article image

Are undiscovered planets hiding deep in the Solar System?

Elizabeth Howell, News Writer
Jan 18, 2015, 19:20 UTC

Sen—Against the findings of other planetary scientists, a new study suggests that there could be "unknown planets" lurking in the Solar System beyond Neptune.

The authors say that at least two large bodies could be altering the orbits and distribution of smaller objects further out in the Solar System than the ice-giant planet.

While the researchers argue that the orbits of these objects should be distributed randomly, they tracked down at least a dozen that strayed from what they said were established parameters: a distance of at least 150 Earth-Sun distances and an orbital inclination of almost 0°, among other things. 

"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution ... and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto," stated co-author Carlos de la Fuente Marcos, a scientist at the Complutense University of Madrid. It was published in the Monthly Notices of the Royal Astronomical Society Letters.

But based on studies from NASA and an established dwarf-planet hunter, there should be no more large objects lurking at the edge of our Solar System.

The California Institute of Technology's Mike Brown delights in the Twitter handle @plutokiller, a name that he chose because the small worlds he discovered about a decade ago led scientists to realize there were other bodies similar to Pluto in the outer Solar System. The International Astronomical Union made a controversial vote in 2006 to call Pluto and similar worlds "dwarf planets", demoting it from full planet status.

"Through this last decade, one thing has always nagged at me: no survey for new objects in the Solar System is going to be 100 per cent effective, Brown wrote in a blog post on 5 January. "If a bright undiscovered planet happened to be lined up perfectly with a random background star at the moment I had looked, I would never have seen a planet."

This spurred Brown and collaborators to use seven years of data from the Catalina Sky Survey to examine the entire sky, and write a paper that will soon be released in the Astronomical Journal.

"There is virtually no chance that anything bright would be able to escape our grasp, because we looked again and again and again and again at each spot in the sky making it impossible for something to be temporarily hiding," Brown added.

A separate study from NASA in 2014 determined it was unlikely that objects the size of Jupiter or Saturn are at the fringes of the Solar System. Using data from the space-based Wide-Field Infrared Survey Explorer, NASA said there is no Saturn-sized object (or larger) out to about 10,000 astronomical units, and nothing bigger than Jupiter to about 26,000 astronomical units.

The survey was based on two full scans of the sky in 2010 and 2011, which found 750 million stars, galaxies and asteroids. NASA has also released data from the survey online for all to search for anything that might have been moving in that time.

"The outer Solar System probably does not contain a large gas giant planet, or a small, companion star," stated Kevin Luhman of Penn State University in Pennsylvania, an author of an Astrophysical Journal paper that contained the results.