NASA's Cassini spacecraft is 18 days from its mission-ending dive
into the atmosphere of Saturn. Its fateful plunge on Sept. 15 is
a foregone conclusion -- an April 22 gravitational kick
from Saturn's moon Titan placed the two-and-a-half ton vehicle
on its path for impending destruction. Yet several mission milestones
have to occur over the coming two-plus weeks to prepare the vehicle
for one last burst of trailblazing science.
"The Cassini mission has been packed full of scientific firsts, and our unique
planetary revelations will continue to the very end of the mission as Cassini
becomes Saturn’s first planetary probe, sampling Saturn's atmosphere up until
the last second," said Linda Spilker, Cassini project scientist from
NASA's Jet Propulsion Laboratory in Pasadena, California. "We'll be sending
data in near real time as we rush headlong into the atmosphere -- it's truly
a first-of-its-kind event at Saturn."
The spacecraft is expected to lose radio contact with Earth within about one
to two minutes after beginning its descent into Saturn's upper atmosphere.
But on the way down, before contact is lost, eight of Cassini's 12 science instruments
will be operating. In particular, the spacecraft‘s ion and neutral mass spectrometer
(INMS), which will be directly sampling the atmosphere's composition, potentially
returning insights into the giant planet's formation and evolution. On the day before
the plunge, other Cassini instruments will make detailed, high-resolution observations
of Saturn's auroras, temperature, and the vortices at the planet's poles.
Cassini's imaging camera will be off during this final descent, having taken
a last look at the Saturn system the previous day (Sept. 14).
In its final week, Cassini will pass several milestones en route to its science-rich
Saturn plunge. (Times below are predicted and may change slightly;
see
https://go.nasa.gov/2wbaCBT for updated times.)
-- Sept. 9 -- Cassini will make the last of 22 passes between Saturn itself
and its rings -- closest approach is 1,044 miles (1,680 kilometers)
above the clouds tops.
-- Sept. 11 -- Cassini will make a distant flyby of Saturn's largest moon,
Titan. Even though the spacecraft will be at 73,974 miles (119,049 kilometers)
away, the gravitational influence of the moon will slow down the spacecraft slightly
as it speeds past. A few days later, instead of passing through the outermost fringes
of Saturn's atmosphere, Cassini will dive in too deep to survive the friction and heating.
-- Sept. 14 -- Cassini's imaging cameras take their last look around the Saturn system,
sending back pictures of moons Titan and Enceladus, the hexagon-shaped jet
stream around the planet's north pole, and features in the rings.
-- Sept. 14 (5:45 p.m. EDT / 2:45 p.m. PDT) -- Cassini turns its antenna
to point at Earth, begins a communications link that will continue until end
of mission, and sends back its final images and other data collected
along the way.
-- Sept. 15 (4:37 a.m. EDT / 1:37 a.m. PDT) -- The "final plunge" begins.
The spacecraft starts a 5-minute roll to position INMS for optimal sampling
of the atmosphere, transmitting data in near real time from now to end of mission.
-- Sept. 15 (7:53 a.m. EDT / 4:53 a.m. PDT) -- Cassini enters Saturn's atmosphere.
Its thrusters fire at 10 percent of their capacity to maintain directional stability,
enabling the spacecraft's high-gain antenna to remain pointed at Earth and allowing
continued transmission of data.
-- Sept. 15 (7:54 a.m. EDT / 4:54 a.m. PDT) -- Cassini's thrusters are at 100 percent
of capacity. Atmospheric forces overwhelm the thrusters' capacity to maintain
control of the spacecraft's orientation, and the high-gain antenna loses its lock
on Earth. At this moment, expected to occur about 940 miles (1,510 kilometers)
above Saturn's cloud tops, communication from the spacecraft will cease,
and Cassini's mission of exploration will have concluded. The spacecraft will break up
like a meteor moments later.
As Cassini completes its 13-year tour of Saturn, its Grand Finale --
which began in April -- and final plunge are just the last beat.
Following a four-year primary mission and a two-year extension,
NASA approved an ambitious plan to extend Cassini's service
by an additional seven years. Called the Cassini Solstice Mission,
the extension saw Cassini perform dozens more flybys of Saturn's moons
as the spacecraft observed seasonal changes in the atmospheres of Saturn
and Titan. From the outset, the planned endgame for the Solstice Mission was
to expend all of Cassini's maneuvering propellant exploring, then eventually arriving
in the ultra-close Grand Finale orbits, ending with safe disposal of the spacecraft
in Saturn's atmosphere.
