by Richard Obousy

Physicist Richard Obousy here takes a look at an intriguing new paper by Mike McCulloch, a researcher at the University of Exeter. In addition to his work in theoretical physics and warp drive possibilities, Obousy is current project leader and primary propulsion design lead for Project Icarus, a joint venture between the British Interplanetary Society and the Tau Zero Foundation to re-think the original Project Daedalus starship design. In the review below, Obousy places McCulloch’s work on the Pioneer anomaly in the context of current thinking on dark matter, dark energy and the nature of mass. Does the Higgs field explain inertial mass, or are there alternatives? Read on.

Few areas of research have garnered as much attention from both the public and scientific communities as those of dark energy and dark matter – and for good reason. Both terms stem from observations of the physical universe that, simply put, don’t belong within the well-understood framework of known physics. Another phenomenon discovered in the nineties concerns an anomalous acceleration of the Pioneer probes. These ostensibly unrelated observations may, in fact, be connected to each other by an intriguing line of research currently being investigated by Mike McCulloch, a researcher at the University of Exeter. Before exploring McCulloch’s research, a brief review of dark energy, dark matter, and the anomalous Pioneer acceleration will be presented.

Dark matter is a proposal put forward to explain the observations first made by Zwicky in 1933 that galaxies were too energetic to be held together by observable matter. Zwicky originally proposed the existence of an unseen form of baryonic matter that provided the necessary gravitational force to hold the galaxies together. Due to constraints imposed by modern cosmology, the idea has evolved to assume this form of matter is non-baryonic (not made of quarks); however, the fundamental idea has remained unchanged. After decades of searching for dark matter, none has been directly detected, but a number of experiments are ongoing.

Dark energy stems from the truly astounding observation made originally by Riese and Perlmutter in the late 90′s that the rate of cosmological expansion, long thought to be either static or decelerating, is actually accelerating. For this to be happening, it is commonly believed that the universe is filled with a ubiquitous and exotic negative pressure field that drives the accelerated expansion. Although we can give this energy a name, and predict what it will do, dark energy as a ‘real’ physical field has never actually been measured in the lab, and today, dark energy remains somewhat of an enigma.

As if dark energy and dark matter haven’t dealt theoreticians enough of a blow, cracks began to appear in our understanding of gravity due to the observation made by Anderson et al in 1996 that both Pioneer 10 and 11 are experiencing an anomalous acceleration of 8.74±1.33×10^-10 m/s² directed approximately towards the sun. It is precisely this anomaly that is studied by Mike McCulloch in his recent publication in Europhysics Letters called Minimum Accelerations from Quantized Inertia (reference below). McCulloch’s work addresses the Pioneer anomaly, and within the framework of his model, one could perhaps come to a deeper understanding of dark matter and dark energy thanks to a novel idea known as MOND, or Modified Newtonian Gravity.

The basic idea that McCulloch explores is the nature of mass, and the possibility that inertial mass, in fact, changes slightly under certain conditions. It has been known since the time of Newton that all bodies attract all other bodies in the universe with a force that is proportional to their mass. This type of mass is what is known as gravitational mass. It is also known that when one applies a force to an object, it accelerates at a magnitude that is proportional to its mass. This type of mass is known as inertial mass. It is commonly assumed that gravitational and inertial mass are identical, and this has been verified by our highest precision instruments to date.

The fundamental nature of inertial mass is not precisely known and is an issue that has been pondered at least since the time of Mach. Recent efforts to codify inertial mass into the Standard Model (SM) of particle physics have resulted in the famous Higgs field, which is a ubiquitous field that bestows mass upon matter via a process known as spontaneous symmetry breaking. Although the Higgs field has not been experimentally detected, many physicists are confident that it will be found at the Large Hadron Collider.

Despite the widespread acceptance in the existence of the Higgs field, there have been alternative attempts to uncover the nature of inertial mass. One paper, Inertia as a Zero Point Lorentz Force, written in 1994 by Rueda, Puthoff and Haisch (RPH), represents a stalwart effort to model inertia as a back-reaction of matter to the quantum vacuum similar to the Unruh field. Despite not gaining widespread acceptance in the theoretical community, the paper galvanized interest in the possibility that the quantum vacuum and inertial mass may be related. The basic premise of the paper was that matter, modeled as a ‘Parton’, interacts with the quantum vacuum in such a way that any acceleration generates a Lorentz-type back-reaction to the vacuum which manifests itself macroscopically as a resistance to acceleration or, more simply, as inertial mass.

The RPH paper was not the first to suggest that accelerated matter is effected by the quantum vacuum. In 1976, Unruh showed that a body undergoing an acceleration in the vacuum sees a thermal radiation of temperature T that is related to its acceleration. Wien’s displacement law tells us that, for a given temperature, there will be a dominant wavelength which, via the Unruh effect, is inversely proportional to the acceleration – namely, as the acceleration gets smaller, the radiation wavelength gets bigger. As the acceleration decreases, this wavelength reaches a limiting value: the wavelength of the observable universe. Milgrom, in 1994, speculated that at this point, there would be a ‘break in the response to the vacuum’ and the Unruh radiation would be unobservable. He further speculated that this could have an effect on inertial mass. Herein lies the crux of this line of thinking – that matter’s response to the vacuum is what generates inertia.

McCulloch further develops the idea of Milgrom by allowing for a more natural development in the Unruh radiation spectrum. In the original idea by Milgrom, only the dominant wavelength was considered. McCulloch, however, develops what he calls a Hubble-Scale Casimir effect, where a range of wavelengths are allowed based on the boundary conditions of the size of the observable universe.

“The new assumption is that this Unruh radiation is subject to a Hubble-scale Casimir effect. This means that only Unruh wavelengths that fit exactly into twice the Hubble scale (harmonics with nodes at the boundaries) are allowed, so that a greater proportion of longer Unruh waves are disallowed, reducing inertia in a new, more gradual, way for low accelerations.”

Using this model, McCulloch is able to develop an equation which illustrates the modification of inertial mass for low accelerations. Put in simpler terms, as the Pioneer probes depart our solar system they experience a force due to the gravitational attraction of the sun. This force generates an acceleration which, due to its extremely small value, modifies the inertial mass of the pioneer probe. Because of this modification, the Pioneer probes, seemingly now less massive, feel a greater acceleration due to the sun than that predicted by Newtonian mechanics, creating the anomalously large acceleration.

How does this all relate to dark energy and dark matter? The answer is in the relationship between certain natural scales that occur in physics. The basic building block is the scale that characterizes the cosmological constant. We call this scale R and it is the distance scale over which the cosmological constant curves the universe. R is about 10 billion light years and is 10⁴⁰ times the size of an atomic nucleus – the scale where the standard model of particle physics is applicable). R is also 10⁶⁰ times the Planck scale – the scale at which we believe in GUT’s (Grand Unified Theories), where all the forces in nature behave identically. It is therefore pragmatic to wonder whether this scale R might be indicative of some new physics.

