1 / 21

Comets and Kuiper Belt Objects

Comets and Kuiper Belt Objects. Announcements. Reading Assignment -- Chapter 30 quiz today In-class activity and course evaluations on Thursday Public lecture tonight – 7:30PM, this room Prof. Alfed McEwan, Mars HiRISE Last Lecture – a week from today Extrasolar planets

ginny
Download Presentation

Comets and Kuiper Belt Objects

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Comets and Kuiper Belt Objects Comets 4/24/07

  2. Announcements • Reading Assignment -- Chapter 30 • quiz today • In-class activity and course evaluations on Thursday • Public lecture tonight – 7:30PM, this room • Prof. Alfed McEwan, Mars HiRISE • Last Lecture – a week from today • Extrasolar planets • Final exam review Comets 4/24/07

  3. Pluto • Most distant “planet” • Most of the time, but not all of the time! Its orbit can bring it inside of Neptune’s (as it did from 1979-1999) • Only “planet” not visited by a spacecraft • New Horizons, launched in Jan. 2006, will reach Pluto in 2015. • Pluto can be seen with an amateur telescope, but it is not easy! • About 14th magnitude • 6th magnitude is the limit for the naked eye • Pluto is about 1600 times dimmer than this Comets 4/24/07

  4. Pluto: Basic Facts • Avg. distance to the Sun • 39.5 AU • Orbital Period • About 250 years • Retrograde rotation • Like Venus and Uranus • Eccentricity • 0.25 • larger than all of the planets Comets 4/24/07

  5. Pluto: Basic Facts • Avg. density • About 1900 kg/m3 • Rock and ice • Diameter • 0.18 Earth Diameters • Not that well known (+/- 1%) • Mass • 0.0021 Earth Masses • Also not well known, although the combined mass of Pluto and Charon is well known • Tenuous atmosphere (but not as we have defined in in class) of N2 that is probably not in equilibrium Comets 4/24/07

  6. Neptune and Pluto are in a 3:2 orbital resonance • Pluto’s orbital period is 1.5 times Neptune’s • Neptune is about 164 years • Pluto is about 249 years • This is a stable configuration and they will never crash into each other • Pluto is like other objects in this sense – comprising a class of objects called “Plutino’s” Comets 4/24/07

  7. Charon: Pluto’s Moon • Discovered in 1978 by Jim Christy. • Prior to that it was thought that Pluto was much larger since the images of Charon and Pluto were blurred together. • Charon is the largest moon with respect to its primary “planet” in the Solar System (a distinction once held by Earth's Moon). • Some prefer to think of Pluto/Charon as a double planet rather than a planet and a moon. Comets 4/24/07

  8. Pluto and Charon are in an unusual resonance. • Charon has an orbital period equal to both its rotational period AND Pluto’s orbital period • From one side of Pluto, Charon just sits in the same place in the sky (never sets, never rises)! Comets 4/24/07

  9. Is Pluto a planet ? • Since the discovery of thousands of objects orbiting the Sun, called Edgeworth-Kuiper objects (or Kuiper-belt objects, KBOs), it has been suggested that Pluto is simply one of these and is not a planet • Many KBO’s are in orbital resonances with Neptune (3:2 resonance  “Plutino”) • This is further complicated by the fact that the recently discovered Eris is larger than Pluto. • In 2006, Pluto was downgraded to a new class of objects called “dwarf planets” • But the debate rages on Comets 4/24/07

  10. Kuiper Belt Red: All objects that are in a resonance with Neptune (Neptune Trojans – 1:1 ; Plutinos – 2:3 ; Twotinos 1:2 ) Blue: “Classical” objects Comets 4/24/07

  11. The IAU’s decision in August 2006 • The IAU...resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way: (1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. • (2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. • (3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies". Comets 4/24/07

  12. Eris Comets 4/24/07

  13. History of planets • Ancients recognized 7 planets • Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn • Earth was not a planet! • 1543, changed from 7 to 6 planets • Definition changed to an object orbiting the Sun • Sun and Moon removed, added Earth • 1852, changed from 23 to 8 planets • Asteroids were demoted since they did not have a resolvable disc • Uranus and Neptune had been discovered by now • 2006, changed from 9 to 8 planets • Pluto demoted Comets 4/24/07

  14. Semantics • Asteroids • Small rocky bodies in orbit about the Sun • Comets • Small bodies that orbit the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail • Meteoroids • Small asteroids • Meteorites • the debris collected on Earth • Meteors • A brief flash of light (i.e. a shooting star) Comets 4/24/07

  15. Asteroids and Comets • Asteroids • Mostly nearly-circular orbits • Mostly confined to the asteroid belt • Close to the ecliptic plane • Relatively short orbital periods • Comets • Highly elliptical orbits • Random inclinations • i.e. not-confined to the ecliptic • Very long orbital periods Comets 4/24/07

  16. Comets: Harbinger’s of Doom • Rome: marked the assassination of Julius Ceaser • England: blamed for bringing the Black Death • Incan Empire: foreshadowed the brutal conquering by Francisco Pizarro Comets 4/24/07

  17. Comets 4/24/07

  18. Comet Types (based on orbital characteristics) • Short-Period Comets • Comet with an orbital period of less than 200 years • Shortest lived • Breakup due to gravitational forces • Life expectancy of about 12,000 years • Long-Period Comets • Comets with orbital periods greater than 200 years (though typically around millions of years) • Other Definitions • Jupiter Family Comets (JFC) • Orbital period less than 20 years • Intermediate-Period Comets • Orbital period between 20 and 200 years Comets 4/24/07

  19. Comet Origin • Kuiper Belt • Jupiter family and intermediate period comets • These comets have low inclinations compared to long-period comets • Oort Cloud • Spherical distribution • Frequent observations of long- and intermediate-period comets indicate that the reservoir must be huge • Cannot be seen directly because it is so far away • Perturbed by passing stars or galactic tides Comets 4/24/07

  20. Comet orbits are often highly inclined • Long-period comets, originating from the roughly spherically distributed Oort cloud have orbits with random inclinations • Intermediate and Jupiter-family comets tend to have orbits more confined to the ecliptic • Asteroids seldom have highly inclined orbits Comets 4/24/07

  21. Appearance of Comets • When comets are far from the Sun, they are dark and hard to see • Low albedos, far away • Because of their large eccentricities, they occasionally come very close to the Sun • The body outgases as it heats and releases dust and cometary atoms • This produces a long visible tail • Directed away from the Sun Comets 4/24/07

More Related