Pluto’s Problematic Cartography

We’re still two years from the New Horizons flyby of Pluto, but the cartography of the solar system’s most famous dwarf planet—based on Hubble imagery—is already several kinds of problematic, as Emily Lakdawalla explains in a post that also explains how the cartography of other worlds is done. (Key challenges include defining the north and south pole—which one is which?—as well as a prime meridian.)

A Topographic Map of Titan

Global topographic map of Titan (NASA/JPL-Caltech/ASI/JHUAPL/Cornell/Weizmann)
NASA/JPL-Caltech/ASI/JHUAPL/Cornell/Weizmann

The Cassini team has released a global topographic map of Saturn’s moon Titan. What makes this map interesting is the fact that, due to its thick atmosphere, Titan can only be mapped by radar during Cassini’s close flybys. As a result, only half of its surface has been imaged, and only 11 percent has topography data. For this map, the remainder was, well, extrapolated:

Lorenz’s team used a mathematical process called splining—effectively using smooth, curved surfaces to “join” the areas between grids of existing data. “You can take a spot where there is no data, look how close it is to the nearest data, and use various approaches of averaging and estimating to calculate your best guess,” he said. “If you pick a point, and all the nearby points are high altitude, you’d need a special reason for thinking that point would be lower. We’re mathematically papering over the gaps in our coverage.”

Topo maps of parts of Titan have been released before, but not for the entire moon. See previous posts on The Map Room: Titan in Stereo; Topography of Titan.

Lunar Gravity Map

Free-Air Gravity Map of the Moon
NASA has released a free-air gravity map of the Moon: “If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. … The free-air gravity map shows deviations from the mean, the gravity that a cueball Moon would have.” Gravity data comes from the GRAIL mission, with the digital elevation model provided by the Lunar Reconnaissance Orbiter laser altimeter. Image credit: NASA’s Goddard Goddard Space Flight Center Scientific Visualization Studio.

New Moon Globe Released

Moon Globe Calling it “the first entirely new globe of the lunar surface in more than 40 years,” Sky and Telescope has announced a new Moon globe based on Lunar Reconnaissance Orbiter imagery. Replogle’s Moon globe has been the standard for decades, but it’s based on 1960s-era charts and, as I said in my review three years ago, doesn’t have a lot of contrast and doesn’t look much like the Moon. Mind you, the new globe costs almost twice as much.

Geologic Map of Io

Geologic map of Io (small)

In my review of Paul Schenk’s Atlas of the Galilean Satellites I noted that the maps of Jupiter’s four largest moons were actually spacecraft imagery placed on a map projection; there were no non-photographic maps. In that context, the geologic map of Io, just out from the U.S. Geological Survey, is both novel and pertinent. The maps are based on Voyager– and Galileo-derived photomosaics of Io’s surface released in 2006, but they’re maps. ASU news release, Universe Today.

Atlas of the Galilean Satellites

Book cover: Atlas of the Galilean Satellites Paul Schenk’s Atlas of the Galilean Satellites (Cambridge University Press, 2010) collects all the imagery gathered by the Voyager and Galileo missions of the four major moons of Jupiter (Callisto, Ganymede, Europa and Io, all discovered by Galileo in 1610) and assembles them into global, quadrangle and area maps. But this heavy, 400-page tome begins with a confession. “This Atlas is not what it should be.” The failure of the high-gain antenna on the Galileo spacecraft meant that far less data could be transmitted back to Earth during its nearly eight-year mission than had been planned. Large tracts of the moons are mapped in low resolution; the fuzzy images yield little detail. But until another mission is sent—the Juno probe now en route to Jupiter will not be studying the moons—this is all there will be for the foreseeable future. For decades, in fact.

Continue reading “Atlas of the Galilean Satellites”

More Moon Maps

Chinese scientists have released a high-resolution map of the Moon based on images from the Chang’e 2 spacecraft; the maps are at a resolution of seven metres (MoonViews, Universe Today). Phil Stooke compares the Chang’e 2 images with those from the Lunar Reconnaissance Orbiter Camera (LROC). Meanwhile, and speaking of the LROC, Jeffrey Ambroziak is making 3D anaglyph maps based on LROC data; he’s launched a Kickstarter campaign to create a 3D digital map of the entire Moon.

A New Lunar Topo Map

LROC topo map of the Moon's far side
A new topographic map of the Moon from the Lunar Reconnaissance Orbiter: “Today the LROC team releases Version 1 of the Wide Angle Camera (WAC) topographic map of the Moon. This amazing map shows you the ups and downs over nearly the entire Moon, at a scale of 100 meters across the surface, and 20 meters or better vertically.” Late last year lunar topo maps were released that were based on laser altimeter data; presumably the WAC data, based on stereo observations, is better. Image credit: NASA/GSFC/DLR/Arizona State University.