Definition Of Planet Research Articles

Physical and dynamical characteristics of icy “dwarf planets” (plutoids)

AbstractThe geophysical and dynamical criteria introduced in the “Definition of a Planet in the Solar System” adopted by the International Astronomical Union are reviewed. The classification scheme approved by the IAU reflects dynamical and geophysical differences among planets, “dwarf planets” and “small Solar System bodies”. We present, in the form of a decision tree, the set of questions to be considered in order to classify an object as an icy “dwarf planet” (a plutoid). We find that there are 15 very probable plutoids; plus possibly 9 more, which require a reliable estimate of their sizes. Finally, the most relevant physical and dynamical characteristics of the set of icy “dwarf planets” have been reviewed; e.g. the albedo, the lightcurve amplitude, the location in the different dynamical populations, the size distributions, and the discovery rate.

The definition of planet: A dynamicist's point of view

It is here argued that the problem of a meaningful definition of 'planet' is best addressed on a dynamical basis; we show that in this way it is possible to obtain a planet definition that is both unambiguous and useful.

Comment: Debates over definition of planet continue and inspire

Comment: Debates over definition of planet continue and inspire

Which are the dwarfs in the Solar System?

The International Astronomical Union recently adopted a new definition of planets in our Solar System. A new category of objects was introduced: a “dwarf planet.” This is “a celestial body that has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and has not cleared the neighborhood around its orbit.” In a footnote, the resolution says: “An IAU process will be established to assign borderline objects into either “dwarf planet” and other categories." In order to contribute to the establishment of this classification procedure, we analyze the problem of the minimum mass required to become a “dwarf planet,” either from the theoretical and the observational perspective. We propose classification criteria for “dwarf planets” based on the available information on the shape and size of asteroids and TNOs, principally the direct or indirect estimates of the diameter and the estimate of the shapes from the lightcurves. We compile the available observational data on large asteroids and TNOs. According to our classification scheme there is only one rocky “dwarf planet” and 12 icy “dwarf planets” among the already discovered objects.

Pluto — An enduringly interesting celestial object

Pluto is a celestial object that had caught the imagination of increasingly ‘sky-aware’ people all around the world, perhaps due to the inspiring story of its discovery by a young amateur astronomer. It was celebrated as the ninth planet of the solar system for decades. A question mark hung over its nomenclature as a planet from the time of the discovery of its moon Charon, when a good estimate of its very small mass in comparison with other planets was obtained. The discovery of UB 313, a body in the outer regions of the solar system that was more massive than Pluto, magnified this question mark and compelled the International Astronomical Union to review the definition of the word ‘Planet’. A new and physical definition was given to this word and Pluto was categorized as a dwarf planet. The beauty of this physical definition of a planet is something that would definitely have been appreciated by Clyde Tombaugh — who once made this beautifully simple statement about Pluto, while its status was being questioned — “It is there, whatever it is”. Yes, whatever it is, Pluto is one celestial object that is somehow very endearing to everyone around the world and is also an object whose studies are compelling certain paradigm shifts in our understanding of the structure and evolution of the solar system.

Who decides? ? Smart finish for SMART-1 ? Thoughts on Pluto ? GCSE Astronomy results ? BGA plans for geophysics education ? AKARI opens its eyes.

Sue Bowler, Editor The on-going debate on the definition of a planet raises issues about authority within the scientific community – and outside. The IAU makes decisions about planets and minor planets (as they were). Their decision-making process, described on pages 16–17 of this issue, resulted in a necessary compromise. And a compromise, of course, contains something for everyone to disagree with. Disagree they did, although all seem to agree that the definition is likely to evolve as we find out more about the solar system. Despite the difficulties in reaching agreement between the many disciplines involved in planetary research – space and planetary scientists, as well as the traditional astronomical observer – it has to be done. And it is the IAU’s job to do it. The job is only going to get harder, for of course, the next step is to consider extrasolar planets. Here it is the big planets that cause the trouble: we need to be able to tell them apart from a star. But perhaps the debate should involve more disparate groups of people. Yes, we should ensure that a range of researchers can get involved, but what about eveyone else? There is great – and often proprietorial – public interest in planets. Many of the of internet petitions that have sprung up in recent weeks have had the general theme of “Put Pluto back”. It is great to have such public interest in astronomy, but a shame that the overall impression seems to be a vague feeling of loss, together with confusion over how many planets there really are. Without going to the lengths of reality television (24-hour payto-view footage and a public vote to keep your favourite planet in the solar system) are there ways that the public could be involved in such a decision? And should they be? As they say on Big Brother: “You decide”. Editorial NEws

