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Paolo
time to start a thread on one of the most interesting UMSF events of 2010...
Published thu on arXiv Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space Telescope
Patteroast
Lutetia will be the largest asteroid visited by a spacecraft, at least until 2011. laugh.gif The current record is held by Mathilde, but Lutetia's twice as big. It'll be the first asteroid of spectral class M to be visited, although it doesn't appear to be metallic... it should be a fun one. smile.gif
Paolo
Actually the class of Lutetia is disputed, and it now seems more likely that it resembles some types of carbonaceous meteorites
these are some papers summarizing the results in support of the Rosetta flyby:
Asteroids 2867 Steins and 21 Lutetia: surface composition from far infrared observations with the Spitzer space telescope
Surface properties of Rosetta's targets (21) Lutetia and (2867) Steins from ESO observations
New visible spectra and mineralogical assessment of (21) Lutetia, a target of the Rosetta mission
Paolo
A quick recap of facts about Lutetia from "Robotic Exploration of the Solar System - Part 3":

QUOTE
Almost 100 km in size, Lutetia was discovered on 15 November 1852 by Hermann M.S. Goldschmidt in Paris and dedicated to the town itself, which was known to the Romans as Lutetia Parisiorum (Lutetia of the Parisii tribe).


QUOTE
On penetrating the asteroid belt for the second time, the vehicle will pass Lutetia on 10 July 2010 at a range of about 3,055 km, traveling at a relative speed of 15 km/s. The data from the IRAS infrared astronomy satellite enabled the average diameter of this object to be roughly estimated during the 1980s at 95.5 km, but a number of light curves obtained since, most recently by the Hubble Space Telescope, have enabled astronomers to determine that it is asymmetric and about 132 x 101 x 93 km across, and to rotate in a little over 8 hours. Observations at a range of ‘look angles’ even revealed variations which hinted at the presence of one or more large craters in the northern hemisphere. Lutetia is therefore one of the best-characterized asteroids to receive a spacecraft inspection. However, despite a large number of spectroscopic studies, its taxonomic class was debated. For a long time it was listed as an M-class object that spectrally resembled some iron-rich meteorites. As yet, no such body has been visited. But this classification was not confirmed by infrared observations by the European Southern Observatory, a telescope in Hawaii and the Spitzer Space Telescope, nor by ultraviolet observations by the Hubble Space Telescope. Hence Lutetia is now regarded as an anomalous C-class object, reflecting more light than other members of the class, possibly implying that its surface is ‘unweathered’. In fact, Lutetia appears similar to some metal-rich carbonaceous chondrite meteorites. Rosetta made observations of Lutetia in January 2007, just before the Mars flyby, in order to assist in characterizing its light curve, rotation period and spin axis.


stevesliva
I just saw a reference to papers by Busarev et al, that suggest Lutetia could be a binary. That would be neat. But alas, perhaps the concavity is more likely.
Paolo
nhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission is now published (and free to access!) in Astronomy & Astrophysics
Paolo
This is interesting: the Ptolemy mass spectrometer on the Rosetta orbiter will attempt to detect a faint exosphere around Lutetia
Explorer1
It would have to be faint indeed. If confirmed, that would be the smallest known body with an atmosphere, correct?
I can't think of anything off the top of my head smaller then Enceladus that has one....
nprev
"Exosphere" in this context seems like a pretty broad application of the term, though. Any solid body is going to emit a certain amount of gas in a vacuum, however exceedingly small that might be.

It's a smart & interesting experiment nevertheless. There appears to be a continuum of possible volatile content levels for members of the Belt's general asteroid population as well as an increasing number of objects that seem to be intermediate between the traditional categories of "comet" & "asteroid". Measuring the emissions of Luetia will provide some very valuable baseline data that directly pertains to all that.
Explorer1
I think a good rule of thumb would be: it's an atmosphere if the body it surrounds is more or less spherical. That's a good a reference point as any right? Lutetia is excluded, but Ceres and maybe Vesta wouldn't be.


I doubt Hyperion or Proteus will break that rule anytime soon...
lyford
This discussion seems to becoming perilously evocative of another debate. I hope we don't have to create a new class of "dwarf atmospheres" biggrin.gif biggrin.gif
nprev
QUOTE (Explorer1 @ May 1 2010, 02:38 AM) *
I think a good rule of thumb would be: it's an atmosphere if the body it surrounds is more or less spherical.