"The end of Cassini's mission will be a poignant moment, but a fitting
and very necessary completion of an astonishing journey," said Earl Maize,
Cassini project manager at NASA's Jet Propulsion Laboratory in Pasadena,
California. "The Grand Finale represents the culmination of a seven-year plan
to use the spacecraft’s remaining resources in the most scientifically productive
way possible. By safely disposing of the spacecraft in Saturn's atmosphere,
we avoid any possibility Cassini could impact one of Saturn's moons
somewhere down the road, keeping them pristine for future exploration."
Since its launch in 1997, the findings of the Cassini mission have revolutionized
our understanding of Saturn, its complex rings, the amazing assortment
of moons and the planet's dynamic magnetic environment.
The most distant planetary orbiter ever launched, Cassini started
making astonishing discoveries immediately upon arrival and continues
today. Icy jets shoot from the tiny moon Enceladus, providing samples
of an underground ocean with evidence of hydrothermal activity.
Titan's hydrocarbon lakes and seas are dominated by liquid ethane
and methane, and complex pre-biotic chemicals form in the atmosphere
and rain to the surface. Three-dimensional structures tower
above Saturn's rings, and a giant Saturn storm circled the entire planet
for most of a year. Cassini's findings at Saturn have also buttressed
scientists' understanding of processes involved in the formation of planets.
The Cassini-Huygens mission is a cooperative project
of NASA, ESA (European Space Agency)
and the Italian Space Agency. NASA's Jet Propulsion Laboratory,
a division of Caltech in Pasadena, manages the mission
for NASA's Science Mission Directorate, Washington. JPL designed,
developed and assembled the Cassini orbiter.
More information about Cassini:
https://www.nasa.gov/cassinihttps://saturn.jpl.nasa.govRelated telecon
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-394-7013
preston.dyches@jpl.nasa.gov Dwayne Brown / Laurie Cantillo
NASA Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown@nasa.gov /
laura.l.cantillo@nasa.gov2017-231
Last Updated: Aug. 29, 2017
Editor: Tony Greicius
---------------------------
https://www.nasa.gov/feature/jpl/saturn-plunge-nears-for-cassini-spacecrafthttps://www.nasa.gov/feature/jpl/new-insights-into-titans-complex-chemistryhttps://www.nasa.gov/feature/jpl/saturn-surprises-as-cassini-continues-its-grand-finalehttps://www.nasa.gov/feature/jpl/cassini-finds-saturn-moon-may-have-tipped-over----------------------------
NASA's Cassini spacecraft still has a few months to go before
it completes its mission in September, but the veteran Saturn explorer
reaches a new milestone today. Saturn's solstice -- that is, the longest
day of summer in the northern hemisphere and the shortest day
of winter in the southern hemisphere -- arrives today for the planet
and its moons. The Saturnian solstice occurs about every
15 Earth years as the planet and its entourage slowly
orbit the sun, with the north and south hemispheres alternating
their roles as the summer and winter poles.
Reaching the solstice, and observing seasonal changes
in the Saturn system along the way, was a primary goal
of Cassini's Solstice Mission -- the name of Cassini's second
extended mission.
Cassini arrived at Saturn in 2004 for its four-year primary mission
to study Saturn and its rings and moons. Cassini's first extended mission,
from 2008 to 2010, was known as the Equinox Mission.
During that phase of the mission, Cassini watched as sunlight
struck Saturn's rings edge-on, casting shadows that revealed
dramatic new ring structures. NASA chose to grant the spacecraft
an additional seven-year tour, the Solstice Mission, which began in 2010.
"During Cassini's Solstice Mission, we have witnessed --
up close for the first time -- an entire season at Saturn,"
said Linda Spilker, Cassini project scientist at NASA's Jet
Propulsion Laboratory, Pasadena, California. "The Saturn system
undergoes dramatic transitions from winter to summer,
and thanks to Cassini, we had a ringside seat."
