by Paul Gilster | Oct 24, 2013 | Outer Solar System |
New views from Cassini are giving us a much better look at Titan’s north pole and the seas and lakes that make the region so distinctive. This is particularly interesting because most of the moon’s lakes are concentrated at its northern latitudes, a fact that demands an explanation. The new near-infrared images show an area of bright terrain in this northern region that had not been observed before. This news release from the Jet Propulsion Laboratory suggests that the surface thus revealed is unique on Titan. If we can figure out what’s going on here, we may have an explanation for the concentration of lakes and seas in these latitudes.
Image: The vast hydrocarbon seas and lakes (dark shapes) near the north pole of Saturn’s moon Titan sprawl out beneath the watchful eye of NASA’s Cassini spacecraft. Scientists are studying images like these for clues about how Titan’s hydrocarbon lakes formed. Titan is the only world other than Earth that is known to have stable bodies of liquid on its surface. Credit: NASA/JPL-Caltech/SSI/JHUAPL/Univ. of Arizona.
One explanation for the bright areas surrounding the lakes is so-called karst terrain, in which liquids have dissolved soluble bedrock — the Carlsbad Caverns in New Mexico are an example of such terrains on Earth. Another possibility: Land that has collapsed after a volcanic eruption, which could explain the distinctive round silhouettes and steep sides of these lakes. For an idea of scale, the largest of the seas, at upper right, is Kraken Mare, which is about the size of the Caspian Sea and Lake Superior put together. Kraken Mare is Titan’s largest sea; Ligeia Mare, the second largest sea, is to its left, a body about 500 kilometers across.
A number of factors make the new imagery possible. The viewing geometry of two recent Titan flybys has been an improvement over previous encounters. We’ve studied much of this terrain with radar, but the partial or oblique views we’ve recorded through Cassini’s visual and infrared mapping spectrometer and imaging science subsystem can now be supplemented with these more detailed images. Moreover, the haze that coated the north pole has broken up with the approach of summer in the area, with cloudless, sunny weather now becoming the norm.
“The view from Cassini’s visual and infrared mapping spectrometer gives us a holistic view of an area that we’d only seen in bits and pieces before and at a lower resolution,” said Jason Barnes, a participating scientist for the instrument at the University of Idaho, Moscow. “It turns out that Titan’s north pole is even more interesting than we thought, with a complex interplay of liquids in lakes and seas and deposits left from the evaporation of past lakes and seas.”
Indeed, we seem to be looking at something like the salt flats found on Earth, only here the evaporated material is likely to be organic compounds originally from particles in Titan’s haze that had once been dissolved in liquid methane. In the image below, these materials appear orange against the green background of water ice. Remember that images like these are colorized mosaics based on mapping infrared colors into the spectrum of visible colors, allowing us to see the variation in the lakes and their surrounding materials.
Image: This false-color mosaic, made from infrared data collected by NASA’s Cassini spacecraft, reveals the differences in the composition of surface materials around hydrocarbon lakes at Titan, Saturn’s largest moon. The orange areas are thought to be evaporite — the Titan equivalent of salt flats on Earth. The evaporated material is thought to be organic chemicals originally from Titan’s haze particles that once dissolved in liquid methane. They appear orange in this image against the greenish backdrop of Titan’s typical bedrock of water ice. Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho.
“Titan’s northern lakes region is one of the most Earth-like and intriguing in the solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We know lakes here change with the seasons, and Cassini’s long mission at Saturn gives us the opportunity to watch the seasons change at Titan, too. Now that the sun is shining in the north and we have these wonderful views, we can begin to compare the different data sets and tease out what Titan’s lakes are doing near the north pole.”
Indeed, and every new revelation from Cassini reminds us of what we might achieve with a new probe to Titan. The ideas are out there even if the funding is not, but the day may come when we see an airborne vehicle like AVIATR, designed to stay aloft for a one-year mission in Titan’s thick atmosphere, eventually reach the distant moon. And the work that has gone into concepts like Titan Mare Explorer and related studies on the Planetary Lake Lander remind us how useful it would be to be able to put an instrument platform into one of these intriguing ethane seas.
by Paul Gilster | Oct 23, 2013 | Exoplanetary Science |
The red giant Kepler-56, some 3000 light years from the Sun, is telling us useful things about planetary alignments. The star is somewhat out of synch with the majority of Kepler targets to begin with. Most of these are unevolved stars near the main sequence, which are those most likely to produce systems in which a terrestrial world can be observed. But Kepler-56 has exhausted its hydrogen core and has evolved into a red giant. Two planet candidates have been identified here, orbiting in 10.5 and 21.4 days respectively. In fact, Kepler-56 turns out to be the most evolved star observed by Kepler with more than a single detected planet.
