Back in June 2016 I advertised a postdoctoral position between me and Steve Desch at ASU for someone to work on the problem of exoplanet interior compositions.

Normally, the way we determine the interior composition of exoplanets is a combination of inference, measurement, and guesswork.  In the Solar System we can study the surface compositions of planets directly, get the bulk density by dividing masses by radii cubed, and a sense of internal structure by looking at how the surfaces have changed or what a body’s gravitational field says about the interior mass distribution. It’s amazing how much we can determine about, say, the interior of Europa!

Evidence from NASA’s Galileo mission suggested that there might be a liquid water ocean underneath Europa’s icy crust. Image credit: NASA/JPL

On Earth we can also use seismology to directly probe the density and composition of the Earth’s interior.  Some things we still don’t know to great precision (the water content of Earth’s mantle is still pretty uncertain, though it’s small) but in general we have a good sense of what’s down there, despite having a very limited set of actual samples from far below the surface (from volcanos, mostly).

Based on this we have a good sense of how the planets formed, and so we can make good inferences and guesses about the parts we don’t know about yet. For instance, we suspect that Jupiter formed around a rocky core of about ten times the mass of the Earth; one of the purposes of Juno is to see if we can better determine Jupiter’s inner composition and perhaps check this model prediction.

This artist’s concept shows the pole-to-pole orbits of the NASA’s Juno spacecraft at Jupiter. Image credit: NASA/JPL-Caltech/SwRI

Exoplanets are much harder.  We generally can measure their masses from radial velocities and radii if they transit, and for planets for which we have both we have bulk densities. By analogy with Solar System planets we can then guess that they have similar compositions to those, and from the compositions of their host stars we can make inferences about how they might differ. But getting anything like a mantle or surface sample seems impossible.

Except…

There is a whole class of planet recently discovered by Kepler (Saul Rappaport and Roberto Sanchis Ojeda did a lot of the pioneering work here) that appears to be evaporating. The transit signatures of these things is amazing; they vary in depth (sometimes disappearing entirely!) and don’t have the usual shape of transiting planets. Apparently, these are small rocky bodies  (which have orbital periods of less than a day and which are too small to see transit at all) have gigantic, variable tails of rock that is condensing from a plume of surface material evaporated by the intense heat of their parent star.

Exoplanet KIC 1255b orbits its parent star followed by a comet-like dust tail. Image credit: Maciej Szyszko.

We sometimes read in the history of astronomy that it was Bessel that finally proved the Earth moves around the sun with the measurement of the parallax of 61 Cygni, one of the brightest and closest stars to Earth in the Northern Hemisphere.

This is because people early on realized that if the stars are different brightnesses because they are at different distances, and if the Earth really does move around the Sun, then we should see the nearby ones appear to move with respect to the background ones annually as our light of sight towards them changes.  The effect is quite small, and it was challenging for 18th and 19th century astronomers to measure the tiny effect using only their eyes to make measurements (the biggest parallaxes are like a part in a million).

And so astronomers put a lot of effort into this, and indeed eventually Bessel pulled it off. But the clinching observational proof actually came about 100 years earlier, based on those same observations!

Astronomers were expecting to see a “reflex” motion: when the Earth moved in one direction the nearby stars would appear to slightly move in the opposite direction, so when the Earth was at one extreme of its orbit they would appear to be a bit closer to the center of Earth’s orbit (i.e. the Sun) than they should be.  Instead, astronomers kept measuring a much larger than expected motion (around 20 arcseconds instead of less than 1 arcsecond) in the wrong direction: the stars seemed to move towards a point about 90 degrees away from the Sun, towards the ecliptic.

This is what was actually happening, but it was actually pretty confusing at the time.  One way they were measuring positions was by using the zenith as an absolute direction (you can use a plumb or a liquid to determine which direction is straight up) and a telescope to see how close stars got to the zenith as they passed overhead.  So they could only measure one component of the star’s motion, so all they knew is that it was large and had the wrong phase (90 degrees from what was expected).

What was actually going on is that the stars were suffering from aberration. Imagine you have a trash can an you want to collect as much rain as possible.  If there is no wind, you should just keep the can vertical.  But, if you are on the bed of a pickup truck moving at 10 mph, then some of the rain that would have fallen into the can will hit the side instead.  To maximize rain collection, you have to tip the bucket towards the front of the truck (i.e. in the direction of the truck’s motion) to get the rain to go straight down into the can.

Wikicommons illustration of the aberration of starlight. Original here. By Brews ohare, CC BY-SA 3.0.

Similarly with telescopes: to get starlight to go straight down the optical axis of the telescope, you actually have to “lead” the motion of the Earth slightly by pointing in the direction of Earth’s motion.  This effect is equal in radians to the speed of the Earth’s orbit divided by the speed of light, or about 20″.  This is what was being observed, and this is what Bradley finally figured out in 1727.