Saturn
During its Solstice Mission, Cassini watched a giant storm erupt
and encircle the planet. The spacecraft also saw the disappearance
of bluer hues that had lingered in the far north as springtime hazes
began to form there. The hazes are part of the reason why features
in Saturn's atmosphere are more muted in their appearance
than those on Jupiter.
Data from the mission showed how the formation of Saturn's hazes
is related to the seasonally changing temperatures
and chemical composition of Saturn's upper atmosphere.
Cassini researchers have found that some of the trace hydrocarbon
compounds there -- gases like ethane, propane and acetylene --
react more quickly than others to the changing amount of sunlight
over the course of Saturn's year.
Researchers were also surprised that the changes Cassini observed
on Saturn didn't occur gradually. They saw changes occur suddenly,
at specific latitudes in Saturn's banded atmosphere.
"Eventually a whole hemisphere undergoes change,
but it gets there by these jumps at specific latitude bands
at different times in the season," said Robert West, a Cassini imaging
team member at JPL.
Rings
Following equinox and continuing toward northern summer solstice,
the sun rose ever higher above the rings' northern face. And as the sun
rises higher, its light penetrates deeper into the rings, heating them
to the warmest temperatures seen there during the mission.
The solstice sunlight helps reveal to Cassini's instruments how particles
clump together and whether the particles buried in the middle of the ring
plane have a different composition or structure than the ones
in the rings' outer layers.
Saturn's changing angle with respect to the sun also means the rings
are tipped toward Earth by their maximum amount at solstice.
In this geometry, Cassini's radio signal passes more easily
and cleanly through the densest rings, providing even higher-quality
data about the ring particles there.
Titan
Cassini has watched Saturn's largest moon, Titan, change with
the seasons, with occasional dramatic outbursts of cloud activity.
After observing methane storm clouds around Titan's south pole
in 2004, Cassini watched giant storms transition to Titan's equator
in 2010. Although a few northern clouds have begun to appear, scientists
have since been surprised at how long it has taken for cloud activity
to shift to the northern hemisphere, defying climate models
that had predicted such activity should have started several years earlier.
"Observations of how the locations of cloud activity change
and how long such changes take give us important information
about the workings of Titan's atmosphere and also its surface,
as rainfall and wind patterns change with the seasons too,"
said Elizabeth Turtle, a Cassini imaging team associate
at the Johns Hopkins University Applied Physics Laboratory
in Laurel, Maryland.
In 2013, Cassini observed a sudden and rapid buildup
of haze and trace hydrocarbons in the south that were previously
observed only in Titan's high north. This indicated to scientists
that a seasonal reversal was underway, in which Titan’s main atmospheric
circulation changes direction. This circulation was apparently channeling
fresh hydrocarbon chemicals from closer to the equator
toward the south pole, where they were safe from destruction
by sunlight as that pole moved deeper into winter shadow.
Enceladus
For Enceladus, the most important seasonal change was the onset
of winter darkness in the south. Although it meant Cassini could no
longer take sunlit images of the geologically active surface,
the spacecraft could more clearly observe the heat coming
from within Enceladus itself. With the icy moon's south pole
in shadow, Cassini scientists have been able to monitor
the temperature of the terrain there without concern
for the sun's influence. These observations are helping researchers
to better understand the global ocean that lies beneath the surface.
From the moon's south polar region, that hidden ocean sprays
a towering plume of ice and vapor into space that Cassini
has directly sampled.
Toward the Final Milestone
As Saturn's solstice arrives, Cassini is currently in the final phase
of its long mission, called its Grand Finale. Over the course
of 22 weeks from April 26 to Sept. 15, the spacecraft is making
a series of dramatic dives between the planet and its icy rings.
The mission is returning new insights about the interior
of the planet and the origins of the rings, along with images
from closer to Saturn than ever before. The mission will end
with a final plunge into Saturn's atmosphere on Sept. 15.
The Cassini-Huygens mission is a cooperative project of NASA,
ESA (European Space Agency) and the Italian Space Agency.
NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena,
California, manages the mission for NASA's Science Mission Directorate,
Washington. JPL designed, developed and assembled the Cassini orbiter.
