Good afternoon. I'm Nancy Neal Jones from
the Office of Communications at NASA's
Goddard Space Flight Center in Greenbelt
Maryland. Today we will reveal new and
unexpected discoveries from NASA's
osiris-rex mission telecon graphics are
available right now at HTTPS: forward slash
forward slash SVS dot GSFC dot nasa.gov forward slash
one three one five four I'll repeat HTTPS
colon slash slash SVS for scientific
visualization studio dot GSFC for
Goddard Space Flight Center dot nasa dot gov
slash one three one five four. The Origins
Spectral Interpretation Resource
Identification Security Regolith Explorer
OSIRIS-REx spacecraft launched September
8 2016 and began orbiting the asteroid
Bennu
on December 31st 2018 Since its arrival at
Bennu, the spacecraft has been
investigating the asteroid and searching
for an ideal site for sample collection
to get more insight on the mission and
new science results today's briefing
panelists include Lori Glaze acting
director NASA planetary science division
Washington Dante Lauretta osiris-rex
principal investigator University of
Arizona Tucson Coralie Adam osiris-rex
flight navigator KinetX Inc space
navigation and flight dynamics, Simi
Valley California, Rich Burns
osiris-rex project manager nasa's
goddard space flight center Greenbelt
Maryland we will now begin with Lori
Lori Thank You Nancy NASA's planetary
science program actually runs several
missions that are studying the small
bodies that include asteroids throughout
the solar system and we studied these
asteroids to learn more about the
history of our solar system and our
origins the small bodies mission both
currently operating and plan for the
future it will help the scientists start
to answer questions like
did we come from how did the major
planets form and how to earth get its
water in first three months the of OSIRIS
REx mission is already given us some
amazing science to dig through and I'm
really excited about the results that
are going to be presented here today
there are some expected results some
surprises but this is an incredible team
who can learn and adapt to achieve the
ultimate goal of this mission which is
to collect a sample of the asteroid
Bennu and bring it back to earth and so
with that I want to hand it over to
Dante and jump right into some of these
results. Thank you, Lori. This is an
incredibly exciting time on the
osiris-rex mission my first graphic is
shows a series of high resolution images
that were taken by our poly cam imager
onboard the spacecraft these were images
were acquired on December 2nd of 2018
right as we were finishing the initial
approach to the asteroid and for most of
the following months they provided our
best characterization of the asteroid
surface and they really demonstrate some
of the surprises that this asteroid
presented to us first but unsurprisingly
because we had characterized the
asteroid using ground-based radar
astronomy. Bennu has an expected spinning
top shape it's roughly spherical with an
equatorial Ridge that seems to be
dominated by its rotation and reflective
of the fact that it's a pile of rubble
or gravel and boulders loosely bound
together by their own small gravity
fields however we had expected from
ground-based infrared and radio
astronomy that the surface was
relatively smooth and dominated by
centimeter scale particles which are
optimal for our touch-and-go sample
acquisition mechanism the device that
will ultimately contact the surface of
the asteroid to collect that material in
fact we see a wide range of very large
boulders on the surface our latest count
is over 200 boulders larger than 10
meters in diameter so there's something
interesting going on with the asteroid
geology not only do we see a lot of
boulders but we see that they have a
very wide range of reflectivity or what
we call normal albedo we're seeing
things as dark
only reflecting about three-and-a-half
percent of the length that's shining on
the surface from the Sun up to over 20
percent reflectance and some of the
brightest particles on the surface as a
sample scientist is interested in
getting this material back into our
laboratories here on earth
this is really exciting because it means
that we're going to have a wide range of
materials to study from the dawn of the
solar system to understand the processes
of planet formation and even whether as a
habitable planet with abundant oceans
and origin of life occurring here
however it may pose some challenges for
our navigation systems which rely on
light our instruments which are lasers
that reflect off the surface to give us
a range to the asteroid as well as image
based technologies to guide us into the
potential sample site we show this movie
with the asteroid rotating one of the
most interesting discovery so far is
that since we've been watching the
asteroid astronomically beginning in
1999 up into observations in 2018 we've
seen the rotation rate of Bennu
increasing because of the latest
observations we can attribute this to a
known phenomena called the YORP effect
which is basically how interaction with
sunlight causes the asteroid rotation
rate to increase and probably the most
easily understandable way to
characterize this is what we call the
YORP doubling time in about a million
and a half years we predict that Bennu
will be spinning at twice its current
rate so we definitely see the asteroid
spinning faster and faster we have
learned a lot about the composition of
Bennu from our initial observations and
we have three instruments that allow us
to determine the minerals that are on
its surface we have a thermal emission
spectrometer called OTES which goes out
to very long infrared wavelengths
capturing the heat that's coming off but
also containing information about the
minerals on the surface we have a
visible and near infrared spectrometer
called OVIRS
which characterizes the way sunlight is
reflected off and gives us additional
indications about the minerals on the
surface and then we have our mapping
camera the mass cam which has color
filters that allow us to look at very
broad variations and reflectance
invisible wavelength ranges we have
learned that
Bennu is dominated by water rich clay
minerals or phyllosilicate minerals
which is very exciting and allows us to
really go after the kind of material
