詹姆斯韦伯太空望远镜会揭示另一个地球吗？

随着 2021 年 12 月詹姆斯韦伯太空望远镜的发射，有史以来最昂贵、最雄心勃勃的科学计划之一开始运行。既然望远镜已成功部署在其在太空中的独特位置，其先进的仪器将能够收集有关科学家曾经梦寐以求的问题的数据。其他星球上有生命吗？超大质量黑洞如何塑造星系中的质量？ JWST 可能很快就能告诉我们。

在这一集中，主持人 Steven Strogatz 与两位领导 JWST 对我们宇宙的观测的研究人员交谈：望远镜近红外相机的首席研究员Marcia Rieke和研究太阳系外行星的天体物理学家Nikole Lewis 。

（有关 JWST 及其建造和发射历史的更多信息，请阅读 Natalie Wolchover 的文章“ 韦伯太空望远镜将改写宇宙历史。如果它有效”，该文章最近荣获2022 年普利策解释性报告奖）。

在Apple Podcasts 、 Spotify 、 Google Podcasts 、 Stitcher 、 TuneIn或您最喜欢的播客应用程序上收听，或者您可以从Quanta流式传输。

玛西娅·瑞克

Marcia Rieke (01:56)：我很高兴来到这里。

Strogatz (01:57)：我很高兴能和你交谈。我的意思是，这些年来你做了这么漂亮的工作，这么重要的工作。事实上，在韦伯太空望远镜的这个主题上——公众如此兴奋是不寻常的。我的意思是，很多媒体对此进行了报道。帮助我们理解为什么这如此令人兴奋？为什么这台新望远镜对天文学和宇宙学如此重要？

Rieke (02:20)：我认为兴奋源于成为哈勃的继任者，人们已经习惯了可爱的哈勃照片，哈勃的伟大发现。韦伯望远镜项目的整个结构是超越哈勃，而是继续兴奋，甚至增加兴奋。因为我们正在开辟电磁频谱的新部分。也就是说，打开光可以具有的一组波长的新部分进行研究。我们正在使用比哈勃望远镜更大的望远镜来做这件事，它的工作波长要长得多。因此，我们将看到一种全新的宇宙观，它将告诉我们很多很多新事物，包括一些我们现在可能没有猜到的东西。

Strogatz (03:08)：我们甚至可能无法想象的事情，就目前而言。许多想象望远镜的人可能会想到其中一个巨大的望远镜，它位于某处山顶的天文台中。但这是一个太空望远镜，韦伯。只是提醒我们，为什么它如此有利 – 真的，你为什么要费心在外太空放置望远镜？

Rieke (03:28): 好吧，我们不厌其烦地把望远镜放在外太空，因为地面上的望远镜必须穿过地球的大气层，这限制了我们的能力。而在韦伯的情况下，我们要观察红外波长，所以望远镜需要冷却。如果你试图将地球山顶上的望远镜冷却到足以看到这些昏暗、微弱、遥远的东西、大气、水等，望远镜上就会结冰，它就不能再使用了。所以我们需要去太空的真空。这让我们可以冷却望远镜，它还可以消除大气的任何吸收。

Strogatz (04:10)：在我们深入研究韦伯之前，让我先想想哈勃一秒钟。我想很多人都会记得，有一张由哈勃拍摄的绝对华丽的照片，真正令人叹为观止的照片，被称为哈勃深场，它让我们在一张快照中看到了数千个星系。但是，我不得不承认，当我看到那张照片时，它看起来非常漂亮。许多看起来令人惊叹的星系以各种不同的角度、不同的颜色和形状倾斜。但我想我可能错过了我们从那幅深场图像中真正学到的东西。这张照片让你和你的同事们兴奋不已？

Rieke (04:48)：哦，令人兴奋的是，我们发现了比以往任何时候都更远的星系。你必须明白，当观察非常遥远的物体时，天文学变成了一种时间机器，因为光需要很长时间才能到达我们身边。因此，哈勃在该深场图像中所做的是揭示了光花了 120 亿年才到达我们的星系。如果你知道宇宙的年龄，你就会知道这意味着我们在观察这些星系时，它们的年龄还不到 20 亿年。当时我们可以识别为有恒星的星系存在这一事实非常令人惊讶。没有人知道会是这样。

Strogatz (05:36)：这真的是对你所掌握的语言的一种美丽、生动的使用，这次是时间机器的类比，它真的是真的，不是吗？我们就是这样，当我们看着这些非常遥远的星系时，我们真的是在回顾过去。

Rieke (05:49)：没错。这就是韦伯背后的目标之一，就是回到更远的时间，回到更接近大爆炸发生的时间，并填写星系如何形成和演化为我们今天所看到的星系的最后剩余步骤。

Strogatz (06:07)：你估计你可以用新望远镜走多远？

Rieke (06:11)：嗯，我们希望能在大爆炸后几亿年内。当你记得宇宙有 137 亿年的历史时，这只是从一切开始的一小部分。

Strogatz (06:27)：假设一切正常，这些将是前所未有的宇宙婴儿照片。

Rieke (06:32)：正是这个想法。我们希望看到大爆炸后星系形成的第一步。

Strogatz (06:39)：那么红外天文学和你自己的专业呢？哈勃和韦伯之间的对比是什么？

Rieke (06:46)：哦，有很大的不同。哈勃望远镜镜保持在 76 华氏度，这是制造它的实验室的温度。这意味着，那个温度，有相当多的热辐射是由望远镜本身发出的。这种热辐射会淹没来自最遥远星系的信号。因为哈勃是温暖的，所以从来没有任何理由安装红外仪器，它的工作波长比可见光波长的三到四倍更长，因为它是如此温暖。

