Hoopworlds: Building Donut Planets

Summary

The video explores hoopworlds: hypothetical, donut-shaped worlds, usually imagined as enormous artificial megastructures.

Shape and Possible Formation

A torus is a ring-like shape defined by two radii: the major radius, measured from the center of the hole to the center of the ring, and the minor radius, which is the radius of the ring’s cross-section.

The video focuses on a ring torus, whose major radius is much larger than its minor radius. Naturally occurring hoop-shaped planets are considered highly unlikely, but two possible formation routes are suggested: formation from a double-planet system or a rapidly rotating planet breaking apart into a ring.

Construction and Potential Uses

A hoopworld could be built using active-support structures. Rapidly orbiting mass would provide the force needed to resist collapse, while magnetic levitation would support a stationary outer layer—the inhabited sheath.

The concept resembles a planetary ring, but made solid and stabilized. Such structures could potentially have many times Earth’s mass and living area.

Other proposed designs include:

• Using the rocky core and gaseous material of a Neptune- or Uranus-mass planet as components.
• Using a molten core or fast-moving filler to generate a strong magnetic field, helping protect the atmosphere and inhabitants from radiation.
• Adding an inhabited inner surface, nested layers with artificial lighting, or a rotating interior habitat that acts as an “underworld.”
• Linking multiple hoops into larger structures, including a chain of worlds arranged around a star.

Gravity and Living Conditions

Gravity is zero at the exact center of a symmetric hoop. Unlike inside a hollow sphere, however, it is not zero throughout the interior. Away from the center, gravity pulls toward the nearest part of the ring, which could make a moon placed inside potentially unstable.

Gravity varies across the inhabited ring. It is weaker on the inner equator than on the outer side. Rotation increases effective gravity on the inside and reduces it on the outside, while gravity is stronger near the poles—especially on the inner side.

A hoopworld could be tilted to produce seasons. Its outer equatorial regions might be warmer, while the inner equator and northern or southern regions could be colder.

Weather would be difficult to predict because gravity varies across the world, and rotation produces substantial centrifugal and Coriolis effects. The video suggests that an Earth-like day length could allow some regions to have broadly familiar conditions.

Because of the hoop’s large radius, geostationary orbit could be relatively close, potentially allowing shorter, simpler space elevators than those on Earth. The center could also be connected by elevators, though they would require stabilization.

A central object might serve as a moon and create tides, but its motion and the hoop’s orientation would need careful stabilization. The video considers it unsuitable as a central artificial sun because its apparent cycle would be too slow.

Researchers and Sources Mentioned

• Anders Sandberg — Created a gravity model for an Earth-like hoopworld and wrote an analysis of torus-shaped planets.
• ANDART — Hosts Sandberg’s article on torus-shaped planets.
• Orion’s Arm — The speculative worldbuilding group cited as an inspiration for the video series.