from the early solar system that were
interested in but with the MapCam we've
been able to get resolved images and in
the graphic number two I'm showing you
in the middle they're different colors
from our approach phase with the MapCam
and then over there on the right on the
top we've got the ratios of those
different colors and this matches a
known mineral called magnetite or iron
oxide or more familiar on earth
sometimes called a lodestone magnetite
very interesting because it also forms
an aqueous systems often as the result
of very intense action of liquid water
so this confirms Bennu as the ideal
choice for our sample return target on
graphic three I reveal probably the
biggest surprise of the early phases of
the of OSIRIS-REx mission and I would
say one of the biggest surprises of my
scientific career when we got into orbit
our first orbital phase a we actually
were expecting that to be a time for the
science team to kind of process the
information that are already been
acquired and for the flight dynamics
team to learn how to operate the
spacecraft in close proximity to the
asteroid but what I'm showing you here
are actually a composite of two
different images from the navigation
camera there's a short exposure image
which is showing you the asteroid
surface in the lower left and then a
long exposure image and if you look just
off the limb towards the center of the
image you'll see a whole series of
bright pixels those are in fact
particles that are ejecting off the
surface at relatively high velocity so
Bennu is part of a category a very
small group of small bodies in the solar
system called active asteroids we are
seeing bending regularly eject material
into outer space we saw the first event
occur on January 6th of this year and
then we instituted a more rigorous
monitoring process using the navigation
camera starting on January 11th we're
able to continue that high cadence of
observations through February 18th and
we have seen about 11
events over that time period more are
being discovered as we get better at
analyzing and processing the data and
extracting small signals from that
information three of those events have
been substantial with dozens or over a
hundred particles being ejected clearly
into the asteroid environment the
particles seem to be in the size ranges
of centimeters up to tens of centimeters
in diameter and they're moving with
velocities of centimeters per second
which is very slow relative to the
asteroids acceleration and escape
velocity up to several meters per second
which means they're clearly being
ejected into interplanetary space and
away from the asteroid some of those
slow moving particles have been observed
over periods of at least a week and they
appear to be trapped in the asteroids
gravity field and are ending up in orbit
around Bennu so they're creating a zone
set of natural satellites and then some
of them have been observed to fall back
on to the surface basically it looks
like Bennu has a continuous population of
particles raining down on it from
discrete ejection events across its
surface this is incredibly exciting we
don't know the mechanism that is causing
this right now in fact we're still
learning how to process the data analyze
the information and make sense of what's
going on at this asteroid and then in my
final graphic graphic number four it's
just an example of one of our highest
resolution images acquired to date this
is a shot from our PolyCam taken from
the first detailed survey station and it
shows the general rugged nature of the
asteroid surface the field of view here
is 70 meters the good news and the
reason I picked this image to show you
is that at smaller scales we are seeing
patches of fine-grained regolith which
is exactly the kind of material that we
expect to be able to collect with our
TAGSAM sampling device so even though
the surface overall looks bouldery and
rugged and rocky and really not what we
expected from our ground-based astronomy
we are owning in on areas of sample
material and those will be obvious areas
of interest as we move forward with the
mission so I'm going to hand it over to
Coralie Adam Corley is the optical
navigation lead for the mission and she
has been
for a large amount of the success of our
operation so far so Coralie Thank You
Dante I'm moving on my first graphic on
December 31st the navigation team
delivered OSIRIS-REx into a
record orbit around Bennu making Bennu
the smallest planetary body to ever be
orbited by a spacecraft the team
achieved another record for the smallest
orbit around a planetary body which is
an elliptical orbit with the closest
distance falling just under a mile from
the asteroid center giving into this
orbit around such a small asteroid is
really challenging given the fact that
the force of the radiation pressure or
the the sunlight acting on the
spacecraft is on the same order of
magnitude as the gravitational pull from
Bennu on the left-hand side of this
graphic you see the orbit as if you're
looking down from the Sun and on the
right-hand side you see a side view you
can see that the orbit plane is facing
the Sun we call this a frozen orbit
because it uniquely balances forces
between the solar radiation pressure and
gravity so it allows for a more
longer-term stability when we got into
this orbit it was so stable that we
didn't need to do any adjustments during
the scheduled eight weeks in orbit
moving on to slide my slide to the
objective of this initial orbit phase
was to transition to a method of
navigation called landmark tracking
which would improve our navigation
performance from future, for future
mission phases instead of finding the
geometric centr of Bennu which you
can see on the left-hand side of the
graphic we now navigate by surface
features which have allowed us to better
understand characteristics of both Bennu
and the spacecraft that affect the
navigation performance now what's really
impressive about the outcome of our time
in orbit is that we have demonstrated
meter level navigation accuracy which is
even better than the earth based GPS on
your smartphone you can see in this, in
these two NavCam views from orbit and as
Dante mentioned that Bennu is very dense
of boulders which
make for a more challenging sample
collection luckily our predictive
