Huge Mountain Among Early Vesta Results

by Paul Gilster on October 13, 2011

So much has been happening in recent weeks that I haven’t had the chance to keep up with all the stories in the queue, and that’s not a bad thing considering that a high level of activity usually means we’re learning new and interesting things. Consider the Dawn mission, which has been orbiting the asteroid Vesta since the middle of July. The Dawn team has been sharing results about Vesta in multiple locations, including the European Planetary Science Congress and the Division of Planetary Sciences Joint Meeting 2011 in Nantes and the annual meeting of the Geological Society of America in Minneapolis. As expected, Vesta turns out to be an intriguing place.

The image below is a look at Vesta’s topography in the southern polar region, with the overall curvature of the tiny world removed, so you’re seeing what it would look like on a flat surface. You wouldn’t have this view on Vesta because many of the features would wrap around below the horizon, but the image gets across the scale of the asteroid’s south polar mountain, which rises a good 22 kilometers above the average height of the terrain around it. And note the large cliff on the right side of the image, which bounds part of Vesta’s south polar depression.

Image: This image of the asteroid Vesta, calculated from a shape model, shows a tilted view of the topography of the south polar region. The image has a resolution of about 1,000 feet (300 meters) per pixel, and the vertical scale is 1.5 times that of the horizontal scale. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

Everything we see here is consistent with a giant impact in Vesta’s past. The surface is rougher than most asteroids we’ve observed in the main belt, and dating methods based on the crater count imply that some areas in the southern hemisphere are 1 to 2 billion years old, quite a bit younger than areas to their north. Dawn has continued in its closing, spiraling orbit around Vesta since July, reaching an orbital altitude of 2700 kilometers in August for mapping with its framing camera and infrared mapping spectrometer. In late August, the spacecraft began to move into its High Altitude Mapping Orbit, reaching 680 kilometers above the surface on September 29.

Carol Raymond (JPL), deputy principal investigator for Dawn, told an October 12 press conference that the fundamental dichotomy between northern and southern hemispheres was striking. She also pointed to the diversity in color on Vesta’s surface:

“We expected to see some variation in reflected light from Vesta, because that has been seen before with telescopes, and we also knew something about the composition of the asteroid from meteorites. But the diversity we saw with Dawn exceeds what we would have expected. The dichotomy in the morphology of the surface is also apparent in the color of the surface. In the southern hemisphere we see colors that are consistent with the basaltic morphology you would expect from meteorite studies, and in the northern hemisphere we see a more spectrally neutral surface punctuated by very distinct color variations that appear to be associated with impacts.”

A long process of analysis lies ahead as the Dawn team works to integrate these findings with the higher resolution observations it is now collecting. When operations in the High Altitude Mapping Orbit have been completed, the spacecraft will spiral into its Low Altitude Mapping Orbit in early December, with results from that regime reported in March of 2012. Dawn will spend a year orbiting the asteroid before departing in July of 2012 for Ceres. 2015 should be a lively year, for not only will Dawn reach Ceres but New Horizons will encounter Pluto/Charon. More on Dawn’s mission in this JPL news release.

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Thoughts on a Different Apollo

by Paul Gilster on October 12, 2011

Did the Apollo missions produce enough good science to justify their cost? It’s a question Freeman Dyson has speculated on in the past, calling the missions a success because they were “conceived and honestly presented to the public as an international sporting event and not as a contribution to science.” Symbolic of this is the fact that the first item to be unpacked after each landing was the television camera that relayed mission imagery back to Earth. Apollo inevitably labored under the camera’s gaze, but no great scientific discoveries came from it, and the entertainment emphasis inevitably detracted from the missions’ scientific objectives.

Image: Buzz Aldrin leaves the lunar lander in this photo snapped by Neil Armstrong.

What might Apollo have been if it had been conceived from the start to produce good science? Imagine this: Our six Apollo landings put two astronauts each on the surface for a period of several days. At their disposal were two tons of supplies and equipment. For the entire project, Apollo gave us a total of about 50 man-days on the Moon using an aggregate 12 tons of equipment. What if Apollo had produced 40 man-days per ton of equipment instead of the 4 it actually delivered? This could have been achieved by unmanned freight carriers conducting half the landings, providing six astronauts with 60 tons of supplies and equipment, sufficient for 400 days on the Moon.

You wind up with 2400 man-days of exploration instead of the 50 we achieved with Apollo. Let me quote John Cramer on this, because I’m drawing these thoughts from a column he wrote for Analog all the way back in 1988. Dyson had been visiting the University of Washington, where Cramer was then on the physics faculty, and his last lecture there contained these thoughts. Cramer took note of the advantages a much longer stay on the Moon could have brought:

With this much time, Dyson suggested, the Apollo project might have achieved some significant science. There would have been time to explore the lunar poles , to circumnavigate the body, to set up radio-astronomy dishes on the Moon’s radio-quiet back side, to take the time to investigate and theorize and observe and test and probe. There would have been the time and opportunity to bring into play those intrinsically human skills which have lead in previous years-long voyages of discovery to new insights and understanding.

The real Apollo, of course, was carried out in a few days by test pilots operating at a dead run, with one eye on the clock and the other on the prime-time news schedule. There was simply no time for science. Dyson’s revisionist version of Apollo is another road not taken.

The Problem of Premature Choice

Apollo was a success, but on the terms the mission was built around, and it could have been done much better. The Space Shuttle, however, was something much different, an example of what Dyson refers to as the ‘Problem of Premature Choice,’ which he defines as ‘betting all your money on one horse before you have found whether she is lame.’ Translated into bureaucratic terms, this means that a project can become large enough that exploring alternative engineering methods is seen as a waste that could become embarrassing to the public officials who have supported the project all along. Thus one of several alternatives is hastily selected, the rest eliminated, and the premature selection prevents the accurate analysis of the other methods.

