by Paul Gilster | Feb 23, 2008 | Exotic Physics |
The more we learn about gravitational lensing, the more it becomes clear how pervasive the phenomenon must be as mass and spacetime interact throughout the cosmos. The most recent findings produced by lensing effects now limn structures so large that they dwarf the galaxy we reside in. Recently detected dark matter filaments, up to 270 million light years in size, are 2000 times the size of the Milky Way, yet would remain unobserved were it not for advanced lensing investigative techniques.
The astronomers behind this work, using data from the Canada-France-Hawaii Telescope Legacy Survey, took advantage of the fact that dark matter should deflect the light from distant galaxies as it travels towards us. The careful measurement of these often tiny effects required the development of new tools for image analysis, but these apparent filaments, sheets and clusters of dark matter seem to gibe with previous theoretical estimates. “Our observations extend the knowledge about the cosmic web far beyond what was known before,” says Liping Fu (Institut d’Astrophysique de Paris). “We confirmed that our model about the Universe is correct even on those very large scales.”
The model Fu is talking about is a paradigm of dark matter that sees galactic clusters and galaxies themselves embedded in the filamentary structures described above. The detection of such structures supports the evolving paradigm; had the filaments not been found, dark matter would be due for a profound re-thinking. Up until now, the observation of gravitational lensing at these weak levels had proven impossible.
Up next: Whole-sky surveys to further study dark matter distribution, probing whether its signature (and that of dark energy) can be explained by modifications to General Relativity. If not, then we do seem to be dealing with a new type of matter and source of energy. Either way, the advance in knowledge will be extraordinary. The paper is Fu, Semboloni et al., “Very weak lensing in the CFHTLS wide: cosmology from cosmic shear in the linear regime,” accepted by Astronomy & Astrophysics and available online.
by Paul Gilster | Feb 23, 2008 | Culture and Society
The 42nd Carnival of Space is online at Chris Lintott’s Universe, good reading for the weekend and a way to keep up with the growing number of astronomy weblogs. Centauri Dreams readers in particular will want to check out Emily Lakdawalla’s Showing Off Saturn’s Moons, examining these exotic bodies in connection with the recent series of articles on Cassini findings in Icarus. Emily discusses image techniques and also links to a Microsoft Access-formatted database of all Cassini images released to the general public up until now. Great stuff for those looking for imagery either for publication or the sheer wonder of the scenery.
by Paul Gilster | Feb 22, 2008 | Exoplanetary Science |
Centauri Dreams has long championed Webster Cash’s innovative New Worlds mission concepts, which would use a ‘starshade’ to block the light of distant stars to reveal their planetary systems. Cash envisions using multiple spacecraft for this assignment, one the starshade itself, the other a telescope that would make the needed observations. After a series of ups and downs, New Worlds now receives new life in the form of a $1 million award from NASA to study the starshade’s possibilities.
Remember that we’re still at an early research level when it comes to funding of this kind — the actual observatory, a design Cash calls New Worlds Observer — would cost an estimated $3.3 billion to design and build. Other mission concepts are still in play (fully nineteen observatory concepts have been chosen for further study), so the road ahead is by no means clear as we look toward space missions that can identify Earth-like planets around other stars. But Cash’s designs are well vetted, and should prove attractive to those responsible for narrowing the field.
At right is a simulation of what New Worlds Observer might see if pointed at Sol from 10 parsecs out. The blue bulge at the top is the Earth; the second object is Venus. To do this kind of work, NWO would use a starshade fifty yards in diameter, placed at Lagrange point 2 (L2), where a stable orbit can be achieved that balances the gravitational effects of the Sun and the Earth. The projected four-meter telescope is considerably larger and more powerful than the Hubble Space Telescope. Telescope and occulter would be stationed some 50,000 kilometers from each other along the line of sight to a nearby star, with the starshade moved as needed to select a variety of targets (you can see that two starshades would make even more sense, one able to move into position on the next star while the first observes its target).
Image: A simulated image of the inner solar system taken at 10 parsecs with a 4-meter telescope. Credit: Phil Oakley.
What to do with New Worlds Observer? The detection of the light of individual planets would allow us to understand the entire exoplanetary system, while using spectroscopy to analyze atmospheres for biomarkers like methane, oxygen and water. Photometric methods could show us variations in color as surface features rotate in and out of view. Take those methods to the max and you may be able to identify oceans, continents, polar caps and cloud banks. New Worlds Observer is a powerful concept that can advance our knowledge of rocky worlds around other stars and pave the way for more expansive missions to come.
by Paul Gilster | Feb 21, 2008 | Exoplanetary Science |
What exactly is that dark material spread so widely over Saturn’s various moons? From Hyperion to Iapetus, Dione and Phoebe, we find a black substance coating a wide range of objects, suggesting that whatever the stuff may be, there must be a common mechanism for moving it from one moon to another. A series of papers on Saturn’s moons appears in the February issue of Icarus, where these interactions are now under study.
Just what the material is remains a mystery. But Roger Clark (US Geological Survey) notes that as the Cassini data build, we’re beginning to track down some of its components, including bound water and, possibly, ammonia. Studying Dione, Clark’s team noted the fine-grained nature of the dark material there. Its distribution and composition indicate the dark material is not native to the moon, and indeed, the same signature appears not only among other moons but also in Saturn’s F-ring. From the abstract to the study by Clarke and colleagues:
Multiple lines of evidence point to an external origin for the dark material on Dione, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the trailing side, exposing clean ice, and slopes facing the trailing direction which show higher abundances of dark material.
