liftoff we have a liftoff 32 minutes
past the hour lift up on apollo 11.
tower cleared
again
one
welcome to this edition of nasa images
i'm lynn bondurant during this show
we're focusing on results of spacecraft
examination of comet halley and the
seventh planet from the sun uranus
let's begin with some images from uranus
acquired in early 1986. the place is the
nasa jet propulsion laboratory in
pasadena california
well just about two minutes ago
voyager 2 passed through its closest
approach
to uranus
next speaker is dr bradford smith the
imaging team leader
just uh just for the moment let me show
you a lower resolution
image that we have
so what you're seeing here is where it
is very red you're seeing a lot of haze
and where it's blue it's relatively free
of haze and the first thing you notice
is though is that as you look toward the
limb of course you're going to be
looking through more atmosphere and
seeing more haze and so we see this
brightish
what we call limb brightening around the
limb of the planet indicating looking
into the atmosphere and seeing quite a
bit of the particulates of haze that are
in the atmosphere
i thought it might be a good time now to
give a summary of what we've learned so
far it's going to be a very brief
summary and i'm certainly not going to
be able to go into many details but at
least just to review where we stand and
what we've done over the last several
hours
we have been seeing the playback of
recorded photographs taken primarily of
the satellites the the major satellites
the five satellites of uranus uh at the
time that we passed by those most
closely
i think that i want to run through some
of those i think we'll start out with
this one of ariel this is a part of a
mosaic
of the
of one of the brightest of the
satellites
and
the whole mosaic
consisted of this in the upper left
and one picture down the lower left and
some of the more interesting things are
such
views as this
a rather
large bright area which is probably
associated with a crater another crater
here bright area
and
then
moving on with another view of ariel the
upper right and some of these canyons
through here
down around this area much of the
unusual terrain and
quite strange
another view the lower right and this
feature right here
it appears that some of these valleys
are
sunken
uh there's been internal activity on
these moons and a lot of it and it's
surprising
move on then to over on this is not as
anywhere near as close as the as the one
we just saw
and miranda this is a somewhat distant
shot of miranda we will get much closer
unusual feature we saw there was called
this chevron formation but we'll get a
better picture of that as we get in
closer to miranda
because indeed we did get close this is
the one where we saw things down to a
kilometer resolution and structure here
in miranda which is quite quite amazing
the black dropout across the middle here
we believe is somewhere in the
transmission and since this is played
back from a tape recorder another
playback will recover the information
from that section
here a
curious flow of material down in this
direction that's what it appears to be
uh but of course it was further analysis
to see what it is but something's been
going on in miranda it's a very small
moon
uh 500 kilometers across and uh
just to have this much activity in such
a moon is quite different than what we
saw
for example in the moons of saturn
another part of the mosaic still another
part again very curious markings on the
surface
and right in the middle the chevron we
saw at a great distance is now
this object here
what is it well further analysis may
tell we hope
and then backing off with a wide-angle
lens to get the comp complete picture
and then looking back toward uranus and
let's now talk a little bit
about all the other things we've seen
besides photographing the satellites
we have
discovered uh
one more small satellite making ten in
all that have been discovered by the
voyager and its approach and near miss
of or close approach to the planet
uranus we also discovered another ring
above so that makes a total of 10
small moons discovered and 10 rings uh
one discovered by voyage by voyager the
other were known previously this is a
ring picture taken from on the approach
to uranus
and you can see the major the i think
this is the epsilon ring is a bright one
and then some others inside of it we
also tried another one going when we got
behind the planet with the sun shining
through the rings toward
the the voyager spacecraft to take a
picture then
we expected to see a very bright glimmer
because of the very small particles in
the ring which
when this backlighting arrangement would
tend to glow just as when you see dust
motes in the sunlight shining through a
window towards you you can see lots more
dust than you can if you actually look
at from this point of view of the sun
small particles tend to scatter light
directly forward keep it going
surprisingly enough we saw very little
in that from that viewpoint which is a
bit of a mystery how come there's a
little dust
we've measured the magnetic field now we
it was very almost before almost we were
almost
two uranus before we discovered that
there was indeed a magnetic field if it
hadn't had no magnetic field that would
have been a real problem but there is
it's about 15 percent weaker than the
earth's on the surface
as curious thing about it is this uranus
has its axis pointed pretty much
it's pole south pole by committee
decision
pointed toward the sun so if the sun's
over there that's where the
this pole is spinning around like this
on that axis the magnetic the magnetic
field however is on a pole at an angle
