Skip to content
Vatican Observatory
  • About
    • Overview
    • Team
    • FAQ
  • Telescopes
    • Overview
    • Telescope Images
  • Latest
    • Overview
    • Resources
    • Press
    • Audio
    • Video
    • Research
    • Authors
      • FAQs
    • Newsletter
    • Tucson Meteor Cameras
  • Podcast
  • Education
    • Overview
    • Resource Center
    • Image Gallery
    • Summer School
    • Books
    • Software
    • Additional Resources
    • ACME
    • Ambassadors
  • Shop
  • Calendar
  • Support
    • Overview
    • Donate Now
    • Sacred Space Astronomy
      • View Content
    • Fr. Coyne Fundraiser
    • Bequests / Trusts
    • The Foundation
      • Newsletters
      • Annual Reports
  • Press
  • Specola Vaticana
  • Contact
    • Contact
  • About
    • Overview
    • Team
    • FAQ
  • Telescopes
    • Overview
    • Telescope Images
  • Latest
    • Overview
    • Resources
    • Press
    • Audio
    • Video
    • Research
    • Authors
      • FAQs
    • Newsletter
    • Tucson Meteor Cameras
  • Podcast
  • Education
    • Overview
    • Resource Center
    • Image Gallery
    • Summer School
    • Books
    • Software
    • Additional Resources
    • ACME
    • Ambassadors
  • Shop
  • Calendar
  • Support
    • Overview
    • Donate Now
    • Sacred Space Astronomy
      • View Content
    • Fr. Coyne Fundraiser
    • Bequests / Trusts
    • The Foundation
      • Newsletters
      • Annual Reports
  • Press
  • Specola Vaticana
  • Contact
    • Contact

Could “Planet Nine” be Considered a Planet?

By Robert Trembley  |  26 Jun 2017

Share:
  • Share on Facebook
  • Share on Twitter
  • Share on LinkedIn
  • Share via Email
Planet Nine Location
Planet Nine Location Possible location for hypothesized Planet Nine. Credit: Universe Sandbox ²/ Bob Trembley

I got to wondering: given the International Astronomical Union‘s (IAU) current definition of a planet, if a hypothesized “Planet Nine” were to be found in the outer reaches of our solar system, could it (or anything in that region) be considered “a planet?”

The IAU definition of a planet is a celestial body that:
(a) is in orbit around the Sun.
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
(c) has cleared the neighborhood around its orbit.

An astronomical units (AU) is a unit of measurement equal to the mean distance from the center of the earth to the center of the sun – 149.6 million kilometers.

The Kuiper belt is a disc-shaped region of icy bodies in the solar system – including dwarf planets such as Pluto – and comets beyond the orbit of Neptune. It extends from about 30 to 55 AU.

A trans-Neptunian object (TNO) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune – 30 AU.

The Oort cloud as a hypothesized bubble of icy debris that surrounds our solar system. This distant cloud may extend a third of the way from our sun to the next star – between 5,000 and 100,000 AU.

The hypothesized location of “Planet Nine” is around 500 and 1200 AU; images I’ve seen all place it in a highly elliptical orbit, pretty near to the ecliptic plane. That puts it out in the trans-Neptunian region, and well into the Kuiper belt. The hypothesized mass of “Planet Nine” is ten times that of Earth, making it much larger than the typical size of trans-Neptunian objects.

The question is: with the existence of the Kuiper Best, and the pretty good chance that the Oort cloud exists, can any object out past Neptune ever be classified as a planet, given the requirement that a planet clear its neighborhood?

Oort Cloud Illustration. Credit: laurinemoreau.com

A related issue is that under the current IAU definition of a planet, exoplanets and satellites in orbit of brown dwarfs cannot be considered planets; I’d suggest a slight rewording to state that a planet must be “planetary mass object in orbit of a stellar or sub-stellar mass parent body.”

More Reading:

  • https://solarsystem.nasa.gov/planet9
  • https://www.forbes.com/sites/startswithabang/2017/06/21/goodbye-planet-nine-new-and-better-data-strongly-disfavors-a-giant-world-beyond-neptune/#200a3a2d60a3
  • http://www.findplanetnine.com/p/blog-page.html
Share:
  • Share on Facebook
  • Share on Twitter
  • Share on LinkedIn
  • Share via Email

Sacred Space Astronomy

The Vatican Observatory’s official digital community and online magazine.

Become a Member

Recent Posts

Lost Video of Georges Lemaître, Father of the Big Bang Theory, Recovered

By Faith and Science  |  6 Feb 2023  |  Resources

European Institute of Science in Management interview with Br. Guy Consolmagno, S.J.

By Robert Trembley  |  4 Feb 2023  |  Sacred Space Astronomy

You Can’t See Atoms, so Why Can You See Stars?

By Mr. Christopher Graney  |  4 Feb 2023  |  Sacred Space Astronomy

A tale of an unexpected comet

By Deirdre Kelleghan  |  1 Feb 2023  |  Sacred Space Astronomy

Archives

      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • October
      • September
      • August
      • July
      • June
      • May
      • April
      • March
      • February
      • January
      • December
      • November
      • August
      • June
      • March
      • January
      • November
      • October
      • December
      • November
      • April
      • May
      • January
      • December
      • September
      • May
      • March
      • December
      • November
      • February

More Posts by
Robert Trembley

European Institute of Science in Management interview with Br. Guy Consolmagno, S.J.

By Robert Trembley  |  4 Feb 2023  |  Sacred Space Astronomy

Detroit Stories Episode 46: ‘Faith and the Cosmos’ (PODCAST) – Detroit Catholic

By Robert Trembley  |  1 Feb 2023  |  Sacred Space Astronomy

ⓜ Full Moon-th Meetup: 5 February, 2023

By Robert Trembley  |  30 Jan 2023  |  Sacred Space Astronomy

How this astrophysicist and Jesuit priest balances science and spirituality

CBC  |  20 Jan 2023  |  Press

Catholic astronomers: Newly discovered planet a testament to Earth’s ‘startling uniqueness’

Catholic News Agency  |  19 Jan 2023  |  Press

Astronomy Picture of the Day (APOD) Authors get Asteroid Named After Them

By Robert Trembley  |  18 Jan 2023  |  Sacred Space Astronomy

View More

Newsletter

Upcoming astronomical events, scientific breakthroughs, philosophical reflections… just a few reasons to subscribe to our newsletter!

  • *
Vatican Observatory
  • About
  • Telescopes
  • Latest
  • Podcast
  • Education
  • Shop
  • Calendar
  • Support
  • Press
  • Specola Vaticana
  • Contact
Privacy Policy  |   Cookie Policy  |   Disclosure Statement

Podcast:

  • Apple Podcasts Listen onApple Podcasts
  • Spotify Listen onSpotify
  • Google Podcasts Listen onGoogle Podcasts
  • Stitcher Listen onStitcher
  • Amazon Alexa Listen onAmazon Alexa
  • TuneIn Listen onTuneIn
Made by Longbeard