Thread by @aussiastronomer

Let’s do it.

Goals of workshop:
1) What is the current state of the field - what do we already know?
2) What are the funded near-future plans? What might we know soon?
3) What are the potential future advances that could be important?
4) How can NASA help?

Intro by @Astro_Wright - what are technosignatures?

(Autocorrect has no idea what to do with the word ‘technosignatures’ if you get even a single letter wrong.)

Technosignatures (TS for the remainder of this thread) are ‘any sign of technology that we can use to infer the existence of intelligent life elsewhere in the universe.’

(i.e. what Buzz Lightyear was looking for)

How do we prioritise the best kinds of TS to go searching for? Here's the workshop evaluation (portion of Figure 1). The best TS to search for are: Information-rich, detectable, unambiguous, long-lived signals for which the search is achievable, cheap and has ancillary benefits.

It also helps if they're more probable - having a believable degree of extrapolation from Earth technology - or even inevitable, like waste heat.

(Earth's gotta lotta waste heat going on at this particular moment.)

TS as a field has had limited resources available to it - sounds like this workshop and document were timely in their ability to bring together the small number of folks scattered across the field!

(Okay this thread is gonna take a brief hiatus while I go pick up a vomiting child from daycare. #ParentsinSTEM #WomeninSTEM).

I realised on the drive home that I should specify that TS are distinct from biosignatures, which are any sign of biological activity (intelligent or not). I guess TS could be thought of as a specific subset of biosignatures? (Unless the intelligent life was NON-BIOLOGICAL!?!)

Okay, so what has been ruled out so far? A couple of attempts (by @Astro_Wright and @jilltarter) estimate that radio surveys have currently searched only 10^(-22) to 10^-18) of the total volume.

That's one quintillionth to 100 septillionths of the total volume.

THAT'S NO MUCH.

Designing an efficient radio survey for TS requires trading off sensitivity and sky coverage. You can look at a lot of sky in a limited way, or a little patch of sky in a focused way. Kind of like the difference between @NASAKepler and @NASA_TESS!

Oh, interesting! There are a couple of ways to search for artificial radio signals - either signals that are so narrow bandwidth there's no natural explanation, or broad(er) band signals that pulsate in time in an unnatural way.

The same two types of 'unnaturalness' (signals that are narrow in wavelength range or have narrow pulses in time) can also apply to optical (visible) and near-infrared (night vision) wavelengths.

Lasers are basically light at a single wavelength - the narrowest wavelength range of all! So, along that train of thought, @awhoward went hunting for aliens pointing laser beams at us as part of his PhD thesis.

I'm having a little trouble interpreting the plot (@awhoward can correct me if I'm wrong), but it looks like in a survey of 13,000 stars, he was able to put pretty strong upper limits on signals that repeated on order of minutes (fewer than 1 in 10,000 stars).

Ooooh the VERITAS collaboration has studied @tsboyajian's WTF star for optical pulses - the story so far?

Okay so besides radio and optical signals, what else have we looked for? Let's get back to waste heat. You do it, your refrigerator does it, the whole planet does it. In fact everything will do it until the heat death of the universe.

If a civilization intercepts almost all the light from its host stellar system, it's called a Dyson sphere. A step down from that is very large structures orbiting the host stellar system, called 'megastructures'. (Made famous by headlines everywhere in 2015!)

If we observe civilizations with Dyson spheres they give off excess heat where we don't expect it in the star's spectrum - in the infrared. So, they should stand out in infrared surveys, and that's where we've been looking for them.

(More vomiting. BBIAB.)

The report talks about the IRAS survey of 545 sun-like stars, and LRS survey of 11,000 stars, neither of which found any good candidates. IIRC people were going to try this again with Gaia, I wonder if any results have come out yet?

Ah yes, here's a paper describing how it can be done: arxiv.org/abs/1804.08351

But I don't see any results yet.

Ooooh now this is cool. People have done surveys of GALAXIES to see if any have evidence of Dyson spheres - the largest survey looked at 100,000 galaxies with @WISE_Mission and 2MASS and found none whose emission couldn't be explained astrophysically.

Okay now the report turns to the solar system, and we come upon 'Oumuamua for the first time (probably not the last 🤣). 'Oumuamua is the interstellar object that briefly visited our solar system in late 2017 before speeding off again.

Huh, even though we've actually BEEN to some of the other bodies in the solar system, there is as yet no quantitative upper limit on evidence for kilometer-scale technology. That's kind of surprising.

