After the final meeting in Paris the draft resolution was completed. One crucial aspect of the resolution is described by Professor Owen Gingerich, Chair of the IAU Planet Definition Committee: " On the scientific side, we wanted to avoid arbitrary cut-offs simply based on distances, periods, magnitudes, or neighbouring objects".
The first draft proposal for the definition of a planet was debated vigorously by astronomers at the IAU General Assembly in Prague and a new version slowly took shape. This new version was more acceptable to the majority and was put to the members of the IAU for a vote at the Closing Ceremony on the 24 August By the end of the Prague General Assembly, its members voted that the resolution B5 on the definition of a planet in the Solar System would be as follows:.
A celestial body that a is in orbit around the Sun, b has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium nearly round shape, and c has cleared the neighbourhood around its orbit.
A new distinct class of objects called dwarf planets was also decided on. It was agreed that planets and dwarf planets are two distinct classes of objects. The first members of the dwarf planet category are Ceres, Pluto and Eris, formerly known as UB Eris was named after the IAU General Assembly in read more Eris is the Greek god of discord and strife, a name which the discoverer Mike Brown found fitting in the light of the academic commotion that followed its discovery.
The dwarf planet Pluto is recognised as an important prototype of a new class of Trans-Neptunian Objects. The IAU has given a new denomination for these objects: plutoids. Today the resolution remains in place and is a testament to the fluid nature of science and how our view of the Universe continues to evolve with changes made by observations, measurements and theory.
On 14 July , NASA's New Horizons spacecraft flew past Pluto, providing numerous imaging, spectroscopy, and in situ datasets that have dramatically altered our knowledge about Pluto and its system of five moons. The images established that Pluto is larger than Eris and is the largest body in the Kuiper Belt. The images also revealed a remarkable landscape containing a variety of landforms, including broad plains, mountain ranges several kilometres high, and evidence for volcanoes. Pluto's surface is unusual for its diversity of surface compositions and colours.
Some regions are as bright as snow and others are as dark as charcoal. Colour imaging and composition spectroscopy revealed a highly complex distribution of surface ices, including nitrogen, carbon monoxide, water, and methane, as well as their chemical byproducts produced by radiolysis. It has also been determined that some surfaces on Pluto are completely free of visible craters, indicating that they have been modified or created in the recent past.
Other surfaces are heavily cratered and appear to be extremely old. No new satellites were detected, nor were rings. Small satellites Hydra and Nix have brighter surfaces than expected. These results raise fundamental questions about how a small, cold planet can remain active over the age of the Solar System.
They demonstrate that dwarf planets can be every bit as scientifically interesting as planets. Equally important is that all three major Kuiper belt bodies visited by spacecraft so far — Pluto, Charon, and Triton — are more different than similar, bearing witness to the potential diversity awaiting the exploration of their realm. Stern, A. Q: What is the origin of the word planet? A: The word planet comes from the Greek word for "wanderer", meaning that planets were originally defined as objects that moved in the night sky with respect to the background of fixed stars.
Q: Why is there a need for a new definition for the word planet? A: Modern science provides much more information than the simple fact that objects orbiting the Sun appear to move with respect to the background of fixed stars. For example, recent new discoveries have been made of objects in the outer regions of our Solar System that have sizes comparable with and larger than Pluto. Historically Pluto has been recognised as the ninth planet.
Thus these discoveries have rightfully called into question whether or not the newly found Trans-Neptunian Objects should also be considered as new planets. Q: How did astronomers reach a consensus for a new definition of planet? A: The world's astronomers, under the auspices of the International Astronomical Union, deliberated on a new definition for the word planet for nearly two years.
Continued evolution of the definition through debate and further discussion allowed a final consensus and vote. Q: What new terms are used in the official IAU definition? A: There are three new terms adopted as official definitions by the IAU. The terms are: planet, dwarf planet and small Solar System body. Q: In plain language, what is the new definition of planet? A: A planet is an object in orbit around the Sun that is large enough massive enough to have its self-gravity pull itself into a round or near-spherical shape.
In addition a planet orbits in a clear path around the Sun. If any object ventures near the orbit of a planet, it will either collide with the planet, and thereby be accreted, or be ejected into another orbit. Q: What is the exact wording of the official IAU proposed definition of planet? A: A planet is a celestial body that a is in orbit around the Sun, b has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium nearly round shape, and c has cleared the neighbourhood around its orbit.
Q: Does a body have to be perfectly spherical to be called a planet? A: No. For example, the rotation of a body can slightly distort the shape so that it is not perfectly spherical. Earth, for example, has a slightly greater diameter measured at the equator than measured at the poles. For example, it could be argued that the Earth, Mars and Jupiter have failed to clear the debris from their own orbits, given the numerous asteroids that still populate the region.
By that measure, he says, Pluto is clearly a planet. Pluto also has its own moon, mile-wide Charon. Pluto was discovered in by Clyde Tombaugh, a young astronomer working at the Lowell Observatory in Flagstaff, Arizona. Astronomers designated it a planet even though was is unlike the next-farthest planets, the gas giants Jupiter, Saturn, Uranus and Neptune.
Not only is Pluto a planet, he says, but so too are the big spherical bodies in the Kuiper belt and, closer to home, some of the largest of the objects in the asteroid belt between Mars and Jupiter. If that pushes up the number of planets into the dozens or even the hundreds, so be it. Read: The most overhyped planet in the galaxy. The experts I talked with for this story had a kaleidoscope of Pluto opinions.
Some have sentimental feelings about Pluto; others are simply over it. For many of them, the results of the New Horizons flyby in make discounting Pluto difficult. The mission gave humankind its first close-up of Pluto, uncovering stunning topography, such as a massive heart-shaped glacier made of nitrogen.
There was a wispy atmosphere, and below that a textured landscape dotted with mountains, their peaks capped with snow made of frozen methane. Let gravity decide.
The New Horizons mission has since moved deeper into the Kuiper belt, toward the outer regions of the solar system, where another planet-related debate has unfolded in recent years.
Astronomers have detected objects moving rather strangely in the distant reaches beyond Pluto, and they believe that a giant, unseen planet, about six times the mass of the Earth, must be tugging at them. After talking with members of both Pluto camps, I wonder, as Lisa Grossman suggested in Science News this week for the anniversary of the Prague meeting, whether having multiple definitions is really such a bad thing.
For all their disagreements, everyone I spoke with was on the same page about one thing: that the question of planethood has no bearing on whether Pluto is a fascinating place to study.
The New Horizons flyby found evidence that Pluto—little Pluto! Skip to content Site Navigation The Atlantic. Popular Latest.
0コメント