by Paul Gilster | Aug 7, 2013 | Asteroid and Comet Deflection |
When we study extrasolar planetary systems, we’re seeing stars and planets in a wide variety of ages and configurations, helpful in making sense out of our own system’s past. New work out of the University of Antioquia (Medellin, Colombia) suggests changes to the main belt of asteroids between Mars and Jupiter of a kind that we may one day be able to spot in the disks around stars younger than the Sun. What Ignacio Ferrin and team have found is that the main belt, already known to house more than a million objects from one meter to 950 kilometers in size, is also what their paper calls “an enormous graveyard of ancient dormant and extinct rocky comets.”
That conclusion emerges from a study of main belt asteroids recently discovered to have cometary characteristics (the paper calls these ‘asteroidal belt comets’, or ABCs). These objects sublimate ices and otherwise behave like comets even though their orbits are entirely asteroidal. The researchers believe that what we are seeing is not rocky asteroids but dormant comets whose remaining ices are hidden deep within the nucleus. Their recent activity is accounted for by slight changes in temperature whose causal agent is disruption by the gravity of Jupiter, which changes the shape of their orbits to bring them slightly closer to the Sun. Says Ferrin:
“These objects are the ‘Lazarus comets’, returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing.”
Image: These illustrations show the asteroid belt in the present day and in the early Solar System, located between the Sun (at center) and four terrestrial planets (near the Sun) and Jupiter (at bottom left). The top image shows the conventional model for the asteroid belt; largely composed of rocky material. The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. The lower diagram shows how the asteroid belt might have looked in the early Solar System, with vigorous cometary activity. Credit: Ignacio Ferrin / University of Antioquia.
A decrease in perihelion distance brings changes in the amount of received energy. A truly extinct comet is one in which all the ices have already sublimated, which can happen to comets with radii in the range of 50 to 150 meters. But a larger nucleus can withstand sublimation up to a certain depth and then become dormant until it encounters an additional source of energy. Orbital changes can account for the difference. From the paper:
If the perihelion distance increases, the thermal wave would penetrate less, would not reach to the deep layer of ices, and the comet would become more dormant. On the other hand, if the perihelion distance were to decrease, the thermal wave would be more intense and would penetrate deeper reaching to the ice layer, thus awakening and rejuvenating the comet. A new round of activity would ensue. Perihelion distances of comets change randomly due to planetary perturbations especially at resonances. An example of this is the comet P/2008 R1 Garradd located very near the 8:3 resonance with Jupiter…
The paper argues that asteroid belt comets have had perihelion decreases in recent times, and presents evidence that most such objects resume activity at or after perihelion, a sharp contrast with normal comets that become active well before their closest approach to the Sun. The asteroid belt of the past, then, may have been littered by thousands of active comets, whose activity subsided as the objects aged. This work presents an alternative to theories that collisions in the asteroid belt or solar wind activity are the cause of ancient comets becoming active again.
The paper is Ferrin et al., “The location of Asteroidal Belt Comets (ABCs) in a comets’ evolutionary diagram: The Lazarus Comets,” in press at Monthly Notices of the Royal Astronomical Society (full text).
by Paul Gilster | Aug 6, 2013 | Culture and Society |
If you can get your head around the idea that architecture can ‘grow’ by using the tools of synthetic biology and ‘smart’ chemistry, you’ll see that what goes on inside a starship may be radically different from anything we’ve imagined before. Rachel Armstrong has done outstanding research in the area of sustainable solutions for both natural and engineered environments, and works daily on design issues raised by new materials. It’s not surprising to find Dr. Armstrong involved with Project Persephone, the attempt by Icarus Interstellar to model environments aboard a long-duration starship that might spend centuries or more getting to its destination.
Image: Sustainability savant Rachel Armstrong, whose work involves ‘living architecture’ that makes it possible for buildings to be constructed with some of the attributes of biological systems. Credit: Icarus Interstellar.
When Richard Obousy reported in these pages last March about developments at Icarus, he noted the challenges posed by a ship like this:
A habitable long duration starship will need evolvable environments that not only use resources efficiently but can respond quickly to the needs of populations and bypass the current necessary time lags that are implicit in the current system – in identifying critical upgrades and then activating industrial supply and procurement chains – which are already playing catch-up by the time they are realized.
