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Bobby
As we finish up our current close-up investigation of bedrock and soil
at a site named Cook Islands next to Resolution Crater.
I think itís time to start a new thread or topic on the drive to come.

As the ripples keep getting smaller in size, when will we start our turn
to the east towards Endeavour Crater? What challenges do we face in
our upcoming journey? Hopefully the right front wheel wonít give us
any more issues. unsure.gif

wheel.gif wheel.gif wheel.gif
Geert
QUOTE (Bobby @ Apr 4 2009, 02:49 AM) *
As the ripples keep getting smaller in size, when will we start our turn
to the east towards Endeavour Crater?


We aren't there yet, this is only a temporary reprieve, the ripples will get nastier again in the area around Porcupine.

Presently it looks like the turn eastwards will only be made after passing Porcupine, and even then it's still a long way to go before she is on 'flat' ground, just hoping the RF wheel will keep going at least till that time.
Tesheiner
If I read correctly the info in the PCDT, Opportunity should be leaving this area today, sol 1850. That is, just in a few hours.
Perhaps moving next to Adventure?
Click to view attachment
RoverDriver
QUOTE (Tesheiner @ Apr 7 2009, 01:37 PM) *
If I read correctly the info in the PCDT, Opportunity should be leaving this area today, sol 1850. That is, just in a few hours.
Perhaps moving next to Adventure?


It seems so. Preliminary data seem to indicate a little shy of 60m. The drive target was Adventure.

Paolo
climber
New Oppy's Adventure:
Click to view attachment

Nice bumpy drive:
Click to view attachment
Ant103
The panoramic view near Adventure Crater smile.gif
JayB
I'm sure it's an artifact but blown up the streak has a pointy bright end and a diffuse® wide tail bit...

http://qt.exploratorium.edu/mars/opportuni...KZP1925L0M1.JPG

fireball on mars?

that would be just typical if the lucky girl imaged one

surely an artifact but a fun thought
Tesheiner
The right eye picture (http://qt.exploratorium.edu/mars/opportuni...KZP1925R0M1.JPG) has no streak at all, so it probably is a cosmic ray hit.

A tiny fireball in any case. smile.gif
Phil Stooke
It's a falling particle all right - a cosmic ray.

Phil
djellison
That's the joy of two 'eyes'. Any interesting feature can be corroborated with the other eye. In this case, just another CR hit - one of thousands in the mission so far.
climber
QUOTE (Ant103 @ Apr 8 2009, 02:47 PM) *
The panoramic view near Adventure Crater smile.gif

It looks like eggs in a basket. Very welcomed crater for Easter biggrin.gif


BTW, Endeavour 's hills are (barely) visible .
sci44
Er, that CR/meteor question.. Hang on guys, not so fast..

Check the time code on the L/R Navcams pics - digits 3-11 code in seconds - isn't there 76 seconds difference in the time for when the two pictures are taken?


http://qt.exploratorium.edu/mars/opportuni...KZP1925L0M1.JPG
http://qt.exploratorium.edu/mars/opportuni...KZP1925L0M1.JPG

(EDIT: - YES THESE ARE WRONG)

Meteors usually pass over in a few seconds. Also that streak is in exactly the right 10% of the picture - not just over the main terrain. As JayB says, it also has a soft tail, sharp head, all in the right direction. While some pics do have long exposures & lots of strikes, this one doesnt..

Not saying for sure, but just pointing it out.. smile.gif

Click to view attachment
mhoward
QUOTE (sci44 @ Apr 8 2009, 10:27 AM) *
Check the time code on the L/R Navcams pics - digits 3-11 code in seconds - isn't there 76 seconds difference in the time when the two pictures are taken?


Sorry, but no. What you have there are two separate left-camera images, not the L/R pair.
sci44
Sorry, wrong about the codes. Are the L/R Navcam pictures always syncronous? When a dust devil is caught by L/R Navcams, is it always in the same place?

