外星人可能是紫色的

外星人可能是紫色的。

That's the conclusion of a new research paper that suggests that the first life on Earth might have had a lavender hue. In the International Journal of Astrobiology, microbiologist Shiladitya DasSarma of the University of Maryland School of Medicine and postdoctoral researcher Edward Schwieterman at the University of California, Riverside, argue that before green plants started harnessing the power of the sun for energy, tiny purple organisms figured out a way to do the same.

這是一篇研究論文的結(jié)論，該論文認為地球上的第一種生命可能是淡紫色色調(diào)的。在《國際天體生物學雜志》上的一篇論文中，馬里蘭大學醫(yī)學院的微生物學家Shiladitya DasSarma和加利福尼亞大學河濱分校的博士后研究員Edward Schwieterman認為，在綠色植物開始利用太陽能之前，微小的紫色有機體用同樣的方法利用太陽能。

Alien life could be thriving in the same way, DasSarma said.

DasARMA認為，外星人也可以用這樣的顏色蓬勃發(fā)展。

"Astronomers have discovered thousands of new extrasolar planets recently and are developing the capacity to see surface biosignatures" in the light reflected from these planets, he told Live Science. There are already ways to detect green life from space, he said, but scientists might need to start looking for purple, too.

“天文學家最近發(fā)現(xiàn)了數(shù)千顆新的太陽系外行星，并且正在發(fā)展從這些行星反射的光線中觀察星球表面生物特征的能力，”他告訴Live Science。他說，現(xiàn)在已經(jīng)有了從太空中觀測綠色生命的方法，但是科學家們也需要開始尋找紫色。

Purple Earth

紫色地球

The idea that the early Earth was purple is not new, DasSarma and his colleagues advanced the theory in 2007. The thinking goes like this: Plants and photosynthesizing algae use chlorophyll to absorb energy from the sun, but they don't absorb green light. That's odd, because green light is energy-rich. Perhaps, DasSarma and his colleagues reasoned, something else was already using that part of the spectrum when chlorophyll photosynthesizers evolved.

早期地球是紫色的想法并不新鮮，DasSarma和他的同事在2007提出了這一理論。理論是這樣的：植物和光合藻類利用葉綠素吸收來自太陽的能量，但它們不吸收綠光。這很奇怪，因為綠光的能量很豐富。DasSarma和他的同事們推斷，也許當葉綠素光合作用物質(zhì)進化出來時，其他一些別的物質(zhì)已經(jīng)在使用這部分光譜了。

That "something else" would be simple organisms that captured solar energy with a molecule called retinal. Retinal pigments absorb green light best. They're not as efficient as chlorophylls in capturing solar energy, but they are simpler, the researchers wrote in their new paper published Oct. 11.

“別的東西”也許是簡單的有機體，用一種叫做“視網(wǎng)膜”的分子捕獲太陽能。視網(wǎng)膜色素吸收綠光效果最好。研究人員在10月11日發(fā)表的新論文中寫道，它們在捕獲太陽能方面不如葉綠素有效，但是它們本身比葉綠素更簡單。

Retinal light-harvesting is still widespread today among bacteria and the single-celled organisms called Archaea. These purple organisms have been discovered everywhere from the oceans to the Antarctic Dry Valley to the surfaces of leaves, Schwieterman told Live Science. Retinal pigments are also found in the visual system of more complex animals. The appearance of the pigments across many living organisms hints that they may have evolved very early on, in ancestors common to many branches of the tree of life, the researchers wrote. There is even some evidence that modern purple-pigmented salt-loving organisms called halophiles might be related to some of the earliest life on Earth, which thrived around methane vents in the ocean, Schwieterman said.

視網(wǎng)膜光采集這種方式在細菌和單細胞生物體中仍然廣泛存在，稱為古生菌。Schwieterman告訴Live Science，從大海到南極干谷再到一般葉子表面，到處都發(fā)現(xiàn)了這些紫色有機物。研究人員寫道，這些色素在許多生物體中的出現(xiàn)表明它們可能很早就在進化樹的許多分支的共同祖先中就進化出來了。甚至有證據(jù)表明，被稱為嗜鹽菌的現(xiàn)代紫色色素鹽生物可能與地球上最早的一些生命有關(guān)，這些生命常出現(xiàn)在海底的甲烷噴口周圍，Schwieterman說。

Purple aliens

紫色外星人

Regardless of whether the first life on Earth was purple, it's clear that lavender life suits some organisms just fine, Schwieterman and DasSarma argue in their new paper. That means that alien life could be using the same strategy. And if alien life is using retinal pigments to capture energy, astrobiologists will find them only by looking for particular light signatures, they wrote.

Schwieterman和DasSarma在他們的新論文中認為，不管地球上演化出來的第一種生命是不是紫色的，但是紫色是適用于某些生命是比較明確的。這意味著地外生命也可以用相同的策略，他們認為，如果外星生命使用視網(wǎng)膜色素來捕獲能量，那么生物學家只能通過尋找特定的光信號來發(fā)現(xiàn)它們。

Chlorophyll, Schwieterman said, absorbs mostly red and blue light. But the spectrum reflected from a plant-covered planet displays what astrobiologists call a "vegetation red edge." This "red edge" is a sudden change in the reflection of light at the near-infrared part of the spectrum, where plants suddenly stop absorbing red wavelengths and start reflecting them away.

葉綠素主要吸收紅光和藍光。但是從被植物覆蓋的行星反射的光譜顯示了生物學家所說的“植被紅邊”。這種“紅邊”的出現(xiàn)是因為光譜的近紅外部分發(fā)生了短時間的變化，植物突然不再吸收近紅外部分，而是轉(zhuǎn)而開始反射這一部分光譜的光。

Retinal-based photosynthesizers, on the other hand, have a "green edge," Schwieterman said. They absorb light up to the green portion of the spectrum, and then start reflecting longer wavelengths away.

另一方面，基于視網(wǎng)膜的光合作用系統(tǒng)具有“綠邊”。它們將光線吸收到光譜的綠色部分，然后開始反射更長的波長。

Astrobiologists have long been intrigued by the possibility of detecting extraterrestrial life by detecting the "red edge," Schwieterman said, but they may need to consider searching for the "green edge," too.

Schwieterman說，一直以來生物學家一直對通過探測“紅邊”來探測外星生命的可能性感興趣，但他們可能也需要考慮尋找“綠邊”。

"If these organisms were present in sufficient densities on an exoplanet, those reflection properties would be imprinted on that planet's reflected light spectrum," he said.

“如果這些有機物在系外行星上以足夠的密度存在，那么這些光反射特性將包含在該行星的反射光譜上”。