Mercury's craters, size, MESSENGER, Vulcan (APOD 21 Jan 08)

Axel · Post by **Axel** » Mon Jan 21, 2008 6:04 am

"Visible on the hot and barren planet are many craters, many appeared to be less shallow than similarly sized craters on the Moon. The comparatively high gravity of Mercury helps flatten tall structures like high crater walls." I don't understand. If the crater walls are flattened, would't that make Mercury's craters shallower than those on the Moon, not less so?

Bubblecar · Post by **Bubblecar** » Mon Jan 21, 2008 8:44 am

Yes, I think they meant to write "more shallow" not "less shallow".

zorro · Post by **zorro** » Mon Jan 21, 2008 1:12 pm

"Visible on the hot and barren planet are many craters, many appeared to be less shallow than similarly sized craters on the Moon. The comparatively high gravity of Mercury helps flatten tall structures like high crater walls."

Wouldn't this make more sense if it said "shallower"?

RJN · Post by **RJN** » Mon Jan 21, 2008 1:59 pm

Yep. Oops. Sorry. Fixed it. - RJN

orin stepanek · Post by **orin stepanek** » Mon Jan 21, 2008 2:02 pm

link http://apod.nasa.gov/apod/ap080121.html
this post is almost the same as zorro's
Orin

neufer · Post by **neufer** » Mon Jan 21, 2008 2:55 pm

Back in the 19th century Le Verrier forecast the existence of the planet Neptune based upon anomalies in the orbit of Uranus.

Le Verrier also forecast the existence of "the planet Vulcan" based upon anomalies in the orbit of Mercury.

These Mercury anomalies were later explained by Einstein's Theory of General Relativity but not before some interesting "sightings of the planet Vulcan"

http://en.wikipedia.org/wiki/Vulcan_(hy ... al_planet)
.
Between 1866 and 1878 no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of 29 July 1878,

http://sunearth.gsfc.nasa.gov/eclipse/S ... Am1851.gif

two experienced astronomers, Professor James Craig Watson, director of the Ann Arbor Observatory in Michigan, and Lewis Swift, an amateur from Rochester, New York, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun, and estimated its magnitude at 4.5. Swift, who was observing the eclipse from a location near Denver, Colorado, saw what he took to be an intra-Mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about 6 or 7 minutes from the "planet". Theta Cancri and the planet were very nearly in line with the centre of the Sun.

Watson and Swift were excellent observers. Watson had already discovered more than twenty asteroids, while Swift had several comets named after him. Both described the colour of their hypothetical intra-Mercurial planet as "red". Watson reported that it had a definite disk – unlike stars, which appear in telescopes as mere points of light – and that its phase indicated that it was approaching superior conjunction.

This sounds like a comet to me such as SOHO observes:

http://antwrp.gsfc.nasa.gov/apod/ap030130.html
http://antwrp.gsfc.nasa.gov/apod/ap071029.html

What do you think?

neufer · Post by **neufer** » Mon Jan 21, 2008 5:04 pm

(U)rbain (L)e (V)errier
Joh{N} {C}ouch {A}dams

(VUL) : {CAN} ?

But Johann Gottfried Galle (June 9, 1812 – July 10, 1910)
http://en.wikipedia.org/wiki/Johann_Gottfried_Galle

outlived both of them and had the last laugh:
http://antwrp.gsfc.nasa.gov/apod/ap990315.html

415monkey · Post by **415monkey** » Mon Jan 21, 2008 6:03 pm

Is there anyone who can give us a scale of the land we're looking at here? Like, that crater in the bottom right is the size of Texas or something?

auroradude · Post by **auroradude** » Mon Jan 21, 2008 7:04 pm

Hi Monkey,
Based on the descrition found here:

http://messenger.jhuapl.edu/gallery/sci ... age_id=122

The large crater at right is about 200km or 120 miles wide - more like the size of a Texan's hat.

415monkey · Post by **415monkey** » Mon Jan 21, 2008 7:58 pm

oh excellent, thanks!

iamlucky13 · Post by **iamlucky13** » Mon Jan 21, 2008 10:44 pm

This might also help give you a perspective on size by comparing the size of the crater to the curvature of the horizon in the picture.

From the left to right: Mercury, Venus, Earth, Mars.

I'm not sure what the funny looking stripe on Mercury is, but I'm guessing it's something from the image editing, not a real feature on Mercury.

Dr. Skeptic · Post by **Dr. Skeptic** » Mon Jan 21, 2008 11:22 pm

The "funny stripe" is colored "missing data", the composite photo is from the Mariner 10 mission (1974 and 1975)

Even though Mercury (4,900 km) has a smaller diameter than Mars (6,800 km) its mass is slightly larger.

