“With your help, we are looking for planets around other stars.” So begins a first-time user’s introduction to Planet Hunters, an online citizen science project that delivers exactly what many of us have been hoping for since the first Kepler results came in — a chance to use our own computers to help analyze data taken by the mission. Kepler has been in operation for the better part of two years now, accumulating what Yale astronomer Kevin Schawinski calls ‘another mountain of data to sort through.’ What better way to sort than with distributed computing?
Schawinski is a co-founder of Planet Hunters, and was deeply involved in the creation of the successful Galaxy Zoo project several years back. In the latter, the involvement of average citizens in astronomy took off, to the tune of hundreds of thousands of Web users sorting through a million images of galaxies and classifying them. Kepler presents its own challenges, monitoring almost 150,000 stars in the constellations of Cygnus and Lyra. The trick with Kepler is to look for the characteristic dimming of a star that could signify a planetary transit.
From the Planet Hunters site:
NASA’s Kepler spacecraft is one of the most powerful tools in the hunt for extrasolar planets. The Kepler team’s computers are sifting through the data, but we at Planet Hunters are betting that there will be planets which can only be found via the remarkable human ability for pattern recognition.
This is a gamble, a bet if you will, on the ability of humans to beat machines just occasionally. It may be that no new planets are found or that computers have the job down to a fine art. And yet, it’s just possible that you might be the first to know that a star somewhere out there in the Milky Way has a companion, just as our Sun does. Fancy giving it a try?
Not every star that dims is experiencing a transit, but some are, and our profoundest hope for Kepler is that it will tease out the signature of a planet not so different from our Earth, a small world in an orbit that would keep water liquid at the surface. Planet Hunters draws on the fact that Kepler data are being released into the public domain. It’s not directly tied to the Kepler mission, but should serve as a useful adjunct to what the Kepler team is doing as it sorts through Schawinski’s ‘mountain.’ The more human intelligence on the job, the better.
Not that computers aren’t critical to the work at hand. But another co-founder of Planet Hunters, Yale’s Meg Schwamb, notes what a good set of eyes and human intelligence bring to the data our computers deliver to the desktop:
“…computers are only good at finding what they’ve been taught to look for, whereas the human brain has the uncanny ability to recognize patterns and immediately pick out what is strange or unique, far beyond what we can teach machines to do.”
That’s the great virtue, proven over time, of the Galaxy Zoo project. In the case of Planet Hunters, the method is to answer a series of questions about the light emitted by a particular star over time, its light curve. Such graphs help astronomers identify the dimming caused by a planetary transit. Planet hunter extraordinaire Debra Fischer notes that even with data from an instrument as precise as the Kepler telescope, picking out the transit signal is exceedingly hard. “Planet Hunters is an experiment,” adds Fischer. “We’re looking for the needle in the haystack.”
Here’s a Planet Hunters video that walks you through the basics of using the site:
Have a look at some of the Planet Hunters introductory material to see how absorbing this work can be. Light curves are stuffed with scatter and often reveal nothing but statistical noise. Some, however, show variability with time. Variability in a light curve is readily caused by starspots, but there are planets hiding within some of these curves, and human classification supplements computer analysis to flag patterns whose variability appears particularly promising. Obviously, large planets with short orbital periods are the easiest targets, while small planets with long periods — the ultimate quarry in the eyes of many planet hunters — require long observation.
It should be obvious by now that citizen science can make serious contributions. If Planet Hunters finds a possible transiting planet, the procedure is to match that potential world up against the Kepler team’s own list of transiting planets. It may be that the light curve is already under investigation, and users will be notified of that fact.
If not, and if several of the Planet Hunters team are flagging the same data, the science team investigates and, if a discovery appears in the offing, the team will obtain spectroscopic data using the Keck instrument in Hawaii. A transit candidate that gets through all these tests will be submitted for publication, with the Planet Hunters participants involved listed as co-authors. Interested? I hope the Planet Hunters site is ready to go, because I expect the initial response will be robust.
Start with Buzz Aldrin’s footprint. Neil Armstrong took the iconic photo that ran around the world — it wasn’t the first footprint on the Moon because neither man took a photo of that, but Aldrin’s ridged bootprint will suffice. Blow the footprint up to full size and it fits neatly across two pages in Richard Gott and Robert Vanderbei’s new book Sizing Up the Universe (National Geographic, 2010). It’s emblematic of Apollo, of our aspirations and, perhaps, of hopes once again deferred.
