[meteorite-list] Mauna Kea's Giant Eyes Reunite Comet Families

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Sep 15 18:49:39 2005
Message-ID: <200509152248.j8FMmSm05075_at_zagami.jpl.nasa.gov>

http://www.gemini.edu/index.php?option=content&task=view&id=154

Mauna Kea's Giant Eyes Reunite Comet Families

Thursday, 15 September 2005

Joint W.M. Keck, Subaru and Gemini Observatories Press Release


Science Contacts:

    * David Harker
      University of Caliifornia, San Diego
      (858) 822-4893
      dharker_at_ucsd.edu
    * Seiji Sugita
      University of Tokyo
      +81-4-7136-5520
      sugita_at_k.u-tokyo.ac.jp
    * Fred Chaffee
      W.M. Keck Observatory
      (808) 885-7887
      fchaffee_at_keck.hawaii.edu

Media Contact:

    * Peter Michaud
      Gemini Observatory, Hilo HI
      (808) 974-2510 (Office)
      (808) 937-0845 (Cell)
      pmichaud_at_gemini.edu

When NASA's Deep Impact mission ploughed into comet 9P/Tempel 1 on July
4th of this year, the giant telescopes on Mauna Kea had a unique view of
the massive cloud of dust, gas and ice expelled during the collision.
See previous Gemini release on observations here.
<http://www.gemini.edu/index.php?option=content&task=view&id=139>

A series of coordinated observations, made under ideal conditions by the
world's largest collection of big telescopes, delivered surprising new
insights into the ancestry and life cycles of comets. Specifically,
materials beneath the comet's dusty skin reveal striking similarities
between two families of comets where no relationship had been suspected.

The observations also allowed scientists to determine the mass of
material blasted out by the collision, which is estimated to be as much
as 25 fully-loaded tractor-trailer trucks.

The findings are based on the composition of rocky dust detected by both
the Subaru and Gemini 8-meter telescopes, and ethane, water and
carbon-based organic compounds revealed by the 10-meter W.M. Keck
Observatory. The results from these Mauna Kea
observations were made available in the September 16, 2005 issue of the
journal Science highlighting results from the Deep Impact experiment.

Comet Tempel 1 was selected for the Deep Impact experiment because it
circles the Sun in a stable orbit that allows its surface to be gently
baked with solar radiation. As a result, the comet has an old, weathered
protective layer of dust that covers the icy material beneath - much
like a snowbank builds up dirt on its surface as it melts in the
springtime sunlight. The Deep Impact mission was designed to dig deep
beneath this crusty exterior to learn more about the true nature of the
comet's underlying dust and ice components. "This comet definitely had
something to hide under its veneer of rock and ice and we were ready
with the world's biggest telescopes to find out what it was," said Chick
Woodward of the University of Minnesota and part of the Gemini observing
team.

The combined observations show a complex mix of silicates, water and
organic compounds beneath the surface of the comet. These materials are
similar to what is seen in another class of comets thought to reside in
a distant swarm of pristine bodies called the Oort Cloud. Oort Cloud
comets are well preserved fossils in the frozen suburbs of the solar
system that have changed little over the billions of years since their
formation. When they are occasionally nudged gravitationally toward the
Sun they warm up and release a profuse amount of gas and dust on a
one-time visit to the inner solar system.

Returning comets like Tempel 1 (known as periodic comets) were believed
to have formed in a colder nursery distinctly different from the
birthplaces of their Oort Cloud cousins. The evidence for two distinct
"family trees" lies in their vastly different orbits and apparent
composition. "Now we see that the difference may really be just
superficial: only skin deep," said Woodward. "Under the surface, these
comets may not be so different after all."

This similarity indicates that both types of comets might have shared a
birthplace in a region of the forming solar system where temperatures
were warm enough to produce the materials observed. "It is now likely
that these bodies formed between the orbits of Jupiter and Neptune in a
common nursery," said Seiji Sugita of the University of Tokyo and Subaru
team member.

"Another question that the Mauna Kea telescopes were able to address is
the amount of mass ejected when the comet was impacted by the chunk of
copper about the mass of a grand piano from the Deep Impact spacecraft,"
Sugita commented. At the time of impact, the spacecraft was traveling
at about 23,000 miles per hour or nearly 37,000 kilometers per hour.

Because the spacecraft was unable to study the size of the crater
created after it was formed, the high-resolution Mauna Kea observations
provided the necessary data to get a firm estimate of the mass ejection
which was about 1000 tons. "To release this amout of material, the comet
must have a fairly soft consistency," Sugita said.

"The splash from NASA's impact probe freed these materials and we were
in the right place to capture them with the biggest telescopes on
Earth," said W.M. Keck Director Fred Chaffee. "The close collaboration
among Keck, Gemini and Subaru assured that the very best science was
done by the best telescopes in the world, demonstrating that the whole
is often greater than the sum of its parts."

All three of Mauna Kea's largest telescopes observed the comet in the
infrared part of the spectrum which is light that can be described as
"redder than red." The Deep Impact spacecraft was not designed to
observe the comet in the mid-infrared (or thermal infrared) part of the
spectrum, which is what Subaru and Gemini were able to do. The Keck
observations used a near-infrared, high-resolution spectrograph. Large
instruments of this sort would have been impossible to fit on the Deep
Impact spacecraft.

"These observations give us the best glimpse yet at what's under the
dusty skin of a comet," said David Harker of the University of
California, San Diego who led the Gemini team. "Within an hour of impact
the comet's glow was transformed and we were able to detect a whole host
of fine dusty silicates propelled by a sustained gas geyser from under
the comet's protective crust. These included a large amount of olivine,
similar in composition to what you would find at the beaches below Mauna
Kea. This data was really a gift from Mauna Kea!"

Instruments that made these observations were:

    * MICHELLE <http://www.gemini.edu/sciops/instruments/michelle/MichIndex.html>
      (Mid-Infrared Echelle Spectrograph/Imager) on the 8-meter Fredrick
      C. Gillett (Gemini North) Telescope
    * NIRSPEC <http://www2.keck.hawaii.edu/inst/nirspec/nirspec.html>
      (Near-Infrared Spectrograph) on the 10-meter on the Keck II
      10-meter telescope
    * COMICS <http://www.naoj.org/Introduction/instrument/COMICS.html>
      (COoled Mid-Infrared Camera and Spectrograph) on the 8-meter
      Subaru telescope

 
Received on Thu 15 Sep 2005 06:48:28 PM PDT