所以韦伯被设计成既冷又能在更长的波长下工作。因此它可以观察到哈勃无法触及的波长的事物。这很重要，因为宇宙正在膨胀，所以会出现红移，与救护车经过并且警报器的音调发生变化时您感觉到的频率变化相同。因此，我们想要探测的这些非常遥远的星系的波长发生了相当大的变化，因此离开星系的可见光现在以红外光的形式出现在我们面前，而哈勃根本无法探测到它们。

Strogatz (08:13)：那么请告诉我们一些关于 Webb 上的一些仪器的信息，以及他们将要关注的内容？

Rieke (08:18)：一共有四种乐器。我是近红外相机NIRCam 的 PI [主要研究员]，它将拍摄类似于哈勃深场的图像。它还会做很多其他事情。

(08:34) 另一种仪器称为 NIRSpec，您可能会猜到，它是近红外光谱仪。这样做是为了如果我们将这些非常遥远的星系之一定位在它的输入端，如果你愿意的话，光会扩散到它的组成波长或颜色中。然后我们可以做更详细的研究，比如了解星系中恒星的相对组成，星系中的恒星可能是如何运动的，很多有趣的事情。

(09:09) 另一种仪器称为 MIRI，代表中红外仪器，它仍然可以在更长的波长下工作。因此，对于那些可能有一些灰尘遮住它们或有非常、非常、非常高的红移、非常遥远的物体，它可能能够检测到它们。它对于研究刚刚在我们自己的银河系中形成并被尘埃云隐藏的系外行星和恒星也非常有用。

(09:43) 第四种仪器称为 NIRISS，近红外无狭缝光谱仪，它具有多种功能。对我来说，最有趣的是它可以获取凌日光谱。那是当一颗系外行星从它的母星前面经过时，星光被系外行星的大气层吸收。如果你拍一张光谱，你就可以确定那颗系外行星的大气成分是什么。这正是 Nikole Lewis 非常感兴趣的数据类型。

Strogatz (10:20)：让我们谈谈你个人和你的团队。您自己有多少时间使用韦伯望远镜进行您想要进行的观测？

Rieke (10:29)：我的团队总共有 900 小时。

Strogatz (10:32)：是一点还是很多？

Rieke （10:33）：嗯，望远镜每年可以观测大约 8,000 小时，所以我会说这是相当多的。

Strogatz (10:42)：是的，听起来是这样。这是全年的很大一部分吗？好的。你会看什么？

Rieke (10:48)：我们有一个非常多样化的计划。我们将做一个非常深入的调查。我们将要做两个领域，一个是原始的哈勃深场，另一个是由哈勃和钱德拉 X 射线望远镜完成的研究非常好的领域，称为超深场。然后下一个最大的时间将用于观察系外行星的凌日，开始了解它们的大气层。

Strogatz (11:14)：你如何做深场图像？

Rieke (11:17)：你要做的就是在你想要将相机指向的地方布置一个图案，这样你就可以覆盖足够的区域。所以你拍一张照片，走一步，拍一张照片，再拍一张照片，等等。实际上，当我们拍照时，我们会指向一个地方大约 20 个小时。我们将改变我们正在观察的波长，再观察 20 小时，然后检查我们正在使用的所有九个滤光片。然后我们将进入下一个位置。对于我们正在进行的深度调查的最大部分，我们将拍摄 7,000 多张单独的图像，这些图像将组合在一起，以制作你在哈勃望远镜上看到的那种深空图像。

Strogatz (12:02)：我想我明白你在说什么。我的意思是，我记得，作为一个孩子，就像打开一个老式相机，长时间曝光，只是指向天空的想法。是这样的吗？你说指向一个方向20个小时？

Rieke (12:17)：是的，但我们不会进行一次 20 小时的曝光，因为在太空中存在一种称为宇宙射线的效应，实际上大部分是从太阳表面沸腾的质子。当它们飞过红外探测器时，会发出一点明亮的光迹。所以我们要做的，为了避免那些完全破坏画面，我们将曝光大约三分之一小时。然后，打个比方，我们会关上百叶窗。然后我们将在读取图像后再次打开它，然后再拍摄一张并重复此操作。而且我们可能会在每次曝光之间稍微改变指向，以便我们可以平均检测器上的一些坏点等等。我们的主要深度调查包含 7,000 多张图像。

Strogatz (13:13)：那么这将是希望，让我们回到最早的日子。你能给我们一些关于星系、恒星起源的标准图片的背景吗？比如，有没有类似于粒子物理学的标准模型的东西？你有星系演化或恒星形成的标准模型吗？

