Observations of their composition are diagnostic of the environment during their formation. Phenomena to be studied are bare cometary nuclei and onset of activity at large heliocentric distances and gas and dust emissions in the inner solar system.
Active comets have high proper motion.
They are tracked in the solar system objects mode. No ephemeris are given here. The astrometric observation of the target objects shortly before launch and during the ISO operation should be used for ephemeris improvement. The estimation of the infrared flux of comets is a most difficult task. Data is only available for relatively bright comets.