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Why Pluto Is No Longer Considered A Planet : Rogue Planets

So, if the planet doesn't orbit a sun, can it still be called a planet?

model planets in a museum

Photo: Mr_Stein (Flickr)

Some planets roam on their own...

Scientists have found planets with masses similar to Jupiter’s so far from any stars, they believe the planets are roaming on their own.

How Do They Know That?

They used a technique called gravitational microlensing to track planets. When a foreground planet passes in front of a distant, background star, it acts like a lens and magnifies the star, displaying a specific light curve.

The height of the light curve’s magnification and the length of time it takes to pass in front of the star, indicate the size of the planet.

Reach For The Stars…

Doesn’t the planet have to pass in front of a lot of stars before they know if it’s orbiting a sun or roaming?

Yes, that’s why scientists came up with the MOA, the Microlensing Observations in Astrophysics study. The team monitored fifty million Milky Way stars for about two years, checking each star about once an hour for changes.

Then they added their data to OGLE, the Optical Gravitational Lensing Experiment to detect roaming planets. After all their analysis was done, they found almost five hundred short duration microlensing events that indicated planets. They also concluded that many of the planets were rogues.

So Long Pluto

So, if the planet doesn’t orbit a sun, can it still be called a planet? I mean, look what happened to Pluto. Maybe they’ll just be called rogues and not planets after all. Either way, I think it’s cool to be a rogue.

  • laurele

    NOT “so long Pluto.” Pluto IS still a planet according to many astronomers, myself included, who favor a broader planet definition encompassing any non-spheroidal body in orbit around a star. Pluto orbits the Sun and is large enough to be rounded by its own gravity. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was opposed by hundreds of professional astronomers in a formal petition led by New Horizons Principal Investigator Dr. Alan Stern. Stern created the term “dwarf planet” in 1991, but he meant for it to designate a third class of planets, small planets large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all. As for rogue planets since they likely orbited a star at one time and were subsequently ejected from that orbit, they would still qualify as planets.

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