土卫六-泰坦

第一张也是唯一一张来自土星最大卫星泰坦的照片- 我们看到了什么

2005年1月 14 日，欧洲航天局的惠更斯探测器从土星最大的卫星泰坦的厚厚云层中急速下降。两个多小时后，它成功降落在这个神秘的表面，拍摄了72分钟的图像，然后与母飞船卡西尼号失去联系，卡西尼号是它与地球的唯一联系，该飞船正在土星上方运行。在从泰坦上空下落并降落在其几乎熟悉的表面的短时间内，惠更斯成功地传输了数百张令人难以置信的图像，以前所未有的方式揭示了这颗大卫星。17 年多过去了，这些图像仍然是我们从土卫六（太阳系最像地球的卫星）表面拍摄的最佳图像。惠更斯号是第一个也是目前唯一一个成功降落在外太阳系另一个世界的航天器。它附着在美国宇航局卡西尼号宇宙飞船的侧面，完成了长达七年的史诗般的土星航行，然后被释放并落入神秘卫星周围的浓雾中。2005 年，当惠更斯号探测器坠入土卫六不透明的大气层时，没有人知道会发生什么。它会掉进外星深海吗？陷入深坑流沙？撞上锯齿状的岩石或从陡峭的峡谷跌落？有一点是肯定的，泰坦是一个谜。除了先驱者 11 号、航海者 1 号和航海者 2 号在许多年前短暂经过之外，人们对这颗大卫星知之甚少。惠更斯下降探测器会发现什么，每个人都在猜测。土卫六厚厚的大气层使得从远处研究它变得异常困难。通过我们大多数的望远镜，它看起来像一个模糊的橙色球。但多亏了卡西尼号和惠更斯号，我们现在知道土卫六是一颗与众不同的卫星。奇怪的是，泰坦可能是最像地球的世界。这是我们所知道的唯一一个表面有液体的地方，但在泰坦的情况下，它不是我们所知道的水，而是主要是液态甲烷，它充满了海洋，在河流中流动，甚至降雨从天上来。然而那里太冷了，我们所知道的生命不可能存在，事实上，山脉和山谷是由比花岗岩更坚硬的水冰构成的。那么，在一个被如此厚的大气层笼罩、看不见其表面的世界上，惠更斯如何能够在着陆时幸存下来呢？嗯，这次任务实际上并不是让探测器着陆，而是为了调查土卫六的大气层，包括它的化学性质、风、温度和压力。然而，万一飞船确实成功着陆，任务团队就为多种条件设计了飞船。工程师们建造了惠更斯号，重量足够轻，可以漂浮，以防万一它溅入海洋，并且电池寿命足够，可以在水面上运行至少一小段时间（假设它在撞击中幸存下来）。但总体而言，惠更斯被设计为一个下降探测器，它将在穿过土卫六大气层时收集其所有主要科学信息。无论它后来看到或没有看到什么，都将是科学上的奖励。当惠更斯号坠入泰坦星云并打开降落伞时，它的相机开始捕捉到其下降过程中令人难以置信的图像。这段视频是根据这些图像创建的，并在短短几分钟内揭示了惠更斯号在 2 小时 27 分钟的旅程中穿越浓重烟雾般的薄雾时所看到的一切。起初，只能看到橙棕色的模糊区域，但随着探测器深入，云层在距地表约 30 英里（距地表约 50 公里）处开始变得清晰，前所未见的大型特征慢慢显现出来。在明亮的丘陵地区之间可以看到黑暗的山谷。在左边的山丘之外，可以看到两条黑暗的平行线，它们是覆盖卫星的巨大沙丘系统的一部分。可以看到复杂的排水渠道网络穿过山坡，这可能是甲烷雨从山坡上倾泻而下的原因。不幸的是，惠更斯在执行任务期间通讯程序出现了问题，z这将它可以传输到卡西尼号的图像数量从700 张限制到只有 376 张。这意味着近一半拍摄的图像永远丢失了。但它确实发送的图像仍然让我们能够以前所未有的细节看到土卫六云层下面的情况，在短短几个小时的时间内，将土卫六从一个模糊的橙色球带到一个完全现实的世界。在经历了湍急的下降之后，惠更斯号安全着陆在地表。幸运的是，它没有撞上尖锐的岩石或坚硬的冰，也没有溅入土卫六的众多湖泊或海洋之一。相反，它轻轻地落到了看起来像由冰粒组成的柔软湿沙的床上。这是迄今为止从土卫六表面拍摄到的唯一景象。图像显示出一片平坦的平原，周围散落着鹅卵石。虽然图像没有显示流动表面液体的迹象，但该区域确实非常类似于干涸的湖泊或河床。远处地平线上，连绵起伏的小山丘清晰可见，所有的鹅卵石都散落一地。整个景观都是由像岩石一样坚硬的水冰构成的。在着陆瞄准处，惠更斯测得的温度为-180摄氏度（-292华氏度），风很小，天空中没有可见的云结构，只有厚厚的雾霾。经过泰坦表面 72 分钟的通信后，与卡西尼号也就是地球的联系最终消失在地平线上。不久之后，惠更斯号的电池就会耗尽，探测器就会悄然关闭。尽管惠更斯号只持续了几个小时，但它揭示了一些令人难以置信的东西：太阳系外层有一颗冰冻的卫星，它比任何人想象的都更像地球。现在我们了解了土卫六的甲烷海和化学复杂的大气层，正在开发未来的任务，以前所未有的方式探索卫星球。美国宇航局正准备通过蜻蜓号将泰坦的探索提升到一个新的水平。该任务计划于2027年发射，并于2034年抵达泰坦。蜻蜓是一种小型无人机，旨在通过围绕泰坦表面进行短途飞行，覆盖比传统着陆器或漫游车更大的地面。类似于最近在火星上进行的“独创性”任务。它的主要目标是弄清楚土卫六是否或曾经适合居住，寻找复杂的化学物质，甚至检查是否有迹象表明这个朦胧的世界确实存在生命。蜻蜓号还将配备龙相机，这是一套微型全景相机，可以拍摄泰坦的地形。为我们带来了这个非凡月亮的新视角。但就目前而言，惠更斯多年前拍摄的令人惊叹的图像是我们在土卫六云层下观察到的最好的图像。