Rieke (13:36)：嗯，现在肯定有一种普遍接受的框架。所以有大爆炸，宇宙开始膨胀。最初，宇宙中的所有物质，气体，主要是氢、氦和其他一些小部分，正在膨胀和冷却。大爆炸后大约 40 万年，它冷却到足以使分离的电子和质子结合形成氢原子。电子基本上绕着氢运行。那是宇宙微波背景发射的时候，就是发生这种情况的时候。

（14:15）随着气体进一步冷却，我们知道其中有一些——我们可能认为是团块或团块。它不是完全光滑的。有一点结构。在氢气多一点的地方，这种气体的引力场会稍高一些，会导致气体聚集在一起。随着越来越多的团块聚集在一起，最终它会达到足够的物质开始形成恒星的程度。然后，这些恒星最终将成为星系的组成部分。但是其中的某些部分我们并不确定它究竟是如何工作的，部分原因是我们知道宇宙中有暗物质，以及暗物质团块如何将氢引导到形成星系的团块中——那里在那个理论中有很多缺失的部分。

(15:12) 但是有什么东西让一切都聚集在一起，恒星形成，然后它们变成了我们可以探测到的星系。一旦我们到达大爆炸后大约 5 亿年，我们就可以很好地了解哈勃望远镜拍摄的星系是什么样子。我们知道有一种星系演化序列，其中一些最初形成的小星系合并在一起形成更大的星系。其他人则更加孤立，而星星只是在进化。它们中的一些保持足够的气体并且正在旋转或其他任何可能影响恒星形成条件的东西，因此它们不一定会同时形成所有恒星。

(15:58) 在这部分图片中甚至还有空隙。因为我们今天知道我们周围有两种主要的星系。有像银河系一样的螺旋线，它们通常仍在形成恒星，周围有大量的气体和尘埃。还有一些我们称之为椭圆的星系，它们看起来有点像图片中的模糊足球。出于某种原因，这些星系很早就吸收了它们所有的气体并形成了恒星，我们说它们的恒星形成已经熄灭。但是为什么这两类星系之间存在这种差异仍然完全不完全清楚。我们有一些想法，但同样，韦伯的观察将非常有助于填补这些模型中的空白。

Strogatz (16:51)：黑洞呢？还是所谓的超大质量黑洞？我们会得到一些关于他们在这个故事中的角色的信息吗？

Rieke (17:00)：哦，确实。事实上，有许多客座观察员提议来研究这个问题。以及为什么我们今天看到银河系中心黑洞的大小与银河系的总质量之间存在这种非常紧密的关系，尽管该质量分布在比黑洞大得多的区域上。为什么存在这种关系是目前黑洞和星系天文学的突出问题之一。

因此，当我们进行这些深度调查时，在红外线等条件下进行这项工作的好处之一是，我们将能够更好地了解其中一些星系的中心是否可能存在黑洞，然后我们将能够进行更多研究，将我们所看到的潜在黑洞联系起来，这可能是使用 NIRSpec 最好的揭示，而银河系的其他特性则最好由 NIRCam 和 MIRI 揭示。因此，我们将能够看到黑洞大小和星系大小之间的这种关系是否可以一直追溯到过去。或者，如果需要一段时间才能建立起来。

Strogatz (18:18)：让我们讨论一下。里面有很多有趣的科学。首先，您指的是黑洞大小与星系本身大小之间的关系。

Rieke (18:28)：对，当我在这里说大小时，我实际上指的是质量。因此，一个黑洞，一个巨大的超大质量黑洞的质量可能是太阳质量的 1 亿倍。它所在的星系可能更像是太阳质量的 100 亿倍。不管它是 100 万太阳质量的黑洞，还是 1000 万太阳质量的黑洞，或者大小范围内的任何地方，如果你去测量黑洞周围星系的质量，它几乎总是完全相同比率。所以如果你把黑洞的质量乘以一个数字，比如——我忘记了确切的值，它在 100 到 1,000 之间。然后你知道它所在的星系的质量，这就自动表明有一些过程使这两者保持同步，而那是什么并不明显。

Strogatz (19:35)：它的引力影响主要集中在它自己附近有什么意义？

Rieke (19:40)：没错。是的，例如，如果你看看我们银河系中的黑洞，它的质量大约是太阳的 400 万倍。它仅在距中心约 10 光年的距离内主导着银河系的引力场，而银河系本身却有 50,000 光年宽。那么这个小区域中的某些东西如何影响它的整个其余部分呢？

Strogatz (20:13)：你说也许我们会发现这种关系甚至可以追溯到最早的星系。

Rieke (20:19)：是的，这就是问题所在。因为这种关系是从什么时候开始建立的？这会告诉你一些关于星系演化的有趣事情。还有一个先有鸡还是先有蛋的问题。哪个先出现，黑洞还是星系？

Strogatz (20:36)：如果我现在可以请你反思一下你的职业生涯——我的意思是，你是在 70 年代开始的。你有没有期望看到詹姆斯韦伯太空望远镜预计会看到什么？

Rieke (20:48)：不，因为当我刚开始的时候，红外天文学还很原始，按照我们现在的标准。我们没有可以拍照的光传感器。可以这么说，我们只有一个像素。为了拍一张照片，你必须测量一个点，移动望远镜，测量这个点，然后你必须绕着天空走一步。这往往意味着，除非它是一个非常有趣的来源，否则我们大多只研究物体上的一个点。所以对于大多数星系，我们只研究星系的中心而不是其他的，因为否则很难做到。所以我可以拍一张照片中会有数千个星系的想法，就像，我不敢相信。

