RamaWhat a starship crossing the Solar System would mean

An interstellar object crosses the Solar System on a hyperbolic orbit and humans try to catch it. Real visitors versus the game's Rama.

The real world has seen three interstellar visitors pass through the Solar System: ʻOumuamua in 2017, Borisov in 2019 and 3I/ATLAS in 2025. All are natural objects. The game's "Rama" is a thought experiment: what if this time the visitor were a cylinder about 50 km long?

This page keeps two things apart. It first covers real interstellar objects and humanity's attempts to chase them, then the physics that gives a cylinder its "gravity", and only then the story the game imagines. Rama itself is fictional.

Real interstellar visitors

  • ʻOumuamua: it was found after it had already passed perihelion, and humans could observe it for only about two and a half months. There is still no agreement on what shape it actually has.
  • 3I/ATLAS: its speed relative to the Sun is about 58 km per second. Some studies estimate its age at between 7.6 billion and 14 billion years, so it may be older than the Solar System.
  • Non-gravitational acceleration: a 2018 analysis found that ʻOumuamua gained a little extra acceleration as it left the Sun, yet no coma could be seen. One explanation proposed in 2023 is that hydrogen built up in the ice under cosmic-ray irradiation and quietly escaped when heated.

After ʻOumuamua left, some people proposed Project Lyra, which studies how to launch a probe to chase it. It was already too fast, and would have to borrow the gravity of Jupiter or the Sun to speed up. Working out where an interstellar object came from is also hard: tracing an orbit back to its source is very difficult, because over millions of years the stars themselves move.

"Gravity" inside a cylinder

  • Spin gravity: spinning a cylinder produces "gravity" on its inner wall. In the 1970s the physicist Gerard O'Neill seriously designed space cities like this.
  • The central plain: inside a spinning cylinder, the "sky" you see when you look up is the ground on the opposite side.
  • The cylindrical sea: inside a spinning cylinder, water spreads into a band running around the inner wall.

Propulsion and machines

All known ways of propulsion throw something backward, because momentum is conserved, so no known method of "reactionless propulsion" exists in reality. Another common idea is a machine that can replicate itself. Von Neumann imagined one, and self-replicating probes are regulars in discussions of the Fermi paradox.

The idea in the game

What follows is game lore. The channel tells of a sky-survey telescope finding an object on a hyperbolic orbit beyond the asteroid belt. It does not belong to the Solar System and will soon leave. It turns out to be a cylinder about 50 km long. It is discovered by completing "Asteroid mining" in the interstellar-civilization era. The mechanic is a timed window: it stays in the Solar System for only about 30 hours, and anything not explored by then can never be seen again in this universe. Every place you discover for the first time leaves behind a "tech shard" that is kept across universes.

In the scenario, explorers meet an airlock at one end of the spin axis, regular trenches and geometric patterns, a band of light running around the inner wall, a sea that never freezes, buildings with no doors or windows, machines that clear the ground, and a star map marking where it came from. It turns once every 4 minutes, and gravity on the inner wall is about 0.6 times that of Earth. Before leaving it changes its orbit but throws out nothing. It has no crew, and perhaps never needed one. Its destination is not the Solar System. The channel has a single ending, "It leaves": it departs with the secrets humans did not finish reading, and its speed does not change at all. All of this is game lore, not real observation.

  • Rendezvous with Rama (Arthur C. Clarke, 1973): ʻOumuamua in 2017, Borisov in 2019 and 3I/ATLAS in 2025 are real interstellar visitors, and all are natural objects. The novel is about a giant cylinder entering the Solar System. Humans send a ship to board it and explore, and never meet its owners.

The studies below concern small bodies, meteorites and interstellar space. They are real science related to the Rama theme, not the basis of the Rama idea.

  • A violent rearrangement of the giant planets' orbits flung many small bodies into the inner Solar System and caused the Late Heavy Bombardment (Gomes, Levison, Tsiganis and Morbidelli, Nature, 2005).
  • Lead isotopes in meteorites gave Earth an age of about 4.55 billion years (Patterson, Geochimica et Cosmochimica Acta, 1956).
  • The decay products of aluminum-26 in meteorites show that a star had just died nearby when the Solar System was born (Lee, Papanastassiou and Wasserburg, The Astrophysical Journal Letters, 1977).
  • Amino acids of extraterrestrial origin were found in the Murchison meteorite, so the raw materials of life may be common in the universe (Kvenvolden et al., Nature, 1970).
  • Under Mexico's Yucatán Peninsula lies a crater about 180 km across, left by an asteroid impact (Hildebrand et al., Geology, 1991).
  • Particle changes measured by Voyager 1 show that it has left the sphere of influence of the solar wind and entered interstellar space (Stone et al., Science, 2013).

