Author Topic: General SETI Thread  (Read 30849 times)

Offline ExoExplorer

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Re: General SETI Thread
« Reply #160 on: 02/06/2018 12:18 AM »
Figure 1 of https://arxiv.org/abs/1411.7412 suggests otherwise, by large factors.

--- Tony
My mistake, I meant to say it was comparable to MS m-dwarfs, not PMS.

Offline Star One

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Re: General SETI Thread
« Reply #161 on: 02/07/2018 07:50 PM »
A search for technosignatures from 14 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz

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Analysis of Kepler mission data suggests that the Milky Way includes billions of Earth-like planets in the habitable zone of their host star. Current technology enables the detection of technosignatures emitted from a large fraction of the Galaxy. We describe a search for technosignatures that is sensitive to Arecibo-class transmitters located within ~450 ly of Earth and transmitters that are 1000 times more effective than Arecibo within ~14 000 ly of Earth. Our observations focused on 14 planetary systems in the Kepler field and used the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. Each source was observed for a total integration time of 5 minutes. We obtained power spectra at a frequency resolution of 3 Hz and examined narrowband signals with Doppler drift rates between +/-9 Hz s-1. We flagged any detection with a signal-to-noise ratio in excess of 10 as a candidate signal and identified approximately 850 000 candidates. Most (99%) of these candidate signals were automatically classified as human-generated radio-frequency interference (RFI). A large fraction (>99%) of the remaining candidate signals were also flagged as anthropogenic RFI because they have frequencies that overlap those used by global navigation satellite systems, satellite downlinks, or other interferers detected in heavily polluted regions of the spectrum. All 19 remaining candidate signals were scrutinized and none could be attributed to an extraterrestrial source.

https://arxiv.org/abs/1802.01081

Offline Star One

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Re: General SETI Thread
« Reply #162 on: 02/09/2018 06:47 AM »
NASA Should Start Funding SETI Again

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The search for extraterrestrial intelligence should be a part of the agency’s Astrobiology mission—but thanks to a 1993 law, it’s not

https://blogs.scientificamerican.com/observations/nasa-should-start-funding-seti-again/

Offline Star One

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Re: General SETI Thread
« Reply #163 on: 02/18/2018 08:41 PM »
Is Humanity Ready for the Discovery of Alien Life?

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Most Americans would probably be thrilled to learn extraterrestrials (intelligent or not) exist. Other nationalities beg to differ

https://www.scientificamerican.com/article/is-humanity-ready-for-the-discovery-of-alien-life/

Offline RotoSequence

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Re: General SETI Thread
« Reply #164 on: 02/23/2018 07:41 AM »
https://arxiv.org/abs/1802.07723

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Possible Photometric Signatures of Moderately Advanced Civilizations: The Clarke Exobelt

Hector Socas-Navarro

(Submitted on 21 Feb 2018)

This paper puts forward a possible new indicator for the presence of moderately advanced civilizations on transiting exoplanets. The idea is to examine the region of space around a planet where potential geostationary or geosynchronous satellites would orbit (herafter, the Clarke exobelt). Civilizations with a high density of devices and/or space junk in that region, but otherwise similar to ours in terms of space technology (our working definition of "moderately advanced"), may leave a noticeable imprint on the light curve of the parent star. The main contribution to such signature comes from the exobelt edge, where its opacity is maximum due to geometrical projection. Numerical simulations have been conducted for a variety of possible scenarios. In some cases, a Clarke exobelt with a fractional face-on opacity of ~1E-4 would be easily observable with existing instrumentation. Simulations of Clarke exobelts and natural rings are used to quantify how they can be distinguished by their light curve.

