47 UMa 'c,' is
off
of each panel to the right, and the central star, 47 UMa, is off
of
each panel to the left. The distance of each object above the
bottom
of the panel corresponds to the eccentricity (or elongation) of
its
orbit. The buildup of terrestrial planets is confined to the
region
inside the inner edge of the habitable zone. At the end of this
simulation, a single planetesimal remains in the habitable zone,
but
this object would be much too small to retain an Earth-like
atmosphere
and would not be habitable.
Credit: G. Laughlin, J. Chambers, and D. Fischer
============================
* LETTERS TO THE MODERATOR *
============================
(6) TERMINATION OF CANADIAN SPACEGUARD PROGRAMME
>From Tom Gehrels <tgehrels@lpl.arizona.edu>
Dear Benny,
Regarding the Canadian report on the termination of David Balam's
asteroid observing for lack of funds (CCNet, 9 January 2002), I
like to
vouch for his competent work at a great telescope that is made
amply
available to him.
I also wonder if we could not reverse the decison by bringing our
concern to the attention of Prime Minister Jean Chretien (accent
over
the first "e"; pm@pm.gc.ca).
He may well like to hear of our interest in
the essential work done at a Canadian Observatory, of the fact
that only a
decent salary for one astronomer is needed, and that this is a
small
insurance premium towards avoidance of a global disaster at
relatively
high chance, about one-in-a-few-thousand in a lifetime.
Cheers!
Tom
=============
(7) BETTER ADVANCE NOTICE, WHAT WOULD IT TAKE?
>From Hermann Burchard <burchar@mail.math.okstate.edu>
Dear Benny,
What would it take to avoid such short notice of warnings against
cosmic impact hazards, as for asteroid 2001 YB5? According
to Larry
Robinson, CCNet 8 Jan 2002, at most only twelve (12) days were
available
this time. Is this something under discussion by people doing the
scanning?
Do our astronomers simply need to point more telescopes at the
sky?
Twice as many? Triple? What is the minimum of time required for
defences
to be launched, all due preparations having been done beforehand?
Everybody agrees nothing could have been done now, but as the
moderator
commented, Dave Morrison's "nor even two years" (CCNet
9 Jan 2002) was
overly pessimistic and Dave surely meant starting from scratch.
Incidentally, was any radar observation done to refine the orbit
of 2001
YB5? (I apologize for riding my hobby horse again.)
Regards,
Hermann
==============
(8) SUPERNOVAE ND UV RADIATION
>From Charles Cockell <csco@bas.ac.uk>
Dear Benny,
I's like to add a couple of comments about the supernovae and
ozone
theory. The Ellis and Scramm paper calculated that depletion of
95%
could occur over Earth as a result of a close (<10 pc)
supernova
explosion. Calculations by Cutzen and Bruhl in a follow-up paper
in PNAS
suggested that ozone desruction from a 10 pc event would be much
less,
perhaps 60% over the poles and 20% over the equator.
Now the latter calculation is interesting because each spring we
see a
60% ozone depletion over the Antarctic and yet no mass
extinction. In a
paper in paleobiology in 1999 (Crises and extinction in the
fossil
record - a role for UV radiation?) I explain that in fact the
lack of
evidence for supernova-induced extinctions is entirely consistent
with
the observations that large-scale depletions over the Antarctic
do not
cause extinctions.
The importance of supernovae is absoluetely dependent on the
amount of
depletion caused and it doesn't take much of a deviation in the
conclusion to relegate supernovae-induced ozone depletions to
something
less than extinctions and at most a subtle biostratigraphical
turnover
(maybe). Supernovae are expected to cause these changes more
permanenetly than human induced changes each spring and over
centuries,
but there is still no real data to suggest that the result would
be a
mass extinction, unless other effects such as muon showers are
invoked,
but the effects of these sorts of mechanisms are unclear.
Charles
__________________________
Dr. Charles Cockell,
British Antarctic Survey,
High Cross,
Madingley Road,
Cambridge.
CB3 0ET. UK
Tel : + 44 1223 221560
e-mail : csco@bas.ac.uk
=============
(10) NO NOVEL ABOUT IMPACTORS
>From Pavel Chichikov <fishhook@erols.com>
Dear Dr. Peiser and all,
In response to Mr. Crouch's letter of 10 January, I am not
planning to
write a novel about Neolithic early warning systems. (Though I
might run
the idea past my agent - thanks Mr. Crouch).
It is obvious though that if our ancestors had been traumatized
by
swarms of comets, it would have deeply affected human culture in
the
long term.
No society mobilizes the effort and wealth to build large
structures
unless there are important social and psychological reasons,
aside from
possible practical ones. These structures are, among other
things,
anxiety relieving mechanisms.
The motives for building barrows, circles and lines of stones are
no
doubt complex. We can learn a lot about ourselves as well as our
situation in the cosmos by trying to understand some of this
complexity.
I bet an anthropologist of five thousand years hence would love
the
chance to interview the ghost of Donald Trump.
A personal but pertinent aside: as I youngster I worked on
several very
large building projects. They are dangerous places to be around,
and
there are always a few people killed or seriously injured before
the job
is over. That would be true of Neolithic projects as well.