navigation performance has been 10 times
better than what we expected before we
arrived at Bennu which means we leave it
we will be able to tighten down our
analyses and and target the more precise
bull's eye tag moving on to the slide 3
now just six days after we got into
orbit we've observed our first particle
event and this discovery was only
observed because of our optical
navigation method of taking long
exposure images of stars which helped
refine our precise measurements so given
the this image based and dynamical
nature of this phenomenon our navigation
team has been able to quickly build up a
toolset to characterize the behaviors of
these particles so work is underway to
use these sparse data just a few images
of pixels emitting from the asteroid to
trace these particles back to the
surface as well as predict where they
were heading
so with that I will close by giving big
kudos to all the hard works and members
of the navigation team and our entire
mission team who have really
demonstrated amazing and unprecedented
capability on this mission so far so
I'll hand the floor over to rich burns
who will further speak to this graphic
before moving on
thank you very much Coralie so it's
currently mentioned we were only six
days in orbit of the smallest orbit ever
around the planetary body when we
observed this event you can imagine we
were mostly concerned about particles
being ejected from the surface of the
asteroid unexpectedly and so that
prompted us to do a quick turnaround
safety assessment in other words how
likely was the spacecraft to be impacted
by these particles were we safe in orbit
we did that very quickly within a day
using the available information we had
and techniques that we were familiar
with with a four low-earth orbit
collision avoidance calculations these
calculations we we did with three
independent party
and all came up with similar results
showing that we were had very low likely
hit likelihood of seeing an impact
resulting from one of these particles
safety analysis was further refined and
and informed by subsequent observations
Dante mentioned the 11 events that we've
seen three of them have been major like
this one you see on this graphic all of
those all that information led us to the
conclusion that we work the spacecraft
was safe in orbit and and we persisted
there to observe observe these events as
the orbital environment was the optimal
for such a such observations if move on
to my first graphic please so what you
see here is another high-resolution
image of a location on the asteroid with
an overlay of a circular region we're
calling the original target area this is
the accuracy with which osiris-rex was
designed to touch the asteroid to
collect the sample so we were looking
originally for a 25 meter radius hazard
free zone you can see from this image
this isn't it and the and the asteroid
is so rugged that there is unlikely to
be any 25 meter radius hazard free zones
what do I mean by hazards those big
boulders represent hazards as do tilts
severe tilts on the surface and slopes
on the surface of the asteroids you do
see an upper left-hand corner a region
of small grained samples which would may
be appropriate for a sample collection
of course that area is much smaller than
the area outlined in in white here the
25 meter radius circle however our
system performance as has been noted by
both Dante and Coralie has been
extraordinary today our spacecraft built
by Lockheed Martin has performed
manoeuvres with very high levels of
accuracy and precision
allowing us to do things like stay in
orbit without trim maneuvers as Coralie
mentioned our navigation performance has
been exquisite the modeling that the
navigation team collaborating with a
with Goddard and KinetX both
collaborating has been extraordinary in
the level of modeling the fidelity of
the modeling of things like solar
radiation pressure Andry radiation from
the spacecraft has been extraordinary so
we feel confident that our systems and
our teams are up to the task of a sample
of a tagging - a sample collection site
of much smaller area than was currently
than was previously envisioned that's
what gives us confidence to move forward
with what we're calling bullseye tag so
bullseye tag you can imagine you're just
shooting at a dart at a dart board just
trying to hit the board well now we're
going to try to hit the center of the
bullseye we feel like the performance of
the system and the team supports that
notion and we are working actively to
make it happen and next graphic please
what you see on the next graphic graphic
is just an animation of our tag sequence
so we will the spacecraft will leave
orbit and you'll see a deployment of the
TAGSAM armed with the TAGSAM head
featured in that deployment the
spacecraft will make two manoeuvres to
descend to the surface of the asteroid
and we will not land on the asteroid
this the the spacecraft will touch the
asteroid with this with the head the
sample head hopefully on a level spot
and we will expel a nitrogen pressurized
nitrogen gas to disturb the regolith
that regolith will be collected within
the sample head itself which looks like
a an air filter more or less
that fine-grained sample will be
collected there we'll back away from the
asteroid and and then once we once we're
away from the asteroid we have some
techniques that we'll use to measure the
the amount the size of the sample that
we got and then we'll stow that sample
in our sample return capsule with all
that said I want to turn it back over to
Dante and let him close things out so
just to summarize first of all the
osiris-rex team continues to perform at
an amazing level of professionalism and
precision and it's an honor to be the
leader of this program I couldn't be
more proud of everything that's been
accomplished so far and because of that
it gives me great confidence that we're
going to be able to target a bull's eye
tag event or summer of 2020 and get that
precious sample for stow and return back
to Earth Bennu has turned out to be an
ideal target from a compositional
perspective we are seeing abundant water
bearing minerals on the surface and
through the magnetite detection
inference of intense aqueous activity in
the past history of this asteroid it
