Good News! Turns Out the Earth Will Never Be Swallowed by the Sun
Good News! Turns Out the Earth Will Never Be Swallowed by the Sun
好消息！地球或许永远不会被太阳吞噬
Some good news and some bad news. The good news is that, contrary to earlier fears, Earth will probably never be swallowed by the sun. The bad news, of course, is that none of us will be around to find out. 这里有一个好消息和一个坏消息。好消息是，与之前的担忧相反，地球可能永远不会被太阳吞噬。当然，坏消息是，我们谁也无法亲眼见证那一刻。
Scientists have long estimated that in about 5 billion years, the sun will run out of fuel, first expanding into a red giant and eventually becoming a white dwarf that will continue cooling for tens—if not hundreds—of billions of years. Amid this dramatic sequence of cosmic events, the fate of Earth remains uncertain. 科学家们长期以来估计，大约 50 亿年后，太阳将耗尽燃料，先膨胀成一颗红巨星，最终演变成一颗白矮星，并在接下来的数百亿年里持续冷却。在这一系列剧烈的宇宙演变中，地球的命运一直悬而未决。
Will it be pulled into the expanding red sun and disappear forever? Or, though long since rendered uninhabitable, will it continue orbiting the white dwarf remnant of the Sun until the universe reaches its eventual heat death? 地球会被拉入膨胀的红色太阳中并永远消失吗？还是说，尽管早已变得不再适宜居住，它仍将继续围绕太阳留下的白矮星残骸运行，直到宇宙最终走向热寂？
Until now, the prevailing view among astrophysicists favored the first scenario. But a new study published in Astronomy & Astrophysics overturns that expectation, presenting new evidence that Earth may survive the sun’s transformation into a red giant after all. 到目前为止，天体物理学界的主流观点倾向于第一种情况。但发表在《天文学与天体物理学》（Astronomy & Astrophysics）杂志上的一项新研究推翻了这一预期，并提供了新的证据，表明地球最终或许能在太阳演变为红巨星的过程中幸存下来。
The Sun’s Life Cycle
太阳的生命周期
To understand what lies ahead for the planets of the solar system, you need to look inside the sun itself. At present, the sun is in its main-sequence phase, a long period of stability that has lasted for about 4.5 billion years, during which it is powered primarily by the fusion of hydrogen into helium. 要了解太阳系行星的未来，必须先了解太阳本身。目前，太阳正处于主序星阶段，这是一个已经持续了约 45 亿年的漫长稳定期，在此期间，太阳主要依靠氢聚变为氦来提供能量。
This phase will continue for billions of years, but the sun will gradually become hotter and more luminous. Eventually, it will grow bright enough to evaporate all of Earth’s surface water, making our planet uninhabitable within the next two billion years. 这一阶段还将持续数十亿年，但太阳会逐渐变得更热、更亮。最终，它的亮度将足以蒸发地球上所有的地表水，使我们的星球在未来 20 亿年内变得不再适宜居住。
About 5 billion years from now, the sun’s long period of stability will come to an end. By then, the hydrogen in its core will have been exhausted. The helium core will contract under its own gravity, heating up and triggering hydrogen fusion in a surrounding shell. As a result, the sun’s outer layers will expand enormously while its surface cools dramatically, giving it the characteristic red color of this stage in a star’s evolution. And this is where the mystery surrounding Earth’s fate begins. 大约 50 亿年后，太阳漫长的稳定期将宣告结束。届时，其核心的氢将耗尽。氦核会在自身引力作用下收缩、升温，并触发周围壳层的氢聚变。结果，太阳的外层会剧烈膨胀，而表面温度则会大幅下降，呈现出恒星演化这一阶段特有的红色。而关于地球命运的谜团，也正是从这里开始的。
A Complex Tug-of-War
一场复杂的“拔河”
The sun’s enormous expansion will profoundly reshape Earth’s orbit through the interplay of two opposing effects. On one hand, the sun will lose a significant amount of mass through powerful stellar winds. As its gravitational pull weakens, Earth’s orbit will gradually drift outward. On the other hand, the planet’s increasing proximity to the sun’s extended gaseous envelope will produce drag, while tidal forces—the difference in gravitational pull exerted on the near and far sides of an object, which can gradually alter planetary orbits—will act as a brake on Earth’s motion. 太阳的剧烈膨胀将通过两种相反效应的相互作用，深刻地重塑地球的轨道。一方面，太阳会通过强大的恒星风损失大量质量。随着引力的减弱，地球的轨道会逐渐向外漂移。另一方面，地球与太阳膨胀的气体包层距离越来越近，会产生阻力；同时，潮汐力（即作用在物体近端和远端的引力差，它能逐渐改变行星轨道）将对地球的运动起到制动作用。
