Mercury Flyby 1 Options

[kenny]

General observation on high resolution imagery of Mercury.

and basin-ejecta-plains (like Apollo 14's Frau Mauro site). What lava plains there are, are hard to tell from welded basin ejecta blankets (Cayley Plains @ Apollo 14).

Cayley Plains were at the Apollo 16 site, Descartes.

[edstrick]

Correct. But more interpreted-as "volcanic" plains that turned out to be anything but.

[Doc]

Observation notes

1) There appears to be lots of 'string of pearls' craters on Mercury (in the new close-up images). Some of them look curiosly like collapsed lava tubes? Does the number of such craters imply to the probablity that falling debris are often torn into 'strings' due to the proximity to the Sun.

2) The craters with bright materials can mostly be found in volcanic plains. Just like on the moon. Why? (difference in composition between volcanic plains and highlands?).

[remcook]

From Emily's blog:

So what do I see in this image? There's lots of craters, of course, but if you look closely at the craters you can see that there's a lot of differences among them. In particular, my eye is immediately drawn to the fact that the craters at the left side of the image mostly have very flat floors, but among them are a few craters that have fairly pristine bowl shapes and central peaks. When craters first form, they all have bowl shapes, or bowls with central peaks, or peak rings. Craters do not form with smooth, flat floors. So something must have happened -- some geologic activity -- to flatten the floors of all those flat craters; most likely they got filled in by some volcanic eruptions. Those volcanic eruptions had to happen before the central-peak craters, which never got filled in by lava. So already there is a geologic history to tell about this tiny area of Mercury, coming out of this one image.

As a complete layman, I wonder: if it's filled in by some lava flow from a volcano, wouldn't you see something at the edges of the crater instead of a nice uninterrupted ring? Or a volcano? These seem much smaller scales than on the moon where I assume a similar thing happed at the Mares. I wonder if it isn't just that below a thin crust the rock is rather soft or 'liquid' (over geological timescales) and that the floor just equilibriated like a lake before cooling down, whereas the ring around it is more rigid, since it is cold crustal material. Please teach me about crater formation

edit - or is what I'm talking about a 'welded basin ejecta blankets'??

[Doc]

Someone in this forum talked about apparent cinder cones in Mariner 10 images.
So far I've seen lots of craters but no cinder cones.......I don't suppose there should be one when you take in to consideration that Mercurian lava is iron-rich. Cinder cones are formed from silic lava.

[Guest_Oersted_*]

http://messenger.jhuapl.edu/gallery/scienc...827082M_web.png

To me the big crater in the lower right side, with a string of minor craters on either side, make me think that this is what Shoemaker-Levy would have looked like, if it had hit a solid surface. Am I completely off on that assumption?

[ngunn]

To me the big crater in the lower right side, with a string of minor craters on either side, make me think that this is what Shoemaker-Levy would have looked like, if it had hit a solid surface. Am I completely off on that assumption?

Sounds about right to me, except that mayby the big crater may be newer than the string. I think Im seeing varying amounts of ray material inside some string craters.

[Phil Stooke]

I'm sure ngunn is right about that - the bright crater is younger and its ejecta covers the crater chain.

This chain of craters is most probably a normal secondary crater chain rather than a disrupted object crater chain. And statistically, secondary chains are much more likely to occur. On the Moon we have thousands of secondary chains and maybe 2 or 3 possible disrupted object chains.

Phil

[MarsIsImportant]

I would like to get a much closer look at some of these crater features. Many are clearly impact origin; but others seem to be collapsed lava tubes. The bright ones with the bright material rays may be caldera. In fact, some of the collapsed lava tube features appear to originate from those bright craters that I think might be caldera.

The point I'm making is that I'm not sure. We need a closer look. And I'd like to know what the surface material is made of.

[SpaceListener]

This chain of craters is most probably a normal secondary crater chain rather than a disrupted object crater chain. And statistically, secondary chains are much more likely to occur. On the Moon we have thousands of secondary chains and maybe 2 or 3 possible disrupted object chains.

How can the chain of craters form?

1. A broken falling rocks into small debris before hitting the surface
2. Ejected a line of rocks from impacted big crater
3. A depression from a subterranean tube spreading from the main crater
4. Whatever else you name it

[ugordan]

Get these while they're hot:

MESSENGER Views Mercury’s Horizon

MESSENGER Reveals Mercury’s Geological History

The second image and a previous one have a bit of overlap, but radically different resolution:

[Juramike]

MESSENGER Reveals Mercury's Geological History

Looks like theres a collapsed area in the middle of the infilled crater in the center of the above image:



-Mike

[Phil Stooke]

"In fact, some of the collapsed lava tube features appear to originate from those bright craters that I think might be caldera."

No... this is exactly the kind of argument that was fought back and forth for decades about the Moon. Read Don Wilhelms' "To a Rocky Moon" to see how it turned out.

The bright fresh craters are impact craters. No calderas like those on Mars are to be expected here, and calderas don't look like this anyway - this is a fresh impact crater with some terracing in its walls, like Kepler. Check out Arsia Mons or Olympus Mons to see what calderas would be like. And what do we expect to see radiating away from fresh impact craters? - chains of secondaries, like those around Copernicus on the Moon.

No reliable identification of any volcanic feature has been made yet on Mercury - no flow fronts, no sinuous rille type lava valleys, no vents. There is a suspected but FAR from certain dome. Like many people I will be looking for volcanic features in these new images. But the features you identify are classic impact morphologies.

Mercury isn't Io, so we know the balance of features has to be at least 99% impact plus a few (if any) volcanic features, just like the Moon. The features you point out are actually very common on Mercury. If your features are volcanic, so is pretty much everything else. That's another line of argument that these are not volcanic.

But keep looking! The real thing might be out there.

Phil

[elakdawalla]

Looks like theres a collapsed area in the middle of the infilled crater in the center of the above image:

I don't know aout that. The linear features in that crater are most likely either lava flow fronts or tectonic ridges. If lava flow fronts, it's just an area where the lava didn't go. If tectonic ridges (which is my favored explanation, considering how many of them appear to have disregard for changing topography, across crater rims for instance), it's true that area was being onlapped by the adjacent materials being shoved up and over it, but the tectonism isn't of a style that's driven by collapse (vertical tension); it's of a style driven by lateral compressional forces. Search on wrinkle ridges. They're common across the terrestrial planets, all over the Moon, Mars, Venus, and Mercury and are even to be found in a few places on Earth (such as the Yakima folds).

--Emily

[Juramike]

Even cooler. The cute little crater cluster abruptly cuts off at the edge of the collapsed area. (Here's a zoomed image showing cutoff point indicated by yellow arrows.)

1) Big crater forms
2) infills with lava and stuff
3) Cute crater cluster forms
4) Area inside crater collapses (slumps) and obliterates cute crater cluster members over collapsed area
5) A few more craters form



-Mike