Earth's mysterious red glow, explained - Zoe Pierrat

譯者: Wei-Yu Shih 審譯者: Helen Chang

In 2009, a satellite circled Earth,

在2009年，一顆衛星環繞著地球，

methodically scanning and sorting the wavelengths

有計畫性的掃描和揀選

reflecting off the planet’s surface.

從地表反射的波長。

Researchers were looking for the spectral signature of carbon dioxide

研究人員本來在尋找 二氧化碳的光譜特徵，

when they noticed something baffling:

但他們發現了令人疑惑的東西：

an unexpected wavelength of unknown origin.

一種意外、來源不明的波長。

They tried looking at Earth with only this wavelength,

他們試著只用這個波長來看地球，

and saw the planet covered in a red hue of varying intensity.

發現地表被不同亮度的 紅色光芒所覆蓋。

This couldn’t have been reflected sunlight

這不可能是太陽光的反射，

because it was a wavelength that never escapes the Sun’s outer atmosphere.

因為這個波長無法穿過 太陽的外大氣層。

And it didn’t correspond with densely populated areas,

而且它和人口密度也無關，

suggesting it wasn’t human-made either.

代表並非人為的。

In fact, it was emanating from places with lots of plants:

事實上，它從有很多植物的 地方散發出來：

the Amazon basin, northern evergreen forests,

像是亞馬遜盆地、北方的常綠林、

and croplands of the Midwestern US were all ablaze.

美國中西部的農田， 全都在發光。

So, what was going on?

所以這是怎麼一回事？

Plants and other organisms use light to grow by way of photosynthesis.

植物和其他生物利用光來生長， 這個過程叫做光合作用。

But that’s just one of three ways that light

但這只是光在這個過程中的

entering a photosynthetic organism is used.

三個作用方式之一。

And this is the key to solving the mystery.

而這就是解開謎題的關鍵。

To understand the others, we need to begin with photosynthesis.

為了要了解其他方式， 我們需要先從光合作用說起。

During this process,

在這個過程中，

sunlight hits structures within a plant’s cells called chloroplasts,

陽光會接觸到植物細胞內 叫做葉綠體的構造，

which are packed with chlorophyll pigments.

裡面有很多的葉綠素。

When chlorophyll molecules absorb light, some of their electrons become excited.

當葉綠素分子吸收光後， 部分的電子會被激發。

They go through a series of reactions,

這些電子經過一系列反應，

which transform light energy into chemical energy.

將光能轉變成化學能。

This powers the conversion of carbon dioxide and water into glucose,

這個過程將二氧化碳和水 轉換成葡萄糖，

the simple sugar plants need to grow.

一種植物生長所需要的單醣。

And of course, this reaction generates an important byproduct.

當然，這些反應也會產生 一個重要的副產物。

Photosynthesis—

光合作用，

which is constantly being carried out by plants, algae, and bacteria—

這個植物、藻類和細菌 不斷在進行的活動，

produces all of Earth’s oxygen.

產生了全地球的氧氣。

But plants regularly absorb more light than they’re able to consume.

但植物通常會吸收超過 它所能消耗的陽光。

For instance, over winter,

舉例來說，在冬天，

the frozen leaves of evergreen trees can't photosynthesize at their usual rate,

長青樹上結冰的葉子沒有辦法 像平常一樣進行光合作用，

but they're still exposed to a lot of sunlight.

但他們還是會照到陽光。

If not dealt with, the excess light can damage their photosynthetic machinery.

如果沒有解決這個問題， 多餘的光會破壞光合作用的系統。

So, the second way plants use light is by transforming it into heat

因此，第二種植物使用光的方法 就是將其轉換為熱能，

and dissipating it out of their leaves.

然後從葉子散熱。

The third way plants interact with incoming light

第三種植物與光的作用

is by radiating it back out at a different wavelength,

則是用不同波長，將它反射回去，

producing what’s called chlorophyll fluorescence.

產生所謂的葉綠素螢光。

During photosynthesis, the chlorophyll’s excited electrons

在光合作用中， 葉綠素內的激發態電子

move through that series of chemical reactions.

會經過一連串的化學反應。

But as some of the excited electrons fall back to their ground states,

但當部分電子還原到它們的基態時，

they emit energy as light.

它們會將光能釋放出來。

Overall, about 1% of the light absorbed is re-emitted

整體來說，大約百分之一 被吸收的光會被排出，

as wavelengths at the red end of the spectrum.

成為光譜上紅色端的波長。

It’s such a small amount that you can’t see it with the naked eye.

不過量太少，無法用肉眼看見。

But plants the world over are fluorescing as they photosynthesize.

但全世界的植物在行光合作用同時， 都會發出紅色光芒。

And this is what’s caused the Earth’s baffling red glow,

這就是地球產生神秘紅光的原因，

as observed by satellite.

就像衛星觀測到的那樣。

It was an accidental discovery, but a huge breakthrough.

雖然是意外的發現， 但這是一個突破。

Tracking chlorophyll fluorescence from space

從太空中追蹤葉綠素螢光

allows us to watch the planet breathe in real time—

讓我們能即時看到地球在呼吸，

and monitor the health of ecosystems worldwide.

並監測全世界生態系統的健康。

Previously, researchers used levels of greenness

在這之前，研究人員是用綠色程度

as the main estimate for plant health.

當作計算地球健康的主要依據。

Because plants generally change colors or lose foliage when they’re stressed,

植物遇到逆境時會變色或落葉，

higher levels of green typically indicate healthier plants.

所以高綠度通常能當作 植物健康的指標。

But this measure can be unreliable.

但這個方法並不可靠。

In contrast, chlorophyll fluorescence is a direct measure

相反的，透過葉綠素螢光 能夠直接地測量

of photosynthetic activity.

光合作用的狀況。

It can help us infer how much oxygen is being released

這能幫助我們推估 被排出的氧氣量，

and how much carbon is being absorbed in a given system.

以及在一個系統中 有多少碳被吸收。

Drops in chlorophyll fluorescence may also occur

葉綠素螢光的減少甚至可在

before visible signs of plant stress, making it a timely measure.

觀察到植物逆境之前發生， 讓這個數字更加即時。

Scientists have already used chlorophyll fluorescence to monitor

科學家已使用葉綠素螢光來監測

harmful phytoplankton blooms,

有害浮游植物的增生、

and track the effects of drought in the Amazon and Great Plains.

和追蹤亞馬遜和大平原的乾旱 所造成的影響。

Going forward, we’ll be investigating photosynthesis from space,

未來我們會持續從外太空 研究光合作用，

and gauging how best to support our silent friends,

然後評估幫助我們 安靜好友的最佳辦法，

who already do so much for us.

畢竟它們已經為我們做這麼多了。