55 degrees so as
as the
as uranus spins around on its spin axis
the magnetic field is spinning around
like this which is making is going to
make some very curious
effects on the total field
we have
displayed now on the screen a picture of
titania there'll be two of these
very much the same one is sort of
insurance for the other
this one is in
and the second one should be coming in
any minute in the meantime
we have also had the best two pictures
of
umbriel which is here very
almost featureless
and by the way these are the two
pictures that came in there
are
very similar to each other
taken very close together
i think the thing which uh surprised uh
most of us was not that miranda
necessarily had all these tectonic
structures uh on the surface but that
there was such a variety
that it was really a very complex
distribution
and i think the other thing that
surprised me was the extreme relief uh
which uh which seems to be present on
the surface it's not a very subtle uh
property at all one sees very very
sharp scarps of ridges one sees a groove
terrain one sees terrain similar to that
which we saw on enceladus which is
somewhat twisted it's just a remarkably
complex surface
and uh
these are those cliffs up at the top
those are very high cliffs
which uh
which are quite remarkable uh they're
they terminate a very rugged hilly
terrain
uh which uh uh may well be a place where
there is a basically lateral thrusting
and
down the lower portion of the planet
we call it a planet it looks like yes
that's right
this moon uranus we saw we see again
some of the same curious lines that are
going that's right that's right
fractures this the surface has been
heavily fractured uh by some sort of
processing uh there may well be some
layering on it in the in the lower right
hand
portion of this image where one sees
these alternating dark and lighter
streaks that's right
perhaps that's layering of material it's
really a remarkably complex surface for
an object that's barely 300 miles in
diameter
the rings of uranus have some provided
some thrills and surprises for several
voyager scientists those who specialize
in studying planetary rings one of those
is dr jeff cuzzy from nasa's ames
research center and he's with me now and
just let's talk about these strange
rings and i'm going to ask if somebody
can to put up
on uh on one of our video ports 70 this
picture we want uh jeff
the rings have been
well we knew about that they were there
before
before voyager got there
but we've discovered quite a bit more
about them and particularly about the
detailed structure since we've been
there what can you say about them well
you know the main rings of uranus oliver
were known from stellar occultations uh
several of us who think about rings
tend to associate small objects debris
if you like of
leftover from the formation of the moons
and the planet that are associated with
rings when you have all this debris
around with the impacting meteoroids
that are always there you always expect
to have dust now this dust is very
short-lived because it drags into the
planet it gets destroyed by the magnetic
fields better way one thing another so
the location of the dust is a very
important tracer of where the material
is and so we were very uh eagerly
anticipating the existence of the
structure of the dust now because of the
magnetic field
and probably because of the the
perturbing effect of the magnetic field
on the charged particles that are small
most of the dust seems to have been
removed from the uranus system and this
is the picture we got at that point yeah
that is an absolutely spectacular
picture and it shows basically that most
of the region
of the known rings is
is more or less replete with dust
the voyager uranus encounter has shed
new light on this unique planet
some of the preliminary findings include
10 new moons were discovered one new
ring was found
two shepherding moons are located near
the epsilon ring
the rings are slightly varying in
composition and color
and are complex in
structure the five known moons are an
ice rock mixture
with evidence of ancient geological
activity
ariel was volcanic in the past
miranda is considered the strangest body
in the solar system by many jpl team
members
it has scarps cliffs and layering
the atmosphere of uranus is 15 helium
and the rest is hydrogen ammonia and
methane
the planet may have a rocky core of the
size of earth
uranus is covered with an ocean of
mostly water methane and ammonia our
next report comes to us from the nasa
ames research center near san francisco
the report was released in 1987
and summarizes some of the findings of
the pioneer venus spacecraft which
earlier examined comet halley as it
looped around the sun
as long as man has been conscious of the
sky
comets have been objects of special
fascination
our ancestors thought they were omens of
ill fortune
today we see them much differently
dr jeffrey cuzzy is a nasa scientist who
specializes in comets today we know
comets are not magical apparitions but
mountain-sized dirty snowballs of ice
and rocky dust there are living fossils
left over from the early days of the
formation of the solar system but there
may have been some truth to the old
superstition
a large comet hitting earth may have
been the cause of the death of the
dinosaurs and other comets may have
caused earlier episodes of mass
extinction
even today earth is not entirely safe
from comets
in 1908 in a remote area in russia 200
square miles of forest were blown down
by an explosion with the force of a 12
megaton bomb
it was probably caused by a large comet
exploding in the atmosphere
experts estimate that a comet strikes
