Through laboratory experiments and observational studies, researchers have discovered that a comet previously thought to be inactive is still active1. Since 2006, each time the comet 49P/Arend-Rigaux has come close to the Sun, it has been gradually losing surface material, exposing the volatile layers and amorphous water ice beneath.
This finding may lead to the discovery of other molecules in water ice, which could provide the basic raw materials for initiating life on Earth-like planets.
Low-activity comets such as Arend-Rigaux are of interest because they are rich in complex molecules that harbour the seeds of life.
To better understand this comet, the researchers analysed data from telescopic observations and low-temperature simulation studies. Laboratory simulations revealed that water ice is amorphous at low temperatures but that it becomes crystalline above 130 kelvin.
Images from telescopes showed that the comet has been losing surface material since 2006, exposing amorphous water ice. The Sun’s energetic photons and heating trigger a phase transition in the surface ice, causing it to change from amorphous to crystalline. This happened during the comet’s nearest approach to the Sun in 2011. The crystalline ice then changed back to amorphous ice as the comet moved away from the Sun.
The detection of amorphous ice on the comet suggests that other molecules that are known to play a major role in prebiotic chemistry could be embedded in the ice matrix, the researchers say.