does present us challenge it's a more
rugged surface than we had predicted
from our ground-based astronomy but we
feel like there are patches of
fine-grained material on the surface
that we can collect with the TAGSAM
device and of course as I hope Coralie
has convinced you the flight dynamics
and navigation team is absolutely the
best in the world
they're cutting edge astrodynamics
techniques are not only going to make
sure the spacecraft remains safe but
also that we collect all the scientific
data we need to make the best sample
site selection decision possible and
ultimately guide us down to get that
material off the surface and then almost
more impressively we have such a tight
coupling between the science and
engineering groups on this program that
they're also making a major contribution
to characterizing these particle
ejection events and the tools and
procedures and analysis capabilities
that they bring to the team are going to
end up producing some of the greatest
scientific discoveries definitely not
what we expected to see if the asteroid
but an excellent opportunity for us to
understand active
asteroids volatile ejection and loss from
these bodies and overall the
distribution of this kind of material in
the solar system and ultimately its
pathway to delivery to the surface of
the earth so thanks to everybody on the
team for their hard work today and
buckle up best times are ahead of us and
it's going to be a great ride thanks
Thank you, Dante. Operator, we're now ready
to take questions from the media please
state your name and affiliation operator
thank you at this time we will begin the
question and answer session if you'd
like to ask a question please press star
one unmute your phone and record your
name when prompted withdraw your
question please please press star 2 one
moment please for the first question
Ivan Colon your line is open
thank you in terms of a probability how
much more risky do you expect the
sampling operation to be because of what
you found out so this is rich I can I
can take that one we don't have a
quantification of that yet because we
are still in the process of mapping the
asteroid to identify the candidates a
candidate sample selection sample sites
so we're going to make a sample site
selection in in the summer months and at
that point we'll have a better idea of
the area of the sample site relative to
our previous requirements will this
delay at all the the the sampling
compared to what you you forecast
initially July 20 2000 after no the
answer is no okay thank you
our next question comes from Marina
Curran your line is open hi this is a
question for Dante you said you don't
know for sure what's causing these
ejections but do you have any ideas
based on the study of other active
asteroids and did you expect to see this
kind of activity on Bennu why or why
not thank you for that that's a great
question we certainly did not expect to
see this activity because there's so few
asteroids that are known to be active
there's about a dozen of them of the
800,000 asteroids that we know in the
solar system so the probability that
Bennu would be active we thought was
very very low that said we did plan for
such an event because we thought it
might be possible and we're very
thorough in how we design the mission
and how we approach the risk and safety
assessments and also take advantage of
scientific opportunities so we actually
do have requirements on the mission to
look for dust and gas plumes and we also
have requirements to search for and
characterize any natural satellites that
may be in bound orbits around the
asteroid we did not expect that there
would be ejections of particles that
we're creating natural satellites that
has never been seen before in any solar
system object in history so that's
really exciting and a great opportunity
for us to learn more about not only the
surface of the asteroid but also its
gravity field these are natural gravity
probes and they're orbiting very close
to the asteroids we'll be able to get a
great understanding of the gravity field
and therefore the internal structure of
the asteroid we do have some mechanisms
that are under evaluation with one of
the very first things I did was we
rallied the science team together we
made up a big list of all possible
things that could eject particles from
the surface it's a long list there's a
very creative team and lots of ideas are
out there so my focus right now is full
characterization of what has happened as
I mentioned we have a great data set
that goes from January 11th through
February 18th we're still developing
software and analysis tools to really
understand what's in that information
and my first objective
which is underway is to compile a table
of the constraints basically what do we
know about the size of the particles the
energy of the events the frequency the
composition the source regions etc and
once I have all of that information
compiled then we'll start to go through
our different possible mechanisms then
evaluate which one we think is the most
likely thank you thank you our next
question comes from Mark Gaucho
your line is open yes good afternoon
ladies and gentlemen first off
congratulations on the incredible
achievements you've made by already
making the long journey to the asteroid
Bennu in talking about the discharges
of particles are these actually uh
storms or small ejections of particles
are you now looking at at this seeing
this as looking at your your bull's eye
collection location as it being
something that you might have to wade
through a long period of these type of
particle ejections or storms the answer
that turn absolutely we're trying to
understand the nature of the ejection
events a couple of things that we do
know is that they are discrete events
they happen near instantaneously and
whenever we see a large number of
particles leaving the surface of the
asteroid they seem to be coming from a
single location we are still working to
determine the exact locations of all the
events that's been observed to date and
I think Coralie can probably tell us a
little bit more because it's the flight
dynamics tools and analyses that are
helping us constrain those and we're
also trying to understand what might be
the driving forces we did go through
