Posted on 06/23/2021 5:34:27 PM PDT by LibWhacker
Scientists at Cornell University and the American Museum of Natural History have identified 2,034 nearby star-systems—within the small cosmic distance of 326 light-years—that could find Earth merely by watching our pale blue dot cross our sun.
That's 1,715 star-systems that could have spotted Earth since human civilization blossomed about 5,000 years ago, and 319 more star-systems that will be added over the next 5,000 years.
Exoplanets around these nearby stars have a cosmic front-row seat to see if Earth holds life, the scientists said in research published June 23 in Nature.
"From the exoplanets' point-of-view, we are the aliens," said Lisa Kaltenegger, professor of astronomy and director of Cornell's Carl Sagan Institute, in the College of Arts and Sciences.
"We wanted to know which stars have the right vantage point to see Earth, as it blocks the Sun's light," she said. "And because stars move in our dynamic cosmos, this vantage point is gained and lost."
Kaltenegger and astrophysicist Jackie Faherty, a senior scientist at the American Museum of Natural History and co-author of "Past, Present and Future Stars That Can See Earth As A Transiting Exoplanet," used positions and motions from the European Space Agency's Gaia eDR3 catalog to determine which stars enter and exit the Earth Transit Zone—and for how long.
"Gaia has provided us with a precise map of the Milky Way galaxy," Faherty said, "allowing us to look backward and forward in time, and to see where stars had been located and where they are going."
Of the 2,034 star-systems passing through the Earth Transit Zone over the 10,000-year period examined, 117 objects lie within about 100 light-years of the sun and 75 of these objects have been in the Earth Transit Zone since commercial radio stations on Earth began broadcasting into space about a century ago.
[Here there is a nice little video showing the band of nearby stars whose inhabitants could be observing us]
Scientists at Cornell University and the American Museum of Natural History have identified 2,034 nearby star-systems that could find Earth merely by watching our pale blue dot cross our sun. Credit: NASA/AMNH OpenSpace via D. Desir "Our solar neighborhood is a dynamic place where stars enter and exit that perfect vantage point to see Earth transit the Sun at a rapid pace," Faherty said.
Included in the catalog of 2,034 star-systems are seven known to host exoplanets. Each one of these worlds has had or will have an opportunity to detect Earth, just as Earth's scientists have found thousands of worlds orbiting other stars through the transit technique.
By watching distant exoplanets transit—or cross—their own sun, Earth's astronomers can interpret the atmospheres backlit by that sun. If exoplanets hold intelligent life, they can observe Earth backlit by the sun and see our atmosphere's chemical signatures of life.
The Ross 128 system, with a red dwarf host star located in the Virgo constellation, is about 11 light-years away and is the second-closest system with an Earth-size exoplanet (about 1.8 times the size of our planet). Any inhabitants of this exoworld could have seen Earth transit our own sun for 2,158 years, starting about 3,057 years ago; they lost their vantage point about 900 years ago.
The Trappist-1 system, at 45 light-years from Earth, hosts seven transiting Earth-size planets—four of them in the temperate, habitable zone of that star. While we have discovered the exoplanets around Trappist-1, they won't be able to spot us until their motion takes them into the Earth Transit Zone in 1,642 years. Potential Trappist-1 system observers will remain in the cosmic Earth transit stadium seats for 2,371 years.
"Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see Earth transit," Kaltenegger said. "If we assume the reverse to be true, that provides a healthy timeline for nominal civilizations to identify Earth as an interesting planet."
The James Webb Space telescope—expected to launch later this year—is set to take a detailed look at several transiting worlds to characterize their atmospheres and ultimately search for signs of life.
The Breakthrough Starshot initiative is an ambitious project underway that is looking to launch a nano-sized spacecraft toward the closest exoplanet detected around Proxima Centauri—4.2 light-years from us—and fully characterize that world.
"One might imagine that worlds beyond Earth that have already detected us, are making the same plans for our planet and solar system," said Faherty. "This catalog is an intriguing thought experiment for which one of our neighbors might be able to find us."
who might have or are observing us would have some type of radio communication on their planet.
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You do realize that the radio spectrum is a tiny part of the electromagnetic spectrum, that radio may not be what most civilizations would use the communicate - See “The Man Who Changed Everything, the Life of James Clerk Maxwell”
Why are these people so self loathing that they always assume we are not the most advanced lifeform of our type in the universe?
