那些年我們追過的“星”

All the planets that I am about to mention have similar atmospheric and environmental conditions as Earth. These planets lie within the \"Goldilocks zone1）\" meaning they are neither too hot nor too cold to support life. And even if there isn't complete proof for the existence of some of the planets， there is a high probability that they exist. Now， there are two possible reasons you are reading this list—either you want to look at future possible homes for humanity or find out about places where aliens might live. Let's see what these Earth-like planets have in store for us.

下面我將要提到的所有行星都和地球有著相似的大氣和環(huán)境條件。這些行星都位于“宜居帶”，也就是說它們既不會太熱，也不會太冷，可以維系生命。盡管并不能完全證明其中一些行星的存在，但它們存在的可能性還是非常大的。此時此刻你閱讀這個行星名單可能出于兩方面的原因——要么是你想要看看人類未來可能的安家之所，要么是想搞清楚外星人可能生活在哪些地方。那么就讓我們來看看這些類地行星都為我們準(zhǔn)備了什么吧。

6. Gliese 581 d

It orbits2） the Gliese 581 red star. It is 6 times larger than Earth3） and about 20.2 light years away from us and in the outer parts of the habitable zone， hence it is possible for water to exist there， with at least one ocean. A year lasts 66.87 days， so expect to spend a fortune on calendars. It is also considered a cold planet since it has no proper atmosphere， but to be fair if Earth had no atmosphere we would also have been considered a cold planet with an average temperature of -18℃. In 2009 we beamed4） 25，880 messages from 190 different countries which were sent towards its sun， probably messages begging them not to invade us.

5. HD 85512 b

Let's go over the basics first， 3.6 times bigger than Earth， gravity of only 1.4 g5） despite its bigger size， a year of 54 days. And it's tidally locked. For those who don't know what tidally locked means， it means that one side is always facing the sun， so basically it is day time on half of the planet while the other half experiences perpetual6） night， so basically it's a vampire's paradise. On a serious note， tidal locking does a number on7） a planet and reduces the chance of life， but that still doesn't mean living on it is impossible. It's one of the most stable exoplanets. The planet receives 1.86 times the amount of light Earth receives， so bring some shades8）. The planet might also have clouds. It would take the Helios probes 156，971 years to reach the planet.

4. Kepler-62e

It's 1.6 times larger than Earth， and has a rocky surface with a high probability of water. It's also almost covered by ocean. Its year is 122 days long and it's 1200 light years away. Just a side note9）， all planets I have mentioned thus far are larger than Earth and that's why they are called \"Super Earths\" which means that they are larger than our planet， but have similar characteristics. Anyway， back to the planet. It has a cloudy sky and is probably \"warm and humid\" everywhere other than the polar caps10）.

3. Kepler-62f

This planet is 1.4 times the size of Earth， its sun is slightly smaller and cooler than ours， and it would appear to be of peach color to the naked eye if you were to stand on the surface. It would have a rocky surface but with a high probability of water there as well. It is on the target list of SETI11） for possible life. Sadly it's 1200 light years away from us， so the peach sun will have to wait.

6. 格利澤581 d

格利澤581 d圍繞著紅矮星格利澤581運行。這顆行星的大小是地球的6倍，它距離我們地球約20.2光年，位于宜居帶的外部，因此可能有水存在，至少有一個海洋。該行星一年有66.87天，所以估計要在日歷上花不少錢了。因為沒有適宜的大氣層，格利澤581 d還被認(rèn)為是一顆寒冷的行星。但平心而論，地球倘若沒有大氣層，也只會是一顆平均溫度為零下18度的寒冷行星。2009年，我們向格利澤581 d的恒星發(fā)送了25880條信息，這些信息來自190個不同的國家，也許都是些懇求他們不要侵略我們的信息吧。

5. HD 85512 b

我們先從最基本的談起。HD 85512 b有地球的3.6倍大，盡管它比地球大那么多，但它的重力卻只有地球的1.4倍。該行星一年有54天，而且是被潮汐鎖定的。為那些不知道什么是潮汐鎖定的人解釋一下：所謂潮汐鎖定，是指行星的一面一直朝向恒星，所以，基本上這個行星的一面一直是白晝，而另一面則在永恒的黑夜中度過，因此它可謂是吸血鬼的天堂。說正經(jīng)的，潮汐鎖定會給行星帶來危害，降低生命存在的幾率，然而這并不意味著在上面生存是不可能的。這顆行星是最為穩(wěn)定的系外行星之一，它所吸收的光照量是地球的1.86倍，所以來的時候帶上幾副太陽鏡吧。這顆行星可能還有云朵。如果乘坐“太陽神號”探測器的話，要花156971年才能到達那里。