You can learn more about this history here. Interestingly, Bradley’s original paper describing the aberration and proving the Earth moves has only one citation in ADS!

So while hunting for the proof of Earth’s motion, astronomers actually discovered a much easier to find proof of Earth’s motion!  But it took decades to understand it.

Today, it’s tricky to repeat these measurements with modern equipment. Finding the zenith to a precision of 1″ is not something most observatories are set up to do; we almost never use high precision, absolute positions with respect the ground in astronomy any more (our instruments tend to change their pointing with temperature, humidity, and other factors, so we calibrate them on actual star positions every now and again to keep our pointing models accurate and precise).

But interestingly, there is a way most college observatories and many amateur ones can find an absolute position: star trails!  By turning off tracking and letting the stars trail, one can identify the center of the trails as the true Celestial Pole.  As the Earth goes around the Sun, one can measure star positions with respect to that and detect the aberration, thus proving the Earth orbits the Sun.

Of course, there are lots of other ways to do this: you could build an R~10,000 spectrograph and feed it light from stars on the ecliptic and measure the Doppler shift caused by Earth’s motion, or you could measure the parallax directly with differential astrometry, like Bessel did. But this is a novel solution that actually doesn’t require special equipment of good seeing, just an ordinary camera.

I was going to try this someday, and even wrote up a whole blog post about it, but finally decided that if I haven’t started by now I probably never will, so I’ve “given the idea away” in the form of a Research Note to the AAS (my sixth!).  One reason I never started is that although the equipment needed isn’t special, there are lots of complications.  One is that the Poles move on their own (due to Earth’s axial precession) so you have to remove that effect first.

As part of my plan to learn Python and Astropy I tried to make a figure showing how the apparent position of the true Celestial North Pole moves with respect to the background stars, showing the precession and the aberration.  It was surprisingly tricky!  Plotting things near coordinate singularities is not something most plotting software does well, so in the end I cheated and just plotted things as a plane chart in ecliptic coordinates and drew the Celestial coordinates in by hand.  I think it came out really well:

Figuring out how to calculate the motion of the Celestial Pole (also affected by nutation) was tricky; it turns out Astropy does not expose those functions to the user so I had to cheat.  In the end, I did it two ways that gave the same answer: I asked for the ICRS (astronomical) coordinates of the zenith at the North Pole of Earth.  Astropy converts from geocentric coordinates to barycentric coordinates by correcting for the orientation of the Earth (the axial motion) and the aberration, so this yields the green curve above.  Almost equivalently, one can ask for the Celestial Pole in CIRS coordinates (the intermediate coordinate system between the Earth and Celestrial Sphere) at many times and then ask Astropy to convert these positions to the ICRS frame.   The latter is faster.

To learn more, you can read my research note describing the experiment here.  And if you try this, please let me know!

Where does the old idiom “finding a needle in a haystack” come from?

According to my physical copy of Bartlett’s Familiar Quotations, the phrase originates with Cervantes in Book III Chapter X of Don Quixote, and indeed most searches online state so with authority.

But I just checked my physical copy and the Project Gutenberg version and not only is there no  Book III, the phrase does not appear!

Some sleuthing of other phrases that do appear reveals that “Book III” refers to what is normally called “Part II”, and indeed there in Chapter X of my copy it reads:

…tracking Dulcinea up and down El Toboso will be as bad as looking for a needle in a haystack or for a scholar in Salmanca.

just as promised.  So why isn’t it in the Project Gutenberg version? There it reads:

looking for Dulcinea will be looking for Marica in Ravena, or the bachelor in Salamanca.

which is not the same thing at all. Indeed, the Spanish original seems to read:

buscar a Dulcinea por el Toboso como a Marica por Rávena, o al bachiller en Salamanca.

So the phrase is actually not in the original!  It seems to be due to Cervantes’ English translators who used the phrase as a more familiar [to English ears] version of “to find Maria in Ravena”.  Bez Thomas helped me to figure this out on the Twitters:

The (originally Italian) idiom paraphrased as “needle in a bottle of hay” is “a Marica por Rávena”, i.e. looking for a particular woman named Maria in Ravenna, where Maria is a very common name. https://t.co/9zvw3kII6S

— Bez Thomas (@BezPublic) June 7, 2018

So where does the phrase “needle in a haystack” originate?  The OED has two attestations that predate Cervantes:

c1530   T. More Let. Impugnynge J. Fryth in Wks. (1557) 837/2   “To seke out one lyne in all hys bookes wer to go looke a nedle in a medow.”

