by Paul Gilster | Oct 17, 2011 | Deep Sky Astronomy & Telescopes |
About a month ago we were looking at the work of Ray Jayawardhana and team on the brown dwarf 2MASS 2139, an interesting case because Jayawardhana (University of Toronto) thinks he has spotted a giant storm raging on the object, or perhaps holes in the cloud deck that allow a glimpse of deeper layers of the atmosphere within. At issue is the striking 30 percent change in brightness of the star within a mere eight hours, seeming to indicate atmospheric changes we can pick up as the brown dwarf rotates. Unlike a normal star, a brown dwarf is hot when young but gradually cools to the point where it has an atmosphere similar to that of a gas giant.
All this is part of a survey program called SONYC – Substellar Objects in Nearby Young Clusters – that uses data from the Subaru Telescope in Hawaii and the Very Large Telescope (VLT) in Chile. SONYC may change the way we look at brown dwarfs, and now it is back in the news. The latest word is that the same team has found over two dozen free-floating brown dwarfs within two young star clusters, including one object just six times more massive than Jupiter. Have a look at the image below, which depicts brown dwarfs in the cluster NGC 1333.
Image: Brown dwarfs in NGC 1333. This photograph combines optical and infrared images taken with the Subaru Telescope. Brown dwarfs newly identified by the SONYC Survey are circled in yellow, while previously known brown dwarfs are circled in white. The arrow points to the least massive brown dwarf known in NGC 1333: it is only about six times heftier than Jupiter. Credit: SONYC Team/Subaru Telescope.
What to make of the smallest of the brown dwarfs yet identified in this cluster? Aleks Scholz of the Dublin Institute of Advanced Studies comments:
“Its mass is comparable to those of giant planets, yet it doesn’t circle a star. How it formed is a mystery.”
Indeed, but the implication is that free-floating objects not a great deal larger than a Jupiter-class planet can form the same way stars form, emerging from contracting gas clouds, although there is also the possibility that some of the smaller brown dwarfs formed around a star and were later ejected from the system. SONYC is all about building a more complete census of brown dwarfs in star-forming regions to resolve questions like this, the ultimate goal being to understand how the early development of stars depends on object mass, which will in turn illuminate models of dynamical interactions and accretion as the nascent objects form. These considerations make brown dwarfs in a mass range that overlaps with massive planets a key area for research.
The SONYC census is developing our database in this area, as described in one of the two papers recently made available on this work:
We find 10 new likely brown dwarfs in this cluster, including one with a spectral type ~L3 and two more with spectral type around or later than M9. These objects have estimated masses of 0.006 to 0.02M [solar masses], the least massive objects identified thus far in this region. This demonstrates that the mass function in this cluster extends down to the Deuterium burning limit and beyond. By combining the findings from our SONYC survey with results published by other groups, we compile a sample of 51 objects with spectral types of M5 or later in this cluster, more than half of them found by SONYC. About 30-40 of them are likely to be substellar.
The astronomers studied both NGC 1333 and the Rho Ophiuchi star cluster with Subaru at both optical and infrared wavelengths. NGC 1333, a young cluster thought to be no more than a million years old, turns out to have a higher population of brown dwarfs than the average young cluster, a fact that may offer clues to different conditions within the cluster that affect brown dwarf formation. The cluster houses half as many brown dwarfs as normal stars.
The paper continues:
The star vs. brown dwarf ratio in NGC1333 is significantly lower than in other nearby star forming regions, possibly indicating environmental differences in the formation of brown dwarfs. We show that the spatial distribution of brown dwarfs in NGC1333 closely follows the distribution of the stars in the cluster. The disk fraction in the brown dwarf sample is < 66%, lower than for the stellar members, but comparable to the brown dwarf disk fraction in 2-3 Myr old regions. The substellar members in NGC1333 show a large fraction of highly flared disks, evidence for the early evolutionary state of the cluster.
