“The Search for Life in the Universe” by Antonio Paris

Nearly 2,500 years ago the Greek philosopher Metrodorus of Chios challenged his students with an analogy. He stated that, because it was unreasonable that in a large field only one shaft of wheat should grow, why then, in an infinite universe, should there be only one living world? Our understanding of how profligate and diverse life is on Earth and recent discoveries in astronomy point to tantalizing possibilities.

When speculating on the nature of advanced extraterrestrial life and a spacefaring extraterrestrial society, some authors go to great lengths to discuss such life forms’ behavior and how they might be disposed toward us, the lifespan of an advanced technological civilization, and so on. At this stage in our understanding, however, all bets are off. If we were to encounter an advanced spacefaring species, we would be confronted with an intelligence that we have never before encountered, one that may not even be possible for us to understand. We cannot assume that an alien species would be motivated as we are, or would share any universal system of values with us, or perhaps even recognize us. At the moment, our understanding of life is confined to its forms, plentiful and varied though they be, found only on our home planet. Assuming that life has arisen elsewhere in our cosmos, it is almost certain to be very different from anything we currently understand, and it would not have the humanoid structure routinely reported in the UFO community or in science fiction.

Biologists define life by four general processes: growth, reproduction, responsiveness, and metabolism. Scientists are in general agreement that if a collection of organic molecules increases in size, if it makes copies of itself, if it somehow responds to its environment, and if it somehow incorporates elements from outside its structure and converts them in a series of controlled internal chemical reactions to compounds needed to grow, reproduce, or physically respond to changes in its environment, it is alive.

In the early 1960s Frank Drake conducted the first search for radio wave signals from potential extraterrestrial civilizations at the National Radio Astronomy Observatory in Green Bank, West Virginia. This began the international effort in astronomy known today as the Search for Extraterrestrial Intelligence, or SETI. In 1961, when the National Academy of Sciences asked him to chair a meeting on the detection of extraterrestrial intelligence, Drake developed his famous equation designed to estimate the number of advanced technical civilizations in our galaxy. In 1980, Carl Sagan popularized this equation in his television series Cosmos to point out to viewers across the world that our own galaxy might well be teeming with not only life but also other advanced technological civilizations. Professor Drake persuaded astronomers and other interested researchers to think seriously about the possibility of other intelligent life in our galaxy, and Sagan persuaded the common man to think about that same possibility, including its implications for our own existence.

We may be assuming too much in thinking that we would be able to recognize an alien intelligence, civilization, or its artifacts. Without a better understanding of how and where life can arise and of what other forms an alien intelligence or civilization can take, any number concerning the Drake Equation is next to meaningless. However, what Professor Drake’s equation has done, even in the absence of hard data, is to stimulate thought and debate about the various factors necessary to predict the likelihood of extraterrestrial civilizations in our galaxy.

It is arguable that any organism possessing spacefaring technology, as we know it, would have had to develop a sophisticated understanding of physics and be able to comprehend mathematical concepts, thereby recognizing a basic order in the universe’s physics and in our symbology. At the same time, of course, symbols such as letters or numerals are normally arbitrary, bearing little resemblance to what they signify, so it is difficult to say whether an alien civilization could make heads or tails of our messages, and vice versa. Still, Drake and Sagan were optimistically banking on the commonalities that we would share with another species. They knew the differences would be vast but thought it better to begin with the traits that we likely share, such as a similar chemistry involving hydrogen, one of the most common elements in the known universe.

For all our cryptographic abilities, however, we again assume much. We assume, for example, that any intelligent recipients generally think the way we do, that they organize information in more or less the same manner we do, and that they are primarily visual creatures. We are limited by our lack of knowledge of how an intelligence from another world might “think.” We must be careful not to assume that life based on a completely different biology would have anything but the most fundamental chemical elements in common with us.

