# Exoplanet Biosignature Detector
The exoplanet biosignature detector is an interactive spectroscopy simulator for exploring how life-related gases might appear in the light filtered through a distant atmosphere. Instead of treating a single molecule as a yes-or-no answer, the tool asks you to align oxygen, methane, and ozone absorption features, then weighs the result against noise, water vapor, carbon dioxide, and host-star behavior.This is the central difficulty of biosignature science: oxygen can be exciting, methane can be exciting, and ozone can be exciting, but none of them is proof by itself. The most persuasive cases combine multiple gases, physical context, and a careful search for non-biological explanations. The simulator makes those tradeoffs visible in a compact lab-style interface.# How Transmission Spectroscopy Reveals Atmospheric Gases
When a planet crosses in front of its star, a tiny fraction of starlight passes through the planet atmosphere before reaching the telescope. Molecules absorb specific wavelengths, leaving narrow or broad dips in the measured spectrum. By comparing observed dips with laboratory line positions, astronomers can infer which gases may be present, although clouds, haze, temperature, stellar spots, and instrumental noise complicate the retrieval.# Oxygen, Methane, and Ozone as a Combined Signal
- Oxygen O2: on Earth, abundant oxygen is maintained by photosynthesis, but abiotic oxygen can accumulate under some planetary histories.
- Methane CH4: methane can come from biology, geology, or impacts. It becomes more suggestive when found with oxidizing gases.
- Ozone O3: ozone is a photochemical product of oxygen and can be easier to detect in some spectral ranges, but it is still an indirect clue.
- Water and CO2 context: water supports habitability, while carbon dioxide helps frame greenhouse state, photochemistry, and false-positive scenarios.
# Why False Positives Matter
A high oxygen score does not automatically mean biology. Water loss can leave oxygen behind, stellar ultraviolet radiation can split molecules, and low volcanic reducing gas output can allow oxygen to build up. Active M dwarfs are especially tricky because flares and photochemistry can reshape atmospheric composition. The false-positive readout rises when noise, star type, or atmospheric context make a biological explanation less secure.| Signal pattern | Interpretation | Caution |
|---|---|---|
| O2 only | Potential oxygen-rich atmosphere | Can be abiotic after water loss or unusual photochemistry |
| CH4 only | Possible reducing atmosphere or active geology | Methane alone is not a strong life claim |
| O2 plus CH4 | Chemical disequilibrium worth follow-up | Requires robust retrieval and contamination checks |
| O2 plus O3 plus water | More coherent Earth-like context | Clouds and stellar activity still matter |