A Spin Through the Inner Solar System

More than 50 years of planetary exploration have yielded a rich harvest of data, including many volumes of pictures. These images have revealed the faces of nearly all the nearby worlds, which have turned out to be both forboding and inviting, alien and familiar. Everywhere there is beauty.

We have enough images, in fact, that for many planets, moons, and small bodies we can construct full, global maps. This has been true for places like Mars for decades. For others, such as Mercury and the asteroid Vesta, it has become possible only in the past few years, thanks to the ongoing work of robotic scouts throughout the Solar System and the dedicated people on Earth who fly them.

Following is a series of short videos showing the worlds of the inner Solar System spinning to show their various faces. With two exceptions, each video resulted from taking thousands of individual observations from spacecraft, and combining the data into a 3D computer model.

This look at the Sun comes from the Solar Dynamics Observatory in orbit around the Earth. It shows the Sun as it appeared over the course of the past few days, as seen by sensors tuned to three different wavelengths of extreme ultraviolet light. Later in the decade, new missions will actually fly close to the Sun for even more detailed shots.

This globe comes from thousands of obesrvations by the MESSENGER spacecraft in orbit around Mercury. MESSENGER carries cameras that can observe many wavelenths of light as it bounces off the planet, in order to spy different minerals on the surface. This map shows greatly exaggerated colors in order to highlight the diversity of geology.

Venus is entirely shrouded in dense clouds, of course, but in the 1990s the Magellan spacecraft mapped the surface anyway using radar. The video highlights two large “continents,” or highlands, Aphrodite Terra and Ishtar Terra, the Maxwell Montes mountain range, and Maat Mons, a large, currently dormant volcano. Notice the motion of the clouds at the beginning. Venus is the one inner planet that rotates “backwards” to the other planets.

This map of the moon comes from thousands of photos sent by the Lunar Reconnaissance Orbiter. Each was taken when the Sun was nearly directly overhead at the moment the image was taken. When all stitched together, they make a globe of striking crispness and clarity.

Here is Mars, showing both the actual relief of its surface features, and a version where the topographical data has been wildly stretched to draw out the planet’s complex landscapes.

Finally, we have Vesta, a tiny place compared to these other worlds, but a giant among the members of the asteroid belt. This rotation is not a computer model, but a series of images stitched together from photos sent by the Dawn spacecraft.

These spinning globes show how much we’ve explored. On the other hand, they serve as a reminder of how much remains unseen. There is no rotating map of the largest asteroid Ceres, or of Pluto. That situation will change next year. However, there are many other worlds in the outer Solar System where there are still blank spaces on the map. Sadly, there are no missions even on the drawing board to explore most of them.

There is still much to do.

This article originally appeared as a guest post on The Planetary Society site.


Venus Approach

A series of images taken from the latest data set that was recently released from the Venus Express mission:

The Venus Express spacecraft falls toward the planet on December 28, 2012 as it completes another polar orbit. This view comes from the orbiter’s Venus Monitoring Camera in ultraviolet light. The color is added. To the naked eye, the planet looks like a smooth, white ball with a slight yellow tinge. Credit: ESA / W. Markiewicz (MPAe, Lindau) / Bill Dunford

Learn more about this mission’s investigations into the planet’s thick, swirling clouds. And check out this animation of an earlier orbit, created by Björn Jónsson:

A Map of the Evening Star

“A map says to you, Read me carefully, follow me closely, doubt me not. I am the Earth in the palm of your hand.”

—Beryl Markham

Beryl Markham knew about maps. She was a pilot, author and racehorse trainer, most famous for being the first woman to fly alone across the Atlantic from east to west, an adventure she recounted in her memoir, West with the Night. As an aviator, she would have been very familiar with the sight of the evening and morning star—the planet Venus—in the sky.

What she didn’t know was that just a few years after her death, a robotic spacecraft would circle Venus, fire powerful bursts of radar through its veil of clouds, and begin to image the strange world’s oven-hot surface. Those radar images would allow a new breed of explorer to make a new generation of maps, including one chart in particular that marks the location of a crater named Markham.

I like maps of the planets beyond Earth. They’re both informative and beautiful. They embody craftsmanship, precision, and art. The US Geological Survey actually produces wall-sized paper maps of nearly every body in the Solar System. I love how these maps allow a mental line to be drawn: from a 17th-century sea captain poring over charts in his cabin as he explores new coastlines, all the way to a 21st-century post-doctoral student in front of a computer monitor, discussing potential landing sites on Europa with her peers on multiple continents in real time.

