Ch 13 Comets There are several kinds of

Ch. 13 – Comets There are several kinds of objects in our Solar System Terrestrial planets and Jovian planets Dwarf planets “small solar system bodies” – asteroids, comets and meteoroids Objects are still being classified: Kuiper Belt Objects, Plutoids

Halley’s Comet was last seen in 1986. The orbital period is about 76 years, so it will be back in 2061.

Comet Tails: ion tail and dust tail Comet Hale-Bopp (1997) had two distinctive tails: http: //apod. nasa. gov/apod/ap 050522. html

The hydrogen envelope is much larger than the tails.

The gas tail has more turbulence and variability.

Comet Encke: the ion (or plasma) tail was blown completely off by a Coronal Mass Ejection. See: Astronomy Picture of the Day for 10/3/07 for details http: //apod. nasa. gov/apod/ap 071003. html

A Comet Trajectory is usually a very narrow ellipse, with eccentricity near 1. 0 Some comets appear to come from almost 100, 000 A. U. from the Sun, in a region called the Oort cloud.

Comet Reservoirs: the Oort Cloud the Kuiper Belt (pronounced Kye-per)

Kuiper Belt Objects appear to move relative to the distant stars in images taken hours apart.

Comet Wild, with two images combined to show a heavily-cratered nucleus and the jets of gas.

Halley’s Comet close-up by a passing spacecraft

Nucleus of Comet Borelly, imaged by Deep. Space 1.

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

A NASA spacecraft, Stardust, went through the tail of comet Wild and obtained samples of dust fragments.

Images of Comet Tempel 1 taken by the Deep Impact Spacecraft.

Comet 67 P/Churyumov–Gerasimenko has been visited by the Rosetta spacecraft which had a lander, Philae.

View of the surface of 67 P from Philae lander. A view of the lander has been superimposed.

Short-period comets result when a comet is deviated from a highly-eccentric orbit by the influence of a Jovian planet. Fragmentation of a comet can occur as it passes Earth.

Ch. 14: Meteors

Meteor Showers are usually due to old comets. There is definite proof that some are due to known comets. Others are probably fragments of asteroids. list of meteor showers: http: //en. wikipedia. org/wiki/List_of_meteor_showers more on meteor showers: http: //en. wikipedia. org/wiki/Meteor_showers

Meteorite – a meteor which reaches the ground Various types: stony, iron-nickel, carbonaceous

Stony meteorites Broken to reveal a dark crust and a rough fracture surface Cut and polished to reveal iron inclusions

Iron meteorites Cut and polished to Reveal crystalline form Rough, as-found

Carbonaceous chondrite meteorite Allende meteorite fragment, found after a fall in Mexico Ruler is 15 cm

Found meteorites - on Arctic Ice

What Killed the Dinosaurs? This is an artistic representation of an asteroid impact in the Yucatan region over 65 million years ago.

Tunguska event, Siberia, June 30, 1908

Tunguska Debris, Siberia, 1908

Barringer Crater in Arizona – a meteor crater

Manicouagan Reservoir: a crater in Canada

Approximate frequency of random impacts

A meteorite fell over Chelyabinsk, Russia on Feb. 15, 2013 Videos of the Chelyabinsk event of 2013 looking up from sidewalk, boom, running and chaos after first minute (4: 45) http: //www. youtube. com/watch? v=b 7 m. LUIDGqmw A 10 minute newscast (in English) with Neil de. Grasse Tyson https: //www. youtube. com/watch? v=_szd 9 B 3 FU 8 Y Videos of blast hitting various locations, mostly taken by indoor cameras (2: 46) http: //www. youtube. com/watch? v=tq 02 C_3 Fv. Fo Mostly outdoor views, from cars and traffic cam (duration 1: 24): (Turn down volume, music added) http: //www. youtube. com/watch? v=90 Omh 7_I 8 v. I&feature=player_embedded An 8 minute newscast (in Russian) http: //www. youtube. com/watch? v=t 3 v. CUdns. Fs 0 A 6 minute newscast (in English) http: //www. youtube. com/watch? v=u. A_o 28 x. F_48 10 minutes of raw video (including most of the above footage) http: //www. youtube. com/watch? v=dpm. Xy. Jrs 7 i. U Some of these will have ads before the video, or on bubbles on top of the video.

Near Earth Objects - NEO There is an automated system to scan the sky for near-Earth objects and report them to a computer system. http: //www. ll. mit. edu/mission/space/linear/ These and other reports are fed into a computer program called the JPL Sentry system: http: //neo. jpl. nasa. gov/risk/ This detected a threat a few years ago, at risk level 2, http: //neo. jpl. nasa. gov/news 149. html which is no longer considered a threat, after new calculations were done. The main NEO page: http: //neo. jpl. nasa. gov/ has various news articles on events of interest as they happen. A longer term threat: Asteroid 1950 DA may collide with Earth in the year 2880 (1 in 300 chance): http: //neo. jpl. nasa. gov/1950 da/

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 belt asteroid carbonaceous 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 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