April has been an excellent month for those studying the outer solar system. The Outer Solar System Origins Survey and its counterpart, Colors of the Outer Solar System Origins Survey, announced the discovery of some interesting new additions to the icy objects past Neptune.
The OSSOS program started observing everything in the outer solar system past Neptune from CFHT in 2013. While their survey was completed in January, they are still analyzing the data and finding new objects. Their paper OSSOS V announced the discovery of an icy body so far from the sun that it takes over 20,000 years to make one, long orbit. Its closest approach to the sun is 50 times farther from the sun than the Earth. The object, designated L91, was later renamed SY99. It is a small, reddish world around 155 miles in diameter. The OSSOS team discovered it using CFHT and then took a closer look at the object using the Gemini and Subaru Observatories.
The next question after finding SY99 is, how did it get there? While it is not alone in the outer regions of our solar system, only a few of these very distant objects are known. Computer simulations done by the OSSOS team show that when SY99 and Neptune are the closest, the gravity of Neptune gently nudges SY99, slowly changing its orbit. Over the 4.5 billion year history of our solar system, these gentle nudges by Neptune may have pushed SY99 to the fringes of the outer solar system.
Moving a bit closer to home, but not much, the Col-OSSOS team announced the discovery of so-called “blue binaries” past Neptune. While the OSSOS team looks for objects past Neptune, the Col-OSSOS team aims to measure the colors of the objects. Through their survey they discovered five blue objects, all binaries. A binary system is when two objects of a similar size orbit each other. The discovery of so many blue binaries in the cold Kupier Belt is tricky to explain.
Neptune again saves the day. Many planetary astronomers believe that Neptune and Uranus formed closer to the sun than their present day locations. At some point in the solar system’s distant past, these two planets moved to their current locations. The question is: were those moves gentle or turbulent on nearby objects? The presence of these blue binary systems indicate a gentle, sweeping movement on Neptune’s part, otherwise the binaries would have split apart.
For the Col-OSSOS observations, the team worked very closely with CFHT and Gemini Observatory to conduct simultaneous observations of their objects. The objects rotate pretty quickly, on the order of one to a few hours. Synchronous observations were essential to make sure the team looked at the same part of the object at the same time, just in different colors.
It was also announced that several members of the OSSOS team recently had asteroids named after them. One of the newly minted asteroids, (11814) Schwamb, was named for Meg Schwamb, an astronomer at the Gemini Observatory in Hilo. Congrats to the OSSOS and Col-OSSOS teams for a really great month.