earth about once every million years
there are a number of reasons for
studying comics well the more we learn
about the material comets are made of
and the way that material is put
together the better idea we'll have of
the situation on which the planets of
the solar system form it is extremely
difficult to reconstruct our planet's
origins by studying the material it is
composed of today
even the oldest rocks on earth have been
changed and modified repeatedly by
geological processes such as melting and
solidification
wind and water erosion
in the 1970s nasa studied a number of
different missions to halley's comet one
of the brightest and best known of the
thousand or so comets that pass
periodically by earth
but budgetary constraints kept such
emission from getting off the ground
nevertheless the 1986 return of halley's
comet
proved to be a scientific spectacular
almost all the world's telescopes were
riveted on the comet
in addition the soviet union japan and
the european space agency launched
spacecraft to rendezvous with a famous
visitor
meanwhile at nasa's ames research center
in mountain view california u.s
scientists found an innovative way to
participate
richard femmel
nasa's pioneer project manager
in 1981 we started looking into how
we could use an existing spacecraft to
make measurements of halley's comet as
it came by
this spacecraft is the pioneer venus
orbiter which was already in orbit
around the planet venus it was inserted
in orbit in december of 1978
the surface of venus is completely
obscured by a heavy cloud cover so we
really knew very little about the
surface
of the planet
the pioneer venus mission consisted of a
pair of
the orbiter and a multi-probe which
carried four instrumented probes which
were released before the spacecraft
reached venus and they plunged to the
surface of venus making their
measurements with the instruments on
board as they were probes were
descending to the planet's surface
together the orbiter and the moly probes
provided information about
the atmosphere of venus and why it is so
searingly hot and dense
also another instrument on board the
spacecraft took thousands of images of
the cloud cover of the planet venus
helping to explain the atmospheric
circulation about the planet and
unraveling many of the mysteries that
venus has held
fortunately the cosmos arranged it so
that we had a ringside seat as halley's
comet came by
in its path closest to the sun which is
the time when the comet is its most
active
halley's like all comets is made up of
several parts
the nucleus is a large dirty snowball
frozen as hard as marble
it is composed of roughly 40 percent
water ice 10 frozen gases and 50
dust and rock
when a comet's looping orbit carries it
close to the sun the intense sunlight
begins to boil dust and gas from its
surface
invisible hydrogen gas forms a large
egg-shaped cloud called a coma and the
comet develops two spectacular tails a
straight tail made of electrically
charged gas
and a curved dust tail
at the university of colorado boulder dr
ian stewart chief scientist of the
pioneer halley's mission determined that
he could make unique and valuable
measurements of the comet using one of
the orbiter's instruments
in 1983 when we looked into the
possibility of observing halle from
pioneer venus we realized that it would
come within shouting distance
celestially speaking and that we could
make really valuable measurements of the
hydrogen coma when dr stewart explained
his conclusions to us we were
immediately enthusiastic
we knew of course that it would mean a
lot of extra work but we also knew that
it would provide the united states with
a unique halle mission capable of making
continuous measurements through the
entire perihelion when the comet was at
its most active relative to using the
ultraviolet spectrometer instrument to
look at comet halley
that was not originally planned as part
of the pioneer venus
orbiter
experiments as they were laid out errol
montoya pioneer program manager for nasa
we had
very innovative bright people say what
if we rotated the cam the spacecraft so
it would look out at comet halley well
it turned out that
the mission could be accomplished the
gathering of these uh of these
measurements using the ultraviolet
spectrometer device at no additional
cost the operation seems to be going
very very smoothly at this point
the spacecraft instrument that dr
stewart used is called an ultraviolet
spectrometer like a prism a spectrometer
divides light into different colors or
wavelengths
by measuring the brightness of the light
at each color scientists can tell a
great deal about its source
dr stewart's ultraviolet spectrometer is
fixed to the rotating orbiter
so the spacecraft had to be reoriented
in order to observe the comet now
normally
the spacecraft in orbit around venus is
orbiting with the high gain antenna
pointed towards the south ecliptic pole
or we would look at it as upside down as
the spacecraft is spinning
in order to
observe halley's comet which is coming
by venus up and above we had to
carefully rotate the spacecraft 135
degrees
so that the ultraviolet spectrometer
would be looking up and have the comet
in its field of view as it rotated once
every 12 seconds
in the process of doing this a number of
things had to be paid attention to we
had to keep the solar panels properly
oriented so they were receiving sunlight
and to provide the power for the
spacecraft we had to make sure that our
star tracker had a bright star in the
field of view so that we were would be
able to maneuver and check the
orientation of the spacecraft and we
also had constraints on the position
