Pluto May get its Planetary Status Back in 2015

Ceres is the biggest object in the asteroid belt, and NASA’s Dawn spacecraft will reach at this dwarf planet on March 6, 2015.

Pluto is the biggest object in the Kuiper belt, and NASA’s New Horizons spacecraft will reach at this dwarf planet on July 15, 2015.

These two occasions will make 2015 a thrilling year for solar system study and discovery. But there is much more to this story than mere science. I suppose 2015 will be the year when general consensus, erected upon our new knowledge of these two objects, will return Pluto and add Ceres to our family of solar system planets.

The efforts of a very small group of Pluto-haters within the International Astronomical Union (IAU) plutoed Pluto in 2006. Of the roughly 10,000 internationally listed members of the IAU in 2006, only 237 voted in favour of the resolution redefining Pluto as a “dwarf planet” while 157 voted against; the other 9,500 associates were not present at the final session of the IAU General Assembly in Prague at which the vote to demote Pluto was taken. Yet Pluto’s official planetary rank was snatched away.

Ceres and Pluto are both spheroidal objects, like Mercury, Earth, Jupiter and Saturn. That’s part of the agreed upon description of a planet. They both orbit a star, the Sun, like Venus, Mars, Uranus and Neptune. That’s also part of the extensively recognised description of a planet.

Contrasting to the larger planets, though, Ceres, like Pluto, according to the IAU definition, “has not cleared the neighbourhood around its orbit.” The asteroid belt is, seemingly, Ceres' neighbourhood while the Kuiper Belt is Pluto’s neighbourhood – however no description of a planet’s neighbourhood exists, and no agreed upon understanding of what “clearing the neighbourhood” yet exists. In addition, no broad-based agreement is present as to why “clearing the neighbourhood” need be a necessity in order for an object to be considered a planet.

Some planetary astrophysicists would claim that where the Earth placed in the Kuiper Belt, it would not be able to clear its neighbourhood and thus would not be considered, by the IAU definition, a planet; apparently position matters. Here a planet, there not a planet. I’d argue that location shouldn't matter; in its place, the inherent properties of the objects themselves should matter more. And so we are led back to Ceres and Pluto.

Never before visited by human spacecraft, Ceres and Pluto, as we will soon bear witness, are both developing, changing worlds. Yesterday, Ceres and Pluto were aliens, distant, barely known smallest members of our solar system. By the end of this calendar year, though, we will have poured both objects with our passion and our attention; we will have greeted them both into our embrace. And we almost surely will once again call both of them planets.
Ceres, temporarily a planet

Ceres, temporarily a planet

Ceres was found on New Year’s Day in 1801, by Italian astrophysicist Giuseppe Piazzi, a member of an international team of astrophysicists dubbed the Celestial Police, who were hunting for an apparently missing planet in between the orbits of Mars and Jupiter. When found, Ceres was straightway accepted as a planet, the eighth one known at the time (neither Neptune nor Pluto had been found yet).

But within a few years, other objects in the asteroid belt were discovered and Ceres no longer appeared to stand out as far from the crowd. In 1802, the great astrophysicist William Herschel proposed that Ceres and Pallas and any other smaller solar system objects should be termed asteroids – meaning star-like. In telescope pictures, they were so tiny that they see point-like, like stars, rather than disk-like, like planets. And so more than a century before Pluto was found, Ceres was plutoed.

But Ceres does still stand out. It’s the biggest asteroid, by far, approximately 1,000 kilometres across (twice as big in diameter as Vesta, the second biggest asteroid), however not perfectly round in shape.

As happened inside Earth and other planets, planetary researchers think that long ago, the denser material in Ceres unglued from the lighter material and descended to form a core.

Astrophysicists think Ceres is rich in water – as much as one-third of Ceres might be water – and may have a thin atmosphere. Bright, white spots on its superficial might even be huge frozen lakes. Ceres may, actually, have as much fresh water as Earth, have Earth-like polar caps, and might even have a sub-surface liquid ocean layer, like Jupiter’s moon Europa and Saturn’s moon Enceladus.

Starting this month, we'll start to study more about these tempting potentials. With our increasing knowledge of and understanding with Ceres, we will no more be able to classify meaningful criteria that will allow us to carry on to classify Ceres as not-a-planet. Ceres will carry on being a small planet, but in 2015 we will come to comprehend that dwarf planets are planets, too.

Pluto’s short planetary rule

When Pluto was found by Clyde Tombaugh in 1930, many astrophysicists were sure that a large planet orbited the Sun beyond Neptune. In its place they discovered Pluto, which turned out to be small related to Earth and Neptune, however more than double the size of Ceres, with a diameter of 2,300 kilometers.

Pluto also has an uncommon orbit, as it crosses Neptune’s orbit, however it does so in such a way that it can never hit Neptune.

Pluto’s modern-day difficulties started in 1992, when astrophysicists David Jewitt and Jane Luu found the first objects in the area of the solar system now known as the Kuiper Belt. Although the asteroid belt where Ceres is situated is made generally of house- and mountain-sized rocks that orbit the Sun in between the orbits of Mars and Jupiter, the Kuiper Belt is made generally of house- and mountain-sized chunks of ice that orbit the Sun beyond the orbit of Neptune. Pluto, as it turns out, is one of the largest objects in the Kuiper Belt.

So what is Pluto?

Pluto is the last unstudied planet in our solar system. And the Kuiper Belt may comprise hundreds of other planetary worlds like Pluto. These may be the most frequent worlds in the solar system; they may comprise, together, the most total surface area of all the solid-surfaced planets.

Pluto has one huge moon, Charon, and at least four small moons: Nix, Hydra, Kerberos and Styx. It has an atmosphere that enlarges and contracts as Pluto warms and cools throughout its 248 year orbit about the Sun. The surface is likely rich in water ice, enriched with methane and nitrogen and carbon monoxide ices; these ices might comprise complex organic molecules.

The New Horizons mission is poised to answer some of our countless questions about Pluto. How did it form? What is the atmosphere made of? What is the surface like? Does Pluto have a magnetic field? What are the moons like? Does Pluto have a subsurface ocean? Is the surface of Pluto’s moon Charon pure water ice?

Pluto has protected its mysteries for four and half billion years. But in a few months, a few fearless humans will pull back the blind on Pluto and say “Hello, Pluto, we're here.” And Pluto will start to share her mysteries with us. When she does, as with Ceres, our knowledge of Pluto will help us identify that Pluto is, was, and has always been a planet, although a small one.

We only get to see Ceres and Pluto for the very first time, once. This year,  March 6 and July 15. In your lifetime. In this unbelievable year of the dwarf planet. Get ready to party. Ceres and Pluto are coming home.

Originally Published on


Dwarf Planets


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