FAST Observations of Four Comets to Search for the Molecular Line Emissions between 1.0 and 1.5 GHz Frequencies

TL;DR

This study used FAST to search for molecular emissions in four comets within 1.0-1.5 GHz but found no clear signals, highlighting the challenges of detecting such lines at low frequencies and suggesting improvements for future observations.

Contribution

First systematic search for molecular lines in comets at low radio frequencies using FAST, demonstrating detection challenges and guiding future observational strategies.

Findings

No molecular emissions detected in the 1.0-1.5 GHz range.

Detection of complex organic molecules at high frequencies remains challenging at low frequencies.

Future improvements could enhance the detectability of weak molecular lines.

Abstract

We used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to search for the molecular emissions in the L-band between 1.0 and 1.5 GHz toward four comets, C/2020 F3 (NEOWISE), C/2020 R4 (ATLAS), C/2021 A1 (Leonard), and 67P/Churyumov-Gerasimenko during or after their perihelion passages. Thousands of molecular transition lines fall in this low-frequency range, many attributed to complex organic or prebiotic molecules. We conducted a blind search for the possible molecular lines in this frequency range in those comets and could not identify clear signals of molecular emissions in the data. Although several molecules have been detected at high frequencies of great than 100 GHz in comets, our results confirm that it is challenging to detect molecular transitions in the L-band frequency ranges. The non-detection of L-band molecular lines in the cometary environment could rule out the possibility of unusually strong lines, which could be caused by the masers or non-LTE effects. Although the line strengths are predicted to be weak, for FAST, using the ultra-wide bandwidth receiver and improving the radio frequency interference environments would enhance the detectability of those molecular transitions at low frequencies in the future.