[Senate Hearing 108-960]
[From the U.S. Government Publishing Office]
S. Hrg. 108-960
THE VIEWS FROM SATURN
=======================================================================
HEARING
before the
SUBCOMMITTEE ON SCIENCE, TECHNOLOGY,
AND SPACE
of the
COMMITTEE ON COMMERCE,
SCIENCE, AND TRANSPORTATION
UNITED STATES SENATE
ONE HUNDRED EIGHTH CONGRESS
SECOND SESSION
__________
JULY 22, 2004
__________
Printed for the use of the Committee on Commerce, Science, and
Transportation
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SENATE COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION
ONE HUNDRED EIGHTH CONGRESS
FIRST SESSION
JOHN McCAIN, Arizona, Chairman
TED STEVENS, Alaska ERNEST F. HOLLINGS, South
CONRAD BURNS, Montana Carolina, Ranking
TRENT LOTT, Mississippi DANIEL K. INOUYE, Hawaii
KAY BAILEY HUTCHISON, Texas JOHN D. ROCKEFELLER IV, West
OLYMPIA J. SNOWE, Maine Virginia
SAM BROWNBACK, Kansas JOHN F. KERRY, Massachusetts
GORDON H. SMITH, Oregon JOHN B. BREAUX, Louisiana
PETER G. FITZGERALD, Illinois BYRON L. DORGAN, North Dakota
JOHN ENSIGN, Nevada RON WYDEN, Oregon
GEORGE ALLEN, Virginia BARBARA BOXER, California
JOHN E. SUNUNU, New Hampshire BILL NELSON, Florida
MARIA CANTWELL, Washington
FRANK R. LAUTENBERG, New Jersey
Jeanne Bumpus, Republican Staff Director and General Counsel
Robert W. Chamberlin, Republican Chief Counsel
Kevin D. Kayes, Democratic Staff Director and Chief Counsel
Gregg Elias, Democratic General Counsel
------
SUBCOMMITTEE ON SCIENCE, TECHNOLOGY, AND SPACE
SAM BROWNBACK, Kansas, Chairman
TED STEVENS, Alaska JOHN B. BREAUX, Louisiana, Ranking
CONRAD BURNS, Montana JOHN D. ROCKEFELLER IV, West
TRENT LOTT, Mississippi Virginia
KAY BAILEY HUTCHISON, Texas JOHN F. KERRY, Massachusetts
JOHN ENSIGN, Nevada BYRON L. DORGAN, North Dakota
GEORGE ALLEN, Virginia RON WYDEN, Oregon
JOHN E. SUNUNU, New Hampshire BILL NELSON, Florida
FRANK R. LAUTENBERG, New Jersey
C O N T E N T S
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Page
Hearing held on July 22, 2004.................................... 1
Statement of Senator Brownback................................... 1
Witnesses
Figueroa, Orlando, Director, Solar System Exploration Division
and Mars Program Office, Office of Space Science, National
Aeronautics and Space Administration; accompanied by Mark Dahl,
Cassini Program Executive and Denis Bogan, Cassini Program
Scientist...................................................... 2
Prepared statement........................................... 5
THE VIEWS FROM SATURN
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THURSDAY, JULY 22, 2004
U.S. Senate,
Subcommittee on Science, Technology, and Space,
Committee on Commerce, Science, and Transportation,
Washington, DC.
The Committee met, pursuant to notice, at 2:35 p.m., in
room SR-253, Russell Senate Office Building, Hon. Sam
Brownback, Chairman of the Subcommittee, presiding.
STATEMENT OF HON. SAM BROWNBACK,
U.S. SENATOR FROM KANSAS
Senator Brownback. The hearing will come to order. Thank
you all for joining us today. We've got another exciting space
hearing. For a guy who grew up on a farm to be able to talk
about Saturn, this is fun, and to be able to do that.
I want to welcome you, Mr. Orlando Figueroa, NASA Solar
System Exploration Director, today, delighted to have you here
with your colleagues to discuss the spectacular discoveries of
the Cassini Huygens mission to Saturn. I'm awestruck at the
pictures, the images I see coming back, and the exploration
that has occurred. As I travel around my home state of Kansas,
so too are the American people.
A few months ago, we watched just two small emissaries from
Earth. The Mars Rover found evidence for a complicated and
interesting past history on the planet Mars, including the
probable presence of significant water on its surface at some
time in the distant past. Now we watch as NASA's mission to the
giant planet Saturn unfolds. Already we are discovering truths
about our own planet's past. Saturn represents a miniature
solar system, and by studying it, we can learn more about how
Earth came to be as it is in the larger solar system.
I have several thoughts I'd like to share with you in which
I'd like your response to. First, both the Saturn mission and
the Mars mission represents considerable international
cooperation. In both cases, the United States worked closely
with our international partners, particularly those in Europe,
to achieve a mission which is more than the sum of its
international parts. I think the key in establishing
relationships is where partners assume a significant portion of
the overall mission and are not just subcontractors on a U.S.
mission. This, of course, means they assume responsibility for
funding their portion of the program.
In the cases of both Mars and Saturn, they have done just
that. I believe this is an essential template as we embark on
even more impressive exploration in support of the President's
expanded vision of space exploration, culminating in human and
robotic exploration of the moon, Mars, and beyond.
My second observation concerns opportunities in the private
sector. I note that both Cassini and the Mars Rover were built
by the most private sector of the NASA centers, the privately
managed jet propulsion laboratory. The recent Aldridge
Commission recommended that all the NASA centers move toward
this private sector management approach. This is an essential
step, and I intend to work hard to make it a reality.
However, I do not think merely managing government centers
by a private concern is sufficient. If we are to achieve the
true promise the solar system offers our children, we must
energize the full talents of the real private sector, men and
women willing to spend their own hard-earned resources in space
in order to achieve the benefits of the new opportunities
there. I think this must start as it did with our own expansion
across the continent two centuries ago. As the government leads
pathfinding exploration of the moon and Mars, it should
purchase its tools and information from that private sector,
just as the government explorers purchased their provisions
from private settlers and outfitters in the 19th century,
beginning with Lewis and Clark.