As we are contemplating extraterrestrial life, one of the more exciting exercises is to imagine what such life might actually look like. If extraterrestrial life is built by DNA, or some equivalent of it, we might hypothesize that such organisms reproduce much as we do. Life evolving on any planet would certainly need to adjust to its gravity, so any sort of alien animal life would have to evolve an anatomy to move through its environment. Such organisms would be very recognizable to us as life forms, but perhaps it is not that simple. British astronomer Martin Rees has posited that there could be organisms and extraterrestrial intelligence in forms we can’t even conceive. We tend to think in terms of “animals” and “plants.” Moreover, the basis of all Earth life appears to be cellular. Whether those cells are eukaryotes, prokaryotes, or archaea, living things on our planet are either single-celled or multicellular organisms. But what if non-Earth life is built of something other than DNA or even an equivalent? We might not recognize it at all. Certainly an intelligence evolved from a profoundly different biology would function very differently than our own. Sagan wrote that extraterrestrial intelligence would be “elegant, complex, internally consistent, and utterly alien.” If we restrict our theorizing to intelligences recognizable to us, however, we could hypothesize that an intelligent extraterrestrial species might have evolved as social life forms. If such a species were also aggressive and highly competitive, as Stephen Hawking recently suggested in an article in the London Sunday Times, we could easily be faced with alien versions of the worst aspects of our human selves. In fact, Hawking cautioned against broadcasting our existence to potential extraterrestrial civilizations, stating that we only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to encounter. Rather than benevolent extraterrestrials as depicted in much science fiction, he posited that intelligent alien life might come to Earth “in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach.” Humanity would almost certainly be helpless in a confrontation with any species advanced enough to locate our planet and travel here.

In all of our theorizing about extraterrestrial intelligence, we may just as easily suppose that, if such a civilization developed technology sufficiently advanced to explore the stars, they must have harnessed that better nature and progressed beyond base instincts. Such a species might therefore not be bent on conquering the Earth or appropriating its resources. It might ignore us altogether, or it might attempt to contact us, perhaps even engage with us. For the moment, until we have irrefutable evidence of intelligent life beyond Earth, it is impossible to know.

Despite the interesting possibilities raised by Drake’s equation and continuing discoveries of new Earth-sized worlds in our galaxy, physicist Enrico Fermi’s question still nags: “Where are they? Where is everybody?” Could humanity be alone in this vast cosmos? For the moment, it seems that we are far distant from any other life forms that we can recognize in our obscure corner of the Milky Way.

“Life, but not as we know it” by Andrew Rader

Earth is quite a lovely little rock in space. While there is no doubt that at least most of our planet supports ideal conditions for human life, and Earth is the most “habitable” world we know of, this doesn’t necessarily mean that Earth is a member of an exclusive a club. It’s not that we magically dropped down out of the sky onto a planet that happened to be perfect. The reality is that our line of organisms has been shaped by billions of years of evolution on this planet. Earth seems so amazingly habitable to us not by happenstance, but precisely because we evolved to thrive in its environment.

Lots of types of worlds may support many types of life, but not necessarily life as we know it. There are of course certain bounds and limits. So far as we know, there must be a temperature range capable of supporting chemical reactions of stable organic molecules, and (we think) some sort of liquid. Water is ideal, but may not be the only liquid capable of serving this purpose. For example, the surface of Saturn’s moon Titan is covered in liquid hydrocarbons at a chilly -180°C (colder than liquid nitrogen). We can’t rule out the possibility of microorganisms or even sizable animals living in this environment, albeit with very un-Earthlike chemistry, relying on a methane cycle not so different from our planet’s water cycle. Perhaps small crystalline “sea snakes” glide through the freezing waters of Titan. 

Life on Earth thrives across an extremely wide array of conditions, and this would be no different from other worlds. Bacteria on Earth live essentially everywhere from the upper atmosphere to the depths of Earth’s crust. They survive extremes of radiation exposure, high and low pressures and temperatures, abundance or lack of light, and utter deprivation of water and nutrients. The live in the thermal pools of Yellowstone National Park at temperatures up to 80°C, dining on a rich array of chemicals leaking from volcanic vents. Microorganisms have been found deep underground in oil wells, and suspended in lakes of liquid water trapped miles under the Antarctic ice sheet. In fact, there’s more life underneath our planet than on top of it. Bacteria live miles underground, never seeing light and consuming nothing but chemicals stored in rocks. There might be as many as a hundred trillion tons of bacteria living beneath our feet. Pile up all the underground bacteria, and it would cover our planet’s surface to a depth of over five feet.

Titan’s hazy atmosphere – the most Earthlike in our solar system
Based on recent estimates from the Kepler Space Telescope, there are billions of Earthlike planets in our galaxy alone – around one per star, on average. With billions of galaxies in the Universe, we now think that there are more Earthlike planets than grains of sand on all the beaches of Earth. That’s a lot of potential life as we know it, but if we include life in more exotic environments like icy moons, the conditions for life are ten time more common than that. Even in our own solar system, there are a dozen worlds that support liquid water and could, by that definition, be considered habitable. 