If you weighed 50 kg on Earth you would weigh 18.9 on Mercury and only 18.8 on Mars

Phil G · Post by **Phil G** » Tue Jan 22, 2008 2:25 pm

I notice that many of the craters have smooth centers and others have a "mount" in the center. Any guesses why the difference? One, center left, looks like it has a steep-sided depression, almost conical, which makes me think it can't be from a subsequent impact. Interesting, to say the least.
Peace, Phil

BMAONE23 · Post by **BMAONE23** » Tue Jan 22, 2008 3:00 pm

Looking at the picture posted above, Mercury appears to be about the size of Earth's Core.

BMAONE23 · Post by **BMAONE23** » Tue Jan 22, 2008 3:04 pm

The one on the left 8pm position does look like it had a secondary impact creating a bullseye crater

auroradude · Post by **auroradude** » Tue Jan 22, 2008 5:43 pm

"I notice that many of the craters have smooth centers and others have a "mount" in the center. Any guesses why the difference? " - Phil G

It appears that most of the craters with central peaks are relatively the same size and smaller than the largest craters. They also seem to be younger than the larger craters as evidenced by their overlying. This would imply a differentation of the size of impactors over the history of the cratering as well as suggesting the larger craters happened at a time when the surface was more liquid and filled in destroying any mounts on the larger impact basins.

There also could be a lower limit to what size of an impactor can form a central peak as smaller craters are lacking one as well. Perhaps there's a little "Goldilocks and the Three Bears" at work here... "This ones too hard. This one's too soft. This one's just right."

iamlucky13 · Post by **iamlucky13** » Tue Jan 22, 2008 7:31 pm

Dr. Skeptic wrote:The "funny stripe" is colored "missing data", the composite photo is from the Mariner 10 mission (1974 and 1975)

I figured that's probably what it was, but I would've expected it to be the other way around...a thin stripe of data acquired rather than a thin stripe missed.

I just noticed, the Venus image is without any atmosphere. In real life you couldn't see those details because of the cloud cover.

BMAONE23 · Post by **BMAONE23** » Tue Jan 22, 2008 8:17 pm

Well,
It looks like all we would need to do is to smack Mars into Venus to complete earth sizing it, wrap the residual debris around Mercury, and relocate Mercury into orbit around Venus to get a new Earth Moon system

Nereid · Post by **Nereid** » Fri Jan 25, 2008 3:03 pm

Several separate threads on the 21 January, 2008 APOD ("Mercury's Horizon from MESSENGER") merged into one.

zbvhs · Post by **zbvhs** » Sat Jan 26, 2008 5:02 pm

A narrow habitable zone should exist in Mercury's terminator region. Just where it would be would depend on cooling rates and heat retention in the Mercurian terrain (Merrain?). Moderate temps would ease stress on equipment and permit longer stay times for future explorers. Explorers would have to keep moving, of course, because the planet does rotate. Even though closer to the Sun, Mercury would be a much easier place to explore than Venus. After Mars, we should go there.

neufer · Post by **neufer** » Sat Jan 26, 2008 5:31 pm

zbvhs wrote:A narrow habitable zone should exist in Mercury's terminator region. Just where it would be would depend on cooling rates and heat retention in the Mercurian terrain (Merrain?). Moderate temps would ease stress on equipment and permit longer stay times for future explorers. Explorers would have to keep moving, of course, because the planet does rotate. Even though closer to the Sun, Mercury would be a much easier place to explore than Venus. After Mars, we should go there.

Why move? One can enjoy water, solar power & shade:

http://en.wikipedia.org/wiki/Chao_Meng-Fu_(crater)
<<Chao Meng-Fu is a 167 kilometer-diameter crater on Mercury named after the Chinese painter and calligrapher Zhao Mengfu (1254 - 1322). Due to its location near Mercury's south pole (132.4° west, 87.3° south) and the planet's small axial tilt, an estimated 40% of the crater lies in permanent shadow. This combined with bright radar echoes from the location of the crater leads scientists to suspect that it may shelter large quantities of ice protected against sublimation into the near-vacuum by the constant -171°C temperatures.>>

zbvhs · Post by **zbvhs** » Thu Jan 31, 2008 5:31 pm

Why move? If the objective is to explore the planet, that can't be done by hiding in a hole at the planet's south pole.

NoelC · Post by **NoelC** » Fri Feb 01, 2008 1:53 am

Yes, but it would be rather handy to be able to build a permanent home base. One with water available would be doubly good. Send out "Mercury rover" missions to explore the surface. And just think how well solar power would work if you hoisted solar cells up into the light...

Might be a bit of a warm ride in the ship to get there though...

-Noel

Starship Asterisk*

Mercury's craters, size, MESSENGER, Vulcan (APOD 21 Jan 08)

Mercury's craters, size, MESSENGER, Vulcan (APOD 21 Jan 08)

Mercury's Horizon from MESSENGER(APOD 21 Jan 2008)

Observations of "the planet Vulcan"

(U)rbain (L)e (V)errier's (VUL)can

The size of Mercury

Craters on Mercury 21 Jan 08

Chao Meng-Fu