The End of An Era

Pluto coming into view as New Horizons approaches.

In early 2015, the world will achieve a major milestone but it will be one which will fall under the radar for most people.  By July of this year, mankind will have completed its initial reconnaissance of the major worlds of our Solar System.  Let that sink in for a moment.  In the last fifty years or so, we have flown-by, orbited, landed-on, and roved seven planets and scores of moons, asteroids, and comets.  Our robotic envoys have traveled billions of miles on our behalf exploring this collection of exotic alien worlds we call the Sol System.

Next month, NASA's remarkable DAWN probe will orbit Ceres, the largest and most massive asteroid and one of the few relatively large Solar System objects yet unexplored.  This is after the intrepid robot had already orbited Vesta, another large body in the asteroid belt.  In July, the New Horizons craft will fly-by Pluto, formerly our ninth planet and a representative of possibly hundreds of similar icy bodies on outskirts of our Solar System.

I grew up in the 1980's and while it was a time in which space exploration had stalled a bit, there was a wealth of information from the amazing missions of the 1970's.  I devoured anything I could read about the historic missions to our family of worlds.  I poured over space probe photographs published in magazines like National Geographic, Astronomy, Sky & Telescope, and the wonderful children's astronomy magazine Odyssey.   In these magazines I saw the desolate beauty of Mars, the glorious churning clouds of Jupiter, and the majestic rings of Saturn.  These images captured my imagination and started a life-long obsession with space exploration.  In the 1990's and 2000's the pace picked up with a number of ambitious missions that deepened our understanding of this wonderful Solar System of ours.

It's fitting that our initial survey of the Solar System ends with Pluto, which at the time the New Horizons probe was launched was considered the ninth and final planet of the Sol System.  After this Pluto encounter, missions will focus on deepening our understanding rather than revealing unseen worlds and while it will always provide exciting discoveries, the reconnaissance of Pluto offers the last chance to reveal a back a well-known but unexplored Solar System body.

To celebrate this milestone, let's look back at what I consider the ten of the most significant missions in the unmanned exploration of our Solar System.

10. NEAR (l. 1996)

NEAR was a true trailblazer.  It was the first spacecraft to orbit and provide an extended look at an asteroid.  In this case, the Near Earth orbiting  and potato-shaped Eros.  Not only did it orbit Eros but it successfully touched down on the surface of the asteroid despite not being designed as a lander. NEAR paved the way to the subsequent missions to asteroids and other small Solar System bodies which will no doubt continue in the the coming decades as we try to better understand these objects and their dangers and benefits to mankind.  I wouldn't be entirely surprised if Eros is visited by astronauts in the not-too-distant future.  Perhaps they can pick up NEAR and bring it back home.

9. Magellan  (l. 1989)

Magellan was important for many reasons, perhaps most importantly because it signaled the return of the U.S. to space exploration.  Launched from the Space Shuttle, it had been the first interplanetary mission launched in eleven years.  A mission to Venus, Magellan not only successfully tested aero-braking techniques but used radar to peer below the Venusian clouds in unprecedented detail increasing our understanding of our closest planetary neighbor and the bizarre features that lie beneath its brutal atmosphere.

8. Mariner 2 (l. 1962)

Another Venusian mission, Mariner 2 was the first successful mission to another planet.  Mariner 2 flew-by Venus in 1962 and effective kicked off our survey of the Solar System.  Mariner 2 proved the techniques on which the entire Mariner and Voyager programs relied.

7. Mariner 9 (l. 1971)

The culmination of the fantastic Mariner program, Mariner 9 was the first spacecraft to orbit another planet, arriving at Mars in 1971.  While previous missions had provided glimpses of Martian regions, Mariner 9 gave us our first global picture of the planet in all its bleak beauty and complexity.  In fact, arguably the most dramatic geological feature on Mars, Mariner Valley, is named for this remarkable robot explorer.




6. Curiosity (l. 2012)

While not the first rover on Mars, Curiosity was larger and better equipped  than  its predecessors to explore the Maritan surface.  Not only was it more independent and mobile thanks to its nuclear power source, Curiosity captured the attention of the entire world in a way that even the adorable Sojourner rover did not thanks to it's dramatic sky-crane assisted descent on to Mars-all of which was captured in Internet-friendly video.  This technology alone will pay dividends in how we deliver payloads onto the surface of other planets in the future.

5. Viking (l. 1975)

While there had been a briefly successful Soviet attempts to land a spacecraft on Mars, the Viking program included the first Mars lander that was an unequivocal success.  And they did it twice.  Man has always imagined the surface of Mars and for the first time we could actually see it  for ourselves. In what would become a common occurrence for American space probes, the Viking probes vastly outlived their projected life-spans and returned data for years to come.

4. Pioneer 11 (l. 1973)

Is there a more aptly named spacecraft?  By the 1970's America had completed its survey of the worlds of the inner Solar System.  Pioneer 10 and 11 began our survey of the outer Solar System both taking advantage of trajectories that would allow fly-bys of Jupiter and Saturn.  Pioneer 11 flew by Jupiter and was the first probe to explore Saturn and exponentially increased our understanding of these worlds and laid the groundwork for Voyager, Galileo, Cassini, and New Horizons.

3. Cassini & Galileo (l. 1989, 1997)

While these are two distinct probes, sent to two distinct planets Galileo and Cassini both followed up on the discoveries of the Pioneer and Voyager probes.  Galileo was the first probe to orbit an outer planet and spent years exploring Jupiter and it's moons and delivered the first atmosphere probe to any of the outer gas giant planets.  Cassini continues its wildly successful mission to Saturn and deployed the first successful lander on a satellite of another world, Saturn's mysterious and cloud covered moon, Titan.

2. Venera 9 (1975)

Despite their many achievements in human spaceflight, the Russians and Soviets have have terrible luck with their interplanetary missions.  While their Mars campaign, in particular, was unsuccessful, they had better luck with their Venus probes. With the Venera lander they achieved the first successful landing on another planet.  What's even more impressive is that it was on the hellish surface of Venus.  The probe sent data for about forty minutes before literally melting under the heat and pressure of Venus's runaway greenhouse effect.

1. Voyager 2 (l. 1977)

In the 1960's, NASA envisioned a "Grand Tour" of the solar system.  The planets had literally aligned so that one could sent four probes on trajectories that would allow them to visit all five of the (then) outer planets.  While the project was scaled back to only two probes, with Voyager 1 sacrificing a Pluto fly-by to get a better look at Saturn's moon Titan, Voyager 2's journey took it to Jupiter, Saturn, Uranus, and finally Neptune.  Not only did Voyager expand our understanding of Jupiter and Saturn but pulled back the curtain on two remote worlds about which we knew little.  Voyager 2 is now technically in interstellar space and still sending back data after thirty years in deep space.  The Voyager mission is without exaggeration, one of the greatest achievements in human history.