Strogatz (21:36)：我相信这对你个人来说是非常令人满意的，一定是，在你的职业生涯中仍然很强大，现在有这种能力来看待事情。你一定很想等待那些第一张图片回来。

Rieke (21:49)：哦，我希望我不会——第一张照片将是我们在望远镜中排列的第一张照片，或者我们看到一颗恒星 18 次，因为这些片段没有排列整齐。没关系，我会很高兴，因为这意味着星光已经通过望远镜，并且已经记录在相机中，我已经等不及了。一旦发生这种情况，我将真正开始放松。

Strogatz (22:15)：那是你的个人本性吗，就像你不想超越自己一样？

Rieke (22:18)：是的，其中有一定的因素。

Strogatz (22:20)：如果不是太荒谬的话，你介意我问你下一代望远镜，太空望远镜吗？您必须提前考虑，对吗？建造其中一个需要几十年的时间。

Rieke (22:30)：对，就是所谓的 Astro2020，一项针对该问题的美国国家科学院十年期调查。事实证明，我已经足够大了，我可能不会再参加另一场了。但天文学家确实有野心，他们正在寻找比韦伯更大、更复杂的野心。但它们要到 2030 年代才会开始。

Strogatz (22:35)：你能给我们粗略的描述一下他们会是什么样子吗？他们会寻找什么？

Rieke (22:59)：十年调查提出了两种不同的类型。一种类似于类固醇的韦伯。它被称为LUVOIR ，LUVOIR。它的目标是明确证明我们发现了一颗能够承载生命的类地行星。望远镜镜面的直径将是韦伯镜面的两倍多，而且它的遮阳板会大得多。这是我有一些怀疑的地方，因为它已经很难测试韦伯的了，但无论如何。

(23:43) 它的基本原理是研究系外行星并寻找生命的证据。另一种策略是使用较小的望远镜，但在望远镜前方可能 20,000 英里外放置一个星盾，而不是遮阳罩，以阻挡来自恒星的光线，以便让望远镜拍摄行星的图像环绕它。这也是一个有趣的想法，所以你可以看到这两个望远镜项目的目的都是比韦伯更详细地研究系外行星。

Strogatz (24:23)：让我感谢你这次非常愉快的谈话，玛西娅。非常感谢。

Rieke (24:28)：谢谢你邀请我。

播音员(24:33)：随时了解科学和数学的最新动态。注册广达杂志通讯。它是免费的，每周五登陆您的电子邮件收件箱。前往 quantamagazine.org 了解有关如何注册的更多信息。

Strogatz (24:53)：我的下一位嘉宾是康奈尔大学的系外行星科学家兼助理教授 Nikole Lewis。 Nikole 和我实际上一起工作并且彼此认识。我们共同建议博士。学生和博士后在一起。但这实际上是我第一次和她谈论她的科学，除了我们对学生的建议，我真的很期待。

(25:16) Nikole 特别关注系外行星大气，以及云和雾霾形成等大气过程。 Nikole 使用来自哈勃太空望远镜的数据，于 2018 年共同领导了 TRAPPIST-1 系统的光谱调查。这是对地球大小的系外行星的首次此类调查。而且，为了让您了解这一切有多新，第一颗系外行星仅在 1995 年被发现。通过詹姆斯韦伯太空望远镜，尼科尔希望更仔细地观察系外行星及其大气。感谢您加入我们的播客，Nikole的喜悦。

妮可·刘易斯

Nikole Lewis (25:54) 很高兴来到这里，史蒂夫。

Strogatz (25:55)：我很兴奋。听到关于行星的消息我真的很兴奋，而且——我的意思是，你会把自己描述为行星科学家，我称你为系外行星科学家，但是——

刘易斯（26:04）：是的，我的意思是，我的培训是作为一名行星科学家，这就是我拥有博士学位的领域，而且，正如你所提到的，系外行星科学领域是如此新，人们无法决定我住的地方。我研究太阳系物体的行星科学兄弟们就像，“你是天文学家！”我的天文学家兄弟们就像，“不，你是行星科学家！”所以，我只是编造了一个新的系外行星科学家类别。

Strogatz (26:25): 只是一秒钟，因为我从来没有上过行星科学的课程，或者肯定没有上过系外行星科学，作为你所在地区的外行，在我看来，这对你来说一定是一个黄金时代.因为在很长一段时间里，像古人一样，肉眼只能看到五颗行星之类的东西。然后，在我整个童年时期，我都被教导有九个行星。但是，我的意思是，现在你有大约 4,500 多个行星需要考虑和观察。

刘易斯(26:54): 是的，这当然是黄金时代，我喜欢告诉人们，我真的很幸运。我进入了我的博士学位。 2007 年的计划，那时可能有大约 20 颗系外行星。从那时起，我就在某种程度上顺风顺水，我的意思是，自从我进入这个领域以来，我们一直在以指数方式增加已知系外行星的数量。所以现在是这样做的好时机。

