of the meteorites on Earth come from stony,
carbon-poor asteroids like Itokawa, not carbon-bearing ones like Ryugu and Bennu (SN Online:
8/25/11). “In the context of [Hayabusa’s] problems,
it’s incredible the amount of data that came out of
that mission,” Thompson says.
While Hayabusa was floundering in space in
2006, Yoshikawa’s team was already suggesting that JAXA fly a follow-up mission. By then,
Yoshikawa had set his sights on an even more
attractive asteroid, Ryugu.
JAXA sent a spacecraft to Itokawa because it
was easy to reach, not because it was scientifically special. But as a carbon-rich asteroid, Ryugu
is thought to consist of the most ancient, pristine
material in the solar system.
Ryugu’s name even references a time capsule from a Japanese folktale, in which the hero
Urashima Taro retrieves a box from a dragon-guarded castle called Ryugu at the bottom of the
sea. When the hero returns to the surface, he finds
that 300 years have passed. When he opens the
box, he becomes an old man, because the box contained all of that elapsed time.
Yoshikawa and his colleagues proposed the
mission every year and were rebuffed each
time — until Hayabusa came home in 2010.
The spacecraft’s return was lauded in Japan,
Yoshikawa says. “Japanese people were very surprised to see that Hayabusa really came to the
Earth.” An editorial in the Japan Times deemed the
spacecraft a “high achiever,” and called for more
funding for JAXA and space research.
In May 2011, the Japanese government
approved the Hayabusa2 mission. Tachibana,
Yoshikawa and the rest of the JAXA team aimed
for the next launch window, in 2014.
Like Hayabusa2, OSIRIS-REx was rejected mul-
tiple times before NASA selected it for flight,
also in May 2011. Because of Bennu’s orbit, the
next launch opportunity to reach the asteroid
wasn’t until September 2016. That two-year gap
between JAXA’s and NASA’s launches inspired
some friendly competition between the teams.
“Of course, we are good friends and we want to
have a good relation,” Tachibana says. “But at the
same time we are rivals.” OSIRIS-REx is bigger
than Hayabusa2 and plans to collect up to 20,000
times as much asteroid dust — up to two kilograms, in the best-case scenario, compared with
Hayabusa2’s total of 100 milligrams. To compete,
Hayabusa2’s team set out to do everything first,
“They were concerned we were going to overshadow them,” Lauretta says. The first few meetings
between the teams were tense, he recalls. But both
groups felt it was best to work together.
“This is the first time since Apollo … that two
sample-return missions are going to the same
kind of target,” Tachibana says. “The U.S. and the
Soviet Union could not talk to each other.” It was
the middle of the Cold War. “This time we can talk
to each other.”
In November 2014, NASA and JAXA signed
a memorandum promising to share data, soft-
ware and samples. JAXA will give 10 percent of
its Ryugu sample to NASA, and NASA will give
0.5 percent of the larger Bennu sample to JAXA.
Still, the two space agencies don’t align on
everything. “Hayabusa2 and OSIRIS-REx have
completely different philosophies of sampling,”
says cosmochemist Keiko Nakamura-Messenger
of NASA’s Johnson Space Center in Houston. She
oversees the sample site selection for OSIRIS-REx
and will be in charge of storing the samples.
Take the mission timelines: OSIRIS-REx will
spend more than a year mapping Bennu in detail.
Its suite of science instruments, including three
cameras, a laser altimeter and three spectrometers, will figure out the asteroid’s composition
all over the surface before the team chooses the
mission’s sole sampling site.
Hayabusa2 scientists, on the other hand, chose
the first of three sampling sites in August, less
than two months after the spacecraft arrived at
Ryugu (SN Online: 8/23/18). Originally the team
Years in the making
The Hayabusa2 and
grew up almost simultaneously on opposite sides
of the world. The close
timing of the Japanese
and U. S. missions means
the two can learn from
Hayabusa2 aims to
gather 0.1 grams of dust
from Ryugu, the weight
of about three grains of
rice. OSIRIS-REx will try
to get up to 2,000 grams
of Bennu’s surface,
about the weight of a
3 grains of rice
1 small Chihuahua
1999 2012 2011 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023
September 11, 1999
May 10, 1999
September 8, 2016
December 3, 2018
OSIRIS-REx arrives at Bennu
September 24, 2023
OSIRIS-REx returns samples to Earth
December 3, 2014
June 27, 2018
samples to Earth