1592   R. Greene Quip for Vpstart Courtier sig. E^v   “He…gropeth in the dark to find a needle in a bottle of hay.”

Where a “bottle” here means “bundle”.  Apparently the translators were using a 100+ year old phrase!   The “haystack” version is from later:

1779   W. Rogers in J. Sullivan Jrnls. Mil. Exped. (1887) 262   “But agreeably to the old adage it was similar to looking for needles in a hay stack.”

And there you have it.  Even an authority as solid as Bartlett’s occasionally gets things wrong, so it’s good to check!

[Update: Apparently Bartlett’s is full of these errors with respect to Don Quixote: see this article here which details the “haystack” mistake and many more.]

We can tell what stars are made of by the colors missing from their spectra, but that’s not really true for hot, rapidly rotating stars. These stars lack convective envelopes, so they lack magnetic dynamos, so they do not spin down as they age. As a result of their rapid rotation, the Doppler shift blurs out their lines and its hard to get a precise measurement of their abundances (except hydrogen, whose lines are so deep you can’t miss them, even blurred out).

But one astronomer’s trash is another’s treasure. These rapidly rotating stars make great sources of light for calibrating spectrographs because you can be sure that any spectral features you *do* see are due to your instrument, not the star. And these stars can be very bright, so it’s a quick test.

The problem is that not all hot stars rotate quickly enough to be “good” calibrators. For instance, here’s what a small portion of a rapid rotator looks like:
This star’s spectrum is flat (or slightly sloped) in this small region of the blue.  The overall mountain shape is the response of the spectrograph, which this star lets you model.  The “fuzz” is photon noise—by chance some channels get more photons than others.  The spike in the middle is a “cosmic ray” event—a high energy particle from somewhere in the dome struck the detector and caused a spike.  The only thing here that’s due to the star are some barely perceptible wiggles.

Here’s a “bad” calibrator star, that is not spinning fast enough to be a “good” calibrator:

Not smooth at all!  Those “bites” taken out are due to elements in the star’s atmosphere absorbing certain shades of blue light, and the bowl shape is due to the way different parts of the stellar surface are moving towards and away from us as the star rotates.

So which stars are “good” and which are “bad” for calibrating high resolution spectrographs Published values of their rotation speeds turn out to be an unreliable guide for this, so observers over the years make lists of “good” hot star calibrators.  For instance, when I need a “good” hot star, I ask Howard Isaacson at Berkeley, who has a list carefully compiled by Kelsey Clubb.  At Berkeley, Kelsey Club went through the California Planet Survey’s library of hot star spectra and separated the wheat from the chaff, which is really useful!

This sort of list isn’t usually publishable—it’s not the sort of scientific advance or discovery that usually warrants a peer-reviewed paper.  But it is the sort of thing scientists should share and that Kelsey should get credit for.

Now, thanks to the new AAS journal “Research Notes of the American Astronomical Society”, we have a good way to share the list.  This new journal is not peer reviewed, but it is free, curated, and has a science editor who accepts papers. They can only be 1,000 words, have one figure or table, and they do not have to be new or novel or anything—just interesting.

But why not just put it to the arXiv, and skip the 1,000 word limit thing?  Well, Geoff Bower asked the same thing on the Twitter, and I came up with two big reasons: RNAAS will curate machine-readable tables, which is great, and as a AAS journal, if your result is (unlike this one) newsworthy, it might get picked up by AAS Nova.  Editor Chris Lintott points out a third:

Permanent DoI too, which helps with long term archiving.

— chrislintott (@chrislintott) March 23, 2018

Anyway, as a journal that emphasizes utility and curates tables, it is the perfect place for Kelsey’s list, so that’s where we published it.  You can find it here.

I was actually worried this would happen.  When RNAAS came out, and then when Overleaf linked directly to it for submissions, I got worried I’d like it too much:

This is cool:https://t.co/mUKNqhvSXv

If I ever find some free time, this combination of Overleaf and RNASS might prove to be pretty potent.

— Jason Wright (@Astro_Wright) November 10, 2017

and (despite my misspelling of RNAAS) I was right.  I’ve now submitted or supervised five of these. Here are the others:

Tabby’s Star Explanations

‘Oumuamua Is Almost Certainly Interstellar

EPRVIII Instruments

Barycentric Corrections in Python

I may have a problem…

As we study more and more exoplanets, one variable that we have not really gotten a great handle on is age.  There are not many planets orbiting stars with very well constrained ages. We’d like to be able to see how, for instance, young planetary systems differ from old ones to study planet-planet scattering, planetary migration, and other effects.

So there have been many studies of planets orbiting stars in star clusters.  Clusters are great laboratories for stars because the stars formed (mostly) at the same time out of the same stuff. The repurposed Kepler mission K2 was great for this because it looked for planets along the Ecliptic Plane, and by a bizarre coincidence almost every important benchmark cluster is in the ecliptic!

