PLEASE NOTE:
*
Date sent: Mon, 09 Jun 1997 09:42:25 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: 1996 TL66 story, significant for NEOs
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
MINI-PLANET OR GIANT COMET OR WHAT?
THE 1996TL66 STORY MIGHT BE SIGNIFICANT FOR NEO RESEARCH
Remember last Thursday's story about a newly discovered
"mini-planet" in THE TIMES? For people interested in
the background
of this discovery and the current thinking about the nature of
this
new object, Duncan Steel [Spaceguard Australia]
<dis@a011.aone.net.au> has sent the following text by Brian
Marsden
for circulation.
NEW TYPE OF TRANSNEPTUNIAN OBJECT RECOGNIZED
by Brian Marsden
The issue of NATURE published today contains a letter
discussing the discovery and likely significance of a 500-km
object
recognized in the transneptunian region of the solar system in
late
1996. News of the object, designated 1996 TL66, was in fact first
published on Minor Planet Electronic Circular 1997-B18 as long
ago
as January 30. In addition to its unusually large size, the
significance of the object lies in the high eccentricity of its
orbit, which takes the object from a distance of 35 astronomical
units from the sun at its closest point to some 130 astronomical
units at its most distant. One astronomical unit is approximately
the earth's distance from the sun and 30 astronomical units is
that
of Neptune.
1996 TL66 was first imaged last October by Jane Luu, Harvard-
Smithsonian Center for Astrophysics, and Dave Jewitt, University
of
Hawaii, during an observing run with two of Jewitt's students on
the 2.2-m telescope the University of Hawaii maintains on Mauna
Kea. At first, and as the result also of follow-up observations
with the Smithsonian Astrophysical Observatory's 1.2-m telescope
in
Arizona a month later, it appeared probable that the object was a
"plutino", one of two main classes of object hitherto
identified in
the Kuiper Belt, an extensive swarm of icy bodies, presumably
proto-comets, identified in recent years as orbiting the sun
beyond
the orbit of Neptune.
"Plutinos", meaning "little Plutos", is a
generic name given
to the class of Kuiper Belt members with orbits that come very
close, and sometimes even cross, the orbit of Neptune. Despite
their often extreme proximity to Neptune's orbit, the plutinos do
not in fact have the possibility of encountering Neptune itself,
because the periods of revolution about the sun of the plutinos
and
Neptune are precisely in a ratio of three to two. This means
that,
after three revolutions of Neptune and two of a plutino (about
500
years), the relative positions of the objects in their orbits
repeat, and this cycle does not give the bodies an opportunity to
pass within 10 or more astronomical units of each other. Although
the cycle may break down eventually, it seems likely that it will
continue to repeat for perhaps tens or hundreds of millions of
years, thereby preventing devastating encounters between a
plutino
and Neptune. Pluto, a 2400-km object discovered in 1930, has been
known since 1964 to exhibit precisely this type of motion, and it
should therefore be considered as the first known member of the
Kuiper Belt; the second member of the group would then be Pluto's
satellite Charon, discovered in 1978 and having about half the
diameter of Pluto.
The plutinos contrast with what may be called the
"cubewanos",
in recognition of their prototype 1992 QB1, also discovered by
Jewitt and Luu. Cubewanos, which comprise perhaps 60-70 percent
of
the known objects in the Kuiper Belt, travel in orbits that are
substantially more nearly circular and closer to the plane of
Neptune's orbit than the plutinos. And whereas the plutinos orbit
the sun at an average distance of 39 astronomical units,
cubewanos have average distances over the range 42-46
astronomical
units. They are therefore well beyond Neptune at all times.
After Carl Hergenrother measured 1996 TL66 with the Arizona
telescope in December, continuing calculations by Brian Marsden
showed that the supposition that 1996 TL66 is a plutino had to be
incorrect. At this stage it became evident that the orbit had to
be
substantially larger and more elongated than that of a plutino.
Nevertheless, the orbit's precise character was unclear,
something
that needed to be settled with further observations.