I must tell you I'm in that way somewhat challenging to
NASA's approach to the first new robotic mission in support of
the President's vision, the lunar reconnaissance observer to be
launched in 2008. This seems to me to be another government-
developed, built, and operated system, not really different
from the past. And I would hope NASA would look at that and we
can have some discussion on that today of why it's not turning
more to the private sector on that issue.
So as we ponder the wonder and opportunity in the solar
system, I'd like to focus our attention on the future. These
magnificent pathfinding missions are only a taste of what's to
come in science, discovery, and most important of all,
opportunity. I believe a new paradigm in our relationships with
international partners is beginning. I also hear the words of
the Aldridge Commission and others calling for a renewed
commitment to private opportunity, and let's make that one real
too.
Mr. Figueroa, thank you very much for coming here today. I
want to congratulate you and NASA on a spectacular Saturn
mission thus far. It really has been mind-opening and another
great success, so I'm delighted to hear that, delighted to see
that, wanted to have you here today to be able to present that,
and then I hope along the way you can answer the two issues
that I raised at some point as well.
STATEMENT OF ORLANDO FIGUEROA, DIRECTOR,
SOLAR SYSTEM EXPLORATION DIVISION AND MARS
PROGRAM OFFICE, OFFICE OF SPACE SCIENCE, NATIONAL
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION;
ACCOMPANIED BY MARK DAHL, CASSINI PROGRAM EXECUTIVE AND DENIS
BOGAN, CASSINI PROGRAM SCIENTIST
Mr. Figueroa. Yes, indeed. Good afternoon and thank you
very much, Mr. Chairman. I am very pleased to be here this
afternoon to discuss the latest success in NASA's space science
program, Cassini's arrival at the lord of the rings, the planet
Saturn.
I want to thank you for holding this hearing and for your
continued support for our programs. I have written and
submitted my written statement and also have left a copy of
this package for you where exquisite details about the mission
is provided.
Senator Brownback. Your full statement will be put in the
record.
Mr. Figueroa. Thank you. If I may, I want to take a moment
to introduce my colleagues, Dr. Denis Bogan to my left, the
program scientist for the Cassini mission, and Mr. Mark Dahl,
the program executive from the mission, both from the NASA
headquarters.
Senator Brownback. Welcome, gentlemen.
Mr. Figueroa. They will certainly help me answer
engineering and science questions that you and others may have.
Today I'm providing summary remarks of my testimony and beg
ahead of time for your indulgence for such an exciting topic,
as it is the arrival at Saturn, and will probably take a few
extra minutes, not many but just a couple.
Senator Brownback. Please take the time you need.
Mr. Figueroa. Now, almost 7 years ago, on October 15, 1997,
to be exact, an anxious and excited group of NASA employees,
the European Space Agency, the Italian Space Agency, 14 other
contributing countries, and thousands of spectators watched as
a massive Titan IV rocket lifted off Pad 41 at Cape Canaveral
Air Force Station and sent the Cassini spacecraft and its
Huygens probe on its long journey to unlock the secrets of
Saturn and its largest moon, Titan.
After having traveled more than 2 billion miles on a
journey that included two gravitational assist flybys of Venus,
one of Earth, and one of Jupiter, I am delighted to say that
the 2,000 pound, nuclear energy-enabled Cassini spacecraft
started its maneuver to enter Saturn's orbit at 7:26 p.m.
Pacific time on June 30.
After what seemed like an eternity, we got confirmation
that the 96-minute engine burn necessary to reduce Cassini's
speed was a success and Cassini was safely in its proper orbit.
This opened a whole new chapter of space exploration. Cassini's
four-year mission of discovery and science promises to surprise
scientists and all the public around the world. Seventy-six
Saturn orbits with 44 Titan flybys should make for an exciting
campaign of exploration around the gas giant, and this is
indeed a giant planet.
Unlike the two Voyager missions that flew by Saturn in the
early 1980s and obtained just days' worth of close-in science,
Cassini Huygens will be for Saturn what the Galileo mission was
for Jupiter, a long-term science observatory. Cassini's Saturn
approach science campaign began in January of this year, and
the majestic image of Saturn presented on my opening is a
product of such a campaign. Upon its arrival, Cassini awed us
with fantastic early images and data. After only 3 weeks in
orbit, we have already discovered a number of new things, some
of which I would like to share with you today.
We have learned that Saturn's moon, Phoebe, has a surface
covered with craters of varying size, probably from meteorite
impacts. The images and data have led scientists to believe
that the tiny object may contain ice-rich material overlain
within a thin layer of darker material perhaps ejected by the
impacts themselves.
Early mapping with spectrometers illustrate what we know
today about Phoebe's composition. This has led some to suspect
that Phoebe may have originated in the outer solar system,
perhaps in the Kuiper Belt, and have been captured by Saturn's
gravity, a longstanding theory. Just 2 days after the Cassini
spacecraft entered Saturn's orbit, preliminary science results
are already beginning to show a far more complex and
fascinating new world, as illustrated by the next two images,
where the structure and dynamics of the rings is evident.
The first image illustrates a complex structure that
resembles braiding in the outer two rings. Although such
braiding seems to have been stable for a long time, we do not
know what could cause such structure.
The second image illustrates the rippling that suggests an
unknown dynamic process shaping the edge of the ring, perhaps
due to an unseen moonlet. We observed hints of these ripples
with Voyager, but now we can see them with much greater
resolution.
While Saturn's rings are almost exclusively composed of
water ice, new findings show that they contain relatively more
dirt than ice in some regions. Further, the particles between
the rings seem remarkably similar to the dark material that
scientists now see on Phoebe. These dark particles refuel the
theory that the rings may be the remnants of the moon.
The day after orbit insertion, Cassini revealed surface
details of Saturn's moon, Titan. Titan's atmosphere is opaque
at most wavelengths, but the spacecraft captured some surface
details, including possible evidence of a geologically active
surface through infrared wavelengths in which the atmosphere is
clear. The light blue around the edge of the disk is the
atmosphere. The white spot, now known as the south polar cloud,
is believed to be methane and seems to be persistent.
