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Cassini Top 10 Science Highlights

Wed, 08 Apr 2009 10:56:01 GMT

While touring the Saturn system in 2008, Cassini enabled great scientific studies and observations. Below is captured the Top 10 Science Highlights of the year as selected by the science teams.

Identification of liquid ethane in a lake on Titan
Polar storms on Saturn
Strong inference of a liquid water layer in Titan's interior
The likelihood of dusty rings around Rhea
The possibility of plate-tectonic-like spreading in the Enceladus south polar region
Water vapor jets inside the plume of gas leaving Enceladus
Moonlet population in and around the F ring
New insights into Saturn's aurora
Three belts of sub-moonlets in the A ring (propellers)
Six month-old lightning storm shatters record for longevity

1) Identification of liquid ethane in a lake on Titan

NASA scientists have concluded that at least one of the large lakes observed on Saturn's moon Titan contains liquid hydrocarbons, and have positively identified the presence of ethane. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.

Scientists made the measurements using data from an instrument aboard the Cassini spacecraft. The instrument identified chemically different materials based on the way they absorb and reflect infrared light. Before Cassini, scientists thought Titan would have global oceans of methane, ethane and other light hydrocarbons. More than 40 close flybys of Titan by Cassini show no such global oceans exist, but hundreds of dark, lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material.

Also see:
NASA Confirms Liquid Lake on Saturn Moon

Cassini Finds Hydrocarbon Rains May Fill Titan Lakes

2) Polar storms on Saturn

Cassini scientists revisited the north polar hexagon last year. This huge polygonal pattern in the clouds was first seen by Voyager in 1980. In 2008, Cassini found that the aurora glows at infrared wavelengths at the same latitude as the hexagon, suggesting a connection over a huge range of altitudes.

In addition, Cassini found a hot spot resembling the eye of a hurricane, but it is locked to the north pole at the center of the hexagon, with swirling cyclonic winds signifying a low pressure center. The hot spot is confined to latitudes above 88 degrees, while the corners of the hexagon are at 75 degrees.

The north polar hot spot resembles one in the south that was imaged in exquisite detail in 2008 These findings cast light on how large vortices - swirling masses of gas - behave in planetary atmospheres throughout the solar system.

The new-found cyclone at Saturn�s north pole is only visible in the near-infrared wavelengths because the north pole is in winter, thus in darkness to visible-light cameras. At these wavelengths, about seven times greater than light seen by the human eye, the clouds deep inside Saturn�s atmosphere are seen in silhouette against the background glow of Saturn�s internal heat.

Peak winds exceed 450 kilometers per hour (280 mph, or 130 m/s) near 88 degrees latitude. New measurements by Cassini show that clouds within the hexagonal feature located near 77 degrees north latitude zoom around the �race track� of the hexagon at this same high speed -- 460 kilometers per hour (127 meters per second, or 285 mph) -- while the hexagonal �race track� itself stays nearly stationary in Saturn�s atmosphere.

3) Strong inference of a liquid water layer in Titan's interior

NASA's Cassini spacecraft has found evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings, made using radar measurements of Titan's rotation, appeared in the March 21 issue of the journal Science.

"With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system," said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., "Now we see changes in the way Titan rotates, giving us a window into Titan's interior beneath the surface."

Subsequent data has suggested that these radar observations may be related to precession, only indirectly related to the presence of an ocean, but other geophysical evidence continues to point to a subsurface ocean. Titan continues to amaze and confound!

4) The likelihood of dusty rings around Rhea

NASA's Cassini spacecraft has found evidence of material orbiting Rhea, Saturn's second largest moon. This is the first time rings may have been found around a moon.

A broad debris disk and at least one ring appear to have been detected by a suite of six instruments on Cassini specifically designed to study the atmospheres and particles around Saturn and its moons.

5) The possibility of plate-tectonic-like spreading in the Enceladus south polar region

The closer scientists look at Saturn's small moon Enceladus, the more they find evidence of an active world. The most recent flybys of Enceladus made by NASA's Cassini spacecraft have provided new signs of ongoing changes on and around the moon. The latest high-resolution images of Enceladus show signs that the south polar surface changes over time.

Close views of the southern polar region, where jets of water vapor and icy particles spew from vents within the moon's distinctive "tiger stripe" fractures, provide surprising evidence of Earth-like tectonics. They yield new insight into what may be happening within the fractures. The latest data on the plume -- the huge cloud of vapor and particles fed by the jets that extend into space -- show it varies over time and has a far-reaching effect on Saturn's magnetosphere.

6) Water vapor jets inside the plume of gas leaving Enceladus

Scientists continue to search for the cause of the geysers on Saturn's moon Enceladus. The geysers are visible as a large plume of water vapor and ice particles escaping the moon. Inside the plume are jets of dust and gas. What causes and controls the jets is a mystery. The Cassini spacecraft continues to collect new data to look for clues.

