[meteorite-list] Does Asteroid Vesta Have a Moon?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 8 Jul 2011 22:15:20 -0500
Message-ID: <439120DD9C54414F82EB0B81E266DA84_at_ATARIENGINE2>

Doug, Richard, List,

Most satellites whose mass ratio (compared to their
primary) is very small are almost certainly "captures."
Deimos, Phobos, the small stuff around the gas giants.
Every satellite has a history of argument about its origins.
Opinion drifts with the decades. Right now we like the
Whack theories for Earth-Moon, Pluto-Charon. Neptune's
Triton is a much disputed case (retrograde orbit). The
formerly popular theory that gas giant satellites formed
in place like little solar systems died away as it became
obvious from computer modeling that "mini-solar-systems"
were a no-go. Odd things happen: it looks like Saturn's
Miranda was blown apart and then re-accreted without
the pieces ever escaping.

As for Vesta, I don't think there are any Vestan moons.
Photographic surveys in the vicinity of Ceres (0.028 gee
and an escape velocity of only 510 m/s) yield a 90%-plus
certainty of no satellite as big (or as small) as 1000 meters
diameter. I suspect the Dawn approach photos are being
done because no one has searched for Vestan satellites
before now, and just think of how embarassing it would
be to run into one....

As for the Vestoids, the energy requirement for ejecta to
be transfered to such orbits is not trivial. The average
delta-v to move a mass from one asteroid orbit to a differing
orbit a fraction of an AU away averages about 5000 m/s of
total velocity change. This implies very energetic events
were required to move the ejecta out and a lot of strong
perturbations over a long time to regularize those orbits.

And, if there is a Vestan satellite, there's a good chance
it will show up in the year that Dawn there, whether
detected in advance or not.


Sterling K. Webb
--------------------------------------------------------------------------
----- 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: Friday, July 08, 2011 7:10 PM
Subject: 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/2011/06jul_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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Received on Fri 08 Jul 2011 11:15:20 PM PDT