Dyson himself has always been an example of independent thinking, but one whose priorities in space exploration favor science, which he thinks should command center stage. As he told his University of Washington audience, the contrast between the Space Shuttle and the International Ultraviolet Explorer (IUE) is instructive. The IUE came with mirror and optics from NASA, a solar power system from ESA, and communications gear from the UK. Countless astronomers and astrophysicists have used it to study tens of thousands of stellar objects in ultraviolet and visible wavelengths, and the IUE was available when supernova SN1987A occurred, providing exceptionally useful light curves that are suddenly back in the news as we try to figure out why neutrinos observed at CERN behaved differently from those from this event.

The IUE, which had been expected to last for three years, ended up serving us for eighteen, being finally shut down in 1996, some eight years after Dyson gave his talk at the University of Washington. The IUE provided a great scientific return in a mission that remains to this day little known. Learning where the payoff is — and deciding what kind of payoff you want to achieve — is key to the process. Looking at NASA’s future as of 1988, John Cramer asked this question:

Will there be further plodding along the dismal path that has lead from the triumph of Apollo to the Challenger Disaster? Will the agency continue to place science far down in the priority queue, going always for the Premature Choice and the job security of mammoth engineering projects? Will NASA continue to withhold any investments in the future, in advanced propulsion technologies, and in new ideas? I hope not.

Choosing the Right Technology

The questions don’t seem to have changed much over the course of the last 23 years, although the scope of our ambitions has been downsized since that even earlier time (1952) when Wernher von Braun proposed a manned expedition to Mars that would have required moving 70 men and 4200 tons of equipment into orbit around the Red Planet, debarking 50 men and 150 tons of equipment to the surface in three ships, using what was essentially World War II technology.

Image: A Chesley Bonestell illustration from a 1952 issue of Collier’s showing his take on the von Braun Mars expedition.

A premature choice would have been dangerous here as well. Among the things Apollo did right was to work with adequate communications channels. Where von Braun chose a 1 kHz bandwidth for the link between the Mars expedition and Earth (essentially allowing the two to communicate via Morse code), Apollo was designed for spectacle and television, and used a communications bandwidth thousands of times broader. Dyson is all about getting the mix right, the right technology (competitively chosen) coupled to serious scientific purpose to achieve a lasting result.

John Cramer’s long-running Alternate View column in Analog can be accessed online. Talking to Cramer at the 100 Year Starship Symposium, I mentioned how useful I had found it over the years, and he told me that the site housing his column had been one of the first to appear on the Internet in Washington, preceding even the Microsoft website. Talk about getting ahead of the curve! Readers will enjoy Dr. Cramer’s take on everything from quantum mechanics to virtual reality over decades of speculation and analysis, a true resource for the interstellar minded. It’s also a source, as this 1988 column showed, of insightful commentary on getting our priorities right.

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The Snows of Enceladus

by Paul Gilster on October 11, 2011

Once again it’s time to catch up with Enceladus, the little moon that has such a huge impact on the planetary system it moves through. We’re learning, for example, how much water vapor is erupting from the features in the moon’s south polar region known as the ‘tiger stripes.’ Cassini measurements (using the Ultraviolet Imaging Spectrograph aboard the spacecraft) had pegged the rate of discharge at 200 kilograms of water vapor every second. New measurements from ESA’s Herschel space observatory match up closely to these findings. Saturn’s E-ring, formed from plume particles, would dissipate in a few hundred years without discharges like these.

You may recall that back in June, Herschel results were announced that showed a huge torus of water vapor circling Saturn itself, one that appeared to be the source of water found in Saturn’s upper atmosphere. More than 600,000 kilometers across and 60,000 kilometers thick, the enormous cloud was produced by Enceladus and picked up by Herschel’s infrared detectors. Water had previously been detected by both Voyager and Hubble in Saturn’s upper clouds, and also spotted by ESA’s Infrared Space Observatory in 1997. These earlier detections had raised the question of how water molecules were entering Saturn’s atmosphere from space.

Studying Herschel’s cloud of water vapor and running computer models that incorporated what we know of Enceladus’ plumes helped researchers put the pieces of the puzzle together. It turns out that most of the water in the torus is lost to space, but enough falls through the rings to enter the planet’s atmosphere to account for the amount of water observed there. Tim Cassidy (University of Colorado, Boulder) is one of those who worked on the data:

“What’s amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren’t expecting such detailed ‘images’ of the torus, and the match between model and data was a wonderful surprise.”

More in this NASA news release. Meanwhile, we have the announcement at the EPSC-DPS Joint Meeting 2011 in Nantes that ice particles from the plumes also fall back onto the surface of Enceladus, building up areas blanketed by super-fine snow whose present state tells us that the plumes have been active for tens of millions of years or more. We already knew that modeling particle trajectories from the plumes produced accumulation on Enceladus itself — this work was done by Sasha Kempf (Max Planck Institute) and Juergen Schmidt (University of Potsdam) in 2010. The new work, by Paul Schenk (Lunar and Planetary Institute, Houston) relies on a painstaking examination of high resolution images in areas of suspected accumulation.

The result: Smooth terrain with topographic undulations suggestive of buried fractures and craters, and changes in slope along the rims of deeper fractures, all consistent with material coating the top of solid crustal ices. The researchers have been able to apply models of deposition showing that the rate of accumulation of these ice particles is less than a thousandth of a millimeter per year. Because the average layer is 100 meters deep in the area studied, the team calculates tens of millions of years would be needed to accumulate the entire amount.

