Yesterday’s post discussed interesting terrain on remote moons, Rhea and Europa among them. But while we can piece together much useful information about a moon’s surface and its history from orbit, some of the most provocative places in the Solar System may well require investigation on the ground. In the case of Europa, that means robotic equipment, but the issue is stark, as Damhnait Gleeson (JPL) recently told Wired.com. “What we can see from orbit is such a simple picture compared to the surface,” Gleeson said in a story on Europa analogues on Earth. “From orbit it’s just ice and sulfur. We really have to go deeper to understand the system.”
That’s just what Gleeson and colleagues have been doing with data and samples gathered at the Borup Fjord Pass on Ellesmere Island, a remote and all but inaccessible place in the Canadian High Arctic. Gleeson, who as a graduate student worked under Europa specialist Bob Pappalardo (JPL), spent time at the pass in 2006, taking samples of the unique yellow stains left by sulfur-rich springs on the surface of the ice. The team’s work proceeded in a starkly beautiful landscape that scientists believe may hold clues about what happens on Europa, with implications for finding life on the moon.
Image: At Borup Fjord Pass, sulfur-rich stains blanket the white, snowy glacier. Credit: Stephen Grasby.
You may have run into this work when The Planetary Society took an interest and provided partial funding for the 2006 study. The reasons for its interest are apparent when you consider that the amount of sulfur at Borup Fjord Pass is what Pappalardo calls ‘an unusual chemical combination.’ The glacial spring at Borup Fjord deposits sulfur, gypsum and calcite across glacial ice. We’d expect pure sulfur to react with oxygen to form gypsum, but the team was able to show that the sulfur was being replenished by microorganisms. Usefully, the sulfur produced by the microbes shows a complicated structure that is not apparent in control samples.
Cut to Europa, where sulfur-rich materials are found concentrated along cracks and ridges on the surface. Do compounds in the ice contain organic material from the ocean below? It’s a huge question, as Gleeson told Astrobiology Magazine in this article last March:
“Europa’s liquid water layer contains twice the volume of all the Earth’s oceans combined, an enormous potentially habitable environment, not billions of years in the past but at the present day. The composition of the ocean directly controls our view of the habitability of the environment, our understanding of whether microbial life could survive there, and if so, what metabolic pathways or geochemical gradients it could utilize to gain energy.”
The Borup Fjord Pass studies, then, are all about comparing Europa’s surface compounds with the sulfur and glacial ice combination found on Ellesmere Island, and indeed, the spectral properties of the glacial ice in the Arctic proved similar to what we see on Europa’s surface. All of this makes Ellesmere Island a potential testbed for instrumentation that will one day travel to Europa. Chemicals circulating between the ocean and the ice layer could produce the energy life needs to exist. The Europan surface is doubtless too saturated with radiation for life to exist there, but a robotic lander might uncover traces of organic material migrating from below.
Image: A Galileo image of the Europan surface. Sulfur-rich materials here may help us understand the composition of the astrobiologically interesting ocean beneath the ice. Credit: NASA/JPL/University of Arizona/University of Colorado.
But absent a lander, this work should prove useful for future orbital observation of Europa as well. The Galileo spacecraft’s spectrometers were able to obtain data in the near-infrared but not enough to resolve the mixture of compounds that left this particular spectral signature. Gleeson’s work continues to investigate the Ellesmere sulfur deposits with spectral studies in the near-infrared and space observations of the site from the Hyperion spectrometer aboard the Earth Observing 1 spacecraft. The next time we get to Europa, we’ll have a better read on what to look for.
The most recent work on Arctic analogues to Europa is Gleeson et al., “Characterization of a sulfur-rich Arctic spring site and field analog to Europa using hyperspectral data,” Remote Sensing of Environment Vol. 114, Issue 6 (15 June 2010), pp. 1297-1311 (abstract).
Cassini continues to wow us with holiday imagery, not the least of which is this view from the Enceladus encounter on the 20th, with not only the plumes from Enceladus clearly visible but the adjacent image of Mimas stealing the show (credit: NASA/JPL/Space Science Institute). It’s raw imagery, still unprocessed, but it gets across the wonder of the occasion. Cassini’s next encounter is with Rhea, a flyby at 76 kilometers scheduled for January 11, but it’s two earlier Rhea flybys (from November of 2009 and March of 2010) that caught my eye this morning.