Somebody please correct me if I'm wrong, but wouldn't a gravitationally-bound gaseous envelope (yep, intentionally avoiding the "A" word, here) be spherically distributed around a body's center of mass regardless of its gross shape? In fact, wouldn't it follow the contours of its Hill sphere?

There might be pronounced local variations if there were very significant asymmetries in a body's internal mass distribution, but they'd have to be really big mascons, almost certainly much, much larger than any you'd expect to find on an asteroid.
Hungry4info
I think you're right, nprev. We don't see the atmospheric pressure at the top of Mt Everest being any higher than at any other equal altitude on Earth (though this may be a bad example due to the high mass of the planet).


Also, just to throw this in, Mercury has a non-spherical exosphere due to stellar wind effects.
JGodbaz
QUOTE (Hungry4info @ May 2 2010, 10:47 AM) *
I think you're right, nprev. We don't see the atmospheric pressure at the top of Mt Everest being any higher than at any other equal altitude on Earth (though this may be a bad example due to the high mass of the planet).


The air pressure tends to be substantially lower at the poles, even at the same altitude. For example, the summit of Denali (at about 6.2 km) has an air pressure equivalent to that at 6.9km altitude in the Himalayas (say Everest).
Hungry4info
Could that be explained by both Earth's rotation and the polar temperature?
Paolo
Lutetia flyby navigation to start end of May http://sci.esa.int/science-e/www/object/in...fobjectid=47040
Note also that Rosetta's instruments have been used to collect a lightcurve of Vesta recently
Explorer1
Incidentally, is there a particular method for pronouncing Lutetia? Is it phonetic or what? It's bothered me for a while and I'd like to clear it up before Rosetta gets any closer. wink.gif
volcanopele
I've been going with LOOT-eh-shee-ah. Not sure if it is right, though.
Paolo
QUOTE (volcanopele @ May 24 2010, 10:06 AM) *
LOOT-eh-shee-ah


should be approximately loot-eh-see-ah
ElkGroveDan
I think Paolo's version is closer, but I've also heard it said as loo-TET'-see-ah
Stu
I'd have thought "Loo-TAY-shee-ah" myself...
ugordan
Loo-TEE-shee-ah?
Bart
Well, since it is the Latin name for Paris, I would defer to our French members.
nprev
Okay, I'll play: "Loo-TEE-sha". smile.gif
jekbradbury
The Wikipedia article says it's /ljuːˈtiːʃiə/ (lew-TEE-shee-uh) but also says it's possible to pronounce it as Latin (Lutētia), that is, loo-TAY-tee-ah.
nprev
Beginning to appreciate the IAU's asteroid numbering system more & more...I know how to say "21". rolleyes.gif
Paolo
There are two very interesting papers on adaptive optics observations of Lutetia on arXiv today:
Physical properties of ESA/NASA Rosetta target asteroid (21) Lutetia: Shape and flyby geometry
The triaxial ellipsoid dimensions, rotational pole, and bulk density of ESA/NASA Rosetta target asteroid (21) Lutetia
turns out Lutetia spins on its side like Uranus, and one entire hemisphere will not be illuminated when Rosetta swings by. As for the shape,

QUOTE
asteroid (21) Lutetia is well described by a wedge of Camembert cheese (justifying the Parisian name of Lutetia)


laugh.gif
charborob
Rosetta has started imaging Lutetia. Not much to see yet. The images are used for navigation purposes.
http://webservices.esa.int/blog/post/5/1191
tasp
Can't see the moons or rings or volcanoes yet . . . .


Reassuring the craft is on target and the trajectory tweaks are being computed. Getting pretty excited to see this rock up close.
dilo
QUOTE (Paolo @ May 31 2010, 03:02 PM) *
There are two very interesting papers on adaptive optics observations of Lutetia on arXiv today:
Physical properties of ESA/NASA Rosetta target asteroid (21) Lutetia: Shape and flyby geometry
...

