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The Exploratory Imperative

by Paul Gilster | Jul 8, 2015 | Culture and Society | 19 Comments

If you're a long-time reader of this site, you doubtless share my fascination with the missions that are defining our summer -- Dawn at Ceres, Rosetta at comet 67P/Churyumov-Gerasimenko, and in the coming week particularly, New Horizons at Pluto. But have you ever wondered why the fascination is there? Because get beyond the sustaining network of space professionals and enthusiasts and it's relatively routine to find the basic premise questioned. Human curiosity seems unquenchable but it's often under assault. 'Why spend millions on another space rock?' was the most recent question I've received to this effect, but beyond the economics, there's an underlying theme: Why leave one place to go to another, when soon enough you'll just want to go to still another place even more distant? The impulse to explore runs throughout human history, but it's shared at different levels of intensity within the population. I find that intriguing in itself and wonder how it plays out in past events....

End of an Era in Planetary Exploration?

by Paul Gilster | Jul 7, 2015 | Uncategorized | 24 Comments

While both Alan Stern and Glen Fountain admitted to having anxious moments over the weekend when New Horizons went silent, it became clear at yesterday's news conference that those moments were short and quickly subsumed with ongoing duties. Stern is principal investigator for New Horizons, and the man most closely identified with making the mission a reality, while Fountain is project manager for New Horizons at JHU/APL in Maryland. It was Stern who pointed out that the spacecraft has been in safe mode a number of times already. Nine times, as a matter of fact, since launch, although as of yesterday we are back in the realm of normal operations. So the circumstances were not unfamiliar even if this safe mode came so close to destination that it raised inevitable concern and a flutter of worry on Twitter. Stern said he was in the control center six or seven minutes after getting the call that something was wrong. It also turns out that this was the first safe mode occurrence in which...

New Horizons: A ‘Timing Flaw’ Scare Resolved

by Paul Gilster | Jul 6, 2015 | Outer Solar System | 12 Comments

You get to expect the unexpected when writing about space probes, but somehow what New Horizons did to my weekend completely blind-sided me. Running a routine check of email before (I thought) sliding into the rest of a relaxing work break, I found messages about the glitch on the Pluto-bound spacecraft. Sunday turned into an all-screens-on exercise in checking multiple feeds and waiting for news. The problem with New Horizons brought to mind a short story I wrote many years ago about an unmanned probe sent to Epsilon Indi on a 90-year journey. The probe is within a month of encounter when all goes silent and Earth controllers can only wait to see what happens. The point of the story (it was called "Merchant Dying," published in Charlie Ryan's Aboriginal Science Fiction in the July/August 1987 issue) was that spacecraft going to another star are going to need autonomous repair capabilities we can only dream of today. New Horizons is a long way out, but we can still work with it...

The Spacecoach Equation

by Paul Gilster | Jul 3, 2015 | Advanced Rocketry | 38 Comments

My view is that the spacecoach, the subject of renewed discussion below by Brian McConnell and a design he and Alex Tolley have created, is the most innovative and downright practical idea for getting crews and large payloads to the planets that I've yet encountered. It's low-cost and uses ordinary consumables as propellant, dramatically revising mission planning. Brian and Alex have continued refining the concept, as explained below in Brian's essay on a modified version of the rocket equation. Have a look and you'll see that planning long duration missions or missions with larger crews becomes a much more workable proposition because more consumables translate into more propellant. Could the spacecoach be our ticket to building a space-based infrastructure, with unmistakable implications for even deeper space? by Brian S McConnell The spacecoach, first introduced here in Spaceward Ho! and A Stagecoach To The Stars and on spacecoach.org, is based on the idea of using consumables...

Thoughts on DE-STAR and Laser Sailing

by Paul Gilster | Jul 2, 2015 | Sail Concepts | 24 Comments

Last week we looked at DE-STAR (Directed Energy Solar Targeting of Asteroids and Exploration), an ambitious program for developing modular phased arrays of kilowatt class lasers. The work of Philip Lubin (UC-Santa Barbara), DE-STAR is envisioned as a way to scale up a space-based system for asteroid mitigation. And in a new NIAC grant, Lubin will study an off-shoot called Directed Energy Propulsion for Interstellar Exploration (DEEP-IN) as a way of driving tiny 'wafer' probes on interstellar journeys. Reading about these ideas, Jim Benford responded with the comments below. A plasma physicist and president of Microwave Sciences (Lafayette, CA), Dr. Benford's work on microwave beaming to sailcraft has included laboratory experiments at JPL with brother Greg that I've written about in these pages. Here are his thoughts on DE-STAR's beaming methods and the issues they invoke. by James Benford The calculations presented by the DE-STAR group are basically a revisit of the work of Bob...