Remember that Cassini’s mission has been extended until 2017, offering us the opportunity to enhance considerably our view of the features on various moons. In fact, the recent images of Rhea have already helped us produce a cartographic atlas of the moon that includes names approved by the International Astronomical Union. The 2009 flyby allowed scientists to create a 3-D image of terrain on Rhea’s trailing hemisphere at higher resolution than ever before, showing a densely cratered landscape bisected by uplifted blocks that suggest recent tectonic stress.
The images also tell us something about where Rhea fits in among the family of Saturnian moons, according to Paul Helfenstein (Cornell University), a Cassini imaging team associate:
“These recent, high-resolution Cassini images help us put Saturn’s moon in the context of the moons’ geological family tree. Since NASA’s Voyager mission visited Saturn, scientists have thought of Rhea and Dione as close cousins, with some differences in size and density. The new images show us they’re more like fraternal twins, where the resemblance is more than skin deep. This probably comes from their nearness to each other in orbit.”
Image: Wispy fractures cut through cratered terrain on Saturn’s moon Rhea in this high resolution, 3-D image from NASA’s Cassini spacecraft. Credit: NASA/JPL/Space Science Institute.
The March flyby featured Cassini’s closest pass yet to Rhea at 100 kilometers, but the January event will be closer still, allowing surface details down to the size of a few meters to be imaged. We’ve been able to discount the idea that a faint ring exists above Rhea’s equator while dramatically enhancing our view of the fractures that the Voyagers found there in 1980 and 1981. Both Rhea and Dione have such features, which were once thought to be deposits from cryovolcanic activity or the residue of icy materials from within the moons. Cassini’s higher resolution shows us that the markings are sections of ice along the walls of steep cliffs.
It’s fascinating how much you can tell about terrain from imagery like this. I’m remembering Richard Greenberg’s book Unmasking Europa (2008), which goes into great detail on the analysis of Europan data returned from the Galileo spacecraft. Europa’s ‘chaotic terrain,’ as analyzed in the famous Conamara Chaos region, shows evidence of melt-through followed by reformation of surface ice, a significant eruption that may have resulted from a breakup caused by tidal forces. In any case, Greenberg shows how to reassemble the ‘rafts’ of individual material, demonstrating how they broke away and migrated to new, equally frozen positions.
On Rhea, we’re not dealing with that fascinating, sub-surface ocean that makes Europa so interesting. But close study of the Cassini images shows how fault topography can cut through craters which are themselves not scarred with smaller internal craters, an indication that they’re comparatively young. Meanwhile, the amount of cratering on Rhea’s plains implies that the moon has had little internal activity to cause repaving of surface materials. All of this makes it appear that whatever tectonic stress has caused the fault topography has made its effects felt comparatively recently.
Image: Hemispheric color differences on Saturn’s moon Rhea are apparent in this false-color view from NASA’s Cassini spacecraft. Credit: NASA/JPL/Space Science Institute.
The false-color view above shows the side of Rhea that always faces Saturn. Like other icy Saturnian moons, Rhea shows clear differences in reflectivity and color between its hemispheres that probably reflect changes in surface composition. One cause for this may be the ‘magnetic sweeping’ that occurs when ions trapped in Saturn’s magnetic field are swept over Rhea’s surface. Another likely cause is the impact of meteoritic debris striking one side of the moon more frequently than the other as the tidally-locked moon moves in its orbit. The view here is from approximately 35,000 kilometers.
Last night’s lunar eclipse is the first I’ve seen used as the hook for a story on exoplanets in the popular press, as it was in this Christian Science Monitor story yesterday. Maybe that’s a sign that we’re beginning to relate the familiar things we see in the sky to the distant and less well understood, placing ourselves in a larger, cosmic context. Or maybe it’s just because the idea of extraterrestrial life sells well in Hollywood and people have gotten enthusiastic about the prospects that it might actually be out there on some distant world. Whatever the case, it’s good to see exoplanet science in the newspapers again (and thanks to Erik Anderson for the tip on the CSM article).
Eclipses and Exoplanetary Science
Eclipses change what we see on the lunar surface as the Earth’s atmosphere affects the color of sunlight passing through it. That’s quite an interesting effect for astrobiologists, because studying the light reflected off the moon during an eclipse is a way for astronomers to practice the detection of biomarkers in an exoplanet atmosphere. A transiting exoplanet gives us the chance to study the spectral signatures of atoms and molecules as starlight passes through its atmosphere. CSM writer Pete Spotts explains how the Moon can help us tune up our techniques, focusing on the work of Enric Palle (Instituto de Astrofisica de Canarias):
From the moon’s perspective during an lunar eclipse, Earth is a transiting planet. It blocks direct sunlight that otherwise would shine on the moon.
