Wednesday, November 26, 2014

Onwards and Outwards

Above: Steven Oleson's concept of a Titan submersible combines two of my favorite ideas for future space exploration in our solar system. Below, the polar layered terrain of Mars as revealed by HiRise is a record of past climate just waiting to be read. The story it tells has significance not just for Mars, but perhaps for the Earth as well.

Spurred on by reporter Matthew Francis, I have recently got to thinking about where in the solar system I would most like to send a space mission if budget were no object. My comments with Matthew made it into an article in Slate which was also picked up by the National Post here in Canada. But there's only so much you can say in a newspaper or magazine article. 

Instead, exploring this topic this seems like excellent material for this space, and you can find my own personal top four below the cut. By the way, I can't forget adding a thank-you to JPL Engineer Keri Bean, currently working with the Dawn mission (though she has shown an affinity for Mars in the past), who recommended me to Matthew in the first place!

I will be the first to admit that my list reveals me as a Planetary Scientist with an Atmospheric/Fluids focus. But of course, that will be no surprise to you, dear reader of this space.

Also, a final note - these are places that we are not currently exploring or for which plans are not solid. In the shorter term I am extremely excited to see the images that come back from Ceres (Dawn), Pluto (New Horizons) and, of course, continuing to help the MSL Team as a participating scientist as we continue to explore Mt Sharp and the environment of Gale Crater. That these places aren't on my list should not be interpreted as a lack of enthusiasm!

Without further Ado:

(1) Images from inside the atmospheres of the giant planets. There is a famous painting by Adolf Schaller commissioned by the famed planetary scientist Carl Sagan called "Hunters, Floaters and Sinkers" which imagines the possibility of an ecology within the clouds of Jupiter. While such a scene may be a bit far fetched, we still have much to learn about the interiors of the giant planets. For instance, investigating these deep atmospheres give us a laboratory to test our theories of fluid dynamics which allow us to build better weather forecasting models right here on Earth. They also tell us about the building blocks of the solar nebula from which the planets formed.

Our only probe to have entered such a deep atmosphere was the Galileo Entry probe of the late 1990s. This little vehicle carried no camera and fell into an unusual part of the atmosphere - a hot spot nearly devoid of clouds. As a result, we still don't have a good picture of how much water and therefore how much oxygen exists in the Giant planets and what the atmospheric dynamics are like at the small scale and below the topmost clouds. While the Juno mission to Juipter will help to answer the oxygen question, its on-board camera - an instrument called Juno Cam - will acquire images in which each pixel will be no smaller than 15 km across. So for now at least, the human scale of the atmosphere, and Sagan's creatures (if they exist) will remain below the threshold of detection.

Note: I've recently published two papers on exploring Jupiter's atmosphere cheaply from the inside out. You can view those papers here (subscription required).

(2) Exploring the seas of the icy moons. If I could pick only one mission that I would like to see happen within my lifetime, it would be the exploration of the liquid water interiors of an icy moon. It is likely that such inner oceans exist on Jupiter's fractured moon Europa and inside Saturn's moon Enceladus from which geysers are building a new ring for Saturn, one eruption at a time. Such oceans, should they exist, would represent the largest habitable volume within the solar system. By examining what lies within those watery spaces, we can find answers to many of our questions about the origins of life on Earth.

But as with all high-reward missions, the risk and the challenge is also considerable. Europa lies within a radiation field that reduces the lifetime of even hardened terrestrial probes to months and the ocean layer would be located underneath miles to tens of miles of hard and solid ice. Still, even in the short term we can make a start along the journey. By mapping out the surface we can find the best landing spots, using radar we can measure the precise depth to liquid and by examining chemicals washed up on the surface we can gain insight into what salts and nutrients might be dissolved below. The Europa Clipper mission proposes to do exactly this.

(3) Roving the surface of Titan by Land or by Sea. One of the joys of exploring Mars with rovers is that sense of the exotic embedded within the familiar. Watching water and dry ice clouds scud along the horizon, or a blue sunset over cracked red rock are relatable on the human scale. So it also would be with Titan, the only other world in our Solar System with a nitrogen atmosphere and where liquid rains from the sky onto parched landscapes. There are seas, rivers, sand dunes and rounded cobbles on Titan, but the liquid is methane and the rocks are water ice at a chilly -290 F.

As with Mars, mobility will be the key to understanding this landscape, one we have only known up close from a single image since the Huygens probe landed here in 2005. On Mars, mobility means rovers, and over much of Titan's landscape it would be the same. But here, and nowhere else, we can also splash down and set off into a light wind and little chop, sailing the seas of Titan and its evocatively named water bodies, such as the Kraken Mare.

(4) Climate Archaeology at the North Pole of Mars. The Earth's ice cores may preserve a record of climate that goes back over a million years, but on Mars there is a record that is far longer and easier to read. The northern cap contains a multitude of layers observed on the surface in high-resolution images and followed to the interior using radar just like a medical x-ray of our own interior structure. Sampling such structure might be as simple as traversing this sublimely sculpted sublimation-dominated landscape. Not only would this tell us about the last 5 to 10 million years of Mars' history and whether the planet periodically comes back to life in a reverse of our freezing ice ages, but would also include history of solar activity which could tell us about our own climate at the time of the dawn of the human race.

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