An animation of three images showing the slow motion of a newly discovered dwarf planet across the sky over three hours. (Source: Outer Solar System Origins Survey) It all began with a small dot moving across a computer screen. That dot has now turned out to be a new dwarf planet, temporarily dubbed "RR245." It's a chunk of rock and ice about two thirds the size of California (north to south) orbiting amidst other small, icy worlds in the nether reaches of the solar system beyond Neptune. Its discovery was announced today by an international team of astronomers. The dwarf planet is roughly 435 miles across (700 kilometers). And it's orbit is one of the largest for any dwarf planet.
"This is a large icy world that’s bright enough that we can now study its surface composition . . . in detail," says Michele Bannister of the Outer Solar System Origins Survey, or OSSOS. "I
t’s on an orbit that’s relatively unusual among the known dwarf planets: quite eccentric, and in the past gravitationally perturbed by Neptune."
According to the International Astronomical Union, which decides such things, dwarf planets are celestial bodies that orbit the sun, are not moons, have enough mass to take on a nearly round shape, and whose gravity has not cleared out the neighborhood around their orbits.
In 2006, the IAU demoted poor Pluto from regular planet to dwarf planet.
OSSOS was designed to map the orbital structure of the outer Solar System. The goal: "To decipher its history," says Brett Gladman of the University of British Columbia in Vancouver. "While not designed to efficiently detect dwarf planets, we're delighted to have found one on such an interesting orbit."
The orbit of the newly discovered dwarf planet, RR245, is shown with the orange line. Objects as bright as, or brighter, than RR245 are labeled. RR245 is the 18th largest in the Kuiper Belt. (Source: Alex Parker, OSSOS team)
I emailed Michelle Bannister to ask her some questions about the nature and significance of the discovery. Here are some of my questions, and her responses:
* Why is it important to identify these objects beyond the orbit of Neptune? What have we been learning about the origin and evolution of the solar system by doing a survey such as this?
With OSSOS, we are mapping the detailed structure of the orbits of the populations in the outer Solar System. The trans-Neptunian objects are the remnant population that trace how the Solar System formed and then changed as a result of the migration of the giant planets. Our survey will help answer when, and how, Neptune migrated.
Bannister is referring to the large gaseous planets of Jupiter, Saturn, Uranus and Neptune, which migrated after their formation during the early evolution of the solar system. The vast majority of dwarf planets were destroyed or thrown from the Solar System in the gravitational chaos that occurred as the giant planets moved out to their present positions. But RR245 appears to be an exception. It survived, turning up in 2016 as a small dot on a computer screen... * I gather that we still do not know the precise physical nature of this dwarf planet. How can some of those details be filled in? And what might they tell us of interest? (Note: I've added the links below to help explain the answer.)
We have upcoming observations planned with larger telescopes to obtain spectra to investigate the surface composition of RR245. Our collaborators will also be looking for opportunities to measure an occultation: If RR245 passes in front of a distant star, the time it takes for the star to blink out and reappear will give us a minimum and very exact size of RR245.
* For readers who may have heard about the evidence published last winter pointing toward the existence of so-called “Planet-X”
, what connection is there between these two realms of research?
No connection. The orbit of RR245, while very distant, is dominated by the gravitational influence of Neptune. This object does not go the many hundreds of AU distance that are needed to provide any constraint on the hypothesis for a ninth planet.
The "AU distance" Bannister refers is an astronomical unit, which is the mean distance from the center of the earth to the center of the sun. * Lastly, how long does RR245 take to make one orbit around the Sun?