Jason Curtis, NSF postdoctoral fellow a Columbia University

Jason Curtis is a Penn State grad now an NSF postdoctoral fellow at Columbia working on the problem of stellar ages and activity, using the topic of his PhD thesis, the nearby open star cluster Ruprecht 147. He campaigned to get NASA to repoint K2 to make sure it would capture the stars of Ruprecht 147 so we could study its properties (and, you know, maybe find some planets).

And it worked! He has now written up the paper, and you can find it on the arXiv, in particular the new hot Neptune K2-231b.

But even more useful, to my mind, than the 231st K2 planet is that this planet has a well constrained age.  If we get a lot more, we can look for those trends we’d like to study about how systems change with age.  Jason helpfully compiled a list of all known planets in clusters, and there put them together in one big table. I imagine that with TESS we’ll end up with so many you won’t be able to fit them on one page, but for now here they are, with references.  For the full thing with working links, be sure to read the paper!

Table-1d4tdc0

It’s a home day for me with the flu, so to recover from a long day of videoconferencing meetings, and because a headache won’t let me concentrate on important stuff, I played around with an idea I wrote up as a high school English project.

Milton wrote the epic Paradise Lost, in which he presents his own cosmology of Heaven, Hell, and Earth. This was an ambitious task, since Dante’s Divine Comedy had set a pretty high standard here.

The geometry of Creation in the Divine Comedy (not to scale) with Hell inside the Earth and heaven outside the final sphere in a Ptolemaic universe.

Milton actually met Galileo in person—he visited Galileo’s estate as a boy when the astronomer was there in his later years under house arrest.

The visit may have left an impression. Milton avoids any reference to where the center of the Solar System is in his cosmology—it’s pretty nebulous exactly how everything is arranged—but in Book 4 the angel Uriel needs to get back to his station in the Sun from Earth. He slid down to Earth on a sunbeam, but fortunately for him the Sun has now set, so the tip of his sunbeam is now up in the air. He just jumps on and slides down:

 …and Uriel to his charge
Returnd on that bright beam, whose point now rais’d 
Bore him slope downward to the Sun now fall’n
Beneath th’ Azores

but how did the Sun get so low? It is “beneath th’ Azores” far to the West:

whither the prime Orb,
Incredible how swift, had thither rowl’d
Diurnal, or this less volubil Earth
By shorter flight to th’ East, had left him there

The “prime Orb” is Ptolemy’s name for the Sun, which had (“incredible how swift”) there “rowl’d Dirunal”—rolled down there over the course of the day.  But Milton did not choose his words lightly.  “Incredible” literally means “beyond credibility”.  He doesn’t buy that it really goes so fast.

Is there an alternative?  Milton dithers.  “Or” he writes “this less volubil Earth” (meaning “less apt to roll” according to the OED) went a much shorter distance the other way and the Sun just stayed where “he” was.  That’s Copernicus’s model for the days!

So he clearly prefers Copernicus’s model, and offers it as an alternative, but opens with the more familiar and established terminology and cosmology of Ptolemy (and Dante).

It’s interesting he didn’t commit.  Perhaps he didn’t want to tie his work to a model that might be wrong, or perhaps he didn’t want to alienate his Ptolemist readership.

I wonder, though, if heliocentrism had been widely accepted a century before, if Paradise Lost would have had a well defined geometry of the universe, like the Divine Comedy famously does, but with Heaven and Hell having distinct places in a heliocentric Solar System?

For a long time after sunspots were discovered telescopically by Galileo, there weren’t any to see. John Eddy has a nice paper on the history of sunspot measurements, showing conclusively that there was an 80-year period, now called the “Maunder Minumum”, in which the Sun just didn’t have any sunspots.

Why not? We’d love to know.  The Solar dynamo is a bit of a mystery, and it just apparently turning off for 80 years is kind of important—it may have even had an effect on climate on Earth, although that case is often overstated (it’s not glaringly obvious from the global temperature anomaly record).

Shivani Shah, Penn State undergrad now applying to a graduate program near you!

Finding another star undergoing such a period would be great. We could study its corona and chromosphere it answer questions like: Is it still undergoing its magnetic cycle, just without sunspots? Is it just an extended minimum that lasts many cycle periods? Or did the dynamo turn off entirely? If we had a sample of them we could ask: is this typical behavior of Sun-like stars? All cycling stars? Just stars of the Sun’s age?

For a while, people looked for extremely inactive “sun-like” stars to find “Maunder minimum stars”, but I showed in my thesis that these stars are in fact not Sun-like (they’re subgiants).