The Earth-Moon Lagrange points (hyperphysics.phy-astr.gsu.edu/hbase/Mechanic…) have been searched for objects and nothing bigger than 1-10m and reflecting > 10% of the light could be there or we would have found it.

End of Section 2 and AFAICT, the story on quantitative upper limits - there aren't many. There have been a number of cool ideas and even extensive surveys, but (as I know from Kepler) - turning a survey into an upper limit can be almost as large a task as the original survey!

Onto Section 3. Which is... surprisingly short?

Oh no! Tragedy strikes! Apparently when I printed it out only printed to page 23.

Will rectify ASAP.

(MORE vomiting. This kid is unwell. 😭).

Section 3: Existing technology! Many of the world's current radio telescopes have at some point undertaken SETI research, either with directed surveys or piggy-backing on astrophysical observations.

(Aside: I've watched the movie The Dish while staying at The Dish. #humblebrag)

Oh wow!! There are still 120,000 people running @BerkeleySETI's SETI@home project! I had no idea. That's awesome. People search through radio data for artificial signals, and help clean the data of pesky Earth-originating radio signals.

(I love @1027KIISFM, but not in my data.)

"Continuous wave lasers can be detected with conventional high-resolution spectrographs, and so can be performed in principle on any new *or archival* spectral data (especially those of nearby stars thought to be candidates for life-bearing planets)."

Emphasis mine. 👀👀👀

There are a couple of ongoing exoplanet surveys I'm familiar with (Automated Planet Finder and Keck-HIRES) and I had NO IDEA those data were being simultaneously searched for narrowband laser transmissions. THAT'S SO COOL.

Oh, here's a fun idea. So far everything I've described has been along the lines of "we could conceive of a technological way we could make this signal, so let's see if anyone else did it too". But what about the true exotica??

Some folks (@david_kipping and @shaka_lulu among them) have thought about how you could search through large survey data (like @NASAKepler) in an agnostic way to let the true weirdos stick out on their own.

Section 3 concludes by noting that due to the lack of systemic funding, current TS searches are sidelined to being 'hobby' projects by those astronomers who are interested in working on them when they have time.

Oh man, Section 4 opens by throwing the fact that we haven't even started considering signals caused by neutrinos, other unique particles, or gravitational waves yet. YOU CAN'T JUST CASUALLY BRING THAT UP IN SECTION 4.

'Oumuamua is back!

Okay, so Section 4 outlines the list of available resources (both in the US and internationally; it's extensive) that could be bent to the TS search, and mentions how one could use those resources to pre-vet and compile a target list for future searches.

Oooh interesting note from the authors that development of better radio technology is one of the areas where astronomy can push industry to do better, so it behooves industry to get involved in TS surveys.

Onto Section 5: Emerging and Future Opportunities. I'm excited by this part.

LET THE RAMPANT SPECULATION BEGIN!

Oh yeah, here's the good stuff.

"What are the likely characteristics of very long-lived planetary societies, and of planets that have been modified by long-term co-evolution of technology with planetary physical and biogeochemical cycles?"

"1) What tracers can and cannot be avoided in the process of civilization
building?
2) Which of these tracers can be detected?"

Communication: is it inevitable? Is using the electromagnetic spectrum inevitable? Is leakage of it inevitable? What about artificial intelligence inevitable?

Atmospheric modification: what detectable molecules in our atmosphere are a result of intelligent life? One well-studied family of molecules is chloroflurocarbons (CFCs) - the nasty things that used to be in our refrigerators that harmed the ozone layer.

Structures: what kinds of structures could civilisations build and how are they detectable? Periodically blocking the light from the star as they orbit between us and the star is a commonly proposed detection method. Just like exoplanets! Except (hopefully) funny-shaped.

Heat Islands: Oooh this is new to me. If civilisations are confined to planets (like us, basically), they likely generate heat islands - where technology and waste heat cluster (like our cities on Earth). These could be observable as hot spots on distant planets.

Artificial Illumination: Analogously to the hot spots, we can already see the cities of Earth at night - by their light! Could we detect intelligent civilsations the same way? It's a tough ask, technologically, but we here we are in the future speculation chapter.

Also in this category - the work by @david_kipping and @alexteachey modelling how a civilisation could increase (or decrease!) their light output to signal (or hide!) their presence to other civilisations.

arxiv.org/abs/1603.08928

What follows is a much too brief discussion of free energy dissipation gradients which leaves me with nothing but questions. Sounds like they don't know how they would observe it yet though.