Best wishes.
Pavel
fishhook@erols.com
===============
(11) BODE'S LAW AND THE DISCOVERY OF CERES
by Michael Hoskin
Churchill College, Cambridge
http://www.astropa.unipa.it/versione_inglese/Hystory/BODE'S_LAW.htm
1. Copernicus
When Copernicus's De revolutionibus appeared in 1543, it was
valued by
the professionals for its innovative planetary models rather than
for
anything it might have to say about which body is at the centre
of the
universe. In a volume dominated by complex geometry, and
introduced by a
misleading preface inserted without the author's authority to the
effect
that what followed was guided by the search for accuracy and
convenience
rather than the quest for truth, the cosmological Book I was
largely
overlooked. In Book I Copernicus shows in broad, qualitative
terms, how
so many of the hitherto-puzzling features of the observed motions
of
these `wandering stars' - such as their retrogressions - are
readily
explained if one begins from the assumption that the Earth is an
ordinary planet orbiting the Sun.
Another consequence of the heliocentric hypothesis outlined in
Book I,
and one especially satisfying to its author, was that the planets
at
last formed a single, integrated system. In the accepted
Ptolemaic
astronomy, even the very order of the planets was uncertain. It
was
supposed that the planets whose movements differed least from the
daily
spinning of the fixed stars - Saturn, and then Jupiter and Mars -
were
physically closest to the stars and so furthest from the central
Earth.
But since Mercury and Venus appear to accompany the Sun around
the sky,
all three seemed to have the same period of one year, and so
their order
of distances was a matter of guesswork. But the heliocentric
hypothesis
revealed that the supposed equal periods were no more than an
illusion
resulting from the status of Mercury and Venus as inner planets.
It also
became clear that the circular movements with a period of one
year that
occurred in the various traditional models of the planetary
orbits were
no more than the reflection of the terrestrial motion; this being
so,
the radius of each of these circles should now be equated to the
astronomical unit, giving a common scale to the models and
permitting
them to be seen as components in an integrated planetary system.
From
this it transpired that the further a planet from the central
Sun, the
longer it took to complete a circuit of sky - an harmonious
relation
that strongly appealed to Copernicus's Platonic intuition.
The planetary system is represented by Copernicus in simplified
form in
his famous diagram in Book I. But his figure is not to scale. A
scale
representation would have made it obvious that there is an
astonishing
gap between the orbit of the fourth planet, Mars, and that of the
fifth,
Jupiter.
2. Kepler
Towards the end of the century, the young Johannes Kepler, in one
of the
first publications that were irrevocably heliocentric, his
Mysterium
cosmographicum (1596), sought to make sense of the dimensions of
the
planetary system. Why, he asked himself, had God been motivated
mathematically to select the planetary orbits in just the way he
had.
``There were'', he tells the reader in the Preface, ``three
things in
particular about which I persistently sought the reasons why they
were
such and not otherwise: the number, the size, and the motions of
the
circles.'' The gap between Jupiter and Mars was especially
awkward to
explain. After various attempts, he tried a novel and bold
approach.
"Between Jupiter and Mars I placed a new planet, and also
another
between Venus and Mercury, which were to be invisible on account
of
their tiny size, and I assigned periodic times to them. For I
thought
that in this way I should produce some agreement between the
ratios, as
the ratios between the pairs would be respectively reduced in the
direction of the Sun and increased in the direction of the fixed
stars.... Yet the interposition of a single planet was not
sufficient
for the huge gap between Jupiter and Mars; for the ratio of
Jupiter to
the new planet remained greater than is the ratio of Saturn to
Jupiter."
[1]
3. Dynamical Explanations of the Mars/Jupiter Gap
Eventually Kepler found suitable motivation for the divine
geometer in a
totally different approach, the nesting of spheres and regular
solids;
but it was one that commended itself to few in the generations
that
followed. Some found an acceptable explanation of the gap in the
sheer
size of the outer planets. Isaac Newton for example regarded the
gap as
part of the divine plan for the stable and clockwork universe:
the
massive planets, Jupiter and Saturn, had been located by
Providence at
the outside of the planetary system, well clear of the smaller
planets
whose orbits their gravitational force would otherwise disrupt.
[2] In
the middle of the eighteenth century Immanuel Kant also sees a
dynamical
justification for the gap in the great mass of Jupiter: ``The
width
between the orbit of Jupiter and Mars is so great that the space
enclosed there exceeds the regions of all lower planetary orbits
taken
together ... that space is worthy of the greatest among all
planets,
namely, of that which has more mass than all the others
together.'' [3]
Johann Heinrich Lambert in 1761 likewise remarks on the gap.
Lambert in
general is as committed to an eternal, unchanging clockwork
universe as
was Newton, but at the level of the solar system he is prepared
to
accept that change has been brought about by the attractive power
of
Jupiter: ``And who knows whether already planets are missing
which have
departed from the vast space between Mars and Jupiter? Does it
then hold
of celestial bodies as well as of the Earth, that the stronger
chafe the
weaker, and are Jupiter and Saturn destined to plunder forever?''