Strogatz (27:17)：令人惊讶。我的意思是，就像发现的时代一样，类比有点愚蠢，就像整个宇宙都打开了。嗯，是。成为行星科学家的好时机。那么，让我们从头开始吧。我们一直在说“系外行星”，但它们是什么？

刘易斯（27:32）：是的，所以，系外行星实际上是太阳系之外的任何行星体。实际上，作为一个有趣的故事，根据国际天文学联合会对行星的定义，系外行星实际上并不是行星。就像冥王星不是行星一样。但它们是与我们自己的太阳系中的行星大致相当大小的物体，只是碰巧绕着其他恒星运行。

Strogatz (27:53)：所以它们不是——说它们不是行星似乎有点奇怪。不过没关系。为什么像你这样的人对它们如此感兴趣？

Lewis (28:00)：它们很有趣，因为它们为我们提供了不同的数据点，基本上，为了理解，实际上是我们自己系统中的行星。尤其是地球，对吧？如果你看看我们自己的太阳系，我们知道有一颗行星在那里诞生了生命。我们有一个邻近的行星，金星，它的大小大致相同。你有两个几乎没有空气的较小的岩石行星。火星的气氛非常稀薄。然后你就有了这些巨大的巨行星。

(28:25) 因此，如果我们试图将自己置于上下文中，并尝试理解，例如，我们是如何到达这里的，我们是一个人吗？我们真的没有足够大的样本，所以对我来说真正令人兴奋的是有 4,500 颗行星的样本可以玩，与我们自己的相比，它们处于所有不同的状态，实际上范围更广太阳系行星。因此，这是走出去以在太阳系中不可能的方式学习物理和化学的好方法。

Strogatz (28:52)：当我今天走过去时，我想到了一种类比。如果在过去，如果你是一名生物学家，你只有九种动物要研究，九种类型，比较这个主题与拥有 4,500 种类型相比会是什么样子。这些动物代表着现在存在的不同种类的行星。

刘易斯（29:10）：是的，确切地说，而且，你知道，第一颗被发现的系外行星是一颗木星大小的行星，它的轨道非常靠近它的主星，称为热木星。人们很长一段时间都不会相信。他们就像，“那不是气态巨行星所在的地方。他们住在离星星很远的地方。”因此，这是我们对行星系统外观理解的真正革命。

Strogatz (29:28)：当你提到岩石行星和巨大的气体行星时，让我们强调一下你在那里所说的内容。岩石行星是什么意思？气体行星是什么意思？

刘易斯（29:38）：是的，所以，当我想到它们时，我实际上会稍微考虑一下它们的气氛，这主要是我研究它们的方式。在我们自己的太阳系中，所有的行星，无论是近的还是远的，都是由同一个星云形成的，实际上，我们的太阳也是由这个星云形成的。所以我们都是从同一个气体和尘埃云中诞生的。随着时间的推移，离太阳更远的行星能够吞噬大量的气体和冰。这就是他们变大的方式。靠近的行星无法接触到这种冰冷的物质。所以他们不能变得很大。最后，它们最初的大气层实际上被吹走了，它们实际上是用从行星表面排出的气体形成了大气层。

所以这就是你最终得到这个，有点，小行星，靠近的方式。我们认为它们是岩石的，因为它们无法将冰融入它们的行星物质中。然后，在我们的太阳系中恰好更远的东西，在太阳系形成期间能够吞噬一堆氢和氦。

Strogatz (30:39)：你提到在它们的恒星附近发现了木星大小或差不多大小的巨大行星——当你谈论系外行星时——这似乎很疯狂，它们可能是这么大，那么近。

刘易斯(30:54)：是的。因此，用于发现周围第一颗系外行星（类似于太阳的恒星）的探测技术与多年来用于研究双星系统的探测技术类型相同。因此，天空中超过一半的恒星实际​​上处于双星或多星系统中。我们有点奇怪，因为我们没有另一颗与我们自己的轨道共享轨道的恒星。所以这些技术被用来寻找越来越小的东西。

所以在这里，人们看到的是一颗恒星的标志，显然它有木星大小的东西在拉扯它。当他们进行计算时，他们说，哦，好吧，那么它必须在这个，基本上是一个四天的轨道。这让每个人都大吃一惊。同样，在我们的太阳系中，水星在 88 天的轨道上。这颗行星，不只是对于气态巨行星，对于任何行星，都异常接近恒星。

Strogatz (31:49)：所以你在这里以各种方式让我大吃一惊。你说，通常情况下，一颗恒星会有一颗伴星，那双星是规则而不是例外？我没听错吗？

刘易斯(31:58)：没错。天空中超过一半的恒星处于双星或多星系统设置中。那是因为你知道，通常形成恒星和行星的尘埃和气体云实际上会产生不止一颗恒星。

Strogatz (32:11) 所以，这真的给了我这样的印象，我想我应该从科学史中知道，我们有一个非常狭隘的观点。你知道，就像，当我们看其他地方时，我们认为它会是这里的样子。事实并非如此。我的意思是，在科学史上，这一次又一次被证明是错误的。

刘易斯(32:29)：是的，非常如此。我将谈谈开普勒任务可能在过去 10 年中发生的最大发现之一，就是我们发现迄今为止我们发现的大多数系外行星实际上都在地球大小之间和海王星。而这些大小的行星实际上并不存在于我们的太阳系中。大多数太阳系形成模型并没有预测到这种规模的形成。它们就像，应该形成地球大小或更小的东西，然后基本上应该形成海王星大小或更大的东西。 And so that sort of blew open, very wide, our understanding of how the solar system formed and the fact that we are actually not the normal thing that we see out there in our galaxy.