perihelion on January 10th so that was
just four days after the first event was
observed but as we said earlier that was
only one week after we got into orbit
when these things were really observable
so we don't know if it's in fact related
to our
closest approach to the Sun and Bennu's
orbit is pretty eccentric it goes from
about point eight nine astronomical
units at the closest approach to the Sun
or perihelion up to one point three five
au aphelion or its farthest point from
the Sun though there's there is a
speculation that this might be related
to the close approach but we haven't
confirmed that yet we have seen the
events continuing into the lake February
timeframe and we're not seeing them but
we also have left orbit and we're much
farther away from the asteroid so
they're not as observable as they were
before so all of these are open
questions it's one of the greatest
things about being a scientist is you
get to go chase down your theories and
click more data to understand them but
Bennu is really teasing us with this I
think it's really every time we think we
understand what's going on a new
manifestation occurs and we go back to
the drawing board and start thinking
over it again so we're super excited but
we're also being very diligent and
careful as we process the data and
Coralie why don't you talk a little bit
about the work you're doing to actually
locate the ejection sites on the surface
sure well what's challenging is that we
have these you know 2d images of
particles and we can what's challenging
is we are trying to link these particles
from one image to the next and then back
out we can measure things in the image
plane in 2d space the position and
movement of the particles and what we're
focusing on is trying to make some good
assumptions about how to project those
2d measurements into 3d space so that we
can measure the 3d velocities the cone
or shape of the ejection and trace the
particles back to an origin site on the
surface as well as predict their their
orbits sub orbits or you know hyperbolic
escape escape trajectories from there
thank you very much you are learning
quite a bit thank you
thank you our next question comes from
Malcolm Ritter Associated Press your
line is open
thank you very much I what I hope is a
simple question you talked about
recovering the sample that you want to
recover and bring back to earth you
talked about this being pieces of
regolith of you know below a certain
size and my audience has no idea what
we're talking about are we talking about
dirt or gravel or pebbles or what is
kind of an everyday English word that
would that would describe the stuff
you're going to collect? This
is Dante so regolith is the term that we
use to describe a loose blanket of rock
and gravel usually on the surface of an
airless body so we talked about the
regolith on the moon or on Mercury and
on asteroids so basically what we're
seeing Bennu being a rubble pile we've
got boulders as large as 80 meters and
we were seeing particles right now down
to a few centimeters basically limited
by the resolution of the images we've
acquired to date so in a sense all of
that would be considered regolith
because we don't have bedrock or the
solid material that makes up the bulk of
the asteroid for osiris-rex specifically
we're looking for fine particulate
regolith and that's driven by the
capability of the sample collector which
can pick up particles about two
centimeters in diameter and smaller so
we're looking for the fine regolith that
is capable of being ingested by the
sampling mechanism so I'm from what you
say I think 270 meters in diameter
that's what a tenth of an inch for
basically yeah so we're basically
looking at there gravel and dirt? I mean
is that a fair way to describe this? Yeah
gravel and sand sized particles we're looking
at the geologic scale so absolutely yes
or grab a little smaller then right yeah
okay and again I'm struck in your paper
you were first author on a paper in
nature that just went live saying that
you know the your the unexpected small
size of safe collection sites
you said the sampling of which poses a
substantial challenge to mission success
and yet here you sound like you're going
to like it's going to be a breeze not a
problem so I'm kind of struck by you
know how confident are you can really
pull this off
sure and I would say everything we're
doing is a substantial challenge and so
we shouldn't diminish the enormous
amount of effort that it takes to make
something like this happen so you know
NASA has a long history of doing very
difficult things and making them look
easy and that is continuing on with the
osiris-rex mission and it is not done it
is not trivial to deliver a spacecraft
with meter scale resolution to the
surface of an asteroid in a microgravity
environment and we take that challenge
very seriously
and the challenge got a lot harder when
we saw the true nature of Bennu's surface
but I am confident that this team is up
to that substantial challenge and that
we will ultimately develop this bullseye
tag capability and be able to
successfully collect the sample from the
surface okay very good thank you all
next our next question comes from Doyle
Rice USA today your line is open
good afternoon thanks for doing this
very interesting stuff I just couple of
quick questions for you just kind of on
a bigger term scale here there's not
anything that you've discovered today or
announcing doesn't really have any
specific impact on you know whether or
not this this particular asteroid will
come closer or farther away to earth
over the next few hundred years it's not
really this doesn't really you know leap
out as a major discovery for whether or
not it's going to potentially come close
to the earth looking at the British
tabloids today they all say that it's
you know it's about ready to hit or some
crazy thing and I just wondered what
your overall perspective is on that well
one of the words in the acronym
OSIRIS-REx is security and Bennu is known as
they potentially hazardous asteroid so
one of our objectives is to really
understand the likelihood that Bennu is
going to impact the earth we have done a
lot of that work even pre-launch with
our extensive astronomical campaign and
we have given an assessment of about a 1
and 2700 chance of an impact late in the
