The search for extraterrestrial intelligence hasn’t found anything yet but it has contributed significantly to astronomy. Breakthrough Listen, an initiative to look for intelligent life elsewhere in the universe, has now published a catalog called Exotica that's comprised of 737 objects, representing “one of everything” there is in the observed universe.

The catalog is a reference guide for what’s out there. If we are to discover intelligent life through the detection of techno-signatures, it is important to have deep knowledge of all the cosmic archetypes.

“Many discoveries in astronomy were not planned,” lead author of the new catalog, Dr Brian Lacki, said in a statement. “Sometimes a major new discovery was missed when nobody was looking in the right place, because they believed nothing could be found there. This happened with exoplanets, which might have been detected before the 1990s if astronomers looked for solar systems very different than ours. Are we looking in the wrong places for technosignatures? The Exotica catalog will help us answer that question.” 

“The catalog is not just limited to SETI, though. My hope is that any program with a new capability may use the Exotica catalog as a shakedown cruise around the Universe.”

The Exotica catalog, which can be perused here, divides the objects into four categories. First, there are the prototypes, or celestial objects: planets, moons, galaxies, and stars. The second group contains the superlatives, essentially objects whose extreme properties make them stand out. This class is for the hottest planet, the most distant quasar, the fastest pulsar, the heaviest black hole, etc.

The third is for the anomalies. In the last few years alone, there have been a couple of intriguing examples such as the Boyajian’s Star, whose brightness has changed dramatically and erratically, as well as ‘Oumuamua, the first interstellar object. This sample is subdivided into six classes, as they are exciting targets for SETI research. The final group is a control sample that should not lead to any discoveries. They are objects that were once considered anomalous or noteworthy but turned out not to be so.

Breakthrough Listen plans to use 10 percent of its observing time (both in radio and optical) on these exotic objects to better understand the natural signals we can expect from the universe and possibly find some that are not.

“There are 737 objects in the total Exotica Catalog, which are sorted into different levels of priority. About a dozen sources will be observed with maximum priority and will include raw voltage data in multiple bands. Most will be low priority and will be observed as allowed by time,” the authors wrote in an accompanying paper. “We hope that the Exotica Catalog will prove useful to other efforts, both within SETI and outside it, in characterizing the whole panoply of objects in the known Universe.”