Offline Star One

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Re: General SETI Thread
« Reply #165 on: 03/15/2018 06:46 AM »

Offline Star One

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Re: General SETI Thread
« Reply #166 on: 04/04/2018 08:11 PM »
A Cloaking Device for Transiting Planets

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The transit method is presently the most successful planet discovery and characterization tool at our disposal. Other advanced civilizations would surely be aware of this technique and appreciate that their home planet's existence and habitability is essentially broadcast to all stars lying along their ecliptic plane. We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission. Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits. We estimate that humanity could cloak the Earth from Kepler-like broadband surveys using an optical monochromatic laser array emitting a peak power of about 30 MW for roughly 10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of approximately 250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just around 160 kW per transit. Finally, we suggest that the time of transit for optical SETI is analogous to the water-hole in radio SETI, providing a clear window in which observers may expect to communicate. Accordingly, we propose that a civilization may deliberately broadcast their technological capabilities by distorting their transit to an artificial shape, which serves as both a SETI beacon and a medium for data transmission. Such signatures could be readily searched in the archival data of transit surveys.

https://arxiv.org/abs/1603.08928

Offline Star One

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Re: General SETI Thread
« Reply #167 on: 04/10/2018 08:38 PM »

Interstellar communication. X. The colors of optical SETI

Michael Hippke
(Submitted on 4 Apr 2018)
It has recently been argued from a laser engineering point of view that there are only a few magic colors for optical SETI. These are primarily the Nd:YAG line at 1064 nm and its second harmonic 532.1 nm. Next best choices would be the sum frequency and/or second harmonic generation of Nd:YAG and Nd:YLF laser lines, 393.8 nm (near Fraunhofer CaK), 656.5 nm (Hα) and 589.1 nm (NaD2). In this paper, we examine the interstellar extinction, atmospheric transparency and scintillation, as well as noise conditions for these laser lines. For strong signals, we find that optical wavelengths are optimal for distances d≲kpc. Nd:YAG at λ=1,064nm is a similarly good choice, within a factor of two, under most conditions and out to d≲3kpc. For weaker transmitters, where the signal-to-noise ratio with respect to the blended host star is relevant, the optimal wavelength depends on the background source, such as the stellar type. Fraunhofer spectral lines, while providing lower stellar background noise, are irrelevant in most use cases, as they are overpowered by other factors. Laser-pushed spaceflight concepts, such as "Breakthrough Starshot", would produce brighter and tighter beams than ever assumed for OSETI. Such beamers would appear as naked eye stars out to kpc distances. If laser physics has already matured and converged on the most efficient technology, the laser line of choice for a given scenario (e.g., Nd:YAG for strong signals) can be observed with a narrow filter to dramatically reduce background noise, allowing for large field-of-view observations in fast surveys.

https://arxiv.org/abs/1804.01249

Offline philw1776

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Re: General SETI Thread
« Reply #168 on: 04/10/2018 08:58 PM »

Interstellar communication. X. The colors of optical SETI

Michael Hippke
(Submitted on 4 Apr 2018)
It has recently been argued from a laser engineering point of view that there are only a few magic colors for optical SETI. These are primarily the Nd:YAG line at 1064 nm and its second harmonic 532.1 nm. Next best choices would be the sum frequency and/or second harmonic generation of Nd:YAG and Nd:YLF laser lines, 393.8 nm (near Fraunhofer CaK), 656.5 nm (Hα) and 589.1 nm (NaD2). In this paper, we examine the interstellar extinction, atmospheric transparency and scintillation, as well as noise conditions for these laser lines. For strong signals, we find that optical wavelengths are optimal for distances d≲kpc. Nd:YAG at λ=1,064nm is a similarly good choice, within a factor of two, under most conditions and out to d≲3kpc. For weaker transmitters, where the signal-to-noise ratio with respect to the blended host star is relevant, the optimal wavelength depends on the background source, such as the stellar type. Fraunhofer spectral lines, while providing lower stellar background noise, are irrelevant in most use cases, as they are overpowered by other factors. Laser-pushed spaceflight concepts, such as "Breakthrough Starshot", would produce brighter and tighter beams than ever assumed for OSETI. Such beamers would appear as naked eye stars out to kpc distances. If laser physics has already matured and converged on the most efficient technology, the laser line of choice for a given scenario (e.g., Nd:YAG for strong signals) can be observed with a narrow filter to dramatically reduce background noise, allowing for large field-of-view observations in fast surveys.

https://arxiv.org/abs/1804.01249

Impressive.  Any back of the envelope calcs on the beam width at varied distances 1pc to 1kpc?

