5.4.1 Hydrogen Ly-α emission by the atmosphere of planets (e.g. Venus, Jupiter)5.4.2 Study of Sungrazing comets5.4.2.1 Understand cometary properties and evolution by mapping the hydrogen Ly-α emission, proportional to the outgassing rate, along its trajectory close to the Sun5.4.2.2 Investigate the fragmentation of the cometary nucleus from the variation with the heliocentric distance of the outgassing rate and from the splitting of the cometary tail
