[meteorite-list] Does Asteroid Vesta Have a Moon?
MexicoDoug
mexicodoug at aim.com
Fri Jul 8 22:17:26 EDT 2011
Hi Richard, Sterling and Listees,I would think some spectroscopic
measurements for starters on the so far undiscovered (but wished for)
ejected fragment "moon" and comparison with other Vestoids - would make
a much stronger link among the V-class asteroids, allegedly Vestoids,
that span the distance between Vesta and the Kirkwood gap of interest
which delivers material to the inner Solar system. Anyway that was a
point I tried to make in my original post, so yes in that sense. It
would be nice to have a sample of said moon to measure ;-)I did a
little bit of digging since I sent my last thoughts on ejection
velocities in response to Sterling's message that ejection of a moon
during "the event" into Vesta orbit was unlikely. Some great
literature is out there and as I naively thought, it is ejecta patterns
that can be used to firm up maximum fragment sizes and their
corresponding impact velocities.In summary we showed in our posts that
the range of ejection velocities needed to be between 247 - 350 m/s.
Well - these same questions interestingly enough came up when Binzel
originally linked the HED meteorites to the V-class asteroids and
suggested how they could reach the Kirkwood gap (3:1). It was
interesting to see the worry in that case: They seemed worried that a
[fast] ejection velocity of 700 m/s was needed to make it all the way
to the gap and thus some get free samples delivered on earth. To
establish this link, they looked at asteroids that were between Vesta
and the gap to make the bridge and thus the whiole idea more palatable;
in order to link them back to Vesta by looking at their orbits and that
of Vesta, they figured it for a match if the actual ejection velocities
were around 500 m/s. So basically, we have a range of Vestoids,
supposedly, with ejection velocities between 500 - 700 m/s ejection
velocities. Now - suddenly the range of 247 - 350 m/s doesn't look bad
at all. More like - how could there not be... They were dealing with
5-10 km diameter Vestoids, to give an idea of size.There has also been
a lot of insteresting stuff published on secondary impact cratering and
predicting ejection velocity - which does allow for the Vesta oribital
velocity range, though they were done only for craters only up to about
100 km in diameter.Finally, this paper should be of great interest!
Here it is for your enjoyment which discussed Vestoid ejection. The
last graph says to me that they used data from Binzel to show that
"Vestoids" ejection velocity clusters around 300 m/s for roughly 6.5 km
fragments which are the size he must have basically gotten data on.
Well, that just happens to fall smack in the middle of the velocity
range which will result in Vesta orbit! I must be reading that
logarithmic graph wrong or squinting too much ... or their 65 km
"impactor radius" is off?ref: Planetary and Space Science 52 (2004)
1103–1108Ejecta size-velocity relation derived fromthe distribution of
the secondary craters of kilometer-sized craters on MarsYoshiaki
Hirasea, Akiko M. Nakamuraa,, Tatsuhiro MichikamibIn conclusion, my
major worry now of finding a genetic Vestoid-type moon now is not
whether it could be ejected into orbit. It's just a gut feeling that
billions of years is a long time to ask for stability in the Solar
system of what's going on around asteroids. At least .... Vesta has
one of the biggest tractor beams in its class ;-) (its gravity is a wee
fraction of a gee to us, but hey - it's just the way a tiny branch is
to a twig - to someone else you are big!). But I think they have a very
good chance. A very, very good chance ... if all the current beliefs
are close to explain what happened.He're a link for
levity:http://www.youtube.com/watch?v=Z_gB9beh0bc#t=00m30sBest
wishesDoug-----Original Message-----From: Richard Montgomery
<rickmont at earthlink.net>To: sterling_k_webb at sbcglobal.net;
baalke at zagami.jpl.nasa.gov; meteorite-list at meteoritecentral.com;
MexicoDoug <mexicodoug at aim.com>Sent: Fri, Jul 8, 2011 8:10 pmSubject:
Re: [meteorite-list] Does Asteroid Vesta Have a Moon?Hi Sterling, Doug
and List... My query concerns what we'll find pending whether a
possible moon is of Vestan origen, or otherwise captured: would not an
escaped impact fragment "off the ol' block," considering the impact and
escape velocities also point to re-crystallization/ re-setting of
certain atomic clocks/ et all, substantiate current theory of our
HEDs? We've got to love the "capture" theory...think of the romance.
