Centauri Dreams
Imagining and Planning Interstellar Exploration
Charon: A Rugged, Cratered Surface
A chasm in Charon’s southern hemisphere turns out to be longer and deeper than Earth’s Grand Canyon, says William McKinnon (Washington University, St. Louis), deputy lead scientist with New Horizon’s Geology and Geophysics investigation team.
“This is the first clear evidence of faulting and surface disruption on Charon. New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity.”
Image: Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon Charon taken by New Horizons on July 11, 2015. Credit: NASA/JHUAPL/SWRI.
The most prominent crater, near Charon’s south pole, is almost 100 kilometers across, and evidently the result of a geologically recent impact. This NASA news release adds that the darkness of the crater floor may be the result of a different kind of icy material being exposed, less reflective than the ices on the surface. Another possibility: The ice of the crater floor has a larger grain size, reflecting less sunlight. This would be the result of ice melting during the impact event and re-freezing into larger grains.
Image: This annotated version of the Charon imagery includes a diagram showing Charon’s north pole, equator, and central meridian, with the features highlighted. Credit: NASA/JHUAPL/SWRI.
Meanwhile, the dark region near Charon’s north pole bears watching, with more detailed images coming up on the 14th.
Last Look at Pluto’s ‘Far Side’
The side of Pluto that always faces its large moon Charon is the side that New Horizons won’t see when it makes its close flyby on July 14. That makes the image below what principal investigator Alan Stern is calling “the last, best look that anyone will have of Pluto’s far side for decades to come.”
Image: New Horizons’ last look at Pluto’s Charon-facing hemisphere reveals intriguing geologic details that are of keen interest to mission scientists. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Four dark spots seem to be connected to the dark belt in Pluto’s equatorial region, their fairly regular spacing a source of considerable curiosity. The large areas are estimated to be roughly 480 kilometers across, with irregular boundaries between light and dark terrain. Jeff Moore (NASA Ames) gives a glimpse of what’s ahead:
“When we combine images like this of the far side with composition and color data the spacecraft has already acquired but not yet sent to Earth, we expect to be able to read the history of this face of Pluto.”
And of course, as this JHU/APL news release reminds us, we’ll soon be seeing the encounter hemisphere from as close as 12,500 kilometers.
New Horizons: Detecting Geology
Pluto’s surface is beginning to be revealed, with the first signs of geological features, as principal investigator Alan Stern explains:
“Among the structures tentatively identified in this new image are what appear to be polygonal features; a complex band of terrain stretching east-northeast across the planet, approximately 1,000 miles long; and a complex region where bright terrains meet the dark terrains of the whale. After nine and a half years in flight, Pluto is well worth the wait.”
Image: Tantalizing signs of geology on Pluto are revealed in this image from New Horizons taken on July 9, 2015 from 3.3 million miles (5.4 million kilometers) away. At this range, Pluto is beginning to reveal the first signs of discrete geologic features. This image views the side of Pluto that always faces its largest moon, Charon, and includes the so-called “tail” of the dark whale-shaped feature along its equator. (The immense, bright feature shaped like a heart had rotated from view when this image was captured. Among the structures tentatively identified in this new image are what appear to be polygonal features; a complex band of terrain stretching east-northeast across the planet, approximately 1,000 miles long; and a complex region where bright terrains meet the dark terrains of the whale. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
The annotated image below includes a reference globe showing Pluto’s orientation, with equator and central meridian in bold.
And the photo below speaks for itself. It’s been nine years. Pluto at last.
Image: Science team members react to the latest New Horizons data from Pluto at the Johns Hopkins University Applied Physics Lab on July 10, 2015. Left to right: Cathy Olkin, Jason Cook, Alan Stern, Will Grundy, Casey Lisse, and Carly Howett. Photo by Michael Soluri.
New Horizons: Flyby Schedule, Images
New Horizons makes its closest approach to Pluto, at approximately 12,500 kilometers above the surface, at 0749 EDT (1149 UTC) on Tuesday July 14. Be aware that for much of that day, we’ll be out of communication with the spacecraft while it’s busy gathering data. About 2102 EDT (0102 UTC on the 15th), we should receive a confirmation of a successful flyby — the spacecraft is scheduled to send a preprogrammed signal that it has survived the close approach. Then the data flow begins and will continue for months.