Of course, these are problems with direct relevance today where urban infrastructures in the era of the mega-city can quickly become outdated. The challenge in both cases is to come up with environmental solutions that can not only last but grow organically with our needs. That obviously takes us out of the realm of traditional architecture, or at least melds it with new disciplines. And it’s just that cross-disciplinary reach that Armstrong is reaching for through the Black Sky Thinking Prize, which will be awarded to an individual who tackles interstellar issues with the same willingness to supercede conventional ideas that Armstrong values so strongly.
In a just published article, Armstrong explains the kind of innovation the prize will honor:
While traditional modes of innovation rely on individuals to develop novel objects around which markets and customers are built, where the product is ‘pushed’ into use – the Black Sky Thinking Prize seeks a different kind of innovation, which is inspired by a pioneering vision that invites others to help its realisation. The Black Sky Thinking Prize therefore encourages ‘pull’, as well as ‘push’ innovation, to unite and motivate communities of interstellar researchers and explorers, to realise a shared goal. This approach to generating novelty is not only crucial for our exploration of the worlds beyond our own but may also help navigate the substantial challenges that we face here on earth, where established frameworks persuade us to constrain our thinking within the limits of incremental innovation which benefits a few, rather than the many.
The plan is for the Black Sky Thinking Prize to be awarded biennially at the Starship Congress organized by Icarus Interstellar, an event that debuts next week in Dallas. The competition begins in 2014 with a judging panel that Armstrong describes as “international experts, visionaries and mouldbreakers” now in the process of being appointed. Winners will present their ideas at the Starship Congress as well as receiving a monetary grant. More on this as it develops, but it’s worth noting here that the prize will favor conceptual breakthroughs that could influence the evolution of interstellar studies over near-term technologies.
Encouraging futurists with grants and an audience keeps new ideas in the mix, always a welcome development considering how hard it is for people to move past their preconceptions. It’s tricky for any worldview to imagine its successors,but people like Intel’s Brian David Johnson put a great deal of time into the effort. I think of Johnson with regard to the Black Sky Thinking Prize because the writer/engineer is tasked by Intel with looking about ten years out to imagine the kind of future the devices that are in the concept stage today will emerge into as products.
As Icarus Interstellar is doing with Black Sky, Intel has been encouraging such thinking for several years through its own Tomorrow Project, which involves working scientists as well as science fiction writers and a cross-disciplinary audience that participates in conversations about these matters worldwide. A current hot topic is how cloud computing, driven by chips that will soon shrink to sizes small enough to be installed on everything from clothing to kitchenware, will aggregate information to provide services whose shape we have yet to define.
The Tomorrow Project’s The Future – Powered by Fiction competition solicits science fiction, essays, comics and videos from people of ages 13-25 all over the world, with ten winners to receive cash prizes and have their work published online. Winners will be announced by the end of this year. As with Armstrong’s Black Sky Thinking Prize, Johnson’s goal is to develop humanized visions of a future that uses intelligent technology to produce sustainable lifestyles. I’m all for prizes like these that set a high bar and encourage broad participation, for the solutions to intractable issues can emerge disruptively and from unexpected quarters.
by Paul Gilster | Aug 5, 2013 | Exoplanetary Science |
On the scale of Jon Lomberg’s Galaxy Garden, discussed here on Friday, the star GJ 504 is less than an inch away, representing some 60 light years. In fact, as Jon reminds visitors to the Garden in Hawaii, almost all the stars visible to the naked eye are contained in the volume equivalent of a single leaf. When I speak about interstellar matters I always try to find comparisons that get across the scale of the galaxy, but I can’t think of a better way to experience that scale than to walk through these gorgeous grounds near Kailua-Kona.
As I think about GJ 504 and the Galaxy Garden, I’m also reminded that Kona is the source of one of my favorite coffees, yet another reason for making the trip. But yesterday afternoon I roasted some excellent El Salvador beans and I’m settling in with a brightly flavored mug as I write, just the thing to kick off the week. I begin it with GJ 504 because a team from the SEEDS project (Strategic Explorations of Exoplanets and Disks with Subaru) led by Japanese astronomer Motohide Tamura (University of Tokyo) has just pulled off an important discovery, the least massive planet yet to be directly imaged, as opposed to detection by transit or radial velocity.