22nd century we haven't learned anything
that would cause us to change that
estimate of Bennu itself impacting but I
will say one of the fun and exciting
offshoots of the particles as we do see
these things leaving the vicinity of the
asteroid and so we think there's a
reasonable probability that there might
actually be a meteor shower associated
with Bennu and small particles might be
coming in the sky and so that would
happen in late September every year and
it would be dominantly occurring in the
southern hemisphere so we're working
with our colleagues at the SETI
Institute in California to set up some
monitoring cameras and actually see if
they've been you if there is a Bennu's
meteor shower in September every year
and that will help us with the science
understanding these particle events
because it will give us a much longer
timeline about how frequently and how
energetic and how many particles may
have been coming off over thousands of
years of Bennu history ok thank you
the line is now open
Kenneth Chang New York Times your line is open
thank you my question is um vehicle to
show that the Hayabusa to mission is
that it also tried to be this spinning
top with a ridge and lots of boulders
that trying to be much more difficult to
examine them initially anticipated just
wanting to tell you something about the
formation process of these rubble piles
that's a great question Kenneth and
absolutely you know having two
spacecraft at two of these objects gives
us an enormous opportunity to advance
our understanding of the field
and I would say already a lot of our
ideas for how the spinning top shape
formed are not being supported by the
data that we've collected so far for
example one of the things you reported
in the nature papers and also at the
lunar planetary science conference today
is that there's a large number of impact
craters on the equatorial ridge of Bennu
which makes it look like the surface is
a hundred million to maybe a billion
years old which implies that the
spinning top shape in that equatorial
region formed very early on in Bennu's
history and we had thought that this was
actually related to the what we call the
YORP effect that I referred to during
the briefing where interaction with
sunlight and re-radiation of that energy
is heat is causing the asteroid to spin
faster and faster and we thought that
was the driving mechanism for production
of the spinning top shapes so we don't
know the answer right now you can
imagine the science teams are really
busy characterizing the data and really
refining those theories and we are
planning a workshop in November both
sponsored by Hayabusa 2 and osiris-rex
coming together to evaluate exactly that
question what have we learned from these
two great missions and what is their
going to tell us about the formation of
spinning top asteroids and then overall
I would like to acknowledge the great
collaboration that we have with our
colleagues at JAXA and the whole
Hayabusa 2 team it's a really great
relationship and they have successfully
sampled from the surface of Ryugu and
in fact I'm leading a contingent of
osiris-rex team members next month in
April to visit them and get lessons
learned about how we can improve the
chances of success for osiris-rex
sampling next question comes from Jason
Davis of the Planetary Society your line is
open
hi thanks for doing this I just had a
question about you said this was an
active asteroid and I was wondering if
you could just clarify a little bit more
about what that means when you say that
is it that the interior is shifting
around somehow and these dozen or so
that you've seen before and also could
you clarify as it has this ever been
seen before by any spacecraft this type
of particle ejection from an asteroid
or theorized to exist in this type of
asteroid? thanks yeah hi Jason thanks for
that question so active asteroids were
first discovered about 15 years ago when
observers were looking at asteroids in
the main belt that clearly had orbits
that placed him well within that family
of small bodies and then they saw that
they were developing extended coma very
much like comets do and so the original
term that was used was main-belt comets
where we had objects in the main belt
they looked dynamically exactly like
every other asteroid that's out there
yet they were showing periodic activity
and examples of this are Elst-Pizarro
is one I think one of the first ones
that was discovered there have been a
roughly a dozen of them that have been
identified since then all of them are
main-belt asteroids and they have shown
a correlation with perihelion although
that correlation is not perfect and the
thinking was that that these were
probably icy bodies that something
happened an impact had occurred on the
surface and subsurface ice had been
exposed and recently and then was now
just going through cometary activity for
a brief period of time other asteroids
were seen to be undergoing the
rotational acceleration via the YORP
effect like we see on Bennu and some of
that if you take that to the extreme
case the rubble pile on asteroids will
actually fly apart because the angular
momentum that's been added to the
surface overcomes any cohesive forces
that are actually holding the body
together including its own self gravity
so it is a class of asteroids that have
been observed it's a very small number
of them and we think probably multiple
things are happening you can imagine the
commentary kind of activity the YORP
spin up or an impact basically anything
that causes an asteroid to develop a
coma of fine particles around it would
would label it an active asteroid but we
have certainly never seen anything like
this from a spacecraft before you know
we looked at the Eros and Itokawa data
and we talked to our friends on Hayabusa
2 and they're looking
around asteroid you goo none of those
missions have ever detected active
particle injection from an asteroid
surface before so it's a really exciting
opportunity to be able to characterize
and understand the phenomena and decide
if it is related to what's happening on
other active asteroids or it's a
completely unique occurrence
one thing that makes Bennu very different
is you wouldn't see this from
ground-based telescopes it's not a