because the high gain antenna can only
move a limited amount in elevation and
that has to stay pointed at earth as it
is de-spun halley's orbit takes it from
the outer reaches of the solar system
about the orbit of uranus to within 55
million miles of the sun well because
halley's comet is most active when it's
close to the sun it is most important to
observe it at that time as halley's
comet made its closest approach to venus
and we were in the midst of our critical
imaging sequence to get an image of the
comet's coma
nature through a number of obstacles in
our way
threatening
to disrupt the entire data stream for us
first we had a giant solar flare which
interfered with radio communications
between the spacecraft and earth that
was followed then by rain
in the mojave desert and snowstorm in
madrid and both of these also
attenuated the radio signal causing more
errors in the data
well in spite of all these problems we
were able to get all of the data that we
needed the centerpiece of our
observations of the of the comet was
this false color image of the hydrogen
coma the scale is immense it's the image
that you see is 12 million by 8 million
miles
and briefly as during its passage past
the sun halley was the largest object in
the solar system the image uses color to
represent brightness the blues and reds
are the darker
levels of light and the yellows and
greens are the brightest parts of the
comet
well analyzing the image and other data
allowed us to
estimate the rate at which water was
subliming away evaporating away from the
ices of the nucleus our measurements
turned out to be in reasonable accord
with european and soviet measurements
and they indicate that the comet is
losing one or two hundredths of a
percent of its total mass each time it
passes the sun
before this last visit many scientists
had assumed hallie's was a relatively
fresh comet so the extent of the erosion
and the amount of dark crust on the
nucleus came as a surprise
pioneer venus observations showed large
daily variations as much as 25 percent
in the rate at which water was boiling
off the comet
the best explanation for this is that
only portions of the comet's surface had
freshly exposed ice that could act as
sources of water vapor
the evaporation rate varied depending on
how much of this fresh material was
exposed to sunlight as the nucleus
rotated
the orbiter's observations fit nicely
with those of the european spacecraft
jato which passed about 300 miles from
the nucleus
its cameras revealed a cold black object
three to four times larger than the size
estimated for a fresh comet
the nucleus also appeared highly
irregular almost potato shaped
suggesting it was once much larger and
has eroded away over a long time
pictures from jotto also showed gas jets
spewing from the nucleus and the orbiter
measured their velocities as high as one
thousand one hundred miles an hour
while the gas escapes most of the dust
that boils off the nucleus remains in
the comet's feeble gravitational grip as
the comet moves back out away from the
sun the dust rains back onto the comet's
surface
scientists have begun to realize that
this dust plays a central role in the
life cycle of a comet well when the
layer of dust becomes about three inches
thick
it'll act as an insulating blanket and
insulate the ice from the heat of the
sun and once that happens the ice no
longer evaporates so the comet loses all
its cometary features like tails and
dust tails and iron tails
and then it looks a lot like an asteroid
scientists estimate that comets make
only a thousand or so passes around the
sun before they're reduced to inactive
objects like asteroids
with even a partial dust crust a comet
is slower to warm up and develop a tail
once heated however the dust blanket
retains the warmth and the comet keeps
its tail longer
that's why halley's was brighter in
april when it was leaving the sun
then in december when it was approaching
the orbiter's observations showed that
the nucleus remains surprisingly
inactive until a few weeks before the
comet's closest approach to the sun
but it stayed 30 percent more active on
the outbound leg of its journey
it is surprising that the activity turns
on so suddenly the comet gets to within
a certain distance of the sun then it
starts to pop like popcorn
the pioneer venus orbiter made a number
of other important observations
for instance it measured the
concentrations of hydrogen oxygen carbon
and hydroxyl ions given off by halley's
nucleus
combined with the observations made by
other spacecraft this information is
helping scientists calculate the comet's
composition
while it has given scientists a much
better picture of what halley's is like
the new data is also raising questions
that can only be answered by future
comet missions
one such mission is craft but comet
rendezvous and asteroid flyby it
involves shooting a probe into the heart
of a comet nucleus to get the first
direct measurements of what it is made
of
scientists will study the new
information on halley's for decades
as a result our knowledge about the
origin of the solar system about its
primordial mountain-sized building
blocks and how they join together to
form the earth and other planets will
continue to grow
in this fashion
humanity will gain the understanding of
its ultimate environment
the cosmos
that's all we have for this edition of
nasa images but before we go let me
remind you that you're cordially invited
to see the displays at the visitor
center here at the nasa lewis research
center
we're located near the hopkins
international airport in cleveland
admission is free
until next time this is lynn bondurant
saying goodbye
you