Nasa's Curiosity Mars rover to ingest drill sample soon
Nasa's Curiosity Mars rover has still to ingest the rock sample it picked up a week ago.
John Grotzinger, the mission's chief scientist, says he expects this to happen very shortly.
The robot, which is investigating a deep crater on the planet, drilled into what appears to be a mudstone.
Some of the grey powder produced in the process should now be sitting in the stem of the tool, and must be moved to the onboard labs for analysis.
"We have to first confirm that the powder has moved up the drill stem," Prof Grotzinger told BBC News.
"From there, it will go into something called the drill assembly, which is about as big as a hockey puck. That's where the sample gets portioned before going through a set of tubes that takes it to some sieves."
They will describe the mineralogical make-up of the mudstone and try to identify any interesting carbon chemistry that might be present.
Curiosity is seeking new insights on past environmental conditions on the Red Planet - conditions that may have supported microbial life many billions of years ago.
It is currently investigating a series of layered deposits about half a kilometre from its landing point last August on the floor of the equatorial Gale Crater.
Already it has seen numerous examples of rocks that were deposited in water or subsequently altered by it.
Water is one of the prerequisites for life as we know it on Earth.
The mudstone unit on which Curiosity is standing has been given the name Sheepbed. It is cut through with veins of what look to be calcium sulphate.
Close-up imaging of the drill hole indicates that some of the sample is likely to include this vein material.
A couple of Curiosity's survey instruments have probed the powder - the mast-held laser spectrometer, Chemcam, and the X-ray spectrometer, APXS, on the end of the robotic arm. These devices can determine some of the basic chemistry in a target rock.
Prof Grotzinger, however, is reluctant to discuss their results just yet, preferring to wait until Chemin and Sam have done their full-on analysis.
One very obvious observation to make is the colour of the powder. The grey stands in contrast to the weathered red outer-coating of the Sheepbed unit, and the darker colour hints at a different oxidation state for iron (Fe) minerals that might be inside the rock.
This is the kind of subtle detail the scientists are looking for as they build a picture of what conditions were like on early Mars and the possibility that the planet could once have harboured simple lifeforms.
"Iron is a transition metal and it can have different oxidised states," explained Prof Grotzinger.
"If you can see that different minerals have different values for whether there's Fe2+ or Fe3+, it means that there were electrons moving through the environment, and it means that there were energy gradients there potentially, [which], if there were microorganisms, they might have been able to use those energy gradients."
The Curiosity scientist was speaking here in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS).
He hopes to have some Chemin and Sam results to report next month at the Lunar and Planetary Science Conference in Texas.
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos