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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 7 Jul 2011 21:54:41 -0500
Message-ID: <4232167DB8074CB2B5BF6493FA0DCFB4_at_ATARIENGINE2>

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 Thu 07 Jul 2011 10:54:41 PM PDT