The paper cited above is Scholz et al., “Substellar Objects in Nearby Young Clusters (SONYC) IV: A census of very low mass objects in NGC1333,” accepted for publication in the Astrophysical Journal (preprint). The second paper on this work is Muzic et al., “Substellar Objects in Nearby Young Clusters (SONYC) V: New brown dwarfs in rho Ophiuchi,” also accepted by the Astrophysical Journal (preprint).
by Paul Gilster | Oct 14, 2011 | Culture and Society |
We’ve been talking lately about space missions designed to maximize science vs. those that are at least partly geared toward public relations. But most missions will have both components, the need for public support being woven into the fabric of our ambitions. As we try, then, to ramp up the scientific return, what can we also do to keep the public engaged and instill interest in space exploration? One answer came from Wernher von Braun’s massive project for space exploration, described in a series of articles on space presented by Collier’s magazine from March of 1952 to April, 1954.
Let’s put aside all the technical problems of the von Braun concept and concentrate on it as an incentive for space missions. Al Jackson, with whom I enjoyed dinner and several good conversations in Orlando at the 100 Year Starship Symposium, recently sent me The Ugly Spaceship and the Astounding Dream, an article he wrote for the AIAA’s Horizons magazine. Al is completely upfront about the fact that it was the Collier’s series that brought him into space research in the first place. Now a visiting scientist at the Lunar and Planetary Institute, Al has seen aerospace from the government side (as astronaut trainer on the Lunar Module Simulator) to industry, knew Robert Bussard as well as Robert Forward, and wrote a number of papers on interstellar matters for JBIS, including work in the late 1970s on a laser-powered interstellar ramjet that I want to discuss soon in these pages.
Image: Chesley Bonestell’s take on the von Braun lunar lander, an ugly spaceship with a mind-blowing cargo of ideas.
The Collier’s series, tapping the artistic genius of Chesley Bonestell, produced what Al calls ‘the most influential feat of popular science writing ever,’ with its depiction of a complete manned space program ranging from Earth-circling space stations to lunar landings and that massive expedition to Mars. And ‘massive’ is the right word, for von Braun imagined a flotilla of ten spaceships with a crew of 70 making the Mars journey, fifty of them landing on the surface. 950 ferry flights were needed to assemble the spaceships, but von Braun’s vision included the space infrastructure to make that happen, all based on ideas he had been working on in 1947 and 1948, published first in a German journal and then brought out in a hardcover edition: Marsprojekt; Studie einer interplanetrischen Expedition. Sonderheft der Zeitschrift Weltraumfahrt (1952).
But it was the October 18, 1952 issue of Collier’s that Al, then almost twelve years old, found the most fascinating, the one with the ugliest, most un-aerodynamic spaceship he had ever seen shown on final descent to the Moon. It was in the pages of this issue that he learned that aerodynamic shapes count for little in space, and as he tells us in his article, the entire series would wind up changing his life:
I came to love that ugly space ship! It cemented itself to my soul. It led me to a life in science, a B.A. degree in Mathematics, an M.A. degree in Physics and a Ph.D. in physics. Most startling, to me, that series led me to 35 years of work in spaceflight, first Apollo, the Shuttle program, and now the ISS. All due to the romance of space expressed by Chesley Bonestell, Wernher von Braun and Willy Ley.
Collier’s produced spectacle and soaring ideas, doubtless contributing to the careers of numerous scientists and engineers, even if we now find the technical specifications of the von Braun program daunting. But I sometimes wonder what we might do today to recapture some of the spectacle produced by the Apollo landings, which similarly energized broad portions of the population. Space-minded people like myself are fascinated with the Dawn mission to Vesta and Ceres, and equally drawn to the allure of the Pluto/Charon encounter coming up in 2015. But what would have the most impact on those less obsessed with deep space?
