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Minor bodies in Solar System

Minor bodies in Solar System. Asteroid Itokawa imaged by the Japanese spacecraft Hayabusa. Announcements. Second project is now due. 6 th HW has been posted to the course website due on Thursday, April 26 last homework set of the class Quiz #3 next Tuesday, April 24

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Minor bodies in Solar System

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  1. Minor bodies in Solar System Asteroid Itokawa imaged by the Japanese spacecraft Hayabusa Asteroids 4/23/09

  2. Announcements • Second project is now due. • 6th HW has been posted to the course website • due on Thursday, April 26 • last homework set of the class • Quiz #3 next Tuesday, April 24 • the last quiz of the class Asteroids 4/19/12

  3. Semantics • Asteroids • Small rocky bodies in orbit about the Sun • Sometimes restricted to minor bodies of the inner Solar System • 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)

  4. Discovery of Asteroid Ceres HST image of Ceres • Giuseppe Piazzi searched for the missing planet and found Ceres • Ceres is about 2.8 AU from the Sun – just as predicted by Bode’s law • However, Ceres looked like a point and not a planet (i.e. its disk was not resolved in early attempts) must be a very small planet ! • It turns out that Ceres is smaller than Pluto, but the largest of the asteroids in the asteroid belt Asteroids 4/23/09

  5. Soon after Ceres was discovered, other small “planets” were found • All about 2.8 AU from the Sun • New technique (ca. 1800’s): • Invented by Max Wolf • long-exposure photography • Look for asteroid trails on photos Asteroids 4/19/12

  6. Discovery of the Asteroid Belt • Astronomers were finding many asteroids with the new technique • Wolf alone discovered over 200 • Modern Technique • CCD images at various times, have a computer look for differences • Have likely found most objects greater than 1km across (in the asteroid belt) Asteroids 4/19/12

  7. Asteroid Names • Many asteroids are discovered by amateurs • The process can take decades • After discovery, it is reported to the Smithsonian Astrophysical Observatory Minor Planet Center • Given a temporary name (1980 JE) • If the object is found at 4 successive oppositions, the discoverer gives it a name and it is assigned a number • 1 Ceres • 2 Pallas • 3834 Zappafrank Asteroids 4/19/12

  8. Origin of Asteroids • It turns out that there is no “missing planet” • Asteroids are not the remains of a long-destroyed large planet (not much combined mass) • The combined mass of all asteroids in the asteroid belt is less than the mass of our Moon • Asteroids are relics of planetesimalsthat failed to accrete into a full-sized planet • effect of Jupiter Asteroids 4/19/12

  9. Jupiter’s effect on the Asteroid Belt • Numerical simulations indicate that the existence of Jupiter makes it unlikely that a planet would have formed in the asteroid belt • If Jupiter were not there, it is likely that a fifth terrestrial planet would have formed • Jupiter also depleted the asteroid belt removing any that got close to Jupiter (and were flung out into the solar system) Asteroids 4/19/12

  10. Kirkwood Gaps • Even today, gravitational perturbations by Jupiter deplete certain orbits within the asteroid belt • The resulting gaps, called Kirkwood gaps, occur at simple fractions of Jupiter’s orbital period • Similar to gaps in planetary rings (but keep in mind eccentricity!) Asteroids 4/19/12

  11. Trojan Asteroids • Asteroids that collect in the Lagrange points of Jupiter • Stable orbits, same period as Jupiter • Named for Trojan war characters • About 50 Trojan’s are known, many more are suspected • Earth has no Trojans • However we have spacecraft at Earth’s Lagrange points (ACE/SOHO/Genesis and others at L1) Asteroids 4/19/12

  12. Asteroids Physical Structure Size and Shape • All are smaller than 1000 km • Ceres is the largest with a diameter of 934 km (more than 2 times smaller than Pluto) • Only the largest are round • Uniform brightness • Most are irregular shaped • Elongated asteroids vary in brightness as seen from Earth as they rotate and present varying amount of cross-sectional area • Some have moons Gaspra

  13. Rubble Pile structure • A survey of asteroid rotation rates show that upper limit of spin rate for larger bodies (>150m) • If an asteroid is a collection of smaller chunks (i.e. a rubble pile), it would not be able to rotate very quickly without flying apart Asteroids 4/19/12

  14. Asteroid Collisions • Some asteroids have huge craters, like 253 Mathilde shown here • Being a rubble pile, it more-easily absorbs energy from the collision and remains intact Asteroids 4/19/12

  15. Near-Earth Asteroids • Asteroids that are within the orbit of Mars are called Near-Earth Objects (NEOs) • 8800 are currently known • 1300 Potentially Hazardous Asteroids are observed. (Larger than 150m) • The larger asteroid 1950 DA (1-km) has a 1:300 chance of striking Earth in 2880 Image by Jim Scotti of LPL’s Spacewatch program Asteroids 4/19/12

  16. → Original meteoroid was 2-5 m in diameter The impact of 2008 TC3 A few months after the impact, fragments of the meteoroid (now meteorites) were found “flare” seen in satellite image from explosion (at altitude)

  17. Trans-Neptunian Objects Asteroids 4/19/12

  18. Pluto is one of many trans-Neptunian Objects

  19. History of the Kuiper Belt Proposed by many astronomers, most notably Kenneth Edgeworth in 1943 Gerard Kuiper in 1951 Somehow Kuiper seems to have won the name game Besides Pluto, the first Kuiper belt object (or KBO) was discovered in 1992 by Dave Jewitt and Jane Luu after 5 years of searching

  20. Looking for more KBOs Since 1992, about a thousand KBOs have been found by telescope surveys It takes large telescopes, and long periods of time to confirm each discovery and to determine what kind of orbits the objects are on You need to observe an object for several years to really determine it’s orbit well! 1992 QB1 – The first KBO

  21. What do we know about the physical properties of KBOs? Just like Pluto and Charon, they seem to be made of mixtures of rock and ice they’re like comets, not asteroids Some might have very very thin atmospheres like Pluto We'll learn more when New Horizons gets to Pluto! (2015)

  22. Source of Comet Long-period comets (P> 200yr) - originated from Oort Cloud Short-period comets Halley-family comets (20yr <P< 200yr) - from Oort Cloud Jupiter-family comets (P< 20yr) - from Scattered disc & Centaurs

  23. Oort Cloud • Spherical clouds of comets • Heliocentric distance ~ 50,000 AU • Ernst Öpik (1932) & Jan Hendrik Oort (1950) postulated the existence Asteroids 4/19/12

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