February 4, 2004
The press briefing is about to begin; notes when it's concluded.
Steve Squyres: Good morning. We've got some really nice stuff for you today. We've taken our first good look at soil in our crater, our home here at Meridiani. There's some really interesting things. Features we've never seen before. I said it was like a cool geologic fieldtrip. Welcome to our first stop. Here you see the Navcam image of the soil in front of the rover and we're zooming in to Pancam image. This caught our eye a couple of days ago. We knew, even from the Navcam images, that we're looking at soil with at least 2 components, at least. We saw a bunch offine grained soil with coarser material on top. The coarser material looked like gravel but when we looked closer, they looked darned round. The nice thing about distinctive characteristics is that every characteristic, a shape, a color, a texture, has a story to tell about how it formed. Only so many ways to make something round. Sort of round could be from tumbling. If they're really round, that narrows down the range of possibilities. Blobs of molten lava thrown in the air, an object accretes layers, ways you can do it. We were very interested to see just how round these stones in Pancam image were. So we stuck out our arm and took a look. We have this robotic arm with a number of instruments, one of which is a Microscopic Imager. MI on the end of the arm. See Hazcam images of arm going through motion of taking image of soil.
Ken Herkenhoff: You've seen pictures from all of Spirit's 10 cameras. Opportunity so far, just 9. Here's the 10th, the Microscopic Imager. Designed to emulate a geologist's 10x handlense. This graphic starts with Pancam view. Zooming in to MI frame. Full field of view is about 3cm across, a little more than an inch. Smallest particles we can resolve are about 1/10th mm across. The larger one is about 3 mm across. MI dust cover has an orange tinted window that can give us crude color information. This is an example of a merge of those two color frames. Zooming in on some particles. Sand grains about 1/10th mm. Various shapes and sizes from 1mm up to a few mm across. The entire image is in full shadow so no sunlight. There's a variety of shapes from spherical to angular. Next image will show an enhanced color version that emphasizes variation in color across these grains. Just right of upper center there's a rather red grain . Those are relatively rare here. Most gains are less red. The variety of particles and shapes here indicates a variety of sources. There are some holes probably from gas bubbles either by volcanic or impact processes that Steve mentioned.
Hap McSween: All of these features are interesting but the really intriguing ones are the round ones. There are a number of geologic process that can yield really round objects. First Pancam suggested little balls, little spheres. MI shows very few are actually spherical, many are flatter or broken and could be derived from the round ones. One process we considered is that grains on a seafloor or in moving water roll around and accrete or grow by adding layers of material. These are called oolites. And we got excited about the possibility that we might have found oolites. The problem is that very few of these objects are spherical balls, they have other shapes, and so they're unlikely to be oolites. Also oolites shouldn't have bubbles, holes we see. Other possibilities is that large meteors when they impact the planet melt some of the target materials and this rock is sprayed out as a fine jet of droplets of liquid, and as they fly through the air they make shapes like dumbbells, teardrops, sometimes buttons. I think I've seen all of those shapes looking at these MI images. They cool quickly into a glass but if a target rock had water, that could cause the gas bubble holes that we see. Volcanoes spew out liquid droplets. But more likely, with violent eruptions have ashes that are buoyed by hot gasses and as they are suspended they begin to coagulate together into rounded pellets we call lapilli. I think it's possible that these things may be lapilli. Also intriguing that many of these things may relate to the outcrop. If this is an ashbed we might be able to find some connections between that, maybe it's weathering and shedding the things that Ken has given us.