From Physics.org, more about the ongoing southern sky survey using the Atacama Cosmology Telescope in Chile found “about 3,500” candidate sources for “Planet Nine” :
“The astronomers scanned about 87% of the sky accessible from the Southern Hemisphere over a six year period, and then processed the millimeter images with a variety of techniques, including binning and stacking methods that might uncover faint sources but at the expense of losing positional information. Their search found many tentative candidate sources (about 3,500 of them) but none could be confirmed, and there were no statistically significant detections.
The scientists, however, were able to exclude with 95% confidence a Planet 9 with the above-estimated properties within the surveyed area, results that are generally consistent with other null searches for Planet 9. The results cover only about 10 to 20% of the possibilities, but other sensitive millimeter facilities are coming online and should be able to complete this search for Planet 9 as hypothesized. “
New Search Results for Planet 9
It's been six years since two astrophysics academics at Caltech asserted that Planet X must exist. Re-branding the fabled world as 'Planet 9', they presented compelling evidence to the world that objects in the outer solar system were being shepherded by a distant, but significant planetary object (1). This theoretical work led to an excited effort to find this undiscovered planet, involving several significant telescope arrays and even a popular citizen science project to help crunch the data (2). In the continuing absence of a direct observation, astrophysicists have passionately argued the merits of the case one way or another (3,4).
Finding this object is fraught with difficulties. There's no reliable treasure map to work with, and the projected brightness of this object is, well, not very bright at all. Planet X may well evade the most sensitive visible light searches available, so searches using other bands on the electromagnetic spectrum become important. For instance, the infrared space telescope WISE had a good hunt around for brown dwarfs in our neighbourhood, and was able to constrain the size and distance of a potential massive Planet X object considerably (5). Another long-term effort has involved a sky search in the millimetre band, using the Atacama Cosmology Telescope in Chile. This hunt has recently published its findings based upon 7 years of ACT data (6). On the face of it, they aren't particularly encouraging - although the search itself only covered about 10-20% of the possible options for Planet 9:
"The astronomers scanned about 87% of the sky accessible from the southern hemisphere over a six year period, and then processed the millimeter images with a variety of techniques including binning and stacking methods that might uncover faint sources but at the expense of losing positional information. Their search found many tentative candidate sources (about 3500 of them) but none could be confirmed, and there were no statistically significant detections." (7)
It's kind of interesting just how many candidate objects popped out of this data. On top of the 3,500 Planet 9-like candidate objects, their paper indicates a further 35,000 'general category' objects. Given the cautious approach applied by astronomers for what is quite a contentious field of study, that's quite a positive. Other research groups based in Chile have been caught out before (8), so no one is going to stick their neck out now unless they're absolutely certain. So, I wonder what happens with the read-out of those Planet 9-like 3500 candidate objects (6)? Does it get passed around in the astrophysical community for others to investigate? Or does it get filed away quietly?
The team 'manually inspected' the top 100 of these candidates which "led to 3 Planet 9–like and 17 general candidates being cut" - likely transient events possibly connected with flaring of background stars (9). They considered the rest not to be statistically significant enough to merit further inspection. Yet, they inject many caveats in their discussion; for example, indicating that a Planet 9 object nearing aphelion might have fallen outside the threshold for their detection (6). In which case, one of those many statistically insignificant detections might be the one, just at the very far end of the range of their search. If these blips are just lost in the cosmic noise, will we ever know for sure?
Written by Andy Lloyd, 21st March 2022
Article and references here: https://www.andylloyd.org/darkstarblog88.htm