There is welcome news from Greg Matloff. His new book, written with the artist C Bangs and physicist Les Johnson (NASA MSFC) will be published by Springer/Praxis in December. Following on the success of Solar Sails, the latest is Paradise Regained, a look at how we might use the resources of the Solar System to alleviate environmental problems here on Earth. Here’s an absorbing video presentation on the book.
Extending Earth’s resource base beyond our atmosphere, and in the process protecting the Earth from asteroid and comet impact, is essential as we gradually become not just a terrestrial but, in Matloff’s words, a cosmic species. “If we are wise enough to work together on this, terrestrial life in the Solar System can live as long as the Sun,” says the author, an optimism that should resonate with Centauri Dreams readers.
Yesterday’s story on IBEX is now complemented by images from the Ion and Neutral Camera, part of the Magnetospheric Imaging Instrument on the Cassini orbiter. The Cassini data confirm the fact that the heliosphere isn’t shaped the way we’ve always thought. The assumption up to now has been that the collision of the solar wind with the interstellar medium would create a foreshortened nose in the direction of the Solar System’s motion, and an elongated tail in the opposite direction.
Both IBEX and Cassini argue otherwise. Stamatios Krimigis (Applied Physics Lab, Laurel, MD) notes the import of these findings:
“These images have revolutionized what we thought we knew for the past 50 years; the sun travels through the galaxy not like a comet but more like a big, round bubble. It’s amazing how a single new observation can change an entire concept that most scientists had taken as true for nearly fifty years.”
Amazing and invigorating, for we’re opening up serious new ground here. Put together, what Cassini and IBEX are telling us is that particle pressure and magnetic field density are what dominate the interaction between the interstellar medium and the heliosphere. We’re getting a look at how a solar system moves through the space around it through twin imaging programs that map an otherwise invisible boundary.
Image: The shape of our solar system moving through the interstellar medium was previously thought to be comet-shaped, with a head pointed into the stream, and a tail flowing downstream. New observations show the shape actually resembles something more like a slippery ball (the hot particles that exert pressure) moving through smoke (the interstellar magnetic field). As the “ball” moves through the “smoke,” the smoke bends and parts to let the ball through, then resumes its previous shape after the ball has passed on. At present, this is only hypothetical: New models will be motivated by these measurements, and will provide a more physically accurate basis for the interaction of the heliosphere with the interstellar medium. Credit: NASA/JPL-Caltech/JHUAPL.
Cassini has been mapping energetic neutral atoms not only near Saturn but across the entire sky. These ENAs, discussed yesterday, are produced by energetic protons that interact with the magnetic field of the interstellar medium. For more on ENAs, I turn to Mike Gruntman’s AstronauticsNow site (thanks to Centauri Dreams reader Carl for the tip). Gruntman is a professor of astronautics at USC, an author, and a mission co-investigator on IBEX. Of ENAs he writes:
The interaction between charged and neutral particles is a common phenomenon in space plasmas. Whenever an energetic ion undergoes a charge exchange process in a collision with a neutral background atom, an energetic neutral atom – ENA – is born. Ion-electron recombination and neutral atom acceleration by the solar gravitation may also contribute to an ENA population under certain conditions. ENAs are ubiquitous in space environment and their study opens a new window on various phenomena in space plasmas with a promise (already partially realized) to qualitatively improve our understanding of global magnetospheric and heliospheric processes.
Gruntman goes on to note that recording ENA fluxes as a function of observational direction allows us to create a global image, which is what we are doing with the interactions at our system’s edge. It’s a method that is paying off handsomely, as Edmond Roelof, a co-investigator on the Magnetosopheric Imaging Instrument, points out:
“Energetic neutral atom imaging has demonstrated its power to reveal the distribution of energetic ions, first in Earth’s own magnetosphere, next in the giant magnetosphere of Saturn and now throughout vast structures in space-out to the very edge of our sun’s interaction with the interstellar medium.”
You can see an animation showing the interstellar medium flowing past the heliosheath here (the heliosheath is a secondary bubble around the heliosphere formed by the interstellar medium’s interactions with the latter). Also note five papers published in Science Express this week on IBEX and Cassini, including Krimigis et al., “Imaging the Interaction of the Heliosphere with the Interstellar Medium from Saturn with Cassini,” (October 15, 2009). Abstract available.