Image: Perspective view of “snow” covered slopes of Enceladus. This heavily fractured terrain lies north of the edge of the active south polar region. The largest of these fractures in the foreground is roughly 1 kilometre wide and 300 meters deep (0.6 miles wide and 1000 feet deep). The fainter dimples on the plateaus are actually older craters and fractures that appear to be covered by thick accumulations of fine particulates, sub-millimetre sized ice grains falling to the surface from the giant plumes to the south. At 12 meters per pixel (~40 feet) this view is one of the highest resolution images Cassini has obtained of Enceladus. Perspective rendering of the surface is derived from colour imaging a stereo topography of Cassini images, produced by D. Paul Schenk (Lunar and Planetary Institute, Houston). See also this ESA news release.

And so we can now talk about the ‘snows of Enceladus.’ They’re important, for their steady accumulation tells us that the heat source that drives the plumes and maintains any liquid water found under the ice crust must have been there for a long time. Schenk says the particles found here are roughly a micron or two across, making them finer than talcum powder that “would make for the finest powder a skier could hope for.” A pleasing thought, but Centauri Dreams assumes the scientist is even happier with the prospect that Enceladus’ snows will help us understand the internal heating mechanism that drives the plumes. What we need now is more high resolution imagery of a world few would have suspected would turn out to be so compelling.

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Updating the 100 Year Starship Symposium

by Paul Gilster on October 10, 2011

I’ve got an out of town speaking gig today and am pressed for time, so this may be a good occasion for something I needed to do anyway for the record, which is to highlight the papers given by Tau Zero Foundation and Project Icarus people at the recent 100 Year Starship Symposium. Most of the following were delivered as individual talks, although some were presented in panels. If you’re interested in reading the papers each author prepared for the conference, many (but not all, evidently) are to be published in the Journal of the British Interplanetary Society. I’ll deliver publishing details when they become available.

Here are the presentations of those associated with Tau Zero:

  • E. Davis, “Faster-Than-Light Space Warps, Status and Next Steps”
  • K. Denning, “Inertia of Past Futures” (anthropology)
  • P. Gilster, “The Interstellar Vision: Principles and Practice”
  • G. Landis, “Plasma Shield for an Interstellar Vehicle”
  • C. Maccone, “Sun Focus Comes First, Interstellar Comes Second (Mission concept)”
  • J. Maclay, “Role of the Quantum Vacuum in Space Travel”
  • G. Matloff, “Light Sailing to the Stars”
  • M. Millis, “Space Drive Physics, Intro and Next Steps”
  • M. Millis, “Cockpit Considerations for Inertial Affect and FTL Propulsion”
  • R. Noble, “Small Body Exploration Technologies as Precursors for Interstellar Robotics”
  • S. White, “Warp Field Mechanics 101”

You may also be interested in Slate’s take on the Symposium, which focuses on some of the breakthrough propulsion concepts at the far edge of the speculative frontier. The Smithsonian’s blog also carried an update about the conference, while MSNBC offered up a look at possible starship destinations, a major interest as we continue to lack planetary data for nearby stars. Finally, I loved Gregory Benford’s article describing the 100 Year Starship Symposium: The First Hard Science Fiction Convention.

Papers and presentations from the Icarus team in Orlando were plentiful indeed:

  • J. Benford, “Recent Developments in Interstellar Beam-Driven Sails”
  • B. Cress, “Icarus Interstellar’s New Icarus Institute for Interstellar Sciences”
  • A. Crowl, J. Hunt, “How an Embryo Space Colonization (ESC) Mission Solves the Time-Distance Problem”
  • J.R. French, “A Review of the Daedalus Main Propulsion System”
  • R. Freeland, “Fission-Fusion Hybrid Fuel for Interstellar Propulsion”
  • P. Galea, “Machine Learning and the Starship: A Match Made in Heaven”
  • A. Hale, “Exoplanet Studies for Potential Icarus Destination Stars”
  • A. Hein, “Technology, Society and Politics in the Next 100-300 Years: Implications for Interstellar Flight”
  • A. Hein, K. Long, “Exploratory Research for an Interstellar Mission: Technology Readiness, Stakeholds and Research Sustainability”
  • R. Obousy, “A Review of Interstellar Starship Designs”
  • R. Obousy, “A 21st Century Interstellar Starship Study”
  • M. Stanic, “Fusion Propulsion Comparison”
  • R. Swinney, “Initial Considerations in Exploring the Interstellar Roadmap”
  • R. Swinney, “Navigational and Guidance Requirements of an Interstellar Spacecraft”
  • A. Tziolas, “Long Term Computing”
  • A. Tziolas, “ Starflight Academy: Education in Interstellar Engineering”

Also, be aware that Ian O’Neill is continuing his coverage of the Icarus study, the latest article being a look at sex in space that circles around to starship design. Icarus team member Tiffany Frierson gives us her personal perspective on the conference (and it was a pleasure to meet Tiffany, who was often to be found circulating near the Icarus and Tau Zero tables snapping photos). Athena Andreadis presents an insightful look at the conception and preconceptions of the conference in If They Come, It Might Get Built. Finally, Centauri Dreams contributor and Astronomy Now editor Keith Cooper offers up his own take on starship design and fusion propulsion in an excellent essay that delivers helpful background and segues into the Icarus team’s thoughts on fusion’s future between the stars.