People looked in M67, a cluster filled with Sun-like stars, to find extremely inactive stars there, but Jason Curtis showed that these stars were not actually all that inactive (the ISM got in the way).

For a long time Steve Saar has advocated using time series to see a star do what the Sun apparently did: go from a cycling state to a quiet state (or the reverse).  This means using the 50+ year baseline of activity measurements we have of stars to find a cycling star that transitions into or out of a cycling state to a “flat activity state”.  That would make for a pretty convincing candidate, I think.

Well, now we have one! Shivani Shah has written up the strange case of HD 4915, a Sun-like star that seems to have had its cycle peter out to almost nothing.  Here’s the killer plot:

Activity history of HD 4915. Larger “S-Value”s mean (presumably) more starspots. Note that the star came down from a (presumed) maximum, came up to a second, weaker maximum, then had a very slow rise to what seems to be a very weak maximum. Is the magnetic cycle of this star dying out?

It’s cool to see something that looks a lot like what we’ve been expecting to see for a while.  For comparison, here are the “grand magnetic minima” the Sun has experienced, measured with sunspots:

Sunspot number vs. time for three magnetic state transitions on the Sun, from the Hoyt & Schatten 1998 historical reconstructions. Note that we have reversed the x-axis on the bottom panel.

Black dots above are the parts of the Solar record we are suggesting to be analogous to the HD 4915 time series.  The red points are our projections of its future behavior if the analogy is perfect.  So, if this is analogous to the “Dalton Minimum” (no, not that Dalton Minimum) then the next cycle should be rather strong; if it’s truly going into a Maunder Minimum-like state we may not see any activity for another 80 years! So only time will tell if this is right, but I think it’s the best candidate I’ve seen so far.  I hope that by studying this star we can finally crack the nut of what the Sun was doing without sunspots for all those decades!

The paper is on the arXiv here.  Comments welcome!

No, this isn’t a post about METI.  This is about an interesting sociological phenomenon about one of the ways in which SETI is marginalized in astronomy.

SETI tends to get media attention, at an amount disproportionate to the amount of SETI work actually done. There are many reasons for this. One is that it is a topic of genuine interest to much of the lay public.  Another is that it is easily sensationalized and conflated with UFOlogy and science fiction by the yellow press.

I’ve had my share of both sides. Take Ross Andersen’s excellent article on Tabby’s Star (which was a scoop; we did not put out a press release or publish anything that triggered it). This story got huge amounts of global media attention, to the point that it appeared on Saturday Night Live and the Tonight Show. This second wave of stories led to the perception that Tabby herself “jumped to aliens” as an explanation, when in fact her paper and press release made no mention of aliens, and the press release announced “comets” as the cause.

The Daily Mail is a sensationalist rag in the UK that seems to have decided I’m their go-to name for all things alien. Sort of like the way that they find a way to shoehorn Stephen Hawking into the headlines of any article they write about space, but to a much smaller degree, they seem to love to claim I’ve found aliens (or that I think I have) when I write the opposite in a public space.  For instance:

1. I had a press release titled “Search for Advanced Civilizations Beyond Earth Finds Nothing Obvious“.  The Mail Online’s lede was that I had “found 50 galaxies that may contain intelligent alien races.”
2. I wrote a paper whose premise was that the question of extraterrestrial life (of any kind) in the Solar System is an “open question”, and in particular that the Solar System apparently lacks any alien artifacts.  The Mail Online article’s subheads claimed that I believe that intelligent “aliens either lived on Earth, Venus or Mars billions of years ago.”
3. And when I wrote a couple of blog posts about how I didn’t think ‘Oumuamua was a great SETI target (but that it should get us thinking about Solar System SETI), they again reversed my meaning and wrote that I claimed ‘Oumuamua “could be an alien spacecraft with broken engines.”

It’s pretty embarrassing to see your work so brazenly sensationalized in the media, but given the Daily Mail’s reputation I’m not sure there’s anything I could have done to prevent it except not talk about SETI at all where it might be overheard. I’ve developed a thick skin about it, but it still smarts to see my name next to pictures of bug-eyed aliens.  I know that colleagues of mine that don’t know the whole story will think less of me because of these false portrayals of me working on “fringe” science or shouting “aliens” at every astronomical anomaly.

