Paper: astro-ph/0510798

Date: Fri, 28 Oct 2005 10:23:28 GMT (316kb)

Title: Modeling the Jovian subnebula: II - Composition of regular satellites
ices

Authors: Olivier Mousis and Yann Alibert

Comments: 9 pages, A&A, in press
\\
We use the evolutionary turbulent model of Jupiter's subnebula described by
Alibert et al. (2005a) to constrain the composition of ices incorporated in its
regular icy satellites. We consider CO2, CO, CH4, N2, NH3, H2S, Ar, Kr, and Xe
as the major volatile species existing in the gas-phase of the solar nebula.
All these volatile species, except CO2 which crystallized as a pure condensate,
are assumed to be trapped by H2O to form hydrates or clathrate hydrates in the
solar nebula. Once condensed, these ices were incorporated into the growing
planetesimals produced in the feeding zone of proto-Jupiter. Some of these
solids then flowed from the solar nebula to the subnebula, and may have been
accreted by the forming Jovian regular satellites. We show that ices embedded
in solids entering at early epochs into the Jovian subdisk were all vaporized.
This leads us to consider two different scenarios of regular icy satellites
formation in order to estimate the composition of the ices they contain. In the
first scenario, icy satellites were accreted from planetesimals that have been
produced in Jupiter's feeding zone without further vaporization, whereas, in
the second scenario, icy satellites were accreted from planetesimals produced
in the Jovian subnebula. In this latter case, we study the evolution of carbon
and nitrogen gas-phase chemistries in the Jovian subnebula and we show that the
conversions of N2 to NH3, of CO to CO2, and of CO to CH4 were all inhibited in
the major part of the subdisk. Finally, we assess the mass abundances of the
major volatile species with respect to H2O in the interiors of the Jovian
regular icy satellites. Our results are then compatible with the detection of
CO2 on the surfaces of Callisto and Ganymede and with the presence of NH3
envisaged in subsurface oceans within Ganymede and Callisto.

\\ ( http://arXiv.org/abs/astro-ph/0510798 , 316kb)

Astrophysics, abstract
astro-ph/0504649

From: Paul Estrada [view email]

Date (v1): Thu, 28 Apr 2005 20:20:34 GMT (67kb)
Date (revised v2): Tue, 10 May 2005 23:19:41 GMT (68kb)
Date (revised v3): Tue, 13 Dec 2005 21:42:03 GMT (107kb)

A Gas-poor Planetesimal Capture Model for the Formation of Giant Planet Satellite Systems

Authors: P. R. Estrada, I. Mosqueira

Comments: 45 pages, 11 figures, 3 appendices, uses rgfmacro.tex, accepted for publication to Icarus

Assuming that an unknown mechanism (e.g., gas turbulence) removes most of the subnebula gas disk in a timescale shorter than that for satellite formation, we develop a model for the formation of regular (and possibly at least some of the irregular) satellites around giant planets in a gas-poor environment. In this model, which follows along the lines of the work of Safronov et al. (1986), heliocentric planetesimals collide within the planet's Hill sphere and generate a circumplanetary disk of prograde and retrograde satellitesimals extending as far out as $\sim R_H/2$. At first, the net angular momentum of this proto-satellite swarm is small, and collisions among satellitesimals leads to loss of mass from the outer disk, and delivers mass to the inner disk (where regular satellites form) in a timescale $\lesssim 10^5$ years. This mass loss may be offset by continued collisional capture of sufficiently small $< 1$ km interlopers resulting from the disruption of planetesimals in the feeding zone of the giant planet. As the planet's feeding zone is cleared in a timescale $\lesssim 10^5$ years, enough angular momentum may be delivered to the proto-satellite swarm to account for the angular momentum of the regular satellites of Jupiter and Saturn.(abridged)

http://arxiv.org/abs/astro-ph/0504649

Paper: astro-ph/0602033

Date: Thu, 2 Feb 2006 02:50:36 GMT (387kb)

Title: A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus

Authors: Franck Marchis, Daniel Hestroffer, Pascal Descamps, Jerome Berthier,
Antonin H. Bouchez, Randall D. Campbell, Jason C. Y. Chin, Marcos A. van Dam,
Scott K. Hartman, Erik M. Johansson, Robert E. Lafon, David Le Mignant, Imke
de Pater, Paul J. Stomski, Doug M. Summers, Frederic Vachier, Peter L.
Wizinovich, Michael H. Wong

Comments: 10 pages, 3 figures, 1 table

Journal-ref: Nature, 439, 565-567, 2006
\\
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.

\\ ( http://arXiv.org/abs/astro-ph/0602033 , 387kb)

Should this be moved to the KBO thread, then?

Suddenly, the Jovian Trojans are begging for a mission...Dawn 2, anyone?

From a manned SF perspective, this could be quite significant as well in the distant future. The Jovian Trojans may have the most economically accessible supply of volatiles in the whole Solar System!