Until now, scientists considered it overwhelmingly likely that these tidal effects would dominate. In that scenario, Earth would gradually lose orbital energy, spiral inward, and ultimately be engulfed by the expanding sun, where it would be completely vaporized. 此前，科学家们认为这些潮汐效应占据主导地位的可能性极大。在这种情况下，地球将逐渐失去轨道能量，螺旋式向内坠落，最终被膨胀的太阳吞噬并彻底汽化。
A New Outlook
新的展望
The new study, based on improved models of tidal dissipation and stellar mass loss during the sun’s transition into a red giant, points to a different conclusion. According to the researchers, tidal dissipation—the process that drains orbital energy and gradually causes elliptical orbits, such as Earth’s, to become more circular—would be less effective than previous models suggested. 这项基于太阳向红巨星过渡期间潮汐耗散和恒星质量损失改进模型的新研究，指向了一个不同的结论。研究人员认为，潮汐耗散（即消耗轨道能量并逐渐使椭圆轨道——如地球轨道——变得更圆的过程）的效果可能比之前模型预测的要弱。
At the same time, observations of the red giant L2 Puppis, located about 209 light-years from Earth, indicate that the sun could lose enough mass for this effect to outweigh the influence of tidal forces. If so, Earth’s orbit would gradually move outward, significantly increasing its chances of surviving the red giant phase. 与此同时，对距离地球约 209 光年的红巨星 L2 Puppis 的观测表明，太阳损失的质量可能足以抵消潮汐力的影响。如果真是这样，地球的轨道将逐渐向外移动，从而大大增加其在红巨星阶段幸存下来的几率。
An Uncertain Future
不确定的未来
Despite the study’s more optimistic outlook, Earth’s ultimate fate remains far from certain. The behavior of stellar winds and the complex thermal pulses that occur during the final stages of a star’s evolution involve many variables that are difficult to predict with precision. If the sun ultimately loses less mass than the new model estimates, tidal forces could still prevail, pulling Earth inward and leading to its destruction. 尽管这项研究的前景更为乐观，但地球的最终命运仍远未确定。恒星风的行为以及恒星演化最后阶段发生的复杂热脉冲涉及许多难以精确预测的变量。如果太阳最终损失的质量少于新模型的估计，潮汐力仍可能占据上风，将地球向内拉扯并导致其毁灭。
While Earth’s future remains an open question, the outlook for the rest of the solar system is much clearer. As the sun expands, Mercury and Venus will be completely engulfed by its outer layers, disappearing forever under the combined effects of intense heat and tidal forces. The outer planets, however, will follow a different path. Mars, although it will experience a dramatic rise in temperature that vaporizes its permanent ice reserves, will migrate to a more distant orbit and avoid physical destruction. 虽然地球的未来仍是一个悬而未决的问题，但太阳系其他行星的命运则清晰得多。随着太阳的膨胀，水星和金星将被其外层完全吞噬，在高温和潮汐力的共同作用下永远消失。然而，外行星将走上不同的道路。火星虽然会经历剧烈的温度升高，导致其永久冰层蒸发，但它会迁移到更远的轨道，从而避免被彻底摧毁。
Farther out, the gas giants Jupiter and Saturn will see the orbits of their moons reshaped, while the increase in solar radiation could temporarily melt the icy crusts of moons such as Europa and Enceladus, creating oceans of liquid water on their surfaces. Which means that these worlds—at least for a time—could become successors to the Blue Planet after Earth has turned into a scorched, barren wasteland. 在更远的地方，气态巨行星木星和土星的卫星轨道将被重塑，而太阳辐射的增加可能会暂时融化木卫二（Europa）和土卫二（Enceladus）等卫星的冰壳，在其表面形成液态水海洋。这意味着，在地球变成一片焦灼、荒芜的废土之后，这些世界——至少在一段时间内——可能会成为“蓝色星球”的继任者。
This story originally appeared on WIRED Italia and has been translated from Italian. 本文最初发表于《连线》意大利版，由意大利语翻译而来。