Asteroid 21 Lutetia.

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Decided to put all Main Belt Asteroid 21 Lutetia imagery to date from the ESA Rosetta Spacecraft in one place.

21 Lutetia has a diameter of approx 132 KM / 82 miles, & orbits the Sun in the main Asteroid Belt between the orbits of Mars & Jupiter.

21 Lutetia orbit's the sun in a mildly elliptical, but stable orbit, with a close point to the sun of 189.63 million miles or 2.04 times the Earth to Sun distance, with a far point of 263.20 million miles or 2.83 times the Earth to Sun distance once every 3 years & 292 days (a 21 Lutetia year).

The large asteroid rotates on it's side with a tilt of approx 85 degrees (Earth has a tilt of 23.5 degrees, hence our seasons), so 21 Lutetia has some severe seasons as around a solstice near enough one 'hemisphere ' of the asteroid is is contant sunlight, whilst the other is in total darkenss, with even amounts of sunlight around the equinoxes. This means that at a 'summer' Solstice the Sun passes almost overhead of a pole, with the equator running along the day / night boundary.

Calculations show that in high Summer, the maximum surface temperature may reach a dizzying high of Minus 7 Celsius / 19 F, we get colder than that here in Ashford, Kent, UK sometimes in Winter & Spring.

However on the shadowed night side, temperatures are likley to drop to around or even below Minus 230 Celsius / Minus 382 F, cold enough to freeze Methane, Oxygen & Nitrogen & liquefy Hydrogen.

Just to report, my take & a few snippets picked up, the images from closest approach are EVEN better than anticipated. The whole of 21 Lutetia at closest approach was seen to 60 metre resolution, due to the precise tracking of Rosetta. 95 metre resolution was anticipated, but 60 being achieved, is just astonishing.

Also 21 Lutetia appears to me (I have been working on a few images, see previous posts) to be a primitive Type C body, though without compositional data, cannot say for sure.

There is a large basin, over 60 KM wide on the 132 KM by 101 KM by 76 KM wide asteroid, there are grooves, very similar to those on the Mars moon Phobos & the few seen on asteroid 951 Gaspra, as seen by the Jupiter bound Galileo Spacecraft.

There are boulders, craters of all sizes, a landslide in at least one crater & the shape of 21 Lutetia is multifaceted (that was expected). There are virtually no changes in albedo.

Later today, Sunday 11th July 2010, there will be full colour images & maybe more B & W imagery. The image from 80,000 KM looking reddish was taken through a red filter & is not actual colour, although 21 Lutetia, may turn out reddish, we'll see.

To me, the approach to 21 Lutetia suggests to me that the large 132 KM wide asteroid rotates in a prograde direction, west to east like Earth & that 21 Lutetia may have been caught near an equinox, based on how the appearance of the shape of 21 Lutetia during approach seem to suggest an equinoxial approach. 21 Lutetia is thought to rotate at a tilt of 85 degrees, on it's side basically, once every 8 hours & 10 minutes.

There appear to be no moons orbiting 21 Lutetia unlike 243 Ida.

Some craters appear to have dark floors like asteroid 243 Ida as seen by the Jupiter bound Galileo Spacecraft.

Other data, concerning potential dust, outgassings & fields & particles will be released later.



Early 21 Lutetia approach images enlarged & sharpened by me.




21 Lutetia with Saturn in background.

21 Lutetia limb.

21 Lutetia. Highly grooved like Phobos.

Two clickable thumbnails for full sized images. 21 Lutetia is highly grooved.

Part of the highly detailed limb enlarged sharpened crop of 21 Lutetia.

Full resolution 'crescent' 21 Lutetia, as Rosetta looks back.

Clickable thumbnail 4 views near closest approach of 21 Lutetia.

One of the final approach images of 21 Lutetia.

An enlarged sharpened crop of some grooves on 21 Lutetia. Boulders can also been seen. My guess is that this area is approx 20 KM wide.

An enlarged sharpened crop of some grooved terrain including a few isolated ones at right angles on 21 Lutetia. My guess is that this area is approx 20 KM wide.