Hints at new physics at the scale R manifest themselves in the cosmic microwave background (CMB) – thermal radiation left over from the Big Bang. This radiation has been cooling as the universe expands, and is now at a fairly uniform temperature of 2.7 degrees Kelvin. Fluctuations in this temperature exist to a level of a few parts per 100,000, and the patterns of these fluctuations provide us with clues to the physics of the early universe.

Analysis of the temperature fluctuations over the last decades illustrate how much energy is contained in this radiation as a function of wavelength. It appears that the CMB is dominated by a single large peak, followed by a number of smaller peaks. It also appears that there is very little energy in the longest wavelength. This data can be interpreted as indicative of a ‘cutoff’, above which the thermal modes are less excited. What is particularly remarkable is that this cutoff occurs on a scale R which we associate with the cosmological constant.

This cutoff is somewhat puzzling from the perspective of inflation theory, which was developed by Alan Guth of MIT and, originally, by Alexei Starobinsky of the Landau Institute for Theoretical Physics in Moscow. According to the theory of inflation, the early and rapid expansion of the universe created huge regions of the cosmos with relatively uniform properties. This region is thought to be much larger than the observable universe. The cutoff indicates that, at the scale R, inflation stopped just at the point where it created a region as large as we now currently observe. If, in fact, inflation ‘switched off’ just at the point where it created the cosmos as large as we currently observe, then some physical mechanism must have been responsible for selecting this unique time to stop. This seems incredibly improbable, since nothing in the physics of inflation says anything about scales on the order of 10 billion light years.

Said another way, if inflation produced a largely uniform universe, then it likely produced uniformity on scales much larger than we observe. Thus, the patterns produced by inflation, the small fluctuations, should be visible beyond the present size of the universe. Instead – what the data indicate is that these fluctuations stop above the scale R.

Another indication that new physics may occur at scales on the order of R is an apparent asymmetry in the distribution of hot and cold spots in the CMB dubbed the ‘Axis of Evil’. This observation was first made in 2005 by Kate Land and Joao Magueijo of Imperial College London. A number of independent studies have confirmed this apparent alignment of anisotropies in the CMB.

There are additional phenomena associated with the scale R that are worth discussing. One way we can explore R is to combine it with additional constants of nature. An interesting place to start is to combine it with the speed of light, c, to give us R/c. Dimensionally, R/c gives us a time, and that time corresponds to the present age of the universe. Taking the reciprocal of this, c/R, gives a frequency, a profoundly low ‘note’ which has completed one oscillation in the entire lifetime of the universe.

Going one step further, we can explore c²/R which, dimensionally, gives us the units of acceleration. Remarkably, this number is the acceleration produced by the cosmological constant. This is the same acceleration that we currently believe dark energy is responsible for and is on the order of 10^-10 m/s. This also happens to be the roughly the same anomalous acceleration that the Pioneer probes are currently experiencing!

The c²/R also crops up when we examine rotational velocity of orbiting stars in galaxies. Recall that stars are seen to rotate at a velocity that would, according to Newtonian Mechanics, be too fast for them to be held in a stable orbit. The contemporary fix for this problem is to introduce dark matter. This is not the only fix, however. For spiral galaxies, in which stars move in circular orbits, anomalous velocities (orbital velocities that, according to Newtonian Mechanics, should not be possible) are only apparent beyond a certain orbit. Within this ‘special’ orbital distance Newtonian gravity works perfectly. Because stars move in a circular orbit they experience an angular acceleration which is related to their velocity (a=v²/r). The breakdown of Newtonian gravity occurring at this ‘special’ orbital distance occurs when the stars are rotating with an angular acceleration of 1.2×10^-10 m/s², almost identical to the scale c²/R. This is thoroughly fascinating, and this string of relationships which appear to be related to the scale R represent tantalizing hints at physics beyond what is currently studied and practiced within the mainstream academic community.

Today, nobody knows for certain what this new physics is (if it really is new physics), and nobody has written down a theory codifying its behavior. Mike McCulloch, however, is arguably helping to increase momentum within this curious and remarkable area of research.

The paper is McCulloch, “Minimum accelerations from quantised inertia,” Europhysics Letters Vol. 90, No. 2 (20 May, 2010). An abstract is available, with full text here. The paper by Rueda, Haisch and Puthoff is “Inertia as a Zero Point Lorentz Force,” Physical Review A, Vol 49, No 2 (February 1994), pp.678-694.

This article was originally posted on Centauri Dreams

Robert Forward’s Indistinguishable from Magic is a genial and absorbing read, a collection of essays and fiction illustrating some of the scientist’s most memorable ideas. And while gigantic lightsails driven by laser beam to other stars always come to mind when Forward’s name is mentioned, it’s fascinating to page through his thoughts on antimatter, black holes and time machines. Long a Forward admirer, I was pleased to see that another of the concepts discussed in this book recently made an appearance at this month’s solar sail conference in Brooklyn.

‘Statites’ are a Forward construct, a word he coined to describe a spacecraft that uses a solar sail to hover over a region rather than orbiting the Earth. Let Forward describe what he calls a ‘technique for hanging things in the sky’:

…I have the patent on it — U.S. Patent 5,183,225 “Statite: Spacecraft That Utilizes Light Pressure and Method of Use”… The unique concept described in the patent is to attach a television broadcast or weather surveillance spacecraft to a large highly reflective lightsail, and place the spacecraft over the polar regions of the Earth with the sail tilted so the light pressure from the sunlight reflecting off the lightsail is exactly equal and opposite to the gravity pull of the Earth.

You can see where Forward is going with this. This is a solar sail that isn’t designed for transport but for station-keeping, and it offers options that other kinds of satellite do not. But maybe satellite is the wrong word:

With the gravity pull nullified, the spacecraft will just hover over the polar region, while the Earth spins around underneath it. Since the spacecraft is not in orbit around the Earth, it is technically not a satellite, so I coined the generic term ‘statite’ or ‘-stat’ to describe any sort of non-orbiting spacecraft (such as a ‘weatherstat’ or ‘videostat’ or ‘datastat’).

Forward always noted that he had made no money from his patent, but said he didn’t want to make the mistake Arthur C. Clarke did when he failed to obtain a patent on his idea of the geosynchronous communications satellite. In a short story included in Indistinguishable from Magic called ‘Race to the Pole,’ Forward writes about a statite called the ‘Hovering Hawke’ that uses a kilometers wide square lightsail to support a powerful broadcast satellite. Such a ‘polesitter’ would, by Forward’s calculations, need to be too distant to serve as a communications satellite, but direct broadcast or weather surveillance would be robust applications.

Just how distant would a polesitter have to be? In this passage from the story, a scientist explains the difficulty a statite would experience maintaining a stable position as the Earth’s seasons change:

“The control problem of keeping the [statite] balanced over the pole is very tricky, especially during the summer season of that hemisphere when the polar axis is over on the sunlit side of the Earth. That’s why ‘pole-sitters’ have to be placed so far away from the Earth. If they get any closer than 250 Earth radii, they become unstable during the summer.”