But the moon still receives and reflects sunlight that passes through Earth’s atmosphere from the daylit half of [the] planet. An observer on the moon would see a dark disk ringed by a thin, brilliant, sunset-like band of orange and red.
Dr. Palle and his colleagues posited that this light, reflected back to Earth from the moon’s surface, would carry the spectral signatures of molecules in Earth’s atmosphere.
During a 2008 eclipse, Palle and his colleagues used spectrometers in two different parts of the world to make measurements in both visible light and the near-infrared, allowing the scientists to find the signatures of water, methane, carbon dioxide, ozone and molecular hydrogen. Find the same signatures in the atmosphere of a transiting Earth-like world and you’ve located a planet of high astrobiological interest. Palle’s work was extended by Alfred Vidal-Madjar (Institut d’Astrophysique de Paris), who observed the same eclipse in greater detail and was able to make measurements of the thickness of the atmosphere as well as atmospheric molecules.
Transit Science Beyond Kepler and CoRoT
Meanwhile, MIT is running a three-part series on the exoplanet hunt, with a look at two space-based missions to follow up Kepler and CoRoT (thanks to NextBigFuture for the pointer). Kepler is tracking plenty of intriguing stars — maybe half of the 750 stars of interest it has thus far found may have planets — but it’s focused on stars far more distant than the nearby stars from whose potential planets we might eventually get spectroscopic atmospheric readings. The Transiting Exoplanet Survey Satellite (TESS) would examine a wider field of G, K and M-class stars using six onboard cameras, working with the brightest 2.5 million stars in the wide field of view of its equipment.
TESS is no stranger to these pages, where we’ve discussed it with enthusiasm because of its potential for detecting between 1600 and 2700 planets within two years (here’s a backgrounder). The TESS team, led by George Ricker (Kavli Institute) hopes to spot between 100 and 300 small planets, including potential Earth analogues. You’ll recall that NASA chose not to follow through on TESS in 2009, but the mission, designed for a small to midsized spacecraft, could rise again as the agency begins accepting new proposals later this year. Don’t count TESS out of the hunt — the budget for missions of this class has almost doubled and TESS could be more attractive than ever if, as deputy mission scientist Sara Seager says, the team can add larger cameras and lenses.
If TESS is a familiar concept, ExoplanetSat is definitely not, but it was inevitable that the tiny CubeSats so many universities are using to conduct observations from space would find their way into one of astronomy’s hottest areas of research. The idea here is to put a single telescope on a single star to search for transits. From the MIT story:
The concept eventually developed into ExoplanetSat, a research program that is designed to launch a fleet of about one dozen “triple CubeSats” (three cubes stuck together), and about another two dozen six-unit CubeSats into low-Earth orbit. Each satellite would have its own computer, processor and tiny camera and would be pointed at an individual star. Although the program doesn’t have funding yet, MIT students will try to build two prototypes within the next two years and then hopefully secure funding for a formal mission to send dozens of the tiny cubes into space.
All of which is exciting news for finding planetary transits, but it’s another issue whether or not we’re going to be able to study the atmospheres of planets as small as the Earth with near-term equipment. It’s one thing to look at reflected light bounced off an object as close as the Moon, but quite another to extract a signature from a small planet awash in the light of its star from dozens of light years away. The James Webb Space Telescope is scheduled for launch in 2014 and should ramp up our ability to study exoplanet atmospheres like those of the ‘hot Jupiters’ we’ve already investigated.
Time will tell whether JWST is up to doing the same for Earth-class planets, but maybe I’ll catch some of Greg Laughlin’s enthusiasm for the idea. Laughlin (UC-SC) had these thoughts on his systemic site last year:
TESS… provides an eminently workable path to the actual characterization of a potentially habitable planet. Included in the 2.5 million brightest stars are a substantial number of M dwarfs. Detailed Monte-Carlo simulations indicate that there’s a 98% probability that TESS will locate a potentially habitable transiting terrestrial planet orbiting a red dwarf lying closer than 50 parsecs. When this planet is found, JWST (which will launch near the end of TESS’s two year mission) can take its spectrum and obtain resolved measurements of molecular absorption in the atmosphere.
As always, we fall back on funding issues and decisions that weigh competing, and often excellent, mission ideas against each other. Let’s pull for TESS even as we continue to follow the fortunes of CoRoT and Kepler in the hunt for smaller planets. TESS would complement both by filling out our knowledge of planets around nearby stars, and as the era of JWST approaches, data from TESS would define our target list for investigating the planets most likely to house life.
