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Mercury Science
ljk4-1
post Nov 16 2005, 02:28 PM
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Astrophysics, abstract
astro-ph/0511419

From: Stan Peale [view email]

Date: Mon, 14 Nov 2005 22:21:56 GMT (314kb)

The proximity of Mercury's spin to Cassini state 1

Authors: S. J. Peale

Comments: 23 pages,12 figures, In press in Icarus

In determining Mercury's core structure from its rotational properties, the value of the normalized moment of inertia, $C/MR^2$, from the location of Cassini 1 is crucial. If Mercury's spin axis occupies Cassini state 1, its position defines the location of the state. The spin might be displaced from the Cassini state if the spin is unable to follow the changes in the state position induced by the variations in the orbital parameters and the geometry of the solar system. The spin axis is expected to follow the Cassini state for orbit variations with time scales long compared to the 1000 year precession period of the spin about the Cassini state because the solid angle swept out by the spin axis as it precesses is an adiabatic invariant. Short period variations in the orbital elements of small amplitude should cause displacements that are commensurate with the amplitudes of the short period terms. By following simultaneously the spin position and the Cassini state position during long time scale orbital variations over past 3 million years (Quinn {\it et al.}, 1991) and short time scale variations from JPL Ephemeris DE 408 (Standish, 2005) we show that the spin axis will remain within one arcsec of the Cassini state after it is brought there by dissipative torques. We thus expect Mercury's spin to occupy Cassini state 1 well within the uncertainties for both radar and spacecraft measurements, with correspondingly tight constraints on $C/MR^2$.

http://arxiv.org/abs/astro-ph/0511419


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Dec 2 2005, 05:21 PM
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Paper (*cross-listing*): gr-qc/0511137

Date: Fri, 25 Nov 2005 13:47:02 GMT (4kb)
Date (revised v2): Tue, 29 Nov 2005 11:55:15 GMT (4kb)
Date (revised v3): Thu, 1 Dec 2005 12:41:58 GMT (4kb)

Title: Can Solar System observations tell us something about the cosmological
constant?

Authors: Lorenzo Iorio

Comments: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added,
typos in the units of Lambda corrected
\\
In this note we show that the latest determinations of the residual Mercury's
perihelion advance, obtained by accounting for almost all known Newtonian and
post-Newtonian orbital effects, yields only very broad constraints on the
cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050
arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2.

The currently accepted value for Lambda, obtained from many independent
cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.

\\ ( http://arXiv.org/abs/gr-qc/0511137 , 4kb)

------------------------------------------------------------------------------

\\

Paper (*cross-listing*): gr-qc/0511138

Date: Fri, 25 Nov 2005 13:50:40 GMT (8kb)

Title: Solar System planetary motions and modified gravity

Authors: Lorenzo Iorio

Comments: Latex2e, 8 pages, 4 tables, no figures, 25 references
\\
According to the braneworld model of gravity by Dvali, Gabadadze and Porrati,
our Universe is a four-dimensional space-time brane embedded in a larger,
infinite five-dimensional bulk space. Contrary to the other forces constrained
to remain on the brane, gravity is able to explore the entire bulk getting
substantially modified at large distances. This model has not only cosmological
consequences allowing to explain the observed acceleration of the expansion of
our Universe without resorting to the concept of dark energy, but makes also
testable predictions at small scales. Interestingly, such local effects can
yield information on the global properties of the Universe and on the kind of
expansion currently ongoing. Indeed, among such predictions there are extra
precessions of the perihelia and the mean longitudes of the planetary orbits
which are affected by a twofold degeneration sign: one sign refers to a
Friedmann-Lemaitre-Robertson-Walker phase while the opposite sign is for a
self-sccelerated phase.

In this paper we report on recent observations of planetary motions in the Solar System which are compatible with the existence of a fifth dimension as predicted in the Dvali-Gabadadze-Porrati model with a self-accelerated cosmological phase, although the errors are still large. The Friedmann-Lemaitre-Robertson-Walker phase is, instead, ruled out.

\\ ( http://arXiv.org/abs/gr-qc/0511138 , 8kb)


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Jan 12 2006, 08:00 PM
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Mercury a Possible Hit-and-Run Planet

http://www.space.com/scienceastronomy/0601...it_and_run.html

New computer modeling shows that the planet Mercury might have formed in a
hit-and-run collision that stripped off its outer layers.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Feb 17 2006, 08:49 PM
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Science/Astronomy:

* Catch Mercury While You Can

http://www.space.com/spacewatch/060217_night_sky.html

Once again it is time to seek out what has often been cited as the most
difficult of the five brightest naked-eye planets to see: Mercury.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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odave
post Feb 18 2006, 12:26 PM
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QUOTE (ljk4-1 @ Feb 17 2006, 03:49 PM) *
...cited as the most difficult of the five brightest naked-eye planets to see


The first time I ever saw Mercury was from behind, during its 1999 transit of the sun wink.gif


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--O'Dave
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JRehling
post Feb 18 2006, 03:55 PM
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QUOTE (odave @ Feb 18 2006, 04:26 AM) *
The first time I ever saw Mercury was from behind, during its 1999 transit of the sun wink.gif


I was lucky to catch that one, too -- it was immediately before sunset at my location. But that was about the hundredth time I'd seen it.

Given its elusiveness, one of the surprising things about it is that it is one of a very few objects that can be, at certain times, the brightest object in the sky. I've seen that.

For anyone capable of programming an ephemeris-generating program, I'd like to propose the challenge of generating all the instances in the last/next X years in which Mercury is the brightest object in the sky. Off topic, but...
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RNeuhaus
post Feb 19 2006, 05:01 AM
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Tomorrow at 7:00 pm, the Mercury will be in half visible as shown in the below picture:
Attached Image

The Mercury view will vanish after March 3.