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A New Slant on ‘The Planet of Doubt’

by Paul Gilster on October 7, 2011

Among all the planets, Uranus seems to get the least play in science fiction, though it does have one early advocate whose work I’ve always been curious about. Although he wrote under a pseudonym, the author calling himself ‘Mr. Vivenair’ published a book about a journey to Uranus back in the late 18th Century. A Journey Lately Performed Through the Air in an Aerostatic Globe, Commonly Called an Air Balloon, From This Terraquaeous Globe to the Newly Discovered Planet, Georgium Sidus (1784) seems to be reminiscent of some of Verne’s work, even if it pre-dates it, in using a then cutting-edge technology (balloons) to envision a manned trip through space.

Image: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

When ‘Vivenair’ wrote, Uranus had just been discovered (by William Herschel in 1781). The author used it as the occasion for political satire, and not a very good one, according to critic James T. Presley, who described it in an 1873 article in Notes & Queries as ‘a dull and stupid satire on the court and government of George III.’ Vivenair evidently put the public to sleep, for Uranus more or less fades from fictional view for the whole of the 19th Century. More recent times have done better. Tales like Geoff Landis’ wonderful “Into the Blue Abyss” (2001) bring Uranus into startling focus, and Larry Niven does outrageous things with it in A World Out of Time (1976). But although it doesn’t hold up well as fiction, Stanley G. Weinbaum’s story about Uranus may sport the most memorable title of all: “The Planet of Doubt” (1935).

What better name for this place? The seventh planet has a spin axis inclined by a whopping 98 degrees in reference to its orbital plane — compare that to the Earth’s 23 degrees, or Neptune’s 29. This is a planet that is spinning on its side. Conventional wisdom has it that a massive collision is the culprit, but the problem with that thinking is that such a ‘knockout blow’ would have left the moons of Uranus orbiting at their original angles. What we see, however, is that the Uranian moons all occupy the same 98 degree orbital tilt demonstrated by their parent.

New work unveiled at the EPSC-DPS Joint Meeting in Nantes, France is now giving us some answers to this riddle. A team led by Alessandro Morbidelli (Observatoire de la Cote d’Azur) ran a variety of impact simulations to test the various scenarios that could account for Uranus’ tilt. It turns out that a blow to Uranus experienced when it was still surrounded by a protoplanetary disk would have reformed the entire disk around the new and highly tilted equatorial plane. The result would be a planetary system with moons in more or less the position we see today, as described in this news release.

But this is intriguing: Morbidelli’s simulations also produce moons whose motion is retrograde. The only way to get around this, says the researcher, is to model the Uranian event not as a single impact but as at least two smaller collisions, which would increase the probability of leaving the moons in their observed orbits. Given all this, some of our planet formation theories may need revision. Says Morbidelli:

“The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised.”

The questions thus raised by the ‘planet of doubt’ may prove helpful in understanding how giant planets evolve. More on this when the paper becomes available.

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Earth’s Oceans: A Cometary Source After All?

by Paul Gilster on October 6, 2011

Getting water into the inner Solar System is an interesting exercise. There has to be a mechanism for it, because the early Earth formed at temperatures that would have caused any available water to have evaporated. Scientists have long speculated that water must have been delivered either through comets or asteroids once the Earth had cooled enough to allow liquid water to exist. The former was preferred because the water content in comets is so much higher than in asteroids.

But the theory had problems, not the least of which was that comets studied in this regard showed deuterium levels twice that of Earth’s oceans. The ratio of deuterium and hydrogen, both made just after the Big Bang, can vary in water depending on its location because local conditions can affect the chemical reactions that go into making ice in space. A comparison of the deuterium to hydrogen ratio in extraterrestrial objects can be compared to water found in Earth’s oceans to identify the source of our water. Now comet Hartley 2 swings into the picture, for researchers have announced that its hydrogen/deuterium ratio is similar to Earth’s oceans.

Image: This illustration shows the orbit of comet Hartley 2 in relation to those of the five innermost planets of the Solar System. The comet made its latest close pass of Earth on 20 October last year, coming to 19.45 million km. On this occasion, Herschel observed the comet. The inset on the right side shows the image obtained with Herschel’s PACS instrument. The two lines are the water data from HIFI instrument. Credit: ESA/AOES Medialab; Herschel/HssO Consortium.

So how do you measure the hydrogen/deuterium ratio in the water of a comet? The answer is an instrument called HIFI, which operates aboard the European Space Agency’s Herschel infrared space observatory. HIFI (Heterodyne Instrument for the Far Infrared) is a high-resolution heterodyne spectrometer developed in The Netherlands that covers two bands from 480-1250 gigaHertz and 1410–1910 gigaHertz. Herschel was examining the comet’s coma, which develops as frozen materials inside vaporize when the comet moves closer to the Sun.

Remember, previous comet studies had found hydrogen/deuterium ratios different from our oceans. The difference between these comets and Hartley 2 may be that Hartley 2 was formed in the Kuiper Belt, whereas other comets studied in this regard are thought to have first formed near Jupiter and Saturn before being flung out by the gravitational effects of the gas giants, returning millions of years later for their pass around the Sun. The hydrogen/deuterium ratio we see in water ice may well have been different in the Kuiper Belt than in ice that first formed in the inner system, where conditions are much warmer. Further comets studies may confirm the idea.

Says Dariusz Lis (Caltech):

“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth.This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”

Surely the early oceans were the result of both comet and asteroid impacts, but the new findings point back to comets as major players. Even so, we have plenty of work to do to understand the role of the lightest elements and their isotopes in the early Solar System. Six comets besides Hartley 2 have been examined for hydrogen/deuterium levels, all with deuterium levels approximately twice that found in Earth water. Kuiper Belt comets were once thought to have even higher deuterium levels than Oort Cloud comets, an idea the Hartley 2 results have now refuted.

