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NEAR Fast Approaching Asteroid 253 Mathilde

Applied Physics Laboratory
Johns Hopkins University
Laurel, Maryland

FOR IMMEDIATE RELEASE: 18 June 1997

NEAR FAST APPROACHING ASTEROID 253 MATHILDE

The Near Earth Asteroid Rendezvous (NEAR) spacecraft is closing in fast
on the main-belt asteroid 253 Mathilde, as scientists prepare for the
closest-ever study of an asteroid. On June 27, starting at about 8:50 a.m.
EDT, NEAR will be streaking past Mathilde at 22,000 miles per hour (10
kilometers per second), just 750 miles (1,200 kilometers) from the asteroid.

For 25 minutes NEAR will take a series of 534 images using a multispectral
imager. "The flyby is an important opportunity to learn more about asteroids
in general and C-type [carbon-rich] asteroids in particular," says Dr. Scott
L. Murchie, Instrument Scientist from The Johns Hopkins University Applied
Physics Laboratory (APL), Laurel, Md. "With the data we get we will be able
to determine Mathilde's size, shape, landforms, brightness, and color
properties."

Using a combination of spacecraft radio tracking and imaging data as well as
Earth-based radar imaging techniques, researchers will be able to determine,
for the first time, accurate bulk density for an asteroid. "The bulk density
will provide clues as to how the asteroid formed and whether it is a
monolithic structure or a collection of smaller fragments," says Dr. Donald
K. Yeomans of NASA's Jet Propulsion Laboratory, who heads up the radio
science experiment.

As NEAR reaches its closest proximity to Mathilde a planned loss of signal
will keep researchers in suspense until the captured data begins to flow
into APL's Mission Operations and Science Data centers at about 9:40 a.m.
The first complete image is expected to be available later that afternoon.

"This is the first science data return of NASA's Discovery Program," says
Dr. Robert W. Farquhar, NEAR Mission Director at the APL, where the
spacecraft was designed and built. "What makes it even more special is that
it is 'bonus science' because it is an add-on to NEAR's primary mission to
study asteroid 433 Eros, at virtually no additional cost."

Because the Mathilde flyby was conceived after spacecraft integration had
begun, the multispectral imager was not designed for a fast flyby. Still,
researchers expect to get images and take measurements that will provide
significant new information about Mathilde, which they can compare with
data the Galileo spacecraft obtained during its flybys of Gaspra (1991) and
Ida (1993) for a better understanding of asteroids.

"Mathilde is a black asteroid made of carbon-rich rock, believed by many to
be the most primitive -- least changed in the last 4.5 billion years --
material left in the asteroid belt," says Dr. Joseph Veverka of Cornell
University, who leads the mission's Science Team. "Such material has never
been studied up close by a spacecraft."

Located in the outer part of the asteroid belt, Mathilde will also be the
largest asteroid ever visited by a spacecraft. It was discovered in 1885 and
is believed to be named to honor the wife of astronomer Moritz Loewy,
then-Vice Director of the Paris Observatory.

Interest in Mathilde was minimal until the NEAR flyby was announced in 1995.
Since then ground-based telescopes have been used to determine, among
other things, that Mathilde is a C-type asteroid and is one of the darkest
objects in the solar system since it reflects only 4 percent of the light
falling on it. It has been determined that Mathilde is approximately 38
miles (61 kilometers) across and has an amazingly slow rotation rate (17.4
days), which intrigues scientists since only two asteroids, 288 Glauke and
1220 Clocus, have longer rotation periods.

When NEAR encounters Mathilde it will be roughly 2.0 astronomical units
from the sun and 2.2 AU from the Earth (AU=the mean distance between the
Earth and sun). The spacecraft's great distance from the sun has resulted in
the decision to use the limited power supplied by the solar cells frugally by
activating only one of NEAR's six instruments, the multispectral imager.

The NEAR spacecraft, launched Feb. 17, 1996, from Cape Canaveral Air
Station in Florida, is the first spacecraft powered by solar cells to operate
beyond the orbit of Mars. Its encounter with Mathilde occurs as the spacecraft
heads back toward Earth after a wide swing around the sun for a "slingshot"
gravity assist in January 1998. The maneuver bends the NEAR trajectory
nearly 11 degrees out of the ecliptic to put it in an orbit that will match
Eros' orbital plane. The spacecraft will reach Eros Jan. 10, 1999, orbit the
asteroid for a year, and end its mission Feb. 6, 2000, with a controlled
landing onto its surface.

NEAR Science Team Group Leaders are: Joseph Veverka, Cornell University;
Jacob I. Trombka, NASA/Goddard Space Flight Center; Mario H. Acuna,
NASA/GSFC; Maria T. Zuber, MIT and NASA/GSFC; and Donald K. Yeomans,
NASA/Jet Propulsion Laboratory. Andrew Cheng, JHU/APL, is the Project
Scientist. Mission Operations have been the responsibility of The Johns
Hopkins University Applied Physics Laboratory.

