A research team led by the Shanghai Astronomical Observatory of the Chinese Academy of Sciences conducted multi-wavelength radio observations of the returning Halley-type comet 12P/Pons-Brooks using the Tianma Radio Telescope. This comet science study successfully measured the water production rate of the comet during its outburst activity and achieved the farthest-ever radio detection of ammonia molecules in a Halley-type comet. The related research results have been published in the journal Astronomy & Astrophysics.
Comets contain various icy substances, with histories tracing back to the early formation of the solar system. When comets approach the Sun, solar radiation heats these ices, causing sublimation and triggering cometary activity. Detecting the composition of these volatile materials helps understand the chemical conditions and thermal history of the primordial solar system.
Comet 12P is a Halley-type comet with an orbital period of about 71 years. During its 2024 return, the comet exhibited frequent outburst activity. From late 2023 to early 2024, researchers carried out a series of multi-wavelength radio observations of Comet 12P using the Tianma Radio Telescope. In the L-band, the team detected hydroxyl lines originating from the photodissociation of water vapor. Through radiative transfer modeling, they calculated the water production rate and gas expansion velocity of the comet before and after several outbursts.
In K-band observations, the researchers detected ammonia molecules at radio wavelengths with 3σ confidence. This is the farthest radio detection of ammonia molecules in a comet to date, marking an important advancement in comet science research. The observational data show that at a distance of about 1 AU from the Sun, Comet 12P had a water release rate exceeding 5 tons per second, with an activity level higher than most short-period comets. During outbursts, its water production rate approximately doubled.
The detected ammonia relative abundance is relatively high. Given ammonia's low sublimation temperature, for short-period comets like 12P that may have depleted more volatile species such as carbon monoxide and carbon dioxide, the high abundance of ammonia and its distribution characteristics within the nucleus may provide clues to explain the comet's frequent outburst mechanisms. This multi-wavelength radio observation study reveals the evolution of material release during the outbursts of Comet 12P, accumulating new observational evidence for understanding cometary activity mechanisms and their internal chemical conditions.