So it’s especially galling when my colleagues accuse me of sensationalizing my work or, worse, only working in SETI at all because I’m after media attention. This attitude is probably widespread, because a few fed-up people have lost their cool and announced it several times in rants online; I can only imagine how many more have kept their cool or only said it where I haven’t noticed.  Some examples (names and links omitted to protect the guilty):

1. About a short ETI discussion in a longer paper (that did not seek or garner any headlines)
   What does the mention of alien civilizations really add to these topics other than an attempt to grab headlines?
   and
   What’s to be gained by a casual mention in the abstract and end of the paper? … this (along with a growing list of other examples in the literature) is an attempt to grab headlines.
2. Rebutting an argument that there is nothing wrong with seriously discussing SETI angles of astronomical anomalies on social media:
   All fine, but there is another component of this, which is cynical citation of ETI as a simple way of gaining attention. Your discussion assumes earnest and honest motivations. I’m not sure that that is always true.
3. Starting a discussion about how SETI astronomers need to stop sensationalizing their work:
   most SETI-related news seems to be interfering with conventional scientific discoveries, stealing the limelight – without following basic rules of science
4. Piling on to that discussion:
   It’s not just SETI you should be dumping on here, if your overall argument is to stop selling bullshit to the media because it’s fun.

At the risk of making an analogy to an infinitely more serious problem, they’re blaming the victims. Here we are getting misquoted and caricatured in the yellow press, and they’re the ones that are offended and embarrassed at what we have put them through. To them, somehow it’s our fault that the Mail misquotes us, and their attitude is that if we didn’t want to be misquoted, then why were we doing that kind of science in the first place? 

The real bad actors here are the yellow journalists, and that is a problem all of us in science and science communication have to deal with all the time; SETI is just a particularly soft target for them.

So, for the record: this kind of media attention is not “fun,” it’s mortifying, and we are not asking for it when we discuss our work in public. Many of the above accusations were surrounded by claims that the writers respect SETI as science, but you don’t really respect scientists’ work if you think it’s irresponsible of them to talk about it out loud, or if you think the only reason they do it is so that they can get their names in the papers.

SETI astronomers have had to deal with conflation with UFOlogy and fringe psuedoscience for decades; I hope that more of our colleagues will recognize that we share their disdain for sensationalism and are pulling in the same direction on the issue of sober science communication about good science.

And I hope that they won’t cast scorn at every SETI paper or reference to ETIs in the literature (“astro-crap” one astronomer called it on Facebook), and not cast aspersions on the authors for working on an important problem (especially junior researchers, who are both the future lifeblood of the field and the most sensitive to these accusations).

SETI gets enough unjustified grief from Congress, the last thing we need is to have to worry about our colleagues in our flanks piling on.

What follows is my submission to the National Academies of Sciences, Engineering, and Medicine ad hoc Committee on Astrobiology Science Strategy for Life in the Universe, 2018. It is available as a PDF here.

Please also see Jill Tarter’s companion white paper here.

I. SETI is Part of Astrobiology

“Traditional SETI is not part of astrobiology” declares the NASA Astrobiology Strategy 2015 document (p. 150). This is incorrect.¹

Astrobiology is the study of life in the universe, in particular its “origin, evolution, distribution, and future in the universe.” [emphasis mine] Searches for biosignatures are searches for the results of interactions between life and its environment, and could be sensitive to even primitive life on other worlds.  As such, these searches focus on the origin and evolution of life, using past life on Earth as a guide.

But some of the most obvious ways in which Earth is inhabited today are its technosignatures such as radio transmissions, alterations of its atmosphere by industrial pollutants, and probes throughout the Solar System. It seems clear that the future of life on Earth includes the development of ever more obvious technosignatures. Indeed, the NASA Astrobiology Strategy 2015 document acknowledges “the possibility” that such technosignatures exist, but erroneously declares them to be “not part of contemporary SETI,” and mentions them only to declare that we should “be aware of the possibility” and to “be sure to include [technosignatures] as a possible kind of interpretation we should consider as we begin to get data on the exoplanets.”

In other words, while speculation on the nature of biosignatures and the design of multi-billion dollar missions to find those signatures is consistent with NASA’s vision for astrobiology, speculation on the nature of technosignatures and the design of observations to find them is not. The language of the strategy document implies NASA will, at best, tolerate its astrobiologists considering the possibility that anomalies discovered in the hunt for biosignatures might be of technological origin.

But there is no a priori reason to believe that biosignatures should be easier to detect than technosignatures—indeed, we have had the technology to detect strong extraterrestrial radio signals since the first radio SETI searchers were conducted in 1959, and today the scope of possibly detectable technosignatures is much larger than this. Furthermore, intelligent spacefaring life might spread throughout the Galaxy, and so be far more ubiquitous than new sites of abiogenesis. Life might be much easier to find than the NASA strategy assumes.   

Indeed it has been cynically, but not untruthfully, noted that NASA eagerly spends billions of dollars to search for “stupid” life passively waiting to be found, but will spend almost nothing to look for the intelligent life that might, after all, be trying to get our attention. This is especially strange since the discovery of intelligent life would be a much more profound and important scientific discovery than even, say, signs of photosynthesis on Ross 128b.