We spend a lot of time talking about how to get an interstellar probe up to speed. But what happens if we do achieve a cruise speed of 12 percent of the speed of light, as envisioned by the designers who put together Project Daedalus back in the 1970s? Daedalus called for a 3.8-year period of acceleration that would set up a 46-year cruise to its target, Barnard’s Star, some 5.9 light years away. That’s stretching mission duration out to the active career span of a researcher, but it’s a span we might accept if we could be sure we’d get good science out of it.
Maximizing the Science Return
But can we? Let’s assume we’re approaching a solar system at 12 percent of c and out there orbiting the target star is a terrestrial planet, just the sort of thing we’re hoping to find. Assume for the sake of argument that the probe crosses the path of this object at approximately ninety degrees to its orbital motion trajectory. As Kelvin Long shows in a recent post on the Project Icarus blog, the encounter time, during which serious observations could be made, is less than one second. A Jupiter-class world, much larger and observable from a greater distance, itself offers up something less than ten seconds at best for scientific scrutiny.
That’s a paltry return on decades of construction and flight time, not to mention the probable trillion or more dollars it would take to build such a probe, and it hardly compares well to what we’ll be able to achieve with even ground-based telescopes as the next generation of optics becomes available. What to do? Long is looking into these issues as part of the Project Icarus team, which is revisiting the Daedalus concept to see how changing technologies could alter the flight profile and produce a mission whose results would be substantially more useful.
Image: The Daedalus starship arrives in the Barnard’s Star system. Credit and copyright: Adrian Mann.
One option is to do the unthinkable. Instead of ramping up flight speed to get to the destination more quickly, perhaps a better alternative is to slow the mission down. There are two ways to do this: 1) Aim for a slower cruise speed in the first place and/or 2) attempt to decelerate the vehicle. The latter choice is a genuine conundrum for reasons Long makes clear:
Another option being examined [for deceleration] is reverse engine thrust, but the problem with this is that if we assume an equal acceleration-deceleration profile then the mass ratio scales as squared compared to a flyby mission and so requires an enormous amount of propellant; definitely a turn-off for a design team seeking efficient solutions.
What this boils down to is that if you want to carry enough propellant to turn your spacecraft around and decelerate, you have to carry that additional propellant with you from the start of the mission. The rocket equation yields a stubborn result — the requirement for propellant increases not proportionally but exponentially in relation to the final velocity required. The initial fuel mass becomes vast beyond comprehension when we apply the numbers to slowing an interstellar craft, which is why the Icarus team, as it looks into deceleration, is examining ideas like magsails, where the incoming vehicle can brake against the star’s stellar wind.
A magsail or, for that matter, various other sail possibilities (Robert Forward described decelerating a manned interstellar vehicle by lightsail in his novel Rocheworld) offers the unique advantage of leaving the fuel out of the spacecraft — you’re braking against a stellar particle flux, or against starlight itself. But whether or not such ideas prove feasible, they’re more likely to at least help if the spacecraft is traveling slower to begin with, making it easier to decelerate further. A slower transit also reduces stress on the vehicle’s engines and structure during the boost phase.
The Case Against Going Faster
Long notes that Project Icarus is far from having answers on just what cruise speed will be optimal — Icarus is a work in progress. But these issues are at the heart of the interstellar quest:
…all of this analysis goes to the heart of whether a flyby probe such as Daedalus is really useful given what it took to get there. The potential science return is massively amplified by performing a deceleration of the vehicle and although it is a significant engineering challenge this is why the Icarus team decided to address this problem; and it is a problem, even if you choose to just decelerate sub-probes. Coming up with a viable solution to the deceleration problem in itself would justify Project Icarus and the five years it took to complete the design process.
Supposing you gave up on trying to stop the probe in the destination system, but simply made your goal to slow it down enough to make protracted scientific observations as it passed through? It’s clearly an option, and again we’re considering a trade-off between the shortest travel time and the ability to maximize science return. Interstellar flight is a challenge so daunting that it makes us question all our assumptions, not the least of which has always been that faster is better. Not necessarily so, the Icarus team now speculates, and perhaps a fusion/magsail hybrid vehicle will emerge, a significant upgrade from the Daedalus design. And this reminds me of something I wrote about magsails back in 2004 in my Centauri Dreams book:
At destination, a magnetic sail is our best way to slow [the] probe down, with perhaps a separate solar sail deployment at the end that can brake the vessel into Centauri orbit. If you had to bet on the thing — if the human race decided a fast probe had to be launched and was willing to commit the resources to do so within the century — this is where the near-term technology exists to make it happen.
