Unit 8: Small Bodies around our Sun Mr. Ross Brown Brooklyn School for Law and Technology

In this unit we will learn about: The different types of small bodies in our Solar System Meteorites and their origins Asteroids and dwarf planets Comets, their orbits, and their structures Results of collisions of these bodies with the Earth The impact on Earth 65 millions years ago and how it led to the demise of the dinosaurs

What small objects also orbit our Sun? 2 February 2016 Do now: Why do we find so few meteorites here on Earth?

What happens when meteors approach the Earth? Meteor: a streak in the night sky made by friction of a solid body passing through Earth’s atmosphere; a shooting star Meteoroid: the solid body Meteorite: if it reaches the Earth

What happens when meteors approach the Earth? As meteoroids enter our atmosphere they encounter friction km/ second Air resistance also slows them, so they can land

What types of meteorites are there? Stony – silicates – Composed of grains of rock (chondrules) stuck together, thus called Chondrites – Carbonaceous chondrites: chondrites in carbon- rich substance, contains amino acids

What types of meteorites are there? Achondrites (without chondrites) – Iron: show crystals, indicating they cooled over millions of years – Stony-iron: rare combination, perhaps from mantle-core boundary of exploding asteroid

What makes an asteroid “an asteroid?” 3 February 2016 Do now: Where did all those asteroids come from?

What makes an asteroid “an asteroid?” Asteroids: small, rocky bodies 2-4 AU from the Sun Aster: Greek for “star” Bode’s Law predicted a planet at 2.8 AU More than 100,000 found, but less than 1/1000 Earth’s mass Ceres is largest

Bode’s Law

What makes an asteroid “an asteroid?”

Ceres has enough mass to produce gravity to make it a sphere; considered a dwarf planet Most are irregularly shaped Eros Itokawa Vesta compared to other asteroids

Ceres

What makes an asteroid “an asteroid?” Many are iron or silicate but not all are solid – Loose rubble held together by gravity – Mathilde density 1.4, Itokawa 1.9

What makes an asteroid “an asteroid?” Composition – Silicate, carbonaceous, or iron-nickel Inner-belt are mostly silicate-rich Outer-belt are mostly carbon-rich

What makes an asteroid “an asteroid?” Origins – Solar Nebula Theory Inner planets silicate based, thus inner asteroids…..

Homework #14 3 February 2016 What is the difference between a meteor, a meteoroid, and a meteorite? What shape are typical asteroids and how do we know? Why does Ceres not have this shape?

Aim: What lies beyond Neptune? 4 February 2016 Do now: Imagine you are in a rocket ship racing past Neptune. What objects might you encounter? What would these be made of?

What happened to Pluto? Trans-Neptunian Objects (TNOs): very small objects orbiting our Sun beyond Neptune’s orbit Pluto! – Discovered in 1930 by reviewing photos to identify objects whose position changed

Pluto Named after the god of the underworld Moon (Charon) discovered in 1978, named after boatman who ferries dead souls across the River Styx to the underworld

Pluto Originally thought to be about Earth-sized By studying Charon’s orbit  Pluto’s mass –.002 Earth mass, 1/20 Mercury – 1/5 Earth diameter – Density 2.1 – Orbit intersects Neptune’s  is it a planet?

What defines a “planet?” International Astronomical Union (IAU) 2006 stated that a planet: 1.is in orbit around the Sun, 2.has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and 3.has "cleared the neighborhood" around its orbit.

Which criterion does Pluto miss?

Plutoids Several hundred other objects kilometers in diameter orbit as far as Pluto – Sedna: 1000 km in diameter, well past Kuiper Belt – Eris: AU from Sun, 2400 km in diameter, orbit inclined 44° – Because of these, and its own orbit and size, the International Astronomical Union defined Pluto and other like bodies as dwarf planets – Plutoids: dwarf planets that orbit our Sun

Plutoids

Plutoid Orbits

So, what are all the things in our Solar System?

Aim: What are comets? 9 February 2016 Do now: Of what are comets made? And from where do they come?

What are comets? Once feared due to their mystery

What are comets? 3 parts – Tail: long, narrow column of dust, can be 100 million km (almost 1 AU) – Coma: cloud of gas, can be 100,000 km diameter (10x Earth) but very little mass – Nucleus: block of frozen ice and gas, about 10 km

Comet Halley

How do comets’ tails form? Comets aren’t visible unless within about 5 AU. Sun’s heat vaporizes ices into gases. Gases blown into an ion tail by solar winds. This points away from the Sun.

How do comets’ tails form? Dust tail: radiation pressure from the Sun pushes the dust coming off the comet.

Of what are comets made? 10 February 2016 Do now: From where do comets originate?

Of what are comets made? How can we tell the composition of a comet? – Fluorescence: wavelength of reflected light From dust from comets

Of what are comets made? 2005, NASA Deep Impact mission – Smashed a probe (370 kg) into Comet Tempel 10 km/ sec – Comet was made of water, silicates, clays

Of what are comets made? If comets pass too close to the Sun…….? – SOHO Observatory shows dozens each year falling into the Sun

Of what are comets made? Comet origins – Oort Cloud: trillions of icy bodies far beyond Neptune Surrounds the Solar System

Oort Cloud

Of what are comets made? Kuiper Belt – Begins about Neptune’s orbit, out to ~ 50 AU

Of what are comets made? Oort Cloud comets may take millions of years to orbit the Sun. Temperatures of 3°K or -454°F.

Of what are comets made? Most comets take millions of years to return Short-period comets – Less than 200 years – Kuiper Belt may contain more than 30,000 – Can they survive?

Homework #15 10 February 2016 Explain the difference between the tail of a meteor and the tail of a comet. Are they made of the same things?

What have been the results of giant impacts? 11 February 2016 Do now: What would happen if a meteor 10 m in diameter hit the Earth? 100 m? 1 km? 10 km?

Meteor Showers Asteroid fragments entering Earth atmosphere from the same orbit. Appear to come from constellation Perseus, hence Perseid Meteor Shower in mid-August.

What have been the results of giant impacts? This happens every few thousand years! 100 tons of meteoroids strike Earth every day – Most are smaller and our atmosphere slows them However……

What have been the results of giant impacts? Scars across our planet – Arizona: 50,000 years ago, 50 meters across – Impact crater 1.2 km across, 200 m deep

What have been the results of giant impacts? 1908, north-central Siberia (Russia) Trees leveled for 30 km

What have been the results of giant impacts? 65,000,000 years ago – End of Cretaceous Period – Iridium found in sediments

What have been the results of giant impacts? Chicxulub Meteor – 10 km across – Equivalent to several billion nuclear weapons – Mass extinction. Bye, bye dinosaurs!