But Gott and Vanderbei aren’t making points about Apollo. They’re up to bigger things, much bigger things. Blow the scale up so that you have a view a thousand times larger than the photo of the bootprint and you can now see an entire asteroid (Itokawa) on the two-page spread, along with a Space Shuttle, the International Space Station and the Hubble Space Telescope. And now things really take off. Blow the scale up to 1:1 million and we can fit a good portion of the arc of Enceladus onto the pages, along with assorted asteroids and comets and a neutron star.
An Expanding View of an Expanding Universe
You get the idea. In the pages of this indescribably lovely volume, enlivened with celestial photography (much of it taken by Vanderbei himself), the two authors set about getting across the scale of things, a subject I played with briefly yesterday as we considered the journey of the Voyager spacecraft. 1:1 billion lets us fit Jupiter and Saturn onto the two-page spread, along with Neptune and Uranus and a host of Kuiper Belt objects and, at lower right, a bit of Proxima Centauri. We’re measuring the size of things, not their position, and when we reach 1:1 trillion, we can fit Rigel on the page, the inner Solar System, and the black hole at galactic center.
How far do we have to go to fit the entire visible universe onto a page? The answer is 1:1 octillion, which is 1027. At that scale, with a clever ‘You are here’ in the center of the spread, we can see everything from the cosmic microwave background to the quasars and galaxies, including the Sloan Great Wall, measured by Gott and entered into the Guinness World Records 2006 as the ‘largest structure in the universe.’ Surely by now we’re through — the Sloan Great Wall, after all, stretches for 1.37 billion light years, one tenth the radius of the visible universe.
But maybe we’re only through in a visual way. Alan Guth’s theory of inflation, which explains so much about what we see in the cosmic microwave background, tells us that the true size of the universe is far greater than what we see. We could take the scale up to 1 googol, which would be 10100 – a one with one hundred zeroes behind it — but that might not catch the true scope of things. Andrei Linde has speculated that our universe could be 1040,000 times larger than what we can see, a runaway expanding universe formed from what Gott and Vanderbei call a ‘high-density inflationary sea of dark energy,’ a dark energy with repulsive gravitational effects whose inflation, at least in our region, ends when the dark energy converts to thermal radiation.
We’ve reached the era of the big bang and its immediate aftermath. Inflation ends but the universe continues to expand. Gott’s own view embraces Linde’s belief that inflationary regions give birth to other inflationary regions through quantum fluctuations, a process he likens to branches growing off a tree. It’s a tree that keeps sprouting branches that grow up to be as big as the trunk, an infinite fractal tree that keeps growing forever. Listen to Gott on this possibility:
Our universe is just one of many on one of these branches. We will never see these other branches, because the space separating us from them is expanding so fast that light can never cross it. Where did the trunk come from? Perhaps it simply popped into existence by a process called quantum tunneling, as proposed by Alex Vilenkin. Or perhaps it formed a time loop, as proposed by me (Gott) and Li-Xin Li, when a branch looped back in time to grow up to be the trunk. We simply don’t know. Super-string theorists Paul Steinhardt and Neil Turok have suggested that our universe is a three-dimensional membrane floating in a ten-dimensional space and that the big bang occurred when our membrane collided with another.
Image: To fit M31, the Andromeda galaxy, into a two-page spread, the scale would have to be 1:1 sextillion. 1 sextillion equals 1021. From the Earth’s surface, M31 appears 2.5 degrees across, five times as wide as the full Moon, but even with a small telescope, we can see only the bright, inner regions, so it appears much smaller. If we had better eyesight, we could see more than a dozen faint objects in the night sky with an apparent size larger than the Moon. Photo credit and copyright: Robert Gendler.
Size, Shape and Context
Gott’s proposal that multiple universes formed from a time loop seems a fitting way to end a book that explores size and scale from the very small to the infinitely large, touching along the way on how ancient astronomers made sense of our planet’s shape and distance from the Sun, how astronomers relate apparent to actual size, and how the entire visible universe can be represented on a single map. Gott manages the latter feat with a well-known four-page gatefold spread of the universe that he has updated and published for the first time in a book. No small part of the narrative is the art of mapping itself, how to render vast concepts like this on a visual but correct scale.
Long an admirer of Gott’s writing (don’t miss his Time Travel in Einstein’s Universe), I had the pleasure of meeting him at a conference in Princeton a few years back, where co-author Vanderbei entertained the scientists with a slide show of images he had made in his driveway. Vanderbei had discovered what other amateur astronomers have learned, that good amateur equipment with the help of CCDs and digital cameras can capture images even in light-polluted areas. Many of the photos he took for this volume seem, at first glance, to be the work of a major observatory, a tribute to what has become possible as amateurs join professionals in making contributions to astronomy.
