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Why are so many nations going to Mars this summer?
今年各国扎堆探索火星 却是为何？
Traveling to Mars is usually a lonely business—
火星之行通常都是一件十分孤独的事情——
with a single spacecraft taking off from a single launchpad for the seven-month trip to the Red Planet.
一艘航天器从一个发射台上起飞，开始为期七个月的火星之行。
That appeared to be the case again on July 30,
7月30日，NASA的“毅力号”火星车
when NASA’s Perseverance rover roared off the pad at Cape Canaveral atop an Atlas V rocket.
搭载着阿特拉斯V号火箭从（佛罗里达州）卡纳维拉尔角发射台呼啸而出时，情况似乎依然如此。
But this time the ship will have plenty of company.
不过，此次发射的飞船会有很多同伴。
On July 19, the United Arab Emirates made its first bid to join the Mars game,
7月19日，阿联酋有史以来首次加入火星竞赛，
launching the 3,000-lb., 10-ft.-tall Amal, or "Hope," spacecraft on a mission to orbit Mars for at least two years while studying its atmosphere.
发射了重3000磅、高10英尺的阿迈勒，又名“希望号”宇宙飞船，执行绕火星飞行，研究火星大气层至少两年的任务。
Four days later, China launched its Tianwen-1, or "Questions to Heaven," spacecraft,
四天后，中国发射“天问一号”（Questions to Heaven）飞船，
a threepart ship with an orbiter, a lander and a sixwheel, 529-lb. rover.
由环绕器、着陆器和一个重达529磅的六轮巡视器三部分组成。
And a fourth mission, a joint Russian-European project, ExoMars, carrying a rover of its own, was also planned for this summer,
近期的第四个探索火星项目则是俄罗斯与欧洲的合作项目“ExoMars”，该探测器携带有自己的火星车，原也计划今年夏天发射，
though it has been postponed to 2022 because of engineering problems with its parachute and avionics.
然而，由于降落伞和航空电子设备方面的工程问题，该项目已经推迟到2022年。
So why all the interest in Mars—and why right now?
为何大家都——又为何都在此时——对火星有了如此大的兴趣？
The timing issue has everything to do with planetary mechanics.
这一时间安排与行星力学有很大关系。
As they fly their differing solar orbits—Earth on the inner track, Mars on the outer—
地球和火星在不同的环日轨道——地球轨道位于内侧，火星轨道位于外侧——上绕太阳飞行时，
the distance between the two worlds is forever changing.
两个行星之间的距离一直是一个变量。
At their greatest remove, when they are on opposite sides of the sun, they are up to 250 million miles apart.
距离最大，也就是它们分别位于太阳两端时，它们之间的距离足足可达2.5亿英里。
But once every two years, they line up on the same side of the sun, with just 35 million miles separating them.
但每隔两年，它们就会出现在太阳的同侧，排成一条直线，此时相距仅3500万英里。
译文由可可原创，仅供学习交流使用，未经许可请勿转载。