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For more information contact Helen Worth, JHU/APL Office of Public Affairs.
Phone: (301) 953-5113; e-mail: Helen.Worth@jhuapl.edu; or fax: (301)
953-6123 or Donald Savage, NASA Headquarters Office of Space Science.
Phone (202) 358-1547; e-mail: dsavage@hq.nasa.gov; or fax: (202) 358-3093.

Mathilde flyby updates can be obtained on the Mathilde homepage at:
http://sd-www.jhuapl.edu/NEAR/Mathilde. Photographs of the first Mathilde
images will be available sometime during the afternoon of June 27. Also
available are photographs of the NEAR spacecraft, launch, and artists'
concepts of the rendezvous at Eros, and a video of Mathilde flyby animation
with B-roll footage of spacecraft development and testing.

Upcoming Media Events:

   * June 23 - 1 p.m. - Media Briefing at NASA Headquarters Auditorium, 300
     E St. SW, Washington, D.C. To be broadcast live on NASA TV with 1-way
     audio access by calling (407) 867-1220.

   * June 27 - 2 p.m. - Encounter Day activities at The Johns Hopkins
     University Applied Physics Laboratory's Kossiakoff Center, Johns
     Hopkins Road, Laurel, Md. Doors will open at 8 a.m. for those who wish
     to follow the encounter.

   * June 30, - 1 p.m. - Press Conference at The Johns Hopkins University
     Applied Physics Laboratory's Kossiakoff Center, Johns Hopkins Road,
     Laurel, Md. To be broadcast live on NASA TV with 1-way audio access by
     calling (407) 867-1220.

*****

Applied Physics Laboratory
Johns Hopkins University
Laurel, Maryland

FOR IMMEDIATE RELEASE: 2 June 1997 (revised 10 June) (revised 16 June)

NEAR EARTH ASTEROID RENDEZVOUS ENCOUNTER WITH ASTEROID
253 MATHILDE

The Near Earth Asteroid Rendezvous spacecraft is quickly approaching a June
27 encounter with asteroid 253 Mathilde. The following media events are
planned:

PRE-ENCOUNTER PRESS BRIEFING: Monday, June 23, 1997
To be held at NASA Headquarters, Washington, D.C., 1 p.m. (See map.)

     Get an overview and update on the NEAR Discovery Mission from Dr.
     Wesley Huntress, NASA's Associate Administrator for Space Science;
     a briefing on the Mathilde encounter from NEAR Mission Director
     Dr. Robert Farquhar of The Johns Hopkins University Applied
     Physics Laboratory (APL); and more. Learn what to expect during
     the flyby and when. Media questions will be taken following the
     presentations.

ENCOUNTER DAY: Friday, June 27, 1997
To be held in the Kossiakoff Center at APL in Laurel, Md. Doors open at 8
a.m.
Formal program begins at 2 p.m. (See maps.)

     Hear status reports on mission operations and, if all goes as
     scheduled, see the first Mathilde images by late afternoon. The
     Kossiakoff Center will open at 8 a.m. for those wishing to follow
     the encounter as it happens.

PRESS CONFERENCE: Monday, June 30, 1997
To be held in APL's Kossiakoff Center, Laurel, Md., starting at 1 p.m. (See
maps.)

     Hear an evaluation of the encounter from Mission Director Dr.
     Robert Farquhar; a report on Mathilde's mass and composition from
     Dr. Donald Yeomans of the Jet Propulsion Laboratory (JPL); and a
     report on the mission's imaging results by Dr. Joseph Veverka
     (Cornell University). Images from the Mathilde flyby will be
     available as handouts. A question and answer session will follow.

The NEAR Mission

The Near Earth Asteroid Rendezvous (NEAR) spacecraft was the first launch in
NASA's Discovery Program. The spacecraft, which was designed and built by
The Johns Hopkins University Applied Physics Laboratory, was launched Feb.
17, 1996, from Cape Canaveral, Fla. NEAR will conduct the first long-term,
close-up look at an asteroid's surface composition and physical properties.
The spacecraft is scheduled to arrive at asteroid 433 Eros on January 10,
1999, and will scrutinize the asteroid's surface from as close as 9 miles
before the mission concludes on Feb. 6, 2000.

Mathilde is a C-type asteroid, the most common type of asteroid in the outer
belt. It was discovered in 1885 and is one of the largest asteroids known.
NEAR's brief Mathilde flyby will provide researchers with a wealth of
information on the asteroid and lay valuable groundwork for the later study
of Eros.

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For more information contact Helen Worth, JHU/APL Office of Public Affairs
by phone at (301) 953-5113; e-mail: Helen.Worth@jhuapl.edu; or fax: (301)
953-6123.