by Paul Gilster | Feb 11, 2009 | Culture and Society |
by Tibor Pacher
My friend Tibor Pacher is joined with me (until 2025, anyway) in our ‘interstellar bet,’ under the auspices of the Long Now Foundation. Trained as a physicist at the Eötvös University in Budapest and the University of Heidelberg, Dr. Pacher has been exploring ways to get across interstellar concepts to the public through venues like his peregrinus interstellar. Social networking is to some of us a new frontier, and I’ve asked Tibor to provide some background on what he is doing to make sure that an obscure wager develops an audience and becomes an effective teaching tool.
Yesterday I watched the movie In the Shadow of the Moon. I must admit, this was not the first time, but I wanted to capture more details and – well, it is just a great film, and, I believe, not only for space heads a ‘must.’ Sober and emotional at the same time, for me it is a perfect example of how the public imagination can be captured about space, in a way which shows the deeply human nature of this adventure.
Now we have a bit different situation if we think of mastering interstellar flight. Reaching for the stars is an unprecedented challenge, even compared to the moon flights, technically as well as for our minds and souls. Start to think about it deeply and you end up inevitably with some serious questions.
But is it enough just pointing this out during a chat to encourage people to dig deeper into these topics? I do not think so. We need more, definitely, but apart from science fiction — good and bad — we have currently little at hand to attract people, especially the youth.
The Internet gives us some new and promising possibilities. Blogging is widespread and we have already some great ‘deep space bloggers’, while space discussion forums are also established. All this marks the beginnings of social networking, which I believe will help us in building our interstellar community. At almost no cost we have the chance to reach a broader audience with interested and passionate users. But, of course, this is only the framework. We still have to build the content, which we can now do together.
We can begin as simply as creating a group within an already established community. How can such an environment help the growth of the group? As an example, take a small albeit common feature of social networking platforms: you can – depending on privacy settings – see what happens in your network, so you become aware if some of your friends joined a group, perhaps with a catchy name, and you become interested. Of course, there are other means as well, such as advertising the group and its topics in other forums of the platform, etc.
To see how this works in real life, I decided to start such a group for our Interstellar Bet. The platform XING – operated by a Hamburg-based company – seemed to be a good choice for me. It is big and diverse – claiming to have more than 6 million members from 200 countries – and I had some good experience there already. In just two months, with some moderate advertising we are now over 100 people, with some focused discussions starting already, and the group keeps growing.
You might take a look at the ‘business card’ of the Friends of Long Bet 395 here – and of course, we are happy if you decide to join and help us to spread the word.
I hope we will see together the birth of new ideas, brought to light by a Long Bet 395 friend – perhaps on making a good interstellar documentary? As stated on the German webpages for In the Shadow of the Moon,
The central theme of the movie – the necessity to make dreams come true and to take risks for getting a new, responsible perspective of life on Earth – is in a new era of global uncertainty more timely than ever before.
I believe that reaching for the stars, barely at its modest beginnings with the Pioneers, Voyager and New Horizons probes, is a good cause for this theme.
by Paul Gilster | Feb 10, 2009 | Astrobiology and SETI |
I promised a quick return to recent work on the Drake Equation, which helps us estimate the number of communicating civilizations in the galaxy, but a BBC story on Duncan Forgan has me back at it even sooner than I had intended. It’s no surprise that the matters encapsulated in Drake’s thinking should be in the news. After all, the era of Fermi and Drake was without firm knowledge of extrasolar worlds, of which we now know over three hundred. For that matter, the concepts of habitable zones around both stars and the galaxy itself had not come to fruition, nor had anyone ever heard of the ‘rare Earth’ hypothesis.
We also work today with knowledge of Charles Lineweaver’s studies of the median age of terrestrial planets in the Milky Way, which point to civilizations around other stars having had as much as two billion years-plus to emerge before our own Earth had even coalesced. Until we know more, I suspect we’ll be adjusting Drake parameters for some time, as Duncan Forgan (University of Edinburgh) does in his new paper.
Hypotheses and Conclusions
Forgan’s simulations, which take current exoplanet findings into account, work with several contrasting hypotheses, for each of which statistical methods were applied. The BBC explains:
The first assumed that it is difficult for life to be formed but easy for it to evolve, and suggested there were 361 intelligent civilisations in the galaxy.
A second scenario assumed life was easily formed but struggled to develop intelligence. Under these conditions, 31,513 other forms of life were estimated to exist.
The final scenario examined the possibility that life could be passed from one planet to another during asteroid collisions – a popular theory for how life arose here on Earth. That approach gave a result of some 37,964 intelligent civilisations in existence.
