Hundreds of new minor planets have just been discovered beyond the orbit of Neptune. How did astronomers find so many trans-Neptunian objects at once?
Astronomers in the Dark Energy Survey (DES) report the discovery of 316 minor planets beyond Neptune. Of these, 139 were entirely unknown before this new study, while 245 were seen in earlier observations by the DES.
More than six years of data about the night sky was compiled during the Dark Energy Survey, compiling the most-detailed images of the southern sky ever assembled. This study did not aim to discover trans-Neptunian Objects (TNO’s), but the comprehensive maps produced by DES turned out to be ideal at finding small bodies beyond the orbit of Neptune.
On April 7, I will interview Dr. Pedro Bernardinelli of The University of Pennsylvania, lead researcher on this study, on the Astronomy News with the Cosmic Companion podcast.
“The number of TNOs you can find depends on how much of the sky you look at and what’s the faintest thing you can find,” says Gary Bernstein of the University of Pennsylvania.
It’s Like a Giant Game of Connect the Dots
At first, the raw data consisted of seven billion dots — where the search picked up an object. Any objects which were in the same place for more than one night (galaxies, stars, etc.) were then removed from the dataset, lowering the number of TNO candidates to 22 million targets. These were then examined for those appearing as pairs or triplets of images, suggesting regular movement, like what would be expected when looking at a TNO. These candidates were further whittled down to just those which were seen on six or more nights.
“We have this list of candidates, and then we have to make sure that our candidates are actually real things,” Pedro Bernardinelli of the University of Pennsylvania explains.
Dedicated searches for TNO’s often photograph objects once every hour or two, making detection of movement more apparent that looking at images taken less frequently.
Bernardinelli developed a new stacking system, allowing researchers to better determine which signals represented actual TNO’s, and which were false signals. The system was tested on known TNO’s, as well as purposely-created false signals, and the tests proved accurate.
Searching the Darkness
The best-known TNO is the dwarf planet Pluto, discovered in 1930, and reclassified as a dwarf planet in 2006. This discovery of 300 new minor planets adds to the 3,000 similar objects known in the frozen depths of our solar system. These objects revolve around the Sun at distances between 30 and 90 times greater than the space between Earth and our parent star (Pluto orbits roughly 40 times as distant).
Future research will continue to examine the entire dataset from DES, with a lower threshold for initial testing. Researchers believe this could result in the detection of as many as 500 previously-unknown minor planets beyond Neptune.
In addition to this remarkable collection of discoveries, this new study also outlines a new means of searching for similar trans-Neptunian objects.
As an example, many of the techniques used in this study could also be employed by astronomers at other telescopes, including the Vera C. Rubin observatory, ready to map the entire southern sky, including objects too dim to be seen in this most recent investigation of the outer solar system.
Such studies will allow astronomers to measure objects beyond Neptune, and map their origins. Researchers know that TNO’s that form close to the Sun have different properties than those that formed in the outer Solar System, and they may have different colors.
During the coming years, astronomers may even be able to learn more about a hypothetical ninth planet which may orbit in the cold, dark, reaches of the outer Solar System.
Analysis of this study was published in The Astrophysical Journal Supplement Series.
James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.
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