The next mission to an icy moon, whether it be Europa or Enceladus should have a
microscope of some kind and we're trying to define the parameters of such a
microscope that will maximize our ability to see life on Earth, because if
we can maximize their ability to see life in all the possible extreme
environments on Earth, then we can be pretty confident we can come as close as possible
to being able to address this on other planets.
Enceladus has raised a lot of recent interest. It is a small moon of Saturn where
there is a clear liquid water ocean under a sheet of ice.
And though this ice there are these geysers or plumes that are emitting material up into space
where they can be sampled and captured by fly-bys. So it makes it a whole lot easier to go to a moon where
you can sample by simply flying through the plumes rather than having to land.
We really want to know if there are microorganisms living in this global ocean.
We believe that there's not enough energy to allow for multicellular life
so we're talking about bacteria, and we would hope that there would be
intact cells in the plumes - possibly even living cells in the plumes of Enceladus.
There are many things you'd have to do in order to see whether there are living bacteria in the plumes of Enceladus.
First of all, these plumes are really no thicker than the smog in Los Angeles,
so you're going to have to fly through probably 12 to 20 times in order to collect
a femtoliter of liquid. If you're flying through,
you're probably flying through at one to five kilometers per second.
Anything you capture either is going to have to be decelerated or is going to be pretty much pulverized.
So, we're trying to develop a bunch of capture techniques and capture substrates
that would maximize the return from any sort of Enceladus fly-by.
Given all of those constraints - how would you know if there are bacteria there?
I think it's going to take a variety of techniques. We're going to start with imaging.
But if you think about your ordinary brightfield microscope - the biggest drawback about it is that
you have to have an expert observer sitting there getting the precise focus to see bacteria.
You can imagine that if you're out on Saturn with one hour light speed delay
you're not going to be able to be twiddling the knobs, getting a focus.
So holographic microscopy is an interferometric technique, and what's good about it is
that it's volumetric, so you don't have to focus - it captures an entire volume in a single hologram.
Then with software techniques you can reconstruct what you see on each focal plane.
To test out some of these techniques, we've been going to so-called "analog sites" on earth,
essentially to ask the question: if we go anywhere at all on Earth - no matter how cold or how dry
and we take up a random sample and stick it in our instrument - are we going to see life there?
And are we going to be able to tell that it's life?
In Spring 2015, we went to Nuuk, Greenland, and sites around there. We looked actually in the sea ice.
When we go to these extreme environments most of the time we have no idea what we're going to see,
but what is cool is that we always see bacteria and we always see life.
We're very interested in that not just for Enceladus but also Europa
and any of these icy moons of Jupiter and Saturn.
How many bacteria do you need to see in an ocean in order to be confident that this is really an ecosystem?
That's the question we don't have an answer to, really.