NASA offers the schedule for the flyby here, with information on NASA TV coverage. We should be looking at close-up images of Pluto and hearing early reactions from the science team by mid-afternoon of Wednesday the 15th. And of course it will be possible to follow the mission on Facebook or on Twitter (also #PlutoFlyby). The nail-biting time will be the wait on the 14th for the signal announcing a successful transit of the system. It doesn’t take a large object to silence a spacecraft moving at 14 kilometers per second and we can only hope for the best.
Meanwhile, the imagery keeps improving, with both Pluto and Charon beginning to swim out of the image-processing mist. We’re seeing bright and dark features on Pluto’s surface, while Charon presents a more uniform light gray terrain with a large dark polar region. This NASA news release speculates on the possibility of impact craters on Charon, quoting Jeff Moore (NASA Ames): “If we see impact craters on Charon, it will help us see what’s hidden beneath the surface. Large craters can excavate material from several miles down and reveal the composition of the interior.”
Image: Pluto from the New Horizons’ Long Range Reconnaissance Imager (LORRI), July 8, 2015. Most of the bright features around Pluto’s edge are a result of image processing, but the bright sliver below the dark “whale,” which is also visible in unprocessed images, is real.
The differences between Pluto and Charon are increasingly apparent, with Charon lacking the reddish color of the former, a hue that has reminded some of us of early, blurry photos of Mars. While frozen ices like nitrogen, carbon dioxide and methane have been detected on Pluto, Charon’s surface seems to be mostly frozen water and ammonia compounds. Unlike Pluto, Charon has no atmosphere, and its interior is composed of rock and ice in equal measures, whereas Pluto’s interior is predominantly rock. The lower surface contrast of Charon has been abundantly clear as New Horizons returns images of the two dissimilar worlds.
Image: Image of Charon from the New Horizons’ Long Range Reconnaissance Imager (LORRI), July 8, 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
As New Horizons nears its closest approach, the Cassini orbiter will take images of Pluto/Charon from its distant station around Saturn, and beginning July 23, the Spitzer Space Telescope will take seven days of observations at infrared wavelengths. The plan is to study ices on Pluto’s surface. New Horizons will also be backed up by Kepler observations, with the K2 mission focusing on Pluto for a three month period beginning in October.
“K2 observations will expand the time coverage of the speedy New Horizons flyby of Pluto, making observations of the dwarf planet-moon system every 30 minutes,” said Steve Howell, project scientist for Kepler/K2 at NASA’s Ames Research Center in Moffett Field, California. “We are excited to turn the planet-hunting Kepler spacecraft’s attention to this distant solar system object to provide additional scientific insight into this far-off, mysterious world, itself a miniature solar system of five moons in orbit about Pluto.”
Image: New Horizons was about 3.7 million miles (6 million kilometers) from Pluto and Charon when it snapped this portrait late on July 8, 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
And we’ve already had one interesting study performed by the SOFIA airborne observatory, an infrared telescope mounted on a 747 aircraft. On June 28, Pluto occulted a distant star, creating a backlighting that could be studied to provide a baseline measurement of Pluto’s atmosphere. All of this, plus the data that the Hubble Space Telescope has gathered about Pluto’s smaller moons, will provide datasets that complement the abundant science return of New Horizons.
Image: This is the same image of Pluto and Charon from July 8, 2015; color information obtained earlier in the mission from the Ralph instrument has been added. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Detection of Pebbles in a Circumstellar Disk
Not long ago we looked at a new paper from Alan Boss that modeled interactions in young protoplanetary disks (A Disruptive Pathway for Planet Formation). The idea here is that as dust grains and larger objects bump into each other on the way to forming planetesimals, a mechanism must exist to keep them from spiraling into their star. Boss’ models show explosive phases in young stars that lead to gravitational instabilities of the sort needed to scatter these small objects outward and preserve their prospects for forming into planetesimals, and perhaps one day, planets.
Watching infant solar systems form is akin to studying embryology in animal species, a chance to understand the myriad interactions that affect growth and set it in particular directions. Now we have work out of the University of St. Andrews, recently presented at the National Astronomy Meeting in Llandudno, Wales, that announces the discovery of a ring of small rocks circling the star DG Tauri, a 2.5 million year old object some 450 light years from Earth.