Strogatz (32:41): Here, I can’t resist trying to make this vivid for anyone who hasn’t thought about these things before. The place where we both live, Ithaca, New York, has this fantastic scale model of our solar system that you can walk through. So everything is 5 billion times smaller than it really is, in this scale model that we call the Sagan Walk . And on that scale, the Sun looks about the size of a dinner plate. Mercury looks about the size of, like a tiny grain of couscous. And the Earth and Venus are sort of like a little pea, very little. And Jupiter is something like about a brussels sprout, maybe. And so when you say that there’s something in between Neptune and Earth, I’m picturing like, a good size pea. Maybe.

Lewis (33:51): I don’t know, maybe a lima — I guess it’s not round.

Strogatz (33:53): A lima bean? Okay.

Lewis (33:54): A lima bean. In between a brussels sprout and a pea. Yeah, so, you know, most of the planets in our galaxy, and we assume in other galaxies, are actually somewhere in between the size of a brussels sprout and a pea on this scale.

Strogatz (34:05): If you’re okay with this. I don’t want to force you into my vegetable analogies here.

Lewis (34:10): No, no, it’s fine. I’m just trying to think of a good vegetable that’s in between the size of a brussels sprout and a pea.

Strogatz (34:16): Like one of the smaller grapes on the bunch.

Lewis (34:18): Yeah, maybe. And we call them, actually, mini-Neptunes and super-Earths. Basically, we just adopted, they’re somewhere in between these two things. So they’re either super-Earths, or they’re mini-Neptunes and so, sure, super-Earths and mini-Neptunes are the size of a grape on the scale of the Sagan Walk.

Strogatz (34:33): Yeah, just in case anyone’s trying to picture this and you haven’t experienced the Sagan Walk. So, it could take you, like, five minutes to walk from one planet to the next, once you’re in the outer part of the solar system. Do we know anything about the exoplanetary systems’ orbital distances from their stars?

Lewis (34:47): Yeah, that’s the other interesting thing is that we’ve actually found — most of the planets we’ve found to date orbit a lot closer to their stars than the planets in our solar system. And part of that is an observational bias, just based on the techniques that we have, but nearly all of the planets that we’ve discovered to date orbit within a year, or what’s called one astronomical unit of their host star, and that means you could have anywhere between one to seven planets actually crammed into the same distance between the Earth and the sun.

Strogatz (35:15): Okay, so if I could ask you for a kind of blanket statement about what do we think we already know about exoplanets? And what do we not know?

Lewis (35:23): That’s a big question.

Strogatz (35:24): Yes, I realize it’s a big question.

Lewis (35:25): Yeah, I mean, I think what we do know about exoplanets is that they’re abundant. So I will use that. For every star in the sky, there’s certainly at least one planet. And so, we should expect that most stars that we look at have planets orbiting them. And you know, part of what the Kepler Mission was actually trying to do was to measure something called eta-Earth, which is the frequency of Earth-size planets in Earth-like orbits around sun-like stars. And unfortunately, we weren’t able to run the Kepler Mission as long as we would have liked to, but we started to get a handle on, sort of that frequency. And it does still seem that Earth-size planets in Earth-like orbits around sun-like stars are not as frequent as we had hoped. But there are literally planets of all shapes and sizes everywhere in our galaxy and also in our universe.

Strogatz (36:11): What about this system that you have taken a special shine to, the TRAPPIST-1 system? Tell us a little about that, and why you find it so interesting.

Lewis (36:19): The TRAPPIST-1 system, it’s been quite a ride. Again, it’s one of these systems that no one expected to be there. And in fact, the team that discovered it had decided that they were going to look for planets around these very, very cool stars. And a lot of planet formation theory was like, there shouldn’t be planets around these cool stars, they’re too small, they’re almost — are so small and cool, they’re actually the size of Jupiter, that they’re kind of on this edge where they might not be able to fuse hydrogen and helium in their core, so therefore, they wouldn’t really be a, you know, a stellar object.

(36:50) Most of the surveys out there had focused more on sun-like stars, stars that are like our own, or, you know, just little variations thereof. And so this team decided, “We’re going to look for planets around these very ultra-cool stars.” And when they went out there with, actually, some fairly small telescopes and started their survey, they kind of hit a gold mine right away. They found this system; they actually were able to see two distinct indications of planets around this star. And then what they thought was a third.

(37:19) This was amazing. Like, first of all, a lot of people were like, “Oh, planets shouldn’t form around these small, low-mass stars.” And they already knew there was two, probably three. And then they were able to use what’s — the Spitzer Space Telescope, which I started my career on, and was retired in 2020, to go and look at the system for a really long duration. And when they did that, they were able to uncover there were in fact, seven Earth-size planets orbiting this star that’s basically the size of Jupiter.

