[meteorite-list] New Horizons: A Hi-Def Peek at Pluto

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 25 Jan 2008 13:53:40 -0800 (PST)
Message-ID: <200801252153.NAA10359_at_zagami.jpl.nasa.gov>

http://pluto.jhuapl.edu/news_center/news/012408.htm

New Horizons: NASA's Pluto-Kuiper Belt Mission

January 24, 2008

A Hi-Def Peek at Pluto

New Horizons made its first detection of Pluto using the high-resolution
mode of its Long Range Reconnaissance Imager (LORRI) during three
separate sets of observations in October 2007.

"LORRI first detected Pluto in September 2006 in its low-resolution
format," says New Horizons Principal Investigator Alan Stern, of NASA
Headquarters, "but this time around we were able to take longer
exposures and to detect Pluto using a camera resolution that is four
times better than before."

New Horizons was still too far from Pluto (3.6 billion kilometers, or
2.2 billion miles) for LORRI to resolve any details on Pluto's surface -
that won't happen until summer 2014, approximately one year before
closest approach. For now the entire Pluto system remains a bright dot
to the spacecraft's telescopic camera, though LORRI is expected to start
resolving Charon from Pluto - seeing them as separate objects - in
summer 2010.

During the October 2007 observations, Pluto was located in the
constellation Serpens, in a region of the sky dense with background
stars. "Using LORRI's high-resolution mode allowed us to more easily
pick out Pluto in a virtual sea of surrounding stars," says New Horizons
Project Scientist Hal Weaver of the Johns Hopkins University Applied
Physics Laboratory (APL), which provided the LORRI instrument.

Marking another first for New Horizons, LORRI also detected clear
variations in Pluto's brightness. Pluto rotates on its axis once every
6.4 days, allowing observers to see different portions of the planet's
surface (i.e., different longitudes). From ground-based and Hubble Space
Telescope observations scientists have seen repeatable, well-defined
differences in Pluto's brightness they believe is caused by variations
in frost cover over its surface. New Horizons will determine whether
that is indeed the correct explanation when the spacecraft flies by
Pluto in July 2015.

"In the meantime, it's gratifying to see that New Horizons itself now
has the capability to track Pluto's brightness variations over the next
seven and a half years, and from a slightly different perspective than
what we normally see from Earth," Weaver says.

[Image]
This image demonstrates the first detection of Pluto using LORRI's
high-resolution mode, which provides a clear separation between Pluto
and numerous nearby background stars. Typically, LORRI's exposure time
in hi-res mode is limited to approximately 0.1 seconds, but by using a
special pointing mode that allowed an increase in the exposure time to
0.967 seconds, scientists were able to spot Pluto, which is
approximately 15,000 times fainter than human eyes can detect.

[Image]
This montage shows the effects of using different resolutions and
exposure times during LORRI observations of Pluto on October 6, 2007.
The top left image was taken with LORRI in high-resolution mode using an
exposure time of 0.967 seconds. The image to its right had the same
exposure time but was taken in LORRI's low-resolution mode with pixels
that are four times larger, which makes the stars and Pluto look
"fatter" and, therefore, less distinct. The image to the lower left is
another LORRI image taken in low-resolution mode, but with an exposure
time that is four seconds longer, which allows us to see "deeper" and
pick up even fainter stars. (Pluto is clearly detected and is circled in
each of these LORRI images.) The lower right image is a digitized
photographic plate of the same portion of the sky taken in July 1986 by
a large telescope in Australia for the Palomar Sky Survey. Pluto is not
in this image, but Pluto's location in the October 2007 observations is
indicated by the small red circle. This image captures stars that are
approximately 40 times fainter than can be seen in the lower left LORRI
image and illustrates the richness of the background star field in this
region of the sky.
Received on Fri 25 Jan 2008 04:53:40 PM PST