Planet X

Cosma / Communication / Knowledge / Realm / Physical / Universe / Solar System / Scattered Disc / Planet X
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Introduction1

TED (YouTube Channel)
TED (Official Website)

Encyclopedia

Planet X was a disproved hypothetical planet proposed in 1906 by Percival Lowell to have existed beyond the planet Neptune. Colloquially, and by extension, any hypothetical trans-Neptunian planet, in particular Planet Nine. — Wikipedia

Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth. These ETNOs tend to make their closest approaches to the Sun in one sector, and their orbits are similarly tilted. These alignments suggest that an undiscovered planet may be shepherding the orbits of the most distant known Solar System objects. Nonetheless, some astronomers question the idea that the hypothetical planet exists and instead assert that the clustering of the ETNOs orbits is due to observational biases, resulting from the difficulty of discovering and tracking these objects during much of the year. — Wikipedia

Planet Nine (Wolfram Alpha)

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Inspiration

Our Solar System Might Have Two Hidden Planets (SciShow, YouTube Video)
Study Suggests Planet 9 May Be Earth Like, Frozen and Much Closer (Anton Petrov, YouTube Video)
Are We Close to Finding Planet 9? (Astrum, YouTube Video)

Articles about Planet Nine (Big Think)

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Innovation

Science

The Super Earth that Came Home for Dinner (NASA/JPL)
Solar System Exploration: Planet X (NASA Science)

Planet X (Mike Brown’s Planets)

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Preservation

History

Planet X, Pluto, and NASA New Horizons (The History Guy, YouTube Video)

Mike Brown (CalTech)
Michael E. Brown (Wikipedia)

Konstantin Batygin (CalTech)
Konstantin Batygin (Wikipedia)

Library

Subject: Planet X (Library Thing)

Subject: Planet X (Open Library)
Subject: Planet Nine (Open Library)

Subject: Planet Nine (WorldCat)

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Participation

Education

MERLOT: Multimedia Educational Resource for Learning and Online Teaching
OER Commons: Open Educational Resources

Community

Organization

International Astronomical Union (IAU)
Asteroids & Remote Planets Section (British Astronomical Association)

News

Planet Nine (Nova Research Highlights, American Astronomical Society)

Planet X (Astronomy Magazine)
Planet Nine (Astronomy Magazine)

Planet X (JSTOR)
Planet Nine (JSTOR)

Planet X (Science Daily)
Planet Nine (Science Daily)

Planet X (Phys.org)
Planet Nine (Phys.org)


Recent News from Phys.org …

  • Groundhogs are lousy forecasters but valuable...
    on January 27, 2026 at 5:26 pm

    Whether you call him groundhog, woodchuck, whistle-pig or use the full genus and species name, Marmota monax, the nation's premier animal weather forecaster has been making headlines as Punxsutawney Phil for decades.

  • Footprint tracker identifies tiny mammals with up...
    on January 27, 2026 at 5:00 am

    It might be less visible than dwindling lion populations or vanishing pandas, but the quiet crisis of small mammal extinction is arguably worse for biodiversity. These species are crucial indicators of environmental health, but they can be very hard to monitor, and many species with very different ecological niches look almost identical.

  • Proposed new mission will create artificial solar...
    on January 26, 2026 at 10:20 pm

    When a solar storm strikes Earth, it can disrupt technology that's vital for our daily lives. Solar storms occur when magnetic fields and electrically charged particles collide with Earth's magnetic field. This type of event falls into the category known as "space weather."

  • Massive cloud with metallic winds discovered...
    on January 21, 2026 at 10:17 pm

    Sweeping winds of vaporized metals have been found in a massive cloud that dimmed the light of a star for nearly nine months. This discovery, made with the Gemini South telescope in Chile, one half of the International Gemini Observatory, offers a rare glimpse into the chaotic and dynamic processes still shaping planetary systems long after their formation.

  • How astronauts will fix their gear using thin air
    on January 19, 2026 at 3:20 pm

    Additive manufacturing, more commonly known as 3D printing, will be an absolutely critical technology for any long-term settlement on another world. Its ability to take a generic input, such as plastic strips or metal powder, and turn it into any shape of tool an astronaut will need is an absolute game changer. But the chemistry behind these technologies is complicated, and their applications are extremely varied, ranging from creating bricks for settlements to plastics for everything from cups […]

returntotop

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Related

Here are links to pages about closely related subjects.

Knowledge Realm

Physical

“Fundamentals”
Law (Constant) Relativity
Force Gravity, Electromagnetism (Light, Color)
Matter (Microscope) Molecule, Atom (Periodic Table), Particle

“Space”
Universe (Astronomical Instrument)
Galaxy Milky Way, Andromeda
Planetary System Star, Brown Dwarf, Planet, Moon

Our Neighborhood
Solar System Sun
Terrestrial Planet Mercury, Venus, Earth (Moon), Mars
Asteroid Belt Ceres, Vesta
Jovian Planet Jupiter, Saturn, Uranus, Neptune
Trans-Neptunian Object
Kuiper Belt Pluto, Haumea, Makemake
Scattered Disc Eris, Sedna, Planet X
Oort Cloud Etc. Scholz’s Star
Small Body Comet, Centaur, Asteroid

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Notes

1.   The resources on this page are are organized by a classification scheme developed exclusively for Cosma.