(37:46) These planets are so close to their stars. So again, the furthest one out is basically in a 20-day orbit. And again, remember that Mercury is an 88-day orbit. So it’s basically this whole, like, scaled-down, size of the solar system. But here, you actually have seven planets that are size of Earth, right? Where in our own solar system, we have two planets that are size of Earth, Earth and Venus. And then, we have big gas giants, and then some smaller, rocky ones. So it was just mind-blowing again. That’s what the data were saying, but everyone’s like, how the heck did this happen? But what it did is that nature gave us an opportunity to study seven Earth-size planets, all in one system. Just imagine if there were seven Earths in our solar system, how much better we’d understand, you know, how we came to be.

Strogatz (38:32): So, let’s start talking about what the Webb Telescope can do for you and for humanity and science. Should we start with the TRAPPIST system? Are you going to try to point the telescope at it?

Lewis (38:43): Yeah, and I’m not alone in pointing the telescope at the TRAPPIST system. All of those planets in the TRAPPIST system, so all seven of them, will be observed. The team that I’m leading will be focused on the planet TRAPPIST-1e, which happens to be the one that’s sort of smack in the middle of what’s called the habitable zone of the system. It’s where we would expect, if liquid water could exist on the surface, then it probably can exist on the surface of TRAPPIST-1e.

And so, what we’re gonna do is actually just try to get in there and figure out if this planet has an atmosphere, and if it does, what’s that atmosphere made of. Because there’s still a lot of people who, again, feel that these small stars, which actually are quite long-lived, but tend to be very active, so they send out lots of flares. And we know from, you know, our sun that those flares can be very powerful, and it actually can strip planets of their atmospheres. And so, that’s what we’re doing. All of us are going in and trying to find signatures of atmospheres on these planets, and that will help us to understand their ability to not only have liquid water on their surface, but potentially to support life.

Strogatz (39:46): When you try to look at atmospheres of these seven Earths, or whatever we’re going to call them, Earth-like planets. What is the technique that lets you make inferences about their atmospheres?

Lewis (39:56): What’s interesting is we do not directly image the TRAPPIST planets. By directly imaging, I mean, for a long time, and thinking about the solar system, we thought that the only way we’d be able to study exoplanets is if we were somehow able to suppress the light of the star such that we could see the faint planet next to it. And it turned out, because we found so many planets that orbit so closely to their host stars, we could take advantage of a technique called the transit method. And this is where the planet actually passes in front of the host star, as seen from Earth. And we, of course, in our own solar system, from Earth, see Venus transit the sun, and Mercury on occasion.

(40:32) And in this configuration, what happens is that as that planet is passing in front of the star, that starlight gets filtered through any atmosphere that the planet may have. And so what we actually end up seeing is these signatures of different chemical species absorbing the starlight, as that light passes through the planetary atmosphere. We’re also able to study light emitted directly from the planet, in the same way. Basically, we’re not looking for the planet in front of the host star, but we’re actually looking for when the planet ducks behind the host star. So when the planet disappears, it allows us to then measure how much of the light from the system was coming from that planet.

(41:08) People, planets, we all emit predominantly infrared light. We reflect a lot of sunlight. That’s how we sense the world around us. But, and the same reason why you would get, you know, night vision goggles to find people out in the forest at night. You can use that same type of technology, but here, we’re going to put it into the James Webb Space Telescope.

Strogatz (41:27): What kinds of things can you learn from these infrared measurements? Or do you hope to learn from the Webb’s infrared measurements?

Lewis (41:33): Infrared wavelengths is actually where most molecules absorb. That’s just, kind of how they bend and wiggle, is they interact strongly with infrared light. And so if you want to study molecules, you want to go to the infrared. Also, if you want to study light emitted from a body that’s, you know, basically room temperature, again, you want to go into the infrared. And so that’s why Webb is very, very powerful. And we can’t access those wavelengths of light from the ground, because in fact our own atmosphere absorbs them. So we can’t look through the atmosphere and see them. So that means we need to put something up in space. And we had the Spitzer Space Telescope, which is really in many ways the precursor to the James Webb Space Telescope, up until 2020. But it was designed during a time when we didn’t even know exoplanets existed. And so it was not optimized to do these types of studies.

Strogatz (42:22): And would you say that the Webb is, I mean, it was built — well, I suppose it was started — was it even started before we knew about exoplanets?

Lewis (42:29): I mean, it was started after we knew about exoplanets. But one of the nice things is — and I will say this as a positive — because of all of the delays that actually happened with the James Webb Space Telescope, there were able to be retrofits put into the facility to make sure that it could do extraordinary exoplanet science. One instrument in particular has an entire, what we call mode, devoted to doing these transiting exoplanet type observations. And all the instruments on the James Webb Space Telescope now have operational modes that are specifically designed for observing exoplanets.

Strogatz (43:03): I’ve heard the phrase “follow the water” used in this connection. What does this mean?

Lewis (43:09): Yeah, I mean, when we think — and again, it’s a very Earth-centric view, right? When we think about life, and life needs a solvent, and water is a great solvent. We do the same thing in the solar system, we follow the water when searching for life, and this is why we’re looking for life in the oceans that exist, say, below the icy surface of Europa or Enceladus. And so we know that where there is water, we have this nice place where you can start to make the soup that’s necessary for life to emerge. And so that’s largely what we’ve been doing in terms of the search for life outside of the solar system as well. We’re looking for planets that are at just the right distance from their stars, such that we think they might have temperatures, surface temperatures, that could sustain liquid water.