Image: Near-infrared color composite images of a “second Jupiter” around the Sun-like star GJ 504. A coronagraph and differential techniques suppress the bright light from the central star. On the left is the intensity image, which shows the radiant power passing through the area, while on the right is the signal-to-noise ratio image, which shows the weakest signal that the detecting system can recognize. Credit: NAOJ.
The star in question is a G-class object which, at 160 million years, is far younger than our Sun. In fact, the age of this system raises questions about the calculated mass of the planet. The SEEDS team comes up with a mass as small as three Jupiter masses, with the distance between star and planet being 44 AU, which would put it out around Pluto’s aphelion in our system. Is this a ‘second Jupiter,’ as this news release states? The answer depends on how accurately we can model a cooling giant planet, for the mass estimate depends upon the age of the host star and luminosity models for objects of planetary size. The paper notes that:
Because massive exoplanets cool and fade with time, direct-imaging searches have been most successful around young stars. Mass estimates for young planets depend strongly on the assumed system age, planetary atmosphere models, and initial thermodynamic state, leading to large uncertainties in the inferred mass.
GJ 504 is evidently old enough for different models – assuming different temperature ranges in early planet formation — to converge, which they do around the 100 million year mark. While the authors go on to say that “no fully established model for estimating the masses of directly imaged planets exists as of yet…,” they add that further direct imaging of older systems whose age is better determined will help us to remove many of these uncertainties.
Discovering worlds like this is going to provide ample fodder for planet formation theorists. Gravitational instability is a formation model that relies on fragmentation of the outer protoplanetary disk and subsequent collapse into a giant planet. The other model, core accretion, depends on planetesimals accumulating and acquiring a gas envelope from the protoplanetary disk. Both of these models run into problems this far out from the parent star, as both require a massive disk in the outer system. We have much to learn about the genesis of gas giants.
SEEDS is proving itself a useful window into outer planets and disk structures, with a plan to observe about 500 stars to develop statistical results on how common outer giant worlds are. But the work extends to protoplanetary disks and, because the mix of stars under investigation varies widely in age, should give us information about how both disks and planets evolve. As the project continues, we can marvel at the success of adaptive optics and coronagraphs at making observations this sensitive from Earth’s surface. It’s important work because direct imaging gives us information about a planet’s temperature, luminosity, atmosphere and orbit.
Image: Gallery of disks imaged in the near-infrared by Subaru SEEDS. Note the spirals and gaps in the disks that the images reveal. (Credit: NAOJ)
Interestingly, GJ 504b turns out to be another blue planet, an indication that its atmosphere is less cloudy than that of other directly imaged planets. Following up from the paper on this work:
…the relatively blue… color of GJ 504 b is consistent with T-type brown dwarfs in the same temperature range… which are representative of less cloudy atmospheres that could occur naturally in this temperature range… In addition, models examining cloud clearing as a function of temperature and surface gravity in Marley et al. (2012) do predict that a temperature of ?500 K and log g of ?4 [a measure of surface gravity], as expected for GJ 504 b… should lead to a clear atmosphere, while the properties of previously imaged planets place them in a cloudy regime. The cold and perhaps less cloudy atmosphere of GJ 504 b thus places it in a physically distinct state from the hotter and cloudier atmospheres of previously imaged planets, and should be highly interesting for further atmospheric studies in the future. These properties imply that GJ 504 b will become a benchmark object for the study of exoplanet atmospheres.
Also setting this world apart from the other directly imaged planets is its cold temperature and comparatively light mass. And while a planet three times as massive as Jupiter is a large world indeed, we can take heart from the continuing success of direct imaging campaigns as we ponder future instruments that will image smaller, Earth-class worlds.
