Hunting for Planet 9

Dr. Sarah Casewell describes the hunt for the mysterious Planet 9 in this blog post for the National Space Centre, and how a citizen science project called Backyard Worlds lets anyone join the search.

Is there a large planet lurking at the fringes of our Solar System awaiting discovery?

Artist’s impression of Planet Nine, with the Sun and Neptune’s orbit in the distance. Credit: nagualdesign, Tom Ruen, ESO

Ever since Pluto’s discovery in 1930 there have been questions about whether our Solar System could host another planet. Now peculiar patterns in the orbits of comet-like bodies out beyond the orbit of Neptune – trans-neptunian objects – seem to suggest there could be a large body, perhaps ten times the mass of Earth, shaping the patterns.

This large body, called Planet 9, would be very far from the Sun, and very cold, orbiting 600 times further away from the Sun than the Earth does.

Finding Planet 9 will probably require searching large areas of sky, and taking multiple pictures to look for faint moving objects. This is exactly what NASA’s Wide-field Infrared Survey Explorer mission (WISE) space mission does. It observes in the mid-infrared, and revisits parts of the sky, so in some cases we have many images spread over 6.5 years.

Now, with the internet we can spend a lot less time than that to discover objects within our solar neighbourhood. However, despite the image processing code we use, we still have artefacts in our images from variable stars, bright stars and other noise due to the cameras used.

This means that human eyes are still the best test of whether an object is really moving or not.

Backyard Worlds citizen science

This is where you can get involved.

Backyard Worlds: Planet 9 is a citizen science project that has created “flipbooks” of these images that anyone can look through to help flag moving objects. The dwarf planet Pluto was discovered via a very similar technique to this. Clyde Tombaugh used a device called a “blink comparator” to search for objects that moved between photographs of the night sky taken days apart. He spotted Pluto after about 7000 hours of searching!

By joining the Backyard Worlds citizen science project, you can help search for the mysterious Planet 9 from home. Working alongside professional astronomers to search images from NASA’s WISE database for nearby fast moving objects, you might discover a rogue world between us and Proxima Centuri – or even the elusive Planet 9.

So far, more than 150,000 participants in the Backyard Worlds projects have made over 5 million classifications of images from the WISE mission.  In fact, some of our most prolific citizen scientists are based here in the UK!

Brown dwarfs and other exotic objects

Most of the new objects we have discovered are brown dwarfs.  Brown dwarfs are often described as “failed stars”. They form like stars, but are only the size of Jupiter, with masses of up to 70 times that of Jupiter. They aren’t massive enough to fuse hydrogen into helium, and as a result, once they are born, they simply cool and fade away, some ending up as cool as 200-300 degrees Celsius.

This means we can’t detect brown dwarfs in the optical wavelengths, as they are very, very faint. But brown dwarfs are much brighter in the mid-infrared, meaning WISE can spot them with ease. We have now discovered over 100 new brown dwarfs, with more than 1200 awaiting follow up data to classify them. One of them has a mysterious companion that confounds our expectations for how binary stars evolve.  We have also discovered a record-setting white dwarf, which is the oldest one known to host a disk of dust around it.

There is much more to do! There is much more data for us to search. There are hundreds more brown dwarfs and other exotic objects to discover. And we haven’t found Planet 9 yet.

To get involved, check out

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