Forgan’s statistical approach relies on so-called Monte Carlo methods that use repeated random sampling to compute results in complex systems. I note this from the Wikipedia article on these algorithms: “Monte Carlo methods are useful for modeling phenomena with significant uncertainty in inputs, such as the calculation of risk in business.” And nothing would suggest uncertainty in inputs more than the classic Drake Equation, especially in terms of the biological factors relating to how life develops and turns into civilizations.
Problems with Exoplanet Modeling
And, of course, there is still much we don’t know about exoplanets, considering that we have yet to observe a single terrestrial world around another star. But in our simulations we can use existing exoplanet data to provide a distribution of planetary parameters. These can then be applied in sampling, including factors such as the planetary mass function, the distribution of planetary orbital radii, and the metallicity of the host stars.
Note what Forgan has to say about this challenge as he threads his way through this statistical analysis of Drake:
…as with the stellar parameters, a population of planets can be created around the parent stars, with statistical properties matching what can be observed. However, this statistical data is still subject to strong observational bias, and the catalogues are still strongly incomplete. There is insufficient data to reproduce a distribution of terrestrial planets: therefore it is assumed that life evolves around the satellites of the planets simulated here. In essence, this constitutes a lower limit on the number of inhabited planets: the work of Ida and Lin… shows that, as a function of metallicity, habitable terrestrial planets are comparable in frequency (or higher) than currently detectable giant planets. This data is hence still useful for illustrating the efficacy of the Monte Carlo method (at least, until observations of terrestrial exoplanets become statistically viable). All this should be borne in mind when the results of this work are considered.
The ‘Single Biosphere’ Issue
And in biological terms, we are even more up the creek, since we base our thinking on observations of a single biosphere, our own. To keep the number of free parameters to a minimum, Forgan works with “a biological version of the Copernican Principle,” the notion that our Terran biosphere is not special or unique, so that we can think about life on other worlds as sharing many of the same characteristic parameters. The thinking on these matters — and the statistical methods used to explore them — forms the most absorbing section of the paper.
About half of all emerging civilizations destroy themselves under two of Forgan’s three hypotheses, the panspermia approach and what he calls the ‘rare life hypothesis,’ while self-destruction is a bit more likely still in the ‘tortoise and hare hypothesis,’ where life evolves easily but evolution toward intelligence is more difficult. We also have to factor in possible ‘reset’ events that may annihilate a biosphere before a civilization can emerge, and make estimates on the amount of time needed between life’s appearance and the first civilization.
There is so much we simply don’t know. But Forgan is no ideologue. He knows he’s working with outputs that are only as accurate as their inputs will allow. Thus this, on planetary modeling:
Current data on exoplanets, while improving daily, is still insufficient to explore the parameter space in mass and orbital radii, and as such all results here are very much incomplete. Conversely, as observations improve and catalogues attain higher completeness, the efficacy of the Monte Carlo Realisation method improves also. Future studies will also consider planetary parameters which are sampled as to match current planet formation theory, rather than current observations.
Where Statistical Analysis Is Taking Us
How much work remains to be done on the ever complicated Drake Equation? Quite a bit, in the opinion of this researcher. Forgan notes that we need an improved three-dimensional galaxy model that incorporates the evolution of the Milky Way over time and takes into account its components, such as the bulge and the bar. We also will continue to plug in better models for star formation and the spatial distribution of stars. New input from our space-based observatories should gradually strengthen our statistical models as we tune what Frank Drake started into an ever more sophisticated instrument for SETI research.
The paper is Forgan, “A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence,” published online by the International Journal of Astrobiology (January 23, 2009) and available here.
by Paul Gilster | Feb 9, 2009 | Interstellar Medium |
Almost four years ago I wrote a Centauri Dreams entry about Dana Andrews’ views on shielding an interstellar spaceship. The paper is so directly relevant to our recent discussion on the matter that I want to return to it here. Andrews (Andrews Space, Seattle) believes that speeds of 0.2 to 0.3 c are attainable using beamed momentum propulsion. That being the case, he turns in his “Things to Do While Coasting Through Interstellar Space” paper to questions of human survival.
Particles with a Punch
Collision with interstellar dust becomes a major issue when you’re traveling at speeds like these, a fact Andrews is quick to quantify. For a starship moving at 0.3 c, a typical grain of carbonaceous dust about a tenth of a micron in diameter should have a relative kinetic energy of 37,500,000 GeV. Our hypothetical star mission with human crew moving at a substantial fraction of light speed will run into about thirteen of these dust particles every second over every square meter of frontal area.