Of these, Jupiter’s moon Europa is perhaps the best prospect for life, with a liquid water ocean heated by regular tidal flexing in mighty Jupiter’s gravitational field. Almost entirely isolated from the outside world (there is evidence that liquid water occasionally rises and bursts through the icy surface), Europa’s ocean floor is in direct contact with the bedrock beneath, where there should be thermal vents spewing out energy and nutrients. On Earth, these ocean floor thermal vents are cradles of life, and similar to the primitive ecosystems that nurtured the origin of life itself.

Europa has a lot more water than even our blue planet
Thus arises a question: since the conditions for life are ubiquitous, is life common in our Universe, or are there challenges to the origin that make life a relative rarity? Although intelligent beings may exist elsewhere in our galaxy, they obviously aren’t exceedingly common or else we would have extraterrestrials roaming around our solar system or perhaps a nearby star. Yet, this tells us nothing about simpler life which may indeed be common, possibly even to be found on another world orbiting our Sun. Beyond, there could be billions of worlds covered in microorganisms or even simple plants and animals, just waiting to be found. Either we’re alone or we aren’t: both prospects are equally terrifying. Our curiosity drives us to search for answers, as living beings connected to the Universe.

“Three Great Astronomy Discoveries I Didn’t Make” by Paul Carr

I have a little training in astronomy, although I can hardly call myself a professional. Becoming a professional at anything is a long, hard road, one I haven’t traveled far down in astronomy. No, I’m decidedly an amateur, and not a highly accomplished amateur at that.

Sadly, the word “amateur” has been cheapened a bit by modern use. It doesn’t really mean inexpert dabbler (although I will cop to that), but “lover.” An amateur does what they do for the love of it, and there are many highly knowledgeable and skilled amateur astronomers who do real science. Far from earning a living at astronomy, amateurs spend considerable sums of their own money - for love. If you are reading this, you probably understand why. The night sky and the cosmos at large combines natural beauty and profound fascination as few other things we can all experience.

In our time, nearly any object - save perhaps the odd undiscovered comet or asteroid - that is accessible to amateur equipment has already been imaged at multiple wavelengths using professional instruments. Sensitive astronomical surveys have been performed and are being performed on a regular basis, and have been for many generations, going back for more than two thousand years to the great Greek astronomer Hipparchus, who since had a major modern catalog named after him.

Since ancient times, the proliferation of astronomical catalogs and atlases has accelerated - from John Flamsteed’s sky atlas, to the 19th century Bonner Durchmusterung, to the Henry Draper catalog, to the US Naval Observatory’s catalog based upon the Palomar Observatory’s photographic sky survey, to the Hubble Guide Star catalog, up until the present, with the Gaia Source List containing more than a billion objects. What is remarkable about this accelerating growth is not only the number of catalogs and the broader coverage of the electromagnetic spectrum, but also the fact that they are now accessible to anyone, and you can also access images from many of these surveys. You no longer need a good university library and stacks of bound volumes to find the information you want.

I should point out that you can do meaningful citizen science at sites like Cosmoquest or Galaxy Zoo, but this does not mean that you can’t poke around at random in the vast library of astronomical knowledge and try to answer your own questions. I do this - and I return from my wanderings  with more questions, and so far, no answers.

Boyajian’s Star

In 2015, when the paper describing Boyajian’s Star and its bizarre lightcurve was first made public on Arxiv, I was curious about what was known about the immediate neighborhood in that patch of sky in the constellation Cygnus. To investigate this, I used a free tool called the Aladin Sky Atlas, provided by the University of Strasbourg in France. Aladin, with a modest learning curve, allows you to overlay many of the most widely used catalogs and image libraries. For example, if you just open up Aladin and enter “Boyajian’s Star” in to the Location field, you will get this window:

Figure 1 - Boyajian’s Star as Viewed in Aladin with Colored Digital Sky Survey


That’s Boyajian’s Star, aka KIC 8462852, centered in the purple reticle. You can zoom in from there and explore to your heart’s content. What I wanted to investigate was what was known about the other stars right around the target, so I zoomed in and overlaid one of the biggest catalogs,
2MASS (2 Micron All Sky Survey). The 2MASS has over 470 million objects in it, so chances are if you can see it in an image, it’s in 2MASS, as shown in Figure 2:

Figure 2 - Zoomed on Boyajian’s Star with the 2MASS catalog overlay.

