Slide 1Asteroids and MeteoritesSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39PYTS/ASTR 206 – Asteroids and Meteorites1AnnouncementsHW4 available todayYou have two weeks for this oneFirst lecture after Spring Break – special topicSeveral options to choose from…Global warmingThe space raceMass extinctions on Earth and ImpactsPYTS/ASTR 206 – Asteroids and Meteorites2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected] and MeteoritesPYTS/ASTR 206 – Asteroids and Meteorites3In this lecture…In this lecture…Discovery of AsteroidsA missing planet?The main asteroid beltWhere did it come from?The Kirkwood gapsTrojansProperties of AsteroidsShapes, sizes, compositionsRubble piles?Near-Earth asteroidsWhere do they come from?How dangerous are they?MeteoritesDifferent types and what they tell usMeteor showersPYTS/ASTR 206 – Asteroids and Meteorites4The solar system in 1800…Mercury, Venus, Mars, Jupiter Saturnknown from antiquityUranus recently discovered With telescopes in 1781Neptune not yet discoveredPluto and the Kuiper Belt not yet discoveredAsteroids not yet discoveredDiscovery of asteroidsDiscovery of asteroidsPYTS/ASTR 206 – Asteroids and Meteorites5Titus-Bode lawMid 1760sA mathematical sequence that seemed to predict the sizes of the planets’ orbitsStart with 0 1 2 4 8 16 32 64 128Multiply by 0.3 0 0.3 0.6 1.2 2.4 4.8 9.6 19.2 38.4Add 0.4 0.4 0.7 1.0 1.6 2.8 5.2 10 19.6 38.8PYTS/ASTR 206 – Asteroids and Meteorites6These numbers are similar to the sizes of the planets’ orbits in AUUranus was discovered ~15 years later and fit right into this schemeHad something been missed between Mars and Jupiter?Planet Titus-Bode ObservationMercury 0.4 0.39Venus 0.7 0.72Earth 1.0 1.0Mars 1.6 1.52- 2.8 -Jupiter 5.2 5.2Saturn 10 9.5Uranus 19.6 19.2- 38.8 -PYTS/ASTR 206 – Asteroids and Meteorites7Astronomers searched with telescopes for this ‘missing planet’.In 1801 a planetary object was foundGiuseppe Piazzi named the object CeresInitial size estimates varied wildly 260-2600kmNow known to be about 950km in diameterCeres is small, dark, far from the Sun and far from the EarthCan’t see it by eye – but small binoculars are enoughPYTS/ASTR 206 – Asteroids and Meteorites8What about the Titus-Bode ‘law’Ceres appeared to follow the same prediction…but, later discovery of Neptune (1846) did notTitus-Bode law no longer considered significantPlanet Titus-Bode ObservationMercury 0.4 0.39Venus 0.7 0.72Earth 1.0 1.0Mars 1.6 1.52Ceres 2.8 2.8Jupiter 5.2 5.2Saturn 10 9.5Uranus 19.6 19.2Neptune 38.8 30.1PYTS/ASTR 206 – Asteroids and Meteorites9The missing planet found? – Yes and NoOther discoveries started to trickle inPallas, Juno, Vesta discovered 1801-1807Astraea, Hebe 1845-1847Started to become obvious that this wasn’t just a small planet…PYTS/ASTR 206 – Asteroids and Meteorites10Astronomical photography – Wolfe 1890sDiscovered hundreds of objectsLong-time exposure reveals moving objectsCurrent population estimate for asteroids >1 km is millionsNow a source of irritation for astronomersMany asteroids seen and not reportedPYTS/ASTR 206 – Asteroids and Meteorites11The solar system this morning.Green, red and blue points are asteroidsMinor planet center keeps track of thesePYTS/ASTR 206 – Asteroids and Meteorites12Earth’s neighborhood is also pretty crowdedPYTS/ASTR 206 – Asteroids and Meteorites13Most asteroids lie between Mars and Jupiter in the ‘main-belt’This belt has gaps thoughCeresPYTS/ASTR 206 – Asteroids and Meteorites14Asteroids get random perturbations from JupiterGravitational tugs as they pass by Jupiter’s positionAsteroids with certain periods get perturbed at the same point in their orbit again and againOrbits of these asteroids become unstableThis make sure that there are no asteroids left with certain periodsOr certain semi-major axesPYTS/ASTR 206 – Asteroids and Meteorites15Kirkwood gaps aren’t visibleAsteroids have eccentric orbits so there are asteroids at all locationsThe gaps are only visible when you look at the asteroid periods/semi-major axesNot like gaps in the rings of Saturn… gaps in the asteroid beltgaps in the rings of SaturnPYTS/ASTR 206 – Asteroids and Meteorites16Trojan asteroids orbit with JupiterGravitationally special location – Lagrange pointsFive such points numbered L1 - L5Used with the Earth to park satellitesPYTS/ASTR 206 – Asteroids and Meteorites17So where did this belt of tiny rocky objects come from?Early theories:The remains of an exploded planet?Components of a planet that never formed?What happened elsewhere in the solar system?The sun forms from a dusty diskRocky planetesimals form from this debris diskPlanetesimals eventually join up into large planets via impactsPYTS/ASTR 206 – Asteroids and Meteorites18Why didn’t the asteroids join up to form a fifth terrestrial planet?They’re moving too fast relative to each otherThings that hit each other slowly stick togetherThings that hit each other quickly break each other apartWhy are the asteroids moving so quickly?Jupiter keeps stirring things upWithout Jupiter’s influence we could have had and extra planet therePYTS/ASTR 206 – Asteroids and Meteorites19What happens when asteroids hit each other? The break-up into lots of smaller asteroids…The result is an asteroid belt with many small objects and only a few large objects Produces families of fragments that stay close together for a while~1 million asteroids > 1km~100 asteroids > 120 kmAsteroids are getting steadily smaller with time (slowly)PYTS/ASTR 206 – Asteroids and Meteorites20Fragments from collisions stick close together and form families of asteroidsSimilar orbital eccentricities and inclinationsEspecially obvious when you check the average eccentricities & inclinationsInherited from parent before it broke upPiotr Deuar, Data from the AstDyn sitePYTS/ASTR 206 –
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