The team led by Paul Hartogh (Max Planck Institute for Solar System Research) has also used the Herschel Observatory to measure the hydrogen/deuterium ratio in comet 45P/Honda-Mrkos-Pajdusakova, another Kuiper Belt comet whose data is now under analysis, so we may soon have new data to add to this story. The paper is Hartogh, “Ocean-like water in the Jupiter-family comet 103P/Hartley 2,” published online in Nature 5 October 2011 (abstract).

And there is further news out of the joint meeting in Nantes, France, of the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences, where this work was announced. As noted in this article in Nature, a new study of the Sun-like star Eta Corvi, which is roughly the same age our Sun was during the Late Heavy Bombardment (when most water is thought to have been delivered to the Earth), shows that the star has an inner ring of warm dust that is rich in carbon and water. Team leader Carey Lisse (JHU/APL) thinks we’re seeing the traces of one or more Kuiper Belt-class comets being flung into the inner system, colliding with a planet there to form the ensuing ring of material.

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Resonance and Probability Around Kepler-18

by Paul Gilster on October 5, 2011

Three planets recently discovered through Kepler data provide an interesting take on how we look at smaller planets. Not that the planets around the star designated Kepler-18 are all that small — two of them are Neptune-class and one is a super-Earth. But what is becoming clear is that given the state of our current technology, we’ll have to get used to a process different from planet verification as we move to ever smaller worlds. The technique is being referred to as planet validation — it helps us determine the probability that the detected object could be something other than a planet.

Image: The orbits of the three known planets orbiting Kepler-18 as compared to Mercury’s orbit around the Sun. Credit: Tim Jones/McDonald Obs./UT-Austin.

The new system shows how this works. Kepler-18 is a star similar to ours, about 10 percent larger than the Sun and with 97 percent of the Sun’s mass. Around it we have Kepler-18 c and d, which turn up through transits. Planet c has a mass of about 17 Earths and is thought to be some 5.5 times the size of Earth. Its orbit takes it around Kepler-18 in 7.6 days. Kepler-18 d is 16 times as massive as the Earth, 7 times Earth’s size, and orbits its primary in 14.9 days. These two Neptune-class worlds are, interestingly enough, in a 2:1 resonance: Planet c orbits the star twice for every single orbit of planet d. The demonstrable resonance is ample proof that these are planets in the same system and not something else mimicking a planetary signature.

But the super-Earth, Kepler-18 b, is something else again. A team led by Bill Cochran (University of Texas at Austin) went to work with the 5-meter Hale Telescope at Palomar, aided by adaptive optics, to examine Kepler-18 to see whether the transit signal they thought to be a super-Earth was genuine. Finding no background objects that could have influenced the finding, they were able to calculate the odds that Kepler-18 b is not a planet at 700 to 1. Cochran thinks this process of planet validation is going to become much more significant as Kepler brings in new data:

“We’re trying to prepare the astronomical community and the public for the concept of validation. The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we’ll have to use a validation process, rather than a confirmation process. We’re going to have to make statistical arguments.”

So we can with a high degree of probability rule out any of the objects — stars, background galaxies — that might in any way compromise the transit data. The planetary signature of the super-Earth seems real enough, though established in a different way than Kepler-18 c and d, whose gravitational interactions can be readily demonstrated. The planet is thought to be 6.9 times Earth mass and twice Earth’s size. All three worlds orbit much closer to their parent star than Mercury does to the Sun, the super-Earth Kepler-18 b being the closest, with a 3.5 day period.

We can also deduce an interesting possibility about Kepler-18 b, as noted in the paper:

The inner, 3.5-day period planet Kepler-18b, is a super-Earth that requires a dominant mixture of water ice and rock, and no hydrogen/helium envelope. While the latter cannot be excluded simply on the basis of the planet’s mass and radius, the evaporation timescale for a primordial H/He envelope for a hot planet such as Kepler-18b is much shorter than the old age derived for the Kepler-18 system, and such a H/He envelope should not be present. Thus, despite its lower equilibrium temperature, Kepler-18b resembles 55 Cnc e and CoRoT-7b… Kepler-18b, together with 55 Cnc e… are likely our best known cases yet of water planets with substantial steam atmospheres (given their high surface temperatures).

The discovery was announced at a joint meeting of the American Astronomical Society’s Division of Planetary Science and the European Planetary Science Conference in Nantes, France. More on the Kepler-18 results in this news release from the University of Texas at Austin. Look for these results in an upcoming issue of the Astrophysical Journal Supplement Series devoted to Kepler, which will appear in November. The paper is Cochran et al., “Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements” (preprint).

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Initial Thoughts on the Starship Symposium

by Paul Gilster on October 3, 2011

I’m just back from the 100 Year Starship Symposium. The thoughts below were written yesterday evening (the 2nd), just after the event ended.

It’s a lovely evening here in Orlando, one I’m enjoying while sitting out in front of the Hilton waiting for my taxi. I got a chuckle out of the audience at my talk at the 100 Year Starship Symposium when I mentioned something that is completely true: I’m actually a very retro kind of guy. Sure, starships are a passion, but I also restore old fountain pens, love film noir, and as I told the audience, chose an overnight sleeper train to come to Florida in rather than an aircraft.

They enjoyed the observation, probably because we’re all an odd mix of personally defined and often contradictory impulses. But as I soak up this gorgeous Florida evening, I’m feeling a profound singleness of purpose. To begin with, it’s clear to me that writing about the starship conference won’t be a matter of a single Centauri Dreams entry but rather a series of thoughts and recollections that will be scattered through any number of future articles. The experience was obviously memorable, the largest conference devoted to interstellar flight that I could have imagined, and as David Neyland, its organizer, told me, it happened because so many people came from so far in the service of a numbingly futuristic idea.

