Carnegie Science | Spring 2019 11 Crunching the Numbers Trujillo and University of Oklahoma’s Nathan Kaib ran computer simulations to see how different Planet X orbits would affect the orbit of 2015 TG387. The simulations included a Super-Earth at several hundred AU on an elongated orbit as proposed by Caltech’s Konstantin Batygin and Michael Brown. Most of the simulations showed that 2015 TG387’s orbit is stable for the age of the Solar System, but it was shepherded by Planet X’s gravity, which keeps the smaller 2015 TG387 away from the massive planet. This gravitational shepherding could explain why the most distant objects in our Solar System have similar orbits that keep them from ever approaching the proposed planet too closely. This is similar to how Pluto never gets too close to Neptune even though their orbits cross. “What makes this result really interesting is that Planet X seems to affect 2015 TG387 the same way as all the other extremely distant Solar System objects. These simulations do not prove that there’s another massive planet in our Solar System, but they are further evidence that something big could be out there,” Trujillo concludes. Background illustration of Planet X is by Roberto Molar Candanosa and Scott Sheppard, Carnegie Institution for Science SUPPORT: NASA Planetary Astronomy grant NNX15AF44G funded this research, based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. These results made use of the Discovery Channel Telescope (DCT) at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. These results used the Large Monolithic Imager, which was built by Lowell Observatory using funds provided by the National Science Foundation (AST-1005313). This paper includes data gathered with the 6.5-meter Magellan telescopes located at Las Campanas Observatory, Chile. The orbits of the new dwarf planet 2015 TG387 and its fellow Inner Oort Cloud objects 2012 VP113 and Sedna are shown compared with the rest of the Solar System. 2015 TG387 was nicknamed “The Goblin” by the discoverers, as its provisional designation contains TG and the object was first seen near Halloween. 2015 TG387 has a larger semi-major axis than either 2012 VP113 or Sedna, which means it travels much farther from the Sun at its most distant point in its orbit, which is around 2,300 AU. Illustration courtesy Roberto Molar Candanosa and Scott Sheppard, Carnegie Institution for Science A comparison of 2015 TG387 at 65 AU is shown with the Solar System’s known planets. Saturn can be seen at 10 AU and Earth is at 1 AU; 1 AU is the distance between the Sun and Earth. Illustration courtesy Roberto Molar Candanosa and Scott Sheppard, Carnegie Institution for Science These are the discovery images of 2015 TG387 taken at the Subaru 8-meter telescope on Mauna Kea in Hawaii on October 13, 2015. The images were taken about 3 hours apart. 2015 TG387 can be seen moving between images near the center while the much more distant stars and galaxies are stationary. Image courtesy Scott Sheppard New Extreme Dwarf Planet: 2015TG387 “TheGoblin” 2015TG387 2012VP113 GiantPlanets KuiperBelt 65AU Sedna GiantPlanets 10 AU 1AU “TheGoblin” 2015TG387 65 AU KuiperBelt 10 AU 1 AU 11 continued on page 12