Take as an example one map in particular, a geological map of the Diana Chasma quadrangle of Venus. Before the space age, the planet Venus was a blank sphere, continuously shrouded in thick layers of clouds. (Many people assumed this meant the planet was covered in steamy jungle. You probably know the reality is starker: the clouds created a runaway greenhouse effect that rendered the surface the hottest in the Solar System, a hell of acidic skies and temperatures in excess of 460 degrees celsius.)

Even to most passing spacecraft, the view of Venus is nothing but cloud tops.

Venus by Galileo – Venus as seen by the Galileo spacecraft as it swung by the planet for a gravitational boost on its way to Jupiter in 1990. The image has been processed to increase contrast and remove minor artifacts. The color is added. Credit: NASA / JPL / Bill Dunford

Several Soviet craft dared a landing. They only survived a few minutes. The key to piercing the veil of Venus planet-wide turns out to be radar. Scientists learned a lot using facilities like the giant antenna at the Arecibo Observatory to bounce radar signals through the clouds, off the surface, and back to Earth for analysis.

Even better, in the 1990s an orbiter named Magellan took up its station at the second planet. It carried a synthetic aperture radar system to map the surface. Radar imaging and altimetric and radiometric mapping covered 98 percent of the planet, with radar resolution of about 120 meters. This allowed Magellan to create lovely images of the landscape, like this one of the area surrounding Markham Crater. Venus explorers think a violent impact dug the crater, and either melted or released molten rock that flowed downhill.

Diana region of Venus
Markham Crater and Surroundings – Markham Crater on Venus, as imaged via radar by the Magellan spacecraft. Markham is the round crater with the light-colored outflow at the upper right. Scientists interpret the feature as impact melt or fluidized ejecta created by meteorite impact. The crater is about 75km across. Credit: NASA / JPL

In this view, we can see some of the planet’s extremes. There are tall raised areas like Miralaidji Corona, which is an example of where hot magma welled up near the surface, creating radial fractures and causing lava to spill out across the plains. But in this same shot we can see part of Diana Chasma, a 900-kilometer-long trough that includes some of the deepest points on the globe. This is among the steepest terrain on Venus, with altitudes ranging from –2.5 to 4.7 km. In some places the slopes incline more than 30 degrees.

Miralaidji Corona and Diana Chasma on Venus
Miralaidji Corona and Diana Chasma – Magellan radar view of two landforms on Venus: Miralaidji Corona (feature at upper right with radiating fractures) and part of Diana Chasma (horizontal structure to the left of Miralaidji). Coronas result from rising bodies of magma that generate volcanic flows and fault patterns. Diana Chasma is one of the deepest points on the planet. Credit: NASA / JPL

All this exploration yields more than pretty pictures. By analyzing data from the full suite of instruments on board Magellan, along with information from other orbiters, landers, and Earth-bound observers, scientists can begin to piece together the geology—and thus the history—of Venus as a whole. All without risking boots (smoking, melted boots) on the ground.

One product of the data collection and painstaking analysis is this gorgeous map of the Diana Quadrangle, including Markham Crater and Miralaidji Corona, along with many other craters, cliffs, and fissures.

Map of the Diana Chasma Quadrangle of Venus – A map of the Diana Chasma quadrangle, an equatorial region of Venus between 0º to 25º S. and 150º to 180º E. that encompasses about 8.4 million square kilometers. It’s home to several large coronae and especially deep trenches, including its namesake. Credit: USGS / Vicki L. Hansen and Heather R. DeShon

You can see more detail by clicking the image, or get the complete map, key, and other notes on the USGS site.

There is still so much to explore, so many places where the maps are incomplete. Pioneering aviator Beryl Markham wrote that, “I learned to wander. I learned what every dreaming child needs to know—that no horizon is so far that you cannot get above it or beyond it.”

But none of this will be easy. She also warned, “We fly, but we have not ‘conquered’ the air. Nature presides in all her dignity, permitting us the study and the use of such of her forces as we may understand. It is when we presume to intimacy, having been granted only tolerance, that the harsh stick falls across our impudent knuckles and we rub the pain, staring upward, startled by our ignorance.”

This post originally appeared as a guest blog entry on The Planetary Society web site.

Venus Approach

The swirling clouds of Venus. Image: ESA/ W. Markiewicz (MPAe, Lindau)/Bill Dunford

With all the attention on Mars and Mercury the past few days, here’s a previously unpublished view of Venus. I constructed this sequence from raw images taken in ultraviolet light by the Venus Monitoring Camera on board the Venus Express orbiter.

Among the mission’s discoveries during its six years at the second planet, Venus Express has recently seen evidence that active volcanoes may be hiding under these seemingly serene clouds.