I think I may have found the right concept. It’s the notion of exploring another planet by balloon, exemplified by MGA, the Mars Geoscience Aerobot, studied by a JPL team in the 1990s under the acronym MABVAP – Mars Aerobot Validation Program. It’s an idea with an international pedigree: A balloon system for Mars designed for a Soviet space probe was also under development through the work of Jacques Blamont (CNES), although the project was eventually dropped for financial reasons.
In essence, though, the ideas are similar. The idea is to deliver a superpressure balloon system to Mars, an aerobot that would remain aloft for as much as three months, circumnavigating Mars more than 25 times. Along with an infrared spectroscopy system, a magnetometer, instruments for studying Martian weather and a radar sounder, the balloon would be equipped with an ultrahigh resolution stereo imager. Robert Zubrin and a team at Martin Marietta have more recently been working on the Mars Aerial Platform (MAP), a plan to use eight balloons to map the global circulation of Mars’ atmosphere, examine its surface and subsurface with remote sensing techniques, and return thousands of high resolution images of the Martian surface.
The views returned by an aerial circumnavigation of Mars would be little short of spectacular, as Zubrin notes in the new edition of his The Case for Mars (2011):
Today, nearly five hundred years since Copernicus and Kepler, Brahe and Galileo, most people still think of Earth as the only world in the universe. The other planets remain mere points of light, their wanderings through the night sky of interest to a select few. They are abstractions, notions taught in schools. The MAP cameras offer the possibility of taking humanity’s eyes to another planet in a way that has never been done before. Through the gondola’s cameras we will see Mars in its spectacular vastness: its enormous canyons, its towering mountains, its dry lake and river beds, its rocky plains and frozen fields. We will see that Mars is truly another world, no longer a notion but a possible destination. And, just as the New World entranced and enticed mariners here on Earth, so can Mars entice a new generation of voyagers, a generation ready to fashion the ships and sails proper for heavenly air.
Remember, I’m thinking in terms of how to kindle public interest in space and keep those fires burning, and to me the ability to see the topography of Mars through close-up imaging of its entire surface could create an experience as breathtaking for some budding scientists as the Collier’s series was for Al Jackson. We go from looking at rover tracks and landscapes limited by a rover’s range to the ability to move freely over Mars, from Olympus Mons to the Valles Marineris.
Similar missions have been proposed for Titan, with a certain scientific return as well as the potential for serious public engagement as the aerobot probes the surface of the mysterious moon. An autonomous flying robot was actually delivered to Venus on each of the two Soviet Vega probes, entering the atmosphere in June of 1985. Both balloons operated for almost two Earth days until their batteries batteries failed [see comments below]. Deployed onto the darkside of the planet at an altitude of about 50 kilometers, the balloons operated for their brief lives in an altitude where pressure and temperature were not dissimilar to those of Earth.
While the scientific return from the Vega balloons was minimal, the concept was validated. Using aerostats equipped with high-definition imaging capabilities on Mars, we may be able to re-create some of the sizzle of exploration that the Voyagers had, giving a boost to science-minded young people and providing vistas for public viewing through remote sensing that could one day be looked back on as the key players in creating new careers in science. We may or may not one day get to the stars, but if we do, it will be because the right people came across the right incentives, leading them into careers that could change the way we do space exploration.
by Paul Gilster | Oct 13, 2011 | Outer Solar System |
So much has been happening in recent weeks that I haven’t had the chance to keep up with all the stories in the queue, and that’s not a bad thing considering that a high level of activity usually means we’re learning new and interesting things. Consider the Dawn mission, which has been orbiting the asteroid Vesta since the middle of July. The Dawn team has been sharing results about Vesta in multiple locations, including the European Planetary Science Congress and the Division of Planetary Sciences Joint Meeting 2011 in Nantes and the annual meeting of the Geological Society of America in Minneapolis. As expected, Vesta turns out to be an intriguing place.
The image below is a look at Vesta’s topography in the southern polar region, with the overall curvature of the tiny world removed, so you’re seeing what it would look like on a flat surface. You wouldn’t have this view on Vesta because many of the features would wrap around below the horizon, but the image gets across the scale of the asteroid’s south polar mountain, which rises a good 22 kilometers above the average height of the terrain around it. And note the large cliff on the right side of the image, which bounds part of Vesta’s south polar depression.