[4]
4. The Possibility of Undiscovered Planets
These speculative dynamical explanations of the `gap' took place
in the
context of a surprising willingness on the part of professionals
and
informed amateurs alike to accept that there may exist planets as
yet
undiscovered, perhaps inside Mercury, but more plausibly beyond
Saturn:
surprising, because no primary planet had been discovered since
history
began. Significantly, just as the most interesting late
seventeenth and
early eighteenth century speculations on cosmology came from
writers
whose interests had a theological dimension, so the same is true
of
speculations about additional planets. So William Wall, cited in
the
Postscript to the second edition (1727) to Tobias Swinden's An
Enquiry
into the Nature and Place of Hell, [5] wrote:
"I think it very probable, that there are, belonging to the
Sun, a great
many more planets, than what we see, some perhaps within the Orb
of
Mercury, never seen nor to be seen by us; but a great number
without, or
beyond the Orb of Saturn, which we can never see ... partly by
reason of
the distance from us, and partly because they, being very remote
from
the Sun, do receive but a weak Light from him, and do much more
weakly
reflect it."
William Whiston hints at the same in his Astronomical Principles
of
Religion, Natural and Reveal'd (London, 1717), when he says
carefully
that ``Mercury is the nearest to the Sun of all the known
Planets'', and
that Saturn is ``the highest and most remote of all the known
Planets''.
[6] As so often, Whiston's views in this book are reflected in
the
writings of that well-known maverick in both astronomy and
theology,
Thomas Wright of Durham. In his Clavis Coelestis (1742) he speaks
of
Mercury as ``the first Planet we know of in the System''
[7][italics
supplied], and Venus as ``the second Planet known in the
System'', while
``Saturn is the last and highest known Planet in the System''.
[8] In
his more famous An Original Theory or New Hypothesis of the
Universe
(1750) he again refers [9] to ``the known Planets''. And in his
often
bizarre Second Thoughts, which remained in manuscript until our
own
time, he is explicit: ``...I am far from supposing our present
knowledge
of ye solar system perfect and fully known''. [10]
"Is it not more reasonable to imagine a coelum in cognito
beyond ye
known planets than to suppose a terra in cognito at present upon
Earth.
It is therefor my opinion, that there are or may be, many more
bodies
belonging to the system of ye Sun, whose more feeble light has
not been
able yet to reach us at ye Earth, besides others perhaps within
ye orbit
of Mercury, though lost or lying hid to us in a too radiant state
of
light." [11]
Another of the mid-eighteenth century speculators to anticipate
an
undiscovered planet was Immanuel Kant. In his Universal Natural
History
...he writes:
"...we see even in our solar world the members of a system
which stand
immensely apart from one another and between which one has not
yet
discovered the intervening parts. Should there be between Saturn,
the
outermost of planets which we know, and the least excentric comet
which
descends to us from perhaps a distance 10 and more times greater,
no
more planet whose motion would come closer to the cometary motion
than
that [of Saturn]...?" [12]
These suggestions concerning planets as yet undiscovered relate
mostly
to the regions outside Saturn. Only a few were concerned with the
gap
between Mars and Jupiter. One who did `surmise' the presence of
one or
more planets in the gap was apparently the Scottish mathematician
Colin
Maclaurin. [13] Another to focus on the gap was Thomas Wright. In
one of
those unexpectedly insightful speculations that make him so
fascinating
a figure, Wright actually suggests in his unpublished manuscript
that
the gap between Mars and Jupiter results from a planet having
broken up
following collision with a comet:
"That comets are capable of distroying such worlds as may
chance to fall
in their way, is, from their vast magnitude, velocity, firey
substance,
not at all to be doubted, and it is more than probable from the
great
and unoccupied distance betwixt ye planet Mars and Jupiter some
world
may have met with such a final dissolution." [14]
Yet the gap was readily apparent to anyone who glanced at the
data for
the planetary orbits. Near the beginning of the eighteenth
century, for
example, William Whiston, Newton's successor in Cambridge, gives
the
actual distances of the planets in millions of miles as 32, 59,
81, 123,
424, 777. [15] We note that there are four planets within 123
million
miles of the Sun, but the gap before the next planet, Jupiter, is
over
300 million miles.
5. The First Statement of the Law
Whiston's contemporary, David Gregory, in his widely-read The
Elements
of Astronomy [16] puts the planetary distances into proportional
numbers: ``...supposing the distance of the Earth from the Sun to
be
divided into ten equal Parts, of these the distance of Mercury
will be
about four, of Venus seven, of Mars fifteen, of Jupiter fifty
two, and
that of Saturn ninety five.'' Gregory's work was published in
Latin in
1702 and again in 1726, and an English translation appeared in
1715 with
a second edition in 1726. The words quoted appear at the very
beginning
of the work, in Proposition 1 of Section 1 of Book I, and are
therefore
in a very prominent position. But they have been overlooked by
historians, who have found exactly the same numbers - indeed, a
paraphrase of the same sentence - in a work published in 1724 by
Christian Wolff: Vernünfftige Gedanken von den Absichten der
natürlichen
Dinge, which was to go through several editions. [17] In 1764,
the
French natural philosopher Charles Bonnet published his
Contemplation de
la Nature, a successful work that was quickly translated into
other
European languages. The German translation was undertaken by
Johann
Daniel Titius of Wittenberg. It had long been common for
translators to
supplement the text they were translating, usually to bring it up
to
date, for in those days when book publishing was even slower than
it is
today, many years often elapsed between first publication and
translation. Translators, that is, took a greater initiative than
is now
thought proper; indeed, it was not unknown for a translator to
conduct a
running battle with his author through the medium of footnotes.