Image: An artist’s impression of the belt of ‘pebbles’ in orbit around the star DG Tauri. The inset is a close up view of a section of the belt. Credit: J. Ilee. Adapted from original work by ESO/L. Calçada/M. Kornmesser, ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO).
The work of Jane Greaves and Anita Richards (University of Manchester) is based on data from the e-MERLIN array of radio telescopes centered in Jodrell Bank (Cheshire) and extending over southern England to form an interferometer, giving it the resolution of a single large telescope. The instrumentation proved up to the considerable challenge, as Greaves relates:
“The extraordinarily fine detail we can see with the e-MERLIN telescopes was the key to this discovery. We could zoom into a region as small as the orbit of Jupiter would be in the Solar System. We found a belt of pebbles strung along a very similar orbit – just where they are needed if a planet is to grow in the next few million years. Although we thought this was how planets must get started, it’s very exciting to actually see the process in action!”
The observations, as this Royal Astronomical Society news release explains, were made at a wavelength of about 4.6 cm. They revealed a signature that requires chunks of rock at least a centimeter in size. This is a useful finding, for as we’ve seen in the work of Alan Boss, we’re in the process of tuning up our computer models of protoplanetary disks and their interactions. Now we can identify, at least in some systems, the location of pebble-like material that will one day accrete into larger objects. A deeper analysis of young disks should emerge from all this.
Image: An e-MERLIN map of the star DG Tauri. The yellow and red areas show what is thought to be a ring of pebble-sized clumps in orbit around the star. Credit: J. Greaves / A. Richards / JCBA.
Studying the results will be, among others, a group called the Planet Earth Building Blocks Legacy e-MERLIN Survey (known by its fitting acronym — PEBBLeS). The team plans to extend studies like this to a number of stars that are in the process of forming their own solar systems. Right now we’re using equipment sensitive to regions as small as Jupiter’s orbit, but the logical goal is to move in five times closer to witness the formation of planets like our own. The researchers believe that upgrades to e-MERLIN and the coming capabilities of the Square Kilometer Array will make such observations possible.
The Exploratory Imperative
If you’re a long-time reader of this site, you doubtless share my fascination with the missions that are defining our summer — Dawn at Ceres, Rosetta at comet 67P/Churyumov-Gerasimenko, and in the coming week particularly, New Horizons at Pluto. But have you ever wondered why the fascination is there? Because get beyond the sustaining network of space professionals and enthusiasts and it’s relatively routine to find the basic premise questioned. Human curiosity seems unquenchable but it’s often under assault.
‘Why spend millions on another space rock?’ was the most recent question I’ve received to this effect, but beyond the economics, there’s an underlying theme: Why leave one place to go to another, when soon enough you’ll just want to go to still another place even more distant? The impulse to explore runs throughout human history, but it’s shared at different levels of intensity within the population. I find that intriguing in itself and wonder how it plays out in past events. The impulse is often cited as a driving motif that has pushed human culture into every corner of the planet, but it comes in waves and can lie fallow until new discoveries bring it to the fore.
Back when I was writing Centauri Dreams (the book), I looked at the Conference on Interstellar Migration, which was held in 1983 at Los Alamos. This was a multidisciplinary gathering including biologists and humanists along with physicists and economists, and a key paper there was the synergistic work of Ben Finney (an anthropologist) and Eric M. Jones (an astrophysicist). Called “The Exploring Animal,” the paper argued that evolution has produced an exploratory urge driven by innate curiosity. The authors considered this the root of science itself.
It was probably the Los Alamos conference that introduced the theme of Polynesia into interstellar studies, the idea being to relate the settlement of the far-flung islands of the Pacific to future missions into the interstellar ocean. From Fiji, Tonga and Samoa and then, in another great wave, to the Marquesas, Hawaii and New Zealand, using double-hulled dugout canoes with outrigger floats, these explorers pushed out, navigating by ocean swells, the stars, and the flight of birds. Finney and Jones call this the outstanding achievement of the Stone Age.
