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.

这是一篇研究论文的结论，该论文认为地球上的第一种生命可能是淡紫色色调的。在《国际天体生物学杂志》上的一篇论文中，马里兰大学医学院的微生物学家Shiladitya DasSarma和加利福尼亚大学河滨分校的博士后研究员Edward Schwieterman认为，在绿色植物开始利用太阳能之前，微小的紫色有机体用同样的方法利用太阳能。

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

DasARMA认为，外星人也可以用这样的颜色蓬勃发展。

"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.

“天文学家最近发现了数千颗新的太阳系外行星，并且正在发展从这些行星反射的光线中观察星球表面生物特征的能力，”他告诉Live Science。他说，现在已经有了从太空中观测绿色生命的方法，但是科学家们也需要开始寻找紫色。

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鲜，DasSarma和他的同事在2007提出了这一理论。理论是这样的：植物和光合藻类利用叶绿素吸收来自太阳的能量，但它们不吸收绿光。这很奇怪，因为绿光的能量很丰富。DasSarma和他的同事们推断，也许当叶绿素光合作用物质进化出来时，其他一些别的物质已经在使用这部分光谱了。

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.

“别的东西”也许是简单的有机体，用一种叫做“视网膜”的分子捕获太阳能。视网膜色素吸收绿光效果最好。研究人员在10月11日发表的新论文中写道，它们在捕获太阳能方面不如叶绿素有效，但是它们本身比叶绿素更简单。

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.

视网膜光采集这种方式在细菌和单细胞生物体中仍然广泛存在，称为古生菌。Schwieterman告诉Live Science，从大海到南极干谷再到一般叶子表面，到处都发现了这些紫色有机物。研究人员写道，这些色素在许多生物体中的出现表明它们可能很早就在进化树的许多分支的共同祖先中就进化出来了。甚至有证据表明，被称为嗜盐菌的现代紫色色素盐生物可能与地球上最早的一些生命有关，这些生命常出现在海底的甲烷喷口周围，Schwieterman说。

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在他们的新论文中认为，不管地球上演化出来的第一种生命是不是紫色的，但是紫色是适用于某些生命是比较明确的。这意味着地外生命也可以用相同的策略，他们认为，如果外星生命使用视网膜色素来捕获能量，那么生物学家只能通过寻找特定的光信号来发现它们。

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.

叶绿素主要吸收红光和蓝光。但是从被植物覆盖的行星反射的光谱显示了生物学家所说的“植被红边”。这种“红边”的出现是因为光谱的近红外部分发生了短时间的变化，植物突然不再吸收近红外部分，而是转而开始反射这一部分光谱的光。

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，基于视网膜的光合作用系统具有“绿边”。它们将光线吸收到光谱的绿色部分，然后开始反射更长的波长。

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说，一直以来生物学家一直对通过探测“红边”来探测外星生命的可能性感兴趣，但他们可能也需要考虑寻找“绿边”。

"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.

“如果这些有机物在系外行星上以足够的密度存在，那么这些光反射特性将包含在该行星的反射光谱上”。