Titius,
probably because he was by nature self-effacing, not only left
his
additions unsigned but actually incorporated them in the text
itself,
with no hint that they were not the original work of the author.
He
chose to make such an addition to the paragraph where Bonnet
remarks
that ``We know seventeen planets that enter into the composition
of our
solar system [that is, major planets and their satellites]; but
we are
not sure that there are no more'', going on to anticipate more
discoveries as telescopes improve. Titius then inserts what we
now know
as Bode's Law:
"Take notice of the distances of the planets from one
another, and
recognize that almost all are separated from one another in a
proportion
which matches their bodily magnitudes. Divide the distance from
the Sun
to Saturn into 100 parts; then Mercury is separated by four such
parts
from the Sun, Venus by 4+3=7 such parts, the Earth by 4+6=10,
Mars by
4+12=16. But notice that from Mars to Jupiter there comes a
deviation
from this so exact progression. From Mars there follows a space
of
4+24=28 such parts, but so far no planet was sighted there. But
should
the Lord Architect have left that space empty? Not at all. Let us
therefore assume that this space without doubt belongs to the
still
undiscovered satellites of Mars, let us also add that perhaps
Jupiter
still has around itself some smaller ones which have not been
sighted
yet by any telescope. Next to this for us still unexplored space
there
rises Jupiter's sphere of influence at 4+48=52 parts; and that of
Saturn
at 4+96=100 parts. What a wonderful relation!" [18]
It is interesting to note that these numbers are not exactly the
ones
listed by Gregory and Wolff; nor do they follow from the actual
distances published by Whiston, which would give 96 for Saturn in
place
of the 95 of Gregory and the 100 of Titius. But it seems that
Wolff was
indeed the immediate source for Titius, for in the fourth edition
of his
translation, by which time he was clearly identifying his own
contributions as such, he adds the comment: ``This relationship
and the
related considerations which Herr Bonnet thought had first been
observed
by Herr Lambert had already been recited by Freyherr von Wolf in
his
German Physics more than forty years earlier.'' [19] How Titius
could
declare that Bonnet had drawn his ideas of unknown planets from
Lambert
is not clear, though perhaps Titius and Bonnet may have
corresponded
over the translation; but this reference of Titius to Wolff
suggests
that Wolff had indeed been Titius's original source.
As it happened, Titius published a second edition of his
translation -
with the law now properly located in a footnote - just as the
promising
young astronomer Johann Elert Bode was putting the finishing
touches to
the second edition of his introduction to astronomy, Anleitung
zur
Kenntniss des gestirnten Himmels, which he had published in 1768
when he
was only nineteen. Bode came across the relationship proposed by
Titius,
was convinced by it, and inserted it as a footnote in his text:
"This latter point seems in particular to follow from the
astonishing
relation which the known six planets observe in their distances
from the
Sun. Let the distance from the Sun to Saturn be taken as 100,
then
Mercury is separated by 4 such parts from the Sun. Venus is
4+3=7. The
Earth 4+6=10. Mars 4+12=16. Now comes a gap in this so orderly
progression. After Mars there follows a space of 4+24=28 parts,
in which
no planet has yet been seen. Can one believe that the Founder of
the
universe had left this space empty? Certainly not. From here we
come to
the distance of Jupiter by 4+48=52 parts, and finally to that of
Saturn
by 4+96=100 parts." [20]
It is clear from the wording that Bode is following Titius,
although he
of course realized that the suggestion that the missing planet
was a
moon of Mars was preposterous, a fact he emphasized in the third
edition
of his book. But he makes no acknowledgement to Titius; indeed,
it is
only in later editions that Bode identifies his source (possibly
because
Titius had pressed him to do so). In the hands of Bode the
relationship
assumed a new importance, for Bode was a professional astronomer
soon to
take on international stature, and he was well-placed to act as
apostle
of the new law.
6. The Discovery of Uranus
Given the willingness on the part of many astronomers to believe
that
there were planets as yet undiscovered, and especially so in
orbit
beyond Saturn, it is a little surprising that it never crossed
the mind
of William Herschel in March 1781 that the ``curious either
nebulous
star or perhaps a comet'' he had noticed in his telescope might
indeed
be a major planet. [21] It is often said that this failure of
imagination was because of the total novelty of his discovery -
that no
primary planet had ever been discovered in historic times, which
of
course is true. But in view of the numerous references we have
seen to
the ``known'' planets, including that of Bode just cited, it
seems more
likely that Herschel - an isolated and self-taught amateur - was
simply
unaware of the professional astronomers' openness to new
discoveries
among the planets. As early as 4 April the Astronomer Royal,
Nevil
Maskelyne, wrote to their mutual friend William Watson of
Herschel's
``comet or new planet'', and on the 23rd he wrote to Herschel:
"I am to acknowledge my obligations to you for the
communication of your
discovery of the present Comet, or planet, I don't know which to
call
it. It is as likely to be a regular planet moving in an orbit
nearly
circular round the sun as a Comet moving in a very excentric
ellipsis."
