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UA PTYS 206 - Lecture Notes

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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 Meteorites1AnnouncementsHW4 available todayYou have two weeks for this oneFirst lecture after Spring Break – special topicSeveral options to choose from…Global warmingThe space raceMass 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 AsteroidsA missing planet?The main asteroid beltWhere did it come from?The Kirkwood gapsTrojansProperties of AsteroidsShapes, sizes, compositionsRubble piles?Near-Earth asteroidsWhere do they come from?How dangerous are they?MeteoritesDifferent types and what they tell usMeteor showersPYTS/ASTR 206 – Asteroids and Meteorites4The solar system in 1800…Mercury, Venus, Mars, Jupiter Saturnknown from antiquityUranus recently discovered With telescopes in 1781Neptune not yet discoveredPluto and the Kuiper Belt not yet discoveredAsteroids not yet discoveredDiscovery of asteroidsDiscovery of asteroidsPYTS/ASTR 206 – Asteroids and Meteorites5Titus-Bode lawMid 1760sA 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 Meteorites6These numbers are similar to the sizes of the planets’ orbits in AUUranus was discovered ~15 years later and fit right into this schemeHad 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 Meteorites7Astronomers searched with telescopes for this ‘missing planet’.In 1801 a planetary object was foundGiuseppe Piazzi named the object CeresInitial size estimates varied wildly 260-2600kmNow known to be about 950km in diameterCeres is small, dark, far from the Sun and far from the EarthCan’t see it by eye – but small binoculars are enoughPYTS/ASTR 206 – Asteroids and Meteorites8What about the Titus-Bode ‘law’Ceres appeared to follow the same prediction…but, later discovery of Neptune (1846) did notTitus-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 Meteorites9The missing planet found? – Yes and NoOther discoveries started to trickle inPallas, Juno, Vesta discovered 1801-1807Astraea, Hebe 1845-1847Started to become obvious that this wasn’t just a small planet…PYTS/ASTR 206 – Asteroids and Meteorites10Astronomical photography – Wolfe 1890sDiscovered hundreds of objectsLong-time exposure reveals moving objectsCurrent population estimate for asteroids >1 km is millionsNow a source of irritation for astronomersMany asteroids seen and not reportedPYTS/ASTR 206 – Asteroids and Meteorites11The solar system this morning.Green, red and blue points are asteroidsMinor planet center keeps track of thesePYTS/ASTR 206 – Asteroids and Meteorites12Earth’s neighborhood is also pretty crowdedPYTS/ASTR 206 – Asteroids and Meteorites13Most asteroids lie between Mars and Jupiter in the ‘main-belt’This belt has gaps thoughCeresPYTS/ASTR 206 – Asteroids and Meteorites14Asteroids get random perturbations from JupiterGravitational tugs as they pass by Jupiter’s positionAsteroids with certain periods get perturbed at the same point in their orbit again and againOrbits of these asteroids become unstableThis make sure that there are no asteroids left with certain periodsOr certain semi-major axesPYTS/ASTR 206 – Asteroids and Meteorites15Kirkwood gaps aren’t visibleAsteroids have eccentric orbits so there are asteroids at all locationsThe gaps are only visible when you look at the asteroid periods/semi-major axesNot like gaps in the rings of Saturn… gaps in the asteroid beltgaps in the rings of SaturnPYTS/ASTR 206 – Asteroids and Meteorites16Trojan asteroids orbit with JupiterGravitationally special location – Lagrange pointsFive such points numbered L1 - L5Used with the Earth to park satellitesPYTS/ASTR 206 – Asteroids and Meteorites17So 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 diskRocky planetesimals form from this debris diskPlanetesimals eventually join up into large planets via impactsPYTS/ASTR 206 – Asteroids and Meteorites18Why didn’t the asteroids join up to form a fifth terrestrial planet?They’re moving too fast relative to each otherThings that hit each other slowly stick togetherThings that hit each other quickly break each other apartWhy are the asteroids moving so quickly?Jupiter keeps stirring things upWithout Jupiter’s influence we could have had and extra planet therePYTS/ASTR 206 – Asteroids and Meteorites19What 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 kmAsteroids are getting steadily smaller with time (slowly)PYTS/ASTR 206 – Asteroids and Meteorites20Fragments from collisions stick close together and form families of asteroidsSimilar orbital eccentricities and inclinationsEspecially obvious when you check the average eccentricities & inclinationsInherited from parent before it broke upPiotr Deuar, Data from the AstDyn sitePYTS/ASTR 206 –


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UA PTYS 206 - Lecture Notes

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