Some astronomers think in our outer solar system there’s a giant, undiscovered world hiding and they call it (for obvious reasons) Planet Nine. Whether it exists, it could be 5-10 times the size of the Earth and orbit Sun hundreds of times farther away than Earth orbiting Sun. Now, a NASA citizen science project called Backyard Worlds: Planet 9 enlists volunteers to help find this hypothetical giant planet.

Ninth Planet, artist's concept

Related: Planet 9 might not exist, many astronomers now think

Image: an illustration of what Planet 9 might look like from an artist’s eye. Caltech/R. Hurt (IPAC)

Search the realm beyond Neptune for new brown dwarfs and planets

Scientists say “There’s still no substitute for the human eye when it comes to recognizing subtle motions in astronomical images.”

Volunteers, or the “citizen scientists” will check telescope images the same way the American astronomer Clyde Tombaugh (February 4, 1906 – January 17, 1997) found Pluto, the original “Planet 9” in 1930, now reclassified as a dwarf planet. In just six days after the project begins, volunteers have found over 100 brown dwarfs (see notes 1).

Users will search for objects that jump around as they look at multiple images of the sky taken at different times. Planet 9 (if exists) should look like a bouncing blue dot in the images. Brown dwarfs should be redder in appearance and move slower – because they are way farther away.

But, there’s no sign of Planet 9 so far.

Backyard Worlds: Planet 9. Subject 27596017
Users will search for objects that jump around as they look at multiple images such as Subject 27596017 of the sky taken at different times. They’ll look for bouncing dots.

About Backyard Worlds: Planet 9

From Backyard Worlds project website:

Is there a large planet at the fringes of our solar system awaiting discovery, a world that astronomers call Planet Nine? We’re looking for this planet and for new brown dwarfs in the backyard of the solar system using data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission. But we need your help! Finding these dim objects requires combing through the images by eye to distinguish moving celestial bodies from ghosts and other artifacts. There are too many images for us to search through by ourselves. So come join the search, and you might find a rogue world that’s nearer to the Sun than Proxima Centauri, or even the elusive Planet Nine.

Discovery of Pluto

In 1930, Clyde Tombaugh was working for the Lowell Observatory in Flagstaff, Arizona as a researcher. He was given the job to perform a systematic search for a trans-Neptunian planet (also called Planet X), which had been predicted by Percival Lowell (see notes 2) based on calculations performed by his student mathematician Elizabeth Williams (see notes 3) and the American astronomer William Pickering (February 15, 1858 – January 16, 1938).

Starting 6 April 1929, Tombaugh used the observatory’s 13-inch astrograph (see notes 4) to take photographs of the same section of sky several nights apart. He then used a blink comparator (see notes 5) to compare the different images. When he shifted between the two images, a moving object, such as a planet, would appear to jump from one position to another, while the more distant objects such as stars would appear stationary.

Tombaugh noticed such a moving object in his search, near the place predicted by Lowell, and subsequent observations showed it to have an orbit beyond that of Neptune. This ruled out classification as an asteroid, and they decided this was the ninth planet that Lowell had predicted. The discovery was made on Tuesday, February 18, 1930, using images taken in January 1930.

Clyde Tombaugh
The astronomer Clyde Tombaugh, discoverer of Pluto here shown with his homemade 9-inch telescope.


  1. A brown dwarf is a type of substellar object that has a mass between those of the heaviest gas giant planets and the least massive stars, i.e. about 13 to 75-80 times that of Jupiter (MJ), or about 2.5×1028 kg to 1.5×1029 kg.
  2. Percival Lawrence Lowell (March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars. He founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death.
  3. Elizabeth Langdon Williams (February 8, 1879, in Putnam, Connecticut – 1981 in Enfield, New Hampshire) was an American human-computer and astronomer whose work helped lead to the discovery of Pluto.
  4. An astrograph (or astrographic camera) is a telescope designed for the sole purpose of astrophotography.
  5. A blink comparator is a viewing device traditionally used by astronomers to discover variations between two different night sky images. It allows for fast switching from viewing one object to viewing the other, “blinking” back and forth between the two photographs taken at different times from the same region of the sky, while all the distant stars remained stationary. It allows the user to identify objects that have changed their positions in the night sky with greater ease.


M. Özgür Nevres

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