How to calculate the orbit, however, was a difficult problem, for
the
body had been observed for only a very tiny fraction of a
complete
orbit. If it was a comet, then it would be simplest to assume a
parabolic orbit. P.-F.-A. Méchain, a French mathematician who
had
discovered several comets, being misled by the earliest
observations
which made it likely that the object was indeed a comet, sent
Herschel a
letter in which he gave the perihelion distance of the supposed
comet as
0.46 AU and perihelion date as 23 May 1781; Anders Johan Lexell,
a
Finnish-born professor of mathematics at St Petersburg who was
visiting
England at the time, soon after proposed a perihelion distance of
16 AU
with perihelion not to be reached until 1789.
On the other hand, if it was a planet, then it was simplest to
assume a
circular orbit, and Lexell was one of a number of astronomers
who,
finding that parabolic orbits were incompatible with the
observations,
investigated circular orbits. Lexell derived for the radius of
the orbit
the excellent value of 18.93 AU - that is, with the radius of
Saturn's
orbit put at 100, a distance that compared well with the
prediction of
196 from the Titius-Bode relation. More sophisticated
calculations
followed, some of them taking into account observations made
years
earlier when the planet had been mistaken for a star; and soon it
was
clear that the object was indeed a planet and, moreover, one that
fitted
well the Titius-Bode relation.
7. The Search for the Planet between Mars and Jupiter
This remarkable confirmation of the relation naturally reinforced
Bode's
belief, and it likewise persuaded Baron Francis Xaver von Zach,
the
court astronomer at Gotha. Both men were convinced there was an
undiscovered planet between Mars and Jupiter, and in 1787 Zach
began to
search for it. Not unreasonably, he limited his investigation to
the
Zodiac, and believing that only a methodical search offered hope
of
success, he produced for himself a catalogue of zodiacal stars
arranged
by right ascension; but without success. The autumn of 1799 found
him
visiting astronomers in Celle, Bremen and Lilienthal, and there
the idea
of a cooperative attack on the problem emerged:
"It was the opinion of these men of discernment, that to get
onto the
trail of this so-long-hidden planet, it cannot be a matter for
one or
two astronomers to scrutinise the entire Zodiac down to the
telescopic
stars." [22]
It was on 21 September the following year that the cooperative
attack -
probably without precedent in the history of science - became a
reality.
On that day six astronomers met in Lilienthal: von Zach himself;
J.H.
Schröter, the chief magistrate of Lilienthal, whose world-famous
collection of instruments included a Herschel reflector of 27ft
focal
length; H.W.M. Olbers, physician from nearby Bremen and longtime
collaborator with Schröter; C.L. Harding, who was employed by
Schröter
and who was himself to discover the third asteroid in 1804; F.A.
Freiherr von Ende; and Johann Gildemeister. They decided that
even six
observers were too few for the task ahead, and nominated instead
a group
of twenty-four practising astronomers chosen from throughout
Europe.
Schröter was to be president and Zach secretary. The entire
Zodiac was
divided up into twenty-four zones each of 15 degrees in
longitude, and
extending some 7 or 8 degrees north and south of the ecliptic in
latitude. The zones were allocated to the members by lot. Each
member
was to draw up a star chart for his zone, extending to the
smallest
telescopic stars,
"and through repeated examination of the sky was to confirm
the
unchanging state of his district, or the presence of each
wandering
foreign guest. Through such a strictly organized policing of the
heavens, divided into twenty-four sections, we hoped eventually
to track
down this planet, which had so long escaped our scrutiny."
[23]
8. Piazzi and the Discovery of Ceres
Zach accordingly sent out the invitations to join this society of
celestial cops. One of those chosen was, naturally, Giuseppe
Piazzi of
Palermo, the southernmost of the European observatories. Piazzi
had been
born in 1746 in Valtellina, in what was then part of Switzerland
but is
now northern Italy. [24] As a young man, Piazzi joined the
Theatine
Order, and afterwards taught mathematics in a number of Italian
cities.
In 1780 he was invited to take the chair of higher mathematics at
the
Academy of Palermo. Arriving at Palermo, Piazzi, although
inexperienced
in astronomy, expressed a wish to found an astronomical
observatory:
Palermo was further south than any existing European observatory
and so
offered access to regions of the sky inaccessible elsewhere. His
royal
patron was in favour, and prepared to forego Piazzi's services
while he
equipped himself and his observatory for the task ahead. Piazzi
accordingly set off for England where he might obtain good
advice, from
such disparate figures as William Herschel and the Astronomer
Royal,
Nevil Maskelyne, and - equally important - good instruments.