Forward’s patent ran out in February of this year, but his idea is beginning to gain traction. At the Second International Symposium on Solar Sailing, which ended just last week, Colin McInnes described what Forward called ‘displaced orbits’ that would allow geosynchronous telecommunications satellites to be deployed to the north or south of the Earth’s equator. Working with graduate student Shahid Baig, McInnes (University of Strathclyde) has published a new paper that shows the viability of displaced orbits. Says McInnes:

“Satellites generally follow Keplerian Orbits, named after Johannes Kepler – the scientist who helped us understand orbital motion 400 years ago. Once it’s launched, an unpowered satellite will ‘glide’ along a natural Keplerian orbit. However, we have devised families of closed, non-Keplerian orbits, which do not obey the usual laws of orbital motion. Families of these orbits circle the Earth every 24 hours, but are displaced north or south of the Earth’s equator. The pressure from sunlight reflecting off a solar sail can push the satellite above or below geostationary orbit, while also displacing the centre of the orbit behind the Earth slightly, away from the Sun.”

Image: Analog‘s December, 1990 issue contained an article by Robert Forward describing the ‘polesitter’ concept, one of many innovative ideas the scientist introduced to a broad audience. Credit: Condé Nast.

No, we’re not in ‘polesitter’ range, not yet, anyway. But these displaced orbits would allow solar sails — McInnes is interested in hybrid sails complemented by electric propulsion systems — to be displaced between 10 and 50 kilometers from the equator. As we continue our work with solar sails, finding ways to make them robust enough to handle polar stationary orbits seems like a reasonable expectation. Another Forward concept thus moves into sharper definition. I can only imagine how much the late Dr. Forward would have enjoyed sitting in on the relevant session at the solar sail conference, and reading the McInnes paper.

The paper is Baig and McInnes, “Light-Levitated Geostationary Cylindrical Orbits are Feasible,” Journal of Guidance, Control and Dynamics, Vol. 33, No. 3 (2010), pp. 782-793 (preprint). You’ll also enjoy reading the non-fiction piece Robert Forward wrote for Analog. It’s “Polesitters,” published in Analog Science Fiction/Science Fact Vol. 110, No. 13 (December, 1990), pp. 88-94.

This article was originally posted on Centauri Dreams

We’re learning a lot more about how planets interact with each other gravitationally. ‘Resonance’ is the operative term here. When planets are locked in a 2:1 orbital resonance, the outer planet orbits the host star once for every two orbits of the inner planet. A 3:2 resonance occurs when the outer planet orbits the star twice for every three orbits of the inner planet.

Resonance (technically ‘mean motion resonance’) prevents close encounters between planets and provides long-term orbital stability. And if the 2:1 resonance is the most common pattern, it’s also true that things can change when planets migrate to different parts of their system. John Johnson (Caltech) describes the result of fast inner migration:

“Planets tend to get stuck in the 2:1. It’s like a really big pothole. But if a planet is moving very fast it can pass over a 2:1. As it moves in closer, the next step is a 5:3, then a 3:2, and then a 4:3.”

Johnson’s work on resonance has born fruit in a new paper in which he and his colleagues discuss the discovery of two solar systems where gas giants in relative proximity to each other have become locked into resonance. Studying the matter helps us understand how solar systems evolve, as planets farther out in the protoplanetary disk migrate inwards, causing gravitational disturbances that can only become stable in orbital resonance.

Studying the star 24 Sextantis, some 244 light years from Earth, using radial velocity methods, the researchers have found two gas giants separated by about 0.75 AU, roughly 113 million kilometers. You can contrast this with the spacing between the largest planets in our system. Jupiter and Saturn are never closer than 531 million kilometers. The planets orbit the star with periods of 455 days and 910 days and are locked in a 2:1 orbital resonance.

A second gas giant pairing occurs around the star HD 200964, some 223 light years from Earth. Here the distance between the two gas giants can close to 0.35 AU (53 million kilometers). Johnson likens the latter pairing to that of Titan and Hyperion, two Saturnian moons, which also show a 4:3 resonance, but notes that the planets orbiting HD 200964 interact far more strongly, each being 20,000 times more massive than the combined mass of Titan and Hyperion. The planets in this system have orbital periods of 630 and 830 days respectively. Johnson adds:

“This is the tightest system that’s ever been discovered, and we’re at a loss to explain why this happened. This is the latest in a long line of strange discoveries about extrasolar planets, and it shows that exoplanets continuously have this ability to surprise us. Each time we think we can explain them, something else comes along.”

Gravitational interactions in this environment are quite powerful. This Caltech news release notes that the gravitational tug between HD 200964’s two planets is 3 million times greater than the gravitational force between Earth and Mars, 700 times larger than that between the Earth and the Moon, and 4 times larger than the pull of the Sun on the Earth.

As to the history of these worlds, the paper on this work notes their current positions and their likely changes over time:

In both the 24 Sex and HD 200964 systems, the planets reside well within the so-called snow line, beyond which volatiles in the protoplanetary disk can condense to provide the raw materials for protoplanetary core growth. For a pre-main-sequence, 1.5 M [solar mass] star the snow line is located beyond 2-3 AU… It is therefore likely that the planets around 24 Sex and HD 200964 formed at larger semimajor axes and subsequently experienced inward orbital migration.

Both of these stars are massive and dying, subgiants that have evolved off the main sequence and have run out of hydrogen for nuclear fusion. The eventual fate of such stars is to become a red giant, but neither of the stars has progressed that far. While red giants are problematic for radial velocity methods because their pulsations mask the spectral shifts that would reveal orbiting planets, subgiants have not expanded to that point and planet hunting remains possible. In fact, using the Keck Subgiants Planet Survey, Johnson and team are learning a great deal about such systems:

“Right now, we’re monitoring 450 of these massive stars, and we are finding swarms of planets. Around these stars, we are seeing three to four times more planets out to a distance of about 3 AU — the distance of our asteroid belt — than we see around main-sequence stars. Stellar mass has a huge influence on frequency of planet occurrence, because the amount of raw material available to build planets scales with the mass of the star.”

The paper is Johnson et al., “Retired A Stars and Their Companions VI. A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextan[t]is and HD 200964,” accepted for publication in The Astronomical Journal (abstract).

This article was originally posted on Centauri Dreams

With more attention now being focused on possible missions to an asteroid, we should keep in mind that DLR, the German Aerospace Center, has been looking into an asteroid mission via solar sail for some time now. One 2006 paper from DLR’s Institute of Space Simulation pondered a 70-meter sail for use in a projected mission to the Near-Earth Object 1996FG3 within ten years of launch. It’s an interesting notion, one that would involve the sail hovering over the NEA hemisphere opposite to the Sun, deploying a lander and return capsule.