Opening the book at random, I’m looking at photos of two sunsets, one showing a beautiful yellow Sun hanging over a seascape with rugged terrain in the background, the sky a deep amber. On the facing page is a shot taken by the Spirit rover at Gusev crater on Mars in 2005. Here the Sun is likewise low on the horizon, just touching the rim of a distant hill, but now it’s a white Sun, the atmosphere being too thin to allow the scattering of blue light that turns an Earthly sunset into a sea of color.
Image: A Martian sunset. Credit: NASA/JPL.
These scenes remind me that the book is all about comparing one thing to another to tease out the reasons for the differences between them. Aristarchus of Samos (320-250 BC) looked at the celestial sphere conceived by Eudoxus (408-355 BC) and saw a different kind of rotation, that of the Earth itself. He went on to measure the angle between the Moon and the Sun as seen from Earth to gather data sufficient to calculate the distance of the Sun (19 times farther away than the Moon, he thought, and thus much larger than it), and concluded that the Earth orbited the Sun 1700 years before Copernicus. The answers are in the natural world if you know where, and how, to look.
Deepening the View
We can still do things in our Solar System the way I remember them being done in grade school — reduce the Earth to the size of a marble (this is a 1:1 billion scale) and Jupiter becomes the size of a grapefruit, and so on. But we’ve learned so much since those days about the true size of things at the upper end. Consider: The Hubble Ultra Deep Field survey saw 10,000 galaxies in only a tiny fraction of sky. Extrapolating from it, we can estimate that more than 140 billion such galaxies are within range of Hubble if we could somehow use it for a whole-sky survey. Then recall that the James Webb Space Telescope will have a primary mirror six times larger than Hubble’s in area, and will be fully a thousand times more sensitive than Hubble in the infrared.
When Vanderbei showed his photos at Princeton, the hardened group of scientists gasped audibly at the sheer spectacle of some of his stellar panoramas. None of us can fully comprehend the majesty of what surrounds us, even if we study these matters every day. But if you know someone who is interested in astronomy but still at the novice level, my hunch is that this book could awaken a lifelong passion. Don’t be surprised to find yourself, long after you’ve read it, picking it back up to gawk at particular plates, like the stunning three-page panorama of the Sloan Great Wall. In addition to everything else, the universe is shatteringly beautiful.
When Voyager 2 was passing Neptune back in 1989, I stuck a video tape in the VCR and recorded the coverage — two video tapes, actually, because I wasn’t sure how much coverage there was going to be, and I didn’t want to miss anything. That meant getting up in the middle of the night to change tapes, but I figured the loss of sleep was worth it. Going back to those tapes today, I’m still struck by the same sense of awe that both the Voyagers were simply going to continue, that although the media spoke as if their journeys were over after their encounters at Titan and Neptune respectively, they still had years of power left and would continue talking to us deep into the 21st Century.
Image: Voyager 1 looks back to capture six planetary portraits. These six narrow-angle color images were made from the first ever “portrait” of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. The spacecraft acquired a total of 60 frames for a mosaic of the solar system which shows six of the planets. Credit: Voyager 1 team/NASA.
The spacecraft nearing Neptune on my tapes was roughly 30 AU from the Sun. As of this morning, twenty-one years later, Voyager 2 is 94.03 AU out, and Voyager 1 (which left the ecliptic to make a flyby of Titan in 1980) is at 115.53 AU. The distances play with the imagination and offer a useful perspective. Voyager 1 is sixteen light hours from Earth — to be reasonably precise, 16 hours, 7 minutes as of 1202 UTC on the 14th. We’ve never sent anything sixteen light hours out before, but even at that distance, we’re only now penetrating the edge of the Solar System.
I have more to say about the size and scale of things, but I’m going to hold most of that for tomorrow in the form of a discussion of an interesting new book. For today, let’s talk about what Voyager 1 has found at 17.4 billion kilometers from the Sun. Out there, at the edge of the heliosphere, the spacecraft has moved into a region where the velocity of hot ionized gas — plasma — from the Sun has slowed to zero. With no outward movement of the solar wind, Voyager is seeing signs that the pressure of the ‘interstellar wind’ has turned the Sun’s wind sideways.
Voyager 1, then, is getting close to interstellar space, a crossing that will be marked by a sudden drop in the density of hot solar wind particles and an increase in the density of cold particles. The velocity of the solar wind has slowed at a rate of about 20 kilometers per second every year since August of 2007, at which point it was moving outward at some 60 kilometers per second. Readings over the last few months show an outward speed of zero since June. Rob Decker (JHU/APL) is a Voyager Low-Energy Charged Particle Instrument co-investigator, working with the instrument that provides the data fueling these results. Says Decker:
“When I realized that we were getting solid zeroes, I was amazed. Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again.”
