Through the eyes of aliens: any signs of life shows the Earth?




Alien spaceship hidden in Earth orbit, could see the lights of cities and pollution of our atmosphere. But what if he was looking for signs of life on Earth from a distance?

This issue is of great relevance to those seeking other Earth outside our solar system. Space Telescope, “Kepler” – just one of the flotilla of telescopes and spacecraft that are looking for rocky planets like ours. After becoming known size and location of a brave new world, the next step is to study the composition of its atmosphere.

From a distance, Earth-like worlds appear as tiny points of light, of which, it would seem difficult to find something great. The best thing we can do with the technology of our telescopes at the moment – the definition of several atmospheric constituents worlds larger than Jupiter. But this does not mean that we should abolish the possibility of detecting planets similar in size to our own. After all, telescopes have grown stronger and more powerful.

“We think about how to use observations of the Earth itself, to understand the things that we can do with the possibilities of future generations of telescopes,” – says Robert Fosbury, honorary astronomer at the European Southern Observatory (ESO), participating in the study.

Fosbury and leading researcher Fei Yang, an astronomer at ESO and the University of Chinese Academy of Sciences, watching the Earth’s shadow during a lunar eclipse. Although ESO has no direct relationship with astrobiology, Fosbury says that scientists are always thinking about the possible life beyond Earth.

Work has appeared in the International Journal of Astrobiology, its preprint available at
Look out of the shadows

Земля и Луна

The main part of the observations occurred in a total lunar eclipse December 10, 2011. Lunar eclipse passed between the Moon and the Sun to be seen everywhere, where the sky was dark and clear.

Lunar eclipse is easier to observe than the sun, which occurs when the Moon passes between the Earth and the Sun. During a solar eclipse, the shadow of the moon is so small that it creates only a few short minutes of “total eclipse” and small “track” shadows observed on the surface of the Earth.

In their study, the scientists made observations with the High Resolution Spectrograph, mounted on a 2.16-meter telescope at the Xinglong Station in China, and the telescope pointed at the area near the lunar crater Tycho, in a place where the moon high reflectivity.

Scientists hope to learn more about the spectrum of the Earth, which is manifested in the moonlight reflection. Spectrum – a group of colors that make up visible light and easiest recognized in the rainbow. Some elements mainly emit certain wavelengths of light and absorb others. Using a spectrograph to explore another planet, you can see which atoms or molecules are present in the atmosphere or surface.

Observation of the Earth’s light reflected by the Moon, similar to the observation of exoplanets, passing in front of its parent star (the so-called transit), astronomers say. In both cases, detection of absorbing molecules in the atmosphere is a subtraction process. In the case of exoplanet astronomers compared the molecular absorption in the light of the stars before and after the transit. In the case of the Moon – the astronomers compared the elements found in the earth’s shadow on the moon, when it is free from the shadows.

During the eclipse, scientists observed the spectra of the Moon in the Earth’s shadow. The moon turns red during this time, because most of the light that you see – it is the refraction of solar rays in the Earth’s atmosphere (all the sunsets and sunrises in the world at the same time). Scientists also evaluated the spectrum of the moon, when it was completely out of the shadows.
Water and pollution


After removal of some of the effects generated by the local atmosphere, scientists have studied the spectrum of colors to figure out which molecules become visible. There were surprises.

For example, they did not see as much water vapor as observed during the eclipse in 2009, which covered much of the Northern Hemisphere.

In the new study, scientists have concluded that the lack of water vapor due to the fact that the “path” Transit 2011 passed through the Antarctic, which explains the absence of large quantities of water – it is frozen.

Another surprise – an abundance of nitrogen dioxide. Typically, nitrogen dioxide is regarded as a pollutant formed as a result of human activity. Antarctica, however, is quite barren – but it has a volcano.

“We have found the trail was close to the volcano, and this volcano can potentially produce nitrogen dioxide,” – said Yang.

He added that there may be another explanation. For example, the volcano (Mount Erabus) may not be sufficiently active to produce large amounts of nitrogen dioxide. Further studies have shown that nitrogen dioxide is a bioproduct nitrous oxide (which is naturally produced by bacteria), which is then retained in the atmosphere and reacts with ozone, creating nitrogen dioxide.

“It was in the spring, and in the spring the ice melted, and, according to volcanologists, melting ice freed up a lot of nitrous oxide,” – says Fosbury.

Ozone on other planets


If we look at the Earth as an exoplanet, is it possible to interpret the presence of nitrogen dioxide as a sign of contamination, microbiological life or actions of a volcano? Fosbury says it all depends on the context. If the planet is replete with volcanoes on its surface, you can imagine that the case in them. If they are not visible, you can suggest the presence of life, though unlikely. Typically, the presence of nitrogen dioxide is connected with pollution.

When searching for extraterrestrial life chemical contamination should be included in the list of “signs” of life. Ozone can also be seen. Fosbury noted that at higher latitudes, on the edge of the Moon’s shadow, you can watch the blue.

“This is one of the indicators of the presence of large amounts of ozone,” – he says.

Ozone is also the reason that the sky is blue during twilight at dawn, for example. (During the day the sky is blue because of the phenomenon called Rayleigh scattering, which mainly scatters blue light on the path of the sun through the air).

“Ozone – a very visible and important marker for Earth-like planets,” – says Fosbury.

ESO, whose astronomical facilities are based in Chile, has made at least two major contributions to the study of exoplanets. Detector HARPS on the 3.6-meter telescope “La Silla” registered a slight variation in the stellar velocities depending on the rotation of the planets in their orbits. This tool was used for the first-ever detection of exoplanets.

Also under construction is the European Very Large Telescope (E-ELT), a 39-meter monster that not only measure the speed of certain planets, but also provide them photos and may characterize their atmospheres. These studies will be useful when the E-ELT and the James Webb Space Telescope will work.

“For a long period of time will be enough investment – adds Fosbury. – The more we learn about the practical implications of these observations, the better our position, not only in terms of observations, but also in terms of the development of the necessary tools. ”
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Tags: Extraterrestrial life , Earth , Exoplanets .


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