Sky & Telescope - July 2024 - 22

CRASHED SPACECRAFT: USAF 388TH RANGE SQUADRON; RYUGU: JAXA / UNIV. OF TOKYO / KOCHI UNIV. /
RIKKYO UNIV. / NAGOYA UNIV. / CHIBA INST. OF TECHNOLOGY / MEIJI UNIV. / UNIV. OF AIZU / AIST
Missions
words of the space agency Roscosmos) it
" ceased to exist as a result of a collision
with the surface of the Moon. "
Trials and Triumphs
But planets and moons aren't the only
targets for sample-return missions. Comets,
asteroids, and even the solar wind
make good sources as well.
The first in situ collection of micrometeoroids
(along with human-made
debris) used aerogel, an ultra-lightweight,
porous, and solid silica gel. The aerogel was lodged in NASA's
Orbital Debris Collector placed outside the Russian Mir space
station, which collected interplanetary dust for 18 months
starting in 1996.
Next up, NASA dispatched the Genesis mission in 2001
to catch solar-wind particles. Genesis used an innovative
array of collectors composed of materials such as sapphire,
gold, and silicon. Team members feared that the mission was
a loss after it slammed into the Utah desert at the end of its
journey on September 8, 2004, but researchers were later able
to salvage shards of the detector plates - with their precious
solar-wind samples - from the crash.
NASA fared better with the Stardust mission, which also
used aerogel to trap particles as it passed through the coma
of Comet Wild 2. It returned samples to Earth on January 15,
2006. The mission team made use of the large citizen-science
project Stardust@home to identify dust-grain tracks through
the gel.
CRASH LANDING Sent to collect solar wind
particles, NASA's Genesis spacecraft crashed
in Utah upon return. Scientists were still able
to salvage samples from the debris.
More recently, Japan's Tanpopo experiment
on the International Space Station,
mounted on the exterior of the Japanese
Experiment Module, Kibo, also collected
cosmic dust from 2015 to 2019.
Although the amounts gathered
in each of these cases were tiny, these
projects have given us insights into the
chemical composition of interplanetary dust, the solar wind,
and cometary comae. The grains from Comet Wild 2, for
example, contain a hodgepodge of materials that suggests
that large-scale mixing in the early solar system mingled stuff
made closer to the Sun with that in the distant reaches.
Japan's Intrepid Hayabusa Missions
The Japan Aerospace Exploration Agency (JAXA) has had its
own sample-return woes. Its first dedicated retrieval mission
to an asteroid, Hayabusa, had to overcome several problems
on its journey to asteroid 25143 Itokawa and back to Earth.
These included a large solar flare, reaction-wheel failures (the
bane of many a mission), and communication issues. Mission
controllers weren't even certain at the time that the collection
mechanism fired properly when it touched the asteroid.
(Spoiler alert: It didn't.)
Still, after team members recovered the Hayabusa capsule
in the Australian outback in 2010, JAXA researchers discovered
about 1,500 dust grains caught in the inner collection
chamber, kicked up from the spacecraft's touchdown on
Itokawa. Despite its setbacks, Hayabusa was the first successful
sample return from an asteroid.
As is often the case in spaceflight, the failures of the past
became lessons that enabled the successes of the present.
JAXA scored the first full-scale success with the Hayabusa 2
sample-return mission. Its 3½-year journey saw the mission
rendezvous with asteroid 162173 Ryugu in June 2018.
Ryugu turned out to be of special interest as an example
of an Ivuna-type carbonaceous (CI) chondrite, a specimen
that's only rarely seen in meteorite form. Such asteroids are
representative of the chemical composition of the early solar
nebula. CI chondrites are also rich in organic molecules -
carbon- and hydrogen-containing compounds, especially
amino acids, which are the precursor building blocks for life.
Ryugu samples have given scientists a chance to study CI
chondrites in pristine, uncontaminated condition.
" The finding that Ryugu properties are consistent with CIALIEN
VISITOR Hayabusa 2 took this selfie of its shadow on
the asteroid Ryugu from an altitude of about 240 meters, as it
was approaching the surface. The " wings " are the spacecraft's
solar panels.
22 JULY 2024 * SKY & TELESCOPE
group [chondrites] was quite surprising, because the spectra
of CI meteorites were very different from that of Ryugu, "
says Seiji Sugita (University of Tokyo). " What was expected is
that we found a large amount of carbon in Ryugu. This was
expected from its very dark appearance. "
Hayabusa 2 was a resounding success, returning in 2020
Sky & Telescope - July 2024

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