Planetoid Pairs Reveal a Kinder, Gentler Neptune

April 3, 2017

It’s a kinder, gentler Neptune, says Gemini astronomer Meg Schwamb in describing a new result that leaves little doubt about how Neptune gently swept a class of planetoid pairs into the outer Solar System.

The study focused on a type of loosely bound pairs of planetoids in the outer reaches of our Solar System that scientists say were likely shepherded by Neptune’s gravitational nudges into their current orbits in the distant Kuiper Belt. The paper is published in the April 4th issue of the journal Nature Astronomy (subscription required).

The research team, led by Wes Fraser of Queen’s University in Belfast, UK, used data collected from the Gemini North Frederick C. Gillett Telescope and Canada-France Hawaii Telescope (CFHT) both on Maunakea in Hawai‘i. The team measured the colors of peculiar new Cold Classical Kuiper Belt Object (CCKBO) pairs as part of the Colours of the Outer Solar System Origins Survey (Col-OSSOS).

The objects are among a category of bodies known as "blue binaries" which are oddball pairs in the Kuiper Belt because they don’t share the very red color that distinguishes most of the other CCKBO’s surfaces. The Kuiper Belt is a huge swarm of icy small planetoids well beyond the orbit of Neptune, and left-over from the formation of our Solar System.

It is believed that the blue binaries migrated from more inward parts of the Solar System out to the present-day Kuiper Belt. It is thought that this migration occurred several billion years ago during profound changes to the orbits of the outer planets Jupiter, Saturn, Uranus and Neptune.

"The red CCKBOs are thought to have formed at the location in the outer Solar System where they currently reside. The blue binaries, on the other hand, are interlopers from closer in hiding out in the Kuiper belt today," says Schwamb, who is also a coauthor on the study.

Fraser and his team compared the observed properties of the blue binaries to models of Neptune’s migration. Fraser found that although these blue binaries have such a tenuous gravitational embrace, these pairs can survive Neptune’s smoothly pushing them over a distance of at least four AU (four times the distance between the Earth and Sun) as the giant planet migrated outward. "The blue binaries are fossils from the long gone planetary disk that our planets formed from. These objects give us a unique new window into the history of the our Solar System," Schwamb adds.

"This research has opened the window to new aspects of understanding the early stages of planet growth,” concludes Fraser. “We now have a solid handle on how and where these blue binaries originated."

Chris Davis, Program Officer at the U.S. National Science Foundation, one of the five partner organizations which support Gemini operations, notes that "This is another great example of the successful use of one of Gemini’s many versatile observing modes. The observatory’s Large and Long Program has allowed the team to find and study these enigmatic objects in amongst a sea of millions of other Kuiper Belt Objects."

The Gemini/CFHT observations help address ongoing questions and debates among scientists about Neptune’s migration from its primordial formation orbital location to its current locale. The team found and characterized the peculiar blue binary objects thanks to CFHT MEGACAM data and confirmed by follow-up observations with the Gemini Multi-Object Spectrograph (GMOS) which was part of an ongoing Large and Long Program at Gemini to study the outer reaches of our Solar System.

The observations required significant coordination between Gemini and CFHT. "Like synchronized swimming, Gemini North and the Canada-France-Hawaii telescopes aligned their movements to observe the Col-OSSOS Kuiper Belt objects at nearly the same time," said Schwamb. "This choreographed ballet on Maunakea allowed us to measure the light from the same side of the Kuiper Belt object, removing one of the main challenges in studying Solar System bodies that rotate."

"Facilitating the simultaneous observations with the Col-OSSOS team and Gemini Observatory was challenging, but paved the way for a greater understanding of the origins of these blue binaries," said Todd Burdullis, Queued Service Operations Specialist at CFHT who helped to coordinate the observations. "In tandem, the two facilities observed all the colors of the outer solar system for the Col-OSSOS team."

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