As of 2020, we know of more than 2,000 trans-neptunian objects (TNOs). How has this number evolved over time?

It's pretty easy to find a chart that shows the number of exoplanets discovered per year, but I haven't found a similar one for TNOs.


1 Answer 1


For this, I'll point you to the IAU's List of Transneptunian Objects. That page provides a table of every known TNO along with all sorts of data about each TNO, including date of discovery. You could very easily determine how the rate of discovery has changed over time.

As a related resource, there is the Wikipedia page List of unnumbered trans-Neptunian objects which actually pulls from that IAU source. On that page, they did the hard work of plotting up the TNOs discovered per year and the graph is reproduced below.

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Just to add some additional context, there's a large spike around 2013-2015 which appears to be a confluence of surveys that kicked off around that time period and found many new TNOs, including

  • OSSOS which observed from 2013-2017 looking for TNOs specifically,
  • the Dark Energy Survey which observed from 2013 onwards (note, this survey only found TNOs incidentally, that was not their focus), and
  • Pan-STARRS which is a collaboration looking for variable objects in the sky (which TNOs certainly are). This survey officially started in 2010, but they didn't really hit their stride until around 2013.

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