首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Why does the professor mention the discovery of a large dark spot on the surface of Titan?
Why does the professor mention the discovery of a large dark spot on the surface of Titan?
admin
2018-08-16
28
问题
Why does the professor mention the discovery of a large dark spot on the surface of Titan?
Listen to part of a lecture in an astronomy class. The professor has been discussing the planet Saturn.
Professor: As you know, we’ve been exploring the flat disk of rocky material that forms the rings which orbit the planet, but there are also over 16 moons orbiting Saturn, each one unique in its own right. Let’s start today by discussing one that’s particularly unusual: Titan. Does anyone remember what make Titan so unusual? Lauren?
Student 1: Well, it’s Saturn’s largest moon and it’s even larger than the planet Mercury.
Professor: Correct. Anyone else? Robert?
Student 2: It’s the only other world we know of, aside from Earth, that has something like a hydrologic cycle.
Professor: Ok, good and what does that mean exactly, hydrologic cycle?
Student 2: It’s a cycle where, where water is moved between liquid and gaseous states, so there’s evaporation, condensation, and precipitation.
Professor: Correct. Of course on Titan, it’s not water that’s involved in the cycle. It’s actually methane and ethane. I know we’re used to thinking of methane as a gas, but on Titan methane can take the form of a liquid and can be found in lakes and puddles. That’s because methane becomes a liquid at about minus 108 degrees Celsius. On Titan, that’s nothing. Titan is so cold, it can reach temperatures as low as minus 183 degrees Celsius. Now, for the past few years we’ve been observing Titan and its atmosphere from a spacecraft called Cassini that’s in orbit around Saturn. And one thing we’ve noticed about Titan’s surface is that it only has lakes at the poles. The equator on the other hand is unusually dry and covered with sand dunes, but there’s also what appear to be dried-up channels and rivers pointing to the possibility of rainfall at some point in the past, which may well be the case because recently we think we’ve seen evidence of rainfall near Titan’s equator. Of course, we can’t actually see it raining from Cassini because it would be obscured by the clouds, but we did see images of a large dark spot near Titan’s equator just after the clouds that passed over that area.
Student 1: Oh, I get it. It’s like when it rains on Earth and the wet sidewalk turns dark.
Professor: Exactly. Also, the dark spot started fading very fast, like when evaporating. Now, this evidence of rain is very significant. Why? Well, it’s the first example of extraterrestrial rain we’ve ever observed, and what may be even more significant is the timing of this rain. See, there’s a model of Titan’s precipitation that predicts that equatorial rain would only occur during spring or autumn, and it was spring on Titan when Cassini took these images. This model is based on something we call the Inter-Tropical Convergence Zone or ITCZ. Can anyone tell me what that is?
Student 1: Yeah, isn’t the ITCZ the area of a planet where like the surface winds from the northern and southern hemispheres meet or converge? It’s an area of precipitation.
Professor: That’s exactly right. Now, on Earth this zone stays within the tropics because the weather systems on both the north and the south sides of the equator block the ITCZ in and don’t allow it to move much. That’s why there’s rainfall on our equator year round, but on Titan, we think the ITCZ migrates almost from pole to pole every half year, so it basically never remains over the equator for a long time. That may be why we hadn’t seen scenes of equatorial precipitation until now when Titan’s ITCZ was passing over its equator at the same time Cassini was in the neighborhood.
Student 2: So what we have to address is what explains Titan’s ITCZ migration?
Professor: Well, most likely because of Titan’s slow rotation period. See, we think that slow rotations cause simpler atmospheric circulation patterns, and simpler circulation patterns mean that there aren’t large weather systems surrounding the ITCZ that would keep it from shifting, from moving from one pole to the other. Not like on Earth and Titan takes nearly 16 Earth days to rotate just once. At any rate, Titan, with its quasi-hydrologic cycle, is definitely a world that we should be doing research on. You see, even though it’s too cold to sustain life, Titan, with its methane clouds, its methane and ethane lakes, Titan may give us some clues as to what our planet was like before the development of life, so this make it imperative that we study Titan to better understand how Earth may have started out.
选项
A、To emphasize that surface winds have changed the landscape
B、To show how lakes are detected on Titan
C、To identify one reason scientists now think that it rains on Titan
D、To point out the difficulty in distinguishing surface and atmospheric features on Titan
答案
C
解析
组织结构题。在解释科学家判定泰坦星上存在雨的结论时(recently we think we’ve seen evidence of rainfall near Titan’s equator), 提到通过卡西尼号探测器(Cassini)看到一个大暗点,即表明此处的large dark spot正是前文提到的evidence,提到暗点的目的是为了说明科学家如何得出存在雨水的结论,因此C选项为正确答案。教授未提到表面风对地形的影响,因此A选项不正确。根据讲座内容:we did see images of a large dark spot near Titan’s equator,即暗点的发现是在赤道。此外,one thing we’ve noticed about Titan’s surface is that it only has lakes at the poles,即湖泊的发现是在两极地区,因此暗点的发现不能说明湖泊是如何发现的,因此B选项不正确。教授也未指出在区分地面和大气特点中存在的困难,因此D选项不正确。
转载请注明原文地址:https://kaotiyun.com/show/8NfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteNOMORETHANTWOWORDSAND/ORANUMBERforeachanswer.AnOverviewofTheResearchonAmberAmb
Completethenotesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.GIVINGASPEECHReasonsfornervousnessLecturers
Choosethecorrectletter,A,BorC.WhydidthelecturerchoosetofocusonthePleasantonTownMarket?
ChooseTWOletters,A-E.WhichTWOpre-existingfeaturesofthesitearenowpartofthenewfacilities?AfootballstadiumBpl
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
Completethenotesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.GIVINGASPEECHReasonsfornervousnessLecturersofte
Completethenotesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.GIVINGASPEECHReasonsfornervousnessLecturersofte
Choosethecorrectletter,A,BorC.Accordingtothespeaker,whatistrueaboutthebus?
ChooseTHREEletters,A-F.WhichTHREEthingsarethestudentsrequiredtosubmittotheirprofessor?AawrittensummaryBnote
随机试题
Jimknowslittleofmathematics,______ofchemistry.
经产妇,68岁,绝经16年。阴道反复流血3个月就诊。查体:肥胖,一般情况好,血压160/110mmHg。妇科检查:阴道少量流血,宫颈光滑,子宫正常大,双侧附件未见异常。下列首选的辅助检查是
A.降气平喘,祛痰止咳B.宣肺降气,清热化痰C.降逆化痰,益气和胃D.降逆止呕,益气清热E.温中益气,降逆止呃
甲从某单位偷了一张金额为20000元的汇票,并将其赠给朋友乙,乙不知道该汇票是甲偷盗所得,在付款提示期限内向银行请求付款,遭到拒绝,对于乙的付款请求,下列说法不正确的是哪些?()
(2017年第89题)关于地下工程墙体施工缝的说法,错误的是()。
某建设项目的进口设备采用装运港船上交货价,则买方的基本义务有()。
费正清在《传统与现代》中说:“中国的政治生活一旦失去了天子的存在就不可避免地走向了崩溃,因为此时的国家首脑已经得不到传统礼教对至高权威持有者的支持了。”费正清这句话旨在说明()。
依据《中华人民共和国行政处罚法》规定,限制人身自由的行政处罚应由()。
某种智力测验的均值为100分,标准差为15分,信度系数为0.96。一名受试的分数是120分,那么该受试真实智力水平的95%的置信区间是
Everyoneknowsthattaxationisnecessaryinamodernstate:withoutit,it【C1】______notbepossibletopaythesoldiersandpol
最新回复
(
0
)