Unfortunately,
1996 TL66 was by then starting to sink into the evening twilight,
and no time had been allocated for follow-up in January on any of
the suitable professional telescopes. It was at this stage that
the
help of an amateur astronomer, Warren Offutt, was solicited. At
his
observatory 1000 meters up in the mountains near Cloudcroft, New
Mexico, Offutt has a well-equipped 0.6-meter telescope and
electronic imaging device. He was already known by then as the
only
amateur in the world to have observed a member of the Kuiper Belt
(other than Pluto) using amateur equipment, so it seemed likely
that he would be able to obtain some measurements that would
clinch
the situation before 1996 TL66 was lost to view. Offutt was
happy to oblige and obtained critical observations on January 10
and 11, thereby providing confirmation of the developing
suspicions
concerning the 1996 TL66 orbit.
Are there other objects like 1996 TL66? The ease with which it
was found, at the start of new wide-field survey, suggests that
there are. Furthermore, some of its colleagues may already have
been inadvertently detected. For every two Kuiper Belt candidates
that are discovered, typically one is lost. Out of the 40 or so
Kuiper Belt candidates known, four of those lost possibly do have
some of the characteristics of 1996 TL66, notably, indications
that
their orbits are quite highly inclined to that of Neptune.
Perhaps
10 percent of what we think of as the Kuiper Belt may therefore
belong to this "scattered" population.
So what is 1996 TL66? Physically, it is probably much the same
as the other icy bodies out there, including Pluto. Dynamically,
some of the Kuiper Belt objects, perhaps principally the
plutinos,
form the reservoir that eventually yields the typical
short-period
comets that at their most distant are near the orbit of Jupiter.
If, eventually, the accumulated gravitational attractions of
Neptune, Uranus, Saturn and Jupiter conspire to dislodge a
plutino,
a plutino can be dragged into the vicinity of those planets, to
spend then perhaps another million years in a very unstable
dynamical situation, bouncing back from one planet to another.
This is known as the "centaur" stage, something
currently being
exhibited by seven known objects. The first of these, named
Chiron
following its discovery in 1977, does sometimes exhibit a coma or
tail and is the largest object known to do so. Eventually,
Jupiter
wins, sending an object in toward the orbits of Mars and the
earth.
About a hundred of these short-period comets are known, all of
them
considerably smaller than Chiron but thereby indicative of the
large number of smaller centaurs and plutinos that must exist. In
very general terms, 1996 TL66 could be considered in the same
category, perhaps also to move up the centaur route -- or once to
have been a centaur. Perhaps, indeed, it is destined to move
farther out than it is now. Perhaps it is on its way out toward
the Oort Cloud. The Oort Cloud of comets surrounding the solar
system at a distance of some 20 percent of the nearest star is
believed mainly to represent icy bodies ejected from the vicinity
of Uranus and Neptune. As many as a trillion proto-comets seem to
exist in the Oort Cloud, drawn out from a planar to a
near-spherical collection as the result of the gravitational
effects of passing stars and giant molecular clouds. To gather a
trillion comets takes a long time, and most of the formation of
the Oort Cloud must have taken place long ago. The existence of
1996 TL66, and presumably of other bodies in its class, indicates
that the process of maintaining the Oort Cloud may still be going
on at some small level.
Brian Marsden, Director, Minor Planet Center
1997 June 5
*
Date sent: Mon, 09 Jun 1997 09:18:26 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: The wild claims about the hail of mini-comets
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
MORE INFORMATION ABOUT MINI-COMETS & A SCEPTICAL RESPONSE
from: Daniel Fischer <dfischer@astro.uni-bonn.de>:
Cc: imo-news@imonews.net
Im sure that most in the meteor community have by now heard about
the revival of the ideas about the hail of 10 m sized and highly
unusual comets that supposedly hit the Earth's atmosphere every
few
minutes. At
http://smallcomets.physics.uiowa.edu
discoverer L. Frank himself tells the story, while various
stories
e.g. at
http://www.sciencenow.org/html/970528b.htm
,
http://www.sciencenews.org/sn_arc97/5_31_97/fob1.htm
and
http://washingtonpost.com:80/wp-srv/WPlate/1997-06/01/117L-060197-idx.html
also give weight to the highly controversial nature of the
claims.
What puzzled me most was a picture released last week, e.g. at
http://smallcomets.physics.uiowa.edu/www/may28-2.html
and
ftp://pao.gsfc.nasa.gov/pub/pao/releases/1997/97-61.jpg
that, according to the caption, "contains the trail of an
object
over the Atlantic Ocean and Western Europe on Sept. 26,1996. The
object was in sunlight but the Earth below was in darkness, so a
map of the Earth has been superposed onto the image as a frame of
reference. According to Dr. Louis A. Frank of the University of
Iowa, the instrumens principal investigator, this time lapse
image
with a duration of 54 seconds shows a small comet the size of a
two-bedroom house that disrupted 5,000 to 15,000 miles above the
Earth."