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There are trillions of galaxies each with over 300 million stars, each of those with at least one planet. How many planets are there?
If only .001% of those planets have advanced civilizations, how many planet is that?
If .001% of those planets have some form of transportation that allows them to cross stellar distances nearly instantaneously, how many planets is that?
Where do puny Earth people get all their hubris from?
That would be a big number but far fewer stars are suitable for enabling life as we know it. Stars fall into one of seven basic types; O,B,A,F,G,K and M. Additional types exist but the bulk fall into OBAFGKM.
Our sun is a type G star which makes up only about 7 percent of all stars.
So, for starters, we should take the numbers you cited and multiply by .07 to narrow the cosmic field down to stars of the same spectral type as our sun.
However, class G stars come in 12 basic variants, our sun being a type G2V.
My point here is that the number of type G or even type G2V stars in the universe is large, but not nearly as large as the absolute total numbers commonly cited.
However, we need to further sort based on the location of a type G star within a galaxy. We have to do this sorting because there is believed to be a galactic-habitable zone.
Most stars in a galaxy do not fall within the habitable zone of the galaxy. Therefore, another big reduction is needed.
Of the type G stars within the habitable zones of galaxies, what percentage have exoplanets? No one knows. To be on the "conservative side" we should assign a number less than 100 percent and thereby reduce the candidate field further.
Of the type G stars within the habitable zones of galaxies, how many have exoplanets of suitable composition orbiting within the star's habitable zone further reduces the field.
So the number gets even smaller and there are additional filtering criteria such as solar systems with gas giants in the outer bands acting as gravitational vacuum cleaners sucking up cosmic debris and thereby protecting the smaller stars within the inner habitable zone. Afterall, it would be hard to form an advanced civilization if your planet was being pummeled by large meteors, comets and other asteroid sized objects.
We must further sort based on planetary composition. If a planet doesn't have an iron core like earth does, it won't have a magnetic field to protect it from cosmic radiation which is in part why Venus and Mars are sterile wastelands.
On and on we can go with the filtering and the number of likely candidates gets smaller and smaller.
If only .001% of those planets have advanced civilizations, how many planet is that?
A thousand times fewer. However, .001 of the total you cited is an incorrect assumption for reasons I just cited and there are many more reasons.
If .001% of those planets have some form of transportation that allows them to cross stellar distances nearly instantaneously, how many planets is that? Where do puny Earth people get all their hubris from?
You are basing your beliefs on absolute total numbers trumpeted by the assorted Carl Sagans who are in position know what they are saying is false.
You never know what their intentions might be. And for their part they have no doubt figured out we're an aggressive and violent bunch. They're probably thinking this is a neighborhood to avoid.
Not really correct because the signals would so weak as to be undetectable at those distances.
Drop a pebble into a completely calm lake and you can only observe the ripples radiate out so far until the energy of the pebble impacting the surface is so diffuse you can no longer see the effect on the water (ripples).
Radio waves behave similarly. Earth based radio transmitting stations do not transmit enough energy to overcome the vast distances of inter-stellar space due to path loss.
Path loss is the reduction in power density which occurs as a radio wave propagates over a distance.
Every time you double the distance, you receive only one-fourth the power. Assume an television station in 1970 transmittd omni-directionally at 100 kW. The signal is now ~51 light years away but because the signal radiates outward like ripples on a pond, the 100kW is now stretching out over an arc length of 320.4 light years.
The amount of energy received at any signle antenna 51 light years away will be so low as to be undetectable.
What I meant was the article is written by people knowingly presenting fantasy as fact.
You are basing your beliefs on absolute total numbers trumpeted by the assorted Carl Sagans who are in position know what they are saying is false.
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Really! And who are you to make such an assumption and what is its basis? And who says intelligent life (sic) has to be “life as we know it”? There is just a host of other assumption you made that are not facts, but theories based on other assumptions - rendering your essay to round file level.
What about my post says assumption?
And who says intelligent life (sic) has to be “life as we know it”?
Did you not notice in my first sentence that I limited what I wrote to life as we know it... aka carbon based life.
There is just a host of other assumption you made that are not facts, but theories based on other assumptions - rendering your essay to round file level.
What of what I wrote is not factual? Are you saying our sun is not a type G star? Do you mean I understated the percentage of type G stars in the universe? Are you saying there isn't such a thing as a habitable zone?
Where were the errors? Help all of us out here.
pointless to argue.
How can there be an argument over facts? Unless you don't have any.
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