Fantastic Photos of our Solar System

In the past decade, extraordinary space missions have found water on Mars, magnetic storms on Mercury and volcanoes on the moons of Saturn

The robotic Cassini spacecraft which is now orbiting Saturn looked back toward the eclipsed Sun and saw a view unlike any other. (CICLOPS, JPL, ESA, NASA)
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We've been looking at other planets through telescopes for four centuries. But if you really want to get to know a place, there's no substitute for being there. And in the past decade, more than 20 spacecraft have ventured into the deepest reaches of our solar system. These probes, unlike the Hubble Space Telescope and other observatories that merely orbit Earth, have actually traveled to other planets and approached the Sun, sending back pictures that humble or awe, even as they advance astronomers' understanding of our corner of the universe.

"The past decade has been spectacular in terms of achievements," says Sean Solomon, an astronomer at the Carnegie Institution of Washington and a leader of recent missions to Mercury and Mars.

Last year, NASA's Messenger mission gave us the first up-close view of parts of Mercury, the planet closest to the Sun. The spacecraft has found extensive ridges along the planet's surface, made as it cooled and shrank over its four billion years. Messenger should nestle into an orbit around Mercury in 2011 and continue to study the planet's geology and magnetic fields.

More missions—19 since the 1960s—have made it to Mars than any other planet, and it's the only one whose surface we've explored with robots. NASA's Sojourner rover rolled along there for three months in 1997; Phoenix performed direct experiments on soil samples during five months in 2008. The superstars of planetary exploration are the Spirit and Opportunity rovers; Spirit analyzed the Martian surface for six years before falling silent, and Opportunity is still sending us data. Thanks to all these efforts, we now know that Mars once had seas and rivers and there's ice there today. In the nine years before it lost contact in 2006, the Mars Global Surveyor satellite detected many changes on the red planet, including two gullies apparently formed by gushing water.

NASA's Galileo mission to Jupiter, focusing on the four moons that the Italian astronomer discovered 400 years ago, observed an atmosphere on Europa, ice at the poles and possibly an underground ocean. Callisto, too, may have a liquid ocean. Ganymede has a magnetic field, and Io sizzles with lava that reaches 3,140 degrees Fahrenheit. After the spacecraft ran out of fuel in 2003, engineers sent it crashing into the planet, and Galileo went out in a blaze of observations.

For breathtaking beauty, no mission can compete with Cassini, which is run by the United States with contributions from 16 other nations. Zipping around Saturn and its moons since 2004, Cassini has detected odd spirals in Saturn's rings and a surprising amount of geologic activity on its moons. Titan, the largest (bigger even than Mercury), has lakes of supercool methane and slushy eruptions of a water-ammonia mix. Enceladus is riddled with geysers so powerful they feed matter into Saturn's rings. Rhea may have its own rings. Saturn is practically a solar system unto itself.

Pluto may not count as a planet anymore, but it has its own mission: NASA's New Horizons, now en route and expected to arrive in 2015.

Laura Helmuth is a senior editor at Smithsonian.

This image is from the Hubble Space Telescope and offers a glimpse of another kind of ring around Saturn, the pole-encircling rings of ultraviolet aurora.

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(J. Trauger, JPL, NASA)

The Cassini spacecraft, which is now orbiting Saturn, looked back toward the eclipsed Sun and saw a view unlike any other. The rings of Saturn light up so much that new rings were discovered.

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(CICLOPS, JPL, ESA, NASA)

New images from the Cassini spacecraft display the slightly different densities of Saturn's rings.

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(Cassini Imaging Team, SSI, JPL, ESA, NASA)

This false-color image is a backlit view of ice geysers erupting on Enceladus, a bright moon of Saturn.

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(Cassini Imaging Team, SSI, JPL, ESA, NASA)

Charged solar particles flow along Saturn's magnetic field to its poles, generating a display (in infrared) akin to Earth's northern lights.

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(Cassini VIMS Team, JPL, ESA, NASA)

Cracks and folds on the ice-covered Saturnian moon Enceladus betray tectonic activity, hinting at liquid water beneath the surface.