Of course, I now look back on that passage and shudder at my use of the phrase ‘near-term’ to describe the vehicle in question, but maybe a very loose definition of ‘near-term’ to mean ‘within the next few centuries’ will suffice (hey, I’m an optimist). In any case, when we’re talking journeys of forty trillion kilometers (the distance to the nearest stellar system) and more, a century or two seems little enough to ask. And while I do believe this, I rejoice at the spirit of Project Icarus, whose team presses on to discover whether such a thing could be attempted in an even shorter time-frame.
Our recent discussion of Richard Gott and Robert Vanderbei’s Sizing Up the Universe has me thinking about representing unfathomably huge scenarios in two-dimensional media, as Gott managed to do so brilliantly with his four-page gatefold map of the universe. How to manage such a feat, and the theory behind map-making of all kinds, can be found in the book, and all of it came to mind as I looked at Ashland Astronomy Studio’s new Stars of the Northern Hemisphere poster. A full color sky map on a 36 x 24 glossy sheet, it’s a handsome rendition of over 2400 stars.
Centauri Dreams regular Erik Anderson is the creator, and he’s been careful to add — beyond the inset closeups of the Pleiades and Hyades star clusters, star names, asterisms and coordinate systems — the location of exoplanet host stars. Exoplanet charting is indeed the new frontier, a depiction of new lands that calls to mind the painstaking efforts of seafaring expeditions that mapped the Pacific archipelagos and the coasts of Africa and South America. Now the trick is not letting the exoplanet count swamp our cartographers, for we’ve already passed 500 exoplanets and there’s every indication that the number will quickly double and more as Kepler results multiply.
The Pioneer Anomaly Resolved?
8.74 x 10-10 m/s2 isn’t much, but it’s an apparent Sun-ward acceleration sufficient to throw the paths of our Pioneer spacecraft off by a few hundred miles from where they ought to be each year. Noticing the effect in 1980, astronomer John Anderson, who was leading the analysis of Pioneer Doppler ranging data as part of a study of gravitational effects in the outer Solar System, came to the conclusion that outgassing from the spacecraft thrusters was responsible, but the effect persisted longer than it should and a whole range of alternate theories soon came into play after Michael Martin Nieto (Los Alamos National Laboratory) began to study the anomaly in terms of modified Newtonian dynamics (MOND).
The background is given in a fine article by Natalie Wolchover for PopSci. What accounted for Nieto’s fascination was the fact that the value of the anomaly almost exactly equaled the speed of light multiplied by the Hubble constant. At that point, with the possibility that the Pioneers were telling us something fundamental about physics, the Pioneer anomaly took on a life of its own. The discovery of dark energy in the same year that Anderson, Nieto and Slava Turyshev announced their findings about the Pioneer acceleration in Physical Review Letters only added to the interest, and hundreds of papers, many but hardly all on MOND notions, followed.
Image: The Pioneer spacecraft opened up an entire sub-field of studies as what some thought to be a gravitational anomaly was identified. Credit: NASA.
Were the Pioneer probes measuring the cosmic expansion whose effects are now thought to be intertwined with dark energy? It was one amongst a sea of possibilities. Wolchover’s article describes how Viktor Toth, running an independent analysis using home computers, became skeptical of the earlier work of Anderson and Turyshev and later, with Turyshev, became instrumental in saving the 30-plus years of Pioneer Doppler data and logbooks. With the help of a retired Pioneer mission control engineer named Larry Kellogg, the two acquired Pioneer telemetry data and went back to work from scratch on a much more thorough analysis.
That was five years ago. The result:
Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10-10 m/s2, and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”
If the Pioneer acceleration declines with time, it’s obviously not the constant force it was originally thought to be. The question of decay in that acceleration, and whether the acceleration is indeed in the direction of the Sun or elsewhere, is still open, and Toth and Turyshev are planning to supplement their recently published review of the phenomenon with a forthcoming publication that recounts their latest work. Wolchover thinks the duo have become convinced that thermal effects aboard the spacecraft themselves are the cause of the anomaly, but Turyshev won’t reveal the results, telling the writer only, “Physics as we know it worked well.”
The review paper is Turyshev and Toth, “The Pioneer Anomaly,” published online in Living Reviews in Relativity 13 (2010).
