For the past half century we have witnessed a golden age of solar system exploration unfold: flybys of all the major planets, followed by orbiters, and on selected worlds, landers.
So where do we go from here? The problem is that much more elaborate and complicated spacecraft are needed to pursue the detailed questions raised by our initial planetary reconnaissance. And, the price tag goes up with level of difficulty.
Our first flyby of Mars cost $84 million (in 1960s dollars). The Mars Science Lab, Curiosity, scheduled to land on the Red Planet in 2012, comes in at just over $2 billion. Missions now being considered could easily be double that cost, or more.
There are places to go and wonders to discover, but very little money to build and fly complex robotic explorers across many millions of miles.
The basic question is, what is the most important thing we want to learn about the solar system next? We’ve seen lots of rocks, volcanoes, ice flows, and even lakes of liquid methane. But they become a bore after a while. The planets present vast wastelands, untouched by any obvious sign of life. Finding a “second Genesis” in our solar system is our ultimate quest.
Waiting in the wings are two very ambitious life-searching missions that would be jointly funded by NASA and the European Space Agency (ESA). Among many other exploration strategies, these two missions are under consideration by the National Research Council’s Planetary Science Decadal Survey (2013-2022) that meets this week in Washington DC. Congress uses the NRC’s recommendations as a guidepost for NASA’s future science direction.
Both missions are looking for a launch by the end of the decade. But there’s probably only money to fund one:
This unique tag-team mission would see NASA building a Jupiter Europa Orbiter (JEO), and the ESA building the Jupiter Ganymede Orbiter (JGO). The JEO and JGO would jointly explore the Jupiter System before settling into orbit around Europa and Ganymede, respectively. The two moons almost certainly have liquid water and probably organic chemistry to build life. But is there enough chemical energy for life in an ocean where sunlight never shines? The orbiters will provide clues but cannot do astrobiology experiments without a surface landing.
A rover (looking like a slightly demonic version of Wall-E) launched in 2018 would collect and store about 20 soil samples in test-tube sized containers. A Mars orbiter would arrive several years later. This would be followed by another lander that would retrieve the bottled samples and put them in a small 11-pound capsule.
The lander would blast off, autonomously dock with the orbiter, and return to Earth. The capsule would make a fiery reentry much like the recent Japanese probe Hayabusa’s return to Earth with asteroid sample material.
Both missions are driven by astrobiology. But which one offers the best chance of providing conclusive evidence for life off the Earth?
A Europa orbiter would bring us to where we are with Mars after three decades of orbiters: snapshots of lots of exotic terrain that is suggestive of habitable conditions. Therefore the Europa orbiter leaves me cold (no pun intended).
“These moons provides a natural laboratory for comparative analysis of the nature, evolution, and potential habitability of icy worlds,” says the mission website. Underscore potential. A sample return mission for Europa has been studied. But that could be two decades away or longer.
NASA astrobiologist Chris McKay says that having an alien biological sample in an earthbound lab is the only way to unequivocally convince everyone that life exists elsewhere. It’s been 35 years since NASA’s Viking landers conducted life science experiments on Mars, and the results are still ambiguous and debatable.
What’s more, an Earth-returned sample would allow us to probe the machinery of life that independently evolved on another world. Therefore, the Mars sample return mission is the biggest high risk/reward concept on the wish list in my opinion. We could actually end up with an alien organism on Earth.
But over a decade ago I warned a NASA “planetary protection” scientist to brace for the public debate concerning a sample return mission. They thought that the public could be “educated” about the potential risk of contaminating Earth. Good luck. Perceived dangers bring an emotional response that is out of proportion with the real threat. NASA will be bedeviled by protesters opposed to taking any risk of damaging our biosphere with an alien life form.
All that opponents have to do is read Michael Crichton’s Andromeda Strain, a story about a secretive military sample return that lets virulent space microbes loose on the Earth.
Astrobiologists say that even if a Mars bug got loose it would have a hard time competing for resources with well-established Earth organisms. But it is an experiment I’d rather not try. We would not want the biological equivalent of the BP Gulf oil spill running amok on our planet.
But finding life elsewhere would be a Copernican class discovery. Such a world-view changing revelation comes along every few hundred years at best. That alone is worth the ticket price.