Findings that are outside our expectations seem par for the course as we explore the Solar System. From the volcanoes of Io to the geysers of Enceladus, unusual things show up with each new mission. Why should IBEX be any different? The Interstellar Boundary Explorer is the first spacecraft expressly designed to study what happens at the edge of the Solar System, where nearby space meets the interstellar medium.
The ‘bubble’ around the Sun called the heliosphere comes about as charged particles in the solar wind move continuously away from the Sun. Although IBEX is far from the heliopause (it’s orbiting the Earth with an apogee of 322,000 kilometers and a perigee of 16,000 kilometers), its instruments are tuned to study energetic neutral particles (ENAs) swept up by the solar wind in the boundary between the edge of the heliosphere and interstellar space beyond. IBEX has been mapping this area since last October.
And here comes the surprise, as explained by IBEX principal investigator David J. McComas (SwRI):
“The IBEX results are truly remarkable, with emissions not resembling any of the current theories or models of this never-before-seen region. We expected to see small, gradual spatial variations at the interstellar boundary, some ten billion miles away. However, IBEX is showing us a very narrow ribbon that is two to three times brighter than anything else in the sky.”
Image: Accurate timing of the incoming ENAs allows the IBEX team to obtain a higher resolution in the latitudinal direction. The inset at right shows some of the fine detail of the ribbon. Credit: SwRI.
Yes, we’ve got two Voyager spacecraft out there, but IBEX is giving us the big picture, imaging the region not with photons but ENAs from its distant vantage in a highly elliptical Earth orbit. It’s focusing on the so-called ‘termination shock,’ where the solar wind collides with interstellar gas. As they pass through the region, neutral hydrogen and oxygen atoms are dragged by the plasma at the interstellar boundary, while neutral helium passes straight through. Tracing their different arrival directions tells the tale.
McComas adds:
“The most astounding feature in the IBEX sky maps — the bright narrow ribbon — snakes through the sky between the Voyager spacecraft, where it remained completely undetected until now.”
Image: This image illustrates one possible explanation for the bright ribbon of emission seen in the IBEX map. The galactic magnetic field shapes the heliosphere as it drapes over it. The ribbon appears to trace the area where the magnetic field is most parallel to the surface of the heliosphere (the heliopause). Credit: SwRI.
We’re learning that our Solar System’s interactions with the interstellar medium are more intense than previously believed. As helpful as Voyager’s point measurements are, we now see the region far more clearly. And because the ribbon these data reveal seems to be governed by the direction of the local interstellar magnetic field, it appears that the interstellar medium has a much greater influence on the heliosphere than we originally thought.
Imagine a boat from Earth drifting across an alien sea. Something like that could happen as early as 2022 if Ellen Stofan (Proxemy Research) can talk the powers that be into the venture. Stofan envisions a new mission to Titan, the only other place in the Solar System known to have bodies of liquid on its surface. The methane and ethane lakes revealed by Cassini show some bodies as large as the Black Sea or the Great Lakes of North America. Stofan’s target: Ligeia Mare or Kraken Mare, two of the larger possibilities revealed by the orbiter.
Image: Radar data from Cassini allowed the creation of this artificially colorized view of Ligeia Mare, with liquid methane/ethane shown in blue. Credit: NASA/JPL/USGS.
What an interesting off-shoot from the conventional rover concept, but then, Titan seems to inspire such things. Various types of airship designs have been put forward for studying the Saturnian moon, and at the Aosta conference in July, Giancarlo Genta described the workings of a hypothetical Titan rover that could take to the lakes as needed, converting itself into a floating research station. Stofan’s idea loses the rover capability. It is all boat, though it may not look like one.
What the planetary geologist envisions is a capsule that would be dropped directly into the target lake, with a mast to hold a camera. Drifting for months, pushed by local winds, the probe would use a nuclear-powered engine to run experiments and return data to Earth. When interviewed recently on National Public Radio, Stofan spoke about conditions in such a lake, including the possibility of a storm:
“In fact, we’d love for that to happen, to be able to return an image showing a rainy day on Titan and to see those methane raindrops falling down into the lake. The wind might kick up a little, but nothing as violent as the tropical storms and hurricanes we get here on Earth.”
