by Paul Gilster | Jul 31, 2008 | Outer Solar System |
Remember those oceans of methane we thought might exist on Titan? They were an exciting thought (I recall hypothetical images of the Huygens probe bobbing in such an ocean at the end of its journey, before we knew what it would actually land on). It’s exciting to confirm that liquid does exist on Titan’s surface in the form of liquid hydrocarbons, with a positive identification of ethane. At least one of the large lakes the Cassini orbiter has found there contains the substance, but we also know that numerous other lake-like areas exist beneath the smog.
Image: The Imaging Science System aboard NASA’s Cassini orbiter took the image, left, of Ontario Lacus in June 2005. (Image credit: NASA/JPL/Space Science Institute.) Cassini’s Visual and Infrared Mapping Spectrometer took the image, right, of Ontario Lacus in December 2007. This view, taken at 5-micron wavelengths from 1,100 kilometers (680 miles) away, shows the part of the lake that is visible on Titan’s sunlit side. What appears to be a beach is seen at the lower right of the image, below the bright lake shoreline. (Credit: NASA/JPL/University of Arizona).
The news should come as no major surprise, just as discovering water ice on Mars is momentous but at the same time long anticipated. But in both cases making the detection has been tricky, on Titan because atmospheric hydrocarbons make observing a challenge. Cassini managed the feat with its visual and infrared mapping spectrometer (VIMS) nonetheless, and we now know that Ontario Lacus, a bit larger than Lake Ontario on Earth and imaged in late 2007 on Titan’s south polar region, is awash. More in this JPL news release.
“Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan,” said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey in Flagstaff, Ariz. “The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan’s atmosphere, raises expectations for exciting future lake discoveries by our instrument.”
And note this, from VIMS principal investigator Robert H. Brown (University of Arizona):
“It was hard for us to accept the fact that the feature was so black when we first saw it. More than 99.9 percent of the light that reaches the lake never gets out again. For it to be that dark, the surface has to be extremely quiescent, mirror smooth. No naturally produced solid could be that smooth.”
Thus we learn more about a hydrological cycle based on methane, with ethane and other hydrocarbons created by the breakdown of atmospheric methane by sunlight. Other evidence of the cycle seems glaringly obvious, in the form of channels evidently carved by fluids, along with evidence of rain and evaporation. Indeed, Ontario Lacus, ringed by a gradually more exposed beach, seems to be evaporating as we watch. Seasonal change in this dynamic environment should be fascinating to monitor as, in a few years, Titan’s north pole emerges into sunlight.
by Paul Gilster | Jul 30, 2008 | Deep Sky Astronomy & Telescopes |
If dark energy is accelerating the expansion of the universe, how can we identify its signature? Researchers at the University of Hawaii have been using microwaves to detect what they believe to be dark energy at work. If their work stands up, it will be a useful step for cosmology, but also a potential boon for those of us with interstellar travel in mind. We obviously want to understand a force that may one day have propulsion implications, and it’s possible that the universe is offering a set of useful clues. Here cosmology and propulsion science share a common interest.
Led by István Szapudi, the researchers zeroed in on galactic superclusters — the largest structures in the universe — and so-called ‘supervoids,’ vast areas with few galaxies in them. Remember the prefix ‘super’ here, for conventional galactic clusters are some ten times smaller and held together by gravity, while the Hawaii team believes galaxies in the supervoids and superclusters are more affected by dark energy than gravity. See the team’s Web site for more on the nature of supervoids and superclusters and its use of the Sloan Digital Sky Survey.
The work proceeded by imposing supervoid and supercluster information on a map of the Cosmic Microwave Background, the most distant light visible to us, stretched by the expansion of the universe into the part of the spectrum we associate with radio rather than light. As microwaves pass through them, the superclusters and supervoids have a decided effect. Says Szapudi:
“When a microwave enters a supercluster, it gains some gravitational energy, and therefore vibrates slightly faster. Later, as it leaves the supercluster, it should lose exactly the same amount of energy. But if dark energy causes the universe to stretch out at a faster rate, the supercluster flattens out in the half-billion years it takes the microwave to cross it. Thus, the wave gets to keep some of the energy it gained as it entered the supercluster.”
The image above gives an idea of the result. Microwaves passing through a supercluster are somewhat stronger than those passing through a supervoid. The team believes we are seeing dark energy at work as it stretches supervoids and superclusters to cool or heat light.
Image: These two images from the team’s paper produce spots that are highly significant; taken together, the spots have only a 1-in-200,000 chance of occurring randomly. This is arguably the clearest detection of the ISW effect (see below) to date. It has been detected before at about the same statistical significance, but those detections involve a somewhat cumbersome combination of galaxies from various heterogeneous galaxy samples (the team used a single sample). Credit: István Szapudi/University of Hawaii.