From first article I made this rough animation of the rotating asteroid (time intervals aren't proportional):
Click to view attachment
North is up/above image plane

EDIT: I removed second frame in order to have more fluid/consistent rotation
cassioli
QUOTE (Bart @ May 24 2010, 07:25 PM) *
Well, since it is the Latin name for Paris, I would defer to our French members.

I'm from Italy and I studied LAtin at school.
I think "LOOT-eh-shee-ah" is wrong due to the "H" in "shee".
I think the best aproximation in your proposals is "loo-TET'-see-ah ", as the second T must be read as a Z; I mean, "Lutetia" would be "Lutezia" in Italian. Unfortunately looks like you have no "Z" sound in English, so you need to "aproximate" it by "ts", just as you like when saying "grazie" (="thanks").
vikingmars
[quote Unfortunately looks like you have no "Z" sound in English... [/quote]
Yes, we have ! laugh.gif
Click to view attachment
Mongo
Both German and Italian use the letter Z to represent the "ts" sound. Strange that both languages' orthographic systems have this feature, since German and Italian are not that closely related within the Indoeuropean language family. Perhaps their time joined together under the Holy Roman Empire was one reason for this shared orthographic feature.
cassioli
QUOTE (Mongo @ Jun 24 2010, 04:32 PM) *
Perhaps their time joined together under the Holy Roman Empire was one reason for this shared orthographic feature.

"Romans. Romans everywhere". unsure.gif
tongue.gif
Hungry4info
Rosetta Right on Target for Lutetia flyby
http://webservices.esa.int/blog/post/5/1223

QUOTE
With the latest orbit determination and following the flight rules, there will be no manoeuvre [needed] at the TCM [trajectory correction manouevre] slot 40 hours before the flyby. Also, it is considered that there will be no need to use the manoeuvre slot at 12 hours before the flyby, unless a anything changes.


Gentle reminder that it's in 3 more days...
alan
Love this quote from the Planetary Society blog
QUOTE
Mindful of media interest in the encounter -- but also of the World Cup schedule -- ESA plans to have the first black-and-white images prepared for public release around 21:05 or possibly later if the Third Place match runs into overtime.
dmuller
The ESA operations center ESOC is in Darmstadt, Germany, and Germany is in that game against Uruguay. So I guess they want to avoid publishing that "spherical leather-like surface with hexagonally shaped canyons" as the surface of Lutetia.
wheel.gif
cassioli
any new image of the approaching?!? huh.gif

which "on ground" resolution will the onboard camera be able to reach?
charborob
QUOTE (cassioli @ Jul 8 2010, 01:50 AM) *
which "on ground" resolution will the onboard camera be able to reach?

If I didn't make mistakes in my calculations, resolution should be around 60m/pixel.
elakdawalla
They won't actually resolve Lutetia as an object with a shape until hours before closest approach, so while they could technically be posting more approach photos, they wouldn't really look any different from the ones already posted.
Enceladus75
Looking forward to this flyby as it will add yet another asteroid to the list of objects visited by a spacecraft and studied up close. smile.gif Will Rosetta be taking other measurements of Lutetia apart from images?
elakdawalla
Enceladus75, the answer to your question was posted earlier today on Rosetta's excellent official blog.
Enceladus75
QUOTE
Enceladus75, the answer to your question was posted earlier today on Rosetta's excellent official blog.



Thanks a million Emily. smile.gif I'll take a look at that link in a short while.
Alan Stern
QUOTE (Enceladus75 @ Jul 8 2010, 02:45 PM) *
Looking forward to this flyby as it will add yet another asteroid to the list of objects visited by a spacecraft and studied up close. smile.gif Will Rosetta be taking other measurements of Lutetia apart from images?



Yes, IR mapping spectroscopy, thermal mapping, UV coma searches, UV reflectance spectroscopy, magnetic field search, the list goes on...
Phil Stooke
http://webservices.esa.int/blog/post/5/1231

Getting bigger!

Phil
dmuller
I have (at last!) added the "angular diameter" and other calculations to my realtime simulation at http://www.dmuller.net/rosetta
belleraphon1
Another worldlet coming into our view... love it!

Craig
maschnitz
(Aside: hey, dmuller - ESA linked to you - http://webservices.esa.int/blog/post/5/1232 smile.gif )
Hungry4info
According to the Rosetta Real-Time Simulation, they've started the flip manouevre.
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