The paper is Tamura et al., “Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504,” accepted for publication in The Astrophysical Journal (preprint).
by Paul Gilster | Aug 2, 2013 | Culture and Society |
The creator of the Galaxy Garden (Kona, Hawaii), Jon Lomberg is an artist working in many media whose work continues to resonate in the space community and the public at large. Centauri Dreams readers will know that he worked with Frank Drake in designing the cover for the Voyager Interstellar Record and the sequence of 120 photographs and diagrams portraying Earth and its inhabitants (soon to become the first human artwork to leave the Solar System). But they’ll also remember COSMOS, the series for which Jon served as chief artist. In fact, he worked as Carl Sagan’s principal artistic collaborator for many years, including key work on the film CONTACT. Here Jon extends his ideas on nature, art and astronomy to venues much larger than the Galaxy Garden itself, a proposal that would model our staggeringly beautiful cosmos. For more on the concept, be aware that Jon discussed these ideas in his talk at the recent Starship Century conference, a video of which is available.
by Jon Lomberg
Astronomy daunts us with its distances. One mind-numbing number after another, equally incomprehensible. Do you have a good sense of the difference between 40 million and 140 million? Such quantities are difficult to scale and difficult to grasp.
One of the hardest concepts to convey is the scale of the Universe. Here is a proposal for a new way to address this problem.
THE MODEL OF THE UNIVERSE is a Pacific-wide system of beautiful and well-crafted markers that place extragalactic objects in an enormous scale model the size of the planet. The three dimensional model is projected onto the surface of the Earth, with the center of the Earth representing the location of the Big Bang in some higher spatial dimension. The center of the projected model is the Milky Way Galaxy Garden in Captain Cook, Hawaii. Scaled to the Galaxy Garden, a model of the Universe would be about the size of the Pacific Ocean.
Markers showing individual objects can be purchased, donated, sponsored, or built by the host business or organization. An umbrella organization and its website will provide educational materials explaining the project and providing, for example, announcements as new markers are added to the model.
The Local Group of Galaxies are scattered in the few square miles surrounding the Galaxy Garden in Honaunau. The Virgo Supercluster extends 20 miles out from the Local Group—approximately the distance between the Galaxy Garden and Kona International Airport. So all the various parks, businesses, schools, and beaches could be the site for the varied galaxies of the Virgo Supercluster.
This presents an opportunity to turn all of West Hawaii into a cosmological model of the Virgo Supercluster. The entire Big Island maps nearby superclusters. Astrotourists can spend part of their holiday exploring the extragalactic environment and getting a real sense of the relative distances to objects that are otherwise just hazily “somewhere out there.”
More distant clusters and cosmological objects are located as shown on the accompanying designs. NOTE: The mapping is preliminary only to suggest the concept.
The Galaxy Garden
If you are not familiar with the Galaxy Garden concept, please take a moment and have a look at www.galaxygarden.net.
The GG is the world’s first large-scale explorable model of the Milky Way Galaxy. Scaled at 1000 light years per foot, this 100′ garden offers visitors a direct, sensory, intuitive way to understand the scale of the solar system compared to the galaxy.
At 83 light years per inch, nearly all the stars visible to the naked eye are in a volume equivalent to a single leaf. Anyone, even a child, can understand the difference between a fraction of an inch and a 100′ garden surrounding. We have found that this conveys the scale of the Galaxy better than any other astronomy educational experience.
The Local Group of Galaxies are scattered in the few square kilometers surrounding the Milky Way in Honaunau.
Traveling toward the town of Kailua-Kona from the Galaxy Garden, the extragalactic explorer encounters many famous galaxies, whose beautiful portraits are displayed on simple but elegant and sturdy markers. Astrotourists can spend part of their holiday exploring the extragalactic environment and getting a real sense of the relative distances to objects that are otherwise just hazily “somewhere out there.”
A few examples:
• NGC 5128, the brilliant radio galaxy Centaurus A, is located in Kealakekua Bay, famous historical site of Captain Cook’s visit, frequented by many tourists.
• Spiral Galaxy M101 is at the West Hawaii Community College.
• M87 is in the town of Kailua-Kona, perhaps on the grounds of the Hulihee Palace or in the lobby of the historic King Kamehameha hotel.
• The Leo Cluster of galaxies is at the Onizuka Space Center at Kona International Airport. The entire area between the Galaxy Garden and the airport is the Virgo Supercluster of galaxies.
• Other superclusters could be located in Waimea, Hilo, and Volcano.
More distant objects are located on the neighbor islands, at appropriate tourist, educational, and community venues.