I’m drawing this from the work of Daniel Huber (NASA Ames) who, with a large team of collaborators, has been studying an apparent anomaly in the Kepler-56 system: The rotation axis of the star is tilted about 45 degrees to our line of sight. The Kepler-56 result was a surprise, says Huber, “because we already knew about the existence of two planets transiting in front of Kepler-56. This suggested that the host star must be misaligned with the orbits of both planets. What we found is quite literally a giant misalignment in an exoplanet system.”
Image: The Kepler-56 planetary system features two inner planets orbiting at a severe tilt to their host star — even though there’s no closely orbiting “hot Jupiter” in the system. Credit: Daniel Huber/NASA’s Ames Research Center.
The contrast with our Solar System is apparent: Our planets orbit within 7 degrees of the plane of the Sun’s equator. Kepler-56 is intriguing because we know of giant planets — ‘hot Jupiters’ — whose orbits are likewise out of alignment with the equator of their host stars. One theory suggests that these planets form far out in the planetary system and then migrate because of interactions with the protoplanetary disk to their current position. But the misalignment implies a different and more chaotic scenario, gravitational mishaps through close encounters with other planets in the system.
Kepler-56 seems to support the second interpretation. For the researchers went beyond Kepler data to get ten radial velocity measurements using the HIRES instrument at the Keck 10-meter telescope. What turns up, along with the Doppler signals of the known transiting planets, is what the paper on this work describes as “a slow velocity drift indicating a third, more massive companion in a wide orbit.” Analyses of the orbits of the transiting planets shows they are nearly circular and co-planar as well as being misaligned with the host star’s equatorial plane.
What to make of this? From the paper:
The radial velocity drift implies a third companion with the mass of a gas-giant planet within a few astronomical units, or a brown dwarf or star within several dozen astronomical units. In either case, if the third companion’s orbit is itself inclined with respect to the inner planetary orbits (for example through planet-planet scattering, if the companion is a planet), it could have torqued the orbits of the inner planets out of the equatorial plane of the host star. The inner planetary orbits would stay aligned with one another because of strong coupling between their orbits, resulting in a misalignment of the two co-planar transiting planets with the host star. Dynamical simulations that include a third companion in an eccentric orbit inclined to the equatorial plane of the host star confirm that such a mechanism can reproduce the architecture of the Kepler-56 system.
We learn from Kepler-56 that ’tilted’ planetary orbits happen in systems without hot Jupiters, with torques induced by wide-orbiting companions a possible cause. What’s ahead for this particular system is further observation to determine whether the third companion of this star is itself a planet or a star. The paper argues that if the third object is a planet, this would imply that the original misalignment happened after the planets had formed. If it is a star, the misalignment would have occurred before planets formed in the primordial protoplanetary disk.
A final issue: Is the equator of a star a reliable marker for the initial orbital plane of the protoplanetary disk in the first place? At least two recent papers have called this into question. “Important test cases,” the Huber paper concludes, “are co-planar multi-planet systems which, if primordial alignments are common, should predominantly show low obliquities. Indeed, until now all transiting multi-planet systems have been found to be well-aligned.”
The paper is Huber et al., “Stellar Spin-Orbit Misalignment in a Multiplanet System,” Science Vol. 342, No. 6156 (18 October 2013), pp. 331-334 (abstract). See also this NASA Ames news release.
by Paul Gilster | Oct 22, 2013 | Sail Concepts |
How do we go about using photons to accelerate a spacecraft to a substantial percentage of the speed of light? Ten percent of c ought to do — it gets us to Alpha Centauri with a mission time of 43 years and would allow us to at least send flyby probes into that system, with the promise of larger decelerating probes as new technologies became available. After yesterday’s post on Young Bae’s photonic thrusters, I went back and read his 2012 paper “Prospective of Photon Propulsion for Interstellar Flight” (reference at the end). 10 percent of lightspeed is indeed the minimum he chooses. It works out to 30,000 kilometers per second.