DLR has been into serious sail studies for some time now, as the photo below attests. It’s a 1999 shot of the ground deployment of a square solar sail 20 meters to the side. As you can see, this is a square sail made up of four triangular sail segments, an exercise that could readily lead to a sail deployment in space if the European Space Agency opts for funding such a mission. Just what ESA has in mind for such technology was the subject of a presentation at the just concluded Second International Symposium on Solar Sailing in Brooklyn.

Image: DLR’s deployed solar sail, seen at the Center’s facility in Cologne. Credit: DLR.

I’m looking at the paper on “The 3-Step DLR-ESA Gossamer Road to Solar Sailing,” available in the proceedings of the conference, and enjoying the ‘gossamer road’ metaphor that is so reminiscent of the fabled Silk Road, that network of trade routes that took its name from the Chinese silk trade and reached across Asia to the Mediterannean, Europe and north Africa. Maybe the ‘gossamer road’ is an indicator of enthusiasm at DLR and ESA for renewing sail work, for late last year the two agreed on the road map to solar sailing presented here.

Three consecutive steps define the roadmap:

• Gossamer-1: A 5-meter square solar sail launched as a deployment demonstrator to a 320 kilometer Earth orbit. Documentation of the deployment is to be handled by two onboard cameras (which inevitably calls up the images of the IKAROS sail deployment, similarly tracked). This demonstrator mission would be launched in 2013.
• Gossamer-2: A 20-meter square sail launched to a 500 kilometer Earth orbit. Here the idea is to test orbit and attitude control of a sail built out of thinner materials than the 7.5 µm Kapton used in Gossamer-1. Launch in 2014.
• Gossamer-3: A 50m x 50m solar sail launched to a 10,000 kilometer Earth orbit, with testing of orbit and attitude control and, as with the earlier missions, documentation by onboard cameras. An acceleration > 0.1 mm/s² is sufficient for the sailcraft to leave the Earth’s gravitational field after a period of about 100 days.

As you see, the gossamer missions build into growing layers of complexity and, because of limited budgets and a tight time schedule, tap the technologies and materials already developed in earlier DLR and ESA sail work. The paper notes that DLR has already done extensive work not only on sail materials but on the boom technology that supports the sail.

Also supporting the Gossamer project is a Light Pressure Measurement Facility (LPMF) set up by the DLR Institute for Space Systems in Bremen and Berlin. This is a key issue, because the reflectivity of the sail materials determines the efficiency of the propulsion achieved, and a variety of processes during a mission can cause that reflectivity to degrade. DLR is also setting up a Complex Irradiation Facility, now being commissioned, to examine the effects of the solar wind and electromagnetic radiation on sail materials. The trick here is to extrapolate from short-period degradation caused by high intensity bombardment in the facility to the longer, slower processes that a sail will experience in the space environment.

It’s interesting to see that so much recent sail technology has revolved around CubeSats, miniaturized satellites weighing no more than one kilogram that typically work with off-the-shelf electronics. CubeSats were developed as a way for universities to become involved in space exploration, but their small size and inexpensive components make them ideal for experimentation of all kinds. These ‘nano-satellites’ play a role in the NanoSail-D and the Planetary Society’s Lightsail-1 projects as well as DLR’s Gossamer program, allowing early risks to be spread over a number of low cost missions. It’s satisfying to think that IKAROS will soon be joined by other experiments shaking out a future workhorse propulsion system.

The asteroid mission referenced above is discussed in Dachwald et al., “Multiple rendezvous and sample return missions to near-Earth objects using solar sailcraft,” Acta Astronautica 59 (2006), pp. 768-776.

This article was originally posted on Centauri Dreams

Time travel holds such perennial fascination that even though its relationship with interstellar issues is slim, I can’t resist reporting on new ideas about it. John Cramer’s time experiments seem stuck in limbo, but now we have new work from Seth Lloyd (MIT) and colleagues about one way out of the paradoxes time travel seemingly creates. The ‘grandfather paradox,’ returning to the past to kill your own grandfather and thus causing your future self not to exist, seems inevitable if we grant the existence of what are called ‘closed timelike curves’ (CTCs), the paths through spacetime that would let a time traveler interact with his or her self in the past.

Ways Around Paradox

Lloyd’s team gets past that problem by describing a particular version of closed timelike curves formed with what is called ‘post-selection.’ The idea is to describe these CTCs in terms of quantum mechanics, starting with the assumption that time travel is a communications channel from the future to the past. Is there, then, a quantum communication channel to the past? The researchers consider quantum teleportation, in which a quantum measurement combined with classical communication lets quantum states be transported between sender and receiver.

The paper then applies quantum teleportation to timelike curves with postselection (P-CTCs):

We show that if quantum teleportation is combined with post-selection, then the result is a quantum channel to the past. The entanglement occurs between the forward- and backward-going parts of the curve, and post-selection replaces the quantum measurement and obviates the need for classical communication, allowing time travel to take place. The resulting theory allows a description both of the quantum mechanics of general relativistic closed timelike curves, and of Wheeler-like quantum time travel in ordinary spacetime.

As best I can untangle this (and we’ll deal with Wheeler in a moment), the post-selection idea means that time travel paradoxes are ruled out. Try to perform the event causing the paradox and something will happen to make the action fail. Moreover, although this theory of post-selection in timelike curves was created to deal with quantum mechanics in CTCs following the principles of general relativity, the authors think it extends to other contexts. Quantum theory that allows entanglement, in other words, seems to allow time travel even when no spacetime closed timelike curve exists.

Tunneling Through Time

Lloyd’s team says this quantum time travel can be thought of as ‘a kind of quantum tunneling backwards in time, which can take place even in the absence of a classical path from future to past.’ That’s a helpful thought, given that the extreme distortions of spacetime required by more traditional time travel thinking in a relativistic context are all but impossible to create.

Interestingly, there already exists a growing literature on entanglement and projection in the development of timelike curves, all described briefly in this paper. But the authors are particularly careful to note John Wheeler’s ideas impinging on quantum time travel, ideas that Richard Feynman described in his Nobel Prize lecture. This is worth repeating:

‘I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, “Feynman, I know why all electrons have the same charge and the same mass.”
“Why?”
“Because, they are all the same electron!”
And, then he explained on the telephone, “Suppose that the world lines which we were ordinarily considering before in time and space – instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time – to the proper four velocities – and that’s equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron.”’

And now we’re really in Wonderland. Post-selection accepts only particular results, meaning that the only states that can be teleported via quantum entanglement are those that are consistent with the world we know. Time travel in this guise is necessarily consistent with our reality and forbids any actions that would create paradoxes. The authors put it this way: “…although any quantum theory of time travel quantum mechanics is likely to yield strange and counter-intuitive results, P-CTCs appear to be less pathological. They are based on a different self-consistent condition that states that self-contradictory events do not happen…”

Ratcheting Up Improbabilities

In an article on this work in Science News, Laura Sanders takes note of the fact that ruling out paradoxes means that unlikely events may happen with greater frequency:

“If you make a slight change in the initial conditions, the paradoxical situation won’t happen. That looks like a good thing, but what it means is that if you’re very near the paradoxical condition, then slight differences will be extremely amplified,” says Charles Bennett of IBM’s Watson Research Center in Yorktown Heights, N.Y.