Otherwise its a very nicely positioned C/R!
djellison
QUOTE (sci44 @ Apr 8 2009, 05:42 PM) *
Sorry, wrong about the codes. Are the L/R Navcam pictures always syncronous?


Yes. The pair are taken together. Dust Devil movies are usually taken with only one camera though - not both.
BrianL
Well, that was an amusing diversion. Now, onto the big question...

Has the rest improved the RF wheel enough that we can swap ends again and get back to those juicy 100m drives?
Nirgal
QUOTE (BrianL @ Apr 8 2009, 07:32 PM) *
Has the rest improved the RF wheel enough that we can swap ends again


I think the next several driving sessions will tell ... Reading the latest JPL update I am very optimistic about the new driving policies will make the best out of the RF wheel smile.gif

QUOTE
and get back to those juicy 100m drives?


That's not even necessary, I think: 50 (safe) meters per Sol would be just fine, if consistently sustained.

Just imagine 4 Weeks of 50 meter drives: that would take us more than 1 kilometer towards our goal biggrin.gif

wheel.gif wheel.gif wheel.gif wheel.gif
RoverDriver
QUOTE (BrianL @ Apr 8 2009, 10:32 AM) *
Well, that was an amusing diversion. Now, onto the big question...

Has the rest improved the RF wheel enough that we can swap ends again and get back to those juicy 100m drives?


We are seeing improvements. I do not know when we will get the OK to start driving forwards again. You'll see when we get the OK. There's a bunch of drivers pacing the sequencing room with their 100-200m drives (JOKING!!!).

Paolo
fredk
To add to Paolo's comments, some details from the latest Oppy update:
QUOTE
The drive went well and the right-front actuator exhibited currents near normal levels, good news.

Opportunity also benefited from a solar array cleaning event which boosted energy levels by about 40 percent, a big increase. Now if only Spirit could get such a cleaning.

40%! smile.gif
djellison
40% - wow! That's got to be up around 500Whrs!

(512 according to the Article smile.gif )
HughFromAlice
.......... and that's at a relatively high tau level of 0.95!! So it's really good.
nprev
Absolutely unreal! wheel.gif wheel.gif wheel.gif


BTW, silly C/R question: Has anyone done any comparison between the frequency of hits observed by the MERs vs. that observed on average by spacecraft in the inner Solar System but outside of the Earth's magnetosphere? Might yield some interesting data about Mars' upper atmosphere.
Tesheiner
After the latest drive, during sol 1852, Opportunity is in between Adventure and Discovery.
Actually, this is a mini and micro-craters' field.
Click to view attachment

BTW, Discovery can be seen in this south looking navcam image (top left corner): http://qt.exploratorium.edu/mars/opportuni...NGP1921L0M1.JPG
Stu
Cobbles? You want cobbles?

Click to view attachment

smile.gif
ElkGroveDan
It's unusual the way that crumpled slab seems to ride the crest of the dune. It's almost like watching ocean waves lifting floating debris.
Fran Ontanaya
Sorry if I missed a previous commentary about it. I was wondering if a left rear wheel cable strap got loose last february:

http://qt.exploratorium.edu/mars/opportuni...BSP1312R0M1.JPG
http://qt.exploratorium.edu/mars/opportuni...J5P1312R0M1.JPG
http://qt.exploratorium.edu/mars/opportuni...PYP1312R0M1.JPG



Geert
QUOTE (ElkGroveDan @ Apr 10 2009, 11:01 PM) *
It's unusual the way that crumpled slab seems to ride the crest of the dune. It's almost like watching ocean waves lifting floating debris.