More information about Cassini:
https://www.nasa.gov/cassinihttps://saturn.jpl.nasa.govPreston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-394-7013
preston.dyches@jpl.nasa.gov2017-150
Last Updated: Aug. 4, 2017
Editor: Tony Greicius
Tags: Cassini, Jet Propulsion Laboratory, Planets, Saturn, Solar System
------------------------
https://www.nasa.gov/feature/jpl/new-movie-shows-cassinis-first-dive-over-saturnhttps://www.nasa.gov/feature/cassini-finds-the-big-empty-close-to-saturnhttps://www.nasa.gov/feature/jpl/cassini-s-first-grand-finale-dive-milestoneshttps://www.nasa.gov/feature/jpl/cassini-heads-toward-final-close-encounter-with-titanhttps://www.nasa.gov/feature/jpl/cassini-sees-flying-saucer-moon-atlas-up-closehttps://www.nasa.gov/feature/jpl/experiments-show-titan-lakes-may-fizz-with-nitrogenhttps://www.nasa.gov/feature/jpl/cassini-sees-heat-below-the-icy-surface-of-enceladushttps://www.nasa.gov/image-feature/jpl/cassini-reveals-strange-shape-of-saturns-moon-panhttps://www.nasa.gov/feature/jpl/an-ice-worldwith-an-oceanhttps://www.nasa.gov/feature/jpl/a-valentine-from-cassini-with-lovehttps://www.nasa.gov/feature/jpl/close-views-show-saturns-rings-in-unprecedented-detailJan. 11, 2017
Huygens: 'Ground Truth' From an Alien Moon
2005 Historic Descent to Titan Revisited
After a two-and-a-half-hour descent, the metallic, saucer-shaped
spacecraft came to rest with a thud on a dark floodplain covered
in cobbles of water ice, in temperatures hundreds of degrees below freezing.
The alien probe worked frantically to collect and transmit images
and data about its environs -- in mere minutes its mothership would
drop below the local horizon, cutting off its link to the home world
and silencing its voice forever.
Although it may seem the stuff of science fiction, this scene played
out 12 years ago on the surface of Saturn's largest moon, Titan.
The "aliens" who built the probe were us. This was the triumphant
landing of ESA's Huygens probe.
Huygens, a project of the European Space Agency, traveled to Titan
as the companion to NASA's Cassini spacecraft, and then separated
from its mothership on Dec. 24, 2004, for a 20-day coast toward its
destiny at Titan.
The probe sampled Titan's dense, hazy atmosphere as it slowly rotated
beneath its parachutes, analyzing the complex organic chemistry
and measuring winds. It also took hundreds of images during
the descent, revealing bright, rugged highlands that were crosscut
by dark drainage channels and steep ravines. The area where the probe
touched down was a dark, granular surface, which resembled a dry lakebed.
Thoughts on Huygens
Today the Huygens probe sits silently on the frigid surface of Titan,
its mission concluded mere hours after touchdown, while the Cassini
spacecraft continues the exploration of Titan from above as part of
its mission to learn more about Saturn and its moons. Now in its dramatic
final year, the spacecraft's own journey will conclude on September 15
with a fateful plunge into Saturn's atmosphere.
With the mission heading into its home stretch, Cassini team members
and NASA leaders look back fondly on the significance of Huygens:
"The Huygens descent and landing represented
a major breakthrough in our exploration of Titan
as well as the first soft landing on an outer-planet moon.
It completely changed our understanding
of this haze-covered ocean world."
-- Linda Spilker, Cassini project scientist at NASA's Jet Propulsion
Laboratory, Pasadena, California
"The Huygens images were everything our images from orbit were not.
Instead of hazy, sinuous features that we could only guess
were streams and drainage channels, here was incontrovertible
evidence that at some point in Titan's history -- and perhaps even now --
there were flowing liquid hydrocarbons on the surface.
Huygens' images became a Rosetta stone for helping us
interpret our subsequent findings on Titan."
-- Carolyn Porco, Cassini imaging team lead
at Space Science Institute, Boulder, Colorado
"Cassini and Huygens have shown us that Titan is
an amazing world with a landscape that mimics Earth
in many ways. During its descent, the Huygens probe captured
views that demonstrated an entirely new dimension
to that comparison and highlights that there is so much more
we have yet to discover. For me, Huygens has emphasized why
it is so important that we continue to explore Titan."
-- Alex Hayes, a Cassini scientist at Cornell University, Ithaca, New York
"Twelve years ago, a small probe touched down on an orangish,
alien world in the outer solar system, marking humankind's
most distant landing to date. Studying Titan helps us tease out
the potential of habitability of this tiny world and better understand
the chemistry of the early Earth."
