Mercury Science Options

[ljk4-1]

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

[Greg Hullender]

Quite easily. Mercury at Aphelion should be about 39 kps. Mariner X was 55 kps. Your probe would be 58 kps.

As before, someone should double-check this before you reply on it to actually launch something. :-) I used this formula from Wikipedia

http://en.wikipedia.org/wiki/Orbital_mechanics#Velocity


--Greg

[tasp]

Wow.

That is getting right up there.

Appreciate the calculations. Gives a vivid idea of the challenges in navigating that region of the solar system. All those sharp, unblurred Mariner 10 pictures are quite an achievement, considering the flyby speed.

(I am not likely to be sending any of my own spacecraft on this trajectory, the Legos would melt)

[Phil Stooke]

Not much action on here, but every workday there's a new image from MESSENGER. Here I have joined two nice color images of the Tolstoj area.

Phil

[Ant103]

Wow ! It looks like a deep field with many galaxies, nebulas and stars. Magnificent !

[CAP-Team]

Reminds me of Callisto

[Explorer1]

First burn in orbit around Mercury (ever!)

http://messenger.jhuapl.edu/news_room/details.php?id=177

[peter59]

First burn in orbit around Mercury (ever!)

Second.
First burn Messenger successfully completed June 15, 2011
http://messenger.jhuapl.edu/news_room/details.php?id=173

[Phil Stooke]

Another composite of two images from the big color basemap now being compiled.

Phil

[Phil Stooke]

A comparison of presumably vent-like structures on Mercury and the Moon at the same scale. The Mercury pic was part of the press conference on JUne 16th, where it was captioned 'Etched Terrain"

Phil

[Dysgraphyk]

New results on mercury shrinkage discussed in at a meeting of the American Geophysical Union in San Francisco, yesterday :

Studies of Mercury show that it has shrunk by about 11 kilometres across since the Solar System's fiery birth 4.5 billion years ago. As the planet cooled and contracted, it became scarred with long curved ridges similar to the wrinkles on a rotting apple.

A new census of these ridges, called lobate scarps, has found more of them, with steeper faces, than ever before. The discovery suggests that Mercury shrank by far more than the previous estimate of 2-3 kilometres, says Paul Byrne, a planetary scientist at the Carnegie Institution for Science in Washington DC. He presented the results today at a meeting of the American Geophysical Union in San Francisco, California.

The finding helps explain how Mercury's huge metallic core cooled off over time. It may also finally reconcile theoretical scientists, who had predicted a lot of shrinkage, with observers who had not found evidence of that — until now. “We are resolving a four-decades-old conflict here,” Byrne told the meeting.

Planetary scientists have been arguing over Mercury's lobate scarps ever since the Mariner 10 spacecraft flew past the planet three times in 1974-75. Researchers can use measurements of the length and height of the scarps to calculate how much planetary shrinkage they represent.


That shrinkage is a product of Mercury's odd composition — “like a core floating through space with a thin outer blanket,” says Byrne. Most of the planet is made of that large core, and so it would have cooled rapidly as heat rushed toward its surface. Modelling studies have long suggested that the planet should have shrunk by 10-20 kilometres over its lifetime, compared to the 2-3 kilometres estimated from Mariner 10 data1.

The latest estimates come from NASA’s MESSENGER probe, which photographs and measures Mercury's topography. Last year, Italian scientists used MESSENGER data covering one-fifth of the planet to show that its shrinkage was probably greater than the Mariner 10 estimates.

The latest work, covering the entire planet, revealed many lobate scarps with sharp vertical relief, Byrne said. It also uncovered details on another kind of surface feature that may be related to shrinkage. These ‘wrinkle ridges’ are less pronounced than the lobate scarps but may also have formed during contraction. Combined, the data on the lobate scarps and the wrinkle ridges suggest that Mercury's diameter has shrunk by 11.4 kilometres, Byrne said. Even leaving out the wrinkle ridges gives 10.2 kilometres of contraction.

Those numbers are plausible to at least one planetary scientist who studied Mercury’s shrinkage using Mariner 10 data in the 1970s. Jay Melosh, a planetary geologist at Purdue University in West Lafayette, Indiana, suspects that even more lobate scarps may be lurking out there. “Many of these things may still be hiding,” he says. “As far as I'm concerned, this may be an underestimate of the amount of shrinkage.”

Nature news Nature doi:10.1038/nature.2013.14331

[Phil Stooke]

http://planetarynames.wr.usgs.gov/Feature/15192


John Lennon's on Mercury now...

Phil

[nprev]

Nobody told him there'd be days like these. An excellent tribute.

[ngunn]

I suppose that's appropriate. "Imagine there's no atmosphere . . "

[tedstryk]

http://planetarynames.wr.usgs.gov/Feature/15192


John Lennon's on Mercury now...

Phil

Roll on John! Perhaps they can bend the rules for Bob Dylan.

[MarcF]

And when will they add Freddy Mercury ?? ;-)

Marc.