“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Star One

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Re: General SETI Thread
« Reply #169 on: 04/10/2018 10:05 PM »

Interstellar communication. X. The colors of optical SETI

Michael Hippke
(Submitted on 4 Apr 2018)
It has recently been argued from a laser engineering point of view that there are only a few magic colors for optical SETI. These are primarily the Nd:YAG line at 1064 nm and its second harmonic 532.1 nm. Next best choices would be the sum frequency and/or second harmonic generation of Nd:YAG and Nd:YLF laser lines, 393.8 nm (near Fraunhofer CaK), 656.5 nm (Hα) and 589.1 nm (NaD2). In this paper, we examine the interstellar extinction, atmospheric transparency and scintillation, as well as noise conditions for these laser lines. For strong signals, we find that optical wavelengths are optimal for distances d≲kpc. Nd:YAG at λ=1,064nm is a similarly good choice, within a factor of two, under most conditions and out to d≲3kpc. For weaker transmitters, where the signal-to-noise ratio with respect to the blended host star is relevant, the optimal wavelength depends on the background source, such as the stellar type. Fraunhofer spectral lines, while providing lower stellar background noise, are irrelevant in most use cases, as they are overpowered by other factors. Laser-pushed spaceflight concepts, such as "Breakthrough Starshot", would produce brighter and tighter beams than ever assumed for OSETI. Such beamers would appear as naked eye stars out to kpc distances. If laser physics has already matured and converged on the most efficient technology, the laser line of choice for a given scenario (e.g., Nd:YAG for strong signals) can be observed with a narrow filter to dramatically reduce background noise, allowing for large field-of-view observations in fast surveys.

https://arxiv.org/abs/1804.01249

Impressive.  Any back of the envelope calcs on the beam width at varied distances 1pc to 1kpc?

Actually it was who the author was caught my attention.

Offline LouScheffer

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Re: General SETI Thread
« Reply #170 on: 04/12/2018 05:41 PM »

Interstellar communication. X. The colors of optical SETI

Michael Hippke
(Submitted on 4 Apr 2018)
It has recently been argued from a laser engineering point of view that there are only a few magic colors for optical SETI. These are primarily the Nd:YAG line at 1064 nm and its second harmonic 532.1 nm. Next best choices would be the sum frequency and/or second harmonic generation of Nd:YAG and Nd:YLF laser lines, 393.8 nm (near Fraunhofer CaK), 656.5 nm (Hα) and 589.1 nm (NaD2). In this paper, we examine the interstellar extinction, atmospheric transparency and scintillation, as well as noise conditions for these laser lines. For strong signals, we find that optical wavelengths are optimal for distances d≲kpc. Nd:YAG at λ=1,064nm is a similarly good choice, within a factor of two, under most conditions and out to d≲3kpc. For weaker transmitters, where the signal-to-noise ratio with respect to the blended host star is relevant, the optimal wavelength depends on the background source, such as the stellar type. Fraunhofer spectral lines, while providing lower stellar background noise, are irrelevant in most use cases, as they are overpowered by other factors. Laser-pushed spaceflight concepts, such as "Breakthrough Starshot", would produce brighter and tighter beams than ever assumed for OSETI. Such beamers would appear as naked eye stars out to kpc distances. If laser physics has already matured and converged on the most efficient technology, the laser line of choice for a given scenario (e.g., Nd:YAG for strong signals) can be observed with a narrow filter to dramatically reduce background noise, allowing for large field-of-view observations in fast surveys.

https://arxiv.org/abs/1804.01249
This is based on Which colors would extraterrestrial civilizations use to transmit signals?: The “magic wavelengths” for optical SETI which in my opinion is a very weak argument.  Just because Nd:YAG lasers are the best for us now does not mean they are the best for everyone, for all time.  Other civilizations may well have discovered different combinations of compunds that are similarly efficient.  Furthermore, there are lots of possible technology developments in metamaterials, quantum waveguides, and so on, that could lead to arbitrary wavelengths.   Also, for long term use, it might be better to pick a technology that can be pumped directly by radiation from the sun, where the easy availability of free power might be cheaper for a given power output, even if the efficiency is lower.

Overall, I think it's way premature to limit our searches to only the laser lines we would pick now.

Offline Star One

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Re: General SETI Thread
« Reply #171 on: 04/12/2018 07:56 PM »
Spot the Doctor Who reference.

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?

