Who Smarted? – Do Scientists Think There’s an Undiscovered Planet X?

Podcast: Who Smarted?
Episode Date: December 8, 2025
Main Theme: The search for an undiscovered ninth planet ("Planet X") in our solar system and the science, history, and imagination wrapped around the mystery.
Host: "Trusty Narrator" (A)
Featuring: Personified Pluto (B), mysterious Planet X (C)

Episode Overview

This episode takes listeners on a hilarious, kid-friendly journey beyond Neptune into the outer edges of the solar system, all in search of the elusive "Planet X"—a world that astronomers suspect might exist but have never seen. With a blend of playful banter between the Narrator and Pluto, fun analogies (like M&Ms for distances), and interactive questions, the episode explores the science behind the search, the evidence for its existence, and the reasons it’s so hard to find (plus, a twist: could it even be a black hole?).

Key Discussion Points and Insights

1. Setting the Scene: Pluto’s Place

• Pluto’s Feelings: The episode opens with Pluto feeling left out after being demoted from planet status.
  • Quote:
    • "You'll always be the ninth planet in my heart." – A (02:22)
• Planetary Classification: The Narrator explains that while Pluto is a dwarf planet, astronomers are searching for a true ninth planet.

2. Distance in the Solar System

• M&M Demonstration: To help kids understand astronomical distances, the podcast uses M&Ms as a fun analogy:
  • 1 M&M = distance from Earth to Sun (1 Astronomical Unit, or AU)
  • To Pluto: 39 M&Ms (39 AU)
  • To Planet X: Could be as far as 600–1,200 AU!
    • Quote:
      • "We're gonna need many bags. Astronomers believe this ninth planet could be 600 to 1200 AU from the sun..." – A (06:32)

3. Why Do Scientists Think Planet X Exists?

• Orbit Oddities: The strange orbits of objects in the Kuiper Belt (like Sedna) suggest that something massive—possibly a new planet—is tugging on them.
  • Quote:
    • "Sedna has an unusual orbit...it’s elongated, stretched out, as if it was yanked by the gravity of a distant object." – A (07:36)
• Evidence for Planet X: At least six other objects share this odd, tilted trajectory, making random chance unlikely.
• Caltech Astronomers' Theory: They suggest an undiscovered planet about 10 times Earth's mass is shaping these orbits.

4. Meet "Planet X" – The Mystery Continues

• What Does 'X' Mean?: In "Planet X," the X stands for something unknown, not 'extra special' or 'X marks the spot.'
• Possible Attributes:
  • Size: Maybe like Uranus or Neptune
  • Mass: About 10x Earth's mass
  • Orbit: Takes 10,000–20,000 years to go around the Sun!
    • Quote:
      • "The answer according to the Caltech astronomers is somewhere between 10,000 and 20,000 years." – A (11:12)

5. If It Exists, Why Haven’t We Found It?

• Visibility Challenge: So distant and faint it can only be seen by the most powerful telescopes.
• "Planet X" is just a placeholder name:
  • Historically, any proposed planet beyond Neptune has been called "Planet X"—even Pluto was once "Planet X."
    • Quote:
      • "You were once Planet X." – A to Pluto (14:17)

6. What If Planet X Isn’t a Planet?

• Alternative Theory: Black Hole?
  • Some scientists speculate that the gravitational influence might come from a tiny black hole, not a planet.
  • If so, "Planet X" could be the size of an orange—with 10x Earth's mass!
    • Quote:
      • "How small would this Planet X be if it's a black hole?...The answer...is C, the size of an orange." – A (15:26)
• Impossible to Find? An object so small and dark would be almost invisible even to strong telescopes.

Notable Quotes & Memorable Moments

• Pluto’s Comic Relief:

  • "So now a mysterious unknown object that might not even be a planet gets to be called Planet X. How is that fair?" – Pluto (13:34)
  • "We're gonna need a bigger bag of M&Ms." – Pluto (06:27)

• Imagination and Encouragement:

  • "Who knows? Maybe a smarty pants listening right now will be the one to find the mysterious Planet X." – A (15:54)

• Mind-Blowing Fact:

  • "That means whenever planet X is found, it will be in a location it hasn’t been in since well before ancient times." – A (11:12)

Important Timestamps

• [01:24] – Episode theme introduction: searching for a new planet beyond Pluto.
• [05:01] – M&M space distance analogy begins.
• [06:27] – Distances to Pluto & Planet X in AUs.
• [07:36] – Sedna’s orbit and clues about Planet X.
• [08:21] – Caltech astronomers' findings on Planet X's possible mass & location.
• [10:05] – Twin planets Uranus and Neptune; Planet X’s possible size.
• [11:12] – Orbit time for Planet X: 10,000–20,000 years!
• [13:34] – Pluto expresses frustration at "Planet X" naming.
• [15:06] – Black hole theory for Planet X.
• [15:54] – Episode wrap and encouragement for curious listeners.

Summary Table

| Timestamp | Segment/Topic | Highlights | |-----------|------------------------------------|--------------------------------------------------------------------| | 01:24 | Introduction to search for Planet X | Pluto joins the adventure; clue setup | | 05:01 | M&M Analogy | Visualizing AU and solar system distances | | 06:27 | Distance Estimates | How far out Planet X could be (600-1200 AU!) | | 07:36 | Sedna and Orbits | Clues from Kuiper Belt; orbits suggest influence of a big object | | 08:21 | Scientist Theories | Planet X might be 10x Earth’s mass | | 10:05 | Twin Gas Giants | Uranus/Neptune comparison | | 11:12 | Orbit Length | Planet X's year = 10,000–20,000 Earth years | | 13:34 | History of Planet X as a Concept | Pluto’s role; the meaning of “Planet X” | | 15:06 | Alternative: Black Hole | Could it be a tiny black hole? | | 15:54 | Ending/Encouragement | Listeners motivated to keep wondering and exploring |

Tone and Style

• Engaging, playful, and humorous, using banter, puns, and silly voices to make complex science accessible and memorable.
• Interactive—asks listeners questions throughout.
• Encouraging curiosity—invites kids to dream about making discoveries themselves.

Episode Takeaways

• Scientists believe there may be a large, distant planet—Planet X—based on how far-off objects move in space.
• If it exists, it could be ten times heavier than Earth, orbiting absurdly far out, and might take 20,000 years to circle the Sun.
• It hasn’t been seen yet because it is SO far away and faint.
• There’s even a possibility it’s not a planet at all—but a tiny, massive black hole!
• Any unknown world past Neptune gets called “Planet X” until it gets found and officially named.
• Listeners are encouraged to keep being curious—maybe THEY will discover Planet X one day!