Yep, but there is no sign the dunes were anyway 'disturbed' by the slabs and the craters, which is a sign that these dunes are ancient and quite stationary, they don't move about as much as some sanddunes on earth.
MahFL
40 %...awesome. Drive drive drive !!!!!!!
wheel.gif wheel.gif wheel.gif

oops...wrong way !...ha ha ha. laugh.gif
Juramike
Crop of cobble on the dune. Contrast enhanced to show reflectivity changes.
Click to view attachment

Comparing with the reflectivity changes on the sand divots (craters) in the wider view image, a crater or depression should have a darker zone in background, and a brighter zone in the foreground from Oppy's viewpoint.

Near the cobble, it is the exact opposite. There is a darker zone in the front, and a brighter zone in the back.

So from this image, it seems like there is an elevated deposit (slight bulge) near the rock, rather than a wind sculpted blowout.

-Mike
Vultur
Is Oppy going to swerve toward Porcupine? It looks like a very old crater ... have any of the craters so far been quite this old?
ElkGroveDan
QUOTE (Vultur @ Apr 10 2009, 02:55 PM) *
Is Oppy going to swerve toward Porcupine? It looks like a very old crater ... have any of the craters so far been quite this old?

Vostok and Erebus which we visited are both really old.
Stu
Some luvverly layers in these rocks...

Click to view attachment
MarkG
This area seems to be a line/zone of small secondary craters, as has been mentioned before. Is there any discussion of what the primary crater might be? If the primary crater is identified, a rough date determination would be possible.

Is anyone looking into this?

-- MarkG
centsworth_II
QUOTE (MarkG @ Apr 11 2009, 11:33 AM) *
This area seems to be a line/zone of small secondary craters...

How can you tell secondary craters from a large impact vs. small craters from a fragmented meteor? My inexpert guess is that a small, heavily pocked area indicates the later.
Shaka
As far as I can tell the freshest crater in the Victoria vicinity is Beagle. It has discernible rays, and its larger ejecta blocks could have flown this far.
Proving a connection between Beagle and any particular pile of rocks is a horse of a different color, however. This nice little Easter Basket of rocks does seem to be the result of a single, large slab smacking down and fragmenting from the shock, followed by wind erosion of the chunks. One could make a stab at estimating the length of time it took for fresh chunks to erode to this condition. That age might then be compared with an estimate for the erosion-age of Beagle, but I don't think I'll try it myself today. rolleyes.gif
Distinguishing eroded secondary craters from clustered primaries is more art than science, but the fresh craters tend to have a deeper profile in the primaries.
If you can line up craters with rays from a primary, you have at least a suggestion that they are secondaries from it. unsure.gif
Tesheiner
Here's a polar view of the navcams taken at the current site, next to Discovery, during sols 1854/55.
Click to view attachment
MarkG
QUOTE (centsworth_II @ Apr 11 2009, 09:43 AM) *
How can you tell secondary craters from a large impact vs. small craters from a fragmented meteor? My inexpert guess is that a small, heavily pocked area indicates the later.


I can try to offer a qualitative answer (I'd need lots of rust-remover to give a quantitative answer...).
The size of a crater is a function of the energy of the impinging object (diam ~ Energy**3 ?). E ~ M*V**2.
So a small object smashing in really fast makes the same size crater as a larger object coming in slower.
There is a dichotomy of approach velocities, with primary objects coming in at or above the Martian escape velocity (5km/sec), and secondary objects being much slower (~2-3 km/sec and under).
Atmospheric drag goes in proportion to the surface area of the impinging object, so smaller objects are more easily slowed down and/or evaporated that large objects. The effect of this is to produce a threshold of size below which crater-producing impacts become unlikely (for given velocity/density/strength/trajectory-angle).
With a large field of meter-ish sized craters, we would expect the group of crater-producing objects to be all within a factor of about 100 in mass (assuming nearly-equal velocities).

Now, I am not sure of the actual numbers, but the Martian atmosphere would essentially filter out smaller impactors. The question to ask here is whether primary impactors that would produce a one-or-two-meter-sized crater are below this threshold, and therefore much less likely?