For instance, a bullet-maker would be inordinately more likely to produce a defective bullet if that very bullet was going to be used later to kill a time traveler’s grandfather, or the gun would misfire, or “some little quantum fluctuation has to whisk the bullet away at the last moment,” Lloyd says. In this version of time travel, the grandfather, he says, is “a tough guy to kill.”

So we have no paradoxes but we seem to be distorting probability, a very strange result but maybe a bit less strange than the paradoxes we’ve avoided. Time travel makes for eerily seductive fiction — who would not wonder about traveling into the past to see loved ones again, or to remedy some unintentional wrong — and judging from the number of emails I received pointing me to this paper, the idea is as compelling now as it has ever been. I hadn’t realized how far back time travel has resonated in history, but the paper notes an account in the Hindu epic called the Mahabarata in which King Revaita visits the Brahma’s palace, stays for only a few days, and returns to Earth only to find that many eons have passed in his absence.

This is more or less the idea behind the creaky science fiction story “Out Around Rigel” (Astounding Stories, December 1931), in which Robert H. Wilson imagines the first journey to another star and uses the event as a way to teach Einsteinian special relativity (the first time this was done in science fiction, to my knowledge). The crew returns to find a thousand years have passed during their six-month journey. But this is a time travel account from the standpoint of relativistic spacetime. Quantum mechanics, in this paper’s estimate, might give us options other than that one-way ticket to the future.

How post-selection would work in quantum mechanics has yet to be determined, but the authors discuss the possibility of testing their theory experimentally by using quantum teleportation. Can people ever hope to take a journey into their own past with a self-consistent, non-paradoxical outcome? Science fiction writers will want to mull over the findings of this thorny, mind-bending paper and especially note the extensive literature treating entanglement and projection in the creation of closed timelike curves.

The paper is Lloyd et al., “The quantum mechanics of time travel through post-selected teleportation,” available as a preprint. Be aware as well of Lloyd et al., “Closed timelike curves via post-selection: theory and experimental demonstration” (preprint). This story on Physorg.com also discusses Lloyd’s work and ponders non-linearity in quantum mechanics.

This article was originally posted on Centauri Dreams

Dimitar Sasselov, a co-investigator on the Kepler mission, said in a TED Talk just posted that Kepler had uncovered numerous terrestrial planet candidates in its early data. Have a look at the video below (around the 8-minute mark). “Small planets dominate the picture,” says Sasselov, showing a chart of planet candidates. A great deal of work has to go into confirming these results, but Sasselov goes on to say “The statistical result is loud and clear, and the statistical result is that planets like our own Earth are out there. Our Milky Way galaxy is rich in these kinds of planets.” How many will be confirmed, and how many shown to be habitable? Much work ahead.

This article was originally posted on Centauri Dreams

The final day of the Second International Symposium on Solar Sailing (ISSS 2010) kicks off this morning with Roman Kezerashvili (City University of New York) discussing solar sail missions as a way of testing fundamental physics. Last year in Aosta I listened with fascination as Kezerashvili discussed close solar passes (‘Sundiver’ missions) that could approach as close as 0.05 to 0.1 AU to the Sun, depending on the development of materials technology. The remarkable feature of his talk, though, was the consideration of General Relativity’s effects in such close proximity to the Sun, which could create huge navigation issues.

The ‘Sundiver’ as an Exercise in Physics

Fail to account precisely for spacetime curvature and frame dragging in this environment and such a mission could find itself with a million-kilometer deflection enroute to its target. Even more exotically, time slows in close proximity to the Sun due to relativistic effects, so that the observer on Earth measures about 31 more seconds per year than the observer at 0.01 AU. It will be interesting to see how Kezerashvili follows up his earlier work with colleague Justin Vázquez-Poritz in Physics Letters B on these issues. Today’s talk, based on a paper with Vázquez-Poritz, looks at the Poynting-Robertson effect on solar sail trajectories, and is available in the proceedings.

The effect now partially named after him was first examined by John Henry Poynting in 1904 and later analyzed as an effect of special relativity by Howard Robertson. It has been analyzed in terms of drag on dust grains in the Solar System, which are found to spiral inward as the result of the tangential component of the Sun’s radiation pressure. In solar sail terms, this drag force can influence long-range missions, for the fraction of the Sun’s radiation absorbed by the sail will produce a drag force sufficient to slow the orbital speed of a sail in a solar orbit, and to decrease the cruising velocity and heliocentric distance of a sail on an escape trajectory.

The Poynting-Robertson effect may sound like a small issue, but weigh it against lengthy mission times of the sort we need to contemplate a journey to the heliopause and beyond. A ‘Sundiver’ sail deployed at 0.02 AU would find its cruising velocity decreased by 20 meters per second, a cumulative effect that would decrease its distance from the Sun by more than 20 million kilometers after a 30-year voyage. By exploring these effects, we learn what adjustments to incorporate in future mission planning and are able to examine exotic physical effects in an environment we can produce in no Earth-bound laboratory.

NASA and the Sail

The ISSS 2010 proceedings are stuffed with good material and it will take a while for me to go through all these papers with care. With IKAROS thus far a triumph, where is NASA in current solar sail research? Les Johnson (MSFC) discussed the agency’s progress in the production and testing of two different 20-meter solar sail systems, one developed by ATK Space Systems and the other by L’Garde. Both successfully underwent vacuum testing in NASA Glenn Research Center’s Space Power Facility at Plum Brook Station, Ohio. The ATK sail is shown at left, the L’Garde sail below, as deployed at the Plum Brook Facility (photo credit: NASA GRC).

In his paper in the proceedings, Johnson goes through the software tools, computational methods and optical diagnostic system developed in support of these sails, along with their structural analysis and attitude control systems. He also discussed the development of NanoSail-D, a small sailcraft system developed around a CubeSat. You may recall the failure of the Falcon-1 rocket in 2008 that destroyed the first of these sails, but the second is to be flown this fall in a test of sail deployment and deorbiting using atmospheric drag (the ‘D’ in NanoSail-D stands for ‘De-orbit,’ growing out of NASA Ames’ interest in developing a way of using atmospheric drag to deorbit a small satellite).

So we have the NanoSail-D flight spare scheduled for a fall launch, but what is the future direction of the already extensive NASA work on solar sails? The sad fact is that NASA is not currently funding solar sail technology. Les Johnson goes on to report the upside:

However, NASA is now preparing for a dramatic change in focus toward the development of advanced space technology that will enable new human and robotic exploration of the solar system. Solar sails are a technology that can support this aim, and it is likely that within the next few years NASA will again be aggressively advancing the technology toward mission implementation.

Maybe the success of IKAROS will be a spur to the other major space agencies to increase their interest and funding in sail technologies. Let’s hope so.

