May 23, 2007, HiRISE release Options

[nprev]

Wait a minute, ustrax...are you sure that's not actually their home?

[Gray]

Marswiggle,

The image of Dena that you posted has much better resolution and lighting than the image published in the Cushing, et al. paper (http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1371.pdf).

Are we actually seeing the bottom of the pit in that one?

[marswiggle]

While I don't know, let them answer, in that very report:

However, a fortunate
MOC observation of Dena at ~2 p.m. (R0800159)
actually does show an illuminated floor, allowing us to
tightly constrain the depth using a 1-D photoclinometry
routine. This routine returns a depth of ~130 m for
the illuminated floor, while the minimum depth estimated
from the THEMIS observation is only ~80 m.
Because THEMIS IR observes at 100-m resolution,
cavern skylights with diameters much smaller
than that are probably not thermally distinguishable
from regular temperature variations on the surface

(The last paragraph also explains why the possible new skylight in S0901483 has not been observed with THEMIS, it evidently and perceivably being less than 100 m in diameter.)

[Gray]

Thanks.
I should do more than look at the pictures.

[tty]

130 meters deep, that is really something for a lava tube. I've tried to find out what the maximum diameter of lava tubes on Earth is and the largest figures I have found is about 40 meters. However I remember seeing a considerably larger collapsed tube on Iceland so very likely it is the high gravity that limits the diameter.
When it comes to lengths, tubes here on Earth can extend many kilometers. Interestingly the longest seem to be on Hawaii (sensu stricto) which of course is the largest shield volcano complex on Earth, so on Mars' vastly larger shield volcanos tubes might very well be hundreds of kilometers long!

A tube 200 km long and 200 meter in diameter, how about that for an underground habitat?

[Stu]

What's causing that lighter area to the top of the hole?



Is wind coming up out of the hole? If so, that could suggest caverns linked by a tunnel network around here, maybe?

Does anyone else think the ground in this lighter area looks more rippled (duned?) than the other terrain?

[dvandorn]

Actually, Stu, I think the lightened area looks roughly the same in terms of the extent of duning as the rest of the surrounding terrain. It looks more to me like the lightened area has seen more deposition than the surrounding terrain -- the underlying lava-flow surface is more muted and softened in the lightened area.

I think what's happening here is that the prevailing winds are coming from the bottom of the image. As they pass over the hole, the air sinks a bit, and winds strike the rim of the hole along the top arc (all directions -- top, bottom, etc. -- relate to the orientation of your posted image). So the top arc of the rim is being eroded a little more rapidly than the rest of the rim, and the erosion product (basaltic dust, most likely) has been deposited on the ground beyond the top rim arc.

It's also at least somewhat possible that winds are entering the hole, swirling around, eroding the interior of the lava tube, and blowing dust out from the cavern and onto the ground above the top rim arc. I just don't think that Martian winds are powerful enough to reach into such a deep hole and scoop dust out of it, but I could be wrong. At any rate, it's impossible to model airflow into and out of that hole without having a decent idea of the size and shape of the empty lava tube, and we really have no way of determining that...

-the other Doug

[Stu]

Actually, Stu, I think the lightened area looks roughly the same in terms of the extent of duning as the rest of the surrounding terrain. It looks more to me like the lightened area has seen more deposition than the surrounding terrain -- the underlying lava-flow surface is more muted and softened in the lightened area.

Ok, just me then!

I did think first about airflow over the crater being responsible for the change in brightness, but I can't help wondering if there are other - smaller, so as yet unseen - holes in this area and they're all linked together... would that allow winds to be generated within a tunnel network leading to a higher-than-usual speed for winds coming up out of a hole like this? Please, no-one cuff me around the ear for asking that if it's impossible or stoopid, I'm just thinking aloud...

And talking about smaller holes... anyone taken a closer look at these dark spots?



No sign of lighter "streaks" above them, so maybe I'm just seeing holes that ain't there... or maybe they are holes that just aren't big enough to generate much airflow...

As I said, just thinking aloud...