Here’s an excerpt that puts the view succinctly:
The whole history of Hominidae has been one of expansion from an East African homeland over the globe and of developing technological means to spread into habitats for which we are not biologically adapted. Various peoples in successive epochs have taken the lead on this expansion, among them the Polynesians and their ancestors. During successive bursts lasting a few hundred years, punctuated by long pauses of a thousand or more years, these seafarers seem to have become intoxicated with the discovery of new lands, with using a voyaging technology they alone possessed to sail where no one had ever been before.
And to me, this resonates when you see something like this:
Image: This map of Pluto, made from images taken by the LORRI instrument aboard New Horizons, shows a wide array of bright and dark markings of varying sizes and shapes. Perhaps most intriguing is the fact that all of the darkest material on the surface lies along Pluto’s equator. The color version was created from lower-resolution color data from the spacecraft’s Ralph instrument. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Are Finney and Jones right that there is an ‘intoxication’ in the discovery of new lands? It’s certainly a sense I have, and most of the people I deal with in aerospace clearly have it. But note as well the fact that these bursts of expansion into the Pacific were also marked by long pauses, thousand-year breaks from the outward movement. We can see this as a process of consolidation, I suppose, or maybe a broader cultural fatigue with the demands of exploration. Are we entering a similar era in space, a time of reflection and retrenching before the next great push? If so, we have no good guidelines on how long that period may last.
In his new book Beyond: Our Future in Space (W.W. Norton, 2015), Chris Impey likewise speculates on the urge to explore. Humans do it differently from animals, after all — we are the only species that moves over large distances with a sense of purpose and organization, sometimes for reasons that have little to do with the availability of resources. Like Finney, Impey cites the Polynesian example, seeing it as driven by a mixture of culture and genetics.
Are there specific genes that come into play in at least parts of the population to make this happen? Because we all know that for some people, exploration is not an option — not even an interest. Most of Europe stayed home when the ships that would open up the Pacific and the Orient to western trade and expansion set sail, and remained at home while emigrants took to the seas to settle elsewhere. Even so, in every era, the exploratory impulse seems firmly planted, which is why even dangerous missions always find no lack of volunteers.
Impey is interested in certain developmental genes that he believes give us advantages over other hominids. In particular, he focuses on a gene called DRD4, which controls dopamine and thus has influence on human motivation and behavior. A variant of this gene known as 7R produces people more likely to take risks, seek new places and explore what is around them. About one person in five carries DRD4 in its 7R form. Impey notes that the 7R mutation occurred first about 40,000 years ago as humans began to spread across Asia and Europe.
Impey doesn’t go so far as to call this an ‘exploration gene,’ but he does think that carriers of 7R are more comfortable with change and are better problem solvers. From the book:
Even if they’re only present in a fraction of the population, the traits that favor adventurousness are self-reinforcing. If the 7R mutation has slightly higher frequency in a population that migrates, that frequency will increase in a finite gene pool. Mobility and dexterity are enhanced as they are expressed. The most successful nomads will encounter new sources of food and new possibilities for enhancing their lifestyle. The best users and makers of tools will be spurred to come up with new tools and novel applications of existing tools. The fulcrum of this feedback loop is our one attribute that’s unparalleled: a big brain.
Is DRD4 7R the source of the internal fire that drives our explorations? It’s a pleasing thought, for it implies that despite periods of pullback, the exploratory impulse is ever outward, for it exists as part of the template of our species. I doubt we can pin curiosity and migration down to this one salient, but our past does imply there is something within us that accounts for our restlessness. Whatever that something is, we find it reinforced in the great explorations of our time. And it seems to be strong enough to survive the periods of retrenchment and apathy that sometimes punctuate our efforts, and that tend to get lost in the big picture of history.
Yesterday’s post asked whether we were nearing the end of an era with the flyby of the last of the ‘classical’ planets. The answer is yes, but the beauty of eras ending is that they have successors, and our inherent human curiosity is not something that can be long suppressed. The Voyagers have already begun the bridge between the interplanetary era and the interstellar, and New Horizons will soon enough follow. Keep in mind the words of Andre Gide when New Horizons swings about to take images of Pluto and Charon receding in the night: “Man cannot discover new oceans unless he has the courage to lose sight of the shore.”
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