Sail/Fusion Hybrids?

And what of deep space concepts? Tau Zero practitioner Pat Galea, whose photos from ISSS 2010 are becoming available on Flickr, today looks at the interesting question of whether there is any synergy between sail and fusion concepts for Project Icarus, the ongoing re-thinking of the Project Daedalus starship design of the 1970s. We’re in the early days of Icarus, with major issues of configuration still unresolved, but Galea uses Daedalus as a starting point and looks to establish boundary conditions, assuming Alpha Centauri A as the probe’s destination.

Icarus has the ambitious goal of reaching speeds between ten and twenty percent of lightspeed, and if at all possible, the designers would like to allow deceleration, either slowing the craft enough to increase encounter time at the target or, in the best case, allowing it to enter an orbit around the star. Remember, Icarus (based on Daedalus) may mass a whopping 50,000 kg after fuel depletion. Galea finds that even assuming an ideal sail, deceleration to orbital capture would involve a sail 944 kilometers in diameter. It would be interesting to compare this number with the specs on a magsail, and I imagine the Icarus team will be running those numbers in the future.

A 944-kilometer sail seems out, but sail technologies can be of use in other aspects of this fusion-centric mission. Galea goes on to ponder using gravitational lensing for communications, noting that solar sail missions to 550 AU and beyond are not all that different from concepts already under discussion for interstellar precursor missions. Claudio Maccone’s FOCAL mission stretches the technology but comes up with realistic methods to reach these distances and deploy tethered-antennae lensing equipment. Maccone has also shown the viability of gravitational lensing for communications at interstellar distances. Thus a mission to 550 AU to establish a communications relay to support Icarus remains a possibility.

Another potential use of sails would be the deployment of sub-probes once Icarus passes through the destination system. The original Daedalus design included up to eighteen sub-probes that would investigate planets in the Barnard’s Star system. Deploying sail-based sub-probes would work if Icarus can decelerate (presumably using its fusion engines) into a stellar orbit. Remaining to be considered is whether solar sails could be of value for these sub-probes in a decelerated flyby, which is the more likely scenario given the huge difficulty in decelerating such a large payload to an orbit in the target system. Galea’s conclusions follow:

The likely large mass of the Icarus craft at launch and arrival in the target system, together with the high interstellar speed renders the use of solar sails implausible for useful acceleration or deceleration of the craft as a whole. However, the two aspects of the mission that could usefully use sails are the deployment of sub-probes in the target system, and the deployment of the gravitational lens communications receiver… Both of these types of craft have similar requirements to solar sails that are traditionally discussed for interplanetary missions.

Finding the Baseline

Figuring out the limits on things is how we proceed with developing new technologies. Not long ago I discussed Ralph McNutt’s recent work at JHU/APL on realistic manned missions to the outer planets. The huge price tag had a number of correspondents baffled. How could we justify the outlay of trillions of dollars on a handful of missions to explore these planets? But nobody was arguing that we should. The point of such studies is to develop the baseline, to tell us where we are today and where we will be in the near future in terms of costs and capabilities. By doing such studies, we learn where we need to improve our methods and revise our thinking.

There is a huge gap between the first successfully deployed sail in space (IKAROS) and the deep space concepts that are kicked around in the literature. But it is only by analyzing those concepts and pushing the limits of our current science that we get a realistic view of the goal. Conferences like ISSS 2010 go from present and near-term all the way to remote future uses of technologies we can’t yet build today. They’re necessary, mind-bending exercises in the art of the possible based on the achievements we’ve already produced. And this year, IKAROS gave every solar sail-minded scientist cause for celebration and renewed effort.

Tomorrow: A look at DLR and ESA’s solar sail work.

This article was originally posted on Centauri Dreams

Before I move into today’s story on Titan, I want to mention that those of us who weren’t able to attend the ongoing Second International Symposium on Solar Sailing (ISSS 2010) can take heart in the fact that selected papers from the proceedings have been quickly published online. Conferences vary tremendously in the resources they make available during and after the event, but the ISSS organizers are obviously intent on wide distribution of these interesting talks. Let’s hope those papers not yet included will find their way online in coming days.

TZF’s Pat Galea has posted a number of photos from day one of the event on Flickr, including this shot of JAXA’s Osamu Mori delivering an early talk on the IKAROS mission. Project leader for IKAROS, this man is a solar sail pioneer.

For those of you who’ve asked, the focus of ISSS 2010 is indeed near-term, although several longer-range papers will be presented. With our first operational solar sail only recently launched, this is a time to evaluate where we are and what the next steps will be. The conference is described in the proceedings as being:

…focused on recent advances in solar sailing technologies, near-term solar sailing missions and the physics of solar sailing. Areas of particular interest included dynamics analysis and testing of solar sails, advanced materials and structural concepts of solar sails, hardware and enabling technologies, mission architectures and programs, navigation, control, and modeling.

A Receding Shoreline on Titan

But on to Titan, where the lake levels of Ontario Lacus have continued to spur interest. Last week we learned that this, the largest lake in Titan’s southern hemisphere, is showing clear signs of liquid methane evaporation. It took an examination of four years of Cassini data to show a 1-meter drop in the lake level per year, evidently the result of seasonal evaporation of liquid methane from the mixture of methane, liquid ethane and propane that fill the lake.

The researchers used data from Cassini’s Synthetic Aperture Radar (SAR), studying the intensity of the radar backscatter to derive information about the composition of surface features. They were also able to tap radar altimetry data collected across part of Ontario Lacus from a December 2008 flyby. Oded Aharonson (Caltech) notes the effectiveness of the instruments and the implications of their findings:

“The combination of SAR and altimetry measurements across the transect gave information about the absorptive properties of the liquid, and argues that the liquids are relatively pure hydrocarbons made up of methane and ethane and not a gunky tar.”

Image: This image of Ontario Lacus, the largest lake on the southern hemisphere of Saturn’s moon Titan, was obtained by NASA’s Cassini spacecraft on Jan. 12, 2010. North is up in this image. Objects appear bright in the radar image when they are tilted toward the spacecraft or have rough surfaces. The lake surface appears dark because it is smooth. The northern shoreline features flooded river valleys and hills as high as 1 kilometer (3,000 feet) in altitude. Credit: NASA/JPL-Caltech.

Cassini’s radar can see through the liquid down to a depth of several meters. The radar will then bounce off the lake floor or, in deeper areas, will be completely absorbed, so that the signature is black. Alexander Hayes, a Caltech graduate student who worked with Aharonson on the project, notes that the lake liquid’s optical properties have been characterized enough to allow the local slope of the lakebed (bathymetry) to be detected. The team was thus able to calculate the slope of the lakebed around the entirety of Ontario Lacus.

The slope turns out to be fairly steep along the lake’s northern boundary as it runs up against a range of mountains, while the lake is at its most shallow and gently sloped along the southern edge, and it is here that sediment is accumulating. Along its eastern shore, the slope of the lake is somewhat steeper. “This is what we are calling the ‘beachhead,’” Hayes says.

