Ch. 8 Vagabonds of the Solar System part 1 - 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.

Best available picture of Pluto, prior to 2015, taken with the Hubble telescope in orbit

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.

The period of Pluto’s orbit is 248 years.

The orbit of Pluto is tilted and elliptical (e = 0.25)

A moon of Pluto was discovered by noticing a bulge in some photos of Pluto.

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

Better photos show two smaller moons: Nix and Hydra.

The New Horizons spacecraft flew by Pluto in July 2015 and greatly increased our knowledge of this dwarf planet. (All this information is NOT in your edition of the book.) Websites: We will show a variety of images from the JHU-APL website, and 3 movies, which can be downloaded at

Pluto images, best seen in a web browser: Methane snow on peaks High resolution pictures of Sputnik Planum, an ocean of solid nitrogen floating ice hills on a solid nitrogen ice ocean geology map with color to denote different types of surface New Horizons trajectory For class, we downloaded 3 videos and saved them to the classroom PC, from these pages:

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. 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:

Eris is a dwarf planet even further than Pluto.

Keck telescope image of Eris and its moon Dysnomia.

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 Dwarf Planets – five known so far

The orbit of Sedna is huge compared to even the Kuiper belt, and may extend to the Oort cloud.

Asteroids: three major groups The Asteroid belt Trojan Asteroids Near-Earth Objects (NEOs)

The Inner Solar System (sizes NOT to scale)

This is a plot of actual positions of known comets and asteroids (April 1, 2005). This shows the inner solar system, out to Jupiter. Notice most of these are in the asteroid belt between Mars and Jupiter.

Expanding the first plot, we get a plot of known comets and asteroids in the region around the Earth. Fortunately, there aren’t very many of these Near Earth Objects (NEOs).

This is the view from the side, i.e., in the ecliptic plane, of the plot of the objects in the inner solar system.

Ceres, the largest asteroid, is also a dwarf planet.

Asteroid Icarus comes close to Earth and to the Sun

Asteroids are often seen as streaks in photos.

The distribution of asteroids is affected by Jupiter.

Ida and its satellite Dactyl

Asteroids and meteoroids are small “rocky” objects The main difference between the two is size.

Some asteroids have been studied up close. Asteroid Eros

Matilde is darker than a briquette of charcoal.

Itokawa was visited by the Japanese spacecraft Hayabusa.

Asteroid Eros was imaged by a spacecraft which then landed on it and sent back data on its composition. NEAR spacecraft site: For a simulation of the orbit of Eros see:

Close-up pictures of Eros crater and surface. Crater about 3 mi across Photo of area 12 m across

The DAWN spacecraft was in orbit around Vesta, the second-largest of the asteroids in the Asteroid Belt, for almost a year, and is now orbiting Ceres Ceres movie: First mapping orbit: Latest news about the Dawn spacecraft: 4 Vesta; see next slide

Vesta

Further out from the asteroid belt, the Trojan Asteroids are clumped in the orbit of Jupiter. Lagrange points are places where asteroids will be trapped in the orbit of Jupiter. On the next slide, the Trojans are in yellow.

This is another plot of actual positions of known comets and asteroids (April 1, 2005). This shows the outer solar system, with the orbit of Jupiter and its Trojan asteroids. Notice there is another belt of objects out past Neptune.

This shows the outer solar system, past the orbit of Jupiter. This is the view from the side, i.e., in the ecliptic plane. Notice that the comets are coming from all directions, but the other objects are in the ecliptic plane.

The orbits of KBOs hint at the existence of another planet far from the Sun

Summary Classifying the Solar System objects Astronomical objects smaller than the eight planets are classified as dwarf planets or small solar-system bodies (SSSBs). A variety of other names, including asteroids, comets, meteoroids, trans-Neptunian objects, Kuiper belt objects (KBOs), and Oort cloud objects, overlap with “dwarf planet” and “SSSB.” KBOs and Oort cloud objects are trans-Neptunian objects—they orbit farther from the Sun than the outermost planet Neptune.

Asteroids Tens of thousands of belt asteroids with diameters larger than a kilometer are known to orbit the Sun between the orbits of Mars and Jupiter. The gravitational attraction of Jupiter depletes certain orbits within the asteroid belt. The resulting Kirkwood gaps occur at simple fractions of Jupiter’s orbital period. Jupiter’s and the Sun’s gravity combine to capture Trojan asteroids in two locations, called stable Lagrange points, along Jupiter’s orbit. The Apollo asteroids move in highly elliptical orbits that cross the orbit of Earth. Many of these asteroids will eventually strike the inner planets. They are also called Near Earth Objects (NEOs).

Comets Many comet nuclei orbit the Sun in the Kuiper belt, a doughnut-shaped region beyond Pluto. Billions of cometary nuclei are also believed to exist in the spherical Oort cloud located far beyond Pluto. Comet nuclei are fragments of ice and rock often orbiting at a great inclination to the plane of the ecliptic. In the Kuiper belt and Oort cloud they have fairly circular orbits. When close to the Sun, they generally move in highly elliptical orbits. As an icy comet nucleus approaches the Sun, it develops a luminous coma surrounded by a vast hydrogen envelope. A gas (or ion) tail and a dust tail extend from the comet, pushed away from the Sun by the solar wind and radiation pressure.

Meteoroids, Meteors, and Meteorites Boulders and smaller rocks in space are called meteoroids. When a meteoroid enters Earth’s atmosphere, it produces a fiery trail, and it is then called a meteor. If part of the object survives the fall, the fragment that reaches Earth’s surface is called a meteorite. Meteorites are grouped in three major classes according to their composition: iron, stony-iron, and stony meteorites. Rare stony meteorites, called carbonaceous chondrites, may be relatively unmodified material from the primitive solar nebula. These meteorites often contain organic hydrocarbon compounds, including amino acids. Fragments of rock from “burned-out” comets produce meteor showers. An analysis of the Allende meteorite suggests that a nearby supernova explosion may have been involved in the formation of the solar system some 4.6 billion years ago. An asteroid that struck Earth 65 million years ago probably contributed to the extinction of the dinosaurs and many other species. Another impact caused the “Great Dying” of life 250 million years ago. Such devastating impacts occur on average every 100 million years.

Key Terms amino acid Apollo asteroid asteroid belt belt asteroid carbonaceous chondrite chondrites coma (of a comet) dust tail (of a comet) dwarf planet gas (ion) tai hydrogen envelope impact crater iron meteorite Kirkwood gaps Kuiper belt long-period comet meteor meteor shower meteorite meteoroid nucleus (of a comet) Oort cloud planet radiation (photon) pressure short-period comet Small Solar- System Bodies (SSSBs) stable Lagrange points stony meteorite stony-iron meteorite Trojan asteroid Widmanstätten Patterns