Its planetary status was first questioned in , when a group of astronomers discovered objects beyond Neptune that were more massive than what was then still the ninth planet.
With more and more trans-Neptunian objects emerging from the darkness of space, the astronomical community started to question what Pluto really was, and the IAU eventually redefined planets.
Unfortunately, Pluto doesn't meet those criteria. It was demoted from planet to dwarf planet. When the IAU was deciding on the new definition of a planet, it also created a class of objects known as dwarf planets, which also included Ceres and Eris.
These trans-Neptunian objects have even been classified by the IAU as plutoids, but some still feel that doesn't make up for downgrading what had been considered a planet for 76 years before that. Some experts immediately questioned the part of the definition about a planet clearing its orbital neighbourhood. This is because Earth shares its cosmic turf with more than 12, near-Earth asteroids.
Thus, some have argued that Earth, Jupiter and other planets also fail to meet the IAU's definition. Speaking just after the vote, Prof Alan Stern, chief scientist for the New Horizons mission, called the outcome "an awful decision" and described the new definition as "internally inconsistent". The low turn-out has been blamed on timing; the vote was held on the last day of the General Assembly when many participants had left or were preparing to fly out from Prague.
The debate has rumbled on ever since, on television, in the pages of books and in public talks. But the latter expert turned down the offer, stating: "I don't have opinions that I require other people to have.
The flyby of Pluto is unlikely to provide any information relevant to a change in Pluto's status. But it will bring into clear focus once more what is, and what isn't, meant by the term "planet". Follow Paul on Twitter. Image source, IAU. 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. But the announcement of Xena's discovery raised a new need for a more precise definition of which objects are planets and which are not. According to Brown, the decision will pose a difficulty for a public that has been accustomed to thinking for the last 75 years that the solar system has nine planets. In fact, the public has had some experience with the demotion of a planet in the past, although not in living memory.
Astronomers discovered the asteroid Ceres on January 1, literally at the turn of the 19th century. Having no reason to suspect that a new class of celestial object had been found, scientists designated it the eighth planet Uranus having been discovered some 20 years earlier.
Soon several other asteroids were discovered, and these, too, were summarily designated as newly found planets. But when astronomers continued finding numerous other asteroids in the region there are thought to be hundreds of thousands , the astronomical community in the early s demoted Ceres and the others and coined the new term "asteroid. Xena is about 2, kilometers in diameter. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Xena is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope.
Brown and his colleagues in late September announced that Xena has at least one moon. This body has been nicknamed Gabrielle, after Xena's sidekick on the television series.
Xena is currently about 97 astronomical units from the sun an astronomical unit is the distance between the sun and Earth , which means that it is some nine billion miles away at present.
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