by Paul Gilster | Jul 25, 2008 | Exoplanetary Science |
Finding transiting planets is no longer a surprise, and we can expect a host of transits from the CoRoT mission, which has the advantage of observing from a space-based platform. Moreover, CoRoT will, in the course of its lifetime, survey as many as 120,000 stars for up to five months. Driving home the advantage is the announcement of a new CoRoT planet known as CoRoT-Exo-4b.
We’re dealing with another Jupiter-sized planet orbiting in close proximity to its star, but this one has a unique claim to distinction: Its host star is rotating at the same pace as the planet’s orbit.
Image: Fixated upon a star: An artists impression of the satellite CoRoT in orbit around the Earth. Credit: CNES.
Moreover, for a transiting world, CoRoT-Exo-4b is a relatively long-period planet, orbiting its F-class primary in 9.2 days. Thus far most transiting worlds have had orbits below about five days, two major exceptions being HD 147506b and HD 17156b, the latter with a period of 21.2 days — both of these planets are in highly eccentric orbits. Working out what’s going on in this system is going to prove interesting, and doubtless illuminating when it comes to other planetary systems. Says Suzanne Aigrain (University of Exeter), who discussed the find at the Cool Stars, Stellar Systems, and the Sun conference being held in St. Andrews:
“We don’t know if CoRoT-Exo-4b and its star have always been rotating in synch since their formation about 1 billion years ago, or if the star became synchronized later. CoRoT will no doubt find many more transiting planets, and by systematically measuring their host stars’ rotation periods we will gain valuable insight into how stars interact with their planets.”
CoRoT’s observations are backed by ground telescopes, but the lack of atmospheric distortion that the spacecraft experiences means that we may be finding interesting worlds not all that much larger than the Earth. Moreover, in the case of larger worlds like CoRoT-Exo-4b, the continuous coverage CoRoT can bring has allowed scientists to make precise studies of the host star between transits, thus providing a way to measure the star’s rotation by tracking dark spots on its surface. So we’ve moved beyond planetary detections into the science of planetary interactions with the primary, as noted in the paper on this work:
This system clearly warrants further observational and theoretical investigation to pin down its tidal and rotational evolution status. For example, more detailed analysis of the out-of-transit light curve should enable the active regions on the stellar surface to be mapped in a time-resolved fashion… to search for signs of star-planet magnetic interaction.
The paper is Aigrain et al., “Transiting exoplanets from the CoRoT space mission IV. CoRoT-Exo-4b: A transiting planet in a 9.2 day synchronous orbit,” now available on the arXiv site and accepted for publication in Astronomy & Astrophysics. A news release from St. Andrews is here.
by Paul Gilster | Jul 24, 2008 | Exotic Physics |
For those of you who don’t see Spaceflight, a magazine published by the British Interplanetary Society, it may be useful to know that an article by Richard Obousy and Gerald Cleaver (Baylor University) on warp drive theory from the April issue is now available on the arXiv server. This material was presented at the November, 2007 symposium held by the BIS in London. Kelvin Long, who organized the session, had earlier passed along several documents from the proceedings that we looked at here, and also wrote up the duo’s ideas in the same issue of Spaceflight.
But let’s backtrack a minute to Miguel Alcubierre’s 1994 paper, which demonstrated that it would be possible — within the context of General Relativity — to envision a space drive that could get you to your destination in a time shorter than it would take light itself to get there. Contracting space in front of the craft while inflating it behind, the drive is permissible because the starship itself would not be going faster than light. Rather, the space around it would be moving in such a way as to make the trip possible.
And that’s the key — the speed of light stricture does not apply to spacetime itself. Can we learn how to generate a region of expanding spacetime and one of contracting spacetime? Obousy and Cleaver argue that nature can offer insights, for spacetime itself is already expanding, a fact we realized with the work of Edwin Hubble in 1929 and have been wrestling with in various ways ever since. A warp drive would demand that the slow expansion of space that we observe be made to function extremely quickly, which makes understanding the cosmological constant the key demand of any attempt to build a true warp drive.