Methane Detection as New Horizons Closes

by Paul Gilster | Jul 1, 2015 | Exoplanetary Science | 9 Comments

As I write, we're thirteen and a half days out from the Pluto/Charon encounter. New Horizons will make its closest approach to Pluto at 0749 EDT (1149 UTC) on July 14. All of which has had me reading Pluto-related science fiction that I missed along the way, including most recently Wilson Tucker's "To the Tombaugh Station." The story, which ran in the July, 1960 issue of Fantasy and Science Fiction, is a murder investigation that includes a journey to the station of the title, which had been established to investigate a 'Planet X' still further out in the system. Isaac Asimov has an essay on Pluto in this issue as well. Image: The cover of the July, 1960 Fantasy and Science Fiction shows a generic moon landing scene by artist Mel Hunter. But if you look at it with our post-1978 (discovery of Charon) eyes, it could be seen as an imaginative take on a Pluto landing, with the Earth on the horizon being replaced by Charon. Given the prominence of "To the Tombaugh Station" on the cover, I...

A Disruptive Pathway for Planet Formation

by Paul Gilster | Jun 30, 2015 | Exoplanetary Science | 8 Comments

Planet formation can be tricky business. Consider that our current models for core accretion show dust grains embedded in a protoplanetary disk around a young star. Mixing with rotating gas, the dust undergoes inevitable collisions, gradually bulking up to pebble size, then larger. As the scale increases, we move through to planetesimals, bodies of at least one kilometer in size, which are large enough to attract each other gravitationally. Some planetesimals break apart through subsequent collisions, but a few grow into protoplanets, then planets themselves. It's a reasonable theory that fits what we see around young stars as solar systems take hold. But what Alan Boss (Carnegie Institution for Science) has been working on is a question raised by the process: How do the dust grains and objects smaller than planetesimals keep from being drawn into the protostar before they can become large enough to attract the materials they need to grow? The pressure gradient of the gas in the disk...

A Planet Reborn?

by Paul Gilster | Jun 29, 2015 | Exoplanetary Science | 9 Comments

Objects that seem younger than they ought to be attract attention. Take the so-called 'blue stragglers.' Found in open or globular clusters, they're more luminous than the cluster stars around them, defying our expectation that stars that formed at about the same time should develop consistent with their neighbors. Allan Sandage discovered the first blue stragglers back in 1953 while working on the globular cluster M3. Because blue stragglers are more common in the dense core regions of globular clusters, they may be binary stars that have merged, but a number of theories exist, most of them focusing on interactions within a given cluster. Image: The center of globular cluster NGC 6397, in an image taken by the Hubble Space Telescope. Credit: Francesco Ferraro (Bologna Observatory), ESA, NASA. Now we may have found a planet that seems to be younger than it ought to be. Michael Jura (UCLA) and team report on the results in the Astrophysical Journal Letters, making the case that a...

The Zoo Hypothesis as Thought Experiment

by Paul Gilster | Jun 26, 2015 | Astrobiology and SETI | 56 Comments

Imagine a civilization one million years old. As Nick Nielsen points out in today's essay, the 10,000 year span of our terrestrial civilization would only amount to one percent of the older culture's lifetime. The 'zoo hypothesis' considers extraterrestrials studying us as we study animals in controlled settings. Can a super-civilization study a planetary culture for the whole course of its technological development? Nielsen, an author and strategic analyst, runs a thought experiment on two possible courses of observation, asking how we would be perceived by outsiders, and how they might relate us to the history of their own development. by J. N. Nielsen In 1973 John A. Ball wrote a paper published in Icarus called "The Zoo Hypothesis" in which he posited an answer to the Fermi paradox involving the deliberate non-communication of advanced ETI (extraterrestrial intelligence) elsewhere in our universe: "…the only way that we can understand the apparent non-interaction between...

Beaming ‘Wafer’ Probes to the Stars

by Paul Gilster | Jun 25, 2015 | Sail Concepts | 13 Comments

The last interstellar concept I can recall with a 20-year timeline to reach Alpha Centauri was Robert Forward's 'Starwisp,' an elegant though ultimately flawed idea. Proposed in 1985, Starwisp would take advantage of a high-power microwave beam that would push its 1000-meter fine carbon mesh to high velocities. As evanescent as a spider web, the craft would use wires spaced the same distance apart as the wavelength of the microwaves that drove it, which is how it could be so lightweight and yet maintain rigidity under the microwave beam. Throw in sensors and circuitry built-into the sail itself and you had no need for a separate probe payload -- Starwisp was its own payload. This was conceived as a flyby mission, in which the microwaves would again bathe the craft as it neared its target, providing just enough energy to drive its communications and sensor array to return data to Earth. What a mission: Starwisp would accelerate at 115 g's, its beam pushing it up to 20 percent of...

Capturing Sedna: A Close Stellar Encounter?

by Paul Gilster | Jun 24, 2015 | Outer Solar System | 13 Comments

With New Horizons scheduled for its flyby of Pluto/Charon in a matter of weeks and a Kuiper Belt extended mission to follow, it’s interesting to note a new paper on objects well beyond Pluto’s orbit. Lucie Jílková (Leiden Observatory) and colleagues address the problem of Sedna and recently discovered 2012VP113. The problem they present is that even at their closest approach to the Sun, these two objects are outside the Kuiper Belt, while their aphelion distances are too short for them to be considered members of the Oort Cloud. So where do Sedna and 2012VP113 belong in our taxonomy of the Solar System? Thirteen such objects have now been discovered, a group collectively referred to as Sednitos. These objects have orbital elements in common: A large semi-major axis (with perihelion beyond 30 AU and aphelion beyond 150 AU), a common orbital inclination, and a similar argument of perihelion. A common origin seems likely. Jílková’s team is interested in the possibility that Sedna and...

Charon’s ‘Dark Pole’

by Paul Gilster | Jun 23, 2015 | Outer Solar System | 12 Comments

An abrupt change: I'm holding today's post (about halfway done, on a stellar flyby that may have produced Sedna and other such objects long in our system's past) to turn to New Horizons' latest imagery, which is provocative indeed. We'll cover the Sedna story tomorrow. What we have from New Horizons is the work of the spacecraft's Long Range Reconnaissance Imager (LORRI) in a series of images that show Pluto and its largest moon Charon as they more than double in size between May 29 and June 19. There's plenty here to marvel at, but what stands out for me is the mysterious dark region that NASA's latest release refers to as 'a kind of anti-polar cap' on Charon. Have a look: Image: These recent images show the discovery of significant surface details on Pluto's largest moon, Charon. They were taken by the New Horizons Long Range Reconnaissance Imager (LORRI) on June 18, 2015. The image on the left is the original image, displayed at four times the native LORRI image size. After...

Yarkovsky and YORP Effect Propulsion for Long-life Starprobes

by Paul Gilster | Jun 22, 2015 | Uncategorized | 25 Comments

Centauri Dreams regular James Jason Wentworth wrote recently with some musings about Bracewell probes, proposed by Ronald Bracewell in a 1960 paper. Bracewell conceived the idea of autonomous craft that could monitor developments in a distant solar system, perhaps communicating with any local species that developed technology. Pondering how such a craft might manage station-keeping over the aeons, Jason hit on the idea of using a natural effect that would draw little attention to itself, one he explains below. An amateur astronomer and interstellar travel enthusiast who worked at the Miami Space Transit Planetarium and volunteered at the Weintraub Observatory atop the adjacent Miami Museum of Science, Jason now makes his home in Fairbanks (AK). He was the historian for the Poker Flat Research Range sounding rocket launch facility near Fairbanks. His space history and advocacy articles have appeared in Quest: The History of Spaceflight magazine and Space News. by James Jason Wentworth...

New Insights into Titan

by Paul Gilster | Jun 19, 2015 | Outer Solar System | 12 Comments

It's hard to consider a place with surface temperatures of -180°C 'Earthlike,' but there are reasons why we see the term so often applied to Titan. The most striking of these is the presence of surface lakes and seas, a phenomenon found nowhere else in the Solar System. The temperatures are cold enough to make the circulating fluid liquid methane and ethane rather than water, but we see things in Cassini imagery that are strikingly familiar, including seas fed by river-like channels and large numbers of shallow lakes that appear in flatter areas. The European Space Agency's Thomas Cornet has been leading a team investigating Titan's surface features in greater detail. In particular, the lakes of Titan do not appear to be fed by rivers, making it likely that they are filled either by rainfall or by liquids welling up from below. Empty depressions can be found where lakes may once have been, and it is believed that some of the lakes dry out during Titan's thirty-year cycle of...

Kepler-138b: A Mars-Size Exoplanet

by Paul Gilster | Jun 18, 2015 | Exoplanetary Science | 6 Comments

Astronomers at Penn State, NASA Ames, the University of Chicago and the SETI Institute are publishing news of an exoplanetary first: A planet smaller than Earth whose mass and size have both been measured. Kepler-138b is a Mars-sized world orbiting a red dwarf about 200 light years from Sol in the constellation Lyra. This is transit work, focusing on a system with two other transiting worlds, all three of which are too close to their parent star to make life a likely possibility. If we look back at how far exoplanet research has come in the last fifteen years, it's startling to realize that Kepler-138b, with a mass of about 6.7 percent that of the Earth, is 3000 times less massive than the first planet whose density was measured. That's the word from Eric Ford (Penn State), a co-author on the study, which is being published today in Nature, and I assume he's talking about HD 209458 b, whose size and density were first measured in 1999. Previous work on the Kepler-138 system had...

Interplanetary Updates: Philae and New Horizons

by Paul Gilster | Jun 16, 2015 | Missions | 24 Comments

Given that the Philae lander has just come to life after seven months without communicating, it's no wonder that the mood among everyone involved with Rosetta's mission to comet 67P/Churyumov-Gerasimenko is exuberant. On the surface of the comet, conditions have been improving for Philae since March, meaning that with higher temperatures and better illumination, it was hoped that the lander might reactivate. That hope was realized on June 13 when Rosetta picked up 330 data packets from an earlier segment of the lander's mission. Stephan Ulamec (DLR), Philae lander project manager, has positive things to say: "We are still examining the housekeeping information at the Lander Control Centre in the DLR German Aerospace Center's establishment in Cologne, but we can already tell that all lander subsystems are working nominally, with no apparent degradation after more than half a year hiding out on the comet's frozen surface." Image: Processed NAVCAM image of Comet 67P/C-G taken on 5 June...

A Cometary Reawakening

by Paul Gilster | Jun 15, 2015 | Missions | 5 Comments

In a summer already packed with interesting missions, we also have the unusual phenomenon of spacecraft ‘waking up’ after unexpected periods of dormancy. The European Space Agency’s Philae lander, which shut down on November 15, 2014 after operating on comet 67P/Churyumov-Gerasimenko for about sixty hours, came out of its hibernation on June 13. ESA reports more than 300 data packets have been received and are being analyzed. Image: Twitter lit up with news of Philae’s reappearance. Be sure to track @ESA_Rosetta to keep up with the latest. This first contact since November lasted for 85 seconds, and according to reports from ESA, made it apparent that the lander had been retrieving data during the time of communications blackout. This ESA update notes that there are more than 8000 data packets in Philae’s memory that can be accessed (we hope) on the next contact, giving us information about the lander’s most recent activity as the comet and orbiting Rosetta continue toward...

Pluto: Surface Features Emerging

by Paul Gilster | Jun 12, 2015 | Outer Solar System | 5 Comments

New imagery from New Horizons continues to dazzle, with the images below taken by the spacecraft's Long Range Reconnaissance Imager (LORRI) instrument from May 29 to June 2. We're beginning to pick up bright areas mixed with dark terrain in what are clearly the best images ever obtained of the remote world. As before, mission scientists are using deconvolution to sharpen the raw images and are also teasing out further details with contrast adjustments. The processing can produce artifacts so that fine details will have to be checked at closer range. Image: These images, taken by New Horizons' Long Range Reconnaissance Imager (LORRI), show four different "faces" of Pluto as it rotates about its axis with a period of 6.4 days. All the images have been rotated to align Pluto's rotational axis with the vertical direction (up-down) on the figure, as depicted schematically in the upper left. From left to right, the images were taken when Pluto's central longitude was 17, 63, 130, and 243...

Ceres Up Close (and a Bit of Bradbury)

by Paul Gilster | Jun 11, 2015 | Outer Solar System | 22 Comments

I know I'm going to remember the summer of 2015 for a long time. The confluence of deep space missions has brought new images every week, including the latest view of Ceres and its enigmatic bright spots, which appears below. I'm already bracing myself for that Voyager-like sense of deflation once New Horizons gets past Pluto/Charon and the long-anticipated targets dwindle. Pluto has a special place for some of us because we grew up with it being considered the ninth planet. Dwarf planet or not, it's the final act of a classic Solar System tour. Not that we won't be returning to many of these places, but the timing is uncertain and once Juno finishes its work at Jupiter, we'll have no missions on their way to the outer planets. That makes this summer both energizing and a bit poignant, but let's enjoy it while we can. This view of Ceres, taken on June 6, really is spectacular. We're seeing the dwarf planet from 4400 kilometers as Dawn flies its second mapping orbit. The resolution is...

Volcanism and Astrobiology

by Paul Gilster | Jun 10, 2015 | Exoplanetary Science | 2 Comments

A question in a grad school astrobiology seminar at the University of Washington prompted Amit Misra to go to work on plate tectonics. The movement of huge blocks of a planetary surface is beneficial to life because it prompts recycling, as materials move back and forth between the inside of the planet and the atmosphere. We've learned a lot about plate tectonics on Earth, but the seminar question stuck with Misra. How could we detect plate tectonics on an exoplanet? The result is a paper in press at Astriobiology. Misra and colleagues make the case that transient sulfate aerosols produced by volcanic outgassing could provide just the signature scientists need. Explosive volcanic events produced by subduction at the edges of tectonic plates inject such aerosols directly into the atmosphere, where they can persist over periods of months to years. The paper argues that future instruments like the James Webb Space Telescope or the European Extremely Large Telescope (E-ELT) will be able...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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