A number of long held ideas are being challenged by the
early Titan results. Surface areas of high reflectants seem to
be composed of mixtures of water ice and complex hydrocarbons,
while dark areas are just water ice. These observations are
exactly backward from our expectations. Once again, Saturn
didn't read our books.
No evidence has been found for liquid hydrocarbons in pools
or lakes. These results have raised questions about whether
Titan possesses a primordial soup of hydrocarbons that could
yield insights about the prebiotic chemistry of Earth. We
cannot wait for the future flybys of Titan at a much closer
distance. The first flyby occurred at roughly 300,000
kilometers from the moon.
We are delighted with the surprises thus far and what they
have revealed in the Cassini mission in these early stages,
surprises at the very heart of science. If there were no
surprises, it wouldn't be science, but we have only begun to
scratch the surface. We are in the very early stage of this
fascinating mission. There will be much more science ahead. We
eagerly await December 24 when the Huygens probe, built by the
European partners, begins its descent toward the murky and
mysterious moon, Titan.
At this moment, Cassini is on a long path toward it before
it will turn around again and come inward toward Saturn on its
way to the next Titan encounter. Let us catch our breath and
prepare for more astonishing discoveries in the days to come.
[The prepared statement of Mr. Figueroa follows:]
Prepared Statement of Orlando Figueroa, Solar System Exploration
Director, National Aeronautics and Space Administration
Mr. Chairman and Members of the Subcommittee, I appreciate the
opportunity to appear here today to discuss NASA's Cassini-Huygens
mission. This has been an amazing year for NASA's Space Science
Program. In January, we landed the twin rovers Spirit and Opportunity
on the surface of Mars, and they have been sending back incredible
scientific data and images since then. Then, just a few short weeks
ago, the world watched again in awe as we navigated the Cassini
spacecraft into orbit around the ``Lord of the Rings''--the planet
Saturn.
Mission Overview
The Cassini mission is an international cooperative effort of NASA,
the European Space Agency (ESA), and the Italian Space Agency (ASI) to
explore the planet Saturn. Eighteen highly sophisticated science
instruments (twelve in the Cassini orbiter, and six in the Huygens
probe) will study Saturn's rings, icy satellites, magnetosphere and
Titan, the planet's largest moon. In December of this year the Cassini
spacecraft will release the Titan atmospheric probe (Huygens) for its
descent through the murky atmosphere of Titan. The probe will collect
data on the composition of Titan's atmosphere and haze layers, and may
also create an image of Titan's surface. Understanding the chemistry of
Titan's atmosphere may be key to understanding the evolution of early
life on Earth. After delivering Huygens, the Cassini spacecraft will
perform several flybys of Saturn's icy satellites, acquire data on
Saturn's rings from various angles, perform radar mapping of Titan's
surface, and take measurements of Saturn's atmosphere, magnetic field,
and charged-particle environment. Cassini's primary science mission
tour is scheduled for 4 years of observations.
Why Saturn?
Saturn offers a rich scientific environment to explore. While the
other giant planets, Jupiter, Uranus, and Neptune, have rings, the
rings of Saturn are unique in the solar system in their extent and
brightness. They are the signature feature by which Saturn is known.
The planet and the ring system serve as a physical model for the disc
of gas and dust that surrounded the early Sun and from which the
planets formed. The success of searches for other planetary systems
elsewhere in our galaxy partly depends upon how well we understand the
early stages of the formation of planets.
Detailed knowledge of the history and processes now occurring on
Saturn's elaborately different moons may provide valuable data to help
understand how our Solar System's planets evolved to their present
states. Represented among Saturn's collection of moons are a huge
variety of chemical, geologic and atmospheric processes. Physics and
chemistry are the same everywhere, and the knowledge gained about
Saturn's magnetosphere or Titan's atmosphere will have applications
here on Earth.
Chief among Cassini's goals within Saturn's system is the unmasking
of Titan. Titan is the only moon in the Solar System that possesses a
dense atmosphere (1.5 times denser than Earth's). The fact that this
atmosphere is rich in organic material and that living organisms, as we
know them, are composed of organic material is particularly intriguing.
(``Organic'' means only that the material is carbon-based, and does not
necessarily imply any connection to living organisms.) Forty-four of
Cassini's 76 orbits through the Saturnian system will include Titan
flybys, and the Huygens probe is dedicated to the study of Titan's
atmosphere.
After decades of speculation and experiment in the modern age,
scientists still seek fundamental clues to the question of how life
began on Earth. Most experts suspect that life arose by chance
combinations of complex carbon compounds in a primeval soup. But all
studies of life's origin are hampered by ignorance about the chemical
circumstances on the young Earth. By understanding what starting
material was present at the beginning of life on Earth, we will better
understand our early beginnings. Cassini-Huygens' study of Titan may go
far toward providing the answer to these and many other questions.
In our Solar System, only Earth and Titan have atmospheres rich in
nitrogen. Earth's siblings in the inner solar system, Venus and Mars,
possess carbon-dioxide atmospheres, while Jupiter and Saturn resemble
the Sun in their high content of hydrogen and helium. Hydrocarbons like
the methane present on Titan may have been abundant on the young Earth.
The importance of Titan in this connection is that it may preserve,
in deep-freeze, many of the chemical compounds that preceded life on
Earth. Some scientists believe we will find that Titan more closely
resembles the early Earth than Earth itself does today.
The results from Cassini's instruments and the Huygens probe, along
with the results of our continuing explorations of Mars, Europa and the
variety of life-bearing environments on Earth, will significantly
enhance scientific efforts to solve the mystery of our origins.
Saturn's Allure
Saturn is easily visible to the naked eye, and was known to ancient
peoples around the world. It was not until the invention of the
telescope, however, that Saturn's characteristic rings began to come
into focus.
The Italian astronomer Galileo was the first to look at Saturn
through a telescope in 1609-10. Viewed through Galileo's crude
instrument, Saturn was a puzzling sight. Unable to make out the rings,
Galileo thought he saw two sizable companions close to the planet.