Now we’re truly in deep water, for attempts to explain the cosmological constant using quantum field theory have been shown to be off by a factor of 10120, an obvious marker of how far from descriptive current explanations are. The authors then turn to supersymmetry — the theory that all particles have an associated superparticle with a differing spin — to explore the question. And in rapid order they consider the cosmological constant in terms of higher dimensions, relating these first to the work of Theodore Kaluza, who suggested a fifth dimension in 1919, and then in ongoing efforts to explore extra dimensions using string theory.
Thus a potential scenario for an Alcubierre-style warp drive emerges:
In a recent paper, we addressed the plausibility of locally in?uencing the size of the extra dimension to locally (by local, we mean in the vicinity of a spacecraft) adjust the cosmological constant. This could theoretically create a modi?cation of spacetime around a craft that could be tuned to acquire the characteristics of the Alcubierre bubble… The basic idea is that by altering the radius of an extra dimension, it would be possible, in principle, to adjust the energy density of spacetime (which relates directly to the cosmological constant which ultimately controls the in?ation/contraction of space itself). We have taken two approaches to this concept: one from the viewpoint of QFT another from GR. The equations of both theories indicated that the physics of the extra
dimensional space e?ects the expansion rate of ‘normal’ space by a ‘dimensional shearing’ e?ect. The equations of GR demonstrated that shrinking the extra dimension would in?ate our space, and that expanding the extra dimension would contract our space. In this way, a bubble of expanding/contracting spacetime could be created at the rear/front of a spacecraft.
How fast might a warp-driven spacecraft go? Obousy and Cleaver work out an upper limit on such a velocity (based upon quantum field theory) of 1032 c, c being the speed of light. Mind boggling to be sure, but tempered by the fact that the energy required for such a velocity is significantly greater than that available in the observable universe. Another of those ‘small problems of engineering,’ as Robert Forward used to call them…
Clearly, we’re up against huge hurdles, many of them suggested by this paper. Will we validate the idea of supersymmetry in the near future? Will some variant of string theory be subjected to experimental analysis, and if so, how? What sort of engineering would actually contribute to manipulating an extra dimension even if we were able to find one? No, I wouldn’t expect a warp drive breakthrough any time soon, but laying a theoretical basis for a technology has to be step one. That means parsing the issues and identifying potential solutions, some of which may be investigated and perhaps demonstrated in subsequent experiments.
The paper is Obousy and Cleaver, “Putting the ‘Warp’ into Warp Drive,” Spaceflight, Vol 50, No.4, April 2008, pp. 149-151 (available online).
by Paul Gilster | Jul 23, 2008 | Deep Sky Astronomy & Telescopes |
How does a planet full of amateur and professional astronomers miss an exploding star that was one of the brightest novae in the past ten years? The fact that the event called V598 Puppis (the brightening of the star USNO-A2.0 0450-03360039) was only spotted days after its explosive appearance by an orbiting space observatory that was turning from one target to another seems remarkable, but maybe it’s a salutary reminder that with resources limited on the professional level, amateurs are still needed to track such interesting events.
The observatory in question was ESA’s XMM-Newton, an X-ray observatory whose data is recorded even as the satellite moves between different objects. That ‘slewing’ data revealed that the star in question had brightened by more than 600 times, as verified by later observers at Las Campanas Observatory in Chile. The evident cause: A white dwarf drawing off gas from a companion star, building sufficient quantities that a nuclear reaction released the observed energies, which were finally seen as an increase in brightness.
Image: The nova V598 Puppis, accidentally discovered in the XMM-Newton slew survey. The X-ray contours, which indicate the position of the nova, are overlaid on an image composite (infrared, red and blue channels) from the SuperCOSMOS Sky Surveys (SSS), Royal Observatory, Edinburgh. Credit: Contours: ESA/ XMM-Newton/ EPIC (adapted from A. Read et al.), Background: SSS.
XMM-Newton, because it operates at X-ray wavelengths, was an unlikely discovery mechanism, X-rays generally being masked by the debris cloud of the detonation before they are detected. That means the explosion took place days before the orbiting observatory spotted it, with no reports from Earth-based sweeps of the sky that look for such events. Once found, the source was the subject of a report quickly circulated on the Internet, and the stars involved subjected to intense study.