People like my friend Adam Crowl, who came all the way from Brisbane, Australia, and with whom I enjoyed good conversation throughout the event. People like Kelvin Long, the man whose inspiration put Icarus into operation, who came with fellow Icarus people like Pat Galea and Rob Swinney from the UK and Andreas Tziolas from Alaska. Marc Millis and I found an excellent Italian restaurant, and the next night I had a wonderful dinner conversation with Greg Benford over salmon and a superb Carneros Pinot Noir (thanks Al Jackson for picking up the wine tab!). I enjoyed my chats with Jim Benford as well, and it was great to see Richard Obousy, who came over from Texas. Special thanks to the many Centauri Dreams readers who introduced themselves as I walked between sessions.

If I had one criticism of what happened here, it’s that there were so many good papers to listen to, so many good people to hear, that the multi-track structure made it impossible to do everything I would have wanted to do. Michael Michaud’s paper on the long term implications of interstellar flight was a priority for me, but I had also committed to a number of readers that I would cover one of the breakthrough propulsion sessions — I was using Twitter to do a bit of live ‘micro-blogging’ — and I not only missed Michael’s talk, but found myself sitting on the floor typing, the session being completely packed as Marc Millis, Jordan Maclay, Eric Davis and Sonny White talked space drives and Alcubierre theory.

OK, you choose. Which of these would you go to and which would you regret missing:

  • “A Review of Interstellar Starship Design” – Richard Obousy (Icarus Interstellar)
  • “Light Sailing to the Stars” – Greg Matloff (New York City College of Technology)
  • “Mass Beam Propulsion: An Overview” – Gerald Nordley
  • Panel: “Structuring the 100 Year Starship” – Mae Jemison, moderator (The Jemison Group)
  • “Making Aliens” – Athena Andreadis
  • “Star Probes and ET Intelligence” – Stephen Baxter

It wasn’t easy, and it was like that all the time.

On the last day, we had a late meeting among Tau Zero and Icarus people and by the time we finished, almost everyone had left the conference facility. The venue was suddenly deserted and quiet, with that eerie sense you get when an enormous structure, seemingly at once, becomes empty. We found unused symposium programs and posters leaning up against a table. Think about this, I joked. We could collect all these and in twenty years, who knows what they would bring on eBay! We were laughing about this but I did cast a wistful glance back. Maybe we really should have picked the extras up…

Anyway, this was really a four-day conference packed into the equivalent of two days, so we were all running from paper to paper, session to session, with little time for breaks and even less time for meals until the day was over. A new meme was emerging – the ‘interstellar buzz’ – and it was palpable. I think everyone was as jazzed as I was about the fact that this meeting was even happening. How often do I get to chat with Jill Tarter in the elevator, catch up on the latest from my friend Claudio Maccone or have dinner conversation with John Cramer and Marc Millis talking about the CERN neutrino results?

Not that I was doing the talking in that conversation — I’m a writer, not a scientist, and I was in Orlando to keep learning as much as I could about a topic that’s so multi-faceted and rich that every new nugget uncovered seems to expose an even deeper vein of ore. So there was much listening to be done, banking on the willingness of scientist after scientist to share ideas and point me in the direction of further sources.

We managed plenty of Tau Zero and Icarus business as well, so in the rare free time discussions continued. The Icarus team was all over the place, and I quickly learned that if I stood even for a moment at the Tau Zero table, I would get pulled into a conversation related to one or the other (as well as my Tau Zero duties, I serve as a consultant for Icarus). My sense is that the starship conference is getting lots of pop from the media, which leads to the question of how long the interstellar buzz can be maintained. Time will tell, but my major goal long-term is to see the public getting back into the space game in terms of enthusiasm and interest, and turning Apollo-like passions toward the interstellar deep.

Can that happen? Maybe some day, and I’m not so unrealistic as to expect that a single symposium can make it happen overnight. But Dave Neyland had the right idea when he got DARPA into this game, because the DARPA imprimatur brought an intensity of focus that the community had been lacking. People who work on these topics invariably do so in their spare time. They’re separated not only by distance but the pressures of work and only occasionally see each other at conferences. An event like this can reveal how concentrated is their interest and how wide their potential audience, as long as we can build on what happened here.

I ran into a friend as I was waiting for my taxi who told me the whole thing was making him emotional, and I had something of the same reaction. What has to be said about many of the people working in this area is that they do it not only because of the utter fascination of the challenge, but because getting to the stars is a multi-generational quest for them, one they generally (though not universally) assume will not be achieved in their lifetimes, but one they believe with a passion their descendants will experience. And it is with a deep sense of commitment that they come forward to offer up their expertise for this gift to an unknowable futurity.

Emotional? Sure. Interstellar flight has long been talked about and it fills the pages of science fiction, but to see some of the best minds in a host of disciplines attacking it as a scientific problem and actually planning to create an organization that can last long enough to bring it seriously closer is a powerful experience. I’m now writing this in Orlando’s train station, having caught that taxi and resumed my work afterwards, and the sense that this was a once in a lifetime event just won’t go away. We’ll have other interstellar gatherings, but this one feels like a game-changer, one we’ll be talking about in various ways for a long time.

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100 Year Starship Meeting

by Paul Gilster on September 30, 2011

Arrived yesterday afternoon at the Orlando Hilton for the 100 Year Starship Symposium. I’ll try to get updates out on my Twitter feed @centauri_dreams when possible. The WiFi here has been mostly good but it did go down this morning for a time, so bear with me.

