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. Q: Based on this new definition, how many planets are there in our Solar System?
Q: Is that all, only eight planets? In addition to the eight planets, there are also five known dwarf planets. Many more dwarf planets are likely to be discovered soon.
Q: What is a dwarf planet? A: A dwarf planet is an object in orbit around the Sun that is large enough massive enough to have its own gravity pull itself into a round or nearly round shape.
Generally, a dwarf planet is smaller than Mercury. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an orbit within the asteroid belt is in a zone with lots of other objects. Q: How many dwarf planets are there? A: Currently there are five objects accepted as dwarf planets.
Ceres, Pluto, Eris, Makemake and Haumea. Q: What is Ceres? A: Ceres is or now we can say it was the largest asteroid, about km across, orbiting in the asteroid belt between Mars and Jupiter. Ceres now qualifies as a dwarf planet because it is now known to be large enough massive enough to have self-gravity pulling itself into a nearly round shape.
Thomas, Ceres orbits within the asteroid belt and is an example of the case of an object that does not orbit in a clear path. There are many other asteroids that can come close to the orbital path of Ceres. Q: Didn't Ceres used to be called an asteroid or minor planet? A: Historically, Ceres was called a planet when it was first discovered in , orbiting in what is known as the asteroid belt between Mars and Jupiter.
In the 19th century astronomers could not resolve the size and shape of Ceres, and because numerous other bodies were discovered in the same region, Ceres lost its planetary status. For more than a century, Ceres has been referred to as an asteroid or minor planet. Q: Why is Pluto now called a dwarf planet? A: Pluto now falls into the dwarf planet category on account of its size and the fact that it resides within a zone of other similarly-sized objects known as the transneptunian region.
Q: Is Pluto's satellite Charon a dwarf planet? A: For now, Charon is considered just to be Pluto's satellite. The idea that Charon might qualify to be called a dwarf planet in its own right may be considered later.
Tombaugh was referring to a ninth planet that had been predicted to orbit the sun beyond Neptune. In , an object about a tenth as wide as Pluto was seen orbiting out beyond it. More than 2, icy bodies have since been found hiding in this frigid outskirt of the solar system known as the Kuiper KY-pur Belt.
And there may be many more still. Finding that Pluto had so many neighbors raised questions. What did these strange new worlds have in common with more familiar ones? What set them apart? In , he spotted the first Kuiper Belt body that appeared larger than Pluto. This icy body was left over from the formation of the solar system.
If Pluto was the ninth planet, Brown argued, then surely Xena should be the 10th. Tensions over how to categorize Pluto and Xena came to a head in Pluto and Xena were deemed dwarf planets. Xena was renamed Eris, the Greek goddess of discord. A fitting title, given its role in upsetting our concept of the solar system. On Twitter, Brown goes by plutokiller, since his research helped knock Pluto off its planetary pedestal.
Right away, textbooks were revised and posters reprinted. But many planetary scientists — especially those who study Pluto — never bothered to change. In part, that might be sass or spite. One appeared as a report in Icarus. The other one is due out soon. For these, the researchers examined hundreds of scientific papers, textbooks and letters. Some of the documents dated back centuries. And why was often not straightforward. Consider Ceres. This object sits in the asteroid belt between Mars and Jupiter.
Like Pluto, Ceres was considered a planet after its discovery. By the end of the s, scientists knew Ceres had hundreds of neighbors. Since Ceres no longer appeared special, the story goes, it lost its planetary title. The largest asteroids still looked like planets. Most small ones, however, turned out to be weird, lumps. This provided evidence that they were fundamentally different than the bigger, rounder planets. And what about moons? The change was driven by nonscientific publications, such as astrological almanacs.
These books use the positions of celestial bodies for horoscopes. But not Pluto. It takes an oval-shaped path with the Sun nowhere near its center. What's more, its path is quite tilted compared to the planets. Natural Color. Pluto is officially classified as a dwarf planet. Majestic Mountains and Frozen Plains.
Kid-Friendly Pluto Pluto is a dwarf planet that lies in the Kuiper Belt, an area full of icy bodies and other dwarf planets out past Neptune. The lives and accomplishments of both women aviation pioneers have now been honored with the naming of landmarks on Pluto.
JPL's lucky peanuts are an unofficial tradition at big mission events. Full Moon Guide: October - November A new paper details how the hydrological cycle of the now-dry lake at Jezero Crater is more complicated than originally thought. This year, the minimum extent of Arctic sea ice dropped to 1. Researchers will use Webb to observe 17 actively forming planetary systems.
The lander cleared enough dust from one solar panel to keep its seismometer on through the summer, allowing scientists to study three big quakes. Scientists found evidence that an area on Mars called Arabia Terra had thousands of "super eruptions" over a million-year period. Perseverance successfully collected its first pair of rock samples, and scientists already are gaining new insights into the region.
Data received late Sept. The rover will abrade a rock this week, allowing scientists and engineers to decide whether that target would withstand its powerful drill. Drought is a complicated problem that requires lots of data.
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