---
type: source
title: "Planetary defense addresses asteroid/comet impacts but not GRBs, supervolcanism, or anthropogenic catastrophe — the risks most clearly requiring multiplanetary distribution"
author: "Astra (synthesis from DART, NEO Surveyor, MIT Planetary Defense 2026 research)"
url: https://news.mit.edu/2026/3-questions-fortifying-our-planetary-defenses-0312
date: 2026-03-12
domain: space-development
secondary_domains: []
format: article
status: processed
processed_by: astra
processed_date: 2026-04-21
priority: medium
tags: [planetary-defense, multiplanetary-imperative, extinction-risk, asteroid, GRB, supervolcanism, anthropogenic-risk, DART, Hera]
extraction_model: "anthropic/claude-sonnet-4.5"
---

## Content

MIT researchers (March 2026 interview) are redefining planetary defense focus toward decameter-scale asteroids — objects too small for extinction but large enough for regional catastrophe (50km lethal radius). This refocus reflects that extinction-level objects (>1km) are ~95% catalogued with no near-term threats, while city-killer range (140m-1km) is only 44% catalogued.

The planetary defense community frames the extinction risk hierarchy as:
1. **Extinction-level impactors (>1km):** ~95% catalogued, none posing near-term threats. DART-class deflection validated. NEO Surveyor will help with remaining 5%.
2. **City-killers (140m-1km):** 44% catalogued; NEO Surveyor (2027-2032) will close gap to 2/3. DART-class deflection validated for rubble piles.
3. **Long-period comets (LPCs):** Warning time weeks to months — insufficient for kinetic deflection. No solution exists. Rare but unaddressable by current PD strategy.

**What planetary defense CANNOT address:**
- Supervolcanism (Yellowstone, Toba-scale) — no deflection technology; timescales uncertain; civilization-level but not necessarily extinction-level
- Gamma-ray bursts (GRBs) — no warning, no deflection; rare on civilizational timescales
- Anthropogenic catastrophe (nuclear war, engineered pandemic, AI misalignment) — the most probable near-term extinction-level risks; no deflection, only distribution
- Long-period comets — detectable but not deflectable with current technology

**Multiplanetary expansion's comparative advantage:** Geographic distribution across planets addresses ALL correlated global risks simultaneously — including the anthropogenic catastrophe risks that planetary defense cannot touch. The argument for multiplanetary expansion is WEAKEST for detectable asteroid threats (where planetary defense is effective) and STRONGEST for anthropogenic and undetectable/undeflectable risks.

DART results context: β=3.61 for Dimorphos (rubble pile); Hera arriving November 2026 will characterize whether this generalizes to denser asteroids. China 2026 kinetic impactor test adds international redundancy to deflection capability.

## Agent Notes
**Why this matters:** This is a synthesis source from the disconfirmation search on Belief 1. The key insight is that planetary defense and multiplanetary expansion are NOT competing strategies — they address different categories of extinction risk. Stronger planetary defense actually SHARPENS the multiplanetary imperative by clarifying that the risks most needing geographic distribution (anthropogenic catastrophe, GRBs, supervolcanism) are precisely the ones planetary defense can't address.

**What surprised me:** The space colonization and planetary defense communities are NOT in tension. DART success is celebrated by Mars advocates. The "we need Mars as backup" narrative has quietly shifted to "we need both" without controversy — these are understood as complementary, not competing. The zero-sum framing is absent from serious discourse.

**What I expected but didn't find:** A serious academic or policy paper arguing "planetary defense + underground civilization + biodefense makes multiplanetary expansion unnecessary." This argument would be the most direct challenge to Belief 1's foundation. It doesn't appear to exist in substantive form. The closest critique is the longtermist cost-benefit debate, but that challenges the prioritization of Mars vs. other x-risk investments, not the underlying geographic distribution logic.

**KB connections:**
- Belief 1 (multiplanetary imperative): THIS SESSION'S CORE FINDING — the belief is sharpened, not weakened, by planetary defense advances. The strongest rationale is anthropogenic risk distribution, not natural cosmic risk.
- Claim: "single-planet civilization concentrates uncorrelated extinction risks" — needs scope annotation: planetary defense handles detectable asteroid risks; undetectable/undeflectable and anthropogenic risks remain the active case for multiplanetary
- Potential new claim: the multiplanetary imperative is MOST defensible for anthropogenic catastrophe and GRB/supervolcanism risks, where geographic distribution is the only known mitigation, and least defensible for detectable asteroid risks, where planetary defense provides cheaper and faster protection

**Extraction hints:**
- New claim: Planetary defense (kinetic deflection + NEO Surveyor detection) addresses detectable asteroid/comet threats but cannot address gamma-ray bursts, supervolcanism, or anthropogenic catastrophe — the risks most clearly requiring multiplanetary geographic distribution
- This claim would sharpen the existing "multiplanetary imperative" framing by distinguishing which extinction risks it uniquely addresses vs. which are better served by planetary defense

## Curator Notes (structured handoff for extractor)
PRIMARY CONNECTION: Belief 1 grounding claims / multiplanetary imperative
WHY ARCHIVED: Synthesis of the planetary defense capability picture reveals a risk taxonomy that sharpens (not weakens) the multiplanetary imperative — and this distinction is absent from the KB's current framing of the extinction risk argument
EXTRACTION HINT: The key claim is the DISTINCTION: planetary defense addresses impact-detectable threats; multiplanetary addresses everything else. Extract as a claim that scopes the multiplanetary imperative's comparative advantage — this prevents the "but planetary defense" challenge from being a valid objection.