In his own description of the image Frank calls it a
"spectacular
disruption (at right) of a small comet the size of a two-bedroom
house [that] took place 5,000 to 15,000 miles above the Atlantic
Ocean at 2228 UT on September 26, 1996. A view of Earth at the
time
of the event has been superposed onto the far-ultraviolet image
as
a frame of reference. This unusually bright and long-lived trail,
which was captured by Earth Camera aboard NASA's Polar
spacecraft,
ends over Germany."
Germany, at 22:28 UTC? That means it was already dark! Which
leads
to the immediate question: Did anyone observe something unusual
on
that Sept. 26, 1996, evening over the British Isles or Central
Europe - or did meteor cameras record something unusual? From the
otherwise undocumented image itself it is impossible to judge the
luminosity (let alone the visual brightness) of the phenomenon,
but
its visual observation (or clear null result) would be an
important
constraint for the physics involved.
Another interesting note for amateur observers: In his new
"FAQ"
list at
http://smallcomets.physics.uiowa.edu/www/faq.htmlx
Frank also addresses amateur astronomy and visual observers
twice:
"Can the small comets be seen by the naked eye?
Yes, but you will need lots of patience--and a little luck. Too
see
a small comet you must stand out on a clear dark night until you
see a short streak that quickly snuffs out. It will be about the
brightness of Venus for about two seconds before it vanishes. But
you will have to be out there for a hundred hours or so to see
one.
A hundred hours of clear night viewing does not happen often in
the
average lifetime.
How can amateur astronomers spot the small comets?
Amateur astronomers whose telescopes have mirrors or lenses
measuring12 inches or larger should be able to sight the small
comets. During the course of a day there are two times for
observation, each about one or two hours long. One ends about 45
minutes before sunrise; the other begins about 45 minutes after
sunset. The small comets will be seen at a distance about 2,500
to
4,500 miles from the observer,so the telescope should be pointed
in
such a way that it is looking for them at these distances, just
outside the Earth's shadow. Inside the shadow the objects are
not illuminated by the Sun and are invisible. Every two hours or
so
a small, quite dim object will slowly move across your view, as
long as your field of view is about four times the size of the
Moon. The object will move at a distance equal to the Moon's
diameter every five seconds or so. Several amateur astronomers
have
reported seeing such objects."
Comments on this remarkable issue - and Frank's wild claims in
the
last two paragraphs in particular - would be highly welcome,
especially since I am right now writing a review article about
it!
Daniel Fischer, dfischer@astro.uni-bonn.de
http://www.geocities.com/CapeCanaveral/5599/mirror.html
----------------------------------------------------------------------
REACTION
From: "Fred H. Francis" <francis@chapman.edu>
Cc: imo-news@imonews.net
Subject: Re: The wild claims about the hail of mini-comets
Dear Daniel,
Which is more "wild", Dr. Frank's theory, or your
analysis?
Did you fail to note in that the photo, as published was clearly
described as a composite (hence, in all probability, a v.l.
representation
of the earth was superimposed for clarity beneath the genuine
image of the
comet)?
Did you fail to note your own recitation of the fact that the
image was
taken in the ultra-violet (hence accounting for the object's
brightness)?
Did you fail to note that, in the description of the phenomenon
itself,
republished with the latest photo, the reason cited for the
almost
complete lack of a v.l. (visual light) signature is that the
snowball
breaks-up almost immediatly upon touching the atmosphere, thus
dissipating
the bulk of its momentum and thus the possibility of normal
luminous
radiation due to atmospheric heating.?
Given that your attack on Dr. Frank's views is so pointed, I must
add
that the fact that you obviously did not read much of te material
you cite
is at least amazing as the fact that you seem to understand so
little of
it. To compound that by writing a review article on it without
actually (apparently) contacting the NASA folks to at least get
their explanation of the facts which seem to confuse you is truly
marvelous.
As you do not, apparently, understand either Dr. Frank's theory
or its
factual/phenomenological basis, I must ask the following
question:
How is it possible to write your article without checking the
facts, or
do you intend to rely upon intuition and 'common sense'?
Sincerely,
Fred H. Francis