Further, since technosignatures might be both obvious and obviously artificial SETI also provides a shortcut to establishing that a purported sign of life is not a false positive, a major and pernicious problem in the hunt for biosignatures. SETI thus provides an alternative and possibly more viable path to the discovery of alien life than is reflected in NASA’s astrobiology roadmap. Indeed, this was recognized explicitly in the panel reports of the Astro2010 decadal survey:

Of course, the most certain sign of extraterrestrial life would be a signal indicative of intelligence. [A radio] facility that devoted some time to the search for extraterrestrial intelligence would provide a valuable complement to the efforts suggested by the PSF report on this question. Detecting such a signal is certainly a long shot, but it may prove to be the only definitive evidence for extraterrestrial life. (p.454, Panel Reports—New Worlds, New Horizons in Astronomy & Astrophysics)

II. Why is SETI Neglected in NASA’s Astrobiology Portfolio?

While it is not completely clear why NASA does not include SETI in its astrobiology portfolio, there are several factors that seem likely to be at play.

The first is the risk of public censure: SETI sometimes suffers from a “giggle factor” that leads some to conflate it with “ufology” or campy science fiction. Indeed, such an attitude likely led to the cancelation of the last NASA SETI efforts in the early 1990’s, after grandstanding by US senators denouncing “Martian hunting season at the taxpayer’s expense” (Garber 1999). Such attitudes harm all of science, and the National Academies should be clear that such a “giggle factor” must not be allowed to influence US science priorities.

The second is the erroneous perception that SETI is an all-or-nothing proposition that yields no scientific progress unless and until it succeeds in detecting unambiguous signs of interstellar communication. On the contrary, even with scant funding, SETI has historically been involved in some of the most important discoveries in astrophysics. Not only have the demands of radio SETI led to breakthroughs in radio instrumentation (see, for instance, the new Breakthrough Listen backend at the Green Bank 100-meter telescope, with bandwidth of up to 10 GHz, an ideal Fast Radio Burst detection device; Gajjar et al. 2017), but some of the most famous SETI false positives have proven to be new classes of astrophysical phenomena, including active galactic nuclei (CTA-21 and CTA-102, Kardashev 1964), pulsars (originally, if somewhat facetiously, dubbed “LGM” for “Little Green Men”), and perhaps the still-not-fully-understood “Tabby’s Star” (KIC 8462852, Boyajian et al. 2016, Wright et al. 2016, Wright & Sigurdsson 2017).

Indeed, exactly because SETI seeks signals of obviously artificial origin, it must deal with and examine the rare and poorly understood astrophysical phenomena that dominate its false positives. Anomalies discovered during searches for pulsed and continuous laser emission (Howard et al. 2007, Wright et al. 2014, Tellis & Marcy 2015, 2017) broadband radio signals, large artificial structures (Dyson 1960, Griffith et al. 2015, Wright et al. 2016), and other astrophysical exotica push astrophysics in new and unexpected directions. If there is a perception that SETI little more than the narrow search for strong radio carrier waves producing a long string of null results it is because historically there has been essentially no funding available for anything else.

Third, there is the erroneous perception that, since radio SETI has been active for decades, its failure to date means there is nothing to find. On the contrary, the lack of SETI funding means that only a tiny fraction of the search space open to radio SETI has been explored (Tarter et al. 2010). Indeed, Robert Gray has estimated that the total integration time on the location of the Wow! Signal (the most famous and credible SETI candidate signal to date) is less than 24 hours (see, for instance, Gray et al. 2002). That is, if there is a powerful, unambiguous beacon in that direction with a duty cycle of around one pulse per day, we would not have detected a second pulse yet. Other parts of the sky have even less coverage. The truth is, we only begun to seriously survey the sky even for radio beacons, and other search methods have even less completeness.

Fourth, there is the erroneous perception that SETI will proceed on its own without NASA support. Indeed, the 2015 NASA Astrobiology Roadmap claims that “traditional SETI is…currently well-funded by private sources.”  Even setting aside the non sequitur of considering the amount of private philanthropic funding when assessing the merits of the components of astrobiology, this is not a fair description of the state of the field. While it is true that the Breakthrough Listen Initiative has pledged to spend up to $100 million over 10 years, in truth its spending has been far below that level, and it is focused on a small number of mature search technologies. Beyond this initiative, private benefactors have supported the SETI Institute’s Allen Telescope Array, but not at the level necessary to complete the array or fund its operations.

