Today, less than 1 percent of Earth’s surface is urbanized, and the chance that any of our great cities would remain over tens of millions of years is vanishingly low, says Jan Zalasiewicz, a geologist at the University of Leicester in England. A metropolis’s ultimate fate, he notes, mostly depends on whether the surrounding surface is subsiding (to be locked in rock) or rising (to be eroded away by rain and wind). “New Orleans is sinking; San Francisco is rising,” he says. The French Quarter, it seems, has much better chances of entering the geologic record than Haight–Ashbury.
“After a couple of million years,” Frank says, “the chances are that any physical reminder of your civilization has vanished, so you have to search for things like sedimentary anomalies or isotopic ratios that look off.” The shadows of many prehuman civilizations could, in principle, lurk hidden in such subtleties.
Taking all this into consideration, what remains is a menu of diffuse long-lived tracers including fossil fuel combustion residues (carbon, primarily), evidence of mass extinctions, plastic pollutants, synthetic chemical compounds not found in nature and even transuranic isotopes from nuclear fission. In other words, what we would need to look for in the geologic record are the same distinctive signals that humans are laying down right now.
“I find it amazing that no one had worked all this out before, and I’m really glad that somebody has taken a closer look at it,” says Pennsylvania State University astronomer Jason Wright, who last year published “a fluffy little paper” exploring the counterintuitive notion that the best place to find evidence of any of Earth’s putative prehuman civilizations may well be off-world. If, for instance, dinosaurs built interplanetary rockets, presumably some remnants of that activity might remain preserved in stable orbits or on the surfaces of more geologically inert celestial bodies such as the moon.
Wright also acknowledges the potential for this work to be misinterpreted. “Of course, no matter what, this is going to be interpreted as ‘Astronomers Say Silurians Might Have Existed,’ even though the premise of this work is that there is no such evidence,” he says. “Then again, absence of evidence is not evidence of absence.”
A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M⊙). This scenario can be further tested through upcoming Gaia data releases.
Ancient aliens. Devious dinosaurs. Benevolent Atlanteans. Could such legendary civilisations have left any trace behind that would survive the eons? Archaeologists are certain: we have … so why not them?
That could soon change. Lawmakers in the House of Representatives recently proposed legislation for nasa’s future that includes some intriguing language. The space agency, the bill recommends, should spend $10 million on the “search for technosignatures, such as radio transmissions” in the next two fiscal years.The House bill—should it survive a vote in the House and passage in the Senate—can only make recommendations for how agencies should use federal funding. But for seti researchers like Tarter, the fact that it even exists is thrilling. It’s the first time congressional lawmakers have proposed using federal cash to fund seti in 25 years.
We present a simplified description of expansionistic life in the standard relativistic cosmology. The resulting model is exactly integrable, yielding a simple set of predictive formulas. This allows one to quickly propose new scenarios for the life appearance rate and the dominant expansion speed and evaluate the observable consequences. These include the expected number and angular size of visible expanding domains, the total eclipsed fraction of the sky, and the life-saturated fraction of the universe. We also propose a simple anthropic bound on observable quantities, as a function of the dominant expansion velocity alone. The goal is to create a simple and intuition-building tool for use in the context of cosmology, extragalactic SETI, and futures studies. We discuss the general predictions of this framework, including conditions giving rise to an "extragalactic Fermi paradox," in which zero civilizations are visible beyond the Milky Way. This can occur even if a substantial fraction of the universe is already saturated with ambitious life.
The Fermi paradox is the conflict between an expectation of a high {\em ex ante} probability of intelligent life elsewhere in the universe and the apparently lifeless universe we in fact observe. The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference. When the model is recast to represent realistic distributions of uncertainty, we find a substantial {\em ex ante} probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it. This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilizations would inevitably fail to have observable effects upon the universe.
Wow, PAGB and supergiant stars have *very* Dyson-spherey spectra. Check out this one. @ESAGaia puts it at 370 pc, but it's spectroscopically a supergiant and the GAIA fit is *terrible*. Probably at 3.7kpc.
We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Our analysis suggests that the search for technosignatures may potentially merit a minimum funding level of $1 million per year.
Long an underfunded, fringe field of science, the search for extraterrestrial intelligence may be ready to go mainstream.Astronomer Jason Wright is determined to see that happen. At a meeting in Seattle of the American Astronomical Society in January, Wright convened “a little ragtag group in a tiny room” to plot a course for putting the scientific field, known as SETI, on NASA’s agenda.The group is writing a series of papers arguing that scientists should be searching the universe for “technosignatures” — any sign of alien technology, from radio signals to waste heat. The hope is that those papers will go into a report to Congress at the end of 2020 detailing the astronomical community’s priorities. That report, Astro 2020: Decadal Survey on Astronomy and Astrophysics, will determine which telescopes fly and which studies receive federal funding through the next decade.
So, during a summer internship at the Berkeley SETI Research Center, he built an algorithm that could comb through the light that data telescopes captured from Tabby’s Star, and flag images that might be signals of artificial activity. Specifically, his algorithm searches for laser activity, which could be an indicator that there was some type of extraterrestrial activity happening around the star.
The DNA of life on Earth naturally stores its information in just four key chemicals — guanine, cytosine, adenine and thymine, commonly referred to as G, C, A and T, respectively.Now scientists have doubled this number of life’s building blocks, creating for the first time a synthetic, eight-letter genetic language that seems to store and transcribe information just like natural DNA.In a study published on 22 February in Science1, a consortium of researchers led by Steven Benner, founder of the Foundation for Applied Molecular Evolution in Alachua, Florida, suggests that an expanded genetic alphabet could, in theory, also support life.
Still, Benner says that the work shows that life could potentially be supported by DNA bases with different structures from the four that we know, which could be relevant in the search for signatures of life elsewhere in the Universe.
Today, Edward Schwieterman at the NASA Astrobiology Institute in Riverside, California, and a few colleagues have revised the definition of a habitable zone to take account of carbon monoxide and carbon dioxide levels. As a result, they say the habitable zone for complex life must be significantly smaller—about a quarter as wide as the previous definition allows. “Our results have a number of important implications for the search for exoplanet biosignatures and complex life beyond our solar system,” say Schwieterman and co.