A primary impactor group would need to split into a number of similar-sized fragments, and the effect of atmospheric drag would tend to scatter their V-squared energy for impact crater size even more.

A large impact producing showers of secondary debris, however, could easily produce a number of similar fragments, since the parent material and the launching shock forces in a given area of the source rock are similar. The ballistic launch of these fragments then has a decent likeleyhood of producing a group of similar-sizes fragments well above the threshold for significant atmospheric drag, but that produce fairly small craters.

(Note that a grazing-impact object might produce a group like this if it breaks up and falls just ballistically...., but that is also a chancey scenario.)

Thus, the secondary impact scenario at this scale seems more probable. Probabilities are the best we can do without samples to analyze. Field trip, anyone?

'Nuff said?

-- MarkG


HughFromAlice
Any news on the dust storms? Couldn't find anything. (PS - Mighty long field trip Mark!)
Deimos
See http://www.unmannedspaceflight.com/index.p...st&p=138671. Over the last 2 weeks the dust has continued to fall to just below 1 optical depth at each rover site, but it's been pretty slow and steady. I think there's a press release on the way, but it may have been preempted by Spirit's problems.
helvick
QUOTE (MarkG @ Apr 13 2009, 08:13 PM) *
Thus, the secondary impact scenario at this scale seems more probable. Probabilities are the best we can do without samples to analyze. Field trip, anyone?

I'm game - where do I sign up? smile.gif If there was time to poke around in some of these smaller craters it might be possible to find enough likely suspects for the impactors to make a call on this but even though I would like to see that done in theory there are far better things to spend the limited rover resources available on.

I ran some back of the envelope numbers on this a long time ago and its pretty clear that despite the fact that the Martian atmosphere is relatively thin it still represents a huge barrier to direct impacts - it's thicker at the ground than Earth's atmosphere is at the altitude where the vast majority of potential terrestrial meteorites get vapourized and by my reckoning you need a fairly large (couple of m diameter, possibly as much as 10) meteor to make it to ground level in one (much ablated) piece. The reality of meteorite impacts on earth shows that smallish fragments do land fairly often, and they do cluster but even so the probability that a given smallish impactor is primary must be small relative to the large amount of secondary debris that goes with each medium\large impact especially given that overall erosion rates are so low.
dvandorn
However, one of the datasets that is not all that well constrained that impacts on this issue (pardon the pun) is the relative flux of impactors of all sizes at Earth's orbit and at Mars' orbit. I'm not certain it's fair to assume that the flux is constant throughout the inner solar system.

I know that on our Moon, the best way to tell a primary from a secondary is to try and quantify the amount of energy released in the impact event. Without an atmosphere, lunar primary craters retain the glassy impact melt created by high-energy impacts and display a lot of regolith breccia formation, while secondaries don't show the same level of energetic materials transformation.

This kind of thing has long since been eroded away or covered up in most Martian craters, but for the micro-craters it just seems to me there has to be some kind of threshold of size-to-crater that, if primaries, would have to have been formed by really tiny, like smaller-than-sand-grain-sized, impactors... unsure.gif

-the other Doug
CosmicRocker
QUOTE (Tesheiner @ Apr 13 2009, 04:27 AM) *
... at the current site ...
What a beautiful location, perched right at the edge of this unusual crater in the drifts. Thank goodness for MMB and a timely metadata update to carry us to this special place. Thanks also to those individuals and organizations providing the raw imagery. I'm kind of getting accustomed to this armchair planetary exploration.

With atmospheric dust levels falling and the recent, significant cleaning event, I can hardly wait to see where Opportunity will next take us.
centsworth_II
QUOTE (MarkG @ Apr 13 2009, 04:13 PM) *
I can try to offer a qualitative answer (I'd need lots of rust-remover to give a quantitative answer...).

And my knowledge is purely anecdotal! laugh.gif
I don't mean to challenge your calculations, only to show how a novice observer may see things.

