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Will Earth Appear Habitable to Alien Astronomers? --NASA: "Ocean Glint May be a Clue" (Today's Most Popular)




If an alien astromer was viewing Earth from space, could they tell that this planet is well-suited for life? Are there telltale signatures in the atmosphere or from our oceans? These are some of the questions that controllers of a lunar spacecraft sought to answer when it took a bit of a side mission. Instead of observing the Moon, NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS) briefly looked at Earth.

“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.”

A paper on the research, “Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations,” is available now on the pre-publishing site Arxiv and has been accepted in the Astrophysical Journal.

LCROSS, which was smashed into the Moon as planned in 2009, had a primary mission to look for the signature of lunar water. About a decade before, NASA’s Lunar Prospector mission found hints of hydrogen in craters at the Moon’s poles. The divots are permanently shadowed from the heat of the Sun.

LCROSS was to follow up on those observations, and it repaid the investment in spades. It tracked what happened after its spent Centaur rocket stage crashed into the crater Cabeus near the Moon’s south pole, and found signs of hydrogen in spectroscopic measurements spanning infrared and ultraviolet light.

When LCROSS crashed into the moon itself, observations with NASA’s Lunar Reconnaissance Orbiter and others revealed about 100 kilograms of water in the crater it punched in the regolith, which was about 20 meters (66 feet) across.

The spacecraft was indeed successful in finding (and helping other spacecraft find) water on the Moon. But could it also find water on our ocean-rich Earth at a distance? Scientists became curious about the prospect, especially after seeing that our oceans make a mirror-like reflection, called “glint,” when a distant Earth appears as a crescent from the perspective of the Moon.

The image at the top of the page shows the first flash of sunlight reflected off a lake on Saturn's moon Titan. The glint off a mirror-like surface is known as a specular reflection. It confirmed the presence of liquid in the moon's northern hemisphere, where lakes are more numerous and larger than those in the southern hemisphere.

LCROSS did three observation sessions of Earth in 2009. Interestingly, the spacecraft was not originally tasked to look at Earth as an exoplanet. Instead, scientists were evaluating how accurately the spacecraft was pointing after launch, said co-author and NASA astrophysicist Kimberly Ennico-Smith. The data was later repurposed for the exoplanet modeling used in this research.

“You never know what else another pair of eyes looking at data can bring you,” she wrote in an e-mail. “That’s why having and maintaining archives is so important.”

For example, finding hydroxyl — a type of water — on the Moon came from combining sets from India’s Chandryaan-1 lunar spacecraft, and NASA’s Cassini spacecraft on its way to Saturn. Both missions were using the Moon to calibrate their instruments; ocean examinations were not the main objective.

Looking at the repurposed data yielded a surprise. Not only did LCROSS see a glint, but it was a lot different than what researchers expected.

“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.”

Specifically, some researchers had tried to make predictions of the Earth’s glint based on gazing at the Moon. When looking at the Moon outside of full phase, it’s possible to see the Earth’s light shining faintly off of it in a phenomenon called “Earthshine.”

By comparing Earthshine data from a crescent-phase Earth with data from other phases, it’s possible to get measurements of how significant glint is in observations of Earth’s crescent sliver. These measurements predicted a much stronger glint than what Robinson’s team saw using the LCROSS data.

What also surprised researchers was how different the glint appeared in different wavelengths of light. At some wavelengths, glint dominated Earth’s appearance, while at other wavelengths, the glint effect was more muted, as it was masked by certain atmospheric phenomenon.

“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.

If over the course of several orbits, a planet is observed as more reflective at crescent phases and less reflective at other phases, then can it be assumed that ocean glint is the cause? Robinson cautions that the answer is not that simple.

“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.”

But there could be other indications of habitability and life as well. One thing they noticed from a distance was ozone, which was not as much of a surprise to scientists but still a useful tool for observations. Ozone especially showed up in ultraviolet light, and it could be a “bio-indicator,” or sign of life, on distant planets, Robinson said.

“Ozone is a key potential indicator of life, and it appears most strongly in ultraviolet observations of Earth,” he said. “So, future telescopes could look to the ultraviolet as a place to more easily detect biosignature gases.”