Real basis

  • Hull: ʻOumuamua was already past perihelion when discovered. Humans could observe it for only about two and a half months, and there is still no consensus on its actual shape.

  • Hyperbolic orbit: 3I/ATLAS moves at about 58 km/s relative to the Sun. Some studies estimate its age at between 7.6 and 14 billion years, possibly older than the Solar System.

  • Chase plan: After ʻOumuamua left, Project Lyra was proposed to study how to launch a probe to chase it. It was already too fast, and could only be caught by gaining speed from Jupiter's or the Sun's gravity.

  • Spin gravity: Spinning a cylinder produces “gravity” on its inner wall. In the 1970s the physicist O'Neill seriously designed space cities like this.

  • Central plain: Inside a spinning cylinder, the “sky” you see when you look up is the ground on the other side.

  • Non-gravitational acceleration: A 2018 analysis found that ʻOumuamua got a small extra acceleration as it left the Sun, with no coma visible. A 2023 explanation: hydrogen builds up in the ice under cosmic-ray bombardment and quietly escapes when heated.

  • Cylindrical sea: In a spinning cylinder, water spreads into a band around the inner wall.

  • Biots: Von Neumann imagined machines that could copy themselves; self-replicating probes are regulars in discussions of the Fermi paradox.

  • Star chart: Tracing an interstellar object's origin back along its orbit is very hard: over millions of years the stars themselves move.

  • Reactionless propulsion: Every known means of propulsion has to throw something backward; that is conservation of momentum.

  • Rendezvous with Rama (Arthur C. Clarke, 1973), the science: 2017’s ʻOumuamua, 2019’s Borisov and 2025’s 3I/ATLAS are real interstellar visitors, and all are natural objects.

Related research

These studies relate to this topic but are not direct proof of this page.

  • The Nice model: A violent reshuffling of the giant planets' orbits flung many small bodies into the inner solar system, causing the Late Heavy Bombardment.

    Source: Gomes, Levison, Tsiganis & Morbidelli, Nature 2005, "Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets"

  • The age of the Earth: Patterson used lead isotopes in meteorites to date Earth at about 4.55 billion years. To eliminate lead pollution, he later pushed for a ban on leaded gasoline.

    Source: Patterson, Geochimica et Cosmochimica Acta 1956, "Age of meteorites and the earth"

  • The aluminum-26 puzzle: Decay products of aluminum-26 in meteorites show that a star had just died nearby when the solar system was born.

    Source: Lee, Papanastassiou & Wasserburg, The Astrophysical Journal Letters 1977, "Aluminum-26 in the early solar system: Fossil or fuel?"

  • Amino acids in space: Amino acids of non-terrestrial origin were found in the Murchison meteorite. The raw materials of life may be common in the universe.

    Source: Kvenvolden et al., Nature 1970, "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite"

  • Finding the crater: Buried under Mexico's Yucatán Peninsula is a crater about 180 km across, exactly what that asteroid left behind.

    Source: Hildebrand et al., Geology 1991, "Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico"

  • Leaving the heliosphere: Particle changes measured by Voyager 1 show it has left the realm of the solar wind and entered interstellar space.

    Source: Stone et al., Science 2013, "Voyager 1 observes low-energy galactic cosmic rays in a region depleted of heliospheric ions"

Game lore (fictional)

  • Node “Airlock”: At one end of the spin axis is a ring of airlocks, one inside another, just big enough for one person to pass.
  • Node “Spin gravity”: It turns once every 4 minutes, and gravity on the inner wall is about 0.6 times Earth’s.
  • Node “Central plain”: The plain has regular channels and neat geometric patterns.
  • Node “Light strips”: Six long strips of light come on at once and light up the whole interior.
  • Node “Cylindrical sea”: A ring of unfrozen sea cuts the cylinder in half around its waist.
  • Node “Empty cities”: On both shores of the sea stand many buildings with no doors or windows, laid out like a circuit board.
  • Node “Biots”: Things like crabs and machines clean the ground, paying no attention to the visitors.
  • Node “Southern spires”: A huge spire stands at the south end, with six smaller ones around it. They are charging.
  • Node “Star chart”: A star chart appears on one wall, marking the route it came by.
  • Node “Reactionless propulsion”: Before leaving it changed its orbit without throwing anything out.
  • Node “Crew”: There is no crew, and no place made for a crew.
  • Node “Destination”: It topped up a little energy here, then hurried on. The destination is not the solar system.
  • Channel ending “It leaves”: It leaves the solar system carrying secrets humans never finished reading, without changing speed at all. In the next universe it will pass by at the same moment.
  • Summary of the novel Rendezvous with Rama: A huge cylinder enters the solar system. Humans send a ship to explore it, but never meet its owners. It is only passing through.
See it in the game