Having recently discovered the major moons of Jupiter, he supposed that
Saturn could have large moons, too. Galileo was even more astonished
when, two years later, he again looked at Saturn through his telescope
only to find that the companion bodies had apparently disappeared. The
rings were simply ``invisible'' because he was now viewing them edge-
on. Two years later, they again reappeared, larger than ever. He
concluded that what he saw were some sort of ``arms'' that grew and
disappeared for unknown reasons. He died never knowing that he had been
the first to observe Saturn's rings.
Nearly half a century later, the Dutch scientist Christiaan Huygens
solved the puzzle that vexed Galileo. Thanks to better optics, Huygens
was able to pronounce in 1659 that the companions or arms decorating
Saturn were not appendages, but rather the planet ``is surrounded by a
thin, flat ring, which nowhere touches the body.'' His theory was
received with some opposition, but was confirmed by the observations of
Robert Hooke and Italian-French astronomer Jean Dominique Cassini.
While observing Saturn, Huygens also discovered the moon Titan. A
few years later, Cassini discovered Saturn's four other major moons--
Lapetus, Rhea, Tethys and Dione. In 1675, Cassini discovered that
Saturn's rings are split largely into two parts by a narrow gap--known
since as the ``Cassini Division.''
NASA's Pioneer 11 spacecraft in 1979, and a few years later the
NASA Voyager 1 and Voyager 2, furthered our knowledge of the ringed
planet by detecting a magnetic field and revealing more details about
Saturn's complex moons and rings. The Voyagers found ring particles
ranging in size from nearly invisible dust to icebergs the size of a
house.
The Ringed Planet
Saturn is the sixth planet from the Sun and is 9.5 times farther
away from the Sun than Earth. From Saturn, the Sun is about 1/10th the
size of the Sun we see from Earth. Sunlight spreads as it travels
through space; because of this fact, the same light-driven chemical
processes in Saturn's atmosphere take 90 times longer than they would
at Earth. The farther away from the Sun, the slower a planet travels in
its orbit. Saturn's year is equal to 29.46 Earth years.
Saturn has the lowest density of all the planets and has a vast,
distended, hydrogen-rich outer layer. Like the other giant planets,
Saturn contains a core of heavy elements including iron and rock of
about the same volume as Earth, but having three or more times the mass
of Earth.
Scientists believe that the core of molten rocky material is
covered with a thick layer of metallic liquid hydrogen and, beyond
that, a layer of molecular liquid hydrogen. This conductive liquid
metallic hydrogen layer, which is also spinning with the rest of the
planet, is believed to be the source of Saturn's magnetic field.
Temperature variations in Saturn's atmosphere are the driving force
for the winds and thus cloud motion. The lower atmosphere is hotter
than the upper atmosphere, causing gases to move vertically.
Temperature variations, combined with the planet's rapid rotation rate
(a Saturn day is only 11 hours), are responsible for the high wind
speeds in the atmosphere.
Titan
Saturn's moon Titan presents an environment that appears to be
unique in the Solar System, with a thick hazy atmosphere containing
organic compounds, a possible organic ocean or lakes and a rich soil
filled with frozen molecules, similar to what scientists believe led to
the origin of life on Earth. In the three centuries since the discovery
of Titan, we have come to see it as a world strangely similar to our
own, yet located almost 900 million miles from the Sun. With a thick,
nitrogen-rich atmosphere, possible seas and a tar-like permafrost,
Titan is thought to harbor organic compounds that may be important in
the chain of chemistry that led to life on Earth.
Titan has been described as having an environment similar to that
of Earth before biological activity forever altered the composition of
Earth's atmosphere. The major difference on Titan, however, is the
absence of liquid water and Titan's very low temperature. Thus there is
no opportunity for aqueous chemistry at Earth-like temperatures--
considered crucial for the origin of life as we know it. Scientists
believe that the surface temperatures on Titan are cold enough to
preclude any biological activity whatsoever at Titan.
The opacity of Titan's atmosphere is caused by naturally produced
photochemical smog. With Titan's smoggy sky and distance from the Sun,
a person standing on Titan's surface in the daytime would experience a
level of daylight equivalent to about 1/1,000th the daylight at Earth's
surface.
The surface of Titan was not visible to Voyager at the wavelengths
available to Voyager's cameras. What knowledge existed about the
appearance of the surface of Titan prior to July 1 of this year came
from Earth-based radar measurements and more recent images acquired
with the Hubble Space Telescope at wavelengths longer than those of
Voyager's cameras. Hubble images from 1994 and later reveal brightness
variations suggesting that Titan has a large continent-sized region on
its surface that is distinctly brighter than the rest of the surface at
both visible and near-infrared wavelengths.
Titan's orbit takes it both inside and outside the magnetosphere of
Saturn. When Titan is outside the magnetosphere and exposed to the
solar wind, its interaction may be similar to that of other bodies in
the Solar System such as Mars, Venus or comets (these bodies have
substantial interaction with the solar wind, and, like Titan, have
atmospheres but no strong internal magnetic fields).
The interaction of Titan with the magnetosphere provides a way for
both the magnetospheric plasma to enter Titan's atmosphere and for
atmospheric particles to escape Titan. Voyager results suggested that
this interaction produces a torus of neutral particles encircling
Saturn, making Titan a potentially important source of plasma to
Saturn's magnetosphere. The characteristics of this torus are yet to be
explored and will be studied by the Cassini orbiter. The interaction of
ice particles and dust from Saturn's rings will play a special role as
the dust moves out towards Titan's torus and becomes charged by
collisions. When the dust is charged it behaves partially like a
neutral particle orbiting Titan according to Kepler's laws (gravity
driven), and partially like a charged particle moving with Saturn's
magnetosphere. The interaction of dust with Saturn's magnetosphere will
provide scientists with a detailed look at how dust and plasma
interact.
