[meteorite-list] Rosetta Flyby of Asteroid 21 Lutetia

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 9 Jul 2010 20:06:08 -0500
Message-ID: <297121F006B14DC2B9280FD215A3B39D_at_ATARIENGINE2>

The density of Lutetia in the most recent
determination is 5.55 +/- 0.88, or between
4.67 and 6.43. Complete data can be found at:
http://home.earthlink.net/~jimbaer1/astmass.txt

The dimensions of Lutetia have been calculated
by some as 115 x 96 x 80 and by (more) others as
120 x 100 x 80, but whatever way you slice the
data it comes to a volume equivalent to a 95.76
kilometer sphere.

There have been two reported stellar occultations
by Lutetia, observed from Malta in 1997 and Australia
in 2003, with only one chord each, roughly agreeing
with IRAS measurements of a spherical shape roughly
~100 km.. See:
    "Tedesco, E.F., P.V. Noah, M. Noah, and S.D. Price.
IRAS Minor Planet Survey. IRAS-A-FPA-3-RDR-IMPS-V6.0.
NASA Planetary Data System, 2004."
http://sbn.psi.edu/pds/resource/imps.html

At this size and the given flyby distance, the image of
Lutetia should subtend about 90 arc-minutes. I expect
plenty of detail. )The Steins image was 60 pixels across,
yet 23 craters were identified and a chain of seven
craters in a row.)

    "There are various indications of a non-metallic
surface: a flat, low frequency spectrum similar to that
of carbonaceous chondrites and C-type asteroids and
not at all like that of metallic meteorites, a low radar
albedo unlike the high albedos of strongly metallic
asteroids like 16 Psyche, evidence of hydrated materials
on its surface, abundant silicates, and a thicker regolith
than most asteroids."
http://en.wikipedia.org/wiki/21_Lutetia
(lots of references)

Oddly, its axis is tilted over at 85-89 degrees, so it rotates
(in 6+ hours) on its side like Uranus. It has been whacked
but good. Did somebody say "breccia"?

Lutetia was discovered on November 15, 1852 by Hermann
Goldschmidt from the balcony of his apartment in Paris.

Now, THAT'S the way to do science!

Maurice, more Champagne, s'il vous plait!


Stderling K. Webb
--------------------------------------------------------------------------------
----- Original Message -----
From: "Jason Utas" <meteoritekid at gmail.com>
To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
Sent: Friday, July 09, 2010 5:49 PM
Subject: Re: [meteorite-list] Rosetta Flyby of Asteroid 21 Lutetia


Hola,
We seem to have a bit of a problem...
The article seems to suggest that carbonaceous chondrites have a
density between nearly 4 and 5 grams per cubic centimeter.
Might anyone on the list be willing to comment on this slight
discrepancy?

>A team of researchers used the VLT
and Keck telescopes to estimate Lutetia's bulk density, finding it to be
in the range 3.98 to 5.00 g cm^-3 , depending on the model that is
adopted. Although no precise value could be determined this range of
density would support a carbonaceous composition (see Drummond et al.,
[2010]).

-As opposed to:

http://www.meteorites.com.au/odds&ends/density.html

The numbers in the article simply stuck me as out of place - yes the
asteroid appears to be less dense than an iron meteorite, but it's a
difference of only 20-30%. If you take a look at the following paper
-

http://www.dnp.fmph.uniba.sk/etext/40/text/MAPS36Welten2.pdf

They assume the density of the given mesosiderite to be 5 grams per
cubic centimeter - a value the authors say is at the more dense end of
the spectrum for even stony-iron meteorites.

Drummond points out in his paper that Lutetia is in fact likely not a
carbonaceous chondrite.

http://arxiv.org/pdf/1005.5353

He suggests that it is most likely an enstatite chondrite, but also
notes that the density body as a whole might be less than its
constituents, as it may be a rubble-pile asteroid (a mix of solid
chunks of matter and empty space). As such, I would have to say that
it is most likely composed primarily of stony-iron or iron material.
A dense stony body would also be a possibility, but as Drummond et al.
note, this body is apparently more dense than your average chondrite
of *any* type.

-And the recently calculated values showed it to be more dense than
earlier estimates!