Image: This image of the asteroid Vesta, calculated from a shape model, shows a tilted view of the topography of the south polar region. The image has a resolution of about 1,000 feet (300 meters) per pixel, and the vertical scale is 1.5 times that of the horizontal scale. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.
Everything we see here is consistent with a giant impact in Vesta’s past. The surface is rougher than most asteroids we’ve observed in the main belt, and dating methods based on the crater count imply that some areas in the southern hemisphere are 1 to 2 billion years old, quite a bit younger than areas to their north. Dawn has continued in its closing, spiraling orbit around Vesta since July, reaching an orbital altitude of 2700 kilometers in August for mapping with its framing camera and infrared mapping spectrometer. In late August, the spacecraft began to move into its High Altitude Mapping Orbit, reaching 680 kilometers above the surface on September 29.
Carol Raymond (JPL), deputy principal investigator for Dawn, told an October 12 press conference that the fundamental dichotomy between northern and southern hemispheres was striking. She also pointed to the diversity in color on Vesta’s surface:
“We expected to see some variation in reflected light from Vesta, because that has been seen before with telescopes, and we also knew something about the composition of the asteroid from meteorites. But the diversity we saw with Dawn exceeds what we would have expected. The dichotomy in the morphology of the surface is also apparent in the color of the surface. In the southern hemisphere we see colors that are consistent with the basaltic morphology you would expect from meteorite studies, and in the northern hemisphere we see a more spectrally neutral surface punctuated by very distinct color variations that appear to be associated with impacts.”
A long process of analysis lies ahead as the Dawn team works to integrate these findings with the higher resolution observations it is now collecting. When operations in the High Altitude Mapping Orbit have been completed, the spacecraft will spiral into its Low Altitude Mapping Orbit in early December, with results from that regime reported in March of 2012. Dawn will spend a year orbiting the asteroid before departing in July of 2012 for Ceres. 2015 should be a lively year, for not only will Dawn reach Ceres but New Horizons will encounter Pluto/Charon. More on Dawn’s mission in this JPL news release.
by Paul Gilster | Oct 12, 2011 | Culture and Society |
Did the Apollo missions produce enough good science to justify their cost? It’s a question Freeman Dyson has speculated on in the past, calling the missions a success because they were “conceived and honestly presented to the public as an international sporting event and not as a contribution to science.” Symbolic of this is the fact that the first item to be unpacked after each landing was the television camera that relayed mission imagery back to Earth. Apollo inevitably labored under the camera’s gaze, but no great scientific discoveries came from it, and the entertainment emphasis inevitably detracted from the missions’ scientific objectives.
Image: Buzz Aldrin leaves the lunar lander in this photo snapped by Neil Armstrong.
What might Apollo have been if it had been conceived from the start to produce good science? Imagine this: Our six Apollo landings put two astronauts each on the surface for a period of several days. At their disposal were two tons of supplies and equipment. For the entire project, Apollo gave us a total of about 50 man-days on the Moon using an aggregate 12 tons of equipment. What if Apollo had produced 40 man-days per ton of equipment instead of the 4 it actually delivered? This could have been achieved by unmanned freight carriers conducting half the landings, providing six astronauts with 60 tons of supplies and equipment, sufficient for 400 days on the Moon.
You wind up with 2400 man-days of exploration instead of the 50 we achieved with Apollo. Let me quote John Cramer on this, because I’m drawing these thoughts from a column he wrote for Analog all the way back in 1988. Dyson had been visiting the University of Washington, where Cramer was then on the physics faculty, and his last lecture there contained these thoughts. Cramer took note of the advantages a much longer stay on the Moon could have brought:
With this much time, Dyson suggested, the Apollo project might have achieved some significant science. There would have been time to explore the lunar poles , to circumnavigate the body, to set up radio-astronomy dishes on the Moon’s radio-quiet back side, to take the time to investigate and theorize and observe and test and probe. There would have been the time and opportunity to bring into play those intrinsically human skills which have lead in previous years-long voyages of discovery to new insights and understanding.