This gets interesting when put in the context of cosmic rays. Most galactic cosmic rays, which as Andrews notes are completely ionized atoms accelerated to extremely high energy states, have energies between 100 MeV and 10 GeV. You can see the overlap. Travel fast enough and even small grains of dust behave like energetic cosmic rays as our vessel encounters them. Clearly, dust between the stars is something we have to reckon with on any interstellar journey.
Absorbing Particles (and the Cost)
In my post on Friday, I looked at the Project Daedalus dust shield and its role in the journey to Barnard’s Star. A key question: Do we want to absorb cosmic rays and dust particles, or redirect them? The former can be envisioned in terms of a human crew surrounded by layers of supplies and equipment, with an outer shell for the spacecraft composed of 25 cm of multiple layers of polyamides, metal foils and polyethylenes to assist in radiation protection. The mass of structure and shielding obviously becomes a major factor. As Andrews writes:
The striking facts from this mass statement are the large masses associated with structure and shielding, and the small masses associated [with] things like food and water. This is because all waste and CO2 is recycled through growing plants and algae to provide clean air, food, and water.
The author is figuring that three percent of food intake would have to be derived from stored supplies to offer the necessary trace minerals and nutrients. He adds a 33 percent margin to that number and bumps the stored food percentage up to four percent, along with an extra year’s food supply as margin in case of intermittent problems with the life support system along the way.
As to protection from galactic cosmic rays (GCR), we can create a workable but quite bulky shielded environment using these methods:
Since 99% of the GCR is ionized hydrogen or helium, it’s obvious why hydrogen makes the best shielding (because like masses scatter better). Hence, plastics with high hydrogen content were selected for the hull and shielding materials. The total shield thickness for the hull alone is about 20 gm/cm2, which will cut the dose rate to about 25 rem/year. Assuming the sleeping quarters are 3 meters by 4 meters and 2.3 meter high we can shield the walls with approximately 30 gm/cm2 of water storage (top and bottom shielded by dry storage and machinery), which should reduce the annual dose to about 15 rem. That’s three times the recommended yearly dosage for radiation workers in the USA, but within (barely) the overall guidelines for astronauts.
A Magnetic Shielding Option
But there is another way to solve the problem. Magnetic shielding, using large current loops of superconducting wire to create a protective magnetic field, could reflect or deflect charged particles around the habitat. And the advantages of using the magnetic approach are considerable.
Get this: Although the mass of the magnetic shielding support structure is close to that of the hull shielding option we looked at above, the living quarters go from a space seven meters high and ten meters long (in three levels) to a habitat 200 meters in diameter with over 6000 cubic meters of usable volume. Foil bumpers are used to break down incoming dust into atoms and ionize the result, which can be then handled by the magnetic field. We arrive at a design like the one below:
Image: Magnetically shielded interstellar habitat (to scale). Credit: Dana Andrews.
Clearly we have a long way to go before building such a vehicle, considering our own halting attempts at sustainable life support (Andrews points to the problems of Biosphere 2, and to the challenging environment aboard the International Space Station). But there is nothing to prevent us from refining these technologies, while magnetic shielding and dust particle ionization is well within the realm of conventional physics. So there are ways around the dust and radiation problem if we do venture between the stars.
Just how a workable life support system could be maintained is the subject of an intriguing appendix. The paper is Andrews, “Things to Do While Coasting Through Interstellar Space,” AIAA-2004-3706, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Fort Lauderdale, Florida, July 11-14, 2004.
by Paul Gilster | Feb 7, 2009 | Astrobiology and SETI |
Centauri Dreams‘ recent post on the Drake Equation triggered a broad range of response, both in comments and back-channel e-mails, the latter of which produced a note from Kelvin Long quoting a rather controversial position on Drake by one leading scientist. Here it is. See if it raises your hackles:
“I reject as worthless all attempts to calculate from theoretical principles the frequency of occurrence of intelligent life forms in the universe. Our ignorance of the chemical processes by which life arose on earth makes such calculations meaningless.”
The words are Freeman Dyson’s, from his essay “Extraterrestrials” in Disturbing the Universe (Harper & Row, 1979), a book I re-read every few years as much to admire the author’s rhetorical skills as to draw again on his insights. Kelvin has differing views on Drake and so do I, but I’m going to quote Marc Millis’ reaction to the Dyson statement, reflecting as it does an approach toward scientific method that I share. Marc writes:
“On Dyson’s views of ‘meaningless’ calculations, I have to agree somewhat if the sole purpose of those calculations is the answer. If, however, the purpose is to increase our wisdom from attempting to solve such seemingly impossible questions, then I vehemently disagree. The value gained in taking the time to think these things through and understand all the factors involved is much greater than the cost of doing the calculations. The improvements in the human condition come not just from what we achieve, but what we learn along the way.”