Objects at cosmological distances could be located at schools and science centers from Alaska to San Diego, as well as Tahiti (Point Venus?) and American Samoa.
Because the network projects the three-dimensional distribution of galaxies onto a spherical surface, the entire Earth becomes a model of the Universe with the center of expansion (the Big Bang) lying in a dimension not accessible from the model Universe. This provides a vivid educational metaphor that helps people to visualize the topology of the expanding universe and facilitates understanding of why there is no defined spot among the galaxies where the Big Bang took place.
Reference 1: The Virgo Supercluster
Reference 2: Other superclusters and voids out to 200 mly
Conversion of Kona to Cosmic Distances
1″ = 83 light years
1 foot = 1000 light years
100′ = 100,000 light years
1000′ = 1 million light years
10,000′ = 10 million light years = ~ 2 miles
20 miles = 100 million light years
200 miles = 1 billion light years
2000 miles = 10 billion light years
3000 miles = 15 billion light years = ~ diameter of Universe
by Paul Gilster | Aug 1, 2013 | Outer Solar System |
I’ve come to believe that building the system-wide infrastructure we’ll eventually need for interstellar flight will depend on satisfying two imperatives: Planetary defense and astrobiology. The first demands the ability to move payloads quickly to distant targets, allowing plenty of time to change the trajectory of problematic objects. The second is all about science and answering key questions about our place in the cosmos. I know few people who think life doesn’t exist elsewhere, but if it really is out there, finding and cataloguing it will involve human crews operating deep in the Solar System.
After all, we’re learning how widespread internal oceans may be, and it’s possible that even places as remote as Triton may have spawned some kind of organisms. And while we’ve had our eye on Europa’s hidden ocean for some time now, Enceladus is a recent entrant into the astrobiology sweepstakes with its jets of water ice and organic particles emmanating from the so-called ‘tiger stripes’ at the south pole. The Cassini orbiter discovered the jets back in 2005, and we’ve been learning more ever since. Now Cassini’s VIMS instrument (Visual and Infared Mapping Spectrometer) has given us data showing that the plumes vary predictably over time.
Image: Effects of the gravitational pull of Saturn on the amount of spray coming from jets at the active moon Enceladus. Enceladus has the most spray when it is farthest away from Saturn in its orbit (inset image on the left) and the least spray when it is closest to Saturn (inset image on the right). This analysis is the first clear finding that shows the jets at Enceladus vary in a predictable manner. The background image is a mosaic made from data obtained by Cassini’s imaging science subsystem in 2006. The inset image on the left was obtained on Oct. 1, 2011. The inset image on the right was obtained on Jan. 30, 2011. Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI.
Cornell University’s Matt Hedman likens what’s happening to adjustable garden hose nozzles. As Enceladus orbits Saturn, the ‘nozzles’ in the south pole fissures close when the moon is closest to the planet, and open again as it swings further away. Think of Enceladus being alternately squeezed and released. The new findings confirm a variability in the plumes that had been long suspected but never observed until now, one that has implications for the moon’s internal structure. Says Christophe Sotin (JPL), a co-author of the paper on this work:
“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water. Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”
Yes, and with New Horizons bearing down on Pluto/Charon, we’re soon going to learn whether there is evidence for internal oceans in this interesting binary system. One day, we’re going to investigate Kuiper Belt objects like Makemake and Haumea, the latter especially interesting because of its ellipsoid shape and the probability this was caused by an ancient impact. We may learn much by comparing and contrasting Haumea with other Kuiper Belt objects as we find out whether radiogenic heating could keep internal oceans liquid even in these environments.
Enceladus itself continues to teach us that objects once thought quiet can be active and filled with potential. The famous jets being sprayed from Enceladus turn out, when examined in the infrared, to be dimmest when the moon is at its closest point to Saturn, while three to four times as bright at its most distant point. Gravitational effects like these are now visible, thanks to Cassini, but they remind us of the unseen internal action taking place as the giant planet squeezes and relaxes tiny Enceladus, an energy source that has shaped the moon and perhaps created conditions hospitable to life.
The paper is Hedman et al., “An observed correlation between plume activity and tidal stresses on Enceladus,” published online in Nature 31 July 2013 (abstract).