Titan may have its own internally generated magnetic field. Recent
results from the Galileo spacecraft at Jupiter indicate the possibility
of an internally generated magnetic field associated with the moon
Ganymede. For Titan there are two possibilities: A magnetic field could
be induced from the interaction of Titan's substantial atmosphere with
the flow of Saturn's magnetosphere (like Venus's interaction with the
solar wind); or a magnetic field could be generated internally from
dynamo action in a fluid core (like Earth's). (Under the dynamo theory,
a magnetic field is created by the circling motion of electrically
conductive fluid in the core.) In addition to being important to
understanding the Titan interaction with Saturn's magnetosphere, a
Titan magnetic field, if generated internally, would help scientists
define the natural satellite's interior structure.
The Rings
From a distance, the majestic rings of Saturn look like symmetrical
hoops surrounding the planet. In the best, most recent pre-Cassini
images, the rings appear to be a still splendid but somewhat unruly
population of ice and rock particles jostling against each other or
being pushed and pulled into uneven orbits by bigger particles and by
Saturn's many moons.
The mass of all the ring particles measured together would comprise
a moon about the size of Mimas, one of Saturn's medium-small moons. The
rings may, in fact, be at least partly composed of the remnants of such
a moon or moons, torn apart by gravitational forces.
Their precise origin is a mystery. It is not known if rings formed
around Saturn out of the initial Solar System nebula, or after one or
more moons were torn apart by Saturn's gravity. If the rings were the
result of the numerous comets captured and destroyed by Saturn's
gravity, why are Saturn's bright rings so different in nature from the
dark rings of neighboring planets? Over the lifetime of the rings,
comets and meteors must have bombarded them continually, and therefore
they should have accumulated a great amount of carbon containing, rocky
debris. However, spectra of the rings indicated a composition of about
98 percent water ice. Saturn's rings, as well as the rings of all the
other large planets, may have formed and dissipated many times since
the beginning of the Solar System. Studies of the main rings show that
the ring system is not completely uniform in its makeup and that some
sorting of materials within the rings exists. Why such a non-uniform
composition exists is unknown.
The Very Recent Past
In recent months, as Cassini drew near to its destination it began
returning images that exceeded the resolution of the best earth and
space based telescopes. This color ``postcard'', sent in February 2004,
offers one of the most stunning images ever of the mysterious ringed
planet. Even though Saturn loomed larger than ever, Cassini was still
more than 43 million miles away!
Two months later, the spacecraft was close enough to observe two
storms in the act of merging into one storm. This is only the second
time in history that this phenomenon has been observed on Saturn. While
storms on Earth have a relatively short lifespan, storms in the giant
planet atmospheres last much, much longer and often merge rather than
just dissipate.
In June, Cassini did a flyby of Saturn's moon Phoebe, thus
completing the first satellite flyby of its four-year prime mission. Up
close and personal, Cassini revealed that Phoebe's surface is covered
with craters of varying sizes, probably from meteorite impacts. The
images led scientists to believe that the tiny object contains water
ice, as was expected, overlain in many areas with one or more thin
layers of darker material that may have been ejected from the depths of
the craters by impact events. . The evidence thus far has strengthened
the belief that Phoebe may have originated in the outer Solar System,
perhaps in the Kuiper Belt, and been captured by Saturn's gravity.
The spacecraft navigators consider the tour to have begun with the
trajectory correction maneuver that targeted Phoebe in May 2004. The
rich science returned from the Phoebe encounter justifies this
viewpoint.
Bull's-eye
After almost seven long years and a journey of more than 2 billion
miles, the 12,000-pound Cassini-Huygens spacecraft successfully entered
orbit around Saturn at 7:26 PDT on June 30. The Saturn Orbit Insertion
maneuvers were orchestrated and executed with flawless precision. After
what seemed like an eternity, flight controllers received confirmation
that Cassini had completed the 96-minute engine burn and been
successfully captured into the correct orbit. And thus began a new
chapter in space exploration: a four-year study of the giant planet,
its majestic rings, and its 31 known moons.
Early Results
Just two days after the Cassini spacecraft entered Saturn's orbit,
preliminary science results were already beginning to show surprises.
The complexity of the rings exceeded our wildest imagination. While a
large number of rings and much structure in the rings were expected,
high-resolution pictures show thousands of alternating light and dark
bands. Theories of ring formation, dynamics, and structure may have to
be completely revised.
Another early result intriguing scientists concerns Saturn's
Cassini Division, the large gap between the A and B rings. While
Saturn's rings are almost exclusively composed of water ice, new
findings show the Cassini Division contains relatively more ``dirt''
than ice. Furthermore, the gaps between the rings seem to be populated
by darker particles remarkably similar to the dark material that
scientists saw on Saturn's moon, Phoebe. These dark particles refuel
the theory that the rings might be the remnants of a moon. The F ring
was also found to contain relatively more dirt. The term ``dirt'' has
been used because the material has thus far defied precise spectral
identification. It is almost certainly an amorphous, and spectrally
very challenging, mixture.
The next day, Cassini revealed surface details of Saturn's moon,
Titan. Titan's dense atmosphere is opaque at most wavelengths, but the
spacecraft captured some surface details, including possible evidence
for a geologically active surface, through infrared wavelengths in
which the atmosphere is clear.
A number of long-held ideas were challenged by the early Titan
results. Surface areas of high reflectance were found to be composed of
mixtures of water ice and hydrocarbon tar. Dark areas were found to be
just ice. These observations are exactly backwards from our
expectations. No evidence was found for liquid hydrocarbons in pools or
lakes. These results have raised questions about whether Titan
possesses a primordial soup of hydrocarbons that could yield insights
about the pre-biotic chemistry of earth. This Titan flyby, the first of
the tour, was at a closest approach distance of 200,000 miles. The tour
includes numerous Titan flybys; some, including an upcoming pass in
Oct. 2004, will be as close as 700 miles. If all goes well we can
expect far better data in the near future and it may be premature to
draw any major conclusions about Titan as an early earth analogue.
Cassini's magnetospheric imaging instrument revealed a vast diffuse
swarm of hydrogen molecules surrounding Titan, well beyond the top of
Titan's atmosphere. This instrument, the first of its kind on any
interplanetary mission, provided images of the huge cloud being dragged
along with Titan in its orbit around Saturn. The cloud is so big that
Saturn and its rings would fit within it.