[djellison]

I doubt it's wind through the lava tube itself. Think of a crater - that can have a dust tail of some sort and there's no network to do that. I imagine it's just a function of prevailing wind and topography. Wind blowing over a lage flat area suddently finding a big hole is going to get chucked up a bit - you might even find that the area under the hole is at a slight negative pressure relative to the surrounding area because of it.

Another thought - given that this tube is beginning to collapse at this one obvious site and potentially many others, it's quite likely that the tube itself isn't much of a tube anymore and more like a range of adjacant chambers. Who knows...I can't imagine we will for a few decades.

Doug

[Stu]

... it's quite likely that the tube itself isn't much of a tube anymore and more like a range of adjacant chambers. Who knows...I can't imagine we will for a few decades.

True... but fun to imagine...

HOLE TRUTH

Look at that beckoning circle of black.
Darker than a dying shark’s eye,
a hole cut out of Mars’ ancient hide
revealing – nothing. Nothing At All.
No light falls on the far-below floor;
this is not a doorway but a pit
and deep inside it secrets lie in wait.
No world beneath is glimpsed
through this perfectly-punched puncture
in the planet’s brittle crust; just
more black, more emptiness,
a lack of everything is all we see
beneath this round-rimmed void.

It’s as if one of Sax’s laser beams
screamed from the salmon sky
and bored into Barsoom right here,
cauterising the wounded, light-seared
land… but more likely a giant’s hand of a meteor
smashed through the stone to the underworld
below, where no sol-light has ever shone
and millennia of darkness have passed
in cold, silt-softened silence.
Once lava, scarlet as Sauron’s eye ran
under here in smoking smears; for years
red and orange rocky vomit belched
through countless corridors of heat-and light-
baked stone yet this one alone has been revealed,
its shielding ceiling stabbed through by
who knows what. All we know is that all
are cold now, weaving and meandering
beneath these badlands like dust-clogged
arteries running through a mummy’s corpse.

If I stood shaking on its crumbling ledge,
daring to gaze o’er the edge of this abyss,
what blissful wonders would I see?
With my torch beam slicing through the gloom
would I swoon at the sight of stalactites
jabbing down like serpents teeth
from the ground beneath my feet?
Or on the shadowed floor far far below
would my sweeping light ray show
a carpet of pastel-paint hued life?
Enough streaks and plumes of green and blue
to make some cry “I KNEW it!”
Or would a Balrog’s fetid breath blow
over me before I felt its flaming whip
grip my ankle and drag me to my doom..?

© Stuart Atkinson 2007

[nprev]

Chilling yet fascinating, Stu...really captures the ominous feel/excitement of what it might be like to stand near the edge of one of these things...well done!

[tty]

And talking about smaller holes... anyone taken a closer look at these dark spots?

I think the two elongated black spots with white rims in the 11 o'clock position from the big hole look like better candidates.

[J.J.]

That. Is. Incredible.

Interesting, how this one image has completely usurped the others in the press release. It's interesting to speculate on what's it's like inside...I wonder if the floor has a thick coating of dust from (perhaps) eons of storms. Any way you slice it's, it's a beautiful image.

P.S.--Groovy poem.

[tuvas]

It's interesting, not since the Victoria crater picture has a HiRISE picture gathered so much interest as this one. And that's the only one that I know of that has surpassed the interest in this picture of any one image we have taken. Kind of funny how that works out sometimes.

[Guest_Oersted_*]

Thinking about the possible pattern of illumination in the cavern made me think again of that wonderful Pantheon photo.

Good one thinking of my photo, I didn't even do that, but yes, there are definitely similarities in the spatial lay-out!

The patch of sunlight in this case might be falling on a horizontal floor, but more likely somewhere part way up one sloping side of the tunnel, thus preferentially illuminating the opposite side with scattered light. I have a sketch of the geometry which could produce the apparent slight grading in interior illumination that may be showing on that image, but unfortunately no easy way of posting it here.

Something like this?



My "Pantheon - Earth and Moon-page":
http://www.dalsgaard.eu/Pantheon/