Is Pluto a planet or a dwarf planet? NASA chief takes sides for emotional debate


Is Pluto a planet, as have learned generations of schoolchildren? Or is it really a dwarf planet, as determined by the official governing body of astronomy?

NASA administrator Jim Bridenstine says it's the first. "Just for you to know, in my opinion, Pluto is a planet," he told reporters Aug. 23, while he was visiting an aerospace engineering lab in Boulder, in the United States. Colorado. "That's what I learned and I'm attached to it."

Bridenstine may be engaged, but the official call of the planet / dwarf planet does not belong to him. This responsibility lies with the International Union of Astronomy, which transferred Pluto from a planet to a dwarf planet 13 years ago.

Since then, scientists and observers have discussed, sometimes fiercely, the status to be attributed to the 1,500 km wide rocky ball that surrounds the sun once every 248 years at the edge of the solar system.

Long-standing quarrel

Bridenstine's comments will probably not solve the debate that began in the 1990s with the discovery of the Kuiper Belt, a ring of rocky or icy objects surrounding the sun beyond Neptune's orbit.

In the light of this discovery, some astronomers and planetary scientists began to claim that Pluto – whose orbit is located in the Kuiper belt – had more in common with these worlds, mostly small and distant, with the eight other planets. Others felt that Pluto still deserved to be a full-fledged planet.

NASA's New Horizons Space Shuttle has captured this image of Sputnik Planitia – a glacier-rich ice surface with nitrogen, carbon monoxide, and methane – that forms the left lobe of a fit element of heart on the surface of Pluto.NASA

To resolve the dispute, the AIU based in Paris published in 2006 a new definition of the term "planet". According to this definition, a planet is a celestial body that revolves around the sun, has enough gravitation to assume an approximately spherical shape, and has been able to clear smaller objects from its orbital trajectory, as would bulky objects because of their gravitational tug.

Pluto fulfills the first two conditions, but not the third – and the members of the organization voted in favor of its reclassification.

As a result of Pluto's change of status, hundreds of world scientists have called for a change in the definition, saying it was ill-conceived. For example, one could argue that the Earth, Mars and Jupiter have failed to clean the debris from their own orbit, given the many asteroids that still populate the region. Critics also point out that only 424 of the approximately 9,000 IAU members took part in the vote.

What makes a planet?

Alan Stern, principal investigator of NASA's New Horizons mission, is among the most ferocious defenders of Pluto. He sent a robotic spacecraft to Pluto in 2015. According to Stern, the decision of the AIU is "wrong," claiming that planetary status should be attributed on the basis of the geophysical characteristics of a celestial object. . By this measure, he says, Pluto is clearly a planet.

"Pluto has an atmosphere, mountain ranges, a core, an inner ocean and many other properties, just like the Earth," he says. Pluto also has its own moon, Charon, 200 km long. "Planetary scientists ignore the definition of IAU and consider Pluto to be a full-fledged planet in their research. It is more important than any vote. "

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