Rodolfo
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Rob Pinnegar
post Feb 20 2006, 06:20 AM
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QUOTE (JRehling @ Feb 18 2006, 08:55 AM) *
For anyone capable of programming an ephemeris-generating program, I'd like to propose the challenge of generating all the instances in the last/next X years in which Mercury is the brightest object in the sky. Off topic, but...

Actually, it might also be interesting to find out how many objects are capable of being the brightest object in the sky. After the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Sirius, how many stars can do it? Can Saturn do it?
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edstrick
post Feb 20 2006, 06:37 AM
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Note that Mercury is actually brightest when it is at superior conjunction, on the far side of the sun. It's not a whole lot further from Earth than when at maximum elongation, is 100% instead of 50% illuminated, and, maybe most importantly, is near zero phase angle where backscatter and the hiding of soil-grain shadows makes the surface dramatically brighter than at phase angles of even 30 or 15 degrees, much less 90 deg.

The Venus cloud-haze is forward scattering, so, together with the much greater size change of the Venusian disk between crescent and gibbous phase, results in a rather fat crescent being the geometry where Venus appears brightest.
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ljk4-1
post Feb 21 2006, 10:28 PM
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NASA Science News for February 21, 2006

Mercury makes a rare appearance in the evening sky this week.

FULL STORY at

http://science.nasa.gov/headlines/y2006/21....htm?list161084

Find out about the Science@NASA Podcast feed at http://science.nasa.gov/podcast.htm .


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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Guest_AlexBlackwell_*
post Feb 21 2006, 10:37 PM
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Guests






A paper currently in press with Icarus:

Evolution of Mercury's obliquity
Icarus, In Press, Corrected Proof, Available online 17 February 2006
Marie Yseboodt and Jean-Luc Margot
Abstract
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ljk4-1
post Apr 5 2006, 02:23 PM
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MERCURY RISING

- Early Mercury Impact Showered Earth

http://www.spacedaily.com/reports/Early_Me...ered_Earth.html

Leicester, England (SPX) Apr 05, 2006 - New computer simulations of Mercury's
formation show some of the resulting ejected material ended up on Earth and
Venus. The simulations, which track the material's path over several million
years, also shed light on why Mercury is denser than expected.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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JRehling
post Sep 28 2007, 07:07 PM
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A question that's nagged me for a long time...

Mariner 10 was in a solar orbit that intersected Mercury's orbit in resonance with the planet, so that it revisted Mercury multiple times (the spacecraft was actually alive for the first three; presumably more encounters, if farther ones, continued to take place after the craft died).

The rub was that Mercury's rotation is also in resonance, so that the same face of Mercury was lit at all three encounters. This is because the orbital period of Mariner 10 was 2 Mercury "years", and the 3/2 resonance of Mercury's revolution and rotation meant that it rotated precisely twice while Mariner 10 and the planet were apart.

The delta-v budget for getting to Mercury was a limiting factor, so the mission could not have gotten into any old Mercury-crossing orbit we wished, but to me, the ten million dollar question is: Why not put it into a solar orbit with a LONGER period that intersected Mercury's orbit at the same location every THREE Mercury "years"? If that had been the mission profile, the likely outcome would have been that the craft would have only survived two such flybys (as it was, it was limping into the third), but they would have shown opposite sides of the planet, giving us an almost full global map, instead of the half-planet coverage we've had to live with for the last 33 years.

In terms of pure delta-v, the longer period should have been easier to achieve. Unless the gravity assist with Venus had some stringent requirements that forbade the longer period, it seems like it would have been a win-win scenario to take the longer period and the full coverage.

This is now a moot point in many ways, but it's stuck in my craw for a long time. Any ideas?
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Greg Hullender
post Sep 28 2007, 10:49 PM
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Have a look at chapter 2 from "The Voyage of Mariner 10"

http://history.nasa.gov/SP-424/ch2.htm

"Early in 1970, Guiseppe Colombo of the Institute of Applied Mechanics in Padua, Italy, who had been invited to JPL to participate in a conference on the Earth-Venus-Mercury mission, noted that in the 1973 mission the period of the spacecraft's orbit, after it flew by Mercury, would be very close to twice the period of Mercury itself. He suggested that a second encounter with Mercury could be achieved. An analytical study conducted by JPL confirmed Colombo's suggestion and showed that by careful choice of the Mercury flyby point, a gravity turn could be made that would return the spacecraft to Mercury six months later."

Sounds as though even the delta-v to get into the 2x orbit was hard to come by.

--Greg
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JRehling
post Sep 28 2007, 10:57 PM
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QUOTE (Greg Hullender @ Sep 28 2007, 03:49 PM) *
Have a look at chapter 2 from "The Voyage of Mariner 10"

http://history.nasa.gov/SP-424/ch2.htm

"Early in 1970, Guiseppe Colombo of the Institute of Applied Mechanics in Padua, Italy, who had been invited to JPL to participate in a conference on the Earth-Venus-Mercury mission, noted that in the 1973 mission the period of the spacecraft's orbit, after it flew by Mercury, would be very close to twice the period of Mercury itself. He suggested that a second encounter with Mercury could be achieved. An analytical study conducted by JPL confirmed Colombo's suggestion and showed that by careful choice of the Mercury flyby point, a gravity turn could be made that would return the spacecraft to Mercury six months later."

Sounds as though even the delta-v to get into the 2x orbit was hard to come by.

--Greg


It definitely was. My question stems from the fact that a 3x orbit should have been easier (less delta-v, anyway) AND scientifically more desirable.

Basically, Earth (and therefore the spacecraft before it was launched) is in a 4x Mercury-period orbit. It takes more delta-v to get the probe down to 2x than just down to 3x.
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