Should 4Vesta indeed have a moon or few, "captured" and not ejected
(per the impact velocity discussion above), the petro- mineral- and
chemical -logic composition of the hostage will be the
cheery-on-top! Alas, we wait and see. As is ours to
discover!! Richard Montgomery ----- Original Message ----- From:
"MexicoDoug" <mexicodoug at aim.com> To: <sterling_k_webb at sbcglobal.net>;
<rickmont at earthlink.net>; <baalke at zagami.jpl.nasa.gov>;
<meteorite-list at meteoritecentral.com> Sent: Thursday, July 07, 2011
9:53 PM Subject: Re: [meteorite-list] Does Asteroid Vesta Have a
Moon? Hi Sterling, For your run of the mill asteroid and some random
impact, that would be a pretty good summary ... But personally, I
think in the case of Vesta is anything but run of the mill (i.e.,
commonplace) - anything could be possible. I think, whether a Moon is
found or not, the answer to Richard's question regarding possibility
could be figured out by looking at the ejecta pattern and size
distribution. You may be right about the possibilities and you severely
limit the case by supposing a 5 km size giant rock. I want to
generalize this more - the article we commented on tenderly referred to
the Dawn Spacecraft becoming a moon of Vesta - so in that spirit we are
talking about a 2 meter diameter one ton cube with Solar Panels and
antenna. Thinking about the Meteor Crater or even bridging it to
Carancas (see the picture of the tossed bedmud ;-) ) e.g., Svend's
first
picture: http://www.meteorite-recon.com/en/meteorite_carancas.htm Could
one such boulder fall into the correct velocity range as you radiate
outwards from the point of impact? Well, what is that
velocity range? Well, Sterling: you gave us the escape velocity, but
that is only one point. To better answer the question, we need to know
the range. As you mentioned, the escape velocity is 350 m/s, so it
would be less: but how much less to get our arms around this beast?
I'll spare the calculation, all you need to do is divide 350 by square
root of 2 to get the minimum velocity to attain orbit around Vest's
surface. So it's 247 m/s. Thus the range of upward velocity (in is 247
to 350 m/s for Vesta. That's a big chunk of range. In English units 552
mph to 783 mph (cruising speeds for commercial airliners up to about
Mach 1). You say: "Only "close" moons are likely to be "chips off the
old block." I disagree with this too: since I don't see a reason that
a 247 - 275 m/s velocity would be favored for example over 275 - 350
m/s in one of these events, but I suppose if you want to focus on the
range close to escape velocity you could argue that point well ... and
that more distant captures are more likely statistically so I'll leave
that one alone since we are now talking about comparing two
probabilities we don't know anything much about. It happens that the
247 - 350 m/s velocity range to launch from and orbit Vesta is right at
the middle of the muzzle velocities of a the common .22 caliber rifle
(which would make Vesta the ideal cartoon world to shoot bullets in
ellipses and have them go around and put a hole in the back of the
shooter's head.) Do I think a small chunk could be ejected and go into
orbit? ===> Most definitely. Do I know the probability? No. Do I think
piles of rubble in the 247 - 350 m/s range could have been ejected -
yes. Could it have been hot from impact? Yes, hypothetically. Would it
form a body - Maybe not, I don't know. But if Carancas and Meteor
Crater are any indication I would think it wasn't as poor odds as your
post might lead one to believe whether you believe in chunks or rubble
piles. Especially considering there were a great deal more of kg's
ejected from Vesta in that impact. It's thought 1% of the Asteroid's
mass, which comes out to 2,500,000,000,000,000,000 kg. Could 1000 of
them be included? Sure! Could anything a lot bigger be ejected in that
velocity range. I dunno but there are many tons of mass to play with in
different impact scenarios in a crater half the size of
Germany. Kindest wishes Doug Think Meteor Crater -----Original
Message----- From: Sterling K. Webb <sterling_k_webb at sbcglobal.net> To:
Richard Montgomery <rickmont at earthlink.net>; Ron
Baalke <baalke at zagami.jpl.nasa.gov>; Meteorite Mailing
List <meteorite-list at meteoritecentral.com> Sent: Thu, Jul 7, 2011 10:54
pm Subject: Re: [meteorite-list] Does Asteroid Vesta Have a
Moon? Given Vesta's relatively low gravity -- 0.022 gee -- and its low
escape velocity -- 350 m/s -- it would be very heard to smash Vesta
hard enough to knock a chunk, oh, say, 5 km across off that hard
rock and yet have it have so little energy that it moved slower than
350 m/s, which is a mere 783 mph. Much more likely scenario of a
"moon" is a capture of a totally unrelated space rock. Lots of
origin theory smoke, no data measurement fire. That is, we don't know
the compositions of the minor planet moons we do know about, and we do
know about quite a
few: http://en.wikipedia.org/wiki/Minor_planet_moon Only "close" moons
are likely to be "chips off the old block." Sterling K.
