2019-06-01+Sky+and+Telescope

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ON FEBRUARY 21ST, the Japanese
spacecraft Hayabusa 2 grabbed its fi rst
sample from the asteroid 162173 Ryugu,
the asteroid it has been orbiting since
last summer (S&T: Oct. 2018, p. 11).
Immediately after the craft touched
down, it fi red a tantalum bullet at the
asteroid’s surface and knocked away
material that fl ew up into a sampling
horn. Then the spacecraft took off
again. Hayabusa 2 has now sealed the
sample collection compartment, saving
the sample for return to Earth.
Finding the right spot to sample
Ryugu was more challenging than
anticipated. When Hayabusa 2 arrived
at Ryugu on June 27, 2018, it found
a uniformly rocky asteroid with no
smooth areas on which it could alight.
The team had to develop new sampling-
site selection criteria, identifying two
extremely narrow locations where
they’d have to navigate the spacecraft
between boulders. The team tried out
descending toward those sites twice.
Back on Earth, they also tested whether
the bullet-fi ring mechanism would

liberate enough material from a rocky
surface. Testing went well, so the team
proceeded.
The spacecraft has no way of mea-
suring just how much material made
it into the collection chamber, so we
won’t know for sure what Hayabusa 2
has collected until it returns to Earth.
However, all the spacecraft telemetry
are consistent with success. The mission
allows for two additional attempts at
sample collection, though the mission
team still has to decide whether obtain-
ing another one would be worth the
added risk.
Hayabusa 2 also has one more exper-
iment to perform: its Small Carry-on
Impactor (SCI), a probe that will carry
explosives to accelerate a 2-kg copper
lump at Ryugu’s surface in an attempt
to create an artifi cial crater. Hayabusa 
will shelter from the impact behind
the asteroid’s bulk, but before it hides,
it will deploy a camera to watch in its
place. The spacecraft will then emerge
to pick up surface debris. Being able
to directly compare material from the

asteroid’s weathered surface to its rela-
tively pristine interior would be a boon
to scientists, who must often determine
bulk composition from remote observa-
tions of asteroids’ surfaces.
Hayabusa 2 will remain in proximity
to Ryugu until November or December.
Its return will take about a year. After
dropping its sample in the Australian
desert in December 2020, the spacecraft
could potentially extend its mission to
fl y past another asteroid.
■ EMILY LAKDAWALLA

SOLAR SYSTEM

Hayabusa 2 Touches Asteroid, Collects Sample


MARS
Opportunity Reaches
the End of the Road

pHayabusa 2 took this picture of Ryugu as
the spacecraft began ascending after its brief
touchdown. Hayabusa 2’s shadow can be seen,
along with a dark splotch where the space-
craft’s thrusters blew away lighter materials on
Ryugu’s surface.

tNASA’s Opportunity rover looked back over
its own tracks on August 4, 2010.

NASA FORMALLY ANNOUNCED the
end of the Opportunity mission on
February 13th. The team last contacted
the rover on June 10, 2018, days before
a dust storm enveloped the planet and
likely coated the rover’s solar panels,
cutting off its power supply. The storm
was both darker and longer than one
that Opportunity had weathered in


  1. The team attempted to make con-
    tact over the following eight months,


10 JUNE 2019 • SKY & TELESCOPE

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