Astronomers are talking about some interesting anomalies they have found on some 70-year-old photographic plates.
Scientists are interested in so-called transients, dots of light that appear on one photo and then disappear on identically oriented photos taken days later. In these early pictures they have excluded meteors or asteroids as an explanation and as the photos were all taken pre-Sputnik, they could not be man-made objects.
A group of researchers are conducting the Vanishing and Appearing Sources during a Century of Observations (VASCO) project to look at these transient light sources.
Here is a paper: https://www.nature.com/articles/s41598-021-92162-7 that examined a nine point transient on red-sensitive photographic plates taken in 1950:
The authors of the paper conlude that after exluding known natural causes (such as meteors, airplaine strobes etc) there are two possible explanations:
- High energy contamination of the photographic plates by radioactive particles from atomic bomb testing.
- ‘Glints of light’ produced by a solar system satellite of artificial or natural origin.
In an interesting follow up paper you can read here: https://doi.org/10.1016/j.actaastro.2022.01.039, researchers propose that reviewing such pre-sattelite photographic plates could provide useful evidence in the search for extraterestrial intelligence (SETI).
They propose that such light glints could be produced by interstellar probes from other civilisations.
Since Earth’s civilisation have proposed a plan to send probes to another stellar system through Breakthrough Starshot, it is therefore reasonable to assume that other civilisation might also be motivated to explore our Solar System. Some of these probes could be in orbit around Earth or pass straight through the Solar System. Albeit continuing to be highly controversial, it has been proposed that the ’Oumuamua interstellar object is a space-craft, based on a number of its anomalous characteristics.
Finding an image with repeating glints along a straight line in a long-exposure image would support a reflected light signature from some form of artifical object. “A rocky surface such as that of an asteroid, has neither the shape or the necessary reflectivity to create the strong sub-second glints produced by an artificial object.”
Finally in this technical paper (not yet peer reviewed): https://arxiv.org/pdf/2204.06091.pdf , a group of researchers examine 83 instances of transients on early photos (including the 1950s photos mentioned above).
They filter these down to a shorlitst of 5 interesting objects taken between 1952 and 1954 and deduce the various reflective shapes that might produce such glinting patterns.
Of course, this is all just scientific speculation. And the veracity of the more technical aspects of these papers is well beyond me.
Even so…I cannot help but think it would be just SO cool if these old-school photographic plates had inadvertently captured the first recorded evidence of extraterrestrial visitation to our solar system.