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Posted: **Sat Oct 08, 2011 4:10 am**

MESSENGER's First Day

Explanation: One solar day on a planet is the length of time from noon to noon. A solar day lasts 24 hours on planet Earth. On Mercury a solar day is about 176 Earth days long. And during its first Mercury solar day in orbit the MESSENGER spacecraft has imaged nearly the entire surface of the innermost planet to generate a global monochrome map at 250 meters per pixel resolution and a 1 kilometer per pixel resolution color map. Examples of the maps, mosaics constructed from thousands of images made under uniform lighting conditions, are shown (monochrome at left), both centered along the planet's 75 degrees East longitude meridian. The MESSENGER spacecraft's second Mercury solar day will likely include more high resolution targeted observations of the planet's surface features. (Editor's note: Due to Mercury's 3:2 spin-orbit resonance, a Mercury solar day is 2 Mercury years long.)

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Posted: **Sat Oct 08, 2011 10:26 am**

I find it interesting how some details are more apparent in the monochrome, while others are more obvious in the colour image. A good view of the first rock from the sun. Still trying to get my head round the idea that a day can be longer than a year . . really twists your melon!

. . . hey!, it has been over six hours since today's picture was put up online and it seems no-one has got anything to say! This is an astronomy picture. Where are all the comments?

Posted: **Sat Oct 08, 2011 11:06 am**

I couldn't spot any "faces" on Mercury's surface. There must be something wrong with this picture

Posted: **Sat Oct 08, 2011 11:37 am**

Here's my comment. How come the image on the right has already be redacted? An upside down "L" around a couple of craters?

Posted: **Sat Oct 08, 2011 12:07 pm**

On Mercury is everyday your birthday?

or is every other year your birthyear?

Posted: **Sat Oct 08, 2011 12:40 pm**

So Mercury isn't quite tidal locked!

Posted: **Sat Oct 08, 2011 1:12 pm**

It's a beauty, in both monochrome and color.

We have the coolest solar system!

Posted: **Sat Oct 08, 2011 1:19 pm**

Very nice work NASA.

Posted: **Sat Oct 08, 2011 1:55 pm**

did anyone notice this black rectangular shaped object on the monochrome map? it seems to be on the surface as a shadow could be seen too. Anyone has any idea what is that?

Posted: **Sat Oct 08, 2011 2:21 pm**

I have a question about the length of the Mercury Solar Day. I homeschool my children and we have been studying Mercury for the last 4 weeks. Every book we checked out from the library and even our astronomy textbook taught us that a day on Mercury was 59 earth days and a year was 88 earth days. Yet, this article and its references all say 176 earth days. Have astronomers changed the number in recent years? The books we checked out and our Astronomy text were all published in the late 90's and early 2000's.

Thanks for helping us understand this.

Tish

Posted: **Sat Oct 08, 2011 2:22 pm**

I also thought Mercury was tidally locked Orin, but according to the Wikipedia article they did radar observations in 1965 that disproved that. I suspect you and I read some of the same pre-'65 Sci Fi.

I found the animation to illustrate a Solar day very confusing. Partly I blame my lack of coffee, soon to be remedied, but also I finally noticed they'd only done half a day. Granted it would be kind of boring to sit there watching the sun not be in the sky but that's better than being led to believe it's always in the sky. I'd welcome a good explanation of why the sun slows down in its crossing of the sky. Or I could have my coffee and try to work it out for myself.

Anyway, very nice APOD, and science-rich.

Posted: **Sat Oct 08, 2011 2:31 pm**

jerloe wrote:Here's my comment. How come the image on the right has already be redacted? An upside down "L" around a couple of craters?

Gray areas are where there is no data. Presumably there was some sort of equipment or transmission failure when those areas were being imaged (we see this all the time with mosaic images). No doubt the data will get filled in after more observations are made.

Posted: **Sat Oct 08, 2011 2:50 pm**

longhorn_tish wrote:I have a question about the length of the Mercury Solar Day. I homeschool my children and we have been studying Mercury for the last 4 weeks. Every book we checked out from the library and even our astronomy textbook taught us that a day on Mercury was 59 earth days and a year was 88 earth days. Yet, this article and its references all say 176 earth days.

Mercury's sidereal rotation period is 58.7 (Earth) days, which is its "true" day length. But its solar rotation period is 176 days- that is, if you were on the planet, it would be 176 days from one noon to the next. This is, of course, much more extreme than on Earth, where a sidereal day is just four minutes shorter than a solar day. This is where the two numbers are coming from; understanding of the nature of Mercury's orbit and rotation hasn't changed in recent years.

Posted: **Sat Oct 08, 2011 2:53 pm**

nstahl wrote:I also thought Mercury was tidally locked Orin, but according to the Wikipedia article they did radar observations in 1965 that disproved that.

Mercury is tidally locked. That's what spin-orbit resonance means. Most tidally locked bodies are in a 1:1 resonance with their companion; Mercury happens to be in a 3:2 resonance. But the dynamics and mechanisms are identical, regardless of the ratio.