At the heart of the search is the question of whether the jets originate from an underground source of liquid water. Some scientists working on the Cosmic Dust Analyzer (CDA) have suggested that the sodium found present in the E ring can be traced back to liquid in Enceladus. Some other theories offer models where the jets could be caused by mechanisms that do not require liquid water. Painstaking detective work by Cassini scientists is testing the possibilities to get closer to an answer.

7) Moonlet population in and around the F ring

A team of scientists led from the UK has found that the rapid changes in Saturn's F ring can be attributed to small moonlets causing perturbations. Their results are reported in Nature (June 5, 2008).

Saturn's F ring has long been of interest to scientists as its features change on timescales from hours to years and it is probably the only location in the solar system where large scale collisions happen on a daily basis. Understanding these processes helps scientists understand the early stages of planet formation.

Models have been developed which clearly imply a population of perhaps hundreds of unseen objects with sizes between 100 meters and 1 kilometer or so, both lying within and also criss-crossing through the narrow F ring core and causing havoc in the orbits of its particles.

Stellar occultations also found a number of clumps and opaque objects, measuring their size directly to be in the few hundred meter size range.

8) New insights into Saturn's aurora

Saturn has its own unique brand of aurora that lights up the polar cap, unlike any other planetary aurora known in our solar system. This odd phenomenon revealed itself to one of the infrared instruments on NASA's Cassini spacecraft.

Also see:
Cassini Finds Mysterious New Aurora on Saturn

9) Three belts of sub-moonlets in the A ring (propellers)

A new comprehensive study established the existence and orbital properties of an order of magnitude more objects of 100-300 metersacross buried in the rings than previously known. These objects have been dubbed "propellors" because of the shape of the surrounding material they disturb. The greatly improved statistics revealed that these large objects occupy three distinct belts in the A ring, which correlate with nearby resonances or gaps in no obvious way. No evidence for such objects has been found in other rings.

It remains unknown if the objects are primordial "shards" or locally grown, but it is now clear that the mass in this population is much smaller than in the visible ring particles themselves.

10) Six month-old lightning storm shatters record for longevity

Two instruments on Cassini regularly team up to monitor lightning storms in Saturn's atmosphere. The RPWS detects radio pulses from the electrical discharges, and the ISS images the storms. The RPWS only detects the electrical discharges when the storm is on the side of Saturn facing the spacecraft or just over the horizon on the night side.

Often a year goes by when there are no discharges, during which time the ISS does not see the storms. Then suddenly the radio signals begin and a new storm appears in the atmosphere. One such storm was identified on November 27, 2007, probably within a day of its birth. Unlike past storms, which lasted for a few weeks at best, this one lasted for 7.5 months and thereby set a new record for longevity of lightning storms throughout the solar system.

Active Galaxies Flare and Fade in Fermi Telescope All-Sky Movie

Tue, 07 Apr 2009 08:40:57 GMT

The gamma-ray sky comes alive in a movie made from data acquired by NASA�s Fermi Gamma-ray Space Telescope during its first three months of operations. Gamma rays from sources near and far turn the sky into a hypnotic froth. The sun arcs serenely across the northern sky as active galaxies called blazars flare up and fade out.

The movie, made from the first 87 days of data from Fermi�s Large Area Telescope (LAT), was revealed today during a live 24-hour video webcast called �Around the World in 80 Telescopes.� Organized by the European Southern Observatory headquartered in Garching, Germany, the webcast is part of the 100 Hours of Astronomy project, a worldwide celebration of astronomy running through April 5.

�The movie shows counts of gamma rays seen by Fermi�s LAT, and each frame shows the gamma rays collected in one day,� said presenter Elizabeth Hays, an astrophysicist on the Fermi team. Only gamma rays with energies greater than 300 million electron volts -- or 150 million times more than that of visible light -- are shown. Brighter colors indicate greater numbers of detected gamma rays and thus the locations of bright gamma-ray sources.

The movie shows the entire sky as northern and southern halves, with the plane of our galaxy, the Milky Way, running along the circular edges. �This presentation provides a better view of sources outside our galaxy,� Hays noted, �but it�s an unusual way to view the sky.� The northern view includes the familiar constellation Ursa Major, part of which forms the Big Dipper. The southern view includes the constellations Cetus and Pegasus.

�One of the first things to notice in the movie is the source that arcs across the northern galactic sky. That�s the sun moving along the ecliptic plane,� Hays said. The sun appears to move through the sky because the Earth revolves around it. This is the same reason constellations progress through the sky during the year.

However, Fermi�s LAT isn�t detecting gamma rays produced directly