-- Jim Green, director of planetary science
at NASA Headquarters, Washington
A collection of Huygens' top science findings is available from ESA at:
http://sci.esa.int/huygens-titan-science-highlightsThe Cassini-Huygens mission is a cooperative project of NASA,
ESA (European Space Agency) and the Italian Space Agency.
NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena,
manages the mission for NASA's Science Mission Directorate, Washington.
JPL designed, developed and assembled the Cassini orbiter.
More information about Cassini:
http://www.nasa.gov/cassinihttp://saturn.jpl.nasa.govPreston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-394-7013
preston.dyches@jpl.nasa.govMarkus Bauer
ESA Communications Office, Villanueva de la Cañada, Spain
Tel: 31 71 565 6799 / Mobile: 31 61 594 3 954
markus.bauer@esa.int2017-006
Last Updated: Aug. 4, 2017
Editor: Tony Greicius
In addition to periodic solicitations for new NAI teams, the Astrobiology
Program offers various other funding opportunities through the NAI.
Information on these opportunities is provided below.
For additional information contact Dr. Edward Goolish
at (650) 604-1961 (Edward.M.Goolish@nasa.gov).
Baruch S. Blumberg NASA/Library of Congress Chair in Astrobiology
The Astrobiology Chair is a distinguished senior research position
in residence at the Library of Congress for a period of up
to twelve months. Using research facilities and services
at the Library of Congress, the scholar engages in research
at the intersection of the science of astrobiology
and its humanistic and social implications. The appointment
ensures the subject of astrobiology’s role in culture and society
receives considered treatment each year in Washington, D.C.
NASA Astrobiology Institute (NAI) Team Solicitations
Solicitations (Cooperative Agreement Notices)
for NAI teams are posted on the NASA Solicitation
and Proposal Integrated Review and Evaluation System (NSPIRES)
website. NAI CANs are awarded for a 5 year period. Currently,
there are seven CAN 7 teams (1/2015 – 12/2019) and five
CAN 6 teams (1/2013 – 12/2017). The intent of release
of the next team solicitation opportunity has been announced,
and CAN 8 was posted to NSPIRES in January 2017.
NASA Astrobiology Conference and Workshop Fund
The NASA Astrobiology Institute supports workshops
and other meetings of its members and the broader
astrobiology community that will advance Astrobiology
Program objectives. These include, but are not limited to,
the integration of astrobiology research, mission planning,
the coordination of field expeditions, international
or inter-agency collaboration, or training in astrobiology.
NASA Astrobiology Institute Director’s Discretionary Fund
The NAI Director’s Discretionary Fund (DDF) makes one-year
awards for research that advances the science of astrobiology,
demonstrates impact to NASA’s space flight programs
or its broader science activities, and/or contributes
to NASA’s role as a federal R&D agency.
NASA Astrobiology Postdoctoral Program Fellowship
The NASA Astrobiology Program element of the NASA
Postdoctoral Program (NPP) provides opportunities
for Ph.D. scientists and engineers of unusual promise
and ability to perform research on problems largely
of their own choosing, yet compatible with the research interests
of the NASA Astrobiology Program.
NASA Astrobiology Minority Institution Research Support (MIRS) Program
The MIRS Program is intended to help train a new generation
of researchers in astrobiology and to increase diversity within the astrobiology community.
Lewis and Clark Fund for Exploration and Field Research in Astrobiology
The American Philosophical Society and the NASA Astrobiology
Institute have partnered to promote the continued exploration
of the world around us through a program of research grants
in support of astrobiological field studies undertaken
by graduate students, postdocs, and junior scientists
and scholars who are affiliated with U.S. institutions.
NASA Astrobiology Early Career Collaboration Award
The Astrobiology Program Early Career Collaboration
Award offers research-related travel support for undergraduate,
graduate students, postdoctoral fellows and junior scientists.
Applicants are encouraged to use these resources to circulate
among two or more NAI Teams, or participating institutions
of the NAI, however any travel that is critical for the applicant’s
research will be considered.)
RAPPORT DU
CITOYEN TIGNARD YANIS
SOUS L'EGIDE DE
LA N.A.SA; E.S.A ET Y'BECCA
Accueil 