By ‘ISW,’ the team refers to the Integrated Sachs-Wolfe effect, which is responsible for the heating or cooling of photons as they pass through the supercluster and supervoid areas — if interpreted correctly, this is a direct signal of dark energy. You can read a University of Hawaii news release here, while the paper to study first is Granett et al., “Dark Energy Detected with Supervoids and Superclusters,” a look at the investigation that will be reported in the Astrophysical Journal in shorter form.
by Paul Gilster | Jul 29, 2008 | Exoplanetary Science |
Astrometry, using the position and motion of celestial objects to further astronomical research, is ever more useful in the study of extrasolar planets. If you can measure how much a given star is displaced by the presence of a planet, you have a valuable adjunct to existing radial velocity and transit methods. Now a new study has examined astrometry’s uses with binary stars, using the Hale telescope on Mt. Palomar and the Keck II instruments on Mauna Kea. And with certain restrictions, adaptive optics may allow us to detect binary star planets.
The targets were seventeen binary or multiple star systems, most of them M-dwarf binaries closer than 20 parsecs from the Sun. Observations were conducted in the near infrared, with relative separations and position angles carefully measured. Study authors Krzysztof Helminiak and Maciej Konacki (Nicolaus Copernicus Astronomical Center, Poland) note the advantage of close systems:
The closure of companions allows one to observe visual binaries in a smaller ?eld, where atmospheric distortions are weakly affecting the measurements, [the] star’s image is better sampled, and the measurements errors in pixels transfer to smaller errors in arcseconds. But, instead of parallax and proper motion, one have to take into account the orbital motion. Note also that in case of a positive detection of a 3-rd body, relative astrometry does not give the information around which particular star of the system the body is orbiting.
The funding-challenged Space Interferometry Mission, unlikely to launch before 2016, will use astrometric techniques in the hunt for terrestrial worlds around nearby stars, a search that will demand an accuracy of one millionth of an arcsecond. A characteristic ‘wobble’ in relation to nearby reference stars may indicate that the target star has a companion; indeed, the mission has the potential of detecting planets smaller than Earth around the closest stars. While we’re waiting for missions like SIM, though, the current paper shows that careful CCD imaging with adaptive optics on Earth can be a successful strategy.
Image: Astrometry focuses on measuring how the position of a star in the sky varies as the star wobbles. If the extrasolar system is seen face-on, this variation will take the form of a circular motion. If the system is seen edge-on, the variation will appear as a back-and-forth motion on the sky. Credit: Rich Townsend/University College London.
Don’t expect the detection of terrestrial worlds from this method — the authors are talking about “…much better precision than 1 milliarcsecond,” or a thousandth of an arcsecond. SIM beats that by far, but what the authors outline may be sufficient for detecting larger worlds around small stars and, of course, it’s doable today. The paper is Helminiak and Konacki, “Precise Astrometry of Visual Binaries with Adaptive Optics. A Way for Finding Exoplanets?” slated to appear in the proceedings of the Les Houches Winter School Physics and Astrophysics of Planetary Systems, (EDP Sciences: EAS Publications Series), and available online.
by Paul Gilster | Jul 28, 2008 | Culture and Society |
Tibor Pacher has gone out on a limb. The founder of peregrinus interstellar and an active supporter of interstellar research, the Heidelberg-trained physicist (now a freelance software consultant) has made a wager on the Long Bets site that should raise eyebrows: “The first true interstellar mission, targeted at the closest star to the Sun or even farther, will be launched before or on December 6, 2025 and will be widely supported by the public.” Note that no crew is assumed, the vehicle presumably being an unmanned flyby probe. We must also assume it will be targeted at the nearest star system, Alpha Centauri. Even so, to pull off the attempt in a mere seventeen years?
But my friend Tibor is a gadfly as well as an optimist. He knows as well as anyone that the time frame is outrageous, but he wants to inspire discussion and keep people thinking about interstellar issues. In the same spirit, he notes the motivations that exist, from the challenge of a seemingly impossible destination to fears about the future and the need to ensure the survival of our species. All of which is true, but I find the challenge of Tibor’s bet irresistible, and have wagered $500 on the Long Bets site that he is wrong. The proceeds would go to the Tau Zero Foundation, so both Tibor and I can win. Come on, Tibor, take the bet.
Image: An early concept for the mission now called Innovative Interstellar Explorer, designed to push several hundred AU from the Sun. I’ll buy this idea by 2025, but launching similar hardware to the Centauri stars may take a bit longer. Maybe I’m wrong, but my money is on the table. Credit: NASA/Johns Hopkins University Applied Physics Laboratory.
