Citizen Science: You could find Planet 9

This is your chance to enter the history books as the discoverer of a ninth planet that astronomers believe is hiding in the outer reaches of our solar system. A space telescope has scanned the skies and may have already seen it, but finding it in the huge data set is proving difficult. So astronomers are asking the public for help.

Planet 9, as it is commonly known, is a hypothetical planet, a bit smaller than the size of Neptune, believed to exist beyond Pluto, on a huge orbit that takes it 10,000 to 20,000 years to circle the sun once. While planets beyond Neptune have been postulated for decades, the evidence for this one lies in the strange orbits of several large snowballs that also exist in the region called the Kuiper Belt. (Pluto is actually one of these, which is why it is no longer called a planet).

Some of these snowballs are aligned in a particular way that suggests the gravitational pull from a large object out there arranged them in that order. It also suggests which areas of the sky the planet would likely be found.

• How science decides if something is a planet

Even though astronomers know generally where to look for Planet 9, finding it turns out to be a difficult task. An object that far from the sun will be very dim and hard to see, and its orbit is so large, the planet will move very slowly among the stars. (The word planet means "wanderer.") But scientists at NASA think the planet may already be hiding in data from a space telescope called WISE, Wide Field Infrared Survey Explorer that has been mapping the entire sky since 2009. Cameras on this telescope see heat, which is one of the best ways to look for dim objects.

Human eye is the best detector

The problem is, the cameras have picked up all kinds of objects, including stars, comets, asteroids, Kuiper Belt Objects, along with "noise" and flashes that are not real objects at all, just artifacts of the camera system. Sifting through this huge data set has proven to be too onerous for computer algorithms that normally spot moving objects. It turns out the human eye is the best detector, so NASA is crowdsourcing for help. 

The program is called Backyard Worlds, and is a collaboration between NASA, UC Berkeley, the American Museum of Natural History in New York, Arizona State University, the Space Telescope Science Institute in Baltimore, and Zooniverse, a collaboration of scientists, software developers and educators who collectively develop and manage citizen science projects on the Internet.

Visitors to the site are given raw data photos of an area of the sky that was photographed on two or three different dates. By flipping back and forth between the photos, anything that changes position will show up. Objects that are close, such as asteroids will move a lot, those farther away, less so. 

Lots of moving objects

The problem is, there are lots of moving objects out there, and most of them are already known, so when you think you have found something, you have to check a catalogue to see if someone beat you to it.

This flipping back and forth between photos technique is how Clyde Tombaugh discovered Pluto in 1930. He used a device called a blink comparator, which allowed him to examine thousands of photographic plates taken by telescopes in search of a 9th planet. It took him thousands of hours of this tedious work to find the tiny world.

NASA doesn't say whether the person who finds Planet 9 gets to name it. Even if you are the lucky one to spot it, you will go down in history as the discoverer, but it won't be named after you. So don't expect the new world to be named George, Betty or Bob. Traditionally planets have been named after mythological figures, such as Mars, the Roman god of war, or Neptune, god of the sea. You may be able to suggest a name, but the ultimate decision for naming all astronomical objects goes to the International Astronomical Union.

Discovering new planets has always been left to those who built their own telescopes, such as William Herschel, who discovered Uranus with his giant reflectors, or those with access to large telescopes operated by universities.

This is the first time that anyone with access to the internet can join the ranks of Columbus, Magellan and Galileo on a voyage of discovery to find new worlds.

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