Strogatz (43:53): Okay, like in the most optimistic scenario, if we were observing life, we wouldn’t be observing life directly, it sounds like. We’re observing life’s impact on the atmosphere. Is that the idea?

Lewis (44:02): Yeah. The fact that life exists on Earth — we cause havoc in our own atmosphere, our atmosphere is actually out of equilibrium compared to what it would look like if, you know, humans and trees and everything else didn’t exist. And so what we want to do is measure the amount of key atmospheric molecules like water and methane, oxygen, and ozone, and maybe carbon dioxide. And by looking at how much of each of those molecules are present in a planet’s atmosphere, we’re able to then say, is this system in equilibrium or out of equilibrium? And if it’s out of equilibrium, could it be that life is causing this disequilibrium?

Strogatz (44:02): Of course, that would be the most amazing thing ever, probably, found in the history of science, right? If we could find convincing evidence of life somewhere else. I can’t think what would be a bigger discovery than that.

Lewis (44:52): Yeah, I mean, it would be huge, but I think we’re all cautious about this, because there are also lots of other processes where light can interact with molecules and cause disequilibrium. And so, lots of people have been trying to run these false positive scenarios. How often if we see disequilibrium can we be 100% sure that it is in fact from life? And so there’s a lot of ambiguity out there. And so, there will be a lot of discussion in the scientific community, when we start to see these signs of disequilibrium, whether or not it’s because of life, or if it’s because of some process on the planetary surface or even in the atmosphere.

Strogatz (45:26): So, personally, though, what is it that you find most exciting about the possible things that you might see, once the Webb Telescope’s making its observations?

Lewis (45:35): So, one of the exciting things for me is, and it’s actually how I started my graduate career, is studying weather on exoplanets. And the weather on these other worlds is extreme. You have winds that are on the order of a kilometer per second. You have temperature differences between the day and the night sides of these planets on the order of 1,000 Kelvin. So, quite a huge difference between the day and the night side. And for me, trying to understand what these planets look like, you have to understand sort of what their weather looks like, right? So, you can make measurements and be like, yes, there’s water in this atmosphere, and there’s carbon dioxide, and maybe there’s some methane, but that doesn’t really paint a clear picture of what that planet looks like.

(46:14) And so, I’m very much focused on observations that are going to help us to be able to visualize planets in three dimensions. And so we’re not going to be able to take pretty pictures of these planets, that’s just not within the capability of Webb or any facility on the horizon. But what we will be able to do is use data that’s of a quality we’ve never known before to discern what these planets actually look like and be able to paint a realistic picture for people to enjoy.

Strogatz (46:41): The Webb Telescope is so exciting, actually, in so many different parts of astronomy and space science. Leaving exoplanets aside for a minute, are there things, like, about the early universe or some other aspect of astrophysics that you find especially thrilling to think about, that the Webb might reveal?

Lewis (47:00): Yeah, I mean, the Webb was designed to look at some of the earliest galaxies that formed in our universe. And again, the way that we do that is we have to look at light in the infrared, because light from those galaxies has been what we call redshifted quite substantially over time. And so we have to keep looking farther and farther into redder and redder wavelengths to see those objects. And so Webb will be able to basically give us pictures. And, you know, I don’t get pictures of my exoplanets, but there are going to be awesome pictures of galaxies that are going to come out of Webb. And some of those pictures of galaxies will be some of the earliest galaxies that ever formed in our universe, which is exciting. I mean, I, you know, I can look at the Hubble Deep Field and I can appreciate it, I actually have an image of the Hubble Deep Field hanging in the workroom in my building. And so, you know, I’m looking forward to seeing all the types of awesome imagery of galaxies and stars and nebulae that we’ve come to love from the Hubble Space Telescope, and see those types of images from the James Webb Space Telescope. Not the same wavelengths of light, but it will still be just as awesome.

Strogatz (48:05): Well, that feels like a great place to wrap up this fascinating conversation about exoplanets and Webb Space Telescope. Thanks so much for joining us today, Nikole.

Lewis (48:14): My pleasure.

Announcer (48:20): Explore more science mysteries in the Quanta book Alice and Bob Meet the Wall of Fire , published by the MIT Press. Available now at amazon.com, barnesandnoble.com or your local bookstore. Also, make sure to tell your friends about The Joy of Why podcast and give us a positive review or follow where you listen. It helps people find this podcast.

Strogatz (41:05): The Joy of Why is a podcast from Quanta Magazine , an editorially independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests, or other editorial decisions in this podcast or in Quanta Magazine . The Joy of Why is produced by Susan Valot and Polly Stryker. Our editors are John Rennie and Thomas Lin, with support by Matt Carlstrom, Annie Melchor, and Leila Sloman. Our theme music was composed by Richie Johnson. Our logo is by Jackie King, and artwork for the episodes is by Michael Driver and Samuel Velasco. I’m your host, Steve Strogatz. If you have any questions or comments for us, please email us at [email protected]. Thanks for listening.