Do you know what the word plutoed means? Chosen by the American Dialect Society as its world of the year in 2006, plutoed or ‘to pluto’ is to demote or devalue someone or something. The word came into existence only months before the end of 2006 when the General Assembly of the International Astronomical Union (IAU) decided that Pluto no longer met its definition of a planet.
Discovered in 1930 by American astronomer Clyde Tombaugh at the Lowell Observatory, Pluto is a mammoth 5.9 billion km from the sun with an average temperature that hovers around -214 degrees Celsius. With a surface that is composed of a mixture of frozen nitrogen, methane and carbon monoxide ices, Pluto has five known moons and polar caps.
Murmurs around Pluto
Since its discovery and classification as a planet in 1930, there were murmurs about Pluto’s status. Considered kind of odd, Pluto’s orbit was eccentric and far from circular. As a result, during its revolution (248 Earth years) around the sun, it gets closer than Neptune for 20 years.
The murmurs only got louder with the passage of time. The 1990s saw the first object, other than Pluto, in the Kuiper Belt (a region in the solar system that extends from about 30 AU (near Neptune’s orbit) to about 50 AU from the sun) being discovered. In the years that followed, many such small frozen worlds were discovered in the region, with Pluto remaining by far the largest.
Enter Eris
That changed in the first decade of the 21st Century when another object, Eris, was discovered. Now known to be at about the same size as Pluto, the fact that Eris was almost as big as Pluto and also goes around the sun in a highly elliptical orbit, taking over 550 years to complete a revolution, threw open the debate regarding Pluto’s classification wide open again.
The questions staring at the scientists were these: if Pluto is a planet, then wouldn’t that mean Eris is a planet as well? And what about the other small worlds discovered in the Kuiper Belt? The cut-off wasn’t quite obvious now and the arguments reached a feverish pitch in the months that followed.
When the IAU gathered for its General Assembly in Prague, Czech Republic, in August 2006, the dilemma hung over the entire meeting. Intense debates, a number of proposals and many arguments took place at the conference, but they were no closer to a resolution than when they had started.
Dwarves are here
Near the end of the meeting, on August 24, 2006, the astronomers who remained voted to create three new categories for objects in the solar system – planets, dwarf planets and small solar system bodies. Pluto and Eris belong to the dwarf planet category as they have not cleared the neighbourhood around their orbit.
The new definitions of these objects and hence the reclassification of Pluto as a dwarf planet wasn’t accepted unanimously. There were complaints that less than 5% of the world’s astronomers had been present for the voting process. Others said that the new definitions were ambiguous. The drama continues as astronomers and other experts continue to discuss the current definitions, hoping to achieve a better one in the process.
Pluto, however, maybe wasn’t plutoed after all. We had classified it as a planet with our existing knowledge in 1930, placing it on a pedestal, perhaps more than that which was warranted. And now, once we have learnt more about these celestial objects, we could reclassify it, placing it in a new category of dwarf planets. This ability of science to change seemingly rigid definitions in light of fresh evidence could well prove to be its biggest strength with time.
***
What the demotion meant to New Horizons
NASA’s New Horizons spacecraft was launched on January 19, 2006 with the objective of becoming the first spacecraft to explore Pluto and its moons up close.
While Pluto was still a planet during the launch, it was soon demoted to a dwarf planet.
NASA, however, went ahead with its mission objective, studying the dwarf planet Pluto, its moons and other objects in the Kuiper Belt.
It became the first spacecraft to perform a Pluto flyby on July 14, 2015. As its distance from Earth was nearly 4.5 light-years and the distance meant ito could transmit data at a rate of only 1-2 kilobits per second, it took over 15 months to officially complete downloading the entire data collected during the encounter.
On January 1, 2019, New Horizons became the first spacecraft to observe a second Kuiper Belt object up close. The Ultima Thule, officially named 2014 MU69, thus became the most distant object ever explored.
With the mission extended through 2021, New Horizons continues to speed deeper in the Kuiper Belt to learn about more objects.
Published - August 24, 2019 11:30 pm IST
