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.