In the vast expanse of the Solar System, a captivating question emerges: Can we discern artificial light sources from natural phenomena? This inquiry, sparked by a tour guide's boast in Abu Dhabi, led Avi Loeb and his Princeton colleague, Ed Turner, to explore the detectability of city lights from distant planets. Their innovative approach, the Loeb-Turner test, involves measuring the brightness of an object as it moves closer to or farther from the Sun, with the aim of distinguishing between objects that reflect sunlight and those that emit their own light. This method, however, is not without its challenges, particularly when dealing with faint sources of light.
Loeb's interest in this topic extends beyond the Solar System. He and Turner published a paper in 2012, suggesting that measuring the brightness change of an object as it moves closer to or farther from the Sun could help determine if it reflects sunlight or produces its own light. This idea builds upon Loeb's earlier work with Turner and Amaya Moro-Martin, where they predicted the detection of interstellar objects with survey telescopes, a concept now being realized with the NSF-DOE Rubin Observatory.
The author reflects on the inefficiencies in scientific discovery, drawing parallels to Otto Struve's 1952 paper on Jupiter-mass planets, which was ignored for decades until its rediscovery in 1995. This led Loeb to question the role of prejudice in scientific progress, suggesting that many discoveries may be 'unborn' due to preconceived notions. He highlights the case of trans-Neptunian objects, where observers assumed they were reflecting sunlight, leading to a lack of further investigation.
Loeb's recent collaboration with postdoc Omer Eldadi examined the brightness variation of trans-Neptunian objects using the Loeb-Turner test. The study revealed that the current data is insufficient for conclusive results, with 53 objects consistent with reflected sunlight, 24 with self-luminous emission, and 109 appearing anomalous. The anomalies are attributed to instrument calibration issues rather than physical mechanisms. However, the NSF-DOE Rubin Observatory's upcoming survey is expected to provide more accurate data, enabling a more definitive application of the Loeb-Turner test.
Looking ahead, Loeb's work continues to explore the detectability of artificial light sources in the Solar System, including the possibility of city-scale lights on spacecraft. He also considers the detection of light on the night side of exoplanets, such as Proxima b, in the habitable zone of its host star, Proxima Centauri. Loeb's research and ideas challenge conventional thinking, pushing the boundaries of our understanding of the universe and the potential for extraterrestrial life.
