Today's press conference described how 'Spirit' has reached the looming 'Columbia Hills'
and will start analyzing the entirely different rock types early next week. It was a two mile
drive that took several months, and now it's here.

In describing what Squyres said was the most significant science finding of Spirit's
expedition so far, he showed how water percolating upwards from underground
and then evaporating at the surface, left rich salt deposits -- Epsom salts, in fact --
just under the surface.

There was a lake there, once, Squyres believes, but it was buried under hundreds of feet
of volcanic dust and other debris dumped there from meteor impacts. Any lake deposits
are far too deep -- and there aren't any handy holes in the ground (craters) to reach
them -- at Spirit's site ('Gusev Crater').

On the other side of the planet ('Meridiani Plains'), the Opportunity rover is perched at the
lip of exactly the sort of hole into the past that geologists were hoping for -- the
stadium-sized 'Endurance Crater'. They are going partially into the crater now, to
reach and study some rock layers that were deposited long before the thin layer
they found in the crater they originally landed in ("That was the last page of Mars
history -- the waters dried up and blew away -- and we want to read earlier pages", Squyres
said.

It's possible the rover won't be able to get out ("If you're going somewhere to read books,
there are worse places to get trapped than in a library," a program manager joked), but the
engineers have tested their gear on simulators that match the traction of the crater side slopes.
Unlike the loose sand that gave so much trouble at Eagle crater where they landed, the
surface material here is rock slabs and 'blueberry' marble-like spheres -- but the rover
wheels grip very well on such a surface, up to and above a 25 degree slope (they simulated
a 30 degree slope and were barely able to still make headway). Their photographs indicate
the slope at Karatepe outcrop to be below 20 degrees.

They will go straight down the slope, inspect the rock layers, and then back right back out again.
They will not go all the way down to the bottom -- at least, not intentionally.

One of Opportunity's instruments, the 'mini thermal emission spectrometer' that tells
the mineral composition of things in its view from their colors, is expected to fail at any
time because its heater has to be turned off overnight and it's about to get as cold as
ground test equipment broke down at (-160 F). The 'deep sleep' power down is
required because a stuck-on heater on the rover is sucking too much juice out of
the batteries -- about a third of the total battery charge every day. Bummer, but not
tragic, since other instruments can get similar data when they are placed up against
rock samples.

And as Leonard David writes in space.com today, the engineers are now planning
the best way to park the rovers, once winter sets in and there isn't enough sunlight
to give adequate power for daily operations, so they can get maximum sunlight and
best radio line-of-sight to relay satellites during those coldest, darkest months, so that
come springtime, they can resume their operations next year. And the year after that,
and after that.... wow!

jimO
www.jamesoberg.com