Back in the 1950s, the German scientist Eugen Sänger talked about a ‘photon rocket’ as a way of reaching the stars, but his design called for annihilating electrons and positrons and using the gamma rays thus produced for thrust. The idea stumbled over the problem of controlling this kind of exhaust stream, for gamma rays penetrate anything we use to contain them. But the insight that photons themselves could be used to impart momentum to a sail was already in the air when Sänger was pursuing these notions, and it would not be long before beamed laser propulsion came to the fore as the subject of numerous papers on interstellar flight.
Beaming Energy to a Sail
Robert Forward’s insights are repeated by Bae in his 2012 paper, which notes that separating the photon generators and the spacecraft pays numerous dividends. Propulsion systems that do not use rockets allow us to keep the heavy parts of the vehicle, especially the energy source, here in our own Solar System, while sending the payload out on its mission. As became clear yesterday, however, beamed laser propulsion also carries its share of problems, including the fact that we need to beam the laser photons over large distances. If you could forgive the need for Kardashev Type II engineering (able to use the entire energy output of its star), you could live with Forward’s huge Fresnel lenses, needed to keep the laser beam collimated, for laser beaming is based on reliably known physics. But we’re not exactly at Type II yet.
Image: Robert Forward, whose work on beamed laser propulsion produced designs that pushed engineering to extreme limits. Credit: UAH Library Robert L. Forward Collection.
Even so, assume a laser beaming capability using abundant solar power from a station near the Sun. A beam is sent out into the Solar System, to be focused by a huge lens presumably built by some kind of nanotech means out of local materials. Forward wanted to coax an interstellar mission out of these ingredients, and various permutations followed, culminating in 1984 in a concept for an interstellar round trip with a human crew. The destination would be Epsilon Eridani, 10.5 light years from Earth, to be reached using a lightsail with a diameter of 1000 kilometers, with a Fresnel transmission lens of the same diameter somewhere past the orbit of Saturn.
The numbers are staggering in every direction. With a total vehicle mass of 80,000 tons, including 3000 tons for the crew and its equipment, the lightsail would reach an acceleration of 0.5 lightspeed in less than two years. It would be accelerated by a 75,000 TW laser system. More on this mind-bending energy problem and its consequences in just a moment.
But first, how do we decelerate when our spacecraft reaches the target system? Without another laser installation already in place, Forward came up with a ‘staged’ sail concept, in which the lightsail is divided into nested circular segments. Approaching Epsilon Eridani (about 0.4 light years out), the rendezvous part of the sail with attached payload including crew detaches from the main body of the sail, allowing laser light to be reflected from what is now a 1000 km ‘ring sail’ back to the rendezvous sail. It’s this reflected light that decelerates the smaller sail and brings it into the Epsilon Eridani system. The sail will be divided again after the crew has finished its explorations. Now laser light beamed from Earth strikes the remaining 320 kilometer ring sail and accelerates the small inner sail and its crew module for the return trip. A final burst of laser light decelerates the spacecraft back into our Solar System.
Image: A four stage roundtrip interstellar flight using Robert Forward’s ‘staged’ sail to decelerate. Credit: Young Bae.
All of this is purely conceptual, but it has led to numerous papers on the methods and materials of beamed laser propulsion, even as we’ve widened the scope of the research to include microwave beaming. Not long ago, Joe Ritter (University of Hawaii at Maui) explained to the 100 Year Starship Symposium his own work on ultra-large, highly adaptive space mirrors, which could have interesting sail implications. Perhaps some of these studies, along with advances in laser capabilities, will make beamed sails commonplace in the Solar System, a period of experimentation that could eventually lead to the first true interstellar missions.
