Astrophyzix Risk Index (ARI)
Definition: The Astrophyzix Risk Index (ARI) is a non-official, heuristic scoring system developed by Astrophyzix for educational visualisation of Near-Earth Object (NEO) close approaches.
Important: ARI is not affiliated with, equivalent to, or a substitute for the Palermo Scale or Torino Scale used by NASA and ESA for formal impact hazard assessment.
Purpose and Scope
The ARI is designed to provide an intuitive, real-time visual indicator of how dynamically "noteworthy" a Near-Earth Object is during close approach monitoring. It is not a probabilistic impact model and does not quantify collision likelihood.
- Provides a comparative visual score between objects in a live dataset
- Highlights proximity, velocity, and size contributions
- Augments — but does not replace — official planetary defence frameworks
ARI operates exclusively as a deterministic scoring heuristic applied to live orbital data from NASA's Center for Near-Earth Object Studies (CNEOS).
Scoring Model (0–100 Points)
The ARI score is constructed from four components, each representing a physically meaningful but simplified contributor to observational relevance.
1. Miss Distance (0–40 points)
Miss distance is expressed in Lunar Distances (LD), where 1 LD = 384,400 km.
Function:
ARIdistance = 40 × e(-0.1386 × missLD)
- Exponential decay model
- Half-life ≈ 5 LD
- Strong weighting toward close approaches
This formulation ensures that objects passing extremely close to Earth dominate the score, while distant objects rapidly lose influence.
---2. Relative Velocity (0–20 points)
Function:
ARIvelocity = min(20, 10 × log10(speed km/s))
- Logarithmic scaling prevents overweighting extreme velocities
- Reflects impact energy potential, not probability
Reference Values:
- ~5 km/s → ~7 points
- ~15 km/s → ~11.8 points
- ~30 km/s → ~14.8 points
3. Estimated Diameter (0–20 points)
Function:
ARIsize = min(20, diameter (m) × 0.05)
- Linear scaling capped at 20 points
- Ensures large objects remain significant without dominating the index
4. NASA PHA Designation Bonus (+18 points)
- Applied if object is classified as Potentially Hazardous Asteroid (PHA)
- PHA criteria: MOID ≤ 0.05 AU and diameter ≥ ~140 m
Adjustment rationale: The bonus was reduced from 30 to 18 points in ARI v2 to avoid double-counting, as PHA classification already encodes proximity and size thresholds.
Final Score Composition
ARI Total = Distance + Velocity + Size + PHA Bonus
- Maximum theoretical score: 98–100 (depending on parameter saturation)
- Typical operational range: 5–60
Interpretation Guide
- 0–10: Routine distant objects
- 10–25: Moderate observational interest
- 25–50: Close approach with notable parameters
- 50–75: High-interest object (close + fast and/or large)
- 75+: Exceptional observational case (rare)
These categories are descriptive only and do not imply impact risk.
Data Sources and Update Model
- Primary data: NASA CNEOS NeoWs API
- Orbital parameters derived from JPL Small-Body Database
- Miss distance converted to Lunar Distances (LD)
ARI scores are:
- Recalculated on every data load
- Not stored as persistent records
- Not used for forecasting or prediction
Scientific Limitations
The ARI intentionally excludes several critical parameters used in professional planetary defence analysis:
- Orbital covariance and uncertainty ellipses
- Observation arc length and quality
- Non-gravitational perturbations (e.g. Yarkovsky effect)
- Full n-body gravitational modelling
- Impact probability calculations
As such, ARI must be understood strictly as a visualisation tool, not a hazard assessment model.
ARI vs Official Impact Hazard Scales
This panel provides a structured comparison between the Astrophyzix Risk Index (ARI) and the internationally recognised Torino Scale and Palermo Technical Impact Hazard Scale. These systems serve fundamentally different purposes and must not be interpreted interchangeably.
| Parameter | ARI (Astrophyzix) | Torino Scale | Palermo Scale |
|---|---|---|---|
| Primary Function | Visual scoring of close approach significance | Public hazard communication | Scientific risk comparison metric |
| Scale Range | 0 – 100 | 0 – 10 (integer) | Logarithmic (negative to positive) |
| Represents Impact Probability? | No | Yes | Yes |
| Includes Orbital Uncertainty | No | Yes | Yes |
| Data Inputs | Distance, velocity, size, PHA flag | Impact probability + kinetic energy | Probability vs background hazard |
| Time Dependency | Real-time snapshot | Dynamic as observations improve | Strongly time-dependent |
| Typical Use Case | Live observatory dashboards | Public alerts & communication | Professional risk analysis |
| Authority | Astrophyzix (non-official) | NASA / ESA | NASA / ESA |
Interpretation Overlay
Key Distinction:
- ARI answers: "How dynamically notable is this close approach?"
- Torino Scale answers: "Should the public be concerned?"
- Palermo Scale answers: "How does this risk compare to the background hazard?"
Critical Disclaimer
High ARI values do not imply impact risk. It is entirely possible for an object to register a high ARI score due to close proximity and large size while having a Torino Scale rating of 0 and a negative Palermo value, indicating no credible threat.
Users must rely on NASA and ESA official scales for any interpretation of impact probability or hazard.
Optional UI Hook (Dynamic Badge)
Example Mapping Logic (Display Only):
- ARI 0–10 → "Routine Object"
- ARI 10–25 → "Moderate Interest"
- ARI 25–50 → "Close Approach Event"
- ARI 50+ → "High-Interest Object"
These labels are visual descriptors only and should never be presented alongside Torino values as equivalent classifications.
Relationship to Official Scales
For formal risk evaluation, refer to:
- Torino Scale — public communication of impact hazard
- Palermo Technical Impact Hazard Scale — logarithmic risk comparison used by specialists
ARI operates independently and serves a fundamentally different purpose: data interpretation and engagement, not risk quantification.
Versioning
- ARI v2 (Current)
- Logarithmic velocity scaling introduced
- PHA bonus reduced to mitigate parameter overlap
Institutional Statement
The Astrophyzix Risk Index (ARI) is developed and maintained by the Astrophyzix CNEO Observatory, a public-facing scientific division of Astrophyzix.org.
All ARI outputs are intended for educational, analytical, and visualisation purposes only and must not be interpreted as predictive or authoritative planetary defence metrics.