The Approach of Autumn

What the researchers have found at Ontario Lacus parallels what Cassini shows about the evaporation of methane from nearby lakes, comparing 2007 data with data from May of 2009. The radar-attenuating liquid decreased or disappeared entirely in these, indicating a reduction of the liquid levels. The same one meter per year loss rate emerges in these results. If you haven’t already seen it, the video tour of Ontario Lacus based on radar data from Cassini’s flybys of Titan is well worth a look.

Cassini’s continued presence in the Saturnian system is paying major dividends. The spacecraft arrived in 2004, when the southern hemisphere of Saturn and its moons was experiencing summer. Now we’re seeing autumn approaching on Titan, a place whose year is the equivalent of about 29 Earth years. As for Ontario Lacus itself, the evaporation now seen from the lake would most likely reverse during winter in the southern hemisphere. It’s breathtaking to consider that we’re dealing with a lake whose surface area (about 15,000 square kilometers) is only slightly smaller than Lake Ontario here on Earth.

This article was originally posted on Centauri Dreams

Solar Sails in Brooklyn

I should probably clean out my office, and would, if I could find the time, but things keep happening in the deep space community and I keep writing about them. I had the program for ISSS 2010 (the Second International Symposium on Solar Sailing) right beside me when I started to write yesterday’s entry, and by the time I got to the part on the conference, the program had disappeared into the wilderness of printouts, notebooks and letters. Thus I missed the fact that Colin McInnes would be in attendance at the sessions, a major addition to the already stellar lineup. McInnes could be said to have written ‘the’ book on solar sailing, a densely packed tome that lays out the principles and speculates on future missions.

Meanwhile, it’s heartening to see how international the solar sail effort has been from the outset, even if all the space agencies have continued to wrestle with their own funding demons. Much good work has gone on at Germany’s DLR, for example, to be reported on in the context of a DLR-ESA roadmap this morning (Tuesday). JAXA is, of course, present in a big way, with performance analyses of the IKAROS sail and discussions of the new technologies, especially in hybrid propulsion, that it represents. Les Johnson will bring the audience up to speed on NASA’s solar sail history and new mission ideas will be represented from each agency.

At left is McInnes’ Solar Sailing: Technology, Dynamics and Mission Applications (Springer/Praxis, 1999), an unfortunately expensive but critical addition to the library on deep space propulsion. I love the quote from Voltaire’s Micromegas (1752) that introduces the volume:

Our traveler knew marvelously the laws of gravitation, and all the attractive and repulsive forces. He used them in such a timely way that, once with the help of a ray of sunshine, another time thanks to a co-operative comet, he went from globe to globe, he and his kin, as a bird flutters from branch to branch.

Hearing those lines and thinking of that fluttering bird inevitably brings IKAROS to mind and those first, thrilling images of a solar sail deployment in space. McInnes will be discussing an idea he also kicked around in the book in a session at ISSS 2010, a near-term ‘pole sitter’ mission using solar sail methods (his title in the conference program indicates ‘hybrid propulsion,’ so I’m wondering if he’s thinking, like JAXA, about onboard solar cells).

Pondering Stellar Destinations

As long as we’re talking about solar sails, we can dream about future interstellar targets that may one day be visited by hybrid versions of this technology, perhaps using beamed propulsion. A new paper about the incidence of binary and multiple star systems is just out (thanks to Antonio Tavani for the pointer on this). It involves systems in which one member is a star like our Sun. The idea that most systems involving a star of our Sun’s mass are binary or multiple is problematic. It implies a lack of planetary stability that could compromise the possibilities for life. Now Deepak Raghavan (Georgia State) and colleagues are reporting the results of their own survey, one that tunes up and extends these earlier assessments.

Raghavan’s team worked with a sample of 454 stars chosen from the Hipparcos catalog, all like the Sun and within a range of 25 parsecs from Sol. What emerges is that 54 percent (plus or minus 2 percent) of Solar-type stars in our neighborhood are single (the earlier best estimate was 43 percent). The authors believe that earlier studies were off-target because they lacked the more accurate astrometry data available from the Hipparcos catalog, and in the case of a major study in 1991, were beset with parallax errors that skewed the results. In addition, the new research works with a much larger sample (454 vs. 164 Solar-type stars).

If we’ve overestimated the number of Sun-like stars with stellar companions, does this change our outlook on life elsewhere? We’re really asking whether planets are as likely to form and be stable in multiple star systems as they are around single stars. We’re accumulating enough data from the ongoing exoplanet hunt to start to make reasonable projections about at least part of this. Let’s wade into the paper to address the question, which resonates in light of that binary system with a distant companion we’ve got a scant 4.3 light years away from Earth. The first point is to examine this study’s conclusions as compared to earlier work:

Contrary to earlier expectations, recent studies… have shown that planetary systems are quite common among binaries and multiple systems. In a comprehensive search for stellar companions to the then known exoplanet hosts, Raghavan et al. (2009) concluded that even against selection effects, as many as 23% (30 of 131) of the exoplanet systems also had stellar companions. A recent report… showed that 17% (43 of 250) of exoplanet hosts were members of binary or multiple systems. In comparison, 30% (11 of 36) exoplanet systems of this study have stellar companions. This represents the largest percentage of stellar companions in any sample yet of exoplanet systems, likely due to the thoroughness of companion detection in this sample of nearby Sun-like stars. This is however still smaller than the 46% of stars having companions in the overall sample, presumably because all the exoplanets discovered to-date are from surveys that avoid known spectroscopic binaries.

So far, so good. The case for planets in binary or multiple systems is strong, although this will obviously depend upon the specifics of the system in question. A strong case can be made for stable planetary orbits out to 3 AU and perhaps a bit farther around Centauri A and B, for example, but whether or not planetesimals have been able to form around these stars that could produce rocky planets is still an open question, one we’ve discussed here on numerous occasions. But it’s clear that ruling out planets because of multiple star systems is a mistake.

Raghavan and colleagues then put numbers to our expectations in such systems (the italics in the quotation below are mine):

One key question is whether binary and multiple systems are equally likely to form planets as are single stars. Our results show that 9% ± 2% of the single stars have planets, compared to 7% ± 2% of binaries and 3% ± 3% of triples. These fractions are statistically equivalent, suggesting that single stars and stars with companions are equally likely to harbor planets. Moreover, while sufficiently short-period binaries will disrupt protoplanetary disks, hampering planet formation around either star… many binaries in this study have sufficiently long periods to foster planet formation around each stellar component.

I’ve left off some of the internal references for clarity as well as one of the supporting figures, but the conclusion seems robust. It remains for us to learn more about long-term planetary stability in the varying multiple systems we’re uncovering.

