Source: https://guthlabs.ai/docs/instruments/exoplanet-transit-depth/mechanism/

instrument mechanism / verified-clean

# Exoplanet Transit Depth mechanism

The inspectable method record for Exoplanet Transit Depth, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The forward formula is correct under the stated uniform-disk approximation, but the instrument claims reverse radius inference without specifying its inverse formula or depth-unit interface. The honest label should also disclose the opaque-planet, non-grazing, no-third-light assumptions; uniform stellar brightness alone is not sufficient to characterize all limitations.

- The forward formula ΔF/F = (Rp/Rs)^2 is standard for a uniform stellar disk when the planet fully occults a region of the stellar disk and there is no contaminating or additional light.

- The claimed reverse calculation is underspecified: the required inverse formula Rp = Rs × sqrt(ΔF/F) is not included.

- The specification does not state whether the supplied depth is a fraction, percentage, or ppm, nor the required conversion between these representations.

- For grazing transits, the simple area-ratio formula is not generally valid because only part of the planet may overlap the stellar disk.

## Units and conventions

- Rp and Rs must be expressed in the same length units before forming Rp/Rs; kilometers, meters, or consistent radius units are acceptable.

- A fractional depth d converts to percent as 100d and to ppm as 1,000,000d.

- A depth supplied in ppm must be converted as d = depth_ppm / 1,000,000 before applying the inverse formula.

- For the inverse calculation, Rp = Rs × sqrt(d), with d dimensionless.

- If nominal IAU radii are used, the specific nominal constants and their units must be exposed consistently; this validation uses 695700 km for the nominal solar radius where applicable.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "planet_radius_km": 69570,
    "star_radius_km": 695700
  },
  "expected_outputs": {
    "depth_fraction": 0.01,
    "depth_percent": 1,
    "depth_ppm": 10000
  },
  "working": "1. Rp/Rs = 69570 / 695700 = 0.1. 2. ΔF/F = (0.1)^2 = 0.01. 3. Percent depth = 0.01 × 100 = 1%. 4. Ppm depth = 0.01 × 1000000 = 10000 ppm."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A zero star radius produces an undefined division, and an oversized planet produces a raw depth above 100% unless the instrument validates or caps the result. Negative-radius input also reveals an unguarded sign-convention hazard.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/exoplanet-transit-depth/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/exoplanet-transit-depth/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/exoplanet-transit-depth/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`