14 Comets & TNOsComets- Dust particles in a mixture of H2O, CO2, Methane, & Ammonia. “dirty snowballs”Comets found in Edgeworth-Kuiper Belt beyond Neptune as solid body called nucleus.When a comet travels in orbit close to sun (near Jupiter), it heats & solar wind forms a Coma (tail-gas & dust).Coma trails behind comet until it moves away from the sun, then the tail is in front of the comet.
15 Comets Halley’s Comet has a orbital period of 76 years. Last visible from Earth in 1986Named from Edmund Halley,18 century English astronomer-accurately predicted it’s arrival by looking at when previous comets had appeared.
16 Continued.. TNOs- Trans Neptunian Objects. Large bodies up to several hundred kilometers.Located in the Edgeworth-Kuiper Belt.
17 Asteroids Solid, rock-like masses. Irregular shape. Believed to be leftover material from solar system formation.Revolve around sun, most in circular orbit in asteroid belt.Some have long elliptical orbits.
18 Continued… Perihelion- closest to sun Theory: an asteroid or comet collided with Earth, causing dinosaur extinction 65 mya.Scientists are currently researching ways to prevent collisions with Earth by diverting objects before they reach Earth.
20 Meteors & MeteoroidsMeteoroid- rock or icy fragment traveling in space. Range of sizes.Meteor- light made by a meteoroid passing through Earth’s atmosphere. (shooting star)Meteor Shower- when Earth passes through a comet’s tail & many particles from tail burn up in Earth’s atmosphere as meteors.
22 MeteoritesThe part of a meteoroid that survives to strike Earth’s surface.3 Types:Stony (94%)iron (5%)stony-iron (1%)Most abundant meteorites in Antarctic ice cap because they are exposed et the surface when wind erodes the ice around them.
23 Impact CratersBowl-shaped depressions made by meteor/object that strikes a surface.About 150 known impact craters on EarthArizona’s Barringer Meteor Crater.Earth is geologically active & erases the marks of impacts. Oldest Earth crater- Vredefort Crater in South Africa 2 byo.
25 What happens to comets as they approach the sun? Assignment: Write down & answer the following questions on a separate sheet of paper.What happens to comets as they approach the sun?Where are most asteroids found?Explain the difference between meteoroid, meteor, & meteorite.Most meteorites formed between 4.55 & 4.65 b.y.a., making them a little older than the oldest moon rocks. Infer why moon rocks are younger than most meteorites.