Quote
If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.

http://xxx.lanl.gov/abs/1804.03748

Offline LouScheffer

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Re: General SETI Thread
« Reply #172 on: 04/13/2018 01:31 AM »
Spot the Doctor Who reference.

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?

Quote
If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.

http://xxx.lanl.gov/abs/1804.03748

Some things we do to geology, like cement filled holes of old oil wells, a meter wide and several km long, perpendicular to the rock layers, should survive for geological times and be unambiguously constructed and not natural.  Finding even one would show a previous civilization.

Offline Star One

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General SETI Thread
« Reply #173 on: 04/13/2018 06:38 AM »
Spot the Doctor Who reference.

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?

Quote
If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.

http://xxx.lanl.gov/abs/1804.03748

Some things we do to geology, like cement filled holes of old oil wells, a meter wide and several km long, perpendicular to the rock layers, should survive for geological times and be unambiguously constructed and not natural.  Finding even one would show a previous civilization.

No guarantee any previous civilisation would extract oil and nor that such activities would last over geological times especially if only in a limited area(s).
« Last Edit: 04/13/2018 06:39 AM by Star One »

Offline missinglink

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Re: General SETI Thread
« Reply #174 on: 04/13/2018 08:06 PM »
I've been told that the zillions of tons of coal burned since the start of the industrial revolution have deposited a thin layer of soot* in the geological record that is distinguishable from the outcome of natural processes.

Hard to imagine a technological civilization that would skip over using coal as fuel altogether.

*Think of it as a "shadow out of time", heh heh.

Offline Star One

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General SETI Thread
« Reply #175 on: 04/13/2018 08:08 PM »
The Breakthrough Listen Search for Intelligent Life: Wide-bandwidth Digital Instrumentation for the CSIRO Parkes 64-m Telescope

Breakthrough Listen is a ten-year initiative to search for signatures of technologies created by extraterrestrial civilizations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two recording modes: a dual-polarization, 1.125~GHz bandwidth mode for single beam observations, and a 26-input, 308~MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3~GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.

https://arxiv.org/abs/1804.04571
« Last Edit: 04/13/2018 08:09 PM by Star One »

Offline Star One

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Re: General SETI Thread
« Reply #176 on: 04/13/2018 08:31 PM »
https://twitter.com/jeff_foust/status/984857830615330816?s=20

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Those at #Discuss2018 may find of interest this language from Sec. 311 of the authorization bill supporting partnerships “to search for technosignatures, such as radio transmissions” from any life in the universe.

Offline tea monster

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Re: General SETI Thread
« Reply #177 on: 04/15/2018 11:35 AM »
Coal and Oil didn't exist back then. We are driving around using oil that is between 60 and 100 million years old*. The Silurian period  was over 400M years old.

If they used wood, then it would just be attributed to forest fires at the time. Maybe look for deposits of depleted uranium at that point in the fossil record.  ;D

* - https://phys.org/news/2005-05-world-age-oil.html
« Last Edit: 04/15/2018 11:52 AM by tea monster »

Offline TakeOff

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Re: General SETI Thread
« Reply #178 on: 04/15/2018 02:34 PM »
It looks like there's a weird pattern to the size of sub-Jupiters, they tend to congregate around certain values. Most common are around 2-3 Earth-radii, about 20% of stars. A sharp drop off above 3 Earth-radii (Neptune/Uranus are around 4.) But also a weird drop around 1.8. Then an increase to the next most common value, 1.3 or so Earth-radii, about 10-15% of stars. Then another dip around 1.2 E(r). Then 1 Earth-radius, about 6% of stars. So Earths aren't the most likely, but they are common as muck. One of the three most common sizes of planets. Pretty mundane, you might say.


Erik Petigura has a potential explanation. Basically the stellar wind removes a hydrogen envelope more quickly the more depleted it gets. So there are planets with big envelopes and planets without any envelope, but only briefly do planets have a small envelope. Thus the gap.
https://webcast.stsci.edu/webcast/detail.xhtml?talkid=6131&parent=1


Offline Star One

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Re: General SETI Thread
« Reply #179 on: 04/18/2018 06:10 PM »
Spot the Doctor Who reference.

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?

Quote
If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.

http://xxx.lanl.gov/abs/1804.03748

More from the author of the paper’s authors.

https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/

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