Why is space so cold if the sun is so hot? Excellent question. Unlike our mild habitat here on Earth, our solar system is full of temperature extremes. The sun is a bolus of gas and fire measuring around 27 million degrees Fahrenheit at its core and 10,000 degrees at its surface. Meanwhile, the cosmic background temperature—the temperature of space once you get far enough away to escape Earth's balmy atmosphere—hovers at -455 F. How can this be?如果太阳那么热，为什么太空那么冷？ 问得好。 与我们地球上温和的栖息地不同，我们的太阳系充满了极端温度。 太阳是一团气体和火，其核心温度约为2700万华氏度，表面温度约为10000华氏度。 与此同时，宇宙背景温度——一旦你离开地球温暖的大气层，太空的温度——徘徊在 -455华氏度。 这怎么可能呢？
Heat travels through the cosmos as radiation, an infrared wave of energy that migrates from hotter objects to cooler ones. The radiation waves excite molecules they come in contact with, causing them to heat up. This is how heat travels from the sun to Earth, but the catch is that radiation only heats molecules and matter that are directly in its path. Everything else stays chilly. Take Mercury: the nighttime temperature of the planet can be 1,000 degrees Fahrenheit lower than the radiation-exposed day-side, according to NASA.热量以辐射的形式在宇宙中传播，这是一种红外能量波，能量从较热的物体传播到较冷的物体。 辐射波激发了它们接触的分子，使它们升温。 这就是热量从太阳传递到地球的过程，但问题是辐射只加热其路径上的分子和物质。 其他所有东西都保持寒冷。 以水星为例: 根据美国宇航局的说法，地球的夜间温度可以比日间暴露在辐射下的温度低1000华氏度。
Compare that to Earth, where the air around you stays warm even if you’re in the shade—and even, in some seasons, in the dark of night. That’s because heat travels throughout our beautiful blue planet by three methods instead of just one: conduction, convection, and radiation. When the sun’s radiation hits and warms up molecules in our atmosphere, they pass that extra energy to the molecules around them. Those molecules then bump into and heat up their own neighbors. This heat transfer from molecule to molecule is called conduction, and it’s a chain reaction that warms areas outside of the sun’s path.相比之下，在地球上，你周围的空气保持温暖，即使你在阴凉处，甚至在某些季节，在黑暗的夜晚。 这是因为热量通过三种方式在我们美丽的蓝色星球上传播，而不是仅仅通过一种方式: 传导、对流和辐射。 当太阳辐射击中并使大气中的分子升温时，它们将额外的能量传递给周围的分子。 然后这些分子碰撞并加热它们自己的邻居。 这种从一个分子到另一个分子的热传导叫做传导，这是一种连锁反应，它使太阳路径以外的区域变暖。
Space, however, is a vacuum—meaning it’s basically empty. Gas molecules in space are too few and far apart to regularly collide with one another. So even when the sun heats them with infrared waves, transferring that heat via conduction isn’t possible. Similarly, convection—a form of heat transfer that happens in the presence of gravity—is important in dispersing warmth across the Earth, but doesn’t happen in zero-g space.然而，空间是真空的ーー也就是说它基本上是空的。 太空中的气体分子太少，距离太远，无法定期相互碰撞。 因此，即使太阳用红外波加热它们，也不可能通过传导来传递热量。 同样，对流(在重力作用下发生的一种热传递形式)对于将热量散布到地球上也很重要，但在零重力空间中不会发生。
These are things Elisabeth Abel, a thermal engineer on NASA’s DART project, thinks about as she prepares vehicles and devices for long-term voyages through space. This is especially true when she was working on the Parker Solar Probe, she says.这些都是美国宇航局 DART 项目的热工程师伊丽莎白 · 阿贝尔在为长期太空旅行准备飞行器和设备时所考虑的事情。 当她在帕克太阳探测器上工作时，情况尤其如此，她说。
As you can probably tell by its name, the Parker Solar Probe is part of NASA's mission to study the sun. It zooms through the outermost layer of the star's atmosphere, called the corona, collecting data. In April 2019 the probe got within 15 million miles of the inferno, the closest a spacecraft has ever been to the sun. The heat shield projected on one side of the probe makes this possible.正如你可以从名字上看出来的，帕克太阳探测器是美国宇航局研究太阳任务的一部分。 它穿过恒星大气层的最外层，即日冕，收集数据。 2019年4月，探测器到达了距离地狱1500万英里的范围内，这是航天器到达太阳的最近距离。 探头一侧的隔热罩使这一切成为可能。
“The job of that heat shield,” Abel says, is to make sure “none of the solar radiation [will] touch anything on the spacecraft.” So, while the heat shield is experiencing the extreme heat (around 250 degrees F) of our host star, the spacecraft itself is much colder— around -238 degrees F, she says.“隔热板的工作，” Abel 说，是确保“太阳辐射不会接触到飞船上的任何东西。” 因此，她说，虽然隔热层正在经历我们的主恒星的极端高温(约250华氏度) ，但航天器本身却要冷得多ーー约238华氏度。
As the lead thermal engineer for DART—a small spacecraft designed to collide with an asteroid and nudge it off course—Abel is taking practical steps to manage the temperatures of deep space. The extreme variation in temperature between the icy void and the boiling heat of the sun poses unique challenges. Some parts of the spacecraft need help staying cool enough to avoid shorting out, while others need heating elements to keep them warm enough to function.作为 dart 的首席热工程师，阿贝尔正在采取实际措施来控制深空的温度。 dart 是一个小型航天器，旨在与小行星碰撞并使其偏离轨道。 在冰冷的空洞和太阳沸腾的热量之间温度的极端变化带来了独特的挑战。 宇宙飞船的某些部分需要帮助保持足够的冷却以避免短路，而其他部分则需要加热元件来保持足够的温度以发挥作用。
Preparing for temperature shifts of hundreds of degrees might sound wild, but it’s just how things are out in space. The real oddity is Earth: Amidst the extreme cold and fiery hot, our atmosphere keeps things surprisingly mild—at least for now.为数百度的温度变化做准备听起来很疯狂，但这就是外太空的情况。 真正奇怪的是地球: 在极端寒冷和炽热的环境中，我们的大气层保持着令人惊讶的温和，至少现在是这样。