Such a telescope, however, will be a couple of decades down the line. While NASA’s James Webb Space Telescope will be an able planet-hunter, it will take the resolution of something like the cancelled NASA Terrestrial Planet Finder project to make better progress in searching these worlds, he said. There were a few different ideas for what it would look like, but one design had intended to combine four, 3.5-meter telescopes in space to look at parameters such as temperature and atmosphere, among others.

Another important aspect of the observations performed by LCROSS is that they become the basis for new telescope designs. NASA’s work allows researchers to gather data on which designs would best pick out certain features of planets, such as the reflectivity or ozone that LCROSS observed.

“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.

The Daily Galaxy via NASA


Would they know? First of all, it would depend on if they were aware of the fact that an atmosphere like ours and a planet in the state ours is could support life in the first place. Just because *we* are carbon-based, doesn't mean they are, or that they've met carbon based life previously.

Secondly, it depends on the tools, and the distance. Telescopes like ours right now? They'd have to be pretty near to us, relatively speaking (no pun intended.) Wide baseline interferometry? Much better. Huge space based individual devices? Even better. Or, tech we are unaware of.

In other words, we don't know. End of answer. :) Tune in again once we meet them and can ask them.

Well, from what we have seen thus far, within our own solar system, and also from recent Kepler-scanning-data, I think it is safe to assume that Earth's electromagnetic output-signatures (including the output signal of high oxygen levels in our atmosphere) are HIGHLY and EXTREMELY unique.

These output signatures are clearly unique enough, to the point that any alien intelligence would quickly realize that Earth is highly "UNUSUAL", and somehow "DIFFERENT" than most other planets, and worthy of at least a very close second close-up inspection.

Even if that alien life is not oxygen based like us Earth-animals, and even if, somehow, stupidly that alien life observing us doesn't think that oxygen (a volatile chemical/element) is a strange factor, you can assume that our radio/TV/radar frequency EM emissions are, in themselves, a very STRONG strange/unusual enough to attract their attention.

So really it does NOT matter whether or not the "aliens" are oxygen breathing like us: in the end there are enough STRONG, "unusual", and "weird" signals coming from planet Earth, that would CERTAINLY attract their attention.

Essentially, planet Earth can NOT hide in the galaxy. If there is another intelligent life-species in our part of the galaxy, then chances are great they VERY LIKELY know about us.

So in short: Earth's output signals into space, are strange/weird enough (whether it is natural oxygen levels, or "artificial" human radio/radar signals) that Earth is VERY OBVIOUSLY unique, and possibly harboring of intelligent/technological lifeforms on our planet, no matter how you look at Earth.

Humanity is totally visible to extraterrestrials.
At a meeting of the Royal Society in London, in trying the explain the current failure of SETI to discover extraterrestrial civilizations, Frank Drake said that phasing out analog transmissions from TV, radio, and radar is making our planet electronically invisible from outer space, because while an old-style TV transmitter might generate a million watts, the power of a digital satellite signal is around twenty watts.
The digital revolution does not make civilizations invisible to extraterrestrial search. On the contrary, the electromagnetic radiation of our civilization is getting stronger and stronger, and we are sending an increasing amount of radio waves into space. The number of TV transmitters, military and science radars, and so on, all around the world and in orbit is increasing. Their power output is also increasing. The total level of electromagnetic noise from the inhabited planets is also growing.
The digital revolution is making the civilizations much more visible to extraterrestrial search.
Some scholars, including Stephen Hawking, are concerned that the deliberate sending of radio signals into deep space and the leakage radiation could be a serious risk, because we are revealing the location of our planet to hostile alien civilizations.
There have even been calls for a moratorium on deliberate radio transmissions into deep space to attract the attention of aliens.
There is absolutely no need to worry about this. The advanced civilizations from our Galaxy know that we exist and know exactly where we are. The spectral analysis of Earth’s atmosphere alone is enough to reveal us, because it is specific to planets with complex life and technological civilizations. We cannot hide our atmosphere.
According to the second law of thermodynamics, the advanced civilizations create entropy in the form of waste heat that is drifting into outer space. It is impossible to hide the faint entropy glow.

According to Alexander Popoff (and his book The Hidden Alpha), the advanced technological civilizations from our Galaxy know where we are and what is our level of development.
For the mega-civilizations, we are like a Monopoly game on the table, next to the sandwiches and the beer. We are totally visible, accessible, and manipulable.

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