Back when I was in school, our solar system had nine planets. Students learned the planets’ order from the sun with the mnemonic, “My Very Educated Mother Just Served Us Nine Pizzas,” for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Alas, Pluto’s been demoted and is now characterized as a dwarf planet. But recent scientific research edges closer to adding back a ninth planet, a heavenly body currently known as Planet Nine.
What’s A Planet?
While lots of objects appear in space, they cannot be planets unless they meet a definition adopted by the International Astronomical Union (“IAU”). This definition contains three requirements to attain planet status:
- It must orbit a star. In our solar system, that’s the Sun.
- It must be big enough to be forced by gravity into a sphere. (Take note, Flat Earthers. Earth can’t be a planet unless it’s round.)
- It must be big enough for its gravity to clear away other objects in its neighborhood of a similar size.
The adoption of this definition in 2006 brought the death knell for Pluto as a planet. It failed to meet the third requirement. Pluto wasn’t tidy enough in its planetary neighborhood, so it got booted from the planet community, now existing as merely a dwarf planet.
Possible New Planet?
Could a new planet be orbiting the Sun out in space somewhere? The best answer at this point is possibly, but no one’s seen it–YET. Seeing the planet before scientists give a definitive yes is an important goal. Historically, physical evidence has been involved to identify a planet. The five planets known to the Greeks (Mercury, Venus, Mars, Saturn, and Jupiter) were visible to the naked eye, and astronomers have pictures of Neptune and Uranus. Seeing is believing, so photographs and eyes on a new planet through a telescope is much stronger than scientific calculations and statistical evidence the ordinary stargazer can’t understand.
But seeing something billions (that’s billions with a “b”) miles from Earth is a challenging task, especially when that planet’s exact location is unknown. Help could be on the way in the form of the Vera C. Rubin Observatory which is currently under construction on a mountain top in northern Chile. Set to become operational in 2025, the facility will boast the largest digital camera ever made for astronomy. How big is big? 6,200 pounds and the size of a small car big.
Why Do Scientists Think A Planet’s Out There?
The idea of another planet existing in our solar system’s outer regions was first suggested in 2014. The unusual orbits of Trans-Neptune Objects (“TNOs”) gave rise to talk of another planet, dubbed Planet Nine. TNOs are farther from the sun than Neptune and have more elongated orbits unaffected by interactions with any known planets. A group of TNOs bunched together with similar orbits pointed to the existence of a massive object (like a planet!) shepherding them.
A team at the California Institute of Technology (“Caltech”) began investigating the possible existence of another planet. Computer simulations required a gravitational kick to explain how bits or rock and ice around Neptune’s orbit ended up close to the Sun. Planet Nine served as the best explanation of these objects’ orbits. Caltech astronomer Mike Brown used archives of data from surveys of the night sky to hunt for this mysterious planet. Brown offered an understandable (to non-scientists), interesting, and humorous explanation of the Planet Nine situation in a TED Talk. (Check it out at https://youtu.be/2UZKME9WP9M.)
What’s Known About Planet Nine?
Much is unknown about Planet Nine (such as its location), but scientists can tell us what they believe based on their work. First, its mass is 5 to 10 times Earth’s, and its radius is 2 to 4 times bigger than Earth’s. Clearly, then, Planet Nine larger than puny Pluto. Second, the planet’s orbit around the sun is elliptical and takes over 10,000 years to complete. (That’s one LOOOOONG year!)
If Planet Nine’s existence is confirmed, it will receive an official name (hopefully a different, more creative one than Planet Nine) from IAU, the organization authorized to name objects in our solar system. What will that name be? Well, other than Earth, all the planets’ names come from Greek and Roman mythology. If that trend continues, it would be nice if the name begins with a “P” so those of us who learned the MVEMJSUNP mnemonic can continue to use it.
Planets As News
Even those of us who don’t have degrees in a scientific field can appreciate news about space. Scientists are always learning something to pass along to us like the possible existence of another planet. Who’s to say there aren’t more planets beyond Planet Nine?
News on scientific discoveries in the heavens continues to awe us about our universe. It also teaches us how little we really know and that we should not to be surprised when what we have learned changes, like the number of planets. Pluto, you’re missed in the planetary lineup. Looking forward to meeting you, Planet Nine!
WONDER-ing Woman:
Do you believe our solar system contains undiscovered planets besides Planet Nine? If Planet Nine is confirmed as a planet, what name would you suggest giving it? If you learned Pluto was a planet when you were in school, were you sad to see it downgraded to a dwarf planet?