The Discovery-class mission being proposed to NASA would launch around 2016 and arrive some six years later, assuming NASA chooses to go with the concept (the agency is going to be issuing a call for proposals for its Discovery missions shortly). So many good mission ideas, so little money to work with! But if by chance the Titan boat makes the cut, just imagine the view we would have from the camera mounted on its mast. You can hear Stofan interviewed on the Titan boat idea at this NPR page.
Thanks to Eric Davis for the tip on Stofan’s work. I’m also reminded that we looked not long ago at Stofan’s fine book (with astronaut Tom Jones) Planetology: Unlocking the Secrets of the Solar System (National Geographic, 2008).
Back when I was a kid I found an old atlas that had been on the family shelves since the early 1900’s. I used to browse through it looking at all the places that had changed. The map of eastern Europe was, as you can imagine, a far cry from what it later became, with the pre-World War I world vividly sketched in those musty pages. But what really caught my eye was one of the maps of South America, showing an area of Brazil that was still marked ‘unexplored.’ It was the only such place I could find on any of the maps, and it filled my adolescent head with thoughts of adventure. I wish I had that atlas nearby to scan from, but the image below gets across the feel of those old maps.
Henry M. Stanley I’m not, but exploration has huge appeal, and to get the pure product today, we have to move into space. Out there most everything could be marked ‘unexplored.’ Sure, we’re getting to know the planets, but we’ve only had a few missions beyond Mars, have yet to see Pluto/Charon close up, and are only now finding the larger Kuiper Belt objects. Looking out to other stars, we can see solar systems from the outside, but are limited by the nature of our measurements to larger planets and large, observable features like dust and debris disks. We’re a long way from knowing whether or not our own Solar System is unusual or rather pedestrian.
Each step forward carries for me the kind of excitement that once must have energized the members of the Royal Geographical Society as explorers addressed them on their travels to far places. And never mind that our new explorers are robotic. Take the Herschel Space Observatory, launched in May, which is going to be telling us much about the physical properties of the objects in the Kuiper Belt. Or maybe I should call them ‘Trans-Neptunian Objects,’ as ESA does in its program “TNOs Are Cool: A Survey of the Trans-Neptunian Region.”
The dark regions beyond Neptune are populated by the remnants of the planetesimal disk from which the planets formed. What we’d like to find as we begin to flesh out the blank places on our Solar System map are TNO properties like albedo, density and size, things that have been hard to measure in the 1,000 or so objects thus far discovered beyond the orbit of Neptune. One way to get at this is to study their thermal emission, using Herschel’s tools to study the far infrared, where such emissions peak. Ideal for the task, Herschel covers the far infrared to submillimeter range of the electromagnetic spectrum.
The TNO survey was announced last week at the Division for Planetary Sciences meeting in Puerto Rico, where attendees were told that it will include observations of about 140 TNOs, 25 of which are known to be multiple systems. Nailing down the physical properties involved should provide constraints on various models for the formation and evolution of the outer system, and should help us understand the disks we see around other stars better. A worldwide call is now in place for open-time projects on Herschel, with 400 hours devoted to the trans-Neptunian project.
We have so much to learn, as the DPS meeting also reminded us in regard to Saturn, where an enormous ring tilted 27 degrees from the main ring plane has been found. Anne Verbiscer (University of Virginia), notes the unusual size and depth of the find, calling it a ‘supersized ring,’ and adding “If you could see the ring, it would span the width of two full Moons’ worth of sky, one on either side of Saturn.” Is ring material the explanation for the odd appearance of Iapetus, with its one bright, one dark side?
Image: This false-color mosaic shows the entire hemisphere of Iapetus (1,468 kilometers across) visible from Cassini on the outbound leg of its encounter with the two-toned moon in Sept. 2007. The central longitude of the trailing hemisphere is 24 degrees to the left of the mosaic’s center. Credit: NASA/JPL/Space Science Institute.
The Spitzer Space Telescope is behind these observations, which track the glow of cool dust in the infrared (the study uses data made before the Spitzer instrument ran out of coolant in May). I look at a Cassini view of Iapetus and ponder the future maps we’ll make as such places become more and more familiar, not to mention the remarkable way distant places will be cataloged and distributed over worldwide Net connections. No shortage of unexplored places in this system, and beyond it, so many more.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
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