massive amount of dust that would show
up as an extended coma when you're
looking at it like a comet thank you
our next question comes from Chance
Theron New York Times. Hi, thanks so much
for taking the call
I was wondering one of the major papers
says that we think that Bennu's surface
has changed over the last million years
do we understand why what process might
be creating that change
thank you that's also a great question
and there looks like there's several
processes that are going on on Bennu's
surface right now one of the things
might be related to this rotational
acceleration so you can imagine Bennu is
spinning faster and faster and as the
rotation rate increases you add angular
momentum to the surface and that can
trigger what we would call like a
landslide or a mass wasting event moving
material downslope filling in low-lying
regions of the asteroid we and we do see
evidence of that happening on the
surface it does look like large amounts
of material have moved on the surface
and are moving down from the polar
regions towards the equatorial areas so
we have active geology going on on the
surface the other thing that we're
seeing are these particle events and the
some of the material is completely
leaving the asteroid but a lot of it is
actually falling back on to the surface
and we've only been watching it for a
few weeks and this might have been going
on for thousands or hundreds of
thousands of years so we're still trying
to understand what kind of resurfacing
might have taken place as a result of
these particle ejection and fallback
events on the surface interesting and do
you happen to know if the [unintelligible]
period that lasted helped create the
spinning top shape or might this activity
be creating that?
and well I would say we we thought
before we arrived that it would be the
increase in rotation rate that would
lead to the spinning top shape that was
the leading theory going into the
encounter with the asteroid but as with
all things once you get there and you
start studying the object itself
you know that idea starts to get
questionable and the real reason we're
questioning that model is because these
large impact craters which are all over
the equator of the asteroid and it would
take a long time we estimate at least a
hundred million years to a billion years
in the main asteroid belt to produce
that crater population so the rotational
acceleration has got to be a relatively
new phenomenon because it's so large
that if it you know been a would have
had to almost be not rotating at all
even eight million years ago to see what
we're seeing right now it probably
started when Bennu shifted from the main
asteroid belt into the near-earth
population so again this is why we
explore we've learned something
surprising and it's making us reevaluate
our understanding of the basic formation
mechanism of spinning top asteroids and
we're still we're still getting
sharpening our pencils and really
collecting the data before we start to
zero in on what we think the answer is
thank you
our next question comes from Rick Lovett
freelance
your line is open thank you yes I have, uh can
you give me the velocity range of the particles
being ejected and why don't they all
either an eject into interplanetary
space or fall back because it seems like
you're basically firing bullets out of
the surface how do they wind up in orbit
right so we are seeing velocities of the
particles from just a few centimeters
per second up to about 3 meters per
second and the fastest moving particles
and really you're seeing a whole range
of velocities there and again remember
we're still in the process of developing
the tools and refining those numbers and
the work that Coralie and her team are
doing are really contributing
substantially to that and so we're
seeing in some cases
of particles that are being ejected in a
single event and you're going to have a
range of velocities some of them are
moving so fast they leave the asteroid
some of them are moving so slow they
basically go up and right back down to
the surface and then some of them are in
the sweet spot where there just happened
to have the right velocity in the right
direction to be injected into orbit
around the asteroid and we're still
trying to understand how long those
orbits are lasting we have seen at least
one particle that orbited for about a
week and then it did fall back down onto
the surface and we're evaluating other
groupings of detections
to see if there's any long-lived orbits
we do know that it's possible through
our amazing radio science team they've
done an analysis of stabilities of
orbits and there are orbits that could
last months or years they're very
special locations so it would just be
fortuitous if a particle got injected
right into that regime where it lasted
for a long time so my prediction right
now and just as a reminder we're still
this is new not even a month old in some
cases data and we're still trying to
figure out what's going on is that most
of these are going to be short-lived
satellites weeks to months and end up
reimpacting the surface okay thank you one
other question this is basically for
NASA where the image is going to be
located online when I went to that
website all I got was the press release
so you're asking about early release
images I mean ultimately the the images
will be planetary data system along with
all the rest of our archived data from
the Planetary Science Division I'm
meaning the ones that we're being
discussed today will we be able to look
at them so we released we released one
image of one of the biggest particle
events and those will be on the asteroid
mission org website and then we are
compiling all of the information and
preparing for publication and I'd like
to say that's happening sooner rather
than later but it's a big effort with a
big team and a lot of people working so
we're we want to make sure we get it
right
when that publication comes out all of
the data that went into the analysis
will be available as well okay thank you
thank you our next question comes from
Emily Conover science news magazine hi
so I'm not sure if I missed this but I was
wondering so for the particles that are
orbiting how high off of the surface of the
asteroid are are these things orbiting