The real Apollo, of course, was carried out in a few days by test pilots operating at a dead run, with one eye on the clock and the other on the prime-time news schedule. There was simply no time for science. Dyson’s revisionist version of Apollo is another road not taken.
The Problem of Premature Choice
Apollo was a success, but on the terms the mission was built around, and it could have been done much better. The Space Shuttle, however, was something much different, an example of what Dyson refers to as the ‘Problem of Premature Choice,’ which he defines as ‘betting all your money on one horse before you have found whether she is lame.’ Translated into bureaucratic terms, this means that a project can become large enough that exploring alternative engineering methods is seen as a waste that could become embarrassing to the public officials who have supported the project all along. Thus one of several alternatives is hastily selected, the rest eliminated, and the premature selection prevents the accurate analysis of the other methods.
Dyson himself has always been an example of independent thinking, but one whose priorities in space exploration favor science, which he thinks should command center stage. As he told his University of Washington audience, the contrast between the Space Shuttle and the International Ultraviolet Explorer (IUE) is instructive. The IUE came with mirror and optics from NASA, a solar power system from ESA, and communications gear from the UK. Countless astronomers and astrophysicists have used it to study tens of thousands of stellar objects in ultraviolet and visible wavelengths, and the IUE was available when supernova SN1987A occurred, providing exceptionally useful light curves that are suddenly back in the news as we try to figure out why neutrinos observed at CERN behaved differently from those from this event.
The IUE, which had been expected to last for three years, ended up serving us for eighteen, being finally shut down in 1996, some eight years after Dyson gave his talk at the University of Washington. The IUE provided a great scientific return in a mission that remains to this day little known. Learning where the payoff is — and deciding what kind of payoff you want to achieve — is key to the process. Looking at NASA’s future as of 1988, John Cramer asked this question:
Will there be further plodding along the dismal path that has lead from the triumph of Apollo to the Challenger Disaster? Will the agency continue to place science far down in the priority queue, going always for the Premature Choice and the job security of mammoth engineering projects? Will NASA continue to withhold any investments in the future, in advanced propulsion technologies, and in new ideas? I hope not.
Choosing the Right Technology
The questions don’t seem to have changed much over the course of the last 23 years, although the scope of our ambitions has been downsized since that even earlier time (1952) when Wernher von Braun proposed a manned expedition to Mars that would have required moving 70 men and 4200 tons of equipment into orbit around the Red Planet, debarking 50 men and 150 tons of equipment to the surface in three ships, using what was essentially World War II technology.
Image: A Chesley Bonestell illustration from a 1952 issue of Collier’s showing his take on the von Braun Mars expedition.
A premature choice would have been dangerous here as well. Among the things Apollo did right was to work with adequate communications channels. Where von Braun chose a 1 kHz bandwidth for the link between the Mars expedition and Earth (essentially allowing the two to communicate via Morse code), Apollo was designed for spectacle and television, and used a communications bandwidth thousands of times broader. Dyson is all about getting the mix right, the right technology (competitively chosen) coupled to serious scientific purpose to achieve a lasting result.
John Cramer’s long-running Alternate View column in Analog can be accessed online. Talking to Cramer at the 100 Year Starship Symposium, I mentioned how useful I had found it over the years, and he told me that the site housing his column had been one of the first to appear on the Internet in Washington, preceding even the Microsoft website. Talk about getting ahead of the curve! Readers will enjoy Dr. Cramer’s take on everything from quantum mechanics to virtual reality over decades of speculation and analysis, a true resource for the interstellar minded. It’s also a source, as this 1988 column showed, of insightful commentary on getting our priorities right.
by Paul Gilster | Oct 11, 2011 | Outer Solar System |
Once again it’s time to catch up with Enceladus, the little moon that has such a huge impact on the planetary system it moves through. We’re learning, for example, how much water vapor is erupting from the features in the moon’s south polar region known as the ‘tiger stripes.’ Cassini measurements (using the Ultraviolet Imaging Spectrograph aboard the spacecraft) had pegged the rate of discharge at 200 kilograms of water vapor every second. New measurements from ESA’s Herschel space observatory match up closely to these findings. Saturn’s E-ring, formed from plume particles, would dissipate in a few hundred years without discharges like these.
