[meteorite-list] Historic Japanese Asteroid Data Amaze Researchers (Hayabusa)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Mar 27 15:53:32 2006
Message-ID: <200603271846.k2RIkxs19494_at_zagami.jpl.nasa.gov>

http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?id=news/032706p2.xml

Historic Japanese Asteroid Data Amaze Researchers
By Craig Covault
Aviation Week & Space Technology
March 26, 2006

SOLAR SYSTEM BABY

Japan's Hayabusa spacecraft that landed twice on the asteroid Itokawa
found it to be a "rubble pile" of 4.5-billon-year-old planetary debris
that loosely coalesced only about 10 million years ago, rather than a
much older intact body like previous asteroids visited.

This means researchers discovered--180 million mi. from Earth--a new
baby of the solar system. It's just one of many findings from the
$100-million mission that will affect theories on the formation of
planets and small bodies around the Sun and other stars.

In addition to being perhaps the youngest known object in the Solar
System, the asteroid is likely a "contact binary--a joined pair of
earlier separate objects--the first such conjoined twins ever viewed up
close in deep space. The juncture between two objects is clearly visible
as a smooth neck area between a rounded head and an elongated body.
There are plenty of rocky boulders up to 150 ft. in diameter, but
minimal evidence of significant craters and regolith that would show the
object to be older.

The Hayabusa data are a reminder "to expect the unexpected" in planetary
exploration, said mission managers at the 37th Lunar and Planetary
Science Conference here in mid-March.

One new revelation is that during one landing, the spacecraft bounced
twice, then remained on the surface an unexpectedly long 35 min. These
bounces and long dwell time could have given asteroid material,
disturbed in microgravity, enough time to inadvertently float into the
spacecraft's collection device, even though a sample blasting mechanism
did not fire properly.

The Hayabusa observations will be a significant element in international
planning for future missions to asteroids and comets. Japanese Aerospace
Exploration Agency (JAXA) managers say the striking findings, and
relative success of the mission, will cause them to elevate future
asteroid missions for approval.

As an Earth-crossing asteroid, Itokawa has a reasonably high statistical
chance of striking Earth in a million or more years from now, JAXA says.
The agency says this means the Hayabusa data are important for risk
assessments for other asteroids colliding with Earth possibly much
sooner with potential catastrophic consequences for mankind.

Several independent researchers here said the data assure a lasting
legacy for the mission, even if it fails to return samples of the
asteroid, its primary goal.

The mission in deep space has been an ongoing drama for the last six
months. Hayabusa landed on the asteroid twice in November in an attempt
to collect samples. Spacecraft telemetry, however, indicates it's
doubtful the sampling system worked properly. But that's yet to be
determined, and samples may actually be on board.

Extreme surface closeups showed even the smooth-looking touchdown area
was made up of marble- or pebble-size rocks solidly packed together. One
researcher compared the Hayabusa surface closeup 180 million mi. away to
a similar closeup picture of gravel pavement at the nearby Johnson Space
Center--and to the amusement of everyone, the two pictures looked about
identical.

A malfunction of the spacecraft's chemical thruster system resulted in a
loss of contact with the vehicle in December. But contact has now been
restored and JAXA managers hope in 2007 to use the spacecraft's ion
engines to propel it back to Earth for retrieval of the sample capsule
in 2010 near Woomera, Australia.

But the ion system has precious little attitude control authority,
compared with the chemical thruster system that failed because of a
leak. As a result, for the next several months, every heat-generating
instrument and system on Hayabusa is being powered on to "bake out" any
remaining chemical propellant that could vent in a propulsive manner,
tumbling the spacecraft beyond the control authority of the ion engine
system (AW&ST Mar. 13, p. 29).

But Hayabusa's high-resolution imaging system and infrared and X-ray
spectrometers have already provided landmark science data.

"Rubble pile asteroids are something we always figured would be out
there, and suddenly, 'voila,' there was one in front of us," says Andy
Cheng, a member of the Hayabusa science team from Johns Hopkins
University's Applied Physics Laboratory (APL).

There are two main theories about how the two objects originated. One
theory, supported by geologic and other data, is that the asteroid could
have been formed by two rubble-pile asteroids that formed separately,
but then collided, Japanese investigators say. Or its genesis could have
been a variation on that theme, where what is now the asteroid was
broken off a much larger single body in a collision. Under this
hypothesis, the larger object could have been blasted by a collision
that broke it into pieces, with the current Itokawa then formed out of
the eventual second collision of two rubble-pile objects blasted from
the parent body.

In either case, the science data indicate two bodies found each other in
space and joined, to form a 2,000 X 400-ft.-wide object that has a
rounded head at one end, an area of more fine-grained material at the
neck and a more rugged boulder-strewn body.

It's a major mystery how two objects each the size of skyscrapers could
collide without blowing each other to smithereens. This is especially
puzzling in a region of the Solar System where gravitational forces
would normally involve collision speeds of 2 km./sec., says Donald
Yeomans, a member of the Hayabusa science team from the NASA Jet
Propulsion Laboratory.

"It is difficult to figure out how these two bodies could have collided
and stuck together, but Mother Nature must have figured this out a long
time ago," he told the planetary conference. A third theory that
received somewhat less discussion is that gravity forces from a
planetary near-miss may have stretched the asteroid into two conjoined
sections.

RUBBLE-PILE ASTEROIDS have long been postulated as being formed when
relatively unheated, unaltered 4.5-billion-year-old debris from the
formation of the rocky planets pulled itself together into loosely
formed bodies by extremely tiny gravity forces. Due to larger
gravitational effects, these bodies formed between Mars and Jupiter--the
asteroid belt with millions of pieces of Solar System debris. Spacecraft
have imaged more homogeneous, intact asteroids, but never a rubble pile.

When the APL Near-Earth Asteroid Rendezvous (NEAR) spacecraft flew to
the much larger asteroid Eros in 2000, researchers expected to find a
rubble-pile asteroid; but they did not.

Eros is a much more solid body, with unusual cracks throughout, but a
more homogeneously formed object with a relatively smooth surface.
"That's still surprising to many people," says Cheng, who was also the
NEAR science manager.

As Hayabusa approached, then flew in formation with Itokawa, the
relatively smooth but grooved terrain found on Eros was nowhere to be
seen. "Instead, we found almost a patchwork-quilt kind of appearance;
you have rough, bouldery sections and then very smooth sections. It was
instantly recognizable as a 'different kind of beast,'" says Cheng.

"And then we realized, this is what a real rubble-pile asteroid looked
like--something like nobody had guessed."

The Lunar and Planetary Science Conference drew more than 1,500 managers
and scientists from diverse exploration programs, including a team led
by David S. McKay of the Johnson Space Center that presented new
research indicating more evidence that ancient life on Mars could have
been preserved in Martian meteorites (AW&ST Mar. 20, p. 28).
Received on Mon 27 Mar 2006 01:46:59 PM PST