Paul Gilster posts:
In interstellar terms, a ‘fast’ mission is one that is measured in decades rather than millennia. Say for the sake of argument that we achieve this capability some time within the next 200 years. Can you imagine where we’ll be in terms of telescope technology by that time? It’s an intriguing question, because telescopes capable of not just imaging exoplanets but seeing them in great detail would allow us to choose our destinations wisely even while giving us voluminous data on the myriad worlds we choose not to visit. Will they also reduce our urge to make the trip?
Former NASA administrator Dan Goldin described the effects of a telescope something like this back in 1999 at a meeting of the American Astronomical Society. Although he didn’t have a specific telescope technology in mind, he was sure that by the mid-point of the 21st Century, we would be seeing exoplanets up close, an educational opportunity unlike any ever offered. Goldin’s classroom of this future era is one I’d like to visit, if his description is anywhere near the truth:
“When you look on the walls, you see a dozen maps detailing the features of Earth-like planets orbiting neighboring stars. Schoolchildren can study the geography, oceans, and continents of other planets and imagine their exotic environments, just as we studied the Earth and wondered about exotic sounding places like Banghok and Istanbul … or, in my case growing up in the Bronx, exotic far-away places like Brooklyn.”
Webster Cash, an astronomer whose Aragoscope concept recently won a Phase I award from the NASA Innovative Advanced Concepts program (see ‘Aragoscope’ Offers High Resolution Optics in Space), has also been deeply involved in starshades, in which a large occulter works with a telescope-bearing spacecraft tens of thousands of kilometers away. With the occulter blocking light from the parent star, direct imaging of exoplanets down to Earth size and below becomes possible, allowing us to make spectroscopic analyses of their atmospheres. Pool data from fifty such systems using interferometry and spectacular close-up images may one day be possible.
Image: The basic occulter concept, with telescope trailing the occulter and using it to separate planet light from the light of the parent star. Credit: Webster Cash.
Have a look at Cash’s New Worlds pages at the University of Colorado for more. And imagine what we might do with the ability to look at an exoplanet through a view as close as a hundred kilometers, studying its oceans and continents, its weather systems, the patterns of its vegetation and, who knows, its city lights. Our one limitation would be the orbital inclination of the planet, which would prevent us from mapping every area on the surface, but given the benefits, this seems like a small issue. We would have achieved what Dan Goldin described.
Seth Shostak, whose ideas we looked at yesterday in the context of SETI and political will, has also recently written on what large — maybe I should say ‘extreme’ — telescopes can do for us. In Forget Space Travel: Build This Telescope, which ran in the Huffington Post, Shostak talks about a telescope that could map exoplanets with the same kind of detail you get with Google Earth. To study planets within 100 light years, the instrument would require capabilities that outstrip those of Cash’s cluster of interferometrically communicating space telescopes:
At 100 light-years, something the size of a Honda Accord — which I propose as a standard imaging test object — subtends an angle of a half-trillionth of a second of arc. In case that number doesn’t speak to you, it’s roughly the apparent size of a cell nucleus on Pluto, as viewed from Earth.
You will not be stunned to hear that resolving something that minuscule requires a telescope with a honking size. At ordinary optical wavelengths, “honking” works out to a mirror 100 million miles across. You could nicely fit a reflector that large between the orbits of Mercury and Mars. Big, yes, but it would permit you to examine exoplanets in incredible detail.
Or, of course, you can do what Shostak is really getting at, which is to use interferometry to pool data from thousands of small mirrors in space spread out over 100 million miles, an array of the sort we are already building for radio observations and learning how to improve for optical and infrared work on Earth. Shostak discusses a system like this, which again is conceivable within the time-frame we are talking about for developing an actual interstellar probe, as a way to vanquish what he calls ‘the tyranny of distance.’ And, he adds, ‘You can forget deep space probes.’
I doubt we would do that, however, because we can hope that among the many worlds such a space-based array would reveal to us would be some that fire our imaginations and demand much closer study. The impulse to send robotic if not human crews will doubtless be fired by many of the exotic scenes we will observe. I wouldn’t consider this mammoth space array our only way of interacting with the galaxy, then, but an indispensable adjunct to our expansion into it.
Of course Shostak takes the long, sensor derived view of exploring the Universe, his life’s work is radio telescopes.
Gilster is correct that interferometry will be an adjunct to sending robotic probes to distant interstellar worlds, you can’t make money by just gawking at places.
Or can you?
The above statement is often attributed to Carl Sagan, usually when describing the amount of inhabitable planets in the Galaxy.