Regards,
Jason


On Fri, Jul 9, 2010 at 9:25 AM, Ron Baalke <baalke at zagami.jpl.nasa.gov>
wrote:
>
> http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=47389
>
> Rosetta flyby of asteroid (21) Lutetia
> Euoprean Space Agency
> July 9, 2010
>
> Discovered in Paris by Hermann Goldschmidt in November 1852, asteroid
> (21) Lutetia has been a cosmic riddle for astronomers. In an attempt
> to
> pin down its properties once and for all, ESA's Rosetta spacecraft
> will
> fly past Lutetia within an estimated distance of close to 3170 km, at
> a
> relative speed of 15 km/s on 10 July 2010 at approximately 15:45 UT
> (spacecraft event time), 18:10 CEST (ground event time).
>
> Follow the flyby live via the webcast
> <http://www.livestream.com/eurospaceagency> from ESA/ESOC: 10 July
> 2010
> starting at 18:00 CEST.
>
> Frequent updates on activities leading up to the flyby can be found on
> the Rosetta blog <http://webservices.esa.int/blog/blog/5/page/1>.
>
> Details of the spacecraft preparations leading up to the flyby,
> including images of Lutetia acquired during the navigation campaign,
> can
> be found in the status reports
> <http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31523&farchive_objecttypeid=30&farchive_objectid=30930>.
>
> This asteroid flyby will address a number of open questions about
> Lutetia; in particular, the observations and measurements obtained by
> instruments on board Rosetta will:
>
> * Attempt to settle the ongoing debate as to the asteroid's true
> composition. In particular to ascertain if it is a C-type or
> M-type asteroid.
> * Determine the mass and density of the asteroid with unprecedented
> precision.
> * Search for an exosphere around the asteroid and determine its
> composition.
> * Provide ground-truth for the better calibration of existing
> observations obtained by ground-based telescopes.
> * Test out the scientific instruments on board Rosetta as it
> continues to travel to its final destination: comet
> 67P/Churyumov-Gerasimenko.
> * Carry out a close-up study of a primitive building block of the
> Solar System, with the intention of using it to decode how our
> solar neighbourhood formed.
>
> Situated in the main asteroid belt and with estimated dimensions of
> 132
> x 101 x 76 km (see Belaskaya et al., [2010]), asteroid (21) Lutetia
> has
> been subjected to intense ground-based scrutiny since it was announced
> as a target for Rosetta in 2004. Initial observations recorded a high
> albedo, suggesting a high metallic content, and led to the body being
> classified as an M-type asteroid (see Bowell et al., [1978]). Should
> (21) Lutetia indeed turn out to be M-type, the Rosetta flyby would be
> the first close encounter of a spacecraft with this class of asteroid.
>
> However, Lutetia's true nature has always been far from clear-cut. One
> difficulty in unambiguously classifying Lutetia is the lack of clear
> features in the spectrum of this asteroid. Recent visual spectroscopic
> studies, reported in Belaskaya et al., and Perna et al., have noted
> different spectral slopes at different rotation phases. This has been
> interpreted as arising from inhomogeneities in the asteroid's make up,
> perhaps caused by local differences in mineralogical or chemical
> content
> of the surface.
>
> Some researchers have suggested the closest analogue to Lutetia's
> surface is a type of carbonaceous chondrite meteorite (see Barucci et
> al.). When Lutetia was at opposition in 2008/2009 the opportunity was
> taken to test this theory further. A team of researchers used the VLT
> and Keck telescopes to estimate Lutetia's bulk density, finding it to
> be
> in the range 3.98 to 5.00 g cm^-3 , depending on the model that is
> adopted. Although no precise value could be determined this range of
> density would support a carbonaceous composition (see Drummond et al.,
> [2010]).
>
> The ground-based observations in preparation for the flyby have also
> allowed astronomers to construct Lutetia's light curve. Most asteroids
> tend to be irregularly shaped and therefore different amounts of
> sunlight are reflected towards the Earth as they rotate. Hence the
> ratio
> between the three major axes defining the asteroid as well as its
> rotational properties can be determined from measuring how this
> reflected light changes with time. Assuming a certain reflectivity
> (albedo) the dimensions of the asteroid can also be estimated.
> Knowing,
> from this preparatory work, that Lutetia rotates with a period close
> to
> 8.17 hours was of great help in planning the scientific measurements
> for
> the flyby.
>
> The encounter of Rosetta with asteroid (21) Lutetia is key to
> understanding the true nature of this puzzling member of the main
> asteroid belt. Only with the close inspection that is possible with a
> flyby can the riddles of Lutetia be solved, as this provides the
> opportunity to measure and analyse many of the asteroid's properties
> including its shape, density, composition and surface topography. The
> instruments on board Rosetta have been designed specifically for such
> tasks and will be able to provide the answers that are sought.
>
> The flyby at Lutetia will be the second time Rosetta has studied an
> asteroid up-close. In 2008 the spacecraft flew past asteroid (2867)
> Steins at a distance of just 802.6 km, only 2.6 km further out than
> baselined. However, these two asteroids are just stepping stones on
> the
> journey to Rosetta's ultimate goal, the rendezvous with comet
> 67P/Churyumov-Gerasimenko, scheduled for 2014. The Rosetta team hopes
> that with this rendezvous they can decipher the enigmas of the
> formation
> of our Solar System, just as its namesake helped unscramble ancient
> Egyptian hieroglyphics.
>
> Orbital and physical characteristics of asteroid (21) Lutetia
> based on pre-Rosetta observations
>
> Semimajor axis, a (AU) 2.44*
> Orbital eccentricity, e 0.16*
> Orbital period (y) 3.8*
> Inclination (deg) 3.07*
> Dimensions (km) 132 x 101 x 76 (From Drummond et al., 2010)
> Taxonomic type C or M
> Sidereal rotation period (h) 8.168270 (from Carry et al., 2010)
> Albedo 0.1-0.22 (estimates vary according to the technique used; see
> Belskaya et al., 2010)
>
> /(* Source: IAU Minor Planet Center
> <http://www.cfa.harvard.edu/iau/Ephemerides/Bright/2000/00021.html>.)/
>
>
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Received on Fri 09 Jul 2010 09:06:08 PM PDT