Why are so many nations going to Mars this summer?
为何今年夏天各国扎堆探索火星？
林晓洁 供稿
Mars has always been a hypothetical second home for humans.
一直以来，火星都被看作是最有可能成为人类第二家园的行星。
Scientists expect that plans to send people and colonize the red planet could start as soon as the next decade. But would people really have what it takes to get to and live on Mars?
科学家预计，最快在下一个十年，派遣人员前往这颗红色星球进行殖民的计划就会启动。但人们真的有能力抵达火星并在火星上定居吗?
The first challenge is getting through the launch.
第一个挑战就是如何顺利到达火星。
This summer has witnessed 3 spacecrafts heading to Mars.
今年夏天有3艘宇宙飞船向火星进发。
On July 19, the United Arab Emirates made its first bid to join the Mars game, launching the Amal Probe , or "Hope," spacecraft on a mission to orbit Mars for at least two years while studying its atmosphere.
7月19日，阿联酋发射了阿迈勒火星探测器（又名“希望号”），标志该国首次加入火星竞赛。该探测器将执行为期至少两年的绕火星飞行任务，对火星的大气层进行研究。
Four days later, on 23 July, China launched its Tianwen-1 spacecraft to Heaven. It’s a three-part ship with an orbiter, a lander and a six-wheel rover, aiming to complete orbiting, landing and roving in one mission. The probe blasted off on China's largest carrier rocket , the Long March 5, from the Wenchang Space Launch Centre in the southern island province of Hainan. It is expected to reach Mars in February where it will attempt to deploy a rover to explore the planet for 90 days.
7月23日，中国发射了天问一号火星飞船。它由环绕器、着陆器和一个六轮火星车三部分组成，目的是通过一次发射任务实现火星环绕、着陆和巡视。天问一号由中国最大的运载火箭长征五号从海南文昌航天发射中心发射升空。预计该探测器将于明年2月抵达火星，并在火星上部署火星车，展开为期90天的地面探索。
On July30, NASA's Mars rover Perseverance has been launched atop an Atlas 5 rocket from Florida on a mission to search for traces of potential past life on Earth's planetary neighbor.
7月30日，美国国家航空航天局（NASA）的“毅力号”火星探测器乘“阿特拉斯5号”火箭从佛罗里达州升空。它的任务是寻找这颗地球相邻行星上曾经存在的生命迹象。
So why all the interest in Mars this summer?
为何各国都在今年执行火星任务?
The timing issue has everything to do with planetary mechanics.
这与行星力学有着很大关系。
As they fly their differing solar orbits with Earth on the inner track and Mars on the outer, the distance between the two worlds is forever changing.
由于地球和火星在不同的公转轨道上，地球轨道位于内侧,火星轨道位于外侧，两颗行星之间的距离每时每刻都在变化。
At their greatest remove, when they are on opposite sides of the sun, they are up to 400 million km apart. But once every two years, they line up on the same side of the sun, with just 5.6 million km separating them.
距离最远时，分别位于太阳两端，相距可达4亿公里。但每隔两年，这两颗行星会出现在太阳的同一侧，并排成一条直线，此时它们之间仅相距5600万公里。
Launches to Mars are targeted at this time because any spacecraft leaving Earth will experience a shorter trip to Mars -- which means less resources such as fuel are needed as well.
在这段时间内发射火星探测器，航天器到达火星的飞行时间比较短，需要的燃料等资源也会更少。
Such an alignment is taking place this summer, dramatically slashing inter planetary travel time to the current seven-month itinerary.
今年夏天就出现了太阳、地球和火星排成一条直线的情形，将探测器到达火星的时间大幅缩短到了目前的7个月。
So that explains the when question.
这就是今年夏天各国扎堆发射火星探测器的原因。
Then why is it so hard to land on Mars?
那为什么着说陆火星很困难?
When it comes to landing spacecraft on planets or moons, there's a lower success rate landing on Mars than on Venus, the moon, the earth even Saturn's moon Titan.
与金星、月球、地球，甚至是土星的卫星泰坦星相比，着陆火星的成功率要更低。
This is because Mars's atmosphere is in the perfect goldilocks zone of being a total headache. On the moon(or an asteroid) you can use lightweight spacecraft made essentially out of tinfoil because there's no air to cause drag or pressure or heat.
原因在于，位于“金发姑娘地带”（适合生命居住的地带）的火星大气层麻烦重重。当着陆月球（或其他小行星）时，人们可以使用锡箔制成的轻型航天器，因为那里没有大气，不会产生阻力、压力和热量。
On earth, or Venus, or Titan, there's enough air that you can land largely unpowered, So you use a lot of weight for heat shields and walls and parachutes, but don't need big rockets or lots of fuel to land.
而地球、金星或泰坦星上则有足够多的大气可以让探测器在大部分时候无动力着陆。虽然探测器需要增加隔热护罩、舱壁和降落伞的重量，但不需要使用大型火箭和过多的燃料。
However, the air on Mars is thick enough that you actually have to deal with it with heat shields and walls, but thin enough that it doesn't help you slow down much and you also need to use rockets.
然而，火星上的大气不厚不薄，不能抵御热能，也无法帮助探测器减速。因此，探测器着陆火星时既需要隔热护罩和舱壁，也需要使用火箭来减速。
【VOCABULARY】
1. hypothetical adj. 假设的；爱猜想的
2. colonize v. 开拓殖民地
3. rover n. 漫游者；流浪者；巡视器
4. blast off 点火起飞；发射升空
5. planetary mechanics 行星力学
6. alignment n. 队列；成直线
7. itinerary n. 旅程；路线