Now according to a paper in Astronomy & Astrophysics (abstract), that just might be true;
Red dwarfs are all over the news thanks to an announcement by the European Southern Observatory. Results from a new HARPS study show that tens of billions of planets not much larger than Earth are to be expected in the habitable zones around this class of star. The finding reinforces the growing interest in M-class stars and becomes especially interesting when you realize that faint red stars like this make up as much as 80 percent of the stars in the Milky Way. That leaves plenty of room for astrobiology, depending on factors we need to discuss below.
Do we suddenly have a close destination for a potential interstellar probe? Well, Barnard’s Star has always been in the running for an early mission because of its relative proximity to us at 5.94 light years. But we still have no word on planets there (despite a much publicized but soon discredited set of observations from a 1969 paper). Proxima Centauri is available at 4.2 light years, but we have yet to learn whether it has planets. And as far as anything closer, a source on the WISE team passes along the information that no new red dwarfs have been discovered, as of yet, within 10 light years, though of course the WISE results are still under heavy analysis.
Image: This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone. Credit: ESO/L. Calçada.
But back to the ESO announcement, which focuses on results obtained with the HARPS spectrograph at La Silla. Let me quote Xavier Bonfils (Institut de Planétologie et d’Astrophysique de Grenoble) directly on this:
“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet. Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”
What the work comes down to is a survey of 102 M-class stars studied over a period of six years, in which nine super-Earths with masses up to ten times that of Earth were found. 460 hours of observing time went into the mix, with 1965 radial velocity measurements made between 2003 and 2009. Interestingly, more massive planets like Jupiter and Saturn turn out to be rare around such stars, with fewer than 12 percent of them expected in M-dwarf systems. From all this, the team thinks that there should be about 100 super-Earth planets in the habitable zones of stars within about 30 light years of the Sun.
We can point to interesting worlds like Gliese 667Cc — discovered in the HARPS survey — as a promising preview of what is out there. This is a planet within a triple star system that is about four times the mass of the Earth and orbits close to the center of the habitable zone. But even assuming an abundance of super-Earths in conditions allowing liquid water on the surface, we still have the old M-class problems to contend with. A habitable world around such a small star needs to orbit close to it, leading to the potential for tidal lock and creating climate conditions that may not favor life. We also know that red dwarfs are frequently flare stars, creating unique evolutionary pressures on any life that does manage to emerge.
Xavier Delfosse (IPAG, Grenoble), another member of the team working the HARPS data, is lead author on one of two papers examining the results that have recently become available. The outlook on tidal locking is troubling but perhaps not a show-stopper for astrobiology, at least not if our own Solar System is any indication. Although a habitable M-dwarf planet is likely to be captured into a spin-orbit resonance, it will not necessarily be forced into synchronous rotation. From the paper (I’ve omitted internal references for brevity — the paper citations are below):
The ﬁnal equilibrium rotation of a tidally inﬂuenced planet depends on both its orbital eccentricity and the density of its atmosphere… Mercury, for instance, has been captured into the 3:2, rather than 1:1, spin-orbit resonance…, and Venus has altogether escaped capture into a resonance because thermal atmospheric tides counteract its interior tides… Whatever the ﬁnal spin-orbit ratio, the tidal forces will inﬂuence the night and day succession, and therefore the climate. As discussed above however, energy redistribution by an atmosphere at least as dense as that of the Earth is eﬃcient… and will prevent glaciation and atmospheric collapse on the night side.
And what about stellar flare activity? M-dwarfs are more active than G-class stars like the Sun, with the result that a planet in the habitable zone of a young M-dwarf takes a huge hit from X-ray and ultraviolet radiation, a period of irradiation 10 times longer than the approximately 100 million years that the Solar System dealt with similar activity on our star. How planetary atmospheres evolve under such conditions, and whether they can actually be stripped away by coronal mass ejections, are issues we haven’t as yet resolved. Digging into the Delfosse paper I find several points worth noting on the matter:
- We don’t have a good read on just how frequent coronal mass ejections from M-dwarfs are, and how intense they tend to be. Right now these questions need more investigation, though the authors believe the frequency may be less than some earlier studies have indicated.
- A strong magnetosphere can help to shield a planet that would otherwise be imperiled.
- The atmospheric chemistry and composition may be key, and there is one study that shows that around active M-dwarfs with an atmosphere consisting mostly of CO2, the atmosphere remains stable despite nearby flare and CME activity.
The paper summarizes the issue this way:
These diﬀerences imply that a planet in the habitable zone of an M dwarf is unlikely to be a twin of the Earth. Habitability however is not restricted to Earth twins, and Barnes et al. (2010) conclude that “no known phenomenon completely precludes the habitability of terrestrial planets orbiting cool stars.” A massive telluric planet, like Gl667Cc (M2.sin i = 4.25 M⊕), most likely has a massive planetary core, and as a consequence a stronger dynamo and a more active volcanism. Both factors help protect against atmospheric escape, and super-Earths may perhaps be better candidates for habitability around M dwarfs than true Earth-mass planets.