An enlarged, sharpened crop of the basin on 21 Lutetia, oblique view earlier during the approach.

An enlarged, sharpened crop of the basin on 21 Lutetia, oblique view later & closer during the approach.

Enlarged, sharpened crop of the 'bottom' south polar region (???) of 21 Lutetia

Enlarged sharpened crop of an area approx 20 KM wide on the terminator. If you look carefully at the craters, some appear to have slightly darker floors, much like some on asteroid 243 Ida.

Enlarged, sharpened contrast enhanced crop of crater approx 20 KM wide with boulders & a possible landslide.

Enlarged, contrast & brightness adjusted sharpened view of 'crescent' 21 Lutetia as Rosetta departed & looked back.

Enlarged, sharpened crop of floor of central 20 KM portion of basin.

Enlarged, sharpened crop of 20 KM wide 'smoother' area, either a ghost crater likely filled with regolith or a massive landslide.

Enlarged, sharpened crop 19.5 KM area enhanced contrast of another region heavily grooved.

Enlarged, sharpened crop of a 16.5 KM area with a sharp crater with interneal striations, certainly debris sliding down the crater walls & at least one large boulder just to the outside at the 1 o'clock position.

Enlarged, sharpened, contrast enhanced crop rotated 90 degrees of a 35 KM portion of limb, rotated to look like a horizon. That lump or mountain is approx 5,000 metres tall.

Below an enlarged, contrast enhanced, sharpened crop of a 17.5 KM wide section of the large basin on the eastern side, showing parallel grooves on 21 Lutetia & these look very much like many of those on the Mars moon Phobos.

Below, Emily Lakdawalla has created a new montage of asteroids & comets to scale, with 21 Lutetia included. Shows how large she really is.

Below is all credit to Emily Lakdawalla, clickable thumbnail of relative sizes of asteroids & comets visited to date.

30 KM wide area on the second to last one during approach of 21 Lutetia (2 minutes prior to closest approach). Both dark floored craters & grooves are visible. At closest approach this area was visible but was very highly foreshortened. Resolution was still an excellent 70 metres (still far superior to what was anticipated for closest approach)

A section of 35 KM wide section of limb rotated 90 degrees, a 5,000 metre tall mountain (was bottom left).

Same area as above but from a slightly different angle.

A 20 KM section of limb rotated 90 degrees. A few narrow grooves are visible, small dark floored craters & what looks like a valley on 21 Lutetia.


Andrew Brown.


Hi Andrew,
Great Pictures thanks. Do you know off hand how the predidcted shape of 21 Lutetia was determined? Was it from ocultaion observations or some other method?


*drools* These are the best pictures we'll have of a really large asteroid until Dawn gets to Vesta and shows us what the phrase "really large asteroid" actually means. Very very cool!


Thanks very much Andrew. She is absolutely beautiful.


A bit of an off the wall question...
Regarding those impossibly large craters that seem to appear on asteroids and small moons. Is there any possibility that instead of being craters caused by impacts that some of them could be large cavities that have collapsed? I've heard these objects being described as of a low density and possibly poreus. I look at 21 Lutetia and imagine something like (I really hate to say this) a chunk of swiss cheese.


Thanks everyone, my health has taken a big hit, but hopefully will be back properly soon.

Interesting kg.

ESA has not released any gravity or compositional data as yet, infact nothing else since the brief flurry after the encounter.

I am of the opinion that the vast majority of the craters are of impact origin, though a few could well be collapsed pits.

If 21 Lutetia turns out to have a low density, like Asteroid 253 Mathilde, Jupiter moon Amalthea & Saturn moon Hyperion, then certainly, there could be internal voids & caverns, thus the possiblilty oif collapse features.

The only collapse feature I've seen to date on 21 Lutetia is a landslide, though that in itself proves nothing other than the material that collapsed was not very coherent, but does not in itself prove that 21 Lutetia is a low density body, if anything may prove the opposite, there's enough gravity on 21 Lutetia to cause collapses.

However until ESA releases the gravity & compostional data, as well as further images, including true colour ones, I can only clutch at straws with what I can see so far.