The First and OnlyPhotos from Titan, Saturn’s Largest Moon - What did We See

On January 14th, 2005, the European space agency's, Huygens probe plummeted through the thick clouds of Saturn's largest moon, Titan.

It successfully landed on the mysterious surface more than 2 hours later, capturing image after image for 72 minutes, before losing contact with its mother spacecraft, Cassini, its only link to Earth, that was orbiting Saturn above. During this short time falling through the skies of Titan and landing on its almost familiar surface, Huygens managed to transmit hundreds of incredible images revealing the large moon like never before. More than 17 years later, these images are still the best we have from the surface of Titan, the solar system's most Earth-like moon. Huygens was the first and currently only spacecraft to successfully land on another world in the outer solar system.

It made the epic seven-year-long voyage to Saturn attached to the side of NASA's Cassini spacecraft, before being released and dropped into the thick haze that surrounds the mysterious moon. When the Huygens probe plunged into Titan's opaque atmosphere in 2005, no one knew what to expect. Would it splash down into a deep alien ocean? Sink into a pit quicksand? Crash into jagged rocks or tumble off a steep ravine? One thing was for sure, Titan was a mystery. Aside from a very brief pass by Pioneer 11, Voyager 1 and Voyager 2 many years before little was known about the large moon. What the Huygens descent probe would find was anyone’s guess. Titan's thick atmosphere makes it extraordinarily difficult to study from afar. Through most of our telescopes, it looks like a fuzzy orange ball.