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Lost in Time and Lost in Space

by Paul Gilster on September 29, 2011

by Dave Moore

Dave Moore, a frequent Centauri Dreams contributor, tells me he was born and raised in New Zealand, spent time in Australia, and now makes his home in California. “As a child I was fascinated by the exploration of space and science fiction. Arthur C. Clarke, who embodied both, was one of my childhood heroes. But growing up in New Zealand in the 60s, anything to do with such things was strictly a dream. The only thing it did lead to was to getting a degree in Biology and Chemistry.” But deep space was still on Dave’s mind and continues to be, as the article below, drawing on his recent paper in the Journal of the British Interplanetary Society, attests. “While I had aspirations at one stage of being a science fiction writer,” Dave adds, “I never expected that I would emulate the other side of Arthur C. Clarke and get something published in JBIS.” But he did, and now explains the thinking behind the paper.

The words from “Science Fiction/Double Feature” in the Rocky Horror Picture Show seem particularly apt after looking into the consequences of temporal dispersion in exosolar technological civilizations.

And crawling on the planet’s face
Some insects called the human race . . .
Lost in time
And lost in space
. . . and meaning.
All meaning.

Hence the title of my paper in a recent issue of the Journal of the British Interplanetary Society (Vol. 63 No. 8 pp 294-302). The paper, “Lost in Space and Lost in Time: The Consequences of Temporal Dispersion for Exosolar Technological Civilizations,” grew out of my annual attendance at Contact in San Jose, an interdisciplinary convention of scientists, artists and science fiction writers. From the papers presented there, I got a general feeling for the state of play in the search for extraterrestrial civilizations but never felt inclined to make a contribution until it occurred to me to look at the results of Exosolar Technological Civilizations (ETCs) emerging at different times. It would be an exercise similar to many that have been done using the Drake equation only, but instead of looking at the consequences of the spatial dispersion, I’d be looking at the consequences of different temporal spreads.

My presentation of the results and my conclusions went over sufficiently well that it was suggested that I turn it into a paper, but not having any experience in publishing papers, I let the project drop until Paul got to see my musings and suggested JBIS as a suitable forum.

The Separation Between Civilizations

The core of the paper is a table showing the number of ETCs you would get and their average separations assuming they arose at various rates from a starting point four billion years ago.

I used an idealized galaxy which was a disk of uniform stellar density, that of our solar neighborhood, to keep things simple. (For the justification of why this is a reasonable assumption and to why it seems quite likely that potential life-bearing planets have been around for eight billion years, I’ll refer you to my paper.)

One of the first things I realized is that the median age of all civilizations is entirely independent of the frequency at which they occur. It’s always approximately one-third the age of the oldest civilization. If ETCs start emerging slowly and their frequency picks up (a more likely scenario), this skews the median age lower, but you are still looking at a period of about a billion years.

And the median age of all civilizations is also the median age of our nearest neighbor. There’s a fifty/fifty chance it will be either younger or older than that, but there’s a 90% chance it will at least be 10% of the median, which means that in all likelihood our nearest neighbor will be hundreds of millions of years older than us. And, if you want to find an ETC of approximately our own age, say within a thousand years of ours, you will on average have to pass by a million older to vastly older civilizations. As you can see from columns 5 and 6 in the table, if ETCs haven’t emerged with sufficient frequency to produce a million civilizations, then you won’t find one.

Once you realize that ETCs are not only scattered through vast regions of space but also scattered across a vast amount of time, then this casts a very different light on many common assumptions about the matter. Take the idea very prevalent in a lot of literature that the galaxy is full of approximately coequally-aged civilizations (emerging within a thousand years of each other), a scenario I will call the Star Trek universe. If you look at the bottom row of the table, you can see there are simply aren’t enough stars in our galaxy for this to work.

After discovering that when dealing with extraterrestrial civilizations, you are dealing with great age, I then began to look at the sort of effects great age would have on civilizations.

Age and Power

The first thing I did was to extrapolate our energy consumption, and I discovered that at a 2% compound growth rate our civilization would require the entire current energy output of the galaxy (reach a Kardashev III level) in less than 3000 years, which doesn’t look likely unless a cheap, convenient, FTL drive get discovered. What this does point out though is that in extraordinarily short times, geologically speaking, civilizations can theoretically grow to enormous power outputs.

The next thing I did was to review the literature on interstellar travel. Many of the interstellar propulsion scenarios have power requirements that cluster around the 100 Terawatt level. This is a million times that of a proposed 100 MW nuclear powered Mars vessel, which is considered to be within our current or near future range of capabilities. Assuming a society with a million times our current power consumption would find a 100 TW vessel similarly within its capabilities, then our first interstellar vessel would be 700 years into our future at a 2% growth rate.

Are these energy levels feasible? If Earth continues its current growth in energy consumption, we will overheat our planet through our waste heat alone in the next century, never mind global warming through CO2 emissions. So, it looks as if we remain confined to our planet, we will probably never have the ability to send out interstellar colony ships. There is, however, a way to have our civilization reach enormous energy levels while still within our solar system.

Our solar system may have as many as a trillion comets and KBOs orbiting it, ten times the mass of the Earth, all nicely broken up. (There may be more comets in our solar system than there are stars in our galaxy.) And as this is the bulk of the easily accessible material, it would be logical to assume that eventually this is where the bulk of our civilization will finish up.

A hydrogen-fusion powered civilization could spread throughout our cometary belt, and with no grand engineering schemes such as the construction of a Dyson sphere, it could, through the cumulative growth of small, individual colonies, eventually build up a civilization of immense power and size. For example, if each of a 100 billion comets were colonized with a colony that used 1000 MW of power (a small city’s worth) then the total civilizational power consumption would be in the order of 1020 Watt. Pushing it a bit, if there was a 20,000 MW colony on each of the 5 trillion comets in the Oort cloud and the postulated Hills cloud, then the total civilizational power consumption would be 1023 Watt, that of a red dwarf star.

