Life elsewhere, 23 October 2013!Scientists know almost nothing about life, but have been interested in finding it 1.elsewhere in the solar system for a long time. !For example, it is discussed in Bernard le Bovier de Fontanelle's book "A A.Plurality of Worlds" which was published in 1695.!The vast majority of books discussing life elsewhere follow the same formula: 2.they list what they know about life, and what they know about elsewhere and see what matches. !The scientific contents in all of these books changes according to what year A.it was written (scientific understanding of biology has improved staggeringly over the last hundred years), but the formula stays the same.!This formula is necessary because astronomers do not have any actual B.information about life elsewhere. !Bottom line: there is no actual data in this lecture, just commentary.!3.Astronomers have constantly searched for life in increasingly clever ways A.and found nothing. !Still, this portion of the course has been considered legitimate for a long B.time. !While scientists don't know everything about biology, the general consensus is 4.that you need molecules that are capable of being chemically complex.!This limits the search for life to a search for carbon, which is the only A.element that forms large complex molecules under any conditions (that scientists know of). !Under any temperature, pressure, solvent, or absence of anything, only a.carbon makes long complex molecules. !Companies have been trying since the 1930s to find another element b.that does this (the results would be extremely valuable), but they have found nothing so far.!Silicon seems a promising element for this because it is right below 1.carbon on the periodic table and has 4 linkage places like carbon.!Unfortunately, the differences between silicon and carbon are much A.greater: !Carbon dioxide makes a good atmosphere, but silicon dioxide is a.an inert sand (not a suitable breathing material).!If you vaporize silicon dioxide (also known as silicate) you still 1.cannot breath it because the molecules have too much energy to hang together.!Even more important, no one has managed to make complex b.silicon molecules. !So far, scientist can only replace 1 carbon with 1 silicon to 1.make silicone, which is a useful chemical for lubricants that can tolerate higher temperatures.!The other elements that are useful for making carbon compounds on c.Earth are hydrogen, oxygen, nitrogen, sulfur, and phosphorous. !In the 1960s, this suggested that there may not be many places in the solar B.system that could have life. However, space craft soon brought back data which showed that carbon (and other elements necessary for life) were abundant throughout the solar system. Needing carbon does not restrict the number of places in the solar system which have potential for life too much. !There are also a lot of these chemicals in the nebula far beyond the solar a.system. !Even with this abundance, scientists have found no life elsewhere. !b.The usual way astronomers search for life in the solar system is to go from 5.object to object and see whether its conditions are suitable for it.!Mercury has some agreeable areas near its pole, but there there is no other A.reason for Mercury to have life. !Most astronomers believe that the surface of Venus is too hot for life, but B.the cloud deck is a comfortable temperature and has carbon dioxide, oxygen, sulfur, water, and phosphorous (chemicals necessary for life). !People who search for life tend to write off Venus when searching for life a.because they are surface chauvinist. They are so tied to their own way of living on the surface of a planet that they do not consider anywhere higher up or deeper down a suitable place for life. !This is a pity, because it is easier to get to the atmosphere of Venus 1.than to get to the surface of other objects with potential for life.!For 150 years, astronomers have considered Mars the most Earth-like place C.in the solar system, and therefore the most likely place to find life. !It is still considered likely, although astronomers haven't found anything a.after sending many probes into Mars' orbit and surface. !This is because their surface chauvinism prevented them from 1.searching for life where it is most likely to occur: !Mars' surface is probably not hospitable for life because too much A.ultraviolet light can get through its thin atmosphere. !However, if you go down into Mars' surface there is a layer of B.water over permafrost which has potential for life: !Although there is still some debate whether Mars has water on a.its surface, there is no question that there is liquid water inMars because where astronomers have seen water on Mars it has been seeping out of the ground. !This water would be a good solvent for biochemistry. !1.It is possible to have life without water, but it is easier to A.have life with water. !There are the right chemicals for life in this part of Mars. !b.Mars' temperature is also agreeable for life. !c.Methane was sporadically detected in Mars' air, which could possibly 2.be from microbes. No one knows for certain. !Professor Sperling proposes that astronomers dig down to Mars' b.permafrost and (respectfully) see if there are microbes there. !The way that scientists are thinking of implementing this plan is by 1.drilling down through the dust. This method is artificially difficult. !This already failed once: a drill on a spacecraft got stuck because A.the surface dust was too sticky. !A much easier way is to use a broom to sweep away the dust on B.Mars' surface. !It does not take high tech to get to permafrost, but it does take a.a mindset which scientists don't have.!The Gas Giants are generally rejected as possible abodes for life because D.they are too cold and do not have a surface. !This is not entirely true: !a.Although the cloud tops are too cold for molecular activity, the 1.insides of the gas planets are very hot. !There should be somewhere in between which is a suitable A.temperature for life. !There is no surface inside the gas planets, but there is a lot of 2.evidence life does not need a surface to form: !Life on earth began in a fluid.!A.Microbes on earth can live in the air, rocks, and at least 10 B.kilometers in the earth. !The ocean under Europa's surface is considered a good place to look for E.life, but it will be difficult to inspect it. !First, astronomers have to fly a spacecraft to jupiter and have it orbit a.near
View Full Document
Unlocking...