Beyond the images though, I was interested in any measurements of the distance to any of these objects, and their proper motions - how fast they appear to be moving against the background of more distant objects. Objects with a distance similar to Boyajian’s Star or with similar proper motions are candidate neighbors, or even companions. The proper motion of Boyajian’s Star has been fairly well known (about 13 thousandths of an arcsecond per year West) for a while now, but it’s distance (a bit under 1500 light years) has only been inferred from its spectral type and apparent brightness.The little red squares in Figure 2 indicate an object in the 2MASS catalog. As you can see, all but some tiny faint smudges are cataloged by 2MASS. Most of these objects are in other catalogs, like the infrared ALLWISE catalog, or the Gaia Source List. If you are interested, you may also want to look up the PanSTARRS images, which don’t seem to be available via Aladin.

It turns out that directly measuring the distance to such a star using subtle variations in its apparent movement, or parallax, as the Earth moves around the Sun is very tricky, and only in recent times have we known more than a handful of these distances. So, we’re still not sure which of those stars are actual neighbors to Boyajian’s Star The only real measurement of its parallax was released only a few months ago by the Gaia team, and still carries a fair bit of uncertainty. We hope that with future Gaia data releases (perhaps one as soon as late 2017), we will have better information, not only about Boyajian’s star, but its neighbors as well.

So, lesson learned - many more objects have been cataloged than have been closely studied. We only know the spectral type and other information about Boyajian’s Star because it’s weird light curve as observed by the Kepler Space Telescope triggered a number of follow-up observations. As I poke around in these catalogs, I notice more and more, and with some guidance from professionals, I am able to start making sense of things, and also learning how to be more cautious.

Did a Star Go into Hiding?

In 2016, three Swedish astronomy students published their finding about a clever new approach to SETI - looking for stars that had vanished between surveys. In the sample of objects they studied, they found one faint object that appeared to be in a US Naval Observatory Catalog, but had vanished from subsequent, more sensitive surveys. I interviewed the lead author, Beatriiz Villarroel for my podcast, the Wow! Signal. Villarroel’s team weren’t sure this object was even a star, but I was intrigued by the possibility of a SETI discovery.

Using Aladin and the Vizier server, I found an image from the Sloan Digital Sky Survey and overlaid the USNO B1 catalog (Figure 3), represented by the red crosses. Right in the center is where the missing object, poetically named 1084-0241525 was, but as you can see, there is nothing there now. It’s also missing from all the other major catalogs, but keep in mind we don’t really know its proper motion. It may have moved a little over the decades, since the Palomar survey images upon which the northern part of USNO catalog is based were mostly taken in the 1950s. In 50 years, this object could have potentially moved a few arcseconds, depending on how close to us it is.

Figure 3 - USNO B1.0-1084-0241525 location on the g band SDSS image in Aladin. The red crosses are objects in the USNO catalog. Unfortunately, the star was too dim to be seen on the old photographic plates at Harvard, or to be regularly monitored by the AAVSO.

The conjecture is that if someone out there was building something around this star (if it is a star) that was hiding it from our cameras, it might be heating up enough to be visible in the infrared.  Villaroel’s team looked for this, but didn’t see anything. However, if we overlay the infrared ALLWISE survey catalog (the little blue circles), and look just outside their 5 arcsecond search radius:

Figure 4 - the ALLWISE catalog overlay around the missing star location in Aladin

You can probably guess what I was thinking. Some object moving fairly fast against the sky - a bit more than a tenth of an arcsecond per year  - had reddened so much that it had once been visible, but was now only visible in the infrared. And yes, that is a bit odd. For that to be a SETI detection is still not a slam dunk, but is much closer than we usually get.There is nothing visible under the reticle, but just to the north, about 6 arcseconds away, is an infrared object spotted by WISE, J145736.52+182507.8, that doesn’t appear to have any corresponding optical counterpart.  

