SEDS
(Students for the Exploration and Development of Space) Homepage
Lots of Pluto Web
Sites
Our solar system may have an outer "edge" just outside the orbit of Pluto,
astronomers announced. Their results suggest that early in the history
of the solar system, some event stripped away most of the planet-building
material beyond 50 times Earth's distance from the sun.
Lynne Allen and Gary Bernstein, of the University of Michigan, and Renu
Malhotra of the University of Arizona Lunar and Planetary Laboratory
presented the evidence at a meeting of the Division of Planetary
Sciences of the American Astronomical Society, October 2000.
It has long been thought that some comets must originate from a collection
of small icy bodies orbiting beyond Neptune. These so-called "Kuiper Belt
Objects" would be left over from the formation of the large planets 5
billion years ago. The Kuiper Belt Objects were purely hypothetical until
1992, when David Jewitt and Jane Luu of the University of Hawaii discovered
the first one. Since that time, over 300 Kuiper Belt Objects have been
discovered - but none of them are more than about 55 times as far from the
sun as Earth, or 55 AU.
Does the solar system really end beyond Pluto's orbit? Or are the more
distant objects just too faint to have been found so far? To address this
question, Allen, Bernstein, and Malhotra searched 6 patches of sky, each
about the size of the full moon, using a state-of-the-art electronic camera
at the Cerro Tololo Inter-American Observatory in the Chilean Andes.
Astronomers have discovered more than 300 Kuiper Belt Objects, but none of
them are more than 55 times as far from the sun as Earth. Does the solar
system really end beyond Pluto's orbit?
These observations, in 1998 and 1999, were sensitive enough to see a
160-kilometer (100-mile) Kuiper Belt Object to at least 65 AU. They
discovered 24 new Kuiper Belt Objects, 9 of which are 160 kilometers or
bigger, but again the most distant is near the outer limit of Pluto's orbit.
This is the strongest evidence yet that more distant objects are missing.
Some of the known Kuiper Belt Objects as well as many comets are on
trajectories that will carry them well beyond the orbit of Pluto. But these
are all believed to have formed inside Pluto's orbit and then been pushed
outward by an encounter with Neptune or another planet. There are still no
known objects which appear to have been created outside Pluto's orbit.
So astronomers are left to wonder what explains this apparent edge: was the
primordial solar system originally "small"? Or were there once more distant
objects that were pulled away by the gravity of a passing star? Astronomers
at telescopes around the world are currently conducting further surveys in
an effort to learn more about the history of our solar system.
This Kuiper Belt survey was funded by grants from NASA and the National
Science Foundation.
Images and text available at
http://www.astro.lsa.umich/users/garyb/WWWKBO.
Astronomers have expressed their major concerns over the NASA-directed
work stoppage for the Pluto-Kuiper Express Mission (PKE). The
American Astronomical Society's Division for Planetary Sciences (DPS)
committee has urged that NASA and the US Congress to find a way to
fund this important mission, but not at the expense of other equally
important planetary missions or its basic research and analysis
programs.
A stop-work order was issued in mid-September, 2000, by NASA Associate
Administrator for Space Science Dr. Edward Weiler. The stated reason
was ballooning costs for the entire Outer Planets set of missions at
JPL (which also includes the Europa Orbiter and Solar Probe), due
largely to increased costs for the launch vehicle and radioactive
thermal generators (RGTs).
The DPS committee noted that if work on PKE is not resumed before the end
of calendar year 2000, it is likely that the 2004 launch opportunity will
be lost, and the earliest arrival date would slip by at least 7 years (from
2012 to 2019 or beyond). Pluto is the only planet not yet explored by
spacecraft and is therefore of great interest and importance to the
planetary science community. It is also moving rapidly outward from the
Sun from its perihelion passage in the early 1990s, and if this mission is
delayed beyond the 2004 launch, the opportunity to study the tenuous Pluto
atmosphere may be lost for centuries.
Pluto Express
Hubble Images Pluto
Pluto has several homepages
Gemini infrared views of Pluto and Charon
Edge to Kuiper Belt Found
Pluto Express Work Stopped
Gemini North's High-Resolution Image of Pluto
The Gemini Observatory's 8.1-m telescope on Mauna Kea, using adaptive optics, has an image of Pluto in the near infrared with resolution of only 0.08 arcsec, fine enough to completely separate Pluto and Charon. http://www.gemini.edu/gallery/observing/pluto.html
M.P.E.C. 1999-C03
Issued 1999 Feb. 4, 16:04 UT
The Minor Planet Electronic Circulars contain information on unusual minor planets and routine data on comets. They are published on behalf of Commission 20 of the International Astronomical Union by the Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
BMARSDEN@CFA.HARVARD.EDU or GWILLIAMS@CFA.HARVARD.EDU URL http://cfa-www.harvard.edu/iau/mpc.html
EDITORIAL NOTICE
On 1801 Jan. 1 Guiseppe Piazzi discovered the object between Mars and Jupiter that he called Ceres Ferdinandea, "the eighth planet". Following the discovery a year later of a similar object, and in subsequent years further objects in what might be termed the "Cisjovian Belt", Piazzi's discovery eventually became known under either the name Ceres or the symbol (1), where the numeral, originally placed inside a complete circle, indicated that this was the first object found in that region of the solar system. By 1849 the sequence of discoveries in the region had reached (10), and 1868 saw the discovery of (100). By 1923, when (1000) was announced, the set of objects, while still mainly members of that Cisjovian Belt (also known simply as the "Asteroid Belt", or "Main Belt" of "minor planets"), also included objects that approached within 0.1 AU of the earth or extended out to the orbit of Saturn.