So there we are: Tens of billions of rocky planets in the habitable zones of red dwarfs, and perhaps 100 relatively near to the Sun, according to the estimates of these researchers. What we need to do now is increase the red dwarf planet inventory with future instruments made to order — state of the art near-infrared spectrographs that, in the authors’ estimate, should be able to identify between 50 and 100 planets in the habitable zones of M-dwarfs. That should be enough, even with a 2-3% transit probability, to find at least one transiting habitable world.
As of now, a project known as SKA (Square Kilometer Array) is being built in order to detect radio transmissions from these supposed planets.
What will we do if we happen to discover one?
Hat tip to Paul Gilster’s Centauri Dreams.
For 50 years, humans have scanned the skies with radio telescopes for distant electronic signals indicating the existence of intelligent alien life. The search — centered at the SETI Institute in Mountain View, Calif. — has tapped into our collective fascination with the concept that we may not be alone in the universe.
But the effort has so far proved fruitless, and the scientific community driving the SETI project has begun questioning its methodology, which entails listening to specific nearby stars for unusual blips or bleeps. Is there a better approach?
In two studies appearing in the June issue of the journal Astrobiology, the Benford brothers, along with James’ son Dominic, a NASA scientist, examine the perspective of a civilization sending signals into space – or, as Gregory Benford puts it, “the point of view of the guys paying the bill.”
“Our grandfather used to say, ‘Talk is cheap, but whiskey costs money,’” the physics professor says. “Whatever the life form, evolution selects for economy of resources. Broadcasting is expensive, and transmitting signals across light-years would require considerable resources.”
Assuming that an alien civilization would strive to optimize costs, limit waste and make its signaling technology more efficient, the Benfords propose that these signals would not be continuously blasted out in all directions but rather would be pulsed, narrowly directed and broadband in the 1-to-10-gigahertz range.
“This approach is more like Twitter and less like War and Peace, ” says James Benford, founder and president of Microwave Sciences Inc. in Lafayette, Calif.
Their concept of short, targeted blips — dubbed “Benford beacons” by the science press — has gotten extensive coverage in such publications as Astronomy Now. Well-known cosmologist Paul Davies, in his 2010 book The Eerie Silence: Renewing Our Search for Alien Intelligence, supports the theory.
James Benford discussing beacons
This means that SETI — which focuses its receivers on narrow-band input — may be looking for the wrong kind of signals. The Benfords and a growing number of scientists involved in the hunt for extraterrestrial life advocate adjusting SETI receivers to maximize their ability to detect direct, broadband beacon blasts.
But where to look? The Benfords’ frugal-alien model points to our own Milky Way galaxy, especially the center, where 90 percent of its stars are clustered.
“The stars there are a billion years older than our sun, which suggests a greater possibility of contact with an advanced civilization than does pointing SETI receivers outward to the newer and less crowded edge of our galaxy,” Gregory Benford says.
“Will searching for distant messages work? Is there intelligent life out there? The SETI effort is worth continuing, but our common-sense beacons approach seems more likely to answer those questions.”
I always speculated that if we happened to catch a snippet of a ‘back-door’ legacy radio signal from an extraterrestrial civilization it would be a digital beacon.
By back-door I mean that it would be a left on, automated signal that would “tweet” every so often just for the expressed purpose of contacting a less advanced culture since the civilization sending it out wouldn’t be using a form of radio any longer as its’ main source of communication.
I could be wrong, but the fun is in the speculation. 😉
The Benfords — Jim at Microwave Sciences, Gregory at the University of California’s Irvine campus, and Dominic (Jim’s son) at NASA GSFC — believe that advanced societies, if they are to be found, ought most likely to exist toward the galactic center, and probably at distances of over a thousand light years. We’re thus talking, in all likelihood, about interstellar beacons rather than targeted transmissions when it comes to SETI. And if beacons are indeed at play, what can we say about their costs, and do our own standards of terrestrial cost have any application in an ETI context?
The message here is that any SETI search has to make assumptions about the beacon builders, and if we can determine something about the economics of the situation, we may learn how to target our searches more effectively. Here’s the essence of the argument about ETI:
We assume that if they are social beings interested in a SETI conversation or passing on their heritage, they will know about tradeoffs between social goods, and thus, in whatever guise it takes, cost. But what if we suppose, for example, that aliens have very low cost labor, i. e., slaves? With a finite number of slaves, you can use them to do a finite number of tasks. And so you pick and choose by assigning value to the tasks, balancing the equivalent value of the labor used to prosecute those tasks. So choices are still made on the basis of available labor. The only case where labor has no value is where labor has no limit. That might be if aliens may live forever or have limitless armies of self-replicating automata, but such labor costs something, because resources, materials and energy, are not free.