Webb --------------------------------------------------------------------
- ----- Original Message ----- From: "Richard
Montgomery" <rickmont at earthlink.net> To: "Ron Baalke"
<baalke at zagami.jpl.nasa.gov>; "Meteorite Mailing
List" <meteorite-list at meteoritecentral.com> Sent: Thursday, July 07,
2011 8:09 PM Subject: Re: [meteorite-list] Does Asteroid Vesta Have a
Moon? > List, > Considering the possible plausibility of a pending
companion 'moon' > orbiting Vesta (or two???); and considering Mexico
Doug's last > contribution.... I pose a question: > > How could that
grand ol' impact evidentiary-crater produce a moon of > the ssame
petrologic composition of Vesta's primary/current > achondritic
compostition be similar, due to a greater resultant
> mb-recrystalization from impact, than the host? > > Curious, Richard
Montgomery > > > > ----- Original Message ----- > From: "Ron
Baalke" <baalke at zagami.jpl.nasa.gov> > To: "Meteorite Mailing List"
<meteorite-list at meteoritecentral.com> Sent: > Thursday, July 07, 2011
10:07 AM Subject: [meteorite-list] Does Asteroid > Vesta Have a
Moon? > >> >> http://science.nasa.gov/science-news/science-at-nasa/2011/0
6jul_vestamoon/ >> >> Does Asteroid Vesta Have a Moon? NASA Science
News July 6, 2011 July 6, >> 2011: NASA's Dawn spacecraft is closing in
on Vesta, and from >> now until the ion-powered spacecraft goes into
orbit in mid-July, >> every >> picture of the giant asteroid will be
the best one ever taken. What will >> researchers do with this
unprecedented clarity? "For starters," says Dawn >> chief engineer Marc
Rayman, "we're going to >> look for an asteroid moon." You might think
of asteroids as isolated >> bodies tumbling alone >> through >> space,
but it's entirely possible for these old "loners" to have >>
companions. Indeed, 19-mile-wide Ida, 90-mile-wide Pulcova,
103-mile-wide >> Kalliope, and 135-mile-wide Eugenia each have a moon.
And 175-mile-wide >> Sylvia has two moons. Measuring 330 miles
across, Vesta >> is >> much larger than these other examples, so a
"Vesta moon" is entirely >> possible. Where do such moons come from?
Rayman suggests one source: >> "When another large body collides
with an >> asteroid, the resulting debris is sprayed into orbit around
the >> asteroid >> and can gradually collapse to form a moon." Another
possibility is >> "gravitational pinball": A moon formed
>> elsewhere >> in the asteroid belt might, through complicated
gravitational >> interactions with various bodies, end up captured by
the gravity of one >> of them. Hubble and ground based telescopes have
looked for Vesta moons >> >> before, >> and seen nothing. Dawn is
about to be in position for a closer look. This >> Saturday, July 9th,
just one week before Dawn goes into orbit around >> Vesta, the moon
hunt will commence. The cameras will begin taking images >> of the
space surrounding the asteroid, looking for suspicious specks. "If >> a
moon is there, it will appear as a dot that moves around Vesta in >>
successive images as opposed to remaining fixed, like background
>> stars," >> says Dawn Co-investigator Mark Sykes, who is also
director of the >> Planetary Science Institute. "We'll be able to use
short exposures to >> detect moons as small as 27 meters in diameter.
If our longer >> exposures >> aren't washed out by the glare of nearby
Vesta, we'll be able to >> detect >> moons only a few meters in
diameter." While you won't see "find a moon" >> among the mission's
science goals, a moon-sighting would be a nice >> feather in Dawn's
cap. Not that it will >> need more feathers. The probe is already
primed to build global maps and >> take detailed images of the
asteroid's surface, reveal the fine >> points >> of its topography, and
catalog the minerals and elements present >> there. >> >> Besides, Dawn
will become a moon itself when it enters orbit around >> Vesta. And the
probe's motions as it circles will provide a lot of >> information
about the rocky relic. Sykes explains: "We'll use the >> spacecraft's
radio signal to measure its motion around Vesta. This will >> give us a
lot of detailed information about the asteroid's gravitational >>
field. We'll learn about Vesta's mass and interior structure, including
>> its core and potential mascons >> (lumpy >> concentrations of
mass)." As you read this, the spacecraft is gently >> thrusting closer
to its target. And with the navigation images alone >> we're already
watching a >> never-before-seen world grow ever larger and clearer.
