What makes tnhis interesting is that it is resolution driven, As that improves, the chances of discovery improves.
however, I am unconvinced we will remain lit up to the extent we are today.
Long term, we will tend to shelter underground for most of our infrastructure. The risks are real enough and the undergound posture is also cheap enough to use.
Searching for Artificial Light Sources in the Solar System Based on the Loeb-Turner Test
https://avi-loeb.medium.com/searching-for-artificial-light-sources-in-the-solar-system-based-on-the-loeb-turner-test-452722c2ac46?
In 2010, I attended the official inauguration conference of a new campus of New-York University in Abu Dhabi, along with my Princeton colleague, Ed Turner. As we were touring Abu Dhabi and Dubai, the tour guide bragged that Dubai’s city lights at night time can be seen all the way from the Moon.
Ed and I were instantly inspired to consider the question: How far away can city lights be observed in the Solar System? In particular, we Googled Tokyo which had its official luminosity listed online, and calculated during some of the boring talks at the conference that Tokyo would detectable at the distance of Pluto by deep exposures of the Hubble Space Telescope. In other words, if a city like Tokyo existed on Pluto, then the Hubble Space Telescope could detect its lights!
But detecting a source of light from an unknown object is insufficient. How can we infer that the light originates from an artificial source rather than the reflection of sunlight from a rock or iceberg? In principle, this can be done by taking a spectrum, namely studying the intensity of the light source as a function of wavelength. Artificial light would typically have a different spectrum than sunlight. However, it is challenging to obtain a spectrum of a faint source of light. Is there another way?
A self-luminous source behaves like a light bulb. It fades inversely with distance squared. However, an object illuminated by a lamppost fades inversely with distance to the fourth power. Ed and I reckoned: all we need to do is measure the change in the source brightness as a function of its distance from the Sun in order to infer whether it reflects sunlight or produces its own light. This was the idea conveyed in a paper that we published in 2012 here.
A few years earlier, I published another original idea here with Ed Turner and Amaya Moro-Martin, where we were first to predict quantitatively that interstellar objects could be detected with survey telescopes, like the NSF-DOE Rubin Observatory. This idea is coming to fruition right now, although the first paper to suggest it is forgotten. This appears to be the fate of pioneering ideas ahead of their time. In 1952, the astronomer Otto Struve suggested in a paper published here the practical methods for discovering Jupiter-mass planets in close-proximity to Sun-like stars. His idea was ignored for 43 years until the first discovery was reported here in 1995 by Michel Mayor and Didier Queloz who won the Nobel Prize for it. Their discovery paper does not reference Struve’s paper. Why is science so inefficient?
The application of the Loeb-Turner test to interstellar objects allows us to distinguish between natural interstellar rocks which reflect sunlight and technological objects which produce their own light. But a much larger population of objects is known to reside inside the Solar System. Have we actually checked whether all known objects beyond Neptune, the so-called trans-Neptunian objects, only reflect sunlight?
When Mike Brown from Caltech, who pioneered the discovery of trans-Neptunian objects, visited my Harvard office a decade ago, I asked him: Did you check whether their brightness declines as expected for the reflection of sunlight? Mike replied: “Why should I check? They are obviously just reflecting sunlight.” His response explains why Struve’s idea in 1952 did not translate to the discovery of a hot-Jupiter decades earlier than 1995. Observers assumed that they understood why Jupiter is far from the Sun and so they chose not to waste observing time searching for Jupiter-mass planets in close proximity to their host star. This led me to wonder: How many scientific discoveries end up as “unborn babies” because of prejudice?
And so today, my brilliant new postdoc, Omer Eldadi, completed a detailed paper in collaboration with me, studying all existing data on the brightness variation of trans-Neptunian objects with distance from the Sun (with the full paper accessible here). By applying the Loeb-Turner test to all objects, we have found that the current data available in the Minor Planet Center archive is of insufficient quality to conduct the test. Of all trans-Neptunian data bins, 53 consistent with reflected sunlight, 24 with self-luminous emission, and 109 appear anomalous. The anomalous bins exhibit slopes outside the expected range, consistent with uncorrected instrument calibration offsets rather than any particular physical mechanism. However, we find that the NSF-DOE Rubin Observatory’s ten-year survey will deliver uniform single-instrument calibration on a tenfold larger sample and resolve the Loeb-Turner test with a statistical confidence better than 10 standard deviations on hundreds of trans-Neptunian objects.
Here’s hoping that thanks to the NSF-DOE Rubin Observatory, we will be able to know within the coming years whether there are any spacecraft with city-scale lights within the Solar System.
In 2001, I also had the idea of detecting light on the night side of the nearest exoplanet, Proxima b, which happens to reside in the habitable zone of its host star, Proxima Centauri. The calculation I posted here with my student, Elisa Tabor, indicated that this might be possible, as long as there is an alien technological civilization on this planet.
No comments:
Post a Comment