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.


The Same Sky

Last Friday, about an hour and a half after sunset, a robot on Mars raised its head. Obeying commands sent earlier from unseen masters, it lifted its camera eyes from the desert floor, and instead stared off toward the west. There, a darkening sky spread out above a line of silhouetted mountains. In the perfectly clean air, the stars began to ignite one by one. The brightest by far was actually two stars, a brilliant white gem and a smaller spark just below it.

But they weren’t stars at all. They were the Earth and the Moon.

Earth seen from Mars; Mars seen from Earth
Earth from Mars, Mars from Earth
Left: the Earth and the Moon in the evening sky of Mars, as seen by the Curiosity rover.
Right: Mars rising over Salt Lake City.
Mars credit: NASA/JPL-Caltech/MSSS/TAMU. Earth credit: Bill Dunford.
Click to enlarge.

Of course, we can see Mars in our own sky. The sibling worlds, Mars and Earth, stare at each other across a yawning gulf of empty space (at the moment it spans almost a hundred million miles).

But are they really very far apart?

Mars may be an alien world, but if you went there and looked up at the night sky you’d see something that might surprise you: the stars would look exactly the same. The distance between the Earth and Mars isn’t nearly enough to change the perspective on the much more distant stars. You’d see all the familiar constellations, the Big Dipper and Orion and the Milky Way. The only difference in the sky, other than the sharp brilliance of everything seen through such thin air, would be that “extra” evening or morning star and its little companion.

You would look at that spark, and you would know you weren’t alone.


The Faces of Mars

The full exploration of Mars began in earnest in 1976, when the audacious Viking mission arrived at the Red Planet. Previous spacecraft had carried out an initial reconnaissance, but Viking went much further. It brought not just one, but two spacecraft, each of which dispatched a complex laboratory to land on the surface. What’s more, both of these Viking orbiters were designed not for a quick fly-by, but for a long-term mapping mission.

Viking 2 Approaches Mars
Viking 2 Approaches Mars – Mars looms before the Viking 2 spacecraft as it approaches the planet in August, 1976. Credit: NASA / JPL / processed by Bill Dunford

Together, the Viking 1 and 2 orbiters captured many thousands of high-quality images of the surface. To this day, Mars explorers consider the data Viking collected part of a valuable knowledge base. Viking 1 spent more than four years in active service, and toward the end of its life it snapped hundreds of pictures during the early northern Martian summer.

The U.S. Geological Survey combined those images into a series of extraordinary mosaics. Instead of focusing on one region or feature on the surface, these new compilations recreated how the entire face of Mars would look to an observer in a spacecraft flying about 2500 kilometers above the ground. These USGS hemispheric mosaics were prepared in high resolution and somewhat enhanced color. The result is a crisp, clear studio portrait of a planet. There’s a word that’s highly overused when describing pictures from space, but these images are, in fact, stunning.

The first mosaic below is one of the most commonly used pictures of Mars. It includes a couple of particularly striking features: the hemisphere-wide gash of Valles Marineris, and three towering volcanoes in Tharsis.

Mars: Valles Marineris Hemisphere
Mars: Valles Marineris Hemisphere – A mosaic of 102 Viking orbiter images of Mars, showing a hemisphere of the planet centered on the immense Valles Marineris canyon system. Prepared by the U.S. Geological Survey. Credit: NASA / JPL / USGS

But it’s not the only portrait in the series. Here are several more, some much less often seen. Together, they reveal the several faces of a world. For all the excitement of following the rovers as they pick their way carefully through an explorer’s playground in Gale and Endeavour, it’s refreshing to see a reminder of this planet’s grand, stark sweep.

Mars: Syrtis Major Hemisphere
Mars: Syrtis Major Hemisphere – Mosaic of 100 Viking orbiter images acquired in 1980, showing a hemisphere of Mars focused on the Syrtis Major region (the dark area at the right). Prepared by the U.S. Geological Survey. Credit: NASA / JPL / USGS
Mars: Cerberus Hemisphere
Mars: Cerberus Hemisphere – A mosaic of 104 Viking orbiter images acquired in February, 1980, showing a hemisphere of Mars featuring the Cerberus region (the large dark spot at the center left). Prepared by the U.S. Geological Survey. Credit: NASA / JPL / USGS
Mars: Schiaparelli Hemisphere
Mars: Schiaparelli Hemisphere – A mosaic of images from the Viking orbiters taken in 1980, showing a hemisphere of Mars centered on the large impact crater Schiaparelli. Prepared by the U.S. Geological Survey. Credit: NASA / JPL / USGS

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


New Views of Martian Weather

We have some new images from the Mars Express orbiter, added to the collection just last week. As always, they’re beautiful. This time, I noticed something of a pattern in the latest shots: lots of weather. Mars may or may not have ever been a home to living creatures, but it’s not a dead world. Here are some pictures as proof.

clouds over Mars
Clouds Over Arabia – The Mars Express orbiter views a cloudy day over unnamed craters at the border of the Acidalia Plains and the highlands of Arabia Terra. Credit: ESA / G. Neukum (Freie Universitaet, Berlin, Germany) / Bill Dunford