Jesse
Ramsden was an instrument-maker without peer, but he was
notorious for
failing to produce on time. Piazzi persuaded him to attempt a 5ft
vertical circle of unique design. The circle, which has been
described
as ``a masterpiece of eighteenth-century technology'', was twice
abandoned by Ramsden, and he completed it eventually in August
1789 only
because Piazzi himself was present in London - indeed, in
Ramsden's
workshop, and quite literally breathing down Ramdsen's neck as
the work
proceeded. The circle gave readings in azimuth by micrometer
microscope,
and readings in altitude by two diametrically opposed
microscopes. The
divisions on the circles were illuminated by an inclined silver
mirror
fixed to each microscope, and the wires in the telescope eyepiece
by
transmitting light from a small lamp through the hollow
tube-axis. [25]
Once the Ramsden circle was installed in Palermo, Piazzi found
himself
in a privileged situation. He had an instrument of unique
quality, a
good climate, and the southernmost latitude of any European
observatory.
He very rightly set to work to exploit these advantages in the
compilation of a star catalogue better than any that had gone
before. A
feature of his painstaking work was the repeated measurement of
stellar
positions on different nights, so that the final coordinates were
accurate to a few seconds of arc. The first of Piazzi's two great
catalogues, with the coordinates of some 6,748 stars, was to
appear in
1803. [26] The accuracy of his work gave astronomers once more
the
confidence to tackle the question of stellar parallax, which had
been
largely in abeyance since it became clear around 1730 that
parallax
could not be much more than a second of arc.
The beginning of 1801 found Piazzi patiently at work on the star
catalogue. As he wrote a few months later,
"...on the evening of the 1st of January of the current
year, together
with several other stars, I sought for the 87th of the Catalogue
of the
Zodiacal stars of Mr la Caille. I then found it was preceded by
another,
which, according to my custom, I observed likewise, as it did not
impede
the principal observation. The light was a little faint, and of
the
colour of Jupiter, but similar to many others which generally are
reckoned of the eighth magnitude. Therefore I had no doubt of its
being
any other than a fixed star. In the evening of the 2d I repeated
my
observations, and having found that it did not correspond either
in time
or in distance from the zenith with the former observation, I
began to
entertain some doubts of its accuracy. I conceived afterwards a
great
suspicion that it might be a new star. The evening of the third,
my
suspicion was converted into certainty, being assured it was not
a fixed
star. Nevertheless before I made it known, I waited 'till the
evening of
the 4th, when I had the satisfaction to see it had moved at the
same
rate as on the preceding days. From the fourth to the tenth the
sky was
cloudy. In the evening of the 10th it appeared to me in the
Telescope,
accompanied by four others, nearly of the same magnitude. In the
uncertainty which was the new one, I observed them all, as
exactly as
possible, and having compared these observations with the others
which I
made in the evening of the 11th, by its motion I easily
distinguished my
star from the others. Mean while however I greatly wished to see
it out
of the meridian, to examine and to contemplate it more at
leisure. But
with all my labour, and that of my assistant D. Niccola
Cacciatore and
[of] D. Niccola Carioti belonging to this Royal Chapel both
enjoying a
sharp sight, and very expert in the knowledge of the heavens,
neither
with the night Telescope, nor with another achromatic one of 4
inches
aperture, was it possible to distinguish it from many others
among which
it was moving. I was therefore obliged to content myself with
seeing it
on the meridian, and for the short time of two minutes, that is
to say
the time it employed in traversing the field of the Telescope;
other
observations, which were making at the same time, not permitting
the
instrument to be moved from its position.
In the mean time, in order to render the observations more
certain,
while I was observing with the Circle, D. Niccola Carioti
observed with
the transit instrument. The sky was so hazy, and often cloudy,
that the
observations were interrupted 'till the 11th of February; when
the star
having approached so near the Sun, it was not possible to see it
any
longer at its passage over the meridian. I intended to search for
it,
out of it [the meridian], by means of the Azimuth; but having
fallen ill
on the thirteenth of February, I was not able to make any further
observations. These, however, which have been made, though they
are not
at the necessary distance from one another in order to assure us
of the
true course which the star describes in the heavens, are,
notwithstanding, sufficient in my opinion, to make us know the
nature of
the same, as one may collect from the results, which I have
deduced from
them." [27]
Piazzi had in fact measured the position of the object on a total
of 24
nights between 1 January and 11 February, though some positions
were
marked as `doubtful' or even `very uncertain'. On 24 January,
Piazzi had
announced his discovery in letters to fellow astronomers, among
them his
fellow-countryman, Barnaba Oriani of Milan. In it, Piazzi
confided to
him that
"I have announced this star as a comet, but since it is not
accompanied
by any nebulosity and, further, since its movement is so slow and
rather
uniform, it has occurred to me several times that it might be
something
better than a comet. But I have been careful not to advance this
supposition to the public." [28]
To the others, he claimed nothing more than the discovery of a
comet,
though making it clear that the `comet' had no nebulosity or
tail.
When after 11 February he could no longer see the object, Piazzi
set to
work to investigate its orbit, though such mathematical
investigations
were not his strength. He began with the assumption that it was
indeed a
comet, and fitted a parabola to three of the observations to see
if the
orbit would account for the others. It did not. A second attempt
with a
different group of three observations likewise failed:
"From the parabolic hypothesis I passed then to the
circular; and having
made a few suppositions, I found two radii, 2.7067 and 2.6862;
with each
of which all the observations were represented a great deal
better than
any parabola. The planets describing ellipses more or less
eccentric,
and not circles, it is to be believed that ours will not deviate
from
this rule. In an ellipsis I should then have continued my
calculations;
but as the arch observed is very small, the results would be very
uncertain, and the labour long and painful. I have therefore
preferred
the circle....