What Next?
On Christmas Day in Europe and Christmas Eve in the US, Cassini
will release the European-built Huygens probe which will coast for 3
weeks and then parachute down through Titan's atmosphere. The recent
SOI was NASA's opportunity to shine and the Huygens probe mission will
be Europe's opportunity. Huygens is equipped with six scientific
instruments powered by batteries with a five-hour lifetime. The descent
will take about 2\1/2\ hours. Huygens was designed to take data
continuously during descent through the atmosphere and it is hoped that
it will also survive the landing and return data from the surface. The
Huygens mission will enhance the value of the Cassini mission, and vice
versa. Both scientifically and operationally, Cassini/Huygens is a true
international collaboration involving 260 scientists from 17 nations.
The missions are thoroughly integrated; many Europeans are on Cassini
science teams and many Americans are on Huygens science teams.
We are delighted with the surprises thus far revealed by the
Cassini mission. Surprise is at the very heart of science. If there
were no surprises, it wouldn't be science. At this moment Cassini is on
a long path outward before it will turn around and again come inward
toward Saturn on its way to the next Titan encounter. Let us catch our
breath and prepare for more astonishing discoveries.
Senator Brownback. So how long will you spend this first
time going around Saturn then with Cassini? What's the length
of time you'll go around?
Mr. Figueroa. The present orbit is approximately 120 days.
Senator Brownback. You'll stay there before you'll do a
burn to go out to Titan, or how will you do that?
Mr. Figueroa. No, we keep making adjustments around in the
present orbit outside of the rings and coming in closer to the
Titan moon as one of the flybys. Mark, you may want to add more
information.
Mr. Dahl. We have a maneuver. Because the Saturn orbit
insertion was so close to the planet, we have a maneuver coming
up in about 4 weeks that will raise the low end of the orbit.
The first orbit is about, as Orlando said, about 120 days, and
then the next time around we stay at the low end of the orbit
is approximately the orbit of Titan. So about every time we
come around we swing by Titan.
Senator Brownback. So you're staying in the same orbit,
just you will encounter at different times because you're in
the same orbital height or orbital distance from Saturn?
Mr. Dahl. No, sir. We actually use Titan to change the
orbit, so every orbit of Saturn will be unique. Some of the
orbits will have different angles with relation to Saturn so
that we'll get better looks at the rings. Some orbits will be
further out on the back side of Saturn so that we can study the
magneto tail. Some of the orbits will get as short as 7 days
close to the end of the 4-year tour. So we'll be quite busy and
every orbit will be unique. We use Titan itself as a gravity
pump to save fuel and change our orbit.
Senator Brownback. Now, you will go around Saturn and be
doing this discovery for a period of about 4 years, and then
what's the plan at that point in time?
Mr. Figueroa. Typically, our missions such as this one, to
the extent that they're healthy, the limiting factor in this
case will be the fuel, how much fuel we have left. We intend to
keep them alive for as long as we possibly can. It's a
valuable, incredibly capable observatory, and we will squeeze
as much science out of it as we possibly can.
Senator Brownback. It looks like it's worked great now, and
I think of something that launched 7 years ago and the burn
goes well after 7 years--that's impressive to be able to keep
that going.
Go into more detail of what you're learning thus far on
Titan in particular. The pictures you've got up here, they look
very--you've got an atmosphere layer and then kind of a green
and yellow and now it's different colors up here. I don't know
the actual colors of what they are. But go into a little more
detail if you would of what we're learning all on Titan.
Dr. Bogan. The colors are----
Senator Brownback. Get the microphone up close to you.
Dr. Bogan. The colors indicate the different infrared
wavelengths that were used. The longest wavelength penetrates
to the greatest depth through the clouds and the haze. And so
what you do experimentally is you look at longer and longer
wavelength images, and when they begin to show the same shapes
over and over again, you know that you've reached the surface.
If those further change, you would know that you were looking
at a cloud and at the longer wavelength you'd penetrated
deeper.
So in those composites you see evidence of a crater. At the
top center there is a large crater which you can faintly make
out with a peak in the middle of it with an impact at some time
in the moon's history, and extending diagonally below that, you
see evidence of a ridge or a rift in the surface. And the
scientists working on this believe that may be evidence of
geologic activity.
The variations between the green and the yellow indicate
the composition, whether it's relatively more water ice, or
whether it's relatively more hydrocarbon. We have not yet seen
evidence of pools of liquid hydrocarbon, but there is
definitely hydrocarbon there on the surface, most likely in the
form of frost or saturated soil.
We're going to get 300 times closer to Titan on the next
pass and we're very excited about that because we're going to
get data, given successful operation of the instruments, which
we have every reason to expect the data will be far beyond
anything we've seen so far.
Senator Brownback. And then you put the probe down in
December?
Dr. Bogan. That's right.
Senator Brownback. Tell me about how that will operate and
what you will be doing with that probe.
Dr. Bogan. That probe will be released on the third pass by
Titan. It will coast for about 3 weeks and then enter the upper
atmosphere. The atmosphere of Titan is very extended and it's
denser than that of Earth, about 50 percent more dense than
Earth, and extends to a very high altitude because of the
relatively weaker gravity of a smaller body.
Senator Brownback. So how high up is this atmosphere?
Dr. Bogan. There may be traces of it at several hundred
kilometers, 500 to 700 kilometers. The closest passes will be
about 950 kilometers, and that number was chosen so as to avoid
aerodynamic drag from the upper atmosphere upon the spacecraft.
And once that probe is in the atmosphere, it will deploy a
parachute, the parachute will slow its descent. The descent
will take 2\1/2\ hours and data will be sent back continuously
to the Cassini spacecraft, which will then relay the data to
Earth. The batteries are designed for a 5 hour lifetime, and so
if there is a successful landing, a landing that survives and
the instruments continue to operate, we'll get a couple of
hours of data from the surface itself.
Senator Brownback. And what type of data will it send back
if all things work?
Dr. Bogan. There's an aerosol pyrolyzer, there is a gas
chromatograph mass spectrometer, which will determine chemical
compositions. There are inertial sensing instruments such that
we can determine the structure of the atmosphere, the winds
that will buffet the probes as it drops through the atmosphere.