Hybrid Missions with the Photonic Laser Thruster
Young Bae believes that beamed laser propulsion when combined with his own photonic laser thruster (PLT) can reduce the power requirements of Forward-style beaming by a factor of ten to one hundred, while using a short wavelength laser can reduce it yet again. Thus an infrastructure that would have become available no sooner than 2500 (Bae bases this on world power production and its yearly growth, recently analyzed by Tau Zero’s Marc Millis) becomes an actuality by the year 2100. His proposal is to perform initial flights of exploration but to follow them up with the construction of the ‘photonic railway’ we looked at yesterday. From the paper:
…the Photonic Railway… aims [at] enabling routine interstellar commutes via Spacetrains. The Photonic Railway, if successful, would radically depart from the conventional spaceship concepts, in which a single spacecraft carries both an engine and a large quantity of fuel. Rather, the Photonic Railway would have permanent reusable space structures that propel Spacetrains, which would consist of mainly crew habitats, and navigation and crew safety equipment. The technological foundation of the Photonic Railway lies on a strategic combination of BLP by Forward and PLT, which is named here PLT-BLP. It is predicted that the development of PLT-BLP can be further expedited by incorporating the anticipated development in x-ray lasers and advanced material science and technologies, and the interstellar PLT-BLP is projected to be within reach in a century.
Image: Young Bae’s ‘photonic railway.’ It consists of four PLTs: two for acceleration and two for deceleration. The spacetrain will have small thrusters for attitude control and most of the onboard spacecraft resources will be dedicated to crew comfort and safety. Credit: Young Bae.
The photonic railway is, then, infrastructure, a permanent transportation system that would link nearby stars. Rather than a single laser beam from Earth, the beam is generated along the way. The structural parts for the lensing and laser systems must be delivered from Earth, but Bae envisions assembly and activation by self-directing robotic systems at the destination world. His paper illustrates a photonic railway using four photonic laser thrusters, two for acceleration and two for deceleration. The vehicle, or ‘spacetrain,’ would have thrusters for attitude control, but most of its resources would be dedicated to crew safety. The paper continues:
One important factor is that the Photonic Railway PLT needs to operate [a] much shorter distance than the distance between the earth and the exoplanet. Typically, depending on the Spacetrain acceleration condition (the optimal case would be 1 g acceleration for maximum crew comfort), the system operation distance would be at least a factor of 3.2 shorter than the flight distance. Because of this, the Photonic Railway optical system can be at least a factor of 10 smaller in size than the PLT-BLP optical system.
The paper goes on to sketch out this permanent transport structure, one based on the idea of photon propulsion that would act much as the transcontinental railway systems did at creating investment interest and economic opportunities. Building the photonic railway would involve a four part process beginning with the use of photonic thrusters in satellite maneuvering and leading to a lunar photonic railway, an interplanetary version, and ultimately the interstellar objective. Bae believes it is critical that each step provides return investment, and cites factors such as NEO mitigation, lunar mining and space solar power as early drivers toward this end.
Ultimately, Bae takes beamed laser concepts that have been extensively studied and combines them with photonic laser thruster technology, adding expected developments in x-ray laser and advanced material science to reduce the power and engineering requirements demanded by the missions Forward looked at. The goal is a photonic railway that is permanent and efficient. The citation is Bae, “Prospective of Photon Propulsion for Interstellar Flight,” Physics Procedia (2012), pp. 253-279. The classic Robert Forward paper is “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft and Rockets 21 (1984), pp. 187-195.
by Paul Gilster | Oct 21, 2013 | Sail Concepts |
A recent article in Popular Mechanics about Young K. Bae’s work on laser propulsion is generating some buzz, enough that I went back to look at the 2008 report Bae did for the NASA Institute for Advanced Concepts. Actually there are two reports, a Phase I and a later Phase II (with additional funding) on the topic of “A Contamination-Free Ultrahigh Precision Formation Flight Method Based on Intracavity Photon Thrusters and Tethers.” Bae was interested in spacecraft formation flight down to precisions of mere nanometers.
The idea relates to missions that would use multiple spacecraft to study astronomical phenomena. In fact, setting up a proper configuration would allow the study of biosignatures in the atmospheres of terrestrial exoplanets, using the technique of interferometry. Here the image produced has a resolution equal to that of a telescope as large as the maximum antenna separation, but the spacecraft involved have to maintain their alignment. Both ESA (with the Darwin mission) and JPL (with one configuration of Terrestrial Planet Finder) have studied interferometry in this context, and Bae’s work would assist such formation flying.
Image: Physicist Young K. Bae. Credit: Y. K. Bae Corporation.