We now have three ongoing planet searches of Centauri A and B and may learn in coming months whether the average separation of these stars (about 24 AU) is sufficient to allow rocky planets to form (our earlier discussion of Ji-Wei Xie’s paper on the matter, which argues that a habitable planet is feasible around Centauri B, is here). It will be fascinating to learn how close stars can be to each other to allow planetary systems to form around each, but it’s clear the search for life will take in many multiple star systems as we learn more about planetary lifetimes.

The paper is Raghavan et al., “A Survey of Stellar Families: Multiplicity of Solar-Type Stars,” accepted for publication by The Astrophysical Journal and available as a preprint.

This article was originally posted on Centauri Dreams

WISE Completes First Full Survey

The WISE mission completed its first survey of the entire sky on July 17, generating more than a million images, of which one of the most beautiful is surely the image of the Pleiades cluster below. We’re looking in the infrared at a mosaic of several hundred image frames with the combined light of WISE’s four detectors working in a range of wavelengths. The cluster of stars in seen in a dense latticework of dust in an area covering seven square degrees, equivalent to about 35 full moons.

Image: In this infrared view of the Pleiades from WISE, the cluster is seen surrounded by an immense cloud of dust. When this cloud was first observed, it was thought to be leftover material from the formation of the cluster. However, studies have found the cluster to be about 100 million years old — any dust left over from its formation would have long dissipated by this time, from radiation and winds from the most massive stars. The cluster is therefore probably just passing through the cloud seen here, heating it up and making it glow. Credit: NASA/JPL-Caltech/UCLA.

In addition to sights like these, WISE has thus far rung up 100,000 asteroids, 25,000 of which were previously undetected. Because Centauri Dreams readers have been concerned about data release (after our discussions of the Kepler policy on these matters), it’s worth noting that the first release of WISE data covering some 80 percent of the sky will be offered in May of next year. WISE goes on to map half the sky again, operating until its solid hydrogen coolant runs out. An extension to the mission using two infrared wavelengths without coolant hasn’t been ruled out.

And as we wait for possible brown dwarf detections, the recent paper by Adrian Melott and Richard Bambach comes to mind. You’ll recall in our discussion of the paper that the researchers found a repetitive 27-million year cycle in extinction events going back some 500 million years, and argued that this weighed against the idea of a dark companion to the Sun (‘Nemesis’) because the orbit of the latter object would be more variable than the extinction cycle. Comments here and on other sites make it clear that the 27-million year cycle may not be as robust as the authors believe, leaving the status of a dark companion unresolved.

Will WISE find a brown dwarf or a gas giant somewhere in the Oort Cloud? Let’s hope the data the mission produces either finds the object or puts ‘Nemesis’ to rest.

Interstellar Ideas at Solar Sail Conference

Tau Zero practitioner Pat Galea will be presenting a paper at the upcoming Second International Symposium on Solar Sailing (ISSS 2010), which convenes at the New York City College of Technology of the City University of New York tomorrow. A member of the Project Icarus team, which is at work designing a fusion-based successor to the Project Daedalus design, Pat will be examining the possible uses of solar sail technology in the mission. How to combine fusion and sail? Here’s the abstract:

Project Icarus is an in-depth theoretical engineering design study of a mission to another star, following on from the historically successful Project Daedalus. While the terms of reference for the project specify that the spacecraft propulsion system will be mainly fusion-based, aspects of the mission and overall architecture could be implemented or assisted by the use of solar sails. This discussion paper gives a brief overview of the aims of Project Icarus, and examines the potential application of solar sails in several areas of the mission. This includes: assisted boosting of the Icarus probe out of our solar system; deploying sub-probes in the target solar system for exploring local planets and other objects of interest; deploying a relay station at the Sun‘s gravitational focus to receive transmissions from the distant Icarus craft. This paper discusses some of the engineering requirements for these potential roles as well as any potential performance enhancements to the mission.

You’ll find the full program for this timely meeting online. I call it timely because of the recent success of JAXA’s IKAROS sail and the upcoming LightSail mission sponsored by the Planetary Society. JAXA’s Osamu Mori, project leader for IKAROS, will be a speaker at the session, as will the Planetary Society’s Lou Friedman, along with sail luminaries from ESA and NASA. Have a look at the program to see how rich this conference should be. I hate to miss any of it, but will particularly regret not hearing Ed Belbruno, Les Johnson, Roman Kezerashvili and Greg Matloff.

Calendar watchers will also note that the International Astronautical Congress 2010 is coming up this September in Prague, during which meeting Pat Galea will be discussing the possibility of using gravitational lensing for communications with an Icarus-style craft. I’ll publish the abstract to that talk as we get closer to the event, but I do want to note that Tau Zero founding architect Marc Millis will be presenting four papers of his own in Prague as part of a robust Tau Zero presence at the meeting (I know Claudio Maccone is going, as is Tibor Pacher, and I’m sure Greg Matloff will be in attendance along with a number of Project Icarus team members including Kelvin Long).

Farside Protection at Ames (and a Lensing Find)

Speaking of Claudio Maccone, the good doctor tells me in a recent email that he will be discussing lunar farside protection this Tuesday at NASA Ames. You’ll recall our recent examination of creating a ‘quiet zone’ on the farside that would keep the area pristine for radio astronomy and SETI work. Maccone is suggesting that the 80-kilometer Daedalus Crater would be an ideal location for a scientific installation, shielded from Earth-made radio pollution. His talk is part of the 3rd annual NASA Lunar Science Forum, which runs through the 22nd at the NASA Ames Conference Center.

Thoughts of the FOCAL mission to the Sun’s gravitational lens are never far when discussing Claudio Maccone, and the recent news out of Caltech and the Ecole Polytechnique Federale de Lausanne (EPFL) instantly caught my eye. Researchers have found the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens. We know about hundreds of gravitationally lensed quasars, magnified by a foreground galaxy, but this is the first example of a background galaxy lensed by the host galaxy of a foreground quasar.

Image: The quasar SDSS J0013+1523 (blue), bracketed by the lensed images of the background galaxy (red), obtained with the W. M. Keck Observatory’s 10-m telescope and Adaptive Optics. Credit: Caltech/EPFL.

I also found the lensing diagram available via Caltech to be helpful:

This ‘reverse lensing’ is extremely useful because quasars, thought to be powered by supermassive black holes in the centers of galaxies, can be a thousand times brighter than the galaxy in which they are embedded. That makes studying the host galaxies quite difficult — EPFL’s Frederic Courbin likens it to staring into car headlights and trying to figure out the color of their rims. But lensing, he adds, changes things: “We now can measure the masses of these quasar host galaxies and overcome this difficulty.”

If quasars are a useful probe of galaxy formation and evolution, as Caltech’s S. George Djorgovski says in this news release, the lensing method itself is away of probing distant astronomical objects as well as those closer to home. Maccone’s FOCAL mission would use the Sun’s gravitational lens at 550 AU to study a variety of astrophysical issues, and could conceivably be used for close study of nearby solar systems. More exotic applications in SETI and, as Pat Galea will describe at the IAC, in communications, may well follow.

This article was originally posted on Centauri Dreams