[meteorite-list] Cornell Imaging Team Hopes Close-Up Picture From Eros Landing Will Solve Puzzle Of Never-Before-Seen Surface Features

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:06 2004
Message-ID: <200102052250.OAA21179_at_zagami.jpl.nasa.gov>

http://www.news.cornell.edu/releases/Feb01/NEAR.landing.deb.html

Cornell imaging team hopes close-up pictures from asteroid landing will
solve puzzle of never-before-seen surface features

FOR RELEASE: Feb. 5, 2001

Cornell University News Service
Contact: David Brand
Office: 607-255-3651
E-mail: deb27_at_cornell.edu

ITHACA, N.Y. -- As NASA's Near Earth Asteroid Rendezvous spacecraft, known
as NEAR Shoemaker, closes in on asteroid 433 Eros, Cornell University
astronomers hope that surface details as small as a hand-size rock will be
captured by the camera before the spacecraft bumps down on the
boulder-strewn surface Feb. 12.

Since last October, the NEAR imaging team has been puzzling over strange
surface features of Eros seen in new, high-resolution images. There is the
hope that the close-up images taken in the final few minutes before the
spacecraft drops onto the surface will help to answer their questions about
the geology of the 22-mile-long asteroid more than 196 million miles (316
million kilometers) from Earth.

"Since last October we have seen details of Eros at 1 meter resolution that
we haven't seen anywhere else before and don't understand," says Cornell
astronomer Joseph Veverka, who heads the imaging team. "That's why we are
so excited about getting close to the surface."

The landing -- what NASA is calling a "controlled descent" -- is a highly
risky maneuver, involving four thruster firings over four hours intended to
slow the rate of descent to 7 mph from 20 mph. In the final 45 minutes,
when the spacecraft is about 3.5 to 4.5 miles (about 6 to 7.5 kilometers)
from its landing site at the edge of the crater Himeros, the camera will
begin taking a new image about every 30 seconds.

The final picture will be captured at just 550 yards (500 meters) from the
surface, enough to capture details as small as perhaps 4 inches (10
centimeters) across. Mission leaders at the Applied Physics Laboratory at
Johns Hopkins University, which built the spacecraft and manages the NEAR
mission, do not expect images to be transmitted from the surface because
Eros's spin and topography will almost certainly prevent communication
between Earth and the craft.

Why does Veverka's team want to get such a close look at Eros' surface
details? Because, says Veverka, who is professor of astronomy at Cornell,
his team is frankly puzzled by what it has seen on Eros over the past few
weeks. Last October, with much of NEAR's mission accomplished, the
spacecraft was sent into orbit just 4 miles (about 6 kilometers) or so from
the asteroid's surface. For the first time the imaging team was seeing
details as small as a yard (.9 meter) across, compared with the
approximately 5.5 yards (5 meters) resolution that had been captured by the
camera since the spacecraft went into orbit around Eros on Feb. 14, 2000.

"Suddenly, we started seeing things we didn't expect and hadn't seen on
other surfaces in the solar system," says Veverka. "It's like another door
has opened."

The biggest surprise, says Cornell researcher Peter Thomas, who has been
interpreting the geology of the asteroid's surface, "is that some small
craters and other small depressions have flat, smooth floors, unlike most
craters you see on Eros and other objects. It looks as if fine-grain
material has slid down the craters' sides and ponded in the bottoms."
Apparently, he says, there is some mechanism "we hadn't anticipated" that
moves fine-grain material around on the surface. Although gravity on Eros
is only one one-thousandth of that on Earth -- an average person would
weigh only an ounce or two -- it is still "very effective in gathering
materials in very flat floors on the bottom of depressions."

Another surprise, says Veverka, is the discovery that some small boulders
are surrounded by material that appears to have disintegrated from the
boulders' surfaces. "There is some process that is very gentle that
somehow disintegrates rock. We haven't seen this on the moon, and we
haven't seen this before on Eros," he says. "But it seems to be very
common."

It is just possible, says Veverka, that the final image will be taken
almost at the surface itself. He explains that the camera will remain in
focus until about 220 yards (200 meters) from the landing site. If the
spacecraft is still on course, it is possible that the camera will take one
final image and have time to send a partial image on its way to Earth
before the spacecraft touches down. It takes 10 milliseconds for the
exposure, 1 second to read the image into the spacecraft recorder and 30
seconds for the data to emerge from the recorder. The data then take 17 to
18 minutes to reach Earth tracking stations.

The imaging team now is getting even higher-resolution images of these
features. On Jan. 24 the spacecraft entered a close flyby sequence,
including a four-day orbit that produced images from as close as 2 miles
(3.2 kilometers) above the surface. These new images are enabling the
Cornell imaging team to accumulate data at a resolution of about 1.1 yards
(1 meter). "The hope is that during the descent we can improve this
resolution by perhaps a factor of 10 so that we can find out more about
what is going on there," says Veverka.

        Related World Wide Web sites: The following sites provide
additional information on this news release. Some might not be part of the
Cornell University community, and Cornell has no control over their content
or availability.

        o Near Earth Asteroid Rendezvous Mission: <http://near.jhuapl.edu/>
Received on Mon 05 Feb 2001 05:50:16 PM PST