[meteorite-list] Eros Findings Reveal New Way to Study Asteroids

From: Dawn & Gerald Flaherty <grf2_at_meteoritecentral.com>
Date: Wed Jul 20 21:03:51 2005
Message-ID: <02b501c58d8f$ff740340$6502a8c0_at_GerryLaptop>

Great application!
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, July 20, 2005 6:40 PM
Subject: [meteorite-list] Eros Findings Reveal New Way to Study Asteroids


>
>
> http://space.com/scienceastronomy/050720_eros_update.html
>
> Eros Findings Reveal New Way to Study Asteroids
> By Robert Roy Britt
> space.com
> 20 July 2005
>
> Most of what geologists know about Earth's interior comes
> from monitoring the seismic waves of earthquakes.
> Knowledge of the Moon's inner secrets was initially gleaned by slamming
> probes into it and studying the shock waves that careened through it.
>
> Now scientists have stumbled on a way to passively monitor the shaking
> of an asteroid to learn what it is made of.
>
> A new study of four-year-old data from NASA's NEAR-Shoemaker mission
> indicates that a set of vibrations caused by a collision with another
> space rock played a major role in sculpting the mug of asteroid Eros.
>
> The idea was first put forth in 2001, but it was speculative. Now, an
> outside expert says, they hypothesis is solid as a rock, and it tells
> a story of Eros' composition.
>
> Importantly, similar analyses could be used to passively peak inside
> other space rocks.
>
> Wild past
>
> Eros is 20 miles (33 kilometers) long and about 8 miles (13 kilometers)
> wide. It is the most well studied asteroid. NEAR-Shoemaker mapped Eros
> in detail back in 2000-2001 before officials executed a controlled and
> dramatic crash landing, the first-ever touchdown on an asteroid.
>
> Like any asteroid, Eros been banging around the solar system in some
> form for about 4.5 billion years.
>
> In the early days of the solar system, when things were more crowded,
> collisions were frequent.
>
> Some large asteroids become smaller. Some small rocks stuck together and
> grew. Many were scooped up by the fledgling Earth and the other planets.
>
> The asteroids that remain, confined mostly to a belt between Mars and
> Jupiter, harbor a tale of the solar system's formation. But first
> scientists have to figure out how to read their language, with an
> alphabet of craters and cracks and a grammar based largely on mineral
> composition and density.
>
> Among Eros' most striking features is an impact crater 4.7 miles (7.6
> kilometers) wide that scientists have determined was carved fairly
> recently. Another curious aspect to Eros is that across nearly 40
> percent of its surface, all craters up to about a third of a mile (0.5
> kilometers) wide have been erased.
>
> The smooth surface has puzzled scientists since the NEAR landing.
>
> Shaken, not stirred
>
> The new study, led by Cornell University researcher Peter Thomas, nixed
> one theory by determining that the vanished craters could not have been
> covered by material ejected in the recent large impact. Further, the
> locations of the erased craters suggests they were jiggled out of
> existence by the internal vibrations caused in the impact.
>
> The hypothesis, if right, can be used to glean an idea of how the
> asteroid is constructed. Scientists have long wondered if asteroids were
> solid rocks or, as is likely in at least some cases, loose piles of
> rubble that have undergone many collisions and managed to hang together.
>
> "Our observations indicate that the interior of Eros is sufficiently
> cohesive to transmit seismic energy over many kilometers, and the outer
> several tens of meters [yards] of the asteroid must be composed of
> relatively non-cohesive material," Thomas and his colleague, Mark
> Robinson of Northwestern University, write in the July 21 issue of the
> journal Nature.
>
> That outer non-cohesive stuff would be regolith, which on Earth is
> called dirt and on our nearest natural satellite is known as Moon dust.
>
> "For the first time, the authors provide convincing evidence that makes
> this conclusion more than just reasonable conjecture," says Erik
> Asphaug, a scientist at the University of California, Santa Cruz who was
> not involved in the study.
>
> New opportunities
>
> The results confirm what Thomas first suspected back in 2001 and what
> University of Arizona's James Richardson Jr. found in separate work
> last year.
>
> The findings are likely to remake the way asteroids are studied.
>
> Scientists have used craters as a way to figure out how ancient or fresh
> a space rock's surface is. Myriad small craters suggest a long history
> and thus an old surface. A smoother surface with fewer craters would
> imply a rock had recently been cleaved or somehow resurfaced.
>
> At least that was the thinking.
>
> "This asteroidal Botox calls into question the habit of dating asteroid
> surfaces through their cratering record," Asphaug writes in a separate
> analysis in the journal.
>
> A rubble pile, Asphaug explains, would dampen vibrations during an
> impact. That would leave more small craters intact, causing the asteroid
> to appear older based on the conventional method of analysis.
>
> Eros, while it has a deep surface of loose material, is solid enough on
> the inside, at least in parts, to transmit seismic waves efficiently.
>
> If convention is indeed overturned, the shift could be a boon to space
> rock studies.
>
> The finding suggests large and newer impact craters, like the one on
> Eros, could be used as proxies for seismic data, Asphaug points out. The
> insides of other asteroids might be probed just by mapping their
> surfaces. "Thomas and Robinson's work also opens up a new way of looking
> at asteroids," he said.
>
> Perhaps the passive technique could even go active.
>
> Given the success of NASA's recent Deep Impact mission, which crashed a
> small probe into a comet, Asphaug sees value in a similar project that
> would first place seismic sensors on a space rock, so that the interior
> could be mapped during the collision.
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
Received on Wed 20 Jul 2005 09:03:24 PM PDT