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Solar System Exploration at 50
Exploration Stories: Favorite Historical Moments

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No Longer
Rob Manning
Systems Engineer, Jet Propulsion Laboratory
Io's volcanic plains are shown in this Voyager 1 image mosaic which covers the area roughly from latitude 60 degrees north to latitude 60 degrees south and longitude 100-345.
Io's volcanic plains are shown in this Voyager 1 image mosaic which covers the area roughly from latitude 60 degrees north to latitude 60 degrees south and longitude 100-345.

What do you think are the most significant events that have occurred in the past fifty years of robotic planetary exploration? Why?

In terms of raw discovery, the flybys of Jupiter and Saturn's moons made by Voyager 1 and 2 in 1979, '80 and '81 were revolutionary.



This is a Voyager image of Enceladus, an icy moon of Saturn.
This is a Voyager image of Enceladus, an icy moon of Saturn.

This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on 9 July 1979.
This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on 9 July 1979.

Our view of these planetary bodies as large, round boring rocks was completely shattered by the flybys. Our solar system suddenly got a lot more exciting.

Layers of haze covering Saturn's satellite Titan are seen in this image taken by Voyager 1 on 12 November 1980
Layers of haze covering Saturn's satellite Titan are seen in this image taken by Voyager 1 on 12 November 1980

In your field of work, what are some examples of the great achievements and discoveries in planetary science and robotic exploration throughout the past 50 years?

Similar to science done on Earth, discoveries made through the exploration of Mars have been like a slow and steady brightening of the proverbial light bulb.

ESA's Mars Express obtained this perspective view of an unnamed impact crater located on Vastitas Borealis, a broad plain that covers much of Mars's far northern latitudes. The crater is 35 km wide and has a maximum depth of approximately 2 km beneath the crater rim. The circular patch of bright material located at the center of the crater is residual water ice.
ESA's Mars Express obtained this perspective view of an unnamed impact crater located on Vastitas Borealis, a broad plain that covers much of Mars's far northern latitudes. The crater is 35 km wide and has a maximum depth of approximately 2 km beneath the crater rim. The circular patch of bright material located at the center of the crater is residual water ice.

While we have discovered that the surface of Mars is lifeless, we have also gradually added chapters to our knowledge of the Red Planet, and in particular about the role H2O has, and continues to play, on Mars (in many forms).

This color view of a mineral vein called "Homestake" comes from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity. The vein is about the width of a thumb and about 45 cm (18 inches) long.  Opportunity examined the mineral vein in November 2011 and found it to be rich in calcium and sulfur, and possibly the calcium-sulfate mineral gypsum.

"This tells a slam-dunk story that water flowed through underground fractures in the rock," said Steve Squyres of Cornell University, Ithaca, N.Y., and principal investigator for Opportunity. "This stuff is a fairly pure chemical deposit that formed in place right where we see it. It's the kind of thing that makes geologists jump out of their chairs."
This color view of a mineral vein called "Homestake" comes from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity. The vein is about the width of a thumb and about 45 cm (18 inches) long. Opportunity examined the mineral vein in November 2011 and found it to be rich in calcium and sulfur, and possibly the calcium-sulfate mineral gypsum. "This tells a slam-dunk story that water flowed through underground fractures in the rock," said Steve Squyres of Cornell University, Ithaca, N.Y., and principal investigator for Opportunity. "This stuff is a fairly pure chemical deposit that formed in place right where we see it. It's the kind of thing that makes geologists jump out of their chairs."

We now have much stronger evidence that Mars was once habitable for Earth-like life on the surface a long time ago. And, what is more, it is not unreasonable to guess that under the surface of Mars there may remain pockets of habitable environments -- could residual life reside there? We don't know ... yet.

False color (blue) shows where water ice is buried beneath the Martian surface in this Mars Odyssey map.
False color (blue) shows where water ice is buried beneath the Martian surface in this Mars Odyssey map.

We got our first huge hint for underground ice with the gamma ray spectrometer (GRS) data from the 2001 Mars Odyssey orbiter in 2002.

The sphere-like grains or "blueberries" distributed throughout the outcrop can be seen lining up with individual layers. This observation indicates that the spherules are geologic features called concretions, which form in pre-existing wet sediments.
The sphere-like grains or "blueberries" distributed throughout the outcrop can be seen lining up with individual layers. This observation indicates that the spherules are geologic features called concretions, which form in pre-existing wet sediments.

Launching in 2003, the twin Mars Exploration rovers (MER) Spirit and Opportunity found water-altered rock on both sides of Mars.

This HRSC image shows a perspective view of a possible dust-covered frozen sea near the Martian equator.
This HRSC image shows a perspective view of a possible dust-covered frozen sea near the Martian equator. Copyright: ESA/DLR/FU Berlin (G. Neukum)

Mars Express later found dust covered glaciers in mid-latitudes, while Mars Reconnaissance Orbiter (MRO) found large areas of minerals that could have been created with water.

In this image from NASA's Mars Reconnaisance Orbiter's High Resolution Imaging Science Experiment (HiRISE) camera, we view Noctis Labyrinthus. Noctis Labyrinthus is a series of pits on the western end of Valles Marineris. These pits were formed several billion years ago: the rocks and sediments on their floors record evidence of water during Mars' history.
In this image from NASA's Mars Reconnaisance Orbiter's High Resolution Imaging Science Experiment (HiRISE) camera, we view Noctis Labyrinthus. Noctis Labyrinthus is a series of pits on the western end of Valles Marineris. These pits were formed several billion years ago: the rocks and sediments on their floors record evidence of water during Mars' history.

Now Curiosity has shown us that single cell prokaryotic life could have been happy living in some clays on Mars in the distant past. We are still far from finding life, but Mars is no longer viewed as a dead red rock.

These veins form when water circulates through fractures, depositing minerals along the sides of the fracture. These veins are Curiosity's first look at minerals that formed within water that percolated within a subsurface environment.
These veins form when water circulates through fractures, depositing minerals along the sides of the fracture. These veins are Curiosity's first look at minerals that formed within water that percolated within a subsurface environment.

From an engineering and humanistic perspective, I think that the landing and egress of the little Sojourner rover off of the Pathfinder lander on 4 and 5 July in 1997 was a poignant moment in planetary history. It marked a moment when humanity found itself free to virtually wander and explore the surface of another planet.

Pathfinder Panorama
An enhanced version of the famous Mars Pathfinder photo of the lander and Sojourner rover.

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