Posted: **Sat Oct 08, 2011 3:37 pm**

Being the closest planet to the sun, Mercury would have the shortest revolutions. However, it would be weird to some how a day on Mercury lasts twice as long as a year.

The second image of Mercury does bring out a lot of the planet's details, such as its cratered and rough terrain.

Posted: **Sat Oct 08, 2011 4:07 pm**

So if humans were to build an outpost there perhaps it would have to be mobile, rolling across the surface, say, just following the sunset. Just warm enough, just cool enough to be comfortable.

Let's see, if it takes 176 days for each part of the surface to see the sun, that would be, at the equator... About 9525 miles in 4224 Earth hours, or about 2 and a quarter miles per hour. You could keep up with the sunset then at just about the speed of a person walking, no?

Or maybe the mobile research station could zip from site to site and spend tens or even hundreds of hours in one spot. That would leave time for research, mining needed materials...

-Noel

Pull the track toward the pole and get a rather slower pace...

Posted: **Sat Oct 08, 2011 4:12 pm**

Is the color photo a TRUE color or color enhanced process.
It is surprisingly bluer than I expected for true color.

Posted: **Sat Oct 08, 2011 4:19 pm**

Magrathea78 wrote:Is the color photo a TRUE color or color enhanced process.
It is surprisingly bluer than I expected for true color.

Almost certainly the colors have been enhanced to highlight subtle variations in surface composition. In a sense the colors are "true", because they aren't mapped from other bands, but the saturation appears to have been increased.

Posted: **Sat Oct 08, 2011 4:23 pm**

NoelC wrote:So if humans were to build an outpost there perhaps it would have to be mobile, rolling across the surface, say, just following the sunset. Just warm enough, just cool enough to be comfortable.

Let's see, if it takes 176 days for each part of the surface to see the sun, that would be, at the equator... About 9525 miles in 4224 Earth hours, or about 2 and a quarter miles per hour. You could keep up with the sunset then at just about the speed of a person walking, no?

Or maybe the mobile research station could zip from site to site and spend tens or even hundreds of hours in one spot. That would leave time for research, mining needed materials...

Pull the track toward the pole and get a rather slower pace...

Pull the track all the way to the pole and one can just stay put (and have water to boot).

http://en.wikipedia.org/wiki/Mercury_%28planet%29 wrote:
<<Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K; far lower than the global average. Water ice strongly reflects radar, and observations by the 70 m Goldstone telescope and the VLA in the early 1990s revealed that there are patches of very high radar reflection near the poles. While ice is not the only possible cause of these reflective regions, astronomers believe it is the most likely. The icy regions are believed to contain about 10¹⁴–10¹⁵ kg of ice, and may be covered by a layer of regolith that inhibits sublimation. By comparison, the Antarctic ice sheet on Earth has a mass of about 4×10¹⁸ kg, and Mars' south polar cap contains about 10¹⁶ kg of water. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by impacts of comets.>>

Posted: **Sat Oct 08, 2011 5:00 pm**

no mountains. I wonder how the mountains were formed on the Earth

Posted: **Sat Oct 08, 2011 5:10 pm**

mister T wrote:On Mercury is everyday your birthday?

or is every other year your birthyear?

if you are ten days old,then you are twenty years old

Posted: **Sat Oct 08, 2011 5:19 pm**

Without a protective atmosphere, the surface chemistry of Mercury would be fascinating. Are there any future plans to obtain surface samples and return them to Earth for study ?

Posted: **Sat Oct 08, 2011 5:22 pm**

deathfleer wrote:no mountains. I wonder how the mountains were formed on the Earth

Mercury does have mountains. Outside of uplift produced by impacts, mountains are the product of volcanism or tectonic activity. Mercury was volcanically active early in its existence, and that has left many structures similar to those seen on the Moon- mountains, plains, scarps, etc. These structures have persisted on Mercury because it is largely free of erosional processes.

Mountains on the Earth are produced by tectonic activity, and are very short lived. No mountains on Earth are more than a few tens of millions of years old (even some "old" mountains, like the Appalachians, are mainly the product of recent uplift bringing up older material). We have mountains on Earth because they are constantly being formed. Without that, the Earth would be almost completely flat- much more so than the Moon or Mercury.

Posted: **Sat Oct 08, 2011 6:28 pm**

deathfleer wrote:no mountains. I wonder how the mountains were formed on the Earth

???
What makes you say that? Did you follow the link to the high resolution imagery?

I see mountain ranges... For example (I added the red tint for emphasis):

-Noel

Posted: **Sat Oct 08, 2011 11:31 pm**

I think that one solar day on Mercury is of 58 Earth days.
But the astronomers says it have a new concept of solar day on Mercury.
It¨s new for me. I don´t understand.

Starship Asterisk*

APOD: MESSENGER's First Day (2011 Oct 08)

APOD: MESSENGER's First Day (2011 Oct 08)

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