Below an enlarged, sharpened crop of a 40 KM wide area from the north rim of the basin on 21 Lutetia, showing a deceptively smooth region. We saw similar on the Saturn moon Mimas with regards to the Herschel Crater.



Andrew Brown.


Just thought I would put this on here too for completeness.

Newly seen image. 21 Lutetia. 3 minutes after CA. Approx 'Last Quarter' phase.


Andrew Brown.


Did any news on Lutetia, especially compositional wise, come out of the DPS 2010 conference?


This is the only one i know of on the subject :

SDC : Huge Asteroid Wrapped in Thick Dust Blanket
By Mike Wall Senior Writer
posted: 05 October 2010
02:46 pm ET

If astronauts ever visit the asteroid Lutetia, they may have to strap on snowshoes to avoid sinking into its nearly half-mile-thick layer of dust.

Dusty debris shrouds the huge asteroid to a depth of at least 2,000 feet (600 meters), scientists have calculated. The dust probably resembles the regolith found on the moon, and it's a result of the intense cosmic pummeling Lutetia has endured from other space rocks since the birth of the solar system.

"It must have been produced by impacts," said Rita Schulz of the European Space Agency in a media briefing yesterday (Oct. 4) in Pasadena, Calif. The announcement came at a conference organized by the American Astronomical Society's Division of Planetary Sciences.
Rosetta has revealed other intriguing details about Lutetia. Using data gathered by the probe's instruments, scientists were able to estimate the asteroid's density. And the results suggest Lutetia is a solid piece of rock, not a loosely agglomerated "rubble pile" that many other asteroids are suspected to be.
Schulz said more Lutetia revelations will be forthcoming after the research team spends more time with Rosetta's data.


marsbug":382rj53n said:
Thanks! At least I didn't miss any big announcements.

Hi marsbug,

Do not fear, there are a few of us on here who are very, very interested in 21 Lutetia updates & would love to know more about this huge mysterious asteroid.

If I miss anything straight away, EarthlingX or Wayne usually picks it up, so if anything else of value turns up, one of us will certainly pick up on it & bring it here or on the Rosetta thread.

ESA still seem to be analysing the data, but it would be nice to get a few more images, some in colour as well as magnetometer & compositional data. No news either on any possible outgassings as Rosetta did carry out a search for an exosphere. I doubt one exists, but you never know!!!!!

At least we have the density now, 3.34 GM[super]3[/super] CM, the same as a solid coherent type S (silicate) rich asteroid, like 951 Gaspra, or 433 Eros. Certainly denser than expected for a type C (Carbonaceous Chondrite), but less dense than a type M (Metallic). Images suggest a very primitive surface, more akin to a type C or D.

Hopefully we'll find out for sure before too much longer.

I checked again earlier, but there's no news regarding 21 Lutetia. Rosetta thpough has made an interesting observation of the object P/2010 2A, the tiny asteroid leaving a dust trail in the Asteroid Belt from a very recent collision, possibly in February or March 2009. Rosetta made the observation back in MARCH, only updated late yesterday on their site.

Andrew Brown.


3488":3vmzxjxh said:
Rosetta thpough has made an interesting observation of the object P/2010 2A, the tiny asteroid leaving a dust trail in the Asteroid Belt from a very recent collision, possibly in February or March 2009. Rosetta made the observation back in MARCH, only updated late yesterday on their site.

Andrew Brown.

Technically, the designation P/2010 2A means the object is being classified a comet, not an asteroid.


MeteorWayne":2ahepod7 said:
3488":2ahepod7 said:
Rosetta thpough has made an interesting observation of the object P/2010 2A, the tiny asteroid leaving a dust trail in the Asteroid Belt from a very recent collision, possibly in February or March 2009. Rosetta made the observation back in MARCH, only updated late yesterday on their site.

Andrew Brown.

Technically, the designation P/2010 2A means the object is being classified a comet, not an asteroid.

Though therys point it to bing a collision right?

Also, my favorite asteroid is now 21 Lutetia.
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