A faint, distant object is found at the outskirts of the Kuiper Belt

MAC
Apr 13, 2017
3 min read

ALMA found some interesting information while investigating the very distant member of our solar system.

AN ARTIST'S REPRESENTATION OF DEEDEE Alexandra Angelich (NRAO/AUI/NSF)

What is it?

2014 UZ224 is a distant dwarf planet discovered by the Dark Energy Survey (DES). It's located in the region of the solar system beyond Neptune known as the Kuiper Belt, and is presently more than 90 astronomical units (AU), or nearly 14 billion km, from the sun. The earth is 1 AU from the sun, so this is one of the most distant solar system objects we know about. Among known solar system objects with well-determined orbits, only the dwarf planet Eris is currently more distant. It's more than twice as far away as Pluto; light from 2014 UZ224 takes 12.5 hours to reach us.

How was it discovered?

We looked in nearly 16,000 images collected by the Dark Energy Survey between 2013-2016. DES is surveying 1/8 of the sky over 5 years using the Dark Energy Camera (DECam) on the 4-meter Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. The main purpose of DES is to collect images of hundreds of millions of galaxies and use them to understand why the expansion rate of the universe is accelerating. It was not designed specifically to look for solar system objects. But the same combination of survey area and depth that make DES a state-of-the-art cosmological survey also make it a powerful tool for discoveries in our own cosmic backyard. The stars and galaxies in our images are stationary, but objects in our solar system appear in different places on different nights. We call an object that changes position or brightness from night to night a "transient". To identify transients, we used a technique known as "difference imaging". When we take a new image, we subtract from it an image of the same area of the sky taken on a different night. Objects that don't change disappear in this subraction, and we're left with only the transients. This technique was originally developed to search for Type Ia supernovae in small regions of our survey. Our collaborators at the University of Pennsylvania led by Professor Masao Sako made the key breakthroughs that allowed us to perform difference imaging over the entire survey area. This is a VERY computing-intensive process: thousands of computers at Fermilab were needed to process hundreds of terabytes of data. On a single computer, it would have taken 300 years! This process yields millions of transients, but only about 0.1% of them turn out to be distant minor planets. To find them, we must "connect the dots" and determine which transients are actually the same thing in different positions on different nights. There are many dots and MANY more possible ways to connect them. This is much too difficult to do by eye, so we wrote computer programs to do it. This process takes months of computing time.

ALMA image of the faint millimeter-wavelength "glow" from the planetary body 2014 UZ224, more informally known as DeeDee. At three times the distance of Pluto from the Sun, DeeDee is the second most distant known TNO with a confirmed orbit in our solar system.

Credit: ALMA (ESO/NAOJ/NRAO)