Infrared spectrum of an Earth-like world. This spectrum shows absorption troughs where molecules in an atmosphere have absorbed infrared radiation. Molecular models are seen for four of the troughs. Water (H2O) forms two broad bands at right and at left. Ozone (O3) absorbs at around 10 micrometres wavelength, while a large absorption is seen for carbon dioxide (CO2, a strong infrared absorber) at 15 micrometres. Infrared radiation can indicate the temperature of the planet. This spectrum shows an Earth-like temperature of about 300 Kelvin (K). Infrared space telescopes will record such spectra from planets orbiting other stars, looking for this spectral fingerprint that indicates life.