There will be cameras and all of this information will be sent
back to Cassini, the orbiter, and it can be relayed to Earth at
leisure.
Mr. Figueroa. It should be a very exciting part of the
mission as well and I must remind all of us that the probe is
not designed to be a lander, so we may get lucky and survive
wherever we land on the surface and get a few more minutes,
perhaps if we're lucky an hour, of additional data from the
surface itself.
Senator Brownback. What the probe is going to be doing is
when it's coming down through the atmosphere, that's your main
data collection time?
Mr. Figueroa. Taking data throughout the whole entry period
and for as long as half an hour after it gets to the surface if
it survives.
Senator Brownback. Can you back up to the rings on the
picture that you had earlier up there, is that possible? Go
through that again. You were saying that there are ripples in
this that you had seen before but now they've come through much
clearer, and what does that indicate?
Mr. Figueroa. This is known as the Encke gap, and I will
let Dr. Bogan explain what the significance of those ripples
are.
Dr. Bogan. We talk about shepherding moons when we talk
about the rings and the moons moving through this material
sweep clean a space near their path, and we have seen in many
instances a kind of a scalloping of the edge of the ring where
the moon passes by. Particles that get too close to the
orbiting moon will either get attracted to it and stick, or
they will get ejected from that region in space. So there is
very complex dynamics going on, and even within the rings, the
particles within those rings, which may be as large as a house
at the largest and baseballs, marbles, bee-bees, and very small
dust, and there are dynamics and motion and collisions going on
among these.
So it's hard to imagine, given a scenario like that, how
you could see regular geometric features that presumably
persist for long periods of time, and the ring experts are
working very hard right now. They were amazed at the detail of
the ring pictures. They saw literally thousands of ringlets as
opposed to the dozen or so identified rings that we have named
based on our observations from Earth-based telescopes.
Senator Brownback. Why thousands? I mean, what do you
speculate?
Dr. Bogan. Very good question. But there are alternating
light and dark bands, and you can count them, and there are
literally thousands of them.
Senator Brownback. And we don't know what makes the
different rings and the different colors?
Dr. Bogan. Well, we do--there is a nice infrared map
showing the water content of the rings. Water ice makes up
about 99 percent or 98 percent of the rings as a whole, but
there are dirtier regions, and the people looking at this have
so far settled on the name dirt because they haven't obtained a
good spectral identification. They are working hard on that.
But there are definitely variations between water ice and this
foreign material or dirt material, whatever you want to call
it, as we go from the innermost rings to the outermost.
Senator Brownback. Why is it flat like that? What do you
speculate? I mean, it appears flat.
Dr. Bogan. It does appear flat, it's very thin, the ring
plane is very thin and most of it's----
Senator Brownback. How fixed are you guesstimating, or do
you have a measure on that?
Dr. Bogan. --a few hundred meters to a few kilometers. And
it's probably an angular momentum effect where that ring sits
right above the equator of the planet, and that's where it has
a stable dynamic situation where it can persist.
Mr. Figueroa. In celestial scales, several hundred meters
or kilometers is a rather thin----
Dr. Bogan. Yes, very thing.
Mr. Figueroa. Mother Nature seems to achieve states where
it's minimum energy, and so you would see these rings closes to
the equator of a planet and remaining a flat form, just like
when our solar system formed where the planets tend to be in
that plane in order around the sun.
Senator Brownback. Do we know--do you have theories on
where the material came from that's in the rings?
Dr. Bogan. The theory of solar system formation, for which
we think this is an analog, is that material is left over after
a planet formation. In the case of Saturn, there's material
left over after a satellite formation. Or perhaps some of the
smaller satellites get broken up by collisions with one another
and the fragments wind up in rings. Other planets have rings,
Jupiter, Uranus, and Neptune have identified rings. Those are
other giant planets, but none of them has rings to the extent
of these very dramatic and bright rings around Saturn, so we
have much to learn.
Senator Brownback. And you don't have a working theory as
to why these rings are so----
Dr. Bogan. There are theories, and in fact, we see even in
distant galaxies we see disks around stars that we believe are
the early stages of planetary system formation. And these
situations, Saturn and its rings may very well be a laboratory
where we can better understand the dynamics of what's happening
in distant galaxies when these planetary systems form.
Senator Brownback. Mr. Figueroa, how's the international
cooperation been on this project? How would you scale that?
Mr. Figueroa. I think it has been exemplary. From the very
beginning, the partnership with ESA, the European Space Agency,
the Italian Space Agency, and the other 14 countries have been
excellent at all levels, at the programmatic levels,
scientific, engineering-wise, and we continue to collaborate
very closely of course to ensure the safe arrival of the
Huygens probe to Titan, and the continued support in providing
and exchanging data and knowledge with our colleagues. It has
been simply excellent.
Senator Brownback. And what's the funding mix on this
mission?
Mr. Figueroa. The total mission cost is approximately $3.3
billion, .7 of which is contributed largely by ESA, about $550-
to $600 million, and the balance the Italian Space Agency.
Other countries have smaller components, but nevertheless very
important to the mission.
Senator Brownback. What has been the public response thus
far in the mission? You got dramatic response on the Mars
Rover. What about on this one?
Mr. Figueroa. Actually we're pumping the images as soon as
we receive them, as soon as possible after receipt we were
putting them on the Web and the traffic on the Web also
increased significantly, matching in some cases the kind of
response we got to the Rovers when they arrived on Mars.
Now, a few days later after we entered the Saturn orbit,
the spacecraft hid behind the sun and it was hard to see it, so
there was a period, a quiet period, and we will start picking
up again in the next few days and we will get to see equally,
if not more exciting, images coming back. The calls and the
interest, judging by the traffic on the website and the
questions we have received and the press requests, have been
very high.
Senator Brownback. What's your Web traffic for this
particular, do you know?
Mr. Figueroa. I do not recall the exact number. Do you
know?
Mr. Dahl. I believe that the first 5 days the NASA website
experienced over one billion hits.
