I know I have defended the robotic missions to Mars against charges that they cost too much, but Robert B. Gagosian, in today’s Washington Post, gives voice to an alternative perspective based on questions about parts of the Earth that we have not yet studied well.

Gagosian, head of Woods Hole, loves the Mars stuff, but offers a strong, apples-to-apples argument about the exploratory science that could be done here on Earth for a comparable cost:

Miniaturization of sensors and telemetry technology has created a new generation of ocean observatories that enable us to learn more at less cost. We needn’t rely only on ships for exploration. Flotillas of battery- and solar-powered observatories, some as small as a soccer ball, can report back measurements 24 hours a day from anywhere on Earth, regardless of weather. Some are anchored in place or flow with ocean currents; some are autonomous robots that swim on a programmed path for months at a time; some are installed on the sea floor, some on the coast, some at the sea surface and some part way down in “mid water.”

We are in a new age of oceanography, one in which giving the ocean its own instrumentation has become an economic and technical possibility.

The cost of building a network of hundreds of sensors to wire the oceans: about $1 billion over 10 years, a little more than the cost of the two Mars rovers.

What’s the payback?

The oceans affect climate and weather, and thus the human condition, around the world. Ocean observatories can reveal conditions that affect fisheries, shifts in weather and long-term climate change. They can illuminate the migratory patterns of marine mammals, the reasons for drought or floods, and the fate and long-term effects of pollutants. They can detect in real time tsunamis, undersea earthquakes, volcanoes and extreme weather at sea, improving prediction of their devastating effects at sea and ashore. Figures we have come up with show that better predictions of ocean conditions could produce $1 billion in annual savings from better mitigation or prevention of damages.

This is clearly not an either-or thing, but when we’re talking about spending a billion dollars for this or that, it’s a useful point of comparison.