The search for extra-terrestrial life has been an ongoing preoccupation for Man, yet how detectable is our own presence in the universe?
Many of the visitors to this site have reason to believe that our planet has been visited by extra-terrestrials for decades, if not longer, but how do other life forms become aware of life on Earth?
A side mission undertaken by NASA's Lunar Crater Observation and Sensing Satellite (LCROSS) looked at Earth from the perspective of an off-earth civilisation, evaluating how they might determine its potential for sentient life forms.
“The LCROSS spacecraft observed the Earth and made statements about ozone in Earth’s atmosphere and also liquid water,” said lead researcher Tyler Robinson, a postdoctoral researcher at the NASA Ames Research Center in Mountain View, Calif. “We also used it to validate a tool to simulate how a distant Earth would appear.”
The research forms part of a paper entitled “Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations,” which has been accepted for publication in the Astrophysical Journal. It is also available for viewing on the pre-publishing site Arxiv.
LCROSS was originally designed for the purpose of water on the moon, landing there in 2009. It was so successful in its mission, finding lunar water by the bucketful, that researchers pondered over whether its attention could be turned to its home planet to see how the Earth might be viewed by the cosmic observer.
Initially, the LCROSS observations were not intending to view the Earth as a new exo-planet, merely to assess the accuracy of the spacecraft after launch, but the data collated at this point was later deemed significant enough to be included in the recent paper, explained co-author and NASA astrophysicist Kimberly Ennico-Smith.
“You never know what else another pair of eyes looking at data can bring you,” she commented. “That’s why having and maintaining archives is so important.”
LCROSS conducted three observations of Earth in 2009, initially looking for signs of liquids, one of the most vital signs of life. Water on other planets, such as the lake on Saturn's moon Titan, can give off a sparkle when hit by sunlight, a flash of light known as secular reflection or a "glint". When scientists turned LCROSS's attentions to Earth, they noted that a similar glint could be observed when our planet was viewed from a lunar perspective, when it appears as a crescent rather than a sphere.
When the data was reviewed, researchers were surprised by what they found.
“The glint detection I found to be surprising for a couple of reasons,” Robinson said. “The spacecraft observation of glint was in disagreement with some previous observations that were done from the ground.”
Ground-level predictions of the way this glint would be perceived in space were based on measurements of its reflection bouncing off the Moon, a glow known as "Earthshine", which is most visible when the Moon is not in full phase. By comparing the data obtained from the crescent-shaped Earth with the Earthshine data, it appeared that the ground predictions were much stronger than those observed by Robinson's team. They also varied when observed in different wavelengths of light; some wavelengths allowed the glint to dominate the appearance of Earth, whereas in others it appeared to be muted.
“Also, the Earth at crescent phase, thanks to the ocean, can be twice as bright. If it’s something you look for in exoplanets, it can be a significant effect,” added Robinson.
This data could change the way variations in planet reflection data is evaluated, as it suggests that ocean glint could affect these measurements, but Robinson warned against over-simplifying the explanation:
“There could be other explanations,” he said. “Clouds have a tendency to reflect better at crescent phases than at other phases, and recent work has shown that, under some circumstances, the ice-covered polar regions can mimic certain glint effects.”
Aside from providing more illuminating data surrounding oceanic glints, LCROSS was able to detect other signs of life on Earth.
Ozone was detectable from a distance, no great surprise there for astronomers but nevertheless still a useful sign of potentially hospitable conditions.
“Ozone is a key potential indicator of life, and it appears most strongly in ultraviolet observations of Earth,” said Robinson. “So, future telescopes could look to the ultraviolet as a place to more easily detect biosignature gases.”
Such telescopes are not yet in existence, however, but LCROSS's observations will form the basis for new telescope designs.
“It’s using current tools to predict and understand what future telescopes might one day see. By studying Earth now, you can ensure that we don’t accidentally engineer the telescope of the future and find out we didn’t build it strong enough,” Robinson said.
So water and ozone were detectable on Earth from a distance, part of the usual criteria considered necessary to support life-forms similar to our own, but the idea of viewing Earth through the telescopic lenses of other life forms had NASA scientists considering other possibilities. Just because our planet is inhabited by carbon-based life forms, it does not necessarily follow that life has evolved on other planets according to the same biological rules.
So does Earth possess any other attributes that might draw a wider cosmic audience towards it, as part of their own search for universal neighbors?
The presence of oxygen might attract attention, as it is a volatile element with great potential, but what if the extra-terrestrial observers were non-oxygen breathers, or even non-breathers?
Sadly, most forms of life inevitably manage to pollute their environment in some way. In Man's case there are a multitude of possibilities in this area, one of the most apparent being radio/TV/radar emissions that could be noted by alien explorers far into space. Kepler-scanning-data indicates that Earth's electromagnetic output-signatures are very unique and would immediately signal to the cosmic observer that our planet was extra-ordinary and worth a much closer look. Light pollution and good old greenhouse gases, methane, nitrous oxide and chlorofluorocarbons (CFCs) might also stand out like a beacon amongst the cosmos.
Viewing our own Earth in this way has been a very useful project, and has assisted NASA in its search for other life-harboring exoplanets elsewhere in the cosmos. Of course, they are still working on the assumption that Earth is, as yet, undetected by alien observers, and that we currently maintain a remote and lonely outpost in our corner of the universe, a view not shared by a large proportion of the Earth's population. A recent poll suggested that 48% of Americans believed that this planet had already been visited by extra-terrestrials.
"It's always been intriguing to me how we act as though only kooks and quacks and little old ladies in tennis shoes believe in flying saucers. And it's never been true, at least for 30 or 40 years," commented former nuclear physicist Stanton Friedman, a civilian investigator of the events surrounding the legendary Roswell, NM, UFO crash of 1947.
Here at the Whitley Strieber's Unknown Country, he shares his own unique perspective on this subject, along with a wealth of evidence suggesting that our home planet caught the attention of other universal dwellers long, long ago.
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