Making it possible, in Bae’s view, was the use of laser methods in combination with tethers, but the work has grown beyond that original concept into what is being described as a ‘photonic laser thrust system,’ in which a laser is generated in a cavity between two mirrors. The resultant beam is fired from a space-based launch platform stabilized by conventional thrusters, and now we’re in territory made familiar by Robert Forward, who envisioned enormous laser installations firing beams to departing ‘lightcraft,’ sails pushed by laser light all the way to nearby stars.
The photonic laser thruster (PLT) is described on Bae’s website as:
…an innovative photon thruster that amplifies photon thrust by orders of magnitude by exploiting an active resonant optical cavity formed between two mirrors on paired spacecraft. PLT is predicted to be able to provide the thrust to power ratio (a measure of how efficient a thruster is in terms of converting power to thrust) approaching that of conventional thrusters, such as laser ablation thrusters and electrical thrusters. Yet, PLT has the highest specific impulse (a measure of how fast the fuel can propel spacecraft) orders of magnitude larger than that of other conventional thrusters.
We’re very early in this game, although a small amount of research on beamed propulsion to sails has been performed in the laboratory by Jim and Gregory Benford. A space-based experiment using what was to have been the Planetary Society’s COSMOS sail never occurred after the sail’s launch failure in 2005, but even then the plan had been to use the Goldstone dish of the Deep Space Network to bounce a microwave beam off the sail to measure the effects. Laser experiments are sure to follow as we gain expertise at operating sails in space.
Forward’s laser installations would use abundant solar power from orbits near that of Mercury, firing out a laser beam that would have to be kept narrow — collimated — by a vast lens built in the outer Solar System. The same problem occurs with Bae’s lasers, but at least in the early days, he’s talking about near-Earth and lunar missions, and eventual flights to Mars. The diffusion problem occurs as we start contemplating significantly longer missions. And note this, from the article: “One compensation is the idea of doing smaller platforms to create a ‘photonic railway,’ each acting as a sort of refueling station in between to get the craft where it needs to be.” Here Charles Quarra’s idea of using multiple lenses for beam refocusing comes to mind.
Popular Mechanics doesn’t mention it, but Quarra’s ‘starway’ concept grows out of work first performed by Geoffrey Landis back in the 1990s and posits an eventual ‘light bridge’ connecting nearby solar systems (see A Light Bridge to Nearby Stars for more). Bae is evidently studying beam collimation in terms of ‘Bessel beams’ as well, beams that do not diffract like a conventional laser. What both these ideas get us away from is the need Forward saw of building a lens somewhere beyond the orbit of Saturn that would focus the laser light tightly on the departing spacecraft. Such lenses would demand building space artifacts the size of Texas.
Photonic laser thrusters have now received a Phase II grant from the resurrected NIAC, with the focus on the near-term development of the technology for spacecraft maneuvering and formation flying. For the longer view, see Dr. Bae’s “Prospective of Photon Propulsion for Interstellar Flight,” in Physics Procedia Vol. 38 (2012), pp. 253-279 (abstract), which describes a ‘photonic railway’ that would, in Bae’s words, “…bring about a quantum leap in the human economic and social interests in space from explorations to terraforming, mining, colonization, and permanent habitation in exoplanets.” That’s an energizing goal, but let’s get formation flying using photonic thrusters demonstrated first to see how all this scales up.
by Paul Gilster | Oct 18, 2013 | Culture and Society |
Diplomat and author Michael Michaud returns to Centauri Dreams with a look at interstellar probes and how we might use them. Drawn from a presentation originally intended for the 100 Year Starship Symposium in Houston, the essay asks what effect our exploring another stellar system would have on its possible inhabitants. And beyond that, what effect would it have on us, as we weigh ethical issues and ponder the potential — and dangers — of highly intelligent artifacts going out into the galaxy? Michaud is the author of the indispensable Contact with Alien Civilizations: Our Hopes and Fears about Encountering Extraterrestrials (Springer, 2007). Among his numerous other works are many on space exploration. He was a U.S. Foreign Service Officer for 32 years, serving as Counselor for Science, Technology and Environment at the U.S. embassies in Paris and Tokyo, and Director of the State Department’s Office of Advanced Technology. He has also been chairman of working groups at the International Academy of Astronautics on SETI issues.
by Michael A. G. Michaud
Although the planets may belong to organic life, the real masters of the universe may be machines. We creatures of flesh and blood are transitional forms.
