Backyard Worlds: Planet 9

We need your help searching for new objects at the edges of our solar system. In this project, we'll ask you to help us distinguish real celestial objects from image artifacts in data from NASA's Wide-field Infrared Survey Explorer (WISE) mission. The real objects are brown dwarfs and low-mass stars, the Sun's nearest neighbors. You may find an object closer than Proxima Centauri (the closest star to the Sun) or even discover the Sun's hypothesized ninth planet, which models suggest might appear in these images.

What are the Sun's nearest neighbors? You may have heard of Proxima Centauri, the star nearest the sun. But most of the Sun's nearest neighbors are not stars, but brown dwarfs, balls of gas too big to be called planets but too small to be called stars. We've learned by extrapolating from recent discoveries that there is likely a hidden population of brown dwarfs floating by the solar system. This population contains the coldest known brown dwarfs, known as "Y dwarfs," which are very similar to planets that just don't orbit other stars. Together, we will try to find these rogue worlds to better understand how both stars and planets form.

How Many Planets Are in the Solar System? So far, we know of eight planets orbiting the Sun, but there could be more out there to find. Patterns in the orbits of the comet-like objects in the outer solar system (the Kuiper belt) suggest that there is a ninth planet orbiting beyond Neptune. Models of this planet imply that we may have already imaged it with NASA's WISE telescope, and simply not recognized it. Together, we're going to look through the data from this telescope in a powerful new way to try to spot it.

Here is a diagram showing some of the orbits of some Kuiper Belt Objects (L91, FT28, SR349 etc.) that point to the presence of planet nine. It also shows a possible orbit for planet nine. Source: (Diagram) G. Grullón/Science; (Data) Scott Sheppard/Michele Bannister.

The WISE All-Sky Infrared Survey We will be scanning the Solar System's frontier using infrared images from NASA's Wide-field Infrared Survey Explorer (WISE) telescope. While ordinary stars and the familiar eight planets shine brightly at visible wavelengths, brown dwarfs glow mainly in the infrared. Planet nine should also glow in the infrared.

Here at Backyard Worlds: Planet 9, you'll look at false-color images that combine two WISE bands that would be impossible for the naked eye to see. Blue represents light with a wavelength of about 3.4 microns; red represents light with a wavelength of about 4.6 microns. We've pre-processed those infrared images from WISE using the unWISE pipeline, combining images that span about 5 years, including images from NEOWISE (the asteroid-hunting portion of the WISE mission). Subtracting images taken years apart creates negative images, which makes faster moving objects look like "movers" and slower moving objects look like "dipoles". When you find these objects of interest, you'll mark them with a marking tool.

Why This Search Requires Human Eyes
While it's possible to process the data to find moving points of light, we can't get rid of all the noise. Spiky images of stars, especially variable stars, are everywhere. Worse, are the optical ghosts, blurry blobs of light that have been scattered around inside WISE's instruments. These can hop back and forth, or even change color. These artifacts can easily fool our image processing software. But with your powerful human eyes, you can help us recognize real objects of interest that move among these artifacts. You'll be able to tell what objects are real by the way they move around differently from the artifacts.

Following in the Footsteps of Clyde Tombaugh In 1930, Clyde Tombaugh discovered Pluto as a small dot on a pair of photographic plates. He used a device called a "blink comparator" to search for objects that moved from one plate to the next. (At the time, Pluto was considered to be a planet.) Here at Backyard Worlds: Planet 9, we are using a very similar technique.

Tombaugh spent about 7,000 hours staring into the blink comparator; it takes hard work and persistence to discover a new planet! But those were the days before the internet. At Backyard Worlds: Planet 9, we're using modern technology to make searching a little more fun. You'll work with our science team, a group of astrophysicists from NASA Goddard Space Flight Center, Berkeley, Arizona State, the American Museum of Natural History and the Space Telescope Science Institute. And you'll join citizen scientists around the world, whom you can interact with easily on the TALK network.

For more information about the science of brown dwarfs and Planet Nine, be sure to check out the FAQ. We hope you make a big discovery!

Thanks to NASA, which has funded this work through the Astrophysics Data Analysis Program and the Science Innovation Fund and the National Science Foundation, which has funded this research through the Astronomy and Astrophysics Research Grant.