Astronomy 1010 Planetary Astronomy Fall_2013 Day-28

Course Announcements Smartworks Chapter 8: Wed. Nov. 6 Smartworks Chapter 9, 10: Mon. Nov. 18 Smartworks Chapter 11, 12, 24: Fri. Dec. 6 Friday Nov. 1 – 3:00pm E306 Dr. Douglas Tucker, Fermilab, The Dark Energy Survey Exam-3 will be returned on Friday Exam-4: Monday Nov. 18 – Ch. 8, 9, 10 Dark Night Observing: Monday, Nov. 4 Starts at 8:30 pm at the Observatory

Rocks returned from Moon missions (1969– 1976) give ages through radioactive dating. Almost all cratering happened in the first billion years of the Solar System.

Hadean Earth, Dawn of Life Late Heavy Bombardment – ~3.9 Gyr ago Relatively quiet between formation and LHB Since then, protected by Jupiter Sterilizing Impacts km in diameter Completely vaporize the oceans Global surface temperature rise 2000 C (3600 F) Last ~ Gyr ago

Concept Quiz The Moon Long Ago Imagine taking a picture of the Moon about 2 billion years ago. What would you expect to see? A.It would have many fewer craters. B.It would have many more craters. C.It would have about as many craters as it does now.

Rock layers are formed through sedimentation. To find the ages of rock in these layers (or from Mars), scientists use radiometric dating. Parent particles decay into stable daughter particles at a steady rate. CONNECTIONS 8.1

Radioactive Dating Some elements can decay from one to another (e.g., uranium to thorium). These changes take place at known rates. Parent element declines, daughter element accumulates. Ratio of parent to daughter abundance gives the age of the rock. Age = time since rock was last molten.

A radioactive isotope decays to half its original amount in a half-life. MATH TOOLS 8.1

We model the Earths interior by studying earthquakes. Seismic waves travel differently through different materials. Some waves are surface waves; others travel through.

Primary waves travel through solids and liquids; they are longitudinal waves. Secondary waves go through solids only; they are transverse waves.

Earth has a crust, mantle, and core (dense materials). Produced by differentiation in the early Earth: Dense materials sink, low-density materials rise.

Current prevailing theory: Moon formed in large collision between Earth + Mars-sized protoplanet. The material collected to form the Moon. The composition of the Moon is like that of Earths crust.

The Moon and the other terrestrial planets have interiors similar to Earth. Deeper in a planet means hotter and more pressure. Formation energy and radioactive material help to heat the interior. Smaller planets lose heat faster; large ones more slowly.

Large planets cool off more slowly than small planets. If we assumed planets all began with the same amount of radioactive material and that the successive decay produced all the internal heat, then the rate of energy loss is dictated by how much energy there is (volume = 4/3 π R 3 ) and where the planet loses the energy (surface area = 4 π R 2 ). The amount of energy that could be lost divided by the area of loss is proportional to R/3, where R is the radius of the planet. MATH TOOLS 8.2

Earths magnetic field acts like a giant bar magnet. It originates from processes deep in the interior that are not understood fully. Iron-bearing minerals tell us the orientation changes over time.

Earth and Mercury are the only terrestrial planets with a substantial magnetic field. It is a puzzle why Venus and Mars do not have one. The Moon had one long ago.

Concept Quiz Internal Heat What should be true about Earths internal heat? A.It is produced by the magnetic field. B.It would have been greater long ago when Earth was young. C.It currently is produced by differentiation.

Tectonism is the deformation of Earths crust. Earths crust is broken into lithospheric plates. Continental drift and plate tectonics describe the movement of those plates.

Crustal plates are moved around by convectionthe rising and falling of hot/cold material. Earth has seven major plates and six smaller ones.

Plates can separate or collide. Because of these motions, most volcanoes and earthquakes occur along plate boundaries.

Exam Sadistics MetricEx-1Ex-2Ex-3 Number Mean StdDev Median Mode High Low302723