Next up - civilisations could either act to damp natural long-lived planetary evolution cycles (e.g. glaciation)... or exacerbate them. Hard to know a priori.

Terraforming! If we see evidence of multiple planets in the same system with suspiciously similar atmospheres/biospheres, it could be evidence of terraforming. That's cool.

In order to define the best observing strategies, it would be good to know two timescales: (1) how long it takes for an intelligent species to emerge, and (2) how long that species lasts (the infamous "L" in the Drake equation).

(Not that Drake.)

What else would it be good to know? The limits of communication, for one thing - linguistics and non-human communication, cryptography, information theory. What archaeology can tell us about the emergence and sustainability of complexity for another.

Also, the development of intelligence - how did it originate and evolve on Earth? Advances in biology and neuroscience (e.g. neuroimaging) are starting to make the idea that we might understand the answers to these questions more feasible.

So, what does the future of detection look like, now that we've explored some ways that TS could be found?

1. Continuing to search through existing and ongoing survey data for signals (transits of megastructures, laser signals in stellar spectra).

2. Building some sweet new instruments. The above set of possible TS to search for naturally produces a list of instrument requirements that looks serendipitously like HabEx or LUVOIR...

There are also some ground-based telescopes in the works (the @TMTHawaii, the @GMTelescope, and the E-ELT) which will have instruments that can start poking at some of these questions in the next decade (...or two).

(Brief aside for "Astronomers Are Bad At Naming Things, Chapter 37". Did you know we have several Large Telescopes, a Very Large Telescope, are building an Extremely Large Telescope, and were once planning an Overwhelmingly Large Telescope?)

The report discusses measuring the light from a distant planet as it rotates (e.g. like the Earth rotates every day) to reverse-engineer a map of the oceans and continents without referencing the work of Ty Robinson or Nick Cowan which seems like a big oversight.

They wrap up the discussion of potential future detections in the optical part of the spectrum by talking about polarisation. This is a subtle concept but basically natural phenomena reflect light a certain way, and artificial phenomena reflect light a different way.

Polarisation has been talked about for a long time, but has only recently started to get some traction by way of instrumentation and results. In the future, it may be used to differentiate natural and artificial phenomena on the surfaces of planets, or orbiting around them.

In terms of new radio instrumentation and algorithms coming online, the report points out the synergy with the search for Fast Radio Bursts, an emerging field of astrophysics (oh and hey, here's where I can loop in @SciBry!), and that the fields can mutually benefit each other.

Okay, now we're stepping out of the electromagnetic spectrum.

OH BOY GRAVITATIONAL WAVES IN THE HOUSE. HOLD ONTO YOUR BUTTS.

Advantages of communicating with GW:
1) Signal strength drops off with increasing distance, instead of increasing distance squared (i.e. it travels further).
2) Nothing scatters or blocks these things. Dust cloud? Ha!
3) The sky is 'dark' in terms of GW, so signals stand out.

(Another aside to say that the twitter GIF library search results for "LIGO" are 50% astrophysics, and 50% people in the shower. What? How? What am I missing??)

The disadvantage of GW is the incredible energy required to create them. Like, we're discovering them based on black holes and neutron stars, some of the densest objects in the universe, slamming into each other at nearly the speed of light. That's... intense.

But, the report points out that as instrumentation comes online to explore multi-messenger astronomy (combining the electromagnetic spectrum, GW, neutrinos, cosmic rays), searches for TS can happen simultaneously with the astrophysics.

The next subsection is basically "Here's all the cool shit coming online in the next few decades which might be relevant for TS but is, did we mention, seriously cool regardless".

It's short so I'll just add the list here for your "THAT'S SO COOL" reading pleasure.

Aaaaand we're at the final section of the report, which can be summed up as:

The authors go through the potential private, industry, philanthropic and government partnerships that could support future TS surveys. The XPrize comes up as a successful model. There is some very thorough identification of potential cross-disciplinary partnerships.

Then we have 10 pages of references and three (!) pages of acronyms and we're done with the NASA Technosignatures Workshop report!

Thanks for sticking with it if you got this far, it's a comprehensive document and I was glad of the excuse to read it properly and break it down.

Congratulations to the authors on their hard work! @Astro_Wright, @ikashell, @nbatalha, @dan_anger, @shasta721, @jessiedotson, @dh4gan, @DrFunkySpoon, @awhoward, @david_kipping, @ravi_kopparapu, @mshabram, @steinly0, @jilltarter, @worden and many more.

arxiv.org/abs/1812.08681