Next month, we shall pass (10000) in what is a collection of small objects that are not obviously cometary (although three members do also have well-documented dual status in the Catalogue of Cometary Orbits) and travel around the sun in independent orbits (i.e., satellites are excluded) that are well determined (i.e., with one exception that will surely be eventually remedied, the positions of the objects are very precisely predictable). Again, although the vast majority of the objects are in the Cisjovian Belt, there are members that are at perihelion significantly closer to the sun than Mercury or are at aphelion beyond the orbit of Neptune. It has been traditional to have a special celebration with each thousandth numbering. For example, (1000) was named in honor of the discoverer of Ceres, (2000) in honor of the discoverer of Uranus, (5000) in honor of the International Astronomical Union and (6000) in honor of the United Nations. Obviously, it would be appropriate to have some very special celebration to acknowledge (10000).
Most readers of these Circulars will be aware of recent discussions in the press concerning a proposal that the number (10000) should be given to Pluto. The principal reasoning for this is the recognition during the past few years that Pluto was the first discovered and largest known member of the "Transneptunian Belt" (sometimes called the "Kuiper Belt" or "Edgeworth-Kuiper Belt") of small objects beyond Neptune that possess some similarity, at least dynamically, to bodies in the Cisjovian Belt. Although as many as 95 members (or possible members) of the Transneptunian Belt are now listed, most of the orbital solutions are very weak, and none of the bodies has so far been included in the collection of those with "guaranteed" orbit determinations. A few of the discoveries from 1992-1994 are now approaching this state, which will also allow them to receive permanent names.
Although it is not unlikely that further Transneptunian Objects as large as Pluto will be discovered in the future, Pluto obviously holds a very special place in our appreciation of this new population, and by assigning to it the number (10000), we should guarantee that Pluto will be at the head of the Transneptunian list. It is also very important to affirm that there is absolutely no implied "demotion" or "reclassification" of Pluto from its position in the list of the "planets" (or "major planets" or "principal planets"). Unfortunately, many of the articles that have appeared in the press have accidentally (or deliberately) misinterpreted this issue. As with (2060) = 95P/Chiron, (4015) = 107P/Wilson-Harrington and (7968) = 133P/Elst-Pizarro, where the choice of "minor planet" or "comet" designation depends on the context, we are proposing that Pluto would have dual status as a "major" and a "minor" body. Readers of these Circulars, in particular, will appreciate that Pluto is sufficiently fainter than the other major planets that it can be confused with many other minor planets. We have in fact identified observations of Pluto several times during the past couple of years in data reported by the survey programs for Near-Earth Objects, and some astrometric observers specifically report to us observations of Pluto. There is currently no outlet for publishing these observations. It should be emphasized that the number (10000) would be used only in the context of publishing such observations or in matters directly related to Pluto's place in the Transneptunian Belt.
Much has been made in the press that the IAU is "voting" on Pluto's status, and at least one astronomical organization issued a press release on the subject. Members of the public seem completely baffled by this kind of attention. The question of relevance to the readers of these Circulars concerns the numbering and naming of (10000). Indeed, the IAU Small Bodies Names Committee has already been working on this particular matter for the past month or so. Progress is slow and uncertain, however, and there are some who think that democracy would be better served by seeking opinions from a larger, but informed community. The astronomers, amateur and professional, who contribute material to these Circulars--astrometric observations, identifications, orbit determinations--are such an informed community.
Accordingly, any reader with an opinion on the subject is invited to e-mail it to us at the Minor Planet Center, preferably using the address mpc@cfa.harvard.edu. Such a message could consist of a brief statement such as "I approve (10000) Pluto" or "I do not approve (10000) Pluto", although the value of the latter choice would be augmented if an appropriate alternative suggestion were made for (10000). Brief comments on the subject (preferably constructive) would also be welcome, and writers are encouraged to identify themselves. Modern bureaucracy rarely pays much attention to comments from even an informed public, but since this issue is of concern principally to our readers (more so, in fact, than to many professional astronomers with little or no interest in solar-system astronomy who just happen to be serving on a committee), we feel that it is appropriate for us to solicit advice in this way. Your early response is desirable. It is not necessary that you actually subscribe to these Circulars in order to respond. Appropriate responses will be examined and considered in connection with the responses will be examined and considered in connection with the deliberations by the Small Bodies Names Committee by their deadline of Feb. 26.