But thanks to Cassini and Huygens, we know now that Titan is a moon unlike any other. In a strange way, Titan may be the most Earth-like world out there. It is the only other place we know of that has liquid on its surface, but in Titan’s case, it is not water as we know it, but instead, mostly liquid methane, which fills up seas, flows in rivers, and even rains down from the sky. It’s so cold there, however, that life as we know it couldn't exist, in fact, the mountains and valleys are made of water ice frozen harder than granite. So on a world shrouded by an atmosphere so thick, its surface could not be seen, how could Huygens survive a landing? Well, the mission wasn't  actually to land the probe, but instead to investigate Titan's atmosphere, including its chemical properties, wind, temperature and pressure.

However, on the off chance, the spacecraft did manage to land, the mission team designed the craft for multiple conditions. Engineers built Huygens light enough to float, just in case it splashed down into an ocean and with enough battery life to operate for at least a short while on the surface, assuming it survived the impact. But overall, Huygens was designed as a descent probe that would collect all of its primary science during a fall through Titan’s atmosphere. Whatever it did or didn’t see afterwards would be a scientific bonus. As Huygens plunged into Titans clouds and deployed its parachute, its cameras began capturing incredible images of its descent. This footage was created from those images and reveals in just a few minutes what Huygens saw during its 2 hours and 27-minute journey through the thick smog-like haze. At first, only an orangey brown blur is visible, but as the probe falls deeper and the cloud starts to clear at around 30 miles above the surface, which is about 50 kilometres above the surface, large never before-seen features are slowly revealed.

A dark valley can be seen between brighter hilly regions. Beyond the hills to the left, two dark parallel lines are visible, which are part of a vast system of dunes that cover the moon. A complex network of drainage channels can be seen cutting through the hillside, a possible

cause of methane rain pouring down its slopes. Unfortunately, Huygens had a problem in the communications program during the mission

that limited the number of images it could transmit to Cassini from 700 to only 376. Meaning that nearly half of the images taken were lost forever. But the images it did manage to send still allow us to see below the clouds of Titan in unprecedented detail, taking Titan from a fuzzy orange ball to a fully realised world, in the span of just a few hours. After its turbulent descent, Huygens landed safely on the surface. Luckily it didn't crash into sharp rocks or hard ice, or splash into one of Titan's many lakes or seas. Instead, it gently dropped down onto a bed of what looks like soft wet sand made of ice grains. This is the only view from the surface of Titan ever captured. The image reveals a flat plain surrounded by scattered pebbles. While the image shows no sign of current surface liquid, the region does strongly resemble a dried-up lake or river bed. In the distance, on the horizon, small rolling hills are visible and all the pebbles scattered

across the landscape are made of water ice frozen as hard as rock. At the landing sight, Huygens measured a temperature of -180 degrees Celsius, which is -292 degrees Fahrenheit, with very little wind and no visible cloud structures in the sky, just thick haze. After 72 minutes of communication from the surface of Titan, eventually, Cassini and so the link to Earth disappeared over the horizon. A short time later and Huygens batteries would run out, and the probe would have quietly shut down. Although Huygens only lasted for a few hours, it revealed something incredible, a frozen moon in the outer solar system that is more like Earth than anyone could have ever imagined. And now that we know about Titan's methane seas, and chemically complex atmosphere, future missions are being developed that will explore the moon like never before. NASA is preparing to take the exploration of Titan to the next level with the Dragonfly

mission, which is scheduled to launch in 2027, arriving at Titan in 2034. Dragonfly is a small drone designed to cover more ground than a traditional lander or rover by making short flights around Titan’s surface. Similar to the recent Ingenuity mission on Mars. Its main goals are to figure out whether Titan is, or ever has been, habitable, look for complex chemistry, and even check if there are signs that this hazy world has actually hosted life. Dragonfly will also be equipped with Dragon cam, a set of microscopic and panoramic cameras that will image Titan's terrain. Bringing us new views of this extraordinary moon. But for now, the stunning images captured all those years ago by Huygens are the best we have when it comes to seeing below the clouds of Titan.