— Arthur C. Clarke
A Paradigm Reversed
For the past forty years, nearly all published work about the impact of contact with an extraterrestrial civilization has foreseen that it will be one way, from the aliens to us. These scenarios have rested on an assumption that any alien civilization detectable by its technological activity must be more scientifically and technologically advanced than we are.
The 100 Year Starship Study is bringing this paradigm into question, because of an anticipated change in human capabilities. We are talking about sending our own machines to visit nearby star and planet systems. This is the beginning of a role reversal.
We could be the first technological civilization to begin expanding its presence into this region of the galaxy. The impact of contact, whether intended or not, might flow from us to others.
If there are alien forms of intelligence in any of the target systems, they may be less scientifically and technologically advanced than we are. If those other sapient beings live in pre-industrial societies, they may not be detectable before our probe arrives.
On Earth, practical ethics imply that we should try to anticipate the effects of our actions. Our plans for our probe’s arrival in an alien system should have an ethical dimension.
Sending Out a Mind
Our first interstellar probe may include the most autonomous artificial intelligence we have built up to that time. While much of its behavior will be pre-programmed, the probe’s actions may not be determined solely by the instructions it receives from its makers. That probe must be able to adapt to unforeseen circumstances, in some cases to make its own decisions. How independent should that intelligence be?
During its long journey, such a machine might evolve by connecting data in new ways. The artificial intelligence could be mutated by the effects of radiation generated when the probe collides with interstellar matter.
An altered machine might make choices different from those its senders intended. Like the HAL 9000 in 2001: A Space Odyssey, the probe might override its programming, making its own choices about which actions it will take.
It may take years for our new instructions to reach the probe. It would take more years to know if the probe has obeyed those instructions.
Robot Warriors
We are seeing a preview of this issue in the military use of robots. Articles in Scientific American have warned of a threat from semiautonomous machines over which humans retain nothing more than last-ditch veto power. Some systems are only a software upgrade away from fully self-sufficient operation.
According to articles in The Economist, humans will increasingly monitor military robots rather than fully control them. Some robot weapons already operate without human supervision to save precious seconds. Defense planners are considering whether a drone aircraft should be able to fire a weapon based on its own analysis.
As autonomous machines become smarter and more widespread, they are bound to end up making life or death decisions in unpredictable situations, thus assuming – or at least appearing to assume – moral agency.
The Singularity
We have heard much about a Singularity predicted for less than twenty years in our future. At that time, human intelligences would be uploaded into machines, eventually becoming independent of biology.
Our interstellar probes could be the most advanced forms of such an uploaded intelligence. Sending out such intelligent machines could be a first step toward a post-biological galaxy.
A Second Singularity may begin when we lose control of the probe. The good news is that we would be sending our creation very far away, where it would pose the least potential risk to Humankind.
Recognizing Evidence
We commonly assume that our probe will give priority attention to whatever planet in the target system is most like Earth. What will our probe look for? High on that list will be evidence of life.
With a limited payload, interstellar probe designers will have to make choices among instruments. Those choices will rest on assumptions about the nature of life that prevail at that time.
Will the probe recognize evidence of life forms very different from the ones we know on Earth? What if the probe reports ambiguous evidence? What if we are not sure whether the phenomenon we discover is life or non-life, because it is so different from the life we know?
Even if forms of life exist on that far off world, the probe’s sensors might not detect them. A report that there are no signs of biology could clear the way for an eventual human colonizing mission.
Will the probe also look for evidence of intelligence? Will it recognize such evidence in a society that does not emit electromagnetic signals and does not pollute its atmosphere with the by-products of industry?
Should our probe send signals to whatever planets it observes? Would local intelligences be able to receive such messages, or understand them?
It is conceivable, though not probable, that our astronomers will remotely detect signs of intelligent life in a nearby system before we launch a probe. Should we send a probe to that destination, or avoid it?
The Consequences of Contact: A Mirror Image
What would be the impact on intelligent beings who detected our probe? How would they react? This could be seen as a mirror image of the debate among humans about the consequences of contact for us.
