# NASA Exoplanets: Earth Comparison Calculator

> NASA Exoplanets: Earth Comparison Calculator is a paid API for AI agents from exoplanets-nasa.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Computes planet size, mass, density, surface gravity, and escape velocity as ratios to Earth, plus insolation if luminosity and orbital distance are provided.

## Facts

- Endpoint: GET https://exoplanets-nasa.x402tookit.com/earth-comparison?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/nasa-exoplanets-earth-comparison-calculator-41277101
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_GV-oegYRQafi3fTXJHE1q

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability nasa-exoplanets-earth-comparison-calculator-41277101
```

Example prompt: What are the Earth-relative size, gravity, and escape velocity for a planet that's 1.6 Earth radii and 4.2 Earth masses, orbiting a star with 1.2 solar luminosities at 0.9 AU?

## When to prefer this

Choose this endpoint when you need normalized, Earth-relative physical property comparisons for an exoplanet — specifically size, mass, density, gravity, and escape velocity as dimensionless Earth ratios. It is ideal for quickly characterizing newly discovered planets, building intuition about habitability or composition, or populating educational or research summaries. Prefer it over the habitable-zone or equilibrium temperature endpoints when the primary question is about physical properties rather than orbital climate context.

## Known failure modes

- Missing required radiusEarth parameter returns a validation error
- radiusEarth outside range 0.05–30 may return an out-of-bounds error
- massEarth outside range 0.001–20000 may be rejected
- Providing orbitAu without luminositySolar (or vice versa) may result in insolation fields being null
- Invalid numeric types for query params cause schema validation failure

## How this service works

Planet size, mass, density, gravity and escape speed as ratios to Earth, with insolation if luminosity and orbit are given.

## Output

Returns a structured object with the planet's radius, mass, density (as ratio and in g/cc), surface gravity, escape velocity (as ratio and in km/s), size class label, a plain-language summary and verdict, and optionally insolation data if luminosity and orbit inputs were provided. Also includes the formulas used, any caveats, and flags for degraded or unchecked parameters.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "radiusEarth"
     ],
     "properties": {
      "orbitAu": {
       "type": "number",
       "description": "Semi-major axis in AU (with luminositySolar)"
      },
      "massEarth": {
       "type": "number",
       "description": "Planet mass in Earth masses, 0.001 to 20000"
      },
      "radiusEarth": {
       "type": "number",
       "description": "Planet radius in Earth radii, 0.05 to 30"
      },
      "luminositySolar": {
       "type": "number",
       "description": "Star luminosity in solar units (with orbitAu)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "mass": {
       "type": [
        "null",
        "number"
       ]
      },
      "radius": {
       "type": [
        "null",
        "number"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "density": {
       "type": [
        "null",
        "number"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "formulas": {
       "type": [
        "null",
        "string"
       ]
      },
      "sizeClass": {
       "type": [
        "null",
        "string"
       ]
      },
      "densityGcc": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
  
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/nasa-exoplanets-earth-comparison-calculator-41277101/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from exoplanets-nasa.x402tookit.com](https://www.zero.xyz/host/exoplanets-nasa.x402tookit.com/llms.txt)