A theory that Mars lost its magnetic field and then its oceans (2022)

Original Article ↗ Hacker News Discussion ↗

Mars’ ancient magnetic field and its disappearance are examined as a leading explanation for how the planet may have once supported oceans and then lost most of its atmosphere and water to space. Commenters contrast this with Earth’s long-lived dynamo and Venus’s dense atmosphere despite lacking a strong magnetic field, arguing that solar distance, gravity, atmospheric chemistry and internal heat may matter more than magnetism alone. The thread also branches into whether terraforming Mars or Venus is physically and politically plausible, and how long-term planetary engineering compares to addressing climate and sustainability challenges on Earth.

Evidence Mars Once Had a Magnetic Field and Oceans

  • Multiple commenters note strong evidence of an ancient Martian dynamo from magnetized crustal rocks and meteorites.
  • Consensus in the thread: Mars did have a global magnetic field for roughly the first ~1–1.5 billion years.
  • Geological evidence also suggests long-lived oceans or even near‑global water coverage during that period, though exact extent and duration remain uncertain.

Debate Over Scientific Language (“Theory” vs “Hypothesis”)

  • Some argue wording like “Mars had…” is too absolute and prefer hedging (“it seems”).
  • Others counter that, in science, “theory” is a well‑supported framework, not a mere guess, and hedging can understate strong evidence.
  • Meta‑concern: moralizing over wording is seen by some as more stifling to discussion than confident, evidence‑based claims.

Planetary Cores and Heat Sources

  • Discussion of Earth’s core heat:
    • Radiogenic heating largely in crust and mantle, not core.
    • Core heat mainly from primordial formation energy, latent heat of inner‑core solidification, and differentiation.
  • Radiogenic heating in the mantle actually enhances mantle convection and speeds core cooling, rather than “blanketing” it.
  • Mars’s smaller size likely led to faster cooling and earlier dynamo shutdown.

Magnetic Fields, Atmospheres, and Planet Comparisons

  • Several posts argue magnetic fields are not the dominant factor in atmospheric retention; gravity and solar flux matter more.
  • Scientific American and other sources are cited: charge exchange allows hydrogen escape even with a magnetosphere.
  • Venus is highlighted as a counterexample: no strong magnetic field, yet a very dense CO₂ atmosphere and intense greenhouse.
  • Newer work (mentioned but not detailed) suggests Venus, Earth, and Mars may lose isotopes at similar rates, weakening the “no field → no atmosphere” story.

Terraforming and Colonization Prospects

  • Opinions split on Mars colonization:
    • Critics call it fantasy due to radiation, thin atmosphere, and long timescales.
    • Supporters argue atmosphere loss is slow (10⁶–10⁸ years), so thickening it is viable if maintained.
  • Proposed solutions: artificial magnetosphere at Mars L1; superconducting rings; huge solar‑powered systems. Disagreement over whether energy requirements are within plausible human capacity.
  • Venus terraforming ideas: solar shades, freezing and tarping CO₂, splitting CO₂ into O₂ and carbon, floating habitats. Major issues: extreme atmospheric mass, lack of water, slow rotation.
  • Many emphasize that fixing Earth and exploring/terraforming other worlds are not mutually exclusive; some frame expansion as insurance against existential risks (the “Great Filter”).

Climate Change and Runaway Greenhouse

  • One line of argument uses Venus as a warning about runaway greenhouse and ocean loss.
  • Others note Earth has had much higher CO₂ in the past without Venus‑like conditions and cite recent work suggesting stabilizing radiative feedbacks; still, long‑term water loss and tectonics stability are flagged as unresolved.

Meta: Article Quality, SEO, and Long-Term Thinking

  • The linked piece is criticized as recycled, SEO‑driven, and somewhat out of date on the role of magnetic fields.
  • Broader reflection on human inability to invest in projects with payoffs beyond decades, contrasted with some long‑lived infrastructure (e.g., qanats, bridges) and the need for multi‑millennial thinking for planetary engineering.