4. 開普勒-62e

開普勒-62e有地球的1.6倍大，擁有巖石地表，有水存在的可能性也非常大。這顆行星幾乎也是被海洋覆蓋著，一年有122天，距離我們1200光年。順便說一下，到目前為止，我前面提到的所有行星都比地球要大，這正是它們被稱為“超級地球”的原因，也就是說，它們是比地球大但與地球有類似特征的行星。好吧，回到開普勒-62e的話題上來。該行星有飄著云朵的天空，很可能到處（除了極地冰冠）都是“溫暖潮濕的”。

3. 開普勒-62f

這顆行星有地球的1.4倍大，它的“太陽”比我們的太陽略小一些，溫度也沒有我們的太陽高。如果站在行星表面放眼望去，它的“太陽”看起來是桃色的。該行星可能擁有巖石地表，但有水存在的可能性也非常大。搜尋地外文明計劃羅列的可能有生命存在的探索目標(biāo)中就有開普勒-62f。令人遺憾的是，它距離我們1200光年，所以想看桃色太陽的話，還得等一等。

2. Gliese 581 g

Gliese 581 g is the unconfirmed sibling of its more famous brother Gliese 581 c. It is 1.5 times the size of Earth and receives a similar amount of sunlight. But before talking about our candidate， let's first talk about its brother. Gliese 581 c is only 20.3 light years away from us， so taking the speed of the fastest man-made objects， the Helios probes， we can travel there in 90，000 years. The planet is famous for being one of the first to be considered habitable and having water. Sadly， it turned out that it was too close to the sun， hence no dice12）. Enter Gliese 581 g—its less known younger brother. The planet might be in the habitable zone. Its surface is rocky with an atmosphere which would support water. In terms of probability， it has the highest chance of harboring13） life， but it loses to No. 1， because there is still debate about its existence.

1. Kepler-22b

The planet is about 2.4 times the radius14） of Earth and has the highest chance of having water in all of the habitable zone planets. If something happens to Earth， this is the place we will probably want to move to. According to estimates temperatures might be -11℃worst case and 22℃ best case scenario15）， noting the absence or presence of a greenhouse capable atmosphere respectively. Either way， it's not that bad. In fact this planet might be so water rich that it might be an \"ocean world\". If that is true， there is a huge potential that there might be life there already， someone to keep us company.

2. 格利澤 581 g

格利澤581 g是格利澤581 c還未被證實的弟弟，不如它哥哥有名。該行星有地球的1.5倍大，和地球接收的光照量差不多。不過在討論我們這顆候選行星之前，先說說它哥哥吧。格利澤581 c距離我們只有20.3光年，所以如果乘坐速度最快的人造飛行器“太陽神號”探測器的話，只需歷經(jīng)90000年我們就可以到那里了。這顆行星之所以有名，是因為它是首批被認(rèn)為適宜人類居住且有水存在的行星之一。但令人遺憾的是，研究結(jié)果發(fā)現(xiàn)它距離它的恒星太近了，所以想去還是沒門兒呀?，F(xiàn)在來說說格利澤581 g這個沒那么有名的弟弟。這顆行星可能位于宜居帶，擁有巖石地表和可以維持水的大氣層。就可能性而言，該行星孕育生命的幾率最高，但它還是敗給了這個名單上的第一名，原因是人們對它的存在還有爭議。

1. 開普勒-22b

這顆行星的半徑是地球的2.4倍，在所有位于宜居帶的行星當(dāng)中，其有水存在的幾率是最高的。如果地球遭遇了什么不測，這就是我們可能想要搬去的地方。據(jù)估計，該行星在最好的情況下溫度可能為22度，在最壞的情況下溫度可能為零下11度，這兩種情況分別考慮的是其有無具有溫室效應(yīng)的大氣層。無論是哪種情況，都不算太糟糕。事實上，這顆行星的水資源可能非常豐富，也許就是一個“海洋世界”。如果這是真的，那里很可能已經(jīng)有生命存在，有陪伴我們的人了。