The thinking among Voyager scientists is that Voyager 1 is still within the heliosheath, the outer shell of the heliosphere (the bubble formed by the solar wind as it fills nearby space). After reaching the termination shock, the solar wind slows down and heats up in the heliosheath. Current models of the heliosphere’s structure, as discussed at the ongoing American Geophysical Union meeting in San Francisco, will be tuned up by the new data, allowing us a better estimate of Voyager 1’s entry into true interstellar space, now thought to be about four years away.
“In science, there is nothing like a reality check to shake things up, and Voyager 1 provided that with hard facts,” said Tom Krimigis, principal investigator on the Low- Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece. “Once again, we face the predicament of redoing our models.”
As we tune those models, we might ponder, along with the distance of the Voyager duo, their speed. Voyager 1 is the faster craft because of gravity assists at Saturn and Titan. It’s moving at about 17 kilometers per second, with Voyager 2 at 15 kilometers per second. Put that into interstellar terms and the scale of things again seizes the imagination. Launched in 1977, the Voyagers have had thirty-three years to get to where they are today. If Voyager 1 were pointed at Alpha Centauri, it would face a journey of 41.5 trillion kilometers. At 17 kilometers per second, that works out to 76,476 years.
As project leader for Project Icarus, the ambitious successor to the British Interplanetary Society’s Project Daedalus starship design, Richard Obousy is deeply engaged with the advanced propulsion community. Here he gives us a report on the recent Advanced Space Propulsion Workshop, which he attended in November. It was a sizable gathering, but Richard focuses here on work of particular relevance to Project Icarus and the Tau Zero Foundation, the twin backers of Icarus.
Recently, several members of the Project Icarus team attended the 2010 Advanced Space Propulsion Workshop (ASPW) at the University of Colorado in Colorado Springs. The event ran from from Monday, November 15 through Wednesday, November 17, with over sixty presentations given by a number of researchers. Project Icarus attendees included James French, Rob Adams, Robert Freeland, Andreas Tziolas and myself.
The ASPW is focused on low Technology Readiness Level (TRL) concepts ranging from TRL 1 to 3. A TRL is a measure of the maturity of an evolving technology, with TRL 1 representing the very lowest level of maturity, with only the basic physical principles of an idea demonstrated. At the other end of the spectrum, TRL 9 represents a system that is, for the most part, tested and operational. A detailed breakdown of the TRL levels can be found here.
A TRL 1 to 3 conference typically brings together a good mix of pioneering thinkers who are willing to think outside of the box and explore untested ideas and concepts. Most of the attendees were either NASA scientists, worked at JPL, or were actively affiliated with a university, so the science that was presented was all very plausible and grounded in ideas that could be brought into fruition within a few decades (earlier in some cases), given a sufficient investment of time and funding.
Image: The conference looked out to Pike’s Peak, a 14, 115 ft (4.3 km) elevation mountain. Credit for all images: Richard Obousy.
A number of talks caught our attention due to their relevance to the Icarus Project. One such talk was delivered by John Slough, who gave an intruguing presentation on his research at the University of Washington on Inductively Driven Liner Compression of Fusion Plasmoids. His was the only team at the conference working on pulse propulsion concepts.
The basic concept involves pulsing fusion fuel plasma at high rates into a reaction chamber where it would undergo fusion via use of metal liners to accomplish compression of a magnetized plasmoid. Although remarkable, the only purpose of the fusion would be to drive the next round of plasmoid firing. Propulsion would be achieved through momentum transfer occurring between the electromagnetic gun and the accelerating plasmoid. In other words, all the fusion gain would be put back into driving the next cycle. This differs markedly from the idea behind Daedalus, where a large fraction of the exploding fusion material itself transfers the momentum.
Image: John Slough(University of Washington) speaking on fusion plasmoids.
Rob Adams (Project Icarus) gave a fascinating talk on a conceptual design of a z-pinch fusion propulsion. The results of a detailed study that he had been involved in were presented. These results included the modeling of the z-pinch fusion rocket, the propulsion characteristics, an evaluation of a magnetic nozzle, mission analysis and overall vehicle design.
Image: Rob Adams (Project Icarus) explaining z-pinch fusion propulsion.
Andreas Tziolas (Project Icarus) gave a thoughtful overview of candidate technologies for interstellar exploration and then went on to discuss various aspects of Project Icarus, including ideas that the team has been discussing including vIcarus, satIcarus and others. Andreas received a number of questions from the audience, including one from Sonny White who suggested that the Icarus team put some effort into possible spin-offs that could be realized within two or three decades.