You may recall that back in June, Herschel results were announced that showed a huge torus of water vapor circling Saturn itself, one that appeared to be the source of water found in Saturn’s upper atmosphere. More than 600,000 kilometers across and 60,000 kilometers thick, the enormous cloud was produced by Enceladus and picked up by Herschel’s infrared detectors. Water had previously been detected by both Voyager and Hubble in Saturn’s upper clouds, and also spotted by ESA’s Infrared Space Observatory in 1997. These earlier detections had raised the question of how water molecules were entering Saturn’s atmosphere from space.
Studying Herschel’s cloud of water vapor and running computer models that incorporated what we know of Enceladus’ plumes helped researchers put the pieces of the puzzle together. It turns out that most of the water in the torus is lost to space, but enough falls through the rings to enter the planet’s atmosphere to account for the amount of water observed there. Tim Cassidy (University of Colorado, Boulder) is one of those who worked on the data:
“What’s amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren’t expecting such detailed ‘images’ of the torus, and the match between model and data was a wonderful surprise.”
More in this NASA news release. Meanwhile, we have the announcement at the EPSC-DPS Joint Meeting 2011 in Nantes that ice particles from the plumes also fall back onto the surface of Enceladus, building up areas blanketed by super-fine snow whose present state tells us that the plumes have been active for tens of millions of years or more. We already knew that modeling particle trajectories from the plumes produced accumulation on Enceladus itself — this work was done by Sasha Kempf (Max Planck Institute) and Juergen Schmidt (University of Potsdam) in 2010. The new work, by Paul Schenk (Lunar and Planetary Institute, Houston) relies on a painstaking examination of high resolution images in areas of suspected accumulation.
The result: Smooth terrain with topographic undulations suggestive of buried fractures and craters, and changes in slope along the rims of deeper fractures, all consistent with material coating the top of solid crustal ices. The researchers have been able to apply models of deposition showing that the rate of accumulation of these ice particles is less than a thousandth of a millimeter per year. Because the average layer is 100 meters deep in the area studied, the team calculates tens of millions of years would be needed to accumulate the entire amount.
Image: Perspective view of “snow” covered slopes of Enceladus. This heavily fractured terrain lies north of the edge of the active south polar region. The largest of these fractures in the foreground is roughly 1 kilometre wide and 300 meters deep (0.6 miles wide and 1000 feet deep). The fainter dimples on the plateaus are actually older craters and fractures that appear to be covered by thick accumulations of fine particulates, sub-millimetre sized ice grains falling to the surface from the giant plumes to the south. At 12 meters per pixel (~40 feet) this view is one of the highest resolution images Cassini has obtained of Enceladus. Perspective rendering of the surface is derived from colour imaging a stereo topography of Cassini images, produced by D. Paul Schenk (Lunar and Planetary Institute, Houston). See also this ESA news release.
And so we can now talk about the ‘snows of Enceladus.’ They’re important, for their steady accumulation tells us that the heat source that drives the plumes and maintains any liquid water found under the ice crust must have been there for a long time. Schenk says the particles found here are roughly a micron or two across, making them finer than talcum powder that “would make for the finest powder a skier could hope for.” A pleasing thought, but Centauri Dreams assumes the scientist is even happier with the prospect that Enceladus’ snows will help us understand the internal heating mechanism that drives the plumes. What we need now is more high resolution imagery of a world few would have suspected would turn out to be so compelling.