As to peregrinus interstellar, it is all about the furthering of research and development into interstellar flight, with studies, projects and educational efforts to be supported by private funding. Working with German science writer Michael Müller, Tibor chose the term peregrinus because, in Hungarian (his native language), the word denotes a wandering student. In Roman times, peregrinus referred to wanderers who had no rights as Roman citizens — strangers in a social sense — but the word also has the connotation of ‘pilgrim.’ Gathering a team of specialists and looking for public support, peregrinus interstellar uses the Internet as its medium in hopes of furthering research and public education, a kind of pilgrimage in its own right and one with potentially celestial rewards.
The community supporting the peregrinus interstellar effort is being built at the PI CLUB site, still under construction, but growing incrementally and reaching out to like-minded people around the globe. Tibor and I have long discussed a renewal of an interstellar bibliography that would gather all work on these topics on a yearly basis and offer a reference for researchers and scholars. Robert Forward and Eugene Mallove produced just such a bibliography many years ago, but just as we currently lack a regular journal of interstellar studies (other than special issues of the Journal of the British Interplanetary Society), we also lack a comprehensive research bibliography. Building such things is essential for furthering the effort to make serious advances in propulsion technology.
The last Forward/Mallove bibliography appeared in JBIS in 1980, including 2700 items in seventy subject categories. Forward was an inveterate organizer — at UAH-Huntsville’s Salmon Library, I sifted through copies of his antimatter newsletter, a laborious compilation of all work completed in that field during the interval since the previous newsletter appeared. Forward would gather the resources and circulate the newsletter to several hundred interested physicists, a labor of love that, like the bibliography, saved countless hours of library search time for others.
Today we use online databases for research, enjoying the benefits of computers but often the victim of fragmentary holdings, forcing us to continually widen the search in other databases with still other journals and conference proceedings. Some of these are full-text, some simply consist of abstracts. Even worse, online databases have scant coverage of older materials that can be crucial in developing a sense of how work on a particular topic has progressed over the years. No, we need better, and I’m looking forward to working with people like Tibor as we try to bring interstellar materials up to speed. His work on the PI Library is currently focused on collecting older materials and tweaking the database format that will support a continued and ever updating effort.
by Paul Gilster | Jul 26, 2008 | Culture and Society |
Is the urge for exploration innate to our species, or is it a vestigial disorder? Rand Simberg takes on the question at The Space Review this week, an article I came across thanks to a link at Music of the Spheres, which hosts the latest Carnival of Space this week. If you have an interest in simulators and flying (and as a now inactive but still interested CFII, I can relate to that!), you’ll want to be reading Music of the Spheres regularly. It’s a fine and enthusiastic blog frequently updated with space-related software discussions, and one I’ve been reading for years to follow Bruce’s adventures with the ORBITER simulator.
But back to exploration: Simberg questions whether the exploratory impulse isn’t disruptive in modern society, pointing out that most people in the world live out their lives within miles of the place where they were born, and suggesting that those who want to push a human agenda in space need a better justification than this. The candidates? Fear is one, as in fear of space debris that could wreak havoc on our planet. An even better one is greed (maybe ‘the profit motive’ sounds a little better):
The vast amount of resources in the universe resides off the planet. For example, there are single asteroids that contain a trillion dollars worth (at current market rates—no doubt retrieving that amount would depress prices considerably, not a bad thing) of platinum-group metals, used for fuel cells and other new energy applications. The same technologies that can divert errant asteroids might also allow us to retrieve and mine them.
Sunlight can be collected continuously in orbit 24/7, and there may be prospects for using it not only off the planet, but sending it down here as well. In general, opening up new natural resources means vastly increasing planetary (and solar system) wealth.
But despite the ‘fear and greed’ emphasis in his post, Simberg believes the biggest reason for opening up space is the opportunity to improve our social and political lives, and the chance to create a new laboratory for advancing the cause of freedom off-planet.
“One in which we can continue to advance the ideals of Locke, Burke, Smith and others, and escape the romantic and misguided ideals of Rousseau about the perfectability of man, rather than his institutions, that resulted in the brutal deaths of tens of millions over the past decades.”
Space offers that laboratory, but Simberg would pitch it in terms not of a vision for space ‘exploration,’ but rather space ‘development.’ Would switching the emphasis renew public interest in space, or would it simply be perceived (if perceived at all) as no more than a marketing change by people with a commercial or governmental funding axe to grind? I’ll stick with that exploratory impulse, thanks — I believe in it — rather than buying into the idea of exploration as a symptom of attention-deficit disorder (Simberg quotes The Economist on that peculiar idea). But attack Rousseau’s intellectual heirs and the so-called ‘perfectability of man’ and I’m on your side, making this provocative piece easy to recommend.
