[meteorite-list] Lutetia: a Rare Survivor from the Birth of the Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 11 Nov 2011 09:52:13 -0800 (PST)
Message-ID: <201111111752.pABHqD2d015322_at_zagami.jpl.nasa.gov>

http://www.eso.org/public/news/eso1144/

Lutetia: a Rare Survivor from the Birth of the Earth
European Southern Observatory
11 November 2011

New observations indicate that the asteroid Lutetia is a leftover
fragment of the same original material that formed the Earth, Venus and
Mercury. Astronomers have combined data from ESA's Rosetta spacecraft,
ESO's New Technology Telescope, and NASA telescopes. They found that the
properties of the asteroid closely match those of a rare kind of
meteorites found on Earth and thought to have formed in the inner parts
of the Solar System. Lutetia must, at some point, have moved out to its
current location in the main asteroid belt between Mars and Jupiter.

A team of astronomers from French and North American universities have
studied the unusual asteroid Lutetia in detail at a very wide range of
wavelengths [1] to deduce its composition. Data from the OSIRIS
camera on ESA's Rosetta spacecraft [2], ESO's New Technology
Telescope (NTT) at the La Silla Observatory in Chile, and NASA's
Infrared Telescope Facility in Hawaii and Spitzer Space Telescope were
combined to create the most complete spectrum of an asteroid ever
assembled [3].

This spectrum of Lutetia was then compared with that of meteorites found
on Earth that have been extensively studied in the laboratory. Only one
type of meteorite - enstatite chondrites - was found to have properties
that matched Lutetia over the full range of colours.

Enstatite chondrites are known to be material that dates from the early
Solar System. They are thought to have formed close to the young Sun and
to have been a major building block in the formation of the rocky
planets [4] , in particular the Earth, Venus and Mercury [5].
Lutetia seems to have originated not in the main belt of asteroids,
where it is now, but much closer to the Sun.

"But how did Lutetia escape from the inner Solar System and reach the
main asteroid belt?" asks Pierre Vernazza (ESO), the lead author of the
paper.

Astronomers have estimated that less than 2% of the bodies located in
the region where Earth formed, ended up in the main asteroid belt. Most
of the bodies of the inner Solar System disappeared after a few million
years as they were incorporated into the young planets that were
forming. However, some of the largest, with diameters of about
100 kilometres or more, were ejected to safer orbits further from the Sun.

Lutetia, which is about 100 kilometres across, may have been tossed out
from the inner parts of the young Solar System if it passed close to one
of the rocky planets and thus had its orbit dramatically altered [6].
An encounter with the young Jupiter during its migration to its
current orbit could also account for the huge change in Lutetia's orbit
[7].

"We think that such an ejection must have happened to Lutetia. It ended
up as an interloper in the main asteroid belt and it has been preserved
there for four billion years," continues Pierre Vernazza.

Earlier studies of its colour and surface properties showed that Lutetia
is a very unusual and rather mysterious member of the asteroid main
belt. Previous surveys have shown that similar asteroids are very rare
and represent less than 1% of the asteroid population of the main belt.
The new findings explain why Lutetia is different - it is a very rare
survivor of the original material that formed the rocky planets.

"Lutetia seems to be the largest, and one of the very few, remnants of
such material in the main asteroid belt. For this reason, asteroids like
Lutetia represent ideal targets for future sample return missions. We
could then study in detail the origin of the rocky planets, including
our Earth/," concludes Pierre Vernazza.
      
Notes

[1] The electromagnetic spectrum represents the complete range of
wavelengths covered by the different types of electromagnetic radiation.
Visible light is the most familiar form, but many others exist. Many of
these types of radiation are used in everyday life, such as radio waves,
microwaves, infrared and ultraviolet light and X-rays.

[2] The Rosetta spacecraft, on its way to comet
67P/Churyumov-Gerasimenko, flew past Lutetia on 10 July 2010.