Senator Brownback. Just for this or that's the broad----
Mr. Dahl. Just for Cassini.
Senator Brownback. They're dramatic pictures. It seems that
the conditions on Saturn's moon, Titan, are pretty harsh. Even
so, do any scientists believe life may exist there in some
different or strange form?
Mr. Figueroa. I think, and Dr. Bogan can expand a little,
but we know the primordial materials may be present and perhaps
giving us clues as to what the early conditions may have been
when life started emerging on Earth during the early days of
our planet.
Dr. Bogan. Yes, when we say primordial material, we mean
material that's never been close to the sun and therefore never
been warmed up and altered by chemistry and various physical
processes. So the Earth's atmosphere is very different than the
early Earth and we call Earth's atmosphere an evolved
atmosphere. Titan's is primitive. And we're looking for the
chemical building blocks of life, the organic materials, the
hydrocarbons, and the temperatures are however low enough that
nobody believes at the present time that life exists there now
or that it could exist at those temperatures.
There is some hope of finding a liquid water ammonia
mixture below the surface in the interior, in the sense that we
have found water in the interior of some of the Galilean
satellites of Jupiter. That material would have to be warmed by
something, and the theory is that there is enough radiologic
heat from radioactive elements within the core of Titan that it
is possible there could be liquid water ammonia solutions. But
no one is expecting life there.
Senator Brownback. What's the temperature on Titan roughly?
Dr. Bogan. It's less than 100 degrees Kelvin, which is 350
degrees or so Fahrenheit below zero.
Senator Brownback. Well, congratulations. I think it has
been exciting to see and to take place. Mr. Figueroa, anything
else on this Saturn mission or the Titan probe that you'd like
to put into the record?
Mr. Figueroa. Well, when we speak of space exploration, and
even though the Cassini mission began before the new vision for
space exploration, it certainly is a key component of it and
illustrates the power of knowledge, the power of ingenuity, and
the power of collaboration to help us expand beyond our own
orbit. We began with pieces of Mars, now the moon, and of
course the outer planets remain incredibly important to the
understanding of the solar system we live in.
Senator Brownback. Do you have other missions going to
other places in the solar system right now?
Mr. Figueroa. In 2000--not at the present time. We have in
2006 the launch of the New Horizons mission to Pluto.
Senator Brownback. And that will take how many years to get
there?
Mr. Figueroa. It is approximately 12 years.
Dr. Bogan. Ten to twelve. And it will depend on the exact
launch window date that eventually is selected.
Senator Brownback. And you've got a lunar reconnaissance
orbiter you're doing in 2008?
Mr. Figueroa. In 2008.
Senator Brownback. I noted that the Chinese are sending an
orbiter to the moon sooner than that period of time, I believe.
Is that accurate?
Mr. Figueroa. I'm not aware of a Chinese mission. I'm
aware, of course, of a European mission, Smart I, the Celine,
and Lunar A, both Japanese missions that are planned.
Senator Brownback. When are they planned for?
Mr. Figueroa. Celine at the moment, due to budgetary
problems, are sort of in limbo, and the Celine mission is
presently scheduled for launch in 2007. Also, budgetary
challenges may alter that. We have begun discussions with them.
We have an ongoing partnership on Lunar A and would like to
establish a similar one for Celine. There is a great deal of
data and information that will be valuable to the long-term
vision of space exploration, beginning with the moon.
Senator Brownback. I noted to you in the opening statement
that--wondered why we didn't follow--or are not following in
the design of the lunar reconnaissance orbiter for 2008 more of
the Aldridge Commission reports or suggestions to involve much
more of the private sector in the data purchases. In other
words, you'd contract it with the private sector and say we're
going to purchase data from you.
Thoughts? I'm sure you must have considered that in NASA
putting together this lunar probe.
Mr. Figueroa. In our view, data for that mission may not be
realistic. We have chosen an approach that we believe was the
best balance of risk and programmatic and technical risk and
delivering the key measurements that we need to get the first
steps in the lunar exploration program going.
Now, I am aware of concerns that exist such as the one that
you mentioned and are looking at other alternatives.
Senator Brownback. Have you reviewed already the
possibility of going more private sector and just purchasing
data back from them? Have you reviewed that idea?
Mr. Figueroa. We will be over the next few months looking
at that idea. We took a look at greater private sector
contributions to the mission, different components on the
mission, even though I think it's fairly significant at the
present time. Going as far as data buy, we made an assessment
based on what we have learned in the past, missions such as Sea
Waves and LANDSAT, where the returns that were expecting never
really materialized and ended up being incredibly expensive and
ineffective.
Senator Brownback. Go into that in more detail. The returns
you expected didn't materialize?
Mr. Figueroa. Well, it ended up being significantly more
expensive to the government and never achieving the full
potential that was expected. This is in a full data-buy mode.
Now, whether there are other approaches that we can look at the
mission, we will be looking at that over the next couple of
months.
Senator Brownback. I just want to make sure that you are
looking at that, because that's something that was outlined and
we've been talking about, others have been too, that if we can
trail blaze and then leave some infrastructure behind. Now, if
it doesn't work, if it's too expensive for us, obviously we
don't want to go those routes. But if there are ways that we
can do that, that can be useful to do.
Gentlemen, thank you very much. I wanted to do this after I
saw these pictures and images and stories coming out in the
press. I wanted to bring you up here to be able to see it, but
also to congratulate you and give you a chance to show off what
all you've been getting, and that's a remarkable achievement, I
think, when you launch something 7 years ago and it still
works, it does what you planned on it to do. I don't think my
minivan will get that done after using it for 7 years. I think
we've put a little more into this than that one costs, but
still that's an impressive scientific achievement, and it is
opening our eyes and yearning us on forward into the solar
system. So another milestone achieved. Congratulations.
Mr. Figueroa. Thank you very much, Mr. Chairman, for the
opportunity. It's a pleasure to be here.
Senator Brownback. We will keep the record open if others
have questions to submit to you or if you have other things you
want to submit for the record. Otherwise, the hearing is
adjourned.
[Whereupon, at 3:15 p.m., the hearing was adjourned.]