-- The above is the Editorial Notice that appears on MPC 33615-33616, dated 1999 Feb. 2
Brian G. Marsden
(C) Copyright 1999 MPC
[An IAU Statement, 2/3/1999]
Recent news reports have given much attention to what was believed to be an initiative by the International Astronomical Union (IAU) to change the status of Pluto as the ninth planet in the solar system. Unfortunately, some of these reports have been based on incomplete or misleading information regarding the subject of the discussion and the decision making procedures of the Union.
The IAU regrets that inaccurate reports appear to have caused widespread public concern, and issues the following corrections and clarifications:
1: No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Accordingly, no such initiative has been considered by the Officers or Executive Committee, who set the policy of the IAU itself.
2: Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet.
A Working Group under the IAU Division of Planetary Systems Sciences is conducting a technical debate on a possible numbering system for TNOs. Ways to classify planets by physical characteristics are also under consideration. These discussions are continuing and will take some time. The Small Bodies Names Committee of the Division has, however, decided against assigning any Minor Planet number to Pluto.
3: From time to time, the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by national or international law, but are accepted because they are rational and effective when applied in practice. It is therefore the policy of the IAU that its recommendations should rest on well-established scientific facts and be backed by a broad consensus in the community concerned. A decision on the status of Pluto that did not conform to this policy would have been ineffective and therefore meaningless. Suggestions that this was about to happen are based on incomplete understanding of the above.
The mission of the IAU is to promote scientific progress in astronomy. An important part of this mission is to provide a forum for debate of scientific issues with an international dimension. This should not be interpreted to imply that the outcome of such discussions may become official IAU policy without due verification that the above criteria are met: The policy and decisions of the IAU are formulated by its responsible bodies after full deliberation in the international scientific community.
Johannes Andersen
General Secretary, IAU
For more information, contact the IAU Secretariat (URL: http://www.iau.org and address below), or the Division President, Prof. Michael A'Hearn, University of Maryland, USA (Tel: (301) 405 6076; Fax: (301) 314 9067; E-mail: ma@astro.umd.edu).
[from the Division of Planetary Sciences of the American Astronomical Society]
Colleagues,
No doubt, you are aware of the recent media attention implying that Pluto has been "officially" downgraded from planetary status. This was stimulated in large part by a suggestion by the Minor Planet Center to assign the minor planet number 10000 to Pluto in conjunction with the numbering of some Trans-Neptunian Objects. The Small Bodies Names Committee (SBNC) of IAU Commission 20 has been discussing this issue for several months, as has the Executive Committee of IAU Division III (Planetary Systems Sciences). It should be emphasized that, in spite of media perceptions, no action or decision has yet been taken. The number 10000 will likely be reached for the numbered asteroids within a few weeks. Mike A'Hearn, as President of IAU Division III, has established a web page with background information which also solicits input from the astronomical community:
http://www.ss.astro.umd.edu/IAU/div3/pluto.shtml
The DPS committee believes that this situation is harmful to our profession and will become more so if not put quickly to rest. The public is confused, acrimonious rifts are being created within our community and many of our colleagues are being diverted from productive work to counter what they perceive to be an alarming and unnecessary crisis. We have therefore adopted the following brief position statement, which will be forwarded to the appropriate IAU committees:
"The Committee of the Division for Planetary Sciences of the American Astronomical Society is opposed to assigning a minor planet number to Pluto. This action would undoubtedly be viewed by the broader scientific community and the general public as a "reclassification" of Pluto from a major planet to a minor planet. We feel that there is little scientific or historical justification for such an action."
We urge DPS members to visit the above web page and express your opinions. Michael A'Hearn (ma@astro.umd.edu) is President of IAU Div. III and Chair of the Small Bodies Nomenclature Committee, and can relay messages to appropriate others in the IAU.
Don Yeomans, Division of Planetary Sciences/Am Astron Soc Chairman and the other members of the DPS Committee
[Postscript from another message from Don Yeomans: Many of us have been asked when the Planet Pluto will once again have the largest heliocentric distance of any of the nine planets. JPL's Myles Standish notes that on 1999 Feb. 11 at 10:09 ET, Pluto's distance will exceed that of Neptune's. This result is based upon JPL's Planetary ephemeris DE405 and the time refers to Pluto and Neptune themselves rather than their respective barycenters (the latter time would be 09:40).]
Note the additional objection from Deborah Pasachoff:
We can now note the nine planets from the initial letters of "My Very Educated
Mother Just Sent Us Nine Pizzas." If we demote Pluto, the mnemonic would become
"My Very Educated Mother Just Sent Us Nothing," which is obviously undesirable.
