Sky and Telescope - June 2018 - 28
The samples returned from both of these groundbreaking
missions and the new knowledge gained about their parent
asteroids will not only ﬁnally tell us how the different ﬂavors
of carbonaceous chondrite meteorites are related to various types of dark asteroids. They'll also provide crucial steps
forward in planetary science and exploration.
One of the most fundamental questions we have about the
formation of our own home world is: Where did Earth's water
and organic materials come from? Were they present in the
material Earth itself formed from, or were they delivered to
Earth after the planet was assembled?
For many years, scientists' favored answer was that Earth's
water came from comets that had hit the planet early on, but
as we've studied comets' compositions we've realized that the
isotopes in their water don't match Earth's. Instead, our plan10 m
et's water might be "native," carried in the rocks that stuck
together to build our world up - the same rocks that endure
p ITOKAWA CLOSE-UP Scientists expect Ryugu and Bennu to have
today as asteroids. Finally getting our hands on samples
rubble-strewn surfaces similar to what the first Hayabusa spacecraft
plucked from the types of asteroids long suspected to be the
found on Itokawa, shown here on November 9, 2005. The crater Komaba
most primitive building blocks of the terrestrial planets will
appears at left, and the smooth region upper right is MUSES-C Regio.
Boulders in this area are generally a few meters wide.
go a long way to answering these questions.
In addition to their compelling scientiﬁc value, the nearEarth
asteroids are literally gold mines in the sky: Not only
a metal detector and a vacuum. Osiris-REX will edge up to
do we think they contain precious metals, they also should
Bennu and plant TAGSAM on the surface. As soon as the
have water that we can convert into spacecraft fuel, providspacecraft senses proper contact, the instrument will spew
ing important in situ resources once we're routinely exploring
out a stream of pure nitrogen gas, kicking up loose material
and navigating the inner solar system.
and blowing it up into the TAGSAM head,
Just operating in close proximity to Ryugu
thereby trapping small pebbles up to 2 cm
Bennu is going to provide crucial knowlin size. As a backup, engineers designed the
that will come in handy as we expand
TAGSAM contact pads to allow some regoAND BENNU
working in space beyond Earth.
lith particles to stick there as well. Although
Osiris-REX is an
Osiris-REX are pioneers in
this strategy will pick up regolith that's been
acronym for Origins,
helping us wrap our heads around the someexposed to space weathering, it does avoid
times counterintuitive working environments
the complicated multi-impact approach
Security, and Regolith
we're going to encounter on the surfaces of
Hayabusa 2 will use.
Explorer. The phrasing
these lumpy little worlds.
Within seconds of collecting its sample,
of the mission's
And of course, there's always the looming
planned for July 2020, Osiris-REX will beat
science goals this way
problem of what to do if an asteroid targets
a comparatively hasty 0.7-meter-per-second
enabled the mission
Earth. Although a civilization-ending hit is
(1.6 mph) retreat off the asteroid. Once the
team to use a name
unlikely (see page 12), smaller rocks could
mission team has veriﬁed that the required
that points to the
come. An asteroid impact is a natural disaster
60 grams or more of carbonaceous regolith
Egyptian god Osiris,
that we can actually prevent, but only if we
has been collected, the spacecraft will stow
who spread knowledge
know more about the asteroids themselves
TAGSAM and its regolith sample in its sample
of agriculture (and
hence life) to the Nile
and how they respond to our poking and
return capsule. Osiris-REX will then begin a
Delta and also was
prodding. So as exaggerated as it sounds,
slow drift away from Bennu before initiating
king of the underworld
these missions might not only tell us about
its return-to-Earth burn in March 2021. The
- two roles that bring
Earth's past - they could also help us presample capsule will plunge through the atmoto mind asteroids'
serve its future.
sphere over the Utah Test and Training Range
potential source of
west of Salt Lake City on September 24, 2023,
marking the end of Osiris-REX's primary
¢ DAN DURDA is a principal scientist at the
and the threat they
mission but just beginning the journey of
Southwest Research Institute in Boulder, Colopose to our planetary
discovery for the worldwide community of
rado, where he studies the evolution of astersafety. "Bennu" was
planetary scientists who will dig in to the
oids and the effects of their impacts on one
another Egyptian deity
gritty treasure from Bennu.
another and on Earth.
associated with rebirth.
J U N E 2 018 * SK Y & TELESCOPE
JA X A
Pushing Back the Frontiers