Fifth, there is the erroneous perception that the search for technosignatures is somehow a more speculative or risky endeavor than the search for biosignatures. We note that the entire field of astrobiology once faced a similar stigma. Chyba & Hand rebutted that perception in 2005:

Astro-physicists…spent decades studying and searching for black holes before accumulating today’s compelling evidence that they exist. The same can be said for the search for room-temperature superconductors, proton decay, violations of special relativity, or for that matter the Higgs boson. Indeed, much of the most important and exciting research in astronomy and physics is concerned exactly with the study of objects or phenomena whose existence has not been demonstrated—and that may, in fact, turn out not to exist. In this sense astrobiology merely confronts what is a familiar, even commonplace situation in many of its sister sciences.

Their rebuttal holds just as well as SETI today. Indeed, Wright & Oman-Reagan (2017) have articulated a detailed analogy between SETI and the relatively uncontroversial search for dark matter particles via direct detection. They argue that unlike with dark matter searches, with SETI, at least, we have the advantage that we know that the targets of our search (spacefaring technological species) arise naturally (because we are one).

Finally, there is an erroneous perception that SETI is exclusively a ground-based radio telescope project with little for NASA to offer. On the contrary, SETI is an interdisciplinary field (Cabrol 2016) and even beyond the potential for NASA’s Deep Space Network to play an important role in the radio component of SETI, archival data from NASA assets have played an important role in SETI for decades: from Solar System SETI using interplanetary cameras, to waste heat searches using IRAS (Carrigan 2009) WISE, Spitzer, and GALEX (Griffith et al. 2015), to searches for artifacts with Kepler (Wright et al. 2016) and Swift (Meng et al. 2017). Future ground-based projects like LSST and space-borne projects like JWST and WFIRST will undoubtably provide additional opportunities SETI research both as ancillary output of legacy and archival programs and through independent SETI projects in their own right.

III. Reinvigorating SETI as a Subfield of Astrobiology

One difficulty SETI faces is a negative feedback between funding and advocacy.

As it stands, SETI is essentially shut out of NASA funding. SETI is not mentioned at all in most NASA proposal solicitations, making any SETI proposal submitted to such a call unlikely to satisfy the merit review criteria. Worse, the only mentions of SETI in the entire 2015, 2016, and 2017 ROSES announcements are under “exclusions,” in the Exobiology section (“Proposals aimed at identification and characterization of signals and/or properties of extrasolar planets that may harbor intelligent life are not solicited at this time”) and the Exoplanets section (as “not within the scope of this program.”) In other words, SETI is ignored entirely in NASA proposal solicitations, except for those most relevant to it, in which cases it is explicitly excluded.

Meanwhile, other parts of astrobiology have flourished under NASA’s aegis, which has incubated strategies for the detection of life elsewhere in the universe, and produced scientists who can advocate for mature roadmaps to the detection of life in the universe as part of NASA’s astrobiology program. But now, twenty years after the last major NASA SETI program was cancelled, there are only a handful of SETI practitioners and virtually no pipeline to train more.

Thus there are only a few well-developed strategies to advocate for, and only a few scientists to advocate for them. This will doubtless be reflected in the number of white papers advocating SETI (like this one) versus those advocating other kinds of astrobiology responsive to the current call. This disparity should not be seen as indicating a lack of intrinsic merit of the endeavor of SETI, but as a sign of neglect of SETI by national funding agencies.

Since SETI is, quite obviously, part of astrobiology, SETI practitioners should at the very least be expressly encouraged to compete on a level playing field with practitioners of other subfields for NASA astrobiology resources.

Doing so will uncork pent-up SETI efforts that will result in significant progress over the next 10 years and beyond. As a fully recognized and funded component of astrobiology, SETI practitioners will be able to develop new search strategies, discover new astrophysical phenomena and, critically, train a new generation of SETI researchers to guide NASA’s astrobiology portfolio to vigorously pursue the discovery of all kinds of life in the universe—both “stupid” and intelligent.

And if, as many suspect, technosignatures prove to be closer to our grasp than biosignatures, then including of SETI in NASA’s astrobiology portfolio will ultimately lead to one of the most profound discoveries in human history, and a reinvigoration of and relevance for NASA not seen since the Apollo era. In retrospect, we will wonder why we were so reluctant to succeed.

IV. Bibliography

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• Domagal-Goldman S. D. & Wright K. E. Astrobiology. August 2016, 16(8): 561-653. 
• Dyson, F. 1960 Science 131, 1667
• Gajjar, V., et al. 2017, The Astronomer’s Telegram, 10675
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• Wright, J. T. & Oman-Reagan, M. P. 2017, Int. Jour. of Astrobiology, arXiv:1708.05318

¹ Indeed, broad swaths of the astrobiology community disagree with NASA’s assertion. For instance, SETI was included as a component of astrobiology in The Astrobiology Primer v.2.0 (Domagal-Goldman & Wright 2016), and SETI activities fall under the Carl Sagan Center for astrobiology at the SETI Institute (which, despite the name, conducts a broad range of science, including many sub-fields of astrobiology).