Our point is that all SETI search strategies must assume something about the beacon builder, and that cost may drive some alien attempts at interstellar communication.
SETI always seems to come with a built-in willingness to think the best of extraterrestrial cultures. If an alien civilization is sending out a message, it must be doing so out of altruism. The Benfords, though, are interested in exploring motivations from a different angle. They’d like to relate them to the only case of a technological civilization we know of, ourselves, and speculate based on human history. From that perspective, there are two reasons for sending out messages across vast time scales.
Think about what people do. You can go to the Tower of London and explore the chambers where famous prisoners like Thomas More were kept. Invariably, on the walls, you’ll find graffiti, names written into the stone. People have an apparently robust need to engage in one-way communication, putting a note in a bottle and throwing it. Indeed, the Pioneer and Voyager spacecraft are examples of the impulse. Is it likely that any of these tiny vessels will ever be intercepted? Yet putting our names, our stories, our music and our pictures on board outgoing vehicles is a method that resonates. We have a need to encapsulate who we are.
A second reason is the drive to communicate the optimum things about our culture, what Matthew Arnold called “…the best that has been thought and said in the world.” Here the Benfords cite time capsules and monuments as examples of our need to propagate our culture. The contemplation of a legacy is involved here, especially in a scenario where human lifetimes are rising. Here again the communication can be one-way. The statue of King Alfred my wife and I admired in Winchester some years back was not built to impress people within a tight time frame, but to stand as a monument that would reach future generations.
So imagine scenarios like this: A civilization with an ability to plan over millennial time scales foresees problems that are beyond its capabilities. A SETI beacon might encapsulate a call for information and help — send us everything you have on stellar warming…
Here’s another: A civilization in its death throes decides to send out an announcement of its existence. We were here and are no longer, but as long as this message endures, so in a sense do we. And let’s not discount sheer pride of the sort that could keep a beacon in operation long after the beings that built it were gone. Robotically maintained, it might boast of achievements set against the backdrop of the ruin that may eventually attend all technological cultures. Or perhaps we’ll run into interstellar proselytes, out to convert the galaxy to a particular set of beliefs by placing their highest values into their outgoing signal.
I’m glad that finally somebody in mainstream SETI studies have proposed something different to think about when it comes to listening to, or broadcasting signals.
While I feel SETI should do more than just do the radio thing and look for possible Bracewell Probe signals, the Benford Clan at least looked outside the box.
The Monument Beacon theory sounds good, but something else should be added onto that.
If a suspected source is found, perhaps we should train all of our available listening, optical, and any other measuring devices we can muster to locate a Transcension Fossil in its general direction.
Yeah I know, semi-religious technorapture crap and such an object would be hard to find, even if the broadcast signal was strong enough.
But if we were lucky enough to intercept a Beacon in the first place, why not trace it back to the source to see if such things as Technological Singularities take place?
It could explain the Fermi Paradox.
And give us a clue to our ultimate fate possibly.
Was This A Message From Extraterrestrials??
Arecibo Radio Telescope, Puerto Rico
Since a number of years, I have been pretty intrigued by the famous ‘reply’ to the Arecibo message. Though it has been mentioned in passing earlier here on ATS, but it hasn’t received the attention I thought it deserves.
That said, in 1974, a powerful broadcast was beamed into space from the Arecibo Radio Telescope, Puerto Rico. The transmission consisted of a simple pictorial message aimed at the globular star cluster M13. This cluster is roughly 21,000 light-years from us, near the edge of the Milky Way galaxy, and contains approximately a third of a million stars.
This was a very powerful emission, equivalent to a 20 trillion watt omni directional broadcast using Arecibo’s megawatt transmitter attached to its 305 meter antenna, concentrating the beam in a very narrow funnel of the sky. The emission, that could be detectable just about anywhere in the galaxy within that funnel, would have been detectable by a receiver similar in size to Arecibo’s. This transmission was the strongest man-made signal ever sent.
The message consisted of 1679 bits, arranged into 73 lines of 23 characters per line. The “ones” and “zeroes” were transmitted by frequency shifting at the rate of 10 bits per second and was transmitted at a frequency of 2380 MHz and modulated by shifting the frequency by 10 Hz. The total broadcast was less than three minutes.
This was the pictorial message sent…