What if the extraterrestrials had believed that they were the universe’s only intelligent beings, as most humans have believed about themselves? What if an alien technological civilization had used astronomical instruments to survey planets around other stars as we are doing now, and had found no evidence of the kind of biochemistry they know? They might have concluded that they were alone.
Even if they had imagined life and intelligence on faraway planets, they may not have thought of interstellar exploration. They may not have anticipated direct contact. Our probe’s arrival in their system could be a startling surprise.
Detecting evidence of an alien technology in their system would tell them that at least one civilization had achieved interstellar flight. They would know that contact could be direct.
To extraterrestrials, we would be the powerful and mysterious aliens, whose character and purposes are unknown. Suddenly, they might feel vulnerable.
Alien impressions of Humankind would be determined by their understanding of our probe. What would they see as our motivation in sending it? Would they think that the detected probe was only one of many, part of a grand scheme of relentless interstellar colonization?
Consider what now seems the most likely form of such an encounter: a fly-through of the alien system. The probe’s high velocity would make the event brief. Our machine might not be detected. If it were, the extraterrestrial equivalent of skeptical scientists might say that a one-time sighting is not proof.
Arthur Clarke described such a scenario in his novel Rendezvous with Rama, in which a giant alien spacecraft flies through our solar system without stopping or communicating. The implied message was deflating: Humankind was not only technologically inferior, but also irrelevant.
Imposing Ethics on a Machine
We humans have set a precedent for regulating our behavior toward possible alien life during our interplanetary explorations. Protocols are in place to avoid contaminating other solar system bodies, and to prevent back-contamination of the Earth.
Implicitly, we have accepted a principle of non-interference with alien biology. Such rules may be extended to an interstellar probe, suggesting that our machine should not enter the atmosphere or land on the surface of a planet suspected to have life.
What should be our probe’s rules of engagement if it encounters intelligent life? Will our machine be able to make ethical choices? Can we give our probe a conscience? Should our probe obey Star Trek‘s often violated Prime Directive, observing the other civilization while keeping our presence secret?
Before Star Trek, Stephen Dole and Isaac Asimov argued that contacts with alien intelligence should be made most circumspectly, not only as insurance against unknown factors but also to avoid any disruptive effects on the local population produced by encountering a vastly different cultural system. After prolonged study, a decision would have to be made whether to make overt contact or to depart without giving the inhabitants any evidence of our visit.
Image: The Hubble view in the direction of Sagittarius, looking toward the center of the Milky Way. The discovery of life around distant worlds raises huge questions of ethics and even self-preservation as we ponder what kinds of future probes we might send. What should a program of galactic expansion look like? Credit: NASA, ESA, K. Sahu (STScI) and the SWEEPS science team.
Future Behavior
Some of those involved in the extraterrestrial intelligence debate have assumed that a program of sending probes, once begun, would continue until all the Galaxy had been explored, perhaps by having probes reproduce themselves. This model has been used to dismiss the idea of extrasolar intelligences; if we don’t see their machines, they must not exist.
This model flies in the face of the only behavioral data base we humans have: our own history. No human expansion has continued unchecked. No technological program continues indefinitely.
Newman-and Sagan argued that self-reproducing probes will never be built because they constitute a potential threat to their builders as well as to other sentient species that encounter them. Wise civilizations would not create potential Berserkers.
What if we send several probes, and none finds a habitable planet? Would our interstellar probe program be abandoned like the Apollo manned missions to the Moon? Sending our first probes might be a technological catharsis, not to be repeated.
Conclusion
You who plan to build starships may be initiating a new phase in Galactic history. If we expand our presence beyond our Solar System through our probes, our role in the galaxy will begin to change.
We cannot foresee all the powers that our machines will have a century in our future, any more than people in 1913 could foresee what powers our machines have now.
We should think through the implications of succeeding ourselves with artificial Intelligence. What motivations should we instill in our intelligent machines? What limits on their behavior can we impose?
For those who would design artificially intelligent probes, I offer a warning. Be careful of what you loose upon the galaxy. Above all, do not give those machines the ability to reproduce themselves.
Someday, Humankind may praise or condemn what interstellar advocates and their successors actually do. Choose wisely.