Says Andy Read (University of Leicester):
“Suddenly there was all this data being collected about the star. For variable star work like this, the contribution of the amateur community can be at least as important as that from the professionals.”
Indeed. Accidental discoveries are among the most exciting events in science, the sort of thing those of us with a yen to get involved may find irresistible to pursue, now that it has become apparent that a nova visible to the naked eye could escape current notice. Plenty of work can be done at the amateur level, which is now feeding useful data to all kinds of professional projects including the hunt for extrasolar planets (see TransitSearch for more on just one such opportunity). As the cost of admission drops with further miniaturization and the inevitable price curve of electronics, the opportunities should only grow.
by Paul Gilster | Jul 22, 2008 | Deep Sky Astronomy & Telescopes |
The image below is striking enough that I would have run it even without the interesting story it tells about the presence of organic materials in Messier 101. Viewed at infrared wavelengths and color-coded, the Pinwheel galaxy’s spiral arms are visible, as is an outer zone, marked by a coral color, in which the organic molecules called polycyclic aromatic hydrocarbons disappear. These hydrocarbons are typically found in areas of star formation, with interesting implications for the appearance of life. So what does an organic-free zone tell us about the Pinwheel galaxy?
“If you were going look for life in Messier 101, you would not want to look at its edges,” said Karl Gordon of the Space Telescope Science Institute in Baltimore, Md. “The organics can’t survive in these regions, most likely because of high amounts of harsh radiation.”
Image: The Pinwheel galaxy, otherwise known as Messier 101, sports bright reddish edges in this new infrared image from NASA’s Spitzer Space Telescope. Research from Spitzer has revealed that this outer red zone lacks organic molecules present in the rest of the galaxy. The red and blue spots outside of the spiral galaxy are either foreground stars or more distant galaxies. Credit: NASA/JPL-Caltech/STScI.
The Pinwheel is also interesting because of its high metal gradient (in astronomical terms, metals are elements heavier than helium), the galaxy showing a wide range between the concentration of metals at its center and those in the outer disk, the result of metal-producing stars being found primarily in the central regions. The gradient of polycyclic aromatic hydrocarbons here acts much the same, decreasing in concentration with distance from the center, but in the case of the organics, these molecules simply disappear in the area of the galactic rim, the victim of radiation.
All of which makes Messier 101 useful indeed. The lack of polycyclic aromatic hydrocarbons sets up a laboratory for the study of star formation in such environments. Their normal contribution is to help cool star-forming clouds, but stars in the rim regions of the Pinwheel must form, as did stars in the early universe, without the help of organic dust. The paper is Gordon et al., “The Behavior of the Aromatic Features in M101 H ii Regions: Evidence for Dust Processing,” Astrophysical Journal 682 (July 20, 2008), pp. 336-354.
Centauri Dreams note: A news item about a galactic rim invariably brings to mind the remarkable A. Bertram Chandler, sailor, merchant marine captain and author of forty novels, as well as over 200 short stories. Born in England, he wound up an Australian, and despite his demanding profession, the chronicler of the distant worlds of the Rim. Chandler’s nautical background fed his settings and plot in both the Rim World series and his novels about space sailor John Grimes, of the Federation Survey Service. I always imagined Chandler in his quarters typing away at a battered keyboard, his log for the day complete, sketching the farthest reaches of space with the calm, practiced skill of a man used to command. I wonder what this ship’s master would have made of the ‘no-organics’ zone around the Pinwheel galaxy…
by Paul Gilster | Jul 21, 2008 | Culture and Society |
It dawned on me over the weekend that Centauri Dreams will soon enter its fifth year of operation, the anniversary being in mid-August. On Sunday I walked the neighborhood, musing over the changes the site has seen and thinking back to its inception. I realized that the actual germ of the idea goes back not to 2004 but to 1986. In those days I was, among other things, writing wine and restaurant reviews, and I found myself in Winston-Salem NC, where I had been sent to review some hot new bistro or other. That night in my hotel room I watched a news item on Voyager, which had just encountered Uranus, and reflected about human futures.
