2012年5月26日
LECTURE 3
主题：Astronomy，讲土星的一个卫星Enceladus，说上面有水。 是一个类似宇宙照相机拍到的叫虎皮条纹- tiger stripes.
说是这点提供了什么证据然后说这么内部的能量是太阳光直接照的，还是放射。以及怎么适合生物存在。
Sscientists observed water vapor spewing from Enceladus's surface. This could indicate the presence of liquid water, which might also make it possible for Enceladus to support life. Candice Hansen,a scientist with NASA's Jet Propulsion Lab, headed up a research team on the plumes after they were found to be moving at 2,189 kilometers per hour (1,360 miles per hour). Since that speed is difficult to attain unless liquids are involved, they decided to investigate the compositions of the plumes.
Eventually it was discovered that in the E-ring about 6% of particles contain 0.5-2% of sodium salts by mass, which is a significant amount. In the parts of the plume close to Enceladus the fraction of "salty" particles increases to 70% by number and >99% by mass. Such particles presumably are frozen spray from the salty underground ocean. On the other hand, the small salt-poor particles form by homogenous nucleation directly from the gas phase. The sources of salty particles are uniformly distributed along the tiger stripes, whereas sources of "fresh" particles are closely related to the high-speed gas jets. The "salty" particles move slowly and mostly fall back onto the surface, while the fast "fresh" particles escape to the E-ring, explaining its salt-poor composition.
The "salty" composition of the plume strongly suggests that its source is a subsurface salty ocean or subsurface caverns filled with salty water. Alternatives such as the clathrate sublimation hypothesis cannot explain how "salty" particles form. Additionally, Cassini found traces of organic compounds in some dust grains. Enceladus is therefore a candidate for harboring extraterrestrial life.
The presence of liquid water under the crust implies that there is an internal heat source. It is now thought to be a combination of radioactive decay and tidal heating, as tidal heating alone is not sufficient to explain the heat. Mimas, another of Saturn's moons, is closer to the planet and has a much more eccentric orbit, meaning it should be exposed to far greater tidal forces than Enceladus, and yet its old and scarred surface implies that it is geologically dead.
LECTURE 4
讲考古学家研究那些古代的tool就自己做一遍
通过做一个东西的三个步骤不同的方法发现了可以这样来判断tool的日期和谁制造的。
举了两个例子：一个bronze做的东西和一个bamboo做的东西
bronze最后其实是祭祀才开始用的。