For this society, interstellar colonization would be but another step.

The End of a Civilization

Ian Crawford has done some analysis of galactic colonization using a scenario in which a tenth-lightspeed colony ship plants a colony on a nearby star system. The colony then grows until it is capable of launching its own ship, and so on. This produces a 1000-2000 year cycle, with the assumptions I’ve been using, but even if you work this scenario conservatively, the galaxy is colonized in 20 million years, which is an order of magnitude less that the expected age of our nearest neighbor.

Of course, all the previous points may be moot if a civilization’s lifetime is short, so I then looked into the reasoning advanced for civilizational termination.

Various external causes have been postulated to truncate the life span of a technological civilization–Gamma Ray Bursters are a favorite. When you look at them though, you realize that anything powerful enough to completely wipe out an advanced technological civilization would also wipe out or severely impact complex life; there’s at most a 10,000 year window of vulnerability before a growing civilization spreading throughout the galaxy becomes completely immune to all these events. This is one fifty-thousandth of the 500 million years it took complex life to produce sentience. So any natural disasters frequent enough to destroy a large portion of extraterrestrial civilizations would also render them terminally rare to begin with. If extraterrestrial civilizations do come to an end, it must be by their own doing.

There’ve been numerous suggestions as to why this may happen, but these arguments are usually anthropocentric and parochial and not universal. If they don’t apply to just one civilization, that civilization can go on to colonize the galaxy. So, at most, self-extinction would represent but another fractional culling akin to the other terms in the Drake equation. There’ve also been many explanations for the lack of evidence of extraterrestrial civilizations: extraterrestrials are hiding their existence from us for some reason, they never leave their home world, our particular solar system is special in some way, etc., but these are also parochial arguments; the same reasoning applies. They also fail the test of Occam’s razor. The simplest explanation supported by the evidence is that our civilization is the only one extant in our galaxy.

Into the Fermi Question

The only evidence we have about the frequency and distribution of ETCs is that we can find no signs of them so far. This has been called the Fermi paradox, but I don’t regard this current null result as a paradox. Rather I regard it as a bounding measurement. Since the formation of the Drake equation, two major variables have governed our search for ETCs: their frequency and longevity. This leads to four possibilities for the occurrence of Exosolar civilizations.

  • i) High frequency and longevity
  • ii) High frequency and short life spans
  • iii) Low frequency and longevity
  • iv) Low frequency and short life spans

These four categories are arbitrary, in effect being hacked out of a continuum. The Fermi paradox eliminates the first one.

We can get a good idea of the limits for the second by looking at an article that Robert Zubrin did for the April 2002 issue of Analog. In it, he postulated a colonization scenario similar to Ian Crawford’s but cut the expanding civilizations off at arbitrary time limits. He then found the likelihood for Earth having drifted through the ETCs’ expanding sphere of influence in the course of our galactic orbit. The results indicated that unless all civilizations have lifetimes of under 20,000 years, we are very likely to have been visited or colonized frequently in the past. But to have every civilization last less than a specified time requires some sort of universalist explanation, which is hard to justify given the naturally expected variation in ETCs’ motivation.

Nothing that we had seen so far eliminates the third possibility however.

Implications for SETI Strategy

Finally, in the paper, I turned to reviewing our search strategies for ETCs in light of what has been learned.

Given that ETCs will most probably be very distant and have a high power throughput, then looking for the infrared excess of their waste heat looks like a good bet. Low frequency but high power also implies searching extra galactically. Take the Oort cloud civilization I postulated earlier and assume it colonizes every tenth star in a galaxy like ours. Its total power consumption would be in the order of 1030 Watt. This would show up as an infrared excess of one part in 107 to 108 of a galaxies’ output.

I found other ideas like searching for ancient artifacts and using gravitational lensing for a direct visual search seem to have some potential, but when I looked at radio searches, this turned out to be one of the least likely ways to find a civilization. The problem quickly becomes apparent after looking at Table I. Any ETCs close enough to us to make communication worthwhile will most likely be in the order of 108 to 109 years old, which gives them plenty of time to become very powerful, and therefore highly visible, and to have visited us. If civilizations occur infrequently, as in the top row of Table I, then the distances are such that the communication times are in the order of 10,000 years. If civilizational lifetimes are short but the frequency is high, then you still have enormous distances. (You can use Table I to get some idea of the figures involved. The last two columns show the distances at various frequencies for civilizations within 1000 years of our age. For ten thousand years move those figures up one row, for 100,000 years two rows, etc.) Under most cases, the signal reply time to the nearest civilization will exceed the civilizations’ lifetime–or our patience. Looking for stray radio signals under the distant but short-lived scenario does not look very hopeful either. To send a signal tens of thousands of light years, an effective isotropic radiated power of 1017 – 1020 Watts is required, and while this is within sight of our current technology, the infrastructure and power levels are far in excess of anything required for casual communication even to nearby stars.

The results of all my thinking are not so much answers but, hopefully, a framing for asking the right questions.

Considerations in SETI searches have tended to focus on the nearby and a close time period and were set when our knowledge in this field was in its infancy. There’ve been some refinements to our approach since them, but generally our thinking has been built on this base. It’s time to carefully go over all our assumptions and reexamine them in the light of our current knowledge. The Fermi paradox needs to be explained — not explained away.

The paper is Moore, “Lost in Time and Lost in Space: The Consequences of Temporal Dispersion for Exosolar Technological Civilisations,” JBIS Vol. 63, No. 8 (August 2010), pp. 294-301.

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