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July 2005
July 29, 2005
It's been a good week on both planets.
A lot of the action was here on Earth this week. The science team for this
mission has been together for about a decade, and during the first eight
months after we landed we were all living and working together in
Pasadena. So we know one another pretty well.
Since last September, though, we've all gone back to our
home institutions, and we do flight operations remotely. While we
talk to one another by phone and videoconference daily -- often for
many hours a day -- we hardly ever see one another face to face any
more.
It all works fine for flight operations, but there's no substitute for
being in the same room together when it's time to really sit down
and argue about the science. So this week the whole team gathered
here in Ithaca for what amounted to a three-day MER science fest.
I try to do a pretty good job of staying on top of all our
discoveries, but still, it was pretty eye-opening to sit in a
room and listen for eight hours a day to new analyses of all our
results. We're really getting some serious science done these
days, with a large set of papers about Meridiani just accepted
for publication by Earth and Planetary Science Letters, and another batch of
papers about Gusev being prepared for the Journal of Geophsyical
Research. There aren't any
really big discoveries in these papers that you haven't heard
about already... we're just adding the richness of detail that a
careful examination of the data over many months allows for.
On top of the science,
it was also just really good to see everybody again. The team got very
close during all those months of living on Mars time. Things change...
one of our team members passed away a few months ago, and several babies
have been born. In fact, there were two little ones less than
a year old
at the meeting. So life goes on.
We've gotten to be a bit like a big, sprawling family, I guess.
One of the most impressive things to me about the whole meeting was
how effective our remote operations procedures have become. We'd stop
the science talks for a couple of hours each day to do tactical
planning meetings for each rover, with people spread all over
the place. As just as one example, at Tuesday
morning's Opportunity SOWG meeting, there were eighty scientists
in a hotel conference room in Ithaca, all making suggestions
for what to do. The Payload Uplink Leads,
who are the people who write commands for the instruments, were on
campus at Cornell and at Arizona State near Phoenix. The guy
at the controls of the computer screen we were all watching
was in Boulder, Colorado, the engineers were all at JPL, and
the leader of the whole meeting was in Flagstaff, Arizona. It
all worked, and we got a good command load put together in time
for the uplink.
So that was Earth. On Mars, Spirit spent the week working over
the fantastic outcrop called Voltaire that we found last week.
You only have to look at the pictures to see that the Voltaire
region is one of the most interesting places we've found on
Husband Hill. There's an incredible amount of variety here,
including some things we've never seen before. Voltaire itself
is a new rock type for us, composed of very large, often angular
grains embedded in a fine-grained matrix. We're just
starting to get a handle on what it's made of, with some key
APXS and Moessbauer data coming down this weekend. The first
first spot on it that we looked at was named Descartes, and
the second one, which we're on now, we named
Bourgeoisie. We're probably going to finish
up Bourgeoisie over the weekend, then bump to the right
a little for some Microscopic Imager work on another rock,
and then -- probably -- do one more full APXS/Moessbauer/MI
workup on one more rock that both Mini-TES and Pancam are
telling us may be something else we've never seen before.
This is turning out to be a surprisingly target-rich
environment, and we've got to work it for all its worth
before we move on.
After that, we head toward the summit. The strong feeling
on the team is that we should try to go for what we've
been calling "Summit 2", which is both closer to us and a little
bit higher than Summit 1. If we get to the actual summit
we'll probably want to take a fairly substantial panorama
there. But the thing we're all most eager for is the
view that we'll get off the south side of the summit,
down onto lower flanks of Husband Hill that we've never
seen before. We're not really convinced that we'll get a
good view of this stuff from the true summit, so if we
do make it to the top, we may not linger there
all that long. It's been an interesting time working on Spirit these
days, as we try to find the right balance between our eagerness to get
moving up the hill and our excitement over all the new
stuff we're finding at Voltaire.
And then there's Meridiani, where Opportunity continues to
work her way southward. Many people at the meeting were
commenting on how ironic it is that the rovers seem to have
switched roles over the past six months. For much of the
early part of the mission, Opportunity grabbed all the
headlines while Spirit struggled gamely across the lava
blocks of the Gusev plains. Today it's the other way around,
with Spirit making discovery after discovery on Husband
Hill and Opportunity struggling gamely across the
sand and the blueberries of Meridiani. The big news,
though, is that we're really starting to see serious
amounts of bedrock with Opportunity now. The farther
south we've gotten the more common these little outcrops
have become, and
as we look southward we see more of them still. For a long time,
we were worried that the bright, mottled stuff that we
see from orbit in the etched terrain might just be
dust. If that were the case, our chances of ever
getting to Victoria Crater might be pretty close to zero.
With all this rock we're seeing, though, it has greatly
buoyed our hopes that we'll find firmer ground, better
driving, and more science as we work our way into the
mottled stuff. It's a good feeling.
So that's the latest.
I should probably mention that it'll be more difficult than
usual for me to do these updates for the next five weeks or
so. I've written a book about MER that comes out next week, and
one unavoidable consequence of authorship these days is the
"book tour" -- a string of appearances hither, thither and yon
to tell the world about
the book. So for a little while I'll
mostly be bopping around the US, Australia and the UK,
popping up here and there and trying to follow what the rovers
are doing from a distance. I'll do the best I can with updates
during that time, and
I should be back to doing daily flight
ops again starting the second week of September.
July 21, 2005
Spirit has had a pretty remarkable week. Back when we were climbing the
lower reaches of Husband Hill, getting anywhere
was a real struggle. The terrain wasn't
all that steep, but the soil
was very loose and slippery. Five meters of
forward progress was a good day, and some days it was less than that
as we slipped and slid and clawed our way up the slope.
