Wandering through the realms of the cosmos, pondering its huge vastness

A Fifth Moon Around Pluto!

July 11, 2012: A team of astronomers using NASA’s Hubble Space Telescope reported the discovery of another new moon orbiting the icy dwarf planet Pluto, meaning the dwarf planet now has 5 moons. So there is Charon, Hydra, Nix, P4 and Yet-to-be-named moon. The 4th moon, P4, was only discovered about a year ago.

The “new” moon is estimated to be irregular in shape and 6 to 15 miles across. It is in a 58,000-mile-diameter circular orbit around Pluto that is assumed to be co-planar with the other satellites in the system.

Pluto’s entire moon system is believed to have formed by a collision between the dwarf planet and another planet-sized body early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto.

Scientists are searching for more possible moons orbiting Pluto and also signs of a possible debris field generated by the theoretical impact billions of years ago.

Meanwhile, this recent discovery has raised the hopes of many Pluto supporters that they call for its reinstatement as the 9th planet.

But would Pluto’s 5th moon make it a Planet?

Unfortunately, no.

This image, taken by NASA's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5, as photographed by Hubble's Wide Field Camera 3 on July 7, 2012.Despite of some determined lobbying by die-hard supporters to change its dwarf planet status, more moons around Pluto  won’t change its classification.

According to Michael Brown, an astronomer at the California Institute of Technology, the discovery of Eris, a rocky object about Pluto’s size with approximately 25% more mass, was a major factor in the IAU’s decision to reassess exactly what constitutes a planet. Hence, the controversial decision of demoting Pluto.

The IAU ruled that to be called a planet, an object has to meet three conditions:

  • It needs to be in orbit around the Sun.
  • It needs to have enough gravity to pull itself into a spherical shape.
  • It needs to have “cleared the neighborhood” of its orbit.
Pluto satisfied all the conditions, except the third one. Any object that doesn’t meet this third criterion is considered a dwarf planet. And so, Pluto is a dwarf planet.  Even with Pluto’s five moons , it doesn’t “clear the neighborhood.” There are still many objects with similar size and mass to Pluto lurking around in its orbit. And until Pluto gets rid of these objects by perhaps, crashing into many of them and gains mass, it will remain a dwarf planet.
Image credit: NASA

2 responses

  1. lovelystar

    if pluto met d third rule of Iua wil people b able 2 live in it???

    August 22, 2012 at 4:01 pm

  2. Michael

    I’m curious what you & other knowledgeable amateurs think about the matter. My own perspective is a bit different from everyone else’s, it seems. I agree with reclassifying Pluto, as there may indeed be many more similar trans-Neptunian objects waiting to be discovered, and it makes sense to have a separate category rather than adding to the number of planets until there are 15? 30? 100? Indeed, history repeats itself; once every new asteroid was being added to the list of planets until they were reclassified in the mid-1800s.

    On the other hand, I question bringing the “clearing the neighborhood” thing into the picture, simply because I think that if the definition of such a basic thing as a “planet” is confusing for a beginner, it’s a sign that the definition needs work. I think that asteroids, major planets, and trans-Neptunian planets should be classified according to location and size range, and perhaps the trans-Neptunians should be equally considered planets, just a different category.

    July 14, 2012 at 12:53 pm

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