Image: Speeding toward pale, icy Dione, Cassini’s view is enriched by the tranquil gold and blue hues of Saturn in the distance. The horizontal stripes near the bottom of the image are Saturn’s rings. Images taken on Oct. 11, 2005, with blue, green and infrared (centered at 752 nanometers) spectral filters were used to create this color view, which approximates the scene as it would appear to the human eye. We have much to learn about this moon’s dark material and its interactions with the rest of the Saturn system. Credit: NASA/JPL/Space Science Institute.
So while much of our attention around Saturn has focused on Enceladus because of its icy plumes (one paper in the Icarus group discusses traces of organic compounds or silicate materials within Saturn’s E-ring, believed to be fed by those very plumes), we are now learning that the planet’s entire ‘system’ is more dynamic than believed. Dione itself, as Clark goes on to report in Icarus, shows some evidence of being geologically active.
Saturn is coming to be seen in terms of a unique ecology, as Cassini scientist Bonnie Buratti notes:
“Ecology is about your entire environment — not just one body, but how they all interact. The Saturn system is really interesting, and if you look at the surfaces of the moons, they seem to be altered in ways that aren’t intrinsic to them. There seems to be some transport in this system.”
A cometary origin for Saturn’s dark materials? Perhaps, but the forces moving these materials between the various moons remain ripe for investigation. Two papers from the special section on Saturn are particularly relevant here, the first being Lopes, Buratti et al., “The Saturn system’s icy satellites: New results from Cassini,” Icarus Volume 193, Issue 2 (February 2008), pp. 305-308 (abstract). Also see Clark et al., “Compositional mapping of Saturn’s satellite Dione with Cassini VIMS and implications of dark material in the Saturn system,” Icarus Vol. 193, Issue 2 (February 2008), pp. 372-386 (abstract).
by Paul Gilster | Feb 20, 2008 | Astrobiology and SETI |
Even the most adamant enthusiasts for METI — Messaging to Extraterrestrial Civilizations — haven’t come up with anything as audacious as what virtual reality guru Jaron Lanier is now talking about. Writing for Discover Magazine, Lanier has the notion of rearranging basic material objects to make them not just noticeable by aliens but blindingly obvious. Nothing new there, as the concept of such messaging goes back to the 19th Century. Mathematician Karl Gauss considered geometric plantings of trees and wheat to create shapes that might be visible from space, while Joseph von Littrow (perhaps basing the idea on Gauss’ work) talked about digging huge ditches and setting kerosene within them on fire at night, for the edification of beings on other worlds.
But Lanier isn’t talking about anything quite so mundane. This is a guy who thinks big — he wants to arrange stars. If you can find a way to create stable patterns of stars that are obviously artificial, then you have a celestial feature that shouts out your presence. Lanier calls such formations graphstellations, the idea being that we are creating an artificial constellation that is also a form of communication or writing. And perhaps other cultures, more advanced than ours, might have already chosen this path to tell us they’re out there.
As to why we might want to do this, Lanier simply accepts that making ourselves known is a good idea:
“Why move stars around? Because then they could be guided into orbital formations that almost certainly would not have occurred naturally. An imaginable set-up period of tens of thousands of years could therefore be leveraged into a much longer period—billions of years, perhaps—during which aliens could observe the fruits of our efforts.”
Judging from the reaction to NASA’s recent stunt — the transmission of a Beatles tune to Polaris — the idea of broadcasting the human presence seems to be settling in as a cultural trope. No one behind the NASA message seemed aware that there might be any controversy over the idea of beaming signals to the stars, and in the popular press the sending of the signal was handled more or less as a trendy cultural happening. Tau Zero journalist Larry Klaes has made the point here and elsewhere that we are soon to arrive at the juncture where individuals will have such powerful computing and transmission resources at their disposal that governmental or societal constraints on broadcasting will simply become moot. NASA’s latest has me wondering if he’s right. Like it or not, we may be moving into the era of METI as fait accompli.
Whatever the case, you have to admire the audacity of Lanier’s concept of star-moving. He imagines huge fleets of gravitational tractors gradually adjusting the trajectories of Kuiper Belt objects over thousands and thousands of years, eventually altering the Solar System’s trajectory through the Milky Way. In perhaps hundreds of thousands of years, our Sun can join up with other nearby stars similarly manipulated into the new graphstellation, a form of self-advertisement unrivaled by any other civilizational accomplishment in or out of Hollywood.
When Lanier took the idea to Piet Hut at the Institute for Advanced Study, the latter suggested a ‘multiply nested binary star graphstellation’ — a pair of a pair of a pair of double stars, sixteen stars in all. “An alien observer,” writes Lanier, “wouldn’t have to be able to discern all the individual stars in order to notice that something funny was going on; the alien would only have to note subtle changes in the qualities of the light, wobbles in the position, and other clues.”
So there you are. The long-term thinker’s brand of METI, played out over hundreds of thousands of years, and perhaps easier to construct than a Dyson sphere. Keeping our eyes open for such obviously artificial configurations would give SETI scientists yet another challenge, though whether any civilization would devote such time and energy into making itself into a cosmic beacon is questionable. Lanier makes me think of Olaf Stapledon, and engineering on cosmic scales of the sort that enlivened early science fiction. It’s a concept that plays against the apparently inexhaustible need of some humans to make our species known.
