After flying by Pluto and its moons back in 2015, researchers behind the New Horizons mission intend to propose a new way to classify planets, which would return Pluto its original classification.

Ten years ago it was decided that Pluto was no longer a planet, but rather an ice dwarf. It is not because Pluto has changed, but because it remains as an astronomical body worthy of exploration and analysis.;

“Pluto’s ice-covered “heart” is clearly visible in this false-color image from NASA’s New Horizons spacecraft. The left, the roughly oval lobe is the basin informally named Sputnik Planitia, which appears directly opposite Pluto’s largest moon, Charon, pictured at top left,” NASA said. Image credit: NASA/JHUAPL/SwRI.

The team is now proposing a geophysical definition of a planet: “A planet is a sub-stellar mass body that has never undergone nuclear fusion, and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.”

An equivalent albeit more simple paraphrase of the definition intended for students would be “round objects in space that are smaller than stars,” although they exclude white dwarfs, neutron stars, and black holes.

Pluto has been reclassified twice, and it has not completed its period

The team suggests that the definition proposed by the International Astronomical Union (IAU) back in 2006 is flawed. Supposedly, it recognizes as planets the objects that orbit the Sun, and not those that orbit freely in the galaxy, such as “rogue planets.” Also, it requires for the orbit to remain free of obstacles during the planet’s period, something that never occurs in practice.

The proposal argues that the IAU recognizes “giant planets” as planets, but refuses to recognize “dwarf planets” as such. Under the new definition, there would be 110 known planets in our Solar System, and the number is expected to grow as more planets are discovered in the Kuiper Belt. In comparison, researchers state that there are 88 official constellations, although people are fine by learning just a few, and the same should be true for planets.

A different way to look at planets in our Solar System, seeing that there would be a hundred new ones, is the natural organization of our galaxy. The zone closest to the sun contains rocky planets, while the middle zone consists of gaseous, rocky, and icy planets. Lastly, the farthest area includes only cold planets. All of the zones have smaller asteroids and comets.

Reaching the farthest regions of the Solar System

According to NASA, the National Academy of Sciences ranked the exploration of the Kuiper Belt of the highest priority for solar system exploration, which is why New Horizons was sent to survey what ten years ago we knew as the ninth planet in our Solar System.

The purpose of the mission was to determine how Pluto and its largest moon Charon fit in our planetary classification. They were put in the “ice dwarf” category, seeing that they have solid surfaces and most of their mass consists of icy material.

Alan Stern, the principal investigator behind New Horizons, is also the leader of the proposal to redefine what “planet” means.

New Horizons was launched in 2006. It managed to swing past Jupiter, using its gravity for a boost and study in 2007, then headed towards Pluto in a journey that would last almost ten years. Pluto is located in the Kuiper belt, a disc circling the Solar System far beyond Neptune’s orbit. It can be compared to the asteroid belt, although it is 20 times as wide and perhaps 200 times more massive. So far, only three dwarf planets have been recognized in the Kuiper belt, these being Pluto, Makemake, and Haumea.

New Horizons revealed many facts about Pluto that were once unknown. First, it was discovered that its four small moons, Hydra, Kerberos, Nix, and Styx, were irregular in their formation and are most likely composed out of clear water ice. The larger ones appear to be four billion years old, being as old as the Solar System itself. Charon is similar to the other four moons, but its surface is known to have ammonia leaks and remnants of other volatile materials. This means that, at some point, Charon could have had an atmosphere of its own.

As the New Horizons probe approached, the research team discovered that Pluto’s atmosphere was denser than predicted. Its surface appears to be younger than 30 million years old, and Stern assures that some regions showcased liquid nitrogen and many unidentifiable frozen geophysical structures. Now, New Horizons is bound towards 2014 MU69, an object discovered in June of that same year that scientists do not know much about. New Horizons is set to perform a flyby in 2019’s New Year’s Eve, becoming the first object targeted for a flyby after the probe had been launched in the first place.

The proposal to redefine the term “planet” will be presented at the Lunar and Planetary Science Conference in March. One of the most obvious faults in the current classification is for a planet’s orbit to be free of obstacles. By the year 2011, surveys had registered over 1,000 potentially hazardous satellites that transited relatively close to Earth, which could result in Earth itself losing its “planet” status under the current terminology.

Source: Popular Mechanics