Astronomers weren’t just being mean when they demoted it

Jul 19, 2015 19:58 GMT  ·  By

This Tuesday, July 14, the New Horizons probe, launched by NASA in January 2006, made space exploration history when it reached the Pluto system, and flew by the orb and its accompanying moons. 

The spacecraft got as close as 7,750 miles (12,470 kilometers) to Pluto. This allowed it to study the chemical makeup of its atmosphere and image landscapes on its surface in exquisite detail.

The thing is that, scientific accomplishments aside, this NASA mission to Pluto grabbed headlines for one other very simple reason: we, Earth dwellers, still haven’t quite come to terms that Pluto is now considered a dwarf planet.

Rather, we still like to think of it as one of the big guys of the Solar System. Sure, we know that Pluto got demoted years ago, but many seem to even now hold a grudge against the scientists who had the Audacity to label it a dwarf.

So, naturally, when New Horizons reached Pluto at long last and close-ups of this orb at the edge of our cosmic neighborhood started pouring in, many got emotional. Even Stephen Colbert did.

Then again, it’s not like the folks who decided to reclassify Pluto as a dwarf planet did it out of spite or because they were terribly bored and had nothing better to do to make the time pass. They had some pretty good reasons.

Sorry, Pluto doesn’t qualify as a planet

When it was discovered by American astronomer Clyde Tombaugh in 1930, Pluto was estimated to be about the size of Earth. It clearly orbited the Sun, albeit at a distance of about 5.9 billion kilometers (3.7 billion miles), so, naturally, it was labeled a planet.

As scientific instruments got more accurate over the years, however, astronomers found that Pluto was not quite as big as they had first assumed. Latest data delivered by NASA’s New Horizons probe puts its diameter at 1,473 miles (2,370 kilometers).

Besides, the orb’s mass is estimated to be merely one-400th that of our planet. Add to this the fact that Earth itself is by no means a giant of the Solar System, and it makes sense that, having determined its size, astronomers demoted Pluto.

Even so, it wasn’t just its not-in-the-least-impressive size that got Pluto in trouble. Thus, it was more than its petite girth that forced scientists to reconsider its status in the Solar System.

Unlike the proper planets of the Solar System, Pluto does not have its orbit all for itself. Rather than move around the Sun all on its own, Pluto is actually part of the Kuiper Belt, a flattened belt of icy, comet-like bodies, which begins just outside Neptune.

To qualify as a planet, an orb must circle the Sun, have sufficient mass and gravity to be nearly round, and clear the neighborhood around its orbit. Pluto meets the first couple of these criteria, but not the third. Hence, it does not deserve being called a planet.

More so since there are many other celestial bodies like it out there. Just take Ceres and Eris, for instance. If Pluto were to be called a planet again, we would have to extend the same courtesy to these other orbs, and the Solar System would get seriously crowded.

So, bottom line, there is no way we can call Pluto a planet, not when it does not meet all the criteria to deserve this label. In fact, the demotion that people are still talking about wasn’t so much a demotion as it was setting the record straight.

Pluto was never a planet. We made a mistake and labeled it as such when we first discovered it, but this celestial body was never like the other planets in the Solar System. It just took us a while to figure it out.

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A view of Pluto
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