搜尋星際嘧啶：收割的季節

Many complex organic molecules (COMs) found in interstellar clouds are prebiotically important and have essential functions in terrestrial biochemistry. Pyrimidine (c-C4H4N2), the building block of nucleic acid, is the unsubstituted ring analogue for three of the DNA and RNA bases: thymine, cytosine and uracil. Evidence for pyrimidine in space comes from the fact that they have been detected in meteorites and may be components of Comet Halley's CHON dust. Pyrimidine is thus a key interstellar molecule for astrochemistry and astrobiology. Although the formation of prebiotic molecules in extraterrestrial environment and their contribution to the origin of life remains unsettled, the connection between interstellar organic chemistry, meteoritic pyrimidines, and the emergence of life on early Earth would be strengthened by the discovery of pyrimidine. Our prior (sub)millimeter search in the Orion KL hot molecular core using the JCMT and SMA suggests possible detections of pyrimidine bandheads at 212.8 GHz and 342.3 GHz. A serendipitous search in ALMA Cycle-0 data discloses possible pyrimidine non-bandhead doublets near the 212-GHz bandhead. Given the fundamental importance of interstellar pyrimidine, we therefore observed nine most favorable pyrimidine bandheads and five strong low-J doublets in the Orion KL hot molecular core in ALMA Band 7 with the ALMA array. This interstellar pyrimidine project was proposed originally as a 2-year project. Although some positive results have been obtained with only 15 months of work on ALMA data analysis, due to the complexity of the project and the complicated nature of Orion KL, however, much more dedicated efforts are required. Only after a full analysis of the ALMA data can be completed, a firm detection of interstellar pyrimidine can be established. This is rather encouraging to all of us as we have never been so close to the finishing line before. This is truly an exciting moment and a time for the harvest. The success of our project not only will test the idea that grain-surface reactions lead to organic ring isomers, more importantly, a detection of pyrimidine in hot molecular cores will have fundamental implications for astrobiology.