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(Cassini Imaging Team, SSI, JPL, ESA, NASA)

In this image, the Cassini spacecraft captured a near alignment of four of Saturn's moons (Titan, Dione, Prometheus and Telesto).

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(Cassini Imaging Team)

Saturnian moon Mimas is shown at the bottom of this image with Saturn's northern hemisphere shown in a true color view.

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(CICLOPS, Space Science Institute)

Aside from its solid core, Saturn is mostly hydrogen and helium. The gas giant hosts lightning, winds and clouds of ammonia and water.

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(Cassini Imaging Team)

Saturnian moons Titan and Tethys in clear view as the shadow of Saturn darkens the far arm of the rings.

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(Cassini Imaging Team)

In this image from the SOHO satellite, a "prominence" erupts from the Sun.

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(SOHO / ESA & NASA)

This is a composite image of the Sun from three wavelengths. It reveals the solar features unique to each wavelength.

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(SOHO / ESA & NASA)

This image shows a coronal mass ejection around the Sun as it blasts billions of particles millions of miles per hour into space. The image of the Sun was enlarged and superimposed.

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(SOHO / ESA & NASA)

The Sun erupts in flares (as seen through a SOHO ultraviolet telescope.)

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(SOHO / ESA & NASA)

This image shows a variety of loops and active regions. The lighter areas on the surface of the Sun are the active regions.

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(SOHO / ESA & NASA)

This image of the Sun was captured by the Hinode satellite. It shows the moon traversing the face of the sun during a solar eclipse on July 22, 2009.

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(NASA / JAXA)

A composite image of multiple solar flares on the Sun.

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(JAXA)

NASA's Mars Exploration Rover Spirit captured this image of the Sun as it dips below the rim of the Gusev crater on Mars.

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(Mars Exploration Rover Mission, Cornell University, JPL, NASA)

The robotic Opportunity rover is currently exploring Mars. This image of Cape St. Vincent is part of the wall of Victoria Crater.

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(Mars Exploration Rover Mission, Cornell University, JPL, NASA)

The Spirit rover on Mars inspecting rocks near the summit of Husband Hill.

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(Mars Exploration Rover Mission, Cornell University, JPL, NASA)

On the left of this image is the shattered heat shield from the Opportunity rover as it descended toward Mars. On the right is another part of the heat shield as well as the impact site.

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(Mars Exploration Rover Mission, JPL, NASA)

The solar panel and robotic arm of NASA's Phoenix Mars Lander.

Image was captured from an animation. Right click to download the animation (Quicktime, 15.94 megabytes).

(NASA / JPL-Caltech / University of Arizona / Texas A&M University)

At Victoria Crater on Mars, the rover Opportunity examined samples of sedimentary rock.

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(Ohio State University / Cornell University / University of Arizona / JPL-Caltech / NASA)

More than three billion years ago, Mercury was slammed by an asteroid or comet that created the Caloris Basin (the vast golden area). Volcanoes erupted at the crater's edges.

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(Science Magazine, AAS / Carnegie Institution of Washington / Arizona State University / Johns Hopkins University Applied Physics Laboratory / NASA)

This image of a crescent Mercury was taken by the MESSENGER spacecraft.

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(MESSENGER, NASA, JHU APL, CIW)

NASA's Galileo spacecraft took this image of Jupiter's ring system. The Sun was behind the planet and Galileo was in Jupiter's shadow looking back toward the Sun.

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(Cornell University)

The Galileo spacecraft captured this image of Jupiter's moon Europa. Visible are ice, cracks that run to the horizon and dark patches that most likely contain ice and dirt.

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(Galileo Project, JPL, NASA, reprocessed by Ted Stryk)

In this image of Jupiter's moon Io, two sulfurous eruptions are visible.

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(Galileo Project, JPL, NASA)

West of Jupiter's Great Red Spot is this turbulent region captured by the Galileo spacecraft.

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(Galileo Project, NASA)

This image is a closeup of the ice crust in the Conamara region of Jupiter's moon Europa.

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(PIRL / University of Arizona)
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