The WISE space telescope, back when it was able to keep its focal plane extremely cold,  took measurements in 4 bands from in the infrared. These bands are called W1, W2, W3, and W4, and run from W1 centered at 3.35 microns wavelength to about 22 microns for W4. For comparison, the light you can see with your eyes is the neighborhood of half a micron in wavelength. Normally, the infrared bands for a star are on what is called the Rayleigh-Jeans tail - that is,  the infrared spectrum is fairly flat, and the brightness wouldn’t vary that much from band to band.

Sadly, what we know from WISE isn’t enough. W1 and W2 are fairly close in brightness, as you would expect, but the signal to noise is too low, and the best you can say is that the source is no brighter than a certain magnitude in W3 and W4 - it could be much dimmer. Maybe someday we’ll have a survey that nails down the infrared spectrum of this object, but WFIRST may not be enough, since it will only survey out to about 2 microns wavelength.  So, I haven’t found the missing star - yet.

The Mysterious Gaia Dipper

I hope you know I’m using the word “mysterious” here ironically. This word used to mean something, but now I’m afraid it’s just cheap clickbait.

ESA’s Gaia mission is doing some really interesting things right at the cutting edge of what is possible. One of the things it does as it scans the sky is measure the brightness of stars in both a blue and red band. The Gaia team keeps track of the brightness measurements for individual objects and publishes an alert when it detects that the brightness has changed by a significant amount. It has spotted quite a few supernovae this way, for example.

A small fraction of the Gaia alerts note when the brightness of the object drops considerably. I started tracking these dippers because I wanted to see if Gaia might possibly spot something that behaves like Boyajian’s Star. No doubt many of the dippers are what are called Young Stellar Objects, stars that have just formed and are still surrounded by a large disk of gas and dust.

One of the first ones of these I noted was Gaia 16bnj. Here’s what its Gaia light curve looked like (Figure 5):

Figure 5 - The lightcurve for Gaia 16bnj

Here’s the colorized WISE image:Those are very sharp dips shown in Figure 5 - quite a bit deeper than Boyajian’s Star, and the two dips are roughly the same size as best as we can tell. Using Aladin, I was able to quickly see that this relatively faint object is also in the ALLWISE catalog, as J200207.30+174649.7.

Figure 6 - Colorized WISE image for Gaia 16bnj

Ah, but you guessed it, wet blanket time. WISE astronomer and SETI researcher Jason Wright pointed out that there were problems with these measurements:The object of interest is at the center of Figure 6, with a little blue circle around it. When I looked at the WISE magnitude data at first, I got pretty excited - it is much brighter in the longer W4 wavelength than in the shorter W1 and W2, and this time these were not limiting magnitudes, as they were for J145736.52+182507.8. A big infrared excess could mean one of our favorite classes of conjecture - a megastructure.

 

Look at the quality control flags:

ccf 00Pp

One character per band (W1/W2/W3/W4) that indicates that the photometry and/or position measurements of a source may be contaminated or biased due to proximity to an image artifact:

P,p = Persistence. Source may be a spurious detection of or contaminated by a latent image left by a bright star.

So, no reason to think this thing has any excess IR emission.

So, it could easily be an imaging artifact and there is no way to tell. You know - the old extraordinary claims/extraordinary evidence thing. We’ll keep looking for more dips, and perhaps we’ll see something interesting in the future, but for now, we’ve got nothing much. However, I’m not overly discouraged. Boyajian’s star doesn’t exhibit an infrared excess, and there’s still lots of interest attached to it.

Are We Any Wiser, Then?

The first lesson from all this is that amateur attempts to mine the astronomical databases for little nuggets of holy cow are likely to be frustrated. We have cataloged billions of objects but only really studied a relative handful. Also, some of the data we do have available for exploration has problems. There might in fact be a star that goes missing from a catalog, but trying to figure out what happened to it will be frustrated by the lack of follow up observations.

For now, most of the people who get credit even for minor astronomical discoveries will overwhelmingly be the ones who make an intelligent choice of targets and point their telescopes at them for years of painstaking observations, followed by sophisticated and careful analysis. As far as I can tell, they are also the ones who deserve the credit.

However, this is not by itself a sufficient reason to give up, since after all, it’s quite pleasing to take a magic carpet ride among the stars looking for rarities. It’s your universe as much as anyone else’s, and we know orders of magnitude more about than our grandfathers did. So, feel free to download Aladin or similar tools and poke around the deep sky in whatever direction you like. Please, just let us know if you find anything.