Mars experiences many kinds of weather, but these views of drifting or hovering clouds just feel so Earth-like.

clouds over Mars
Cloudy Crater – Moreux crater in the Protonilus Mensae region of Mars fills with clouds in this recent Mars Express image. North is to the right; color is approximate. Credit: ESA / G. Neukum (Freie Universitaet, Berlin, Germany) / Bill Dunford

That said, it’s a very thin and cold wind that blows on Mars.

clouds over Mars
Weather in Tantalus Fossae – Mars Express spied this view of the Tantalus Fossae region just north of Alba Patera. Credit: ESA / G. Neukum (Freie Universitaet, Berlin, Germany)

But the fact that we can observe the weather day in and day out, not just on one world, but several—there’s a sign we’re living in an amazing future.

clouds over Mars
Clouds on the Horizon – A recent view from the Mars Express spacecraft: the planet’s limb on a cloudy day. The contrast in the thin atmosphere has been boosted. Credit: ESA / G. Neukum (Freie Universitaet, Berlin, Germany) / Bill Dunford

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


Through a Glass, Darkly

If you’ve ever tried photography, you know that not every picture can be a prize winner. Sometimes, no matter how carefully you prepare, there’s not enough light, or the sun flares in the lens, or the model blinks. Of course, there is some comfort in the fact that even top professionals face the same problems every now and then.

Even when it comes to machines that people have used to create some of the most unforgettable images in history, robotic spacecraft in deep space, not every shot that comes down to Earth is ready for the cover of National Geographic. In fact, some of the better ones still require a little bit of clean-up, whether it’s removing a spot of digital noise or correcting color to more closely match what you’d see with your own eye if you could stand on Mars. Some of the pictures are just disasters.

All photography in space faces challenges. Many of these are the usual questions of exposure, framing, and focus, but complicated by extreme changes in lighting conditions, and cameras mounted on platforms that are traveling at thousands of kilometers per hour relative to their subjects. Others problems are endemic to space travel, such as cosmic rays and other forms of radiation interfering with the camera sensor, not to mention the glitches that can crop up in the custom computer systems on board the spacecraft or somewhere else along the line within the Deep Space Network that carries the signals.

Even so, when you’re talking about our handsome Solar System, even the throw-away pictures offer their own kinds of rewards. Consider the following set of raw or very lightly processed images that I’ve come across in the archives. All of them suffer from one photographic malady or another. I’m still glad I saw them.

The Shores of the Seventh World – Digital noise in this raw Voyager image of Uranus almost looks like electronic surf. Credit: NASA / JPL

I’ll admit it: I actually like images like these. They remind me that the spacecraft are real. These are not excercises in CGI. They are physical machines of aluminum and silicon, built by human hands, graceful, precise, yet flawed.

Blinded by the Light – Saturn not quite eclipsing the Sun, which is overloading the Cassini spacecraft’s cameras. Credit: NASA / JPL / SSI

They fly through physical space at great speed, beset by storms of radiation and the contstant threat of meteorite impact…or just the wear and tear of travel across millions of kilometers and years of time.

Martian Sunshine – The robotic geologist Opportunity faces a low sun on the horizon. Credit: NASA / JPL

The places they reach are also real. Harsh, unforgiving, but only so because reality itself can be harsh and unforgiving. These are not paintings we’re looking at here. It’s not a movie. If you could ride with New Horizons, if there were a window where you could press your nose, you could see the glare of the very real Sun in the glass.

Jupiter’s Rings – The New Horizons probe, passing by Jupiter on its way to Pluto, spied Jupiter’s relatively faint rings (the long, horizontal arc at the center of the image). Credit: NASA / JHUAPL

Flawed, unprocessed images from space also make me think about the collaboration between human and machine. Who takes a picture of the rings of Saturn: Cassini or the people on the Cassini imaging team? Surely it’s some of both. The people who fly the missions overcome terrific technological hurdles just to get the spacecraft to the right place at the right time to make a photograph. When the shots don’t quite turn out, it’s reminder of how stunning it is when they do.

Sparkling Io – The Galileo spacecraft catches a peek at Jupiter’s moon Io in a raw image full of cosmic ray hits and other noise. Credit: NASA / JPL

Besides, just because an image isn’t perfectly pretty, that doesn’t mean it’s not useful. Science and engineering teams can, and routinely do, squeeze knowledge out of every pixel in images that are never widely published.

So I keep looking at these pictures, the throw-aways. I think about the smell of rockets exploded on the launch pad and the silence in a control room after a spacecraft’s signal has unexpectedly gone dead. About how we can’t help but explore anyway, about the way the imperfect mechanical world reaches out to the sublime natural.

The Machine, at the Edge of Forever – A raw image sent by Voyager 2 from Neptune’s moon Triton, just before the spacecraft slipped away into the darkness beyond the planets, never to return. Credit: NASA / JPL

These pictures aren’t perfect. But if you look closely you can see ourselves in them.

Earth Rise – The Kaguya lunar orbiter catches a ray of sunlight as the Earth and Sun emerge from behind the Moon. Credit: JAXA / NHK

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