Teaching What a Planet Is: A Roundtable on the Educational Implications of the New Definition of a Planet

Abstract A quick review of the August 24, 2006, decision by the International Astronomical Union about how todefine a planet in our Solar System is followed by commentary from planetary scientists and educatorsfrom various settings. A table of relevant dates and a list of useful resources are appended, and readers areinvited to participate in the discussion. Preface Readers of the Astronomy Education Review are often the ones on the front lines of our educationalsystem, teaching students, meeting with planetarium and museum audiences, and responding to mediarequests for information. Given all the hoopla about the new definition of a planet in our Solar System bythe International Astronomical Union (IAU) at its meeting in Prague in August 2006, we thought it mightbe interesting to gather a cross-section of reactions from noted astronomy educators and then invite ourreaders to voice their opinions.We begin with a personal report by David Morrison, who was in Prague and served on one of thecommittees that considered the issue of defining a planet. This is followed by comments from OwenGingerich, the chair of the IAU Planet Definition Committee, and a statement from Richard French, thechair of the main organization of planetary astronomers in the United States. We then continue withcommentary from a number of planet experts and several formal and informal educators, including threetextbook authors. (The authors of each comment wrote independently, and there is thus a small amount ofoverlap in their comments that we have left in when needed for clarity.)

Pluto: the backlash begins

Astronomers petition against new definition of a planet.

国際天文学連合 (IAU) 第26回総会と惑星の定義

国際天文学連合 (IAU) 第26回総会と惑星の定義

Working Group on Definition of Planet

The Working Group was formed at the request of the Board of DivisionIII and approved by the IAU Executive committee in March 2004. This was in recognition of the fact that discoveries in the Trans Neptunian region were repeatedly raising the question of “what is a planet”. The task of the WG was to investigate the options available and give indications of the level of support and opposition for each if more than one option was emerging.

What is a planet?

Atmospheric scientists, forensic scientists, life scientists, neuroscientists, ocean scientists, plant scientists, and almost all other scientists know what lies at the heart of their respective fields, but planetary scientists do not. The last generally accepted definition of a planet, a "wanderer," comes from the ancient Greeks.Although the need for an updated definition has existed since the discovery of the asteroid belt two centuries ago, recent discoveries of objects in the KUiper belt and in orbit around other stars have reminded planetary scientists of this unsatisfactory situation.

Puny Star or Pudgy Planet?

ASTROPHYSICS The distinction between stars and planets has been blurred by observations of low-mass objects in a variety of astrophysical environments. These objects do not have enough mass to sustain hydrogen burning and cannot be characterized by standard evolutionary diagrams, although they may be stars that never reached thermal equilibrium and could be burning lithium or deuterium at lower temperatures. Some of the very low mass objects probably cannot even burn deuterium and may be planets. However, some of these do not orbit a star, so if they are planets, they must have formed differently from a normal planet or have been ejected from their planetary system. Without substellar evolutionary diagrams or a mechanistic definition of a planet, the observed low-mass objects are difficult to classify. Chabrier et al . have brought some order to this problem by developing evolutionary diagrams for low-mass objects that burn deuterium. They have combined an interior model of deuterium burning in the core and convection of the deuterium to the surface with atmospheric models of deuterated water in order to determine the mass, temperature, luminosity, and spectral characteristics of deuterium-burning stars as a function of age. These models will help to distinguish puny stars from relatively massive planets. — LR Astrophys. J. 542 , L119 (2000).

What is a planet” When is a discovery?

The news item above reports on the sighting of a planet outside our solar system, the first time such a discovery has been made. As with many scientific discoveries, however, things are not quite as simple as they seem. The problem with this discovery is that the two groups of astronomers invoked cannot quite agree on who saw what first. Or to put it another way: When is a planet not a planet but a Brown Dwarf and when is a discovery not a discovery but a confirmation? Astronomers from the U.S. Naval Observatory and the University of Arizona are having a little trouble sorting this out.Both groups do agree on the data. A substellar body has been directly and indirectly observed orbiting the intrinsically faint star Van Biesbroeck 8 (VB S) in a constellation of the Milky Way. In fact, both groups agree that the observed substellar body can be called a Brown Dwarf. The definition of a Brown Dwarf, it is agreed, lies somewhere in between the definition of a planet and that of a star. Herein lies the crux: can a Brown Dwarf be called a planet? Richard Harrington, an astronomer with the U.S. Naval Observatory, says that a Brown Dwarf is not a planet. Donald McCarthy, of the University of Arizona, says that it is.