To which I’ll add that what we learn along the way is often surprising and sometimes turns back around to affect what we can achieve in new directions. Widen this out to the field of interstellar propulsion and a further thought arises. Achieving a particularly ambitious goal, such as one day developing a way to travel faster than light, may or may not be possible. But if decades and even centuries of applied study demonstrate that it is not, that result will not be a failure. We will have learned from it essential facts about the nature of the universe, and that in itself is what science, ever widening its range, properly sets out to do.
by Paul Gilster | Feb 6, 2009 | Interstellar Medium |
It would be helpful if space were a bit more empty. A key problem facing an interstellar probe would be encounters with dust in the planetary system it leaves and, as it reaches cruising speed, dust impact in space between the stars. Although our Solar System seems to be in an unusually sparse pocket of space, the galaxy-wide distribution of hydrogen is roughly one atom per cubic centimeter. Dust — bits of carbon, ice, iron compounds, and silicates — is far rarer still, but enough of a factor to a ship moving at a significant fraction of the speed of light that the designers of the Project Daedalus craft built in a payload shield 32-meters in radius to protect their starship.
Then again, much depends on your location. Have a look at the image below. It’s an area called the Red Rectangle some 2300 light years from Earth in the constellation Monoceros. Although the center of the image seems to be a single star, it’s actually the double star system HD 44179. The Red Rectangle is a nebula, a cloud of gas and dust that shows what can happen when we move into areas of intense dust concentration. You can imagine that movement through an environment like this one would demand serious shielding requirements for any craft on a mission of interstellar exploration. And although we can avoid nebulae, any interstellar flyby probe has to reckon on the gas and dust within its destination system as it screams through to study the inner planets.
Obviously, we’d like to know more about dust, and that’s a problem. Donald York (University of Chicago) states the matter baldly, saying of interstellar dust “We not only do not know what the stuff is, but we do not know where it is made or how it gets into space.” York and collaborators have been studying the Red Rectangle looking for clues, and they’ve turned up a workable hypothesis.
Image: A Hubble Space Telescope image of the Red Rectangle. What appears to be the central star is actually a pair of closely orbiting stars. Particle outflow from the stars interacts with a surrounding disk of dust, possibly accounting for the X shape. This image spans approximately a third of a light year at the distance of the Red Rectangle. Credit: Credit: NASA; ESA; Hans Van Winckel (Catholic University of Leuven, Belgium); and Martin Cohen (University of California, Berkeley).
One of the stars at the heart of the Red Rectangle nebula has burned through its initial hydrogen, collapsing upon itself until it could generate the heat to burn helium. Such stars go through a period of transition that, in a matter of tens of thousands of years, causes the star to lose an outer layer of its atmosphere. The thinking is that dust forms in this cooling layer and is then pushed out from the star by radiation pressure, along with large amounts of gas. The larger star in the Red Rectangle is too hot to concentrate dust in its atmosphere, but double-star systems like this one often show a disk of material forming around the second star, creating a jet that blows dust out into the interstellar medium. Here’s Adolf Witt (University of Toledo) with more detail:
“Our observations have shown that it is most likely the gravitational or tidal interaction between our Red Rectangle giant star and a close sun-like companion star that causes material to leave the envelope of the giant. The heavy elements like iron, nickel, silicon, calcium and carbon condense out into solid grains, which we see as interstellar dust, once they leave the system.”
Take the Red Rectangle process and make it ubiquitous and you’ve located one source for the dust that is such a factor in interstellar space. Back to Daedalus, which was designed to move at 12 percent of lightspeed for the fifty year journey to Barnard’s Star. Along with its beryllium shield for the cruise phase, Daedalus would have needed additional protection for the stellar encounter, which designer Alan Bond suggested could take the form of a cloud of dust deployed from the main vehicle, heating and vaporizing any larger particles before they could damage the payload. And because Daedalus would deploy smaller probes within the system, each would need a cloud of its own.
Gregory Matloff and Eugene Mallove once suggested that a starship could use, in addition to a shield, a high-powered beamed energy device to destroy or deflect any larger objects in its path. So the options for interstellar protection are slowly being placed on the table. But first we have to learn more about the nature of the problem, which means studies like these that tell us how dust forms in the first place. The paper is Witt et al., “The Red Rectangle: Its Shaping Mechanism and its Source of Ultraviolet Photons,” accepted for publication in the Astrophysical Journal and available online. A University of Chicago news release is available.