thank you again we're still evaluating
all of the orbits we certainly have a
lot more detection than orbital
solutions at this point and it's a
tricky problem because not only are we
dealing with the gravity from the
asteroid which is very small but because
of that the radiation pressure from
sunlight and even thermal radiation from
the asteroid and from the particle
itself end up influencing its trajectory
most of the really I've only seen for
orbital solutions coming from the team
so far and maybe Coralie wants to
comment on this as well most of those
have been in very low altitudes within
the range of 100 300 meters from the
surface we had one that actually got up
to about 1.2 kilometers from the surface
right around the range that the
osiris-rex spacecraft was orbiting and
so that's kind of the bounds that we have
so far but again there's a lot more data
than we've been able to obtain orbital
solutions for and maybe Coralie do you
want to speak to how we're going about
orbit determination on the particles? Uh,
yeah it takes some identifying particles
associating them with each other from
image to image so we're developing
software toolset to have still have a
human in the loop but make it easier to
identify and track those initial some of
the initial particle ejection events and
then if we want to get an initial kind
of prediction for where they were going
then we go look in more images into the
future and see if we can observe detect
more observations of these particles to
refine their orbits so we're work is
underway to to build up the toolset and
and we studied a few particles so far
our next question comes from Kimberly
Cartier EOS.org your line is open
hi thank you for taking my question
you spoke about the composition of Bennu
being phyllosilicates and other clay
minerals how similar is this - some
meteorites that we've seen fall to earth
or measure our other asteroids we've
measured in space thank you that's a
great question and I can say that we we
are seeing nice correlations between the
spectral characteristics of Bennu both
from the OVIRS visible and infrared
instrument and from the OTES thermal
emission spectrometer and they look a
lot like the rarest most fragile friable
meteorites in our collections these are
special types of carbonaceous chondrites
and we use letters to designate them and
they look a lot like the CM chondrites
which are related to a big event in
Australia where we have most of that
material in 1969 in Murchison and so
we're optimistic that we have material
similar in mineralogy to what we've seen
in those very organic rich and water
rich meteorites I will say I'm a
meteorite scientist by training and
background and when I look at the rocks
on the surface of Bennu they don't look
like those meteorites do in hand samples
so there's definitely other things going
on there it's very exciting from that
perspective so and we're also seeing
things at meters and tens of meter
scales that we never had meteorites in
our collections that look like that but
I would say spectrally and mineralogically
they look like they match those rare
carbonaceous chondrites but the nature of
the boulders are suggesting there's more
to the story than what we know from our
meteorite samples so far thank you
I'm Ken Kramer Space UpClose your line
is open
hi thanks for taking my question and for
doing this yeah my question is about the
the compositions actually I wanted to
know what what do you know about the
composition of the ejecta particles
the phyllosilicates what did you expect
to see that on the surface or not and
have you seen any any carbon compounds
at all thank you those are all great
questions so I'll start with what we
have seen which are the both the
phyllosilicates and the iron oxides and
those are not unexpected those were
actually kind of the minerals we were
hoping to see water rich materials
basically indicating that sometime in
the ancient past probably very soon
after the solar system formed in a much
larger asteroid which we think was
Bennu's parent there was icy material
and rocky material that got a little bit
heated up and the water reacted and
formed those clay minerals we haven't
detected the carbon bearing compounds of
the organic molecules yet we do expect
that they're there just by similarity
with the carbonaceous chondrite
meteorites whenever we have those water
rich clay minerals they're associated
with organic material and we think one
of the reasons we haven't been able to
detect them is the wavelength range
where those spectral signatures occur
are longer wavelengths more heat that's
coming off the asteroid would make it
harder to detect that signal and the
good news is the asteroid is getting
farther away from the Sun the surface is
going to be cooling off and by the time
we get to the mapping station that's
optimized for the detection of organics we
expect that the amount of interference
from the thermal radiation from the
surface will decrease and then on to
your question about the particle
composition we're looking at particles
that are centimeter to tens of
centimeters in size and there's hasn't
been an opportunity to get the
spectrometers on those to see if we can
detect them and that's going to be a
challenging observation because the
particles occur unexpectedly we can't
predict when they're going to eject from
the surface and we can't just be
scanning all the time in the space
around the asteroid and hope of catching
one so it will be fortuitous if we
actually make a measurement that has
particles in the spectrometer fields of
view but that doesn't mean we're not
going to try in one of the survey
that are coming up in a few months is
optimized for looking at plumes and and
particles being ejected from the surface
we basically get behind the asteroid so
we're looking at the night side and the
limb will be illuminated by the Sun
which will be on the opposite side of
the asteroid so if there's dust or gas
that will be really well seen with the
cameras because the light will be
scattered and they'll really show up
with a nice strong signal and we'll also
have the spectrometers on to try to
characterize the plume events in that
instance thanks there will be no further
question thank you for participating and
have a great day this concludes today's
briefing.