Ch. 12 Dwarf Planets There are several kinds of objects in our Solar System Terrestrial planets and Jovian planets, with satellites (moons) Dwarf planets (which can also have moons) and “small solar system bodies” – asteroids, comets and meteoroids Objects are still being classified: Kuiper Belt Objects, Plutoids, Plutinos, Trans-Neptunian Objects (TNOs), Oort cloud objects

From largest to smallest, the objects in the Solar System can be classified into categories Notice that there is some overlap among objects of the same size. FIGURE 9-1 Different Classifications of Solar System Objects Some of the definitions of the different types of objects in the solar system overlap. For example, the largest asteroids are also being classified as dwarf planets; various trans-Neptunian objects (TNOs) are asteroids or comets; some comets are satellites of Jupiter; some Kuiper belt objects (KBOs) are satellites of other KBOs. Furthermore, TNOs exist in two groups: Kuiper belt objects and Oort comet cloud bodies.

Best available picture of Pluto, prior to 2015, taken with the Hubble telescope in orbit FIGURE 9-2 Pluto This Hubble Space Telescope image of Pluto shows little detail but indicates that the major features of Pluto’s surface each cover large amounts of its area. (Alan Stern, Southwest Research Institute; Marc Buie, Lowell Observatory; NASA; and ESA)

Pluto can barely be resolved by telescopes from Earth Pluto can barely be resolved by telescopes from Earth. This image of Pluto is from the Hubble telescope.

Small objects are discovered by comparing photos taken at different times or days. Pluto was discovered by this method in 1930. FIGURE 9-3 Discovery of Pluto Pluto was discovered in 1930 by searching for a dim, starlike object that slowly moved against the background stars. These two photographs were taken 1 day apart. (UC Regents/Lick Observatory)

The period of Pluto’s orbit is 248 years. FIGURE 9-4 Orbit of Pluto (a) The high-eccentricity orbit of dwarf planet (and KBO) Pluto stands out compared to the orbits of the outer three planets. Notice how many significant events occurred on Earth during Pluto’s present orbit of the Sun. (b) Details of Pluto’s passage inside the orbit of Neptune. The two bodies will never collide.

The orbit of Pluto is tilted and elliptical (e = 0.25) FIGURE 9-4 Orbit of Pluto (c) A nearly edge-on view of the ecliptic and Pluto’s orbit compared to it.

A moon of Pluto was discovered by noticing a bulge in some photos of Pluto. FIGURE 9-5 Discovery of Charon Long ignored as just a defect in the photographic emulsion, the bump on the upper left side of this image of Pluto led astronomer James Christy to discover the moon Charon. (U.S. Naval Observatory)

Pluto and its moon Charon are almost like a double planet. Better photos show two smaller moons: Nix and Hydra.

smaller moons: Nix and Hydra. Better photos show two smaller moons: Nix and Hydra. FIGURE 9-6 Pluto’s moons Nix and Hydra Observations by the Hubble Space Telescope in 2005 revealed two small moons, each about 5000 times dimmer than Pluto. Named Nix and Hydra, they are between two and three times farther from Pluto than is Charon. The lines radiating from Pluto and Charon are artifacts of the exposure. (NASA)

Websites: http://pluto.jhuapl.edu/ The New Horizons spacecraft flew by Pluto in July 2015 and greatly increased our knowledge of this dwarf planet. Websites: http://pluto.jhuapl.edu/ http://www.nasa.gov/mission_pages/newhorizons/main/index.html We will show a variety of images from the JHU-APL website, and 3 movies, which can be downloaded at http://pluto.jhuapl.edu/Multimedia/Science-Photos/ FIGURE 9-7 Pluto and Charon This picture of Pluto and its moon, Charon, is a composite of Hubble Space Telescope images. It shows the greatest detail we have of Pluto’s surface. Pluto and Charon are separated here by only 19,700 km. Inset: A map covering 85% of Pluto’s surface. The contrast between dark and light strongly suggests regions covered with ice and regions covered with rocky material. (Pluto: Alan Stern/SwRI, Mar Cuie/Lowell Observatory, NASA, & ESA; Charon: R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility, and NASA; inset: A. Stern/SwRI, M. Buie/Lowell Observatories, NASA, and ESA)

http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php

Pluto images, best seen in a web browser: Methane snow on peaks http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&gallery_id=2&image_id=420 High resolution pictures of Sputnik Planum, an ocean of solid nitrogen http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=2&gallery_id=2&image_id=402 floating ice hills on a solid nitrogen ice ocean http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&gallery_id=2&image_id=408 geology map with color to denote different types of surface http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&gallery_id=2&image_id=410 New Horizons trajectory http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php For class, we downloaded 3 videos and saved them to the classroom PC, from these pages: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=4&gallery_id=2&image_id=309 http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=4&gallery_id=2&image_id=326 http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=2&gallery_id=2&image_id=383

The Pluto–Charon Orbit is so unusual that it probably means Charon is captured, and not co-evolved with Pluto

Kuiper Belt Objects Compared to Moon and Earth Kuiper Belt Objects Compared to Moon and Earth. Notice that we think Triton was captured by Neptune, and is really an object like Pluto and the KBOs. However, the New Horizons results show that Triton and Pluto are quite different. Also see this web page about KBOs: http://www2.ess.ucla.edu/~jewitt/kb.html

Eris is a dwarf planet even further than Pluto. FIGURE 9-9 Dwarf Planet Eris (a) Orbit of Eris and Dysnomia compared to the planets and Pluto. Their orbit around the Sun ranges from 38 to 98 AU, with orbital eccentricity, e, of 0.44 and orbital inclination of 44o. (b) Keck Telescope image of dwarf planet Eris and its moon Dysnomia. (a: Orionist; b: M.E. Brown, W.M. Keck Observatory)

Keck telescope image of Eris and its moon Dysnomia. FIGURE 9-9 Dwarf Planet Eris (b) Keck Telescope image of dwarf planet Eris and its moon Dysnomia. (a: Orionist; b: M.E. Brown, W.M. Keck Observatory) Keck telescope image of Eris and its moon Dysnomia.

Dwarf Planets – five known so far Dwarf planets are round due to gravity, but not big enough to clear out the other objects in their orbit. In 2006 three objects—Pluto, Ceres, and Eris—were classified as dwarf planets. Later, we observed Haumea and Makemake, so there are 5 dwarf planets. Ceres is in the asteroid belt; the other dwarf planets are in the Kuiper Belt out past Neptune . Many other objects orbit the Sun beyond Neptune. For example, at least 1277 KBO’s have been observed. A few potential Oort cloud objects have also been identified. New classification schemes are being proposed. Lists are at https://en.wikipedia.org/wiki/Dwarf_planet

The orbit of Sedna is huge compared to even FIGURE 9-20 Sedna’s Orbit (a) The farthest known body in the solar system is in a highly elliptical orbit (b) that ranges from the outer reaches of the Kuiper belt and possibly extends to the inner Oort comet cloud. (NASA/Caltech) The orbit of Sedna is huge compared to even the Kuiper belt, and may extend to the Oort cloud.