Fast forward eight or nine months... we had a drive this week in which we covered five
meters vertically. That's five meters of elevation gain, over a
drive that totaled something like 30 meters horizontally. It's
amazing to me how solid the ground has gotten as we've begun to
approach the summit of the hill. The terrain is pretty steep here,
and I thought this could be one of the hardest parts of the climb.
Instead, Spirit has been scampering up it.
Covering all that ground, of course, offers the chance to find new
things, and if you've looked at the most recent images you've seen
that we've happend upon yet another nice outcrop... a pretty
big one this time. So we're going to stop and work it over a
little bit
before we move on.
As always, we've been having fun lately naming things. In our big
Independence Day panorama, all the rocks were named after
different kinds of fireworks. Since then, starting around
July 14th, we've been using mostly French names, in honor of
Bastille Day. So the outcrop we've just arrived at has been
named Voltaire. After we're done with Voltaire,
we'll resume the push to the summit. The plan is to
name the rocks we begin to see next after famous mountaineers.
Meanwhile, over at Meridiani, you look at the lastest
pictures and they're enough to make you think we're ready
to shout "Land Ho!".
We're covering a solid 30 meters a sol with our new
drive techniques now, and as we look around us we're starting
to see more and more little tiny outcrops of rock. The
big expanses of rock we're hoping for aren't in view yet,
but still... we feel like sailors who have been at sea for
months, starting now to see driftwood and bits of seaweed
that are telling us that solid ground may not be far
over the horizon.
Oh yeah, and we've just had another one of our lovely "cleaning
events", with gusts of wind sweeping dust off of Opportunity's
solar arrays. So both rovers are now in very solid shape
power-wise. It was a good week on Mars.
July 15, 2005
I'm really sorry it's been so long since I've done an update! I try to
do them at least weekly, but occasionally the workload just gets to be
a little too much.
We're making some real progress at Meridiani. Our little jog to the north
revealed a good southward route on the eastern side of Purgatory Dune, so
that's what we went for. Since then we've been making steady southward
progress, and as of now we're almost 90 meters south of Purgatory.
Driving in this stuff is an interesting challenge. We are literally in a maze.
The easiest going is to stay within the troughs between the ripple
crests, which run roughly north-south. So the best way to make
southward progress is to follow a trough until it peters out, make
a "lane change" to a nearby trough, and continue onward.
But then there's the issue of the "Erebus Highway". This is a stretch
of light-toned terrain that we've seen from orbit, and that we're
guessing may have some exposed bedrock in it that'll make for easier
going. We also like the idea of getting to bedrock from a science
perspective... it's been a long time since we've looked
at any rock with Opportunity.
But there's a catch. The entrance to the Erebus Highway is not
straight south of us, along the troughs... it's a bit off to
the east, on a heading closer to 160 degrees or so. That means
that in order to get to it, we'd have to head off cross-country,
going up and over quite a few ripple crests. That's
do-able, but it's also a lot slower than just bombing straight
south down a
nice trough.
So: If we do head for the highway, we make slow progress for
awhile, but
maybe we get to a better route
to Erebus Crater. If we head down
the troughs instead, they take us at a pretty decent speed directly
to... Erebus Crater. So it should work either way.
We're planning the weekend drive as I
type this, and after a bit of discussion we've decided to stay
for now in this nice wide trough that we've found, and try to
get as much southward distance within it as we can. Whether or not
we're actually going to "hit the Highway" is an open question
at this point, but Erebus isn't too far off either way you cut it.
And have you noticed how the terrain seems to be changing as
we get south of Purgatory? Fewer tall dunes, more pebbles in
the troughs, even what might be tiny outcrops of bedrock?
I don't want to jump to conclusions, but the driving definitely
looks a little nicer here than it did a hundred meters
back.
Over at Gusev, Spirit has had a great couple of weeks. During
our ascent of Husband Hill we stumbled fortuitously across a
very cool outcrop of layered bedrock that we named Independence
Rock. We've thoroughly worked it over with all of the arm
instruments now, and it's very strange stuff... one of the
oddest things that we've seen at Gusev. It's not like Peace
and Alligator, and it's not like Methuselah either.
I'm not ready to go into much detail here
about the chemistry and mineralogy yet, since we're
still chugging through the data. But it's clearly highly
altered, and it's got an unusually low iron content, which
isn't something we've seen much of before.
The low iron is interesting and very cool, but it also slows us
down a bit. Our Moessbauer spectrometer tells us what
iron-bearing minerals are in a rock, and the more iron there
is, the stronger the Moessbauer signal. So when the iron
content is low, like it is in Independence,
the Moessbauer signal from the rock is weak.
And when the signal is weak, we have to take a longer
measurement to be able to get the information we want from
the rock.
The other thing that's making Moessbauer measurements tough these
days is that the radiation sources in the instruments are getting
pretty weak. Each Moessbauer instrument has a tiny nugget of
radioactive cobalt-57 in it that we use to irradiate the target
with gamma rays. The half life of cobalt-57 is 271 days... in
other words, every time 271 days goes by, the strength of the
source is cut in half. Back when we thought the mission was
going to be 90 days long, this wasn't a big deal. But we have
now been on Mars two entire cobalt-57 half lives, which means that our
Moessbauer radiation sources are now only one-quarter the strength
that they were when we landed. Combine that fact with the low
iron content in Independence and we had to do a
Moessbauer measurement on it that was four sols long.
We're done with Independence now, and we've resumed the climb. The
ground is real solid here, and the climbing is good. I still don't
know if we'll reach the summit or not, but the recent progress has
been excellent. The coming week may reveal a lot.