The agreement of the observed longitudes with the calculated ones
in the
circular hypothesis, its motion in the Zodiac, from which it only
departs a little way in the greatest latitudes, and its position
between
Mars and Jupiter, leave no doubt that this new star is a true
planet...." [29]
But how to recover the now-lost planet at some future date? In
Piazzi's
opinion, the best hope lay in identifying some past occasion when
the
planet had been observed in the belief that it was a star. He
thinks it
may well have been the object observed by Bode in 1772, and that
it had
probably been listed at some time or other by la Caille or by
Tobias
Mayer:
"In the catalogues of the Zodiacal stars of these two
Astronomers, there
are some observed only once, which I could never find, though I
have
sought them several times, and on different occasions. If the
original
observations of Mayer are preserved at Göttingen, and those of
la Caille
at Paris, it is possible that some light may be thrown by them on
this
matter. At the end of my work on the position of the fixed stars,
... I
shall give a catalogue of lost stars, which will much facilitate
this
research." [30]
We can well believe Piazzi when he says that not only Oriani, but
more
especially Bode of the celestial cops, ``were instantly of the
opinion
that it was a new planet; and settled nearly the same elements of
its
orbit, as I have done''. One can imagine the German's delight
that the
hoped-for planet had been found, even if the discovery owed
nothing to
the celestial cops themselves.
But now Piazzi himself was beginning to have doubts. He had
estimated
the size of the object from the fact that it was almost, but not
quite,
covered by one of the wires of his telescope, and his conclusion
was
that it was larger than the Earth. However, it would seem that in
the
hazy nights that followed, the true (and much smaller) size of
the
object became more evident to the Palermo astronomer, who began
to think
that the object was diminishing in size and therefore moving
rapidly
away, so that it must be a comet after all:
"As after the 23rd [of January] the star began sensibly to
diminish in
size and brightness, uncertain whether it was to be attributed to
its
rapid receding from the Earth, or rather to the state of the
atmosphere,
which became after that still more dark and hazy, I began to
doubt of
its nature, so as even to believe it was a comet and not a
planet." [31]
Eventually, in April, when illness had prevented him from making
further
progress in the investigation of the object's orbit, Piazzi sent
his
complete observations to Oriani, Bode, and Lalande in Paris,
together
with his suspicions that it might be a comet after all. And with
that,
Piazzi's own role in the story comes to an end, save for his
naming the
body - should it ever be recovered - Ceres Ferdinandea, Ceres for
the
patron goddess of Sicily, and Ferdinandea for Piazzi's royal
patron.
It is one of the problems of writing history, that no story ever
has a
tidy ending. One would wish to go on to discuss the mathematical
analysis of Piazzi's observations by Gauss that enabled Zach to
recover
it at the end of the year; the discovery of Pallas by Olbers in
March
1802; the announcement by William Herschel [32] in May that these
bodies
were tiny compared to the planets - he estimated Ceres had a
diameter of
only 162 English miles (though this is perhaps a quarter of what
we
consider the true value), and proposed that these bodies should
be
termed asteroids rather than planets, much to Piazzi's annoyance;
the
discovery of Juno by Harding in 1804, and of Vesta by Olbers in
1807;
and indeed the role of Bode's Law (or better, as we have seen,
the
Titius-Bode Law) in the discovery of Neptune in 1846. But in this
celebration of the bicentenary of Palermo Observatory, we are
perhaps
justified in ending this story with the most famous discovery
ever made
here - but a discovery made possible by the fine instrument
Piazzi had
managed to acquire, and by Piazzi's dedication in using it
towards the
compilation of his two great star catalogues - catalogues that
raised
European standards of precision astronomy in the opening years of
the
new century.
References
1. Johannes Kepler Mysterium cosmographicum (Tübingen, 1596),
pp. 7-8;
transl. by A.M. Duncan, The Secret of the Universe (New York,
1981), pp.
63-64.
2. Isaac Newton, letter to Richard Bentley, 10 Dec. 1692 (Four
Letters
from Isaac Newton to Doctor Bentley (London, 1756), p. 9.
3. Immanuel Kant, Allgemeine Naturgeschichte und Theorie des
Himmels
(Königsberg and Leipzig, 1755), p. 163; transl. by S.L. Jaki,
Universal
Natural History and Theory of the Heavens (Edinburgh, 1981), p.
177.
4. J.H. Lambert, Cosmologische Briefe (Augsberg, 1761), p. 7;
transl. by
S.L. Jaki, Cosmological Letters (Edinburgh, 1976), p. 57.
5. Tobias Swinden, An Enquiry into the Nature and Place of Hell,
2nd edn
(London, 1727), pp. 354-5.
6. William Whiston,Astronomical Principles of Religion, Natural
and
Reveal'd (London, 1717), pp. 15, 19.
7. Thomas Wright of Durham, Clavis Coelestis (London, 1742), p.
16.
8. Ibid., pp. 17, 33.
9. Thomas Wright of Durham, An Original Theory or New Hypothesis
of the
Universe (London, 1750), p. 31.
10. Thomas Wright of Durham, Second or Singular Thoughts upon the
Theory
of the Universe, ed. by M.A. Hoskin (London, 1968), p. 45.
11. Ibid., p. 50.
12. Kant, op. cit. (ref. 3), p. 17; transl. by Jaki, pp. 108-9.
13. James Ferguson, Astronomy Explained upon Sir Isaac Newton's
Principles, 12th edn (London, 1809), p. 37: ``By comparing the
great
interval between the Orbits of Mars and Jupiter, it was surmised
upwards
of seventy years ago, by Mr. Maclaurin and others, and lately by
C.
Loft, Esq that there must, at least, be one planet, whose orbit
is
exterior to that of Mars, and interior to the Orbit of Jupiter.''
I have
not located the work in which Maclaurin makes this suggestion.
14. Wright, Second or Singular Thoughts, p. 24.
15. William Whiston, Praelectiones astronomicae (London, 1707),
Lectio
VII.
16. David Gregory, Astronomiae elementa (Oxford, 1702), Book I,
Section
I, Prop. I; transl. from the English edn (London, 1715), p. 2.
17. The best source for the post-Gregory story of this section is
M.M.
Nieto, The Titius-Bode Law of Planetary Distances (Oxford, 1972).
As the
distances quoted by Whiston would convert (to the nearest
integer) to
give Saturn the figure 96 rather than 95, it is likely that Wolff
took
the numbers directly from Gregory rather than deriving them
himself.
Roger Long, Astronomy (2 vols, Cambridge, 1742, 1754), vol. 1, p.
339,
gives 32, 59, 82, 125, 426 and 780 millions of miles. Ferguson,
Astronomy Explained..., 1st edn (London, 1756), gives Whiston's
values.
18. Johann Daniel Titius, Betrachtung über die Natur, vom Herrn
Karl
Bonnet (Leipzig, 1766), pp. 7-8; transl. by Stanley Jaki in ``The
early
history of the Titius-Bode Law'', American Journal of Physics,
vol. 40
(1972), pp. 1014-23.
19. Titius, Betrachtung..., 4th edn (Leipzig, 1783), p. 13;
transl. by
Nieto, The Titius-Bode Law, p. 11.
20. Johann Elert Bode, Anleitung zur Kenntnis des gestirten
Himmels, 2nd
edn (Hamburg, 1772), p. 462; transl. by Jaki, op. cit. (ref. 18).
For a facsimile of the original entry in Herschel's observing
book, see
21. The Scientific Papers of Sir William Herschel, ed. by J.L.E.
Dreyer
(2 vols, London, 1912), vol. 1, p. xxviii. In the following pages
Dreyer
gives further details of the discovery and its aftermath. For
futher
information, see the articles by R. Porter, J.A. Bennett, M.
Hoskin,
E.G. Forbes and R.W. Smith in the section on ``History of the
Discovery
of Uranus'' in Uranus and the Outer Planets, ed. by Garry Hunt
(Cambridge, 1982). For early attempts to determine the orbit of
Uranus,
see A.F. O'D. Alexander, The Planet Uranus: A History of
Observation,
Theory and Discovery (London, 1865), chap. 2.
22. The story is told by F.X. von Zach, ``Über einen zwischen
Mars und
Jupiter längst vermutheten, nun wahrscheinlich entdeckten neuen
Hauptplaneten unseres Sonnen-Systems'', Monatliche Correspondenz,
June
1801, 592-623, quotation from p. 602.
23. Ibid., pp. 602-3.
24. On Piazzi see the article by Giorgio Abetti in Dictionary of
Scientific Biography, and the bibliography therein.
25. W. Pearson, Introduction to Practical Astronomy, vol. 2
(London,
1829), pp. 413-17.
26. G. Piazzi, Praecipuarum stellarum inerrantium positiones
mediae
ineunte saeculo decimonono ex observationibus habitis in specula
panoramitana ab anno 1792 ad annum 1802 (Palermo, 1803).
27. G. Piazzi, Risultati delle Osservazioni della Nuova Stella
(Palermo,
1801), pp. 3-6. I have used (without amendment) the English
translation
by one Antonio Parachinatti, ``teacher of the Italian language'',
prepared for Nevil Maskelyne (Cambridge University Library, RGO
ms
4/221). Quoted by courtesy of the Syndics of Cambridge University
Library and of the Director of the Royal Greenwich Observatory.
28. Cited by Abetti, op. cit. (ref. 24).
29. Piazzi, op. cit. (ref. 27), pp. 7-8, 13.
30. Ibid., pp. 13-14.
31. Ibid., p. 16.
32. W. Herschel, ``Observations on the Two Lately Discovered
Celestial
Bodies'', Philosophical Transactions, vol. 92 (1802), 187-98. As
early
as 18 February 1802, and before the discovery of Pallas, Herschel
had
told the Royal Society that Ceres was much smaller than the Moon:
``Observations of the New Planet'', first published in The
Scientific
Papers of Sir William Herschel (ref. 21), vol 1, pp. cix-cxi.
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