A 'Dawn 2' launched on an orbit with a perihelion at earth's orbit that aphelions quite a ways past Jupiter and that had a 4 year period from crossing Jupiters orbit outbound to inbound (sorry, not smart enough to figure out the rest of the orbit parameters), would if launched at the right time, cross 60 degrees ahead of Jupiter and 60 degrees behind.

This would give you a fair chance to look over at least 2 Jovian Trojans, and maybe some mainbelt asteroids both ways. If total period of orbit is close to an integral number of years, earth gravity could send craft on to Chiron (timed correctly) for a look at that interesting piece of real estate.

No heavy radiation shielding as we don't get close to Jupiter, but we do get to pass down range through Jupiters magnetotail 2 years after first Trojan encounter.

Let's get going!

Yeah! We could call it "TRACE": TRojan Asteroid/Chiron Explorer!

Heck, maybe this is actually a job for a New Horizons 2...seems like a better platform for multiple flybys and long-endurance transit to the outer system (gotta lose the solar arrays).

A catchy acronym is the halfway point for getting a mission off the ground!

Okay... ... here are a few attempts at that, then:

BOLD/FACE: Belt Object (Lagrangian) Discoverer/Flyby Assessment of Chiron Environment
JOLT-CE: JOvian Leading Trojans-Chiron Explorer
JAR/CARFET: Jovian Asteroid Reconnaissance/Chiron After Redirected Flyby of Earth (Tentative)

L unar
I nserted
P olar
O rbiting
T est
O bservatory
V ehicle
A ssembly
N etwork

A-D Vehicles would be intended as stress analysis missions, perhaps sponsored by JAXA.

Bob Shaw

There has already been a lot of interest in a solar-powered Trojan flyby mission -- maybe even one that flies by more than one Trojan -- which could very likely be made within the Discovery cost cap. Beth Ellen Clark of Cornell was associated with one such Discovery proposal called "Andromache", although it's hard to find anything on it.

But: there is also now a proposal floating around -- neat acronym and all -- to actually have a New Frontiers-class craft orbit one or maybe even two Trojans. It's called PARIS; it would use the new concept of a low-powered but long-duration ion drive powered by a particularly large 1-kilowatt RTG (which must use the new, more efficient future RTG designs to reduce its plutonium load); and there have already been at least two abstracts on it, the most recent being at http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1922.pdf . (This new type of propulsion system is attracting increasing interest; it would apparently also allow a relatively low-cost giant planet orbiter which could do an awful lot of putt-putting around the planet's system of moons -- including orbiting one or more of them -- after the orbiter was initially braked into orbit around the planet by aerocapture.)

Some JPL documents on the overall subject:

Trojan flybys:
http://trs-new.jpl.nasa.gov/dspace/bitstre...9/1/95-0948.pdf

Trojan REP orbiter:
http://trs-new.jpl.nasa.gov/dspace/bitstre...1/1/05-2069.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...0/1/05-2173.pdf

someone really needs to email this to our JAXA blogger friend...
and thanks Bruce for those links.

Review: Europa, the Ocean Moon

Thu, 16 Feb 2006 - Our five senses are all we have to allow our brains to interact with the world outside our bodies. Space exploration relies almost entirely on one, the sense of sight. Space probes send us images of planets, moons and other objects which we then have to decipher as best we can.

Richard Greenberg in his book Europa, The Ocean Moon uses recent images of Europa, together with our understanding of celestial mechanics and plate tectonics, to unravel this little moon's mysteries. For Europa's biggest mystery is whether it harbours life who may be looking right back at us from their own little world.

http://www.universetoday.com/am/publish/bo...on.html?1622006

Huh... Here's another review, from Mike Belton, leader of the Galileo Imaging Team.

Excerpts:

The descriptions of how Greenberg developed,
promoted, and defended his ideas is another significant part of
the book and one that I find at times to be absurd, generally
irreverent, and, in professional terms, possibly approaching
suicidal.

...

Paranoia is not a word to be used lightly, but there is much that I
am certain is delusional in this aspect of the book. We see this
even in the preface (though there similar instances
throughout the book): “I never felt welcomed by the team…
Then, when it became clear that my field was the key to
understanding what we saw at Europa and evident how
significant those discoveries were, attempts to keep me
marginalized were driven by transparent social, political, and
financial motives.” This is absurd. The book is filled with
words and phrases like: “professional gladiators,” “powerful
infighters,” “perverted definition of ‘team’,” “sycophantic,”
“hustlers,” “enforcers,” “malignity, envy, and ignorance,”
“locked out,” “pontificating,” “jealousy,” and “animosity.”
Nowhere, as far as I can see, do the concepts on which the
everyday world of our profession is based, that is, integrity,
trust, and skeptical inquiry, get a fair shake. Even the players
who are mentioned by name are stereotyped. Those who
worked with the author are uniformly brilliant and insightful;
those who question or raise opposing ideas are to one degree
or another vilified. As I noted before: this is absurd.