Possible Ice Volcanoes on Titan
Two peaks more than 1000 meters tall show a topography that looks like cryovolcanism on Saturn’s moon Titan. Such an ‘ice volcano’ would evidently be fueled by subterranean geological activity that warms ice and other materials into a slush and propels it through an opening onto the surface. The site on Titan, called Sotra Facula, shows the finger-like flows one would expect from this process and does not appear to be associated with river activity that could otherwise explain the flows. Jeffrey Kargel (University of Arizona at Tucson) thinks cryovolcanism is likely:
“This is the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite. It’s possible the mountains are tectonic in origin, but the interpretation of cryovolcano is a much simpler, more consistent explanation.”
Image: Scientists believe Sotra is the best case for an ice volcano — or cryovolcano — region on Titan. The flyover shows two peaks more than 1,000 meters (3,000 feet) tall and multiple craters as deep as 1,500 meters (5,000 feet). It also shows finger-like flows. All of these are land features that indicate cryovolcanism. The 3-D topography comes from Cassini’s radar instrument. Topography has been vertically exaggerated by a factor of 10. The false color in the initial frames shows different compositions of surface material as detected by Cassini’s visual and infrared mapping spectrometer. In this color scheme, dunes tend to look relatively brown-blue. Blue suggests the presence of some exposed ice. Scientists think the bright areas have an organic coating that hides the ice and is different and lighter than the dunes. The finger-like flows appear bright yellowish-white, like the mountain and caldera. The second set of colors shows elevation, with blue being lowest and yellow and white being the highest. Dunes here appear blue because they tend to occupy low areas. The finger-like flows are harder to see in the elevation data, indicating that they are thin, maybe less than about 100 meters (300 feet) thick. Credit: NASA/JPL-Caltech/USGS/University of Arizona.
Randolph Kirk, who led the 3-D mapping work that points to this result, likens Sotra Facula to Earth volcanoes like Iceland’s Laki and Italy’s Mt. Etna. His team worked with Cassini radar images to create a topographic map, using data from Cassini’s infrared mapping spectrometer to show that the flows had a composition different from the surrounding surface. A process like this would be useful, explaining the reintroduction of methane into Titan’s atmosphere even though sunlight continues to break the molecule down. Announced at the recent American Geophysical Union meeting, Titan’s potential cryovolcanoes give us a look at yet another force shaping a landscape that offers a deep-freeze counterpoint to our own warm planet.
Echoes of an Earlier Universe
Teasing out information about previous incarnations of the universe may be the ultimate investigation for cosmologists — it’s hard to see how you go farther than into another universe, or at least, into an earlier version of this one. Roger Penrose (Oxford University) and Vahe Gurzadyan (Yerevan State University) have been much in the news since announcing last month that they had done just this, using studies of the cosmic microwave background that suggested the presence of concentric rings resulting from super-massive black hole collisions that became imprinted on the CMB. The New York Times’ Dennis Overbye picks up the story:
The rings seen by Dr. Penrose and Dr. Gurzadyan are thin bands in which the noisy pattern of heat and cold in the early universe, as recorded by the Wilkinson satellite and other experiments, is slightly less splotchy than normal. They posted a copy of their paper on the Internet on Nov. 16, noting that the rings confirmed a prediction of a theory recently proposed by Dr. Penrose, one of the world’s distinguished mathematicians, called Conformal Cyclic Cosmology. It is the subject of a new book by him, “Cycles of Time: An Extraordinary New View of the Universe,” due out in May from Knopf.
The thrust of Overbye’s article is that criticism from other cosmologists is growing, including groups at the University of Oslo and the University of British Columbia, both of whom find the rings consistent with chance events in the earliest moments of our own universe. I’m looking forward to reading Penrose’s new book, as I’ve read all his others, but I also pay close attention to David Spergel (Princeton University), who was one of the members of the Wilkinson satellite team. Overbye quotes Spergel’s skeptical response:
“While it would have been exciting to see circles from the pre-Big Bang universe, I view this as science at its best. Exciting claims are made and they draw the attention of cosmologists throughout the world. Because the WMAP data is publicly available, groups throughout the world were able to check the claim. A universe with dark matter, dark energy and inflation is bizarre enough — we don’t, however, get to detect circles from alternative universes.”
Image: The controversial rings in the cosmic microwave background, highly modified and highlighted for effect. Credit: Roger Penrose and Vahe Gurzadyan.
Now that we’ve been through the era of the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP), we’re focused on results from the European Planck satellite, which will tell us yet more about fluctuations in the microwave data. For now, the paper to look at is Gurzadyan and Penrose, “Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity” (preprint).