My stew of thoughts (just add salt):

Earth's atmosphere must provide an even better filter for meteors than Mars', and yet we see news reports of fireballs followed by pictures of people holding small fragments that have littered the ground. So I don't have a hard time imagining the same on Mars.

I get the feeling that most or all of the craters in Opportunity's area of Meridiani are very old. They have been buried and exhumed and their ejecta has been weathered to nothing, perhaps by the same steady winds that formed the now still ripples, leaving only berries behind. I don't recall what the informed opinion is on the relative ages of the craters and the ripples.

If it's true that all the nearby largish craters are older than the ripples, then the mini craters in the ripples could not be from their ejecta. I would expect ejecta from craters farther away to be more spread out and not form tight impact clusters.

Anyway that's my two,
centsworth. biggrin.gif
Poolio
QUOTE (djellison @ Apr 9 2009, 06:35 PM) *
40% - wow! That's got to be up around 500Whrs!

Does anyone know if there was an impact on the Mini-TES? Weren't they going to leave the cover open and hope for a good gust of wind?

EDIT: It's also worth noting, I think, that Oppy's last drive (1856) appears to have been accomplished driving forward.
MarkG
QUOTE (centsworth_II @ Apr 13 2009, 11:34 PM) *
...
Earth's atmosphere must provide an even better filter for meteors than Mars', and yet we see news reports of fireballs followed by pictures of people holding small fragments that have littered the ground. So I don't have a hard time imagining the same on Mars.
...


If meteors (or their fragments) get slowed down to near-subsonic after hitting the atmosphere, then they just fall like rocks. They hit the ground and maybe bounce and maybe crack or chip the surface, but they don't create an explosive crater. Oppy has already passed by and looked at some of these meteorites laying about on the Meridiani ripples (like the one near the heat shield).

(Well, remembering Oppy passing by that heat shield and meteorite seems like a long time ago... and it was!)


--MarkG
Astro0
Wind cleaning event - 40% power improvement!
I knew it got windy at Meridiani, but according to the Midnight Mars Browser I think that even this might be considered a bit excessive laugh.gif
Click to view attachment

Believe it or not, after all these years I'm just getting into MMB. What a fantastic tool.
If you've never downloaded it, give it a try. Take the time to learn how to use it for yourself as well. That's the effort that real 'armchair explorers' have to make.

Astro0
nprev
laugh.gif ...yeah, that'd be your basic hypersonic windstorm there, Astro!

Speaking of hypersonic & meteorites, what's the terminal velocity on Mars anyhow? I suspect that fragments from a high-altitude breakup could hit the ground pretty hard indeed.
helvick
I ran the numbers on this quite some time ago - Some terminal velocities on Mars.

The short answer is around 155m/sec (560km/h) for a small (2cm) rocky object. As the diameter and density increases that number will rise.

This guy ran the numbers a different way to get the Terminal velocity for a human - 261m/sec (9503km/h). This seems right to me.

Basically it's pretty fast, and rapidly gets into supersonic terrain once objects get big\dense enough which will complicate things quite a bit.
centsworth_II
QUOTE (MarkG @ Apr 14 2009, 08:53 PM) *
If meteors (or their fragments) get slowed down to near-subsonic after hitting the atmosphere, then they just fall like rocks. .....Oppy has already passed by and looked at some of these meteorites...

....remembering Oppy passing by that heat shield and meteorite seems like a long time ago...

And don't forget Bounce rock, a possible ejecta fragment from a large crater far from Opportunity's landing site. Both Heat Shield and Bounce are lying on the surface now, but I wonder if this is the same surface they landed on, or if that surface and any impact feature on it is long ago worn away.

Is there a difference between a micro crater made by a "falling like a rock" fragment from broken up meteor and a "falling like a rock" piece of ejecta?


Shaka
The first is made by a "falling star"; the second by a "falling rock".
Which would you rather have?
cool.gif
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