The thinking went like this: Launched in 1977, the Voyagers could accomplish their prime mission easily within the lifetimes of those who sent them (their extended mission beyond the heliopause wasn’t much discussed back then). But I began to imagine truly long-haul missions that would be brought home not by the people who sent them but by the next generation, or perhaps the one after that. The idea of handing off ideas and technologies went into the Centauri Dreams book that I wrote almost two decades later, and the imperatives of long-term thinking continue to be a major thematic focus for the site that has evolved from it.
On Friday, I ran into a 1984 paper by Thomas Sebeok, cited on the Long Now Foundation’s site. Sebeok was writing about the problems of communicating with the future. Specifically, how do you let people for a period covering the next 10,000 years know that a nuclear waste site is dangerous? The author’s proposal was to divide up the 10,000 year period — approximately 300 human generations — into much shorter periods, perhaps three generations long. That way you can leave messages in modern languages that can be understood, supplementing them as necessary with pictorial information whose cultural background would be relatively familiar.
Sebeok goes on:
This message, however, would have to be supplemented by a metamessage — coded in the same combination of familiar verbal/averbal signs — incorporating a plea and a warning that the object-message at the site be renewed by whatever coding devices seem to be maximally efficient, roughly, 250 years since. That future object-message should, in turn, incorporate a similar metamessage for the generation 500 years from now to act comparably, and so on, and on, up to 10,000 years ahead.
It is the meta-message that keeps the concept alive. And so we have another instance of information being handed down, a particular ‘artifact’ that must be preserved and understood over hundreds of generations. Science fiction writers have toyed with the concept of information handoffs for a long time. You can see something of the concept in fine novels like Brian Aldiss’ Starship (originally published in Britain as Non-Stop), where the basic parameters of the mission are gradually lost and must be reacquired by the crew on a multi-generational voyage spanning thousands of years. Heinlein, of course, plays with this familiar trope, as have many writers, and we’ve seen the multi-generational starship being explored by groups such as The Ultimate Project today.
My hope for Centauri Dreams actually fits into this paradigm. I would like to think that I can keep this site active for a long time, promoting the spread of news about interstellar subjects as well as a philosophy of engagement and exploration of the cosmos that will resonate with like-minded people and perhaps win over some who are skeptical of the whole notion of going into space. But when I do stop working, I would like to hand Centauri Dreams off to someone who will keep it going. If I can indulge an extravagant notion, I would hope to see Centauri Dreams in some form survive to keep pushing these ideas through different successors until the first interstellar mission actually leaves the Solar System.
Sure, this sounds preposterous. Who knows when and if an interstellar mission — especially one with a human crew — will every fly? But even if it takes centuries, there should always be a core of people fascinated with the interstellar idea who continue to work on it. The premise of the Tau Zero Foundation is to build incrementally (ad astra incrementis), so that while none of us may live to see such a mission, the steps we take now will have played some small role in arriving at that outcome.
Image (above): An interstellar ramjet, one of the many concepts developed by 20th Century theorists to manage the daunting distances between the stars. How will these ideas change in our century? Credit: ITSF/Manchu.
Think of the familiar computer voice on Star Trek’s Enterprise. Somewhere in that circuitry is a digital history recording every possible scrap of human history. It would be a thrill to think that a future star mission might have in some tiny corner of its vast computer memory the history of the earliest days of the interstellar effort, and that the words assembled here might one day be read in such a setting, by some historian trying to follow the development of the idea and how it played long before.
Fanciful? Sure, and who’s to say that a nuclear-tipped civilization will survive long enough to build starships? I certainly don’t have the answer, but building toward an interstellar future demands optimism of the sort I hope these pages convey. We all try to get through the next 24 hours doing the best we can in the context of an envisioned future that will be better than today, carrying the conviction that hope is not a futile thing. Civilization is all about handing off knowledge, to the people around you and those who come after. Eventually that knowledge gets re-coded, like Sebeok’s constantly re-written warning, but the meta-message is the key. It tells us to keep renewing what we do to bring the idea home.
