Jakarta, CNNIndonesia —
Pluto had become one of the planets in Solar system although there was a change in 2006. What made him lose that status?
The solar system, as was echoed in past science textbooks, has nine planets, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, with Pluto being the farthest. On August 24, 2006, Pluto was revoked from planet status.
At that time, the International Astronomical Union (IAU) chose to reclassify Pluto and change its status to a dwarf planet, reducing the total number of planets in the Solar System to only eight.
The IAU itself defines a planet as a celestial body which orbits the Sun, which is nearly spherical in appearance, and which does not have much debris in its orbital environment.
Meanwhile, a dwarf planet is defined as a spherical celestial object whose orbit is not clear of celestial debris or asteroids. In addition, a dwarf planet is not a satellite of a planet.
“Pluto is a dwarf planet by definition and is recognized as the prototype of a new category of trans-Neptunian objects,” said a resolution approved in 2006. Space.
Early start
Pluto was classified as a planet in 1930 (the IAU itself was formed in 1919). This happened after astronomer Clyde Tombaugh of the Lowell Observatory in Arizona compared photo plates of the sky on different nights.
He then saw a small dot floating back and forth against the background of the stars.
Its orbit is highly eccentric, tilted with respect to the ecliptic (the apparent path of the Sun as viewed from Earth), and far from the definition of a circle. Pluto is actually closer to the sun than Neptune in 20 of its 248 year total orbit.
In 1992, scientists discovered the first Kuiper Belt object, 1992 QB1, a small object that orbits around Pluto and beyond the orbit of Neptune.
More such objects were found, showing a belt of small, frozen worlds similar to the asteroid belt between Mars and Jupiter.
In July 2005, astronomers discovered the distant object Eris, which was initially thought to be larger than Pluto. Its orbit is also tilted with respect to the ecliptic.
With all these findings, the researchers wondered: if Pluto is a planet, does that mean Eris is also included? What about all the other icy bodies in the Kuiper belt, or the smaller objects in the asteroid belt? Where is the limit for a celestial body to be called a planet?
Fierce debate followed, with many new proposals for the definition of a planet being offered.
“Every time we think some of us have reached a consensus, someone says something and makes it very clear that we haven’t,” said Brian Marsden, member of the IAU Executive Committee responsible for finding a new meaning for planets, in 2005.
In 2006, during eight days of the IAU General Assembly meeting in Prague, astronomers failed to reach agreement on four proposals. One of them brings the total number of planets in the Solar System to 12, including Ceres, the largest asteroid, and Pluto’s moon Charon.
Astronomer Mike Brown of Caltech, Eris’ discoverer, called the suggestion “a complete mess”.
Near the end of the Prague conference, the remaining 424 astronomers voted to create three new categories for objects in the Solar System. Since then, only Mercury through Neptune will be considered planets.
Pluto and its relatives, spherical bodies sharing an orbital environment with other entities, are hereinafter referred to as dwarf planets. All other objects orbiting the sun would be known as minor solar systems.
At that time less than 5 percent of the total 10,000 world astronomers who participated in the vote.
“I’m ashamed of [dunia] astronomy,” said Alan Stern, leader of NASA’s New Horizons mission, which flew by Pluto in 2015.
The New Horizons mission is a significant turning point in the planet debate. After passing through Pluto, it reveals a much more dynamic world than anyone could have imagined.
Huge mountains, broken craters and signs of flowing fluids on their surface all point to a world that underwent massive geological changes since its inception.
On this basis alone, people like Stern say Pluto should be considered a planet because it is a dynamic place, one that is not so static that only micrometeorites disturb its surface.
In 2018, Stern, along with planetary scientist David Grinspoon, wrote an opinion piece for The Washington Post. They described the IAU’s definitions as “hastily drawn” and “flawed” and asked astronomers to reconsider their ideas.
When children ask their teacher what a planet is, astronomers are still debating about that definition and admit that the answer is not easy.
Humans have to look beyond the Solar System first to consider what makes an object a planet or not.
As the historian of science Owen Gingerich, who chairs the IAU’s definition of planetary committee, puts it, that “planet is a culturally defined word that changes over time.”
(lom/lth)
