Searches for Planet Nine

Since Mike Brown and Konstantin Batygin announced evidence for the existence of a distant ninth planet in the solar system, astronomers have been furiously analyzing and collecting data in hopes of being the first to spot it. A lot of the excitement is driven by the fact that planet nine may already have been detected in existing data sets. Astronomers love the idea of sifting through a huge pile of data to make that one epic discovery, and planet nine is the ultimate “needle in a haystack” adventure.

The standard approach to detecting a faint Trans-Neptunian Object (TNO) such as planet nine is to look for its reflected sunlight using the biggest ground-based visible light telescopes on Earth. There are several planet nine searches of this type currently underway. Mike Brown is using the Subaru 8 meter telescope on the Mauna Kea mountain top in Hawaii. Scott Sheppard is leading a dedicated TNO survey using the Dark Energy Camera (DECam) instrument on the Blanco 4 meter telescope at Cerro Tololo, in Chile. David Gerdes is also using archival DECam data to hunt for planet nine, and recently discovered “DeeDee” a possible dwarf planet over ninety times more distant from the Sun than the Earth. However, none of these surveys has yet or ever will cover the entire sky.

Aerial photograph of CTIO, Cerro Tololo, Blanco 4-meter, SMARTS, 2006
Multiple teams are using the Blanco 4 meter telescope at Cerro Tololo in Chile to search for Planet Nine. I traveled there myself most recently last December

Since April 2016, I have been performing an automated planet nine search using WISE data, with help from my colleagues Benjamin Bromley, Peter Nugent, David Schlegel, Scott Kenyon, Edward Schlafly, and Kyle Dawson. WISE is a bit of an “X factor” when it comes to the search for planet nine, because using it to look for TNOs is very unconventional. WISE is comparatively a tiny telescope (0.4 meter diameter), and observes in the infrared from low-Earth orbit (as opposed to visible light from the ground). With WISE, we are searching for intrinsic emission from planet nine itself, rather than reflected sunlight. The big advantage of WISE is that it has already covered the entire sky more than six times. However, the main disadvantage is that there is an enormous uncertainty in how bright or faint planet nine might appear in the infrared. So planet nine might very well exist, even if it turns out that WISE can’t detect it.

neowiseinorbit_cropped_small
Artist’s rendering of the WISE spacecraft in orbit. Both Backyard Worlds: Planet 9 and my automated searches for Planet Nine use data from this infrared telescope.

My automated planet nine searches will likely have major problems in certain areas of the sky, particularly in the plane of our Milky Way galaxy, where there are huge numbers of background stars. This is where we really need Backyard Worlds: Planet 9. In the search for rare moving objects, professional astronomers often painstakingly blink through thousands or even millions of images by eye. Having a team of citizen scientists look through the WISE images will help make sure that no brown dwarf or ninth planet in this data set evades discovery.

Backyard Worlds: Planet 9 is my first time being involved in a citizen science project, and it’s been a lot of fun so far, even though I know we’re just getting started. Thanks for joining the search!

Aaron Meisner

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