"The pictures are >> beginning to reveal the surface of this battered,
alien world," says >> Rayman. "They're more than enough to
tantalize us. >> We've been in flight for four years, we've been
planning the mission for >> a decade, and people have been looking at
Vesta in the night sky for two >> centuries. Now, finally, we're coming
close up to it, and we'll be >> getting an intimate view of this
place." This is not only the first time >> a spacecraft has visited
this alien world, it's also the first time a >> spacecraft has visited
a massive body we haven't approached previously. >> In the past, rocket
ships have >> orbited >> Earth, the moon, Mars, Venus, Jupiter, Saturn,
and Mercury. "In each >> case, flyby missions occurred first, providing
a good >> estimate >> of the target's gravity along with information on
other aspects of its >> physical environment, including whether any
moons are present. This time >> we're much less certain what we'll
find." At a recent press conference, >> NASA Planetary Science Deputy
Director Jim Adams told reporters that Dawn >> will "paint a face on a
world seen >> only >> as a 'fuzzy blob' up to now." What does Rayman
think Vesta's face >> will >> look like? "Wrinkled, ancient, wizened,
with a tremendous amount of >> character that bears witness to some
fascinating episodes in the solar >> system's >> history." >> >> If a
new moon is among the episodes, Rayman has a name in mind. "How >>
about 'Dawn'?" Author: Dauna Coulter Editor: Dr. Tony Phillips Credit:
>> Science at NASA More Information Dawn Journal
>> <http://dawn.jpl.nasa.gov/mission/journal_06_23_11.asp> -- >> penned
by Dawn's chief engineer Marc Rayman Footnotes: (1) In addition to >>
having moons, asteroids can also be double: Binary >> asteroids
<http://apod.nasa.gov/apod/ap001101.html> sometimes form when a >>
spinning parent body splits. The body is spun up by a phenomenon called
>> YORP that occurs when the body absorbs photons from the sun and >>
reradiates them as heat: more >>
<http://www.news.cornell.edu/stories/March07/margot.yorp.html>. (2)
Dawn >> will perform dedicated observations in search of moons for
about 15 >> hours. However, if no moon is found at Vesta on July 9th,
that doesn't >> mean there isn't one. Rayman says: "If there is a moon,
it might show up >> by coincidence in other observations, but we have
no other observations >> dedicated in this mission to finding a moon.
There is just so much to >> learn about Vesta itself, that that is
where we are >> focusing >> our time." (3) From NASA press release:
When Vesta captures Dawn into its >> orbit on July 16, there will be
approximately 9,900 miles (16,000 >> kilometers) between them. When
orbit is achieved, they will be >> approximately 117 million miles (188
million kilometers) away from Earth. >> During the initial
reconnaissance orbit, at approximately 1,700 miles >> (2,700
kilometers), the spacecraft will get a broad overview of Vesta >> with
color pictures and data in different wavelengths of reflected light. >>
The spacecraft will move into a high-altitude mapping orbit, about 420
>> miles (680 kilometers) above the surface to systematically map the
parts of >> Vesta's surface illuminated by the sun; collect stereo
images to see >> topographic highs and lows; acquire higher-resolution
data to map >> rock >> types at the surface; and learn more about
Vesta's thermal >> properties. >> Dawn then will move even closer, to a
low-altitude mapping orbit >> approximately 120 miles (200 kilometers)
above the surface. The >> primary >> science goals of this orbit are to
detect the byproducts of cosmic rays >> hitting the surface and help
scientists determine the many kinds of atoms >> there, and probe the
protoplanet's internal structure. As Dawn spirals >> away from Vesta,
it will pause again at the high-altitude mapping orbit. >> Because the
sun's angle on the surface will have progressed, scientists >> will be
able to see previously hidden terrain while obtaining different >>
views of surface features. Credits: Dawn's mission to Vesta and Ceres
is >> managed by JPL for NASA's Science Mission Directorate in
Washington. Dawn >> is a project of the directorate's Discovery
Program, managed by NASA's >> Marshall Space >> Flight Center in
Huntsville, Ala. UCLA is responsible for overall >> Dawn >> mission
science. Orbital Sciences Corp. of Dulles, Va., designed and >> built
the spacecraft. The German Aerospace Center, the Max Planck >>
Institute for Solar System Research, the Italian Space Agency
and the >> Italian National Astrophysical Institute are part of the
mission >> team. >> JPL is managed for NASA by the California Institute
of Technology in >> Pasadena. For more information about Dawn, visit:
>> http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov >>
<http://dawn.jpl.nasa.gov/> . You can also follow Dawn on
Twitter at: >> http://www.twitter.com/NASA_Dawn . >>
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