Image: Andreas Tziolas giving his talk on interstellar enabling technologies.
I had the pleasure of presenting a talk on Day 1 that introduced Project Icarus. I spent some time discussing our overall objectives and who makes up our team. I also talked about the original Daedalus propulsion systems and described the essential features, including the cryogenic storage, Deuterium – Helium3 pellet design, injector nozzles, electron beams and the reaction chamber and magnetic nozzles.
Image: Richard Obousy talking about Project Icarus, and the Daedalus propulsion systems.
Day 1 ended in the local student union building with dinner and drinks, which the team enjoyed thoroughly.
The plenary session of Day 2 was opened by Les Johnson, Deputy Manager for the Advanced Concepts Office at NASA MSFC in Huntsville. Les described the limitations of chemical rocket propulsion and illustrated an overall technology roadmap that could provide NASA with the pathways required to meet the space agencies exploration goals for the 21st century. The technologies Les described would enable more effective exploration of our Solar System.
Image: Les Johnson speaking on Day 2 of ASPW 2010.
The renowned Robert Frisbee gave a talk titled ‘To The Stars, One Way or Another,’ which described the details of several studies he had performed while working at JPL over the years. These studies were aimed at identifying propulsion technology requirements for interstellar missions. He explained to us that these studies were made intentionally difficult, and would involve a rendezvous mission as well as a top speed of 0.5c. He also briefly reflected on some breakthrough propulsion ideas, including wormholes and warp drives, and also an analysis of the negative energy requirements for these schemes. This was the first time I have seen Robert speak, and I want to emphasize that he was a thoroughly entertaining and enjoyable presenter. I was surprised at how animated and enthusiastic he was during his presentation, and enjoyed the many clever ‘wise-cracks’ he managed to throw into his talk.
Image: Robert Frisbee giving his talk “To the Stars, One Way or Another.”
Day 3 included a number of fascinating talks, including a talk by David Kirtley (MSNW LLC) who spoke on the concept of ‘Macron Propulsion’, an idea that involves firing small fuel pellets in front of a spacecraft which would then be utilized by that craft for fuel. This ingenious, yet complex approach is attractive, since it overcomes the Rocket Equation as the fuel is not stored onboard the craft. The talk had very interesting parallels to the Daedalus electromagnetic pellet launcher. MSNW has built and is currently testing a 20 Tesla launcher and also a prototype pulsed power bank.
James French (Project Icarus), a veteran rocket scientist who worked on the Saturn V engines, gave a talk on Gas Core Nuclear Rockets. He first gave an overview of the solid and liquid core rockets, and then discussed some of the challenges associated with heat transfer for the working fluid, cooling of the solid parts of the engine and also the problem of how to start and stop a gas-core rocket.
James illustrated the potential use of the Gas Core rocket for Icarus by illustrating a calculation that revealed a potential course correction for a probe released from the main Icarus ‘mother-ship’ traveling at a reasonable fraction of c. The conclusion at which James arrived was that there is potential utility for gas core rockets within Project Icarus.
Image: James French (Project Icarus) talking on Gas Core Nuclear Rockets.
Rob Adams (Project Icarus) gave his second talk of the conference, and explained the Oberth two-burn maneuver. While it was the most amusing talk of the conference (Rob cracks a lot of jokes), it also detailed Rob’s process of rediscovering the Oberth maneuver. This relatively unknown effect is often confused with the gravitational slingshot, but differs markedly in its application. When a spacecraft executes the Oberth maneuver, it is able to obtain far more useful energy for greater delta v than a stationary rocket. Rob believes this maneuver is generally unknown, even among experts, and emphasized its scientific value. He also explained that the maneuver could be used effectively for future missions to obtain higher delta v.
Robert Frisbee gave the final talk of the day, which was largely to encourage all present to ‘think big’, and to explore low TRL technologies so that breakthroughs in understanding can be accomplished. I particularly enjoyed one of Robert’s quotes where he explained that “It’s all science fiction until somebody goes out and does it.” Robert received a standing ovation at the end of his presentation, which was a fitting end to the conference.
Image: From left to right: Andreas Tziolas, Rob Adams, Richard Obousy, Jerry Winchester, Robert Freeland, Jim French.
A phone call from NASA’s Kim Newton at Marshall Space Flight Center confirms what some of us were beginning to fear, that the ejection sequence that would separate NanoSail-D from FASTSAT, at first thought successful, has apparently malfunctioned. Although telemetry from FASTSAT looked good and seemed to confirm the ejection, the NanoSail-D team has no beacon from the sail, and while attempts to locate it will continue throughout the weekend, the outlook has suddenly turned grim.
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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