with the osiris-rex mission nasa will do something that it has never
done before collect and return a bit of dust from
one of the solar system's small asteroids it's a rocky relic named
bennu bennu resembles two giant rocky cones
that have been smashed together creating an asteroid that's roughly the height of
the empire state building it carries what may be the very dust
that made the planets and the very molecules that led to life
on earth nasa's spacecraft osiris-rex plans to
collect at least 60 grams of the asteroid's dusty surface
to ship back to earth but to get even a sample from a small
body like bennu is not easy the first challenge is
gravity gravity on a fairly big body like the
moon is a fraction of earth's in the moon's case it's about 1 6 but
that's still a heavy tug compared with comets and asteroids which
can be one eighty thousandth of earth's gravity bennu's gravity is
one ten thousandth that of earth's to stay in orbit or
touch the surface osiris-rex can't move quickly in fact it
needs to move only a few times faster than a
slithering snail when osiris-rex heads toward the surface
it can gently glide down sample and with a slight push go the
second and bigger challenge is finding a safe
place to sample many small bodies including bennu are
rubble piles heaps of rocks that pulled together from
their mutual gravity everything from microscopic dust grains
to house-sized boulders cover the asteroid leaving almost no
flat surface for the spacecraft to touch down
so how do you safely collect a sample from these solar system light weights
for osiris-rex nasa turned to the small body mapping tool
it's a program designed at the johns hopkins applied physics laboratory in
maryland the program can take images and other
surface data collected by the spacecraft and project them onto a 3d
object that's shaped like the asteroid in the case of bennu
the program combined 3d maps of the asteroid surface
that were made using two techniques the first technique
looks at how shadows and surface brightness change on a crater
boulder or other surface feature on the asteroid during the day
that information can be used to determine a feature's
shape curvature and slope it can even find cracks or pebbles
that are less than one inch long the other method comes from a laser
instrument called the osiris-rex laser altimeter or ola
ola scans sections of bennu's surface dozens of times
determining the height of each feature by how long it takes a laser beam to
return from that spot scientists at apl and york university
in canada use these scans to triangulate points on the surface
they then turn these points into a 3d cloud shaped like the surface
both of these techniques can be used to distinguish large rocks that the
spacecraft needs to avoid from smooth areas it can sample when
combined with apl's small body mapping tool
these maps create a complete 3d reconstruction of the asteroid surface
every bump pebble and crevice can be seen within
inches of its actual location this is how nasa
identified the few places safe enough for osiris-rex to sample
including nightingale the crater where the spacecraft will briefly touch down
but the 3d maps were also key to helping tell the spacecraft how to get to the
sample site without any instruction scientists and engineers typically rely
on gravity to help steer a spacecraft to the
correct position when landing on a planet
but on bennu where gravity is weak that method just wouldn't fly
instead engineers identified waypoints on the surface of bennu
apl scientists with colleagues from the planetary science institute and york
university built 3d maps of these landmarks these
maps are embedded in osiris-rex when the spacecraft flies over bennu it
can compare the surface below with its on-board model as it finds the
waypoints the spacecraft automatically adjusts
itself until it flies to the sample site osiris-rex will be the first spacecraft
to ever use such autonomous technology to collect a sample
scientists have found a clever way to navigate and safely land
on one of the solar system's lightweights