[3] Rosetta's OSIRIS camera provided data in the ultraviolet, ESO's NTT
provided data in visible light, while NASA's Infrared Telescope Facility
in Hawaii and Spitzer Space Telescope provided data in the near-infrared
and mid-infrared respectively.

[4] The enstatite chondrites (E chondrites) are a unique class of
meteorites that account for only about 2% of the recovered meteorite
falls. The unusual mineralogy and chemistry of E chondrites is
consistent with formation relatively close to the Sun. This is further
supported by isotope measurements (verified for oxygen, nitrogen,
ruthenium, chromium and titanium): E chondrites are the only groups of
chondrites that have the same isotopic composition as the Earth and Moon
system. This strongly suggests that the Earth formed from enstatite
chondrite-type materials and also that E chondrites formed at about the
same distance from the Sun as the Earth.

In addition it has been recently shown that formation from enstatite
chondrite bodies can explain Mercury's unusual and previously
inexplicable composition. This suggests that Mercury - like the Earth -
largely accreted from enstatite chondrite-like materials.

[5] Although they all formed from similar material, it remains a mystery
why the inner three planets are so different.

[6] This process is very much like the gravitational assist methods used
to change the direction and speed of space probes by arranging for them
to fly close to a planet.

[7] Some astronomers think that the gaseous giant may have been closer
to the Sun in the early days of the Solar System, before moving outwards
to its current position. This would have caused havoc in the orbits of
other objects of the inner Solar System due to the huge gravitational
pull of Jupiter.

More information

This research was presented in a paper, "Asteroid (21) Lutetia as a
remnant of Earth's precursor planetesimals", to appear in the journal
Icarus.

The team is composed of P. Vernazza (Laboratoire d'Astrophysique de
Marseille (LAM), France; European Southern Observatory, Germany), P.
Lamy (LAM, France), O. Groussin (LAM, France), T. Hiroi (Department of
Geological Sciences, Brown University, USA), L. Jorda(LAM, France), P.L.
King (Institute for Meteoritics, University of New Mexico, USA), M.R.M.
Izawa (Department of Earth Sciences, University of Western Ontario,
Canada), F. Marchis (Carl Sagan Center at the SETI Institute, USA;
IMCCE, Observatoire de Paris (OBSPM), France), M. Birlan (IMCCE, OBSPM,
France), R. Brunetto (Institut d'Astrophysique Spatiale, CNRS, France).

ESO, the European Southern Observatory, is the foremost
intergovernmental astronomy organisation in Europe and the world's most
productive astronomical observatory. It is supported by 15 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland
and the United Kingdom. ESO carries out an ambitious programme focused
on the design, construction and operation of powerful ground-based
observing facilities enabling astronomers to make important scientific
discoveries. ESO also plays a leading role in promoting and organising
cooperation in astronomical research. ESO operates three unique
world-class observing sites in Chile: La Silla, Paranal and Chajnantor.
At Paranal, ESO operates the Very Large Telescope, the world's most
advanced visible-light astronomical observatory and two survey
telescopes. VISTA works in the infrared and is the world's largest
survey telescope and the VLT Survey Telescope is the largest telescope
designed to exclusively survey the skies in visible light. ESO is the
European partner of a revolutionary astronomical telescope ALMA, the
largest astronomical project in existence. ESO is currently planning a
40-metre-class European Extremely Large optical/near-infrared Telescope,
the E-ELT, which will become "the world's biggest eye on the sky".

Contacts

Pierre Vernazza
ESO, Astronomer
Garching bei M?nchen,, Germany
Email: pvernazz at eso.org

Philippe Lamy
Laboratoire d'Astrophysique de Marseille, Directeur de Recherche
Marseille, France
Tel: +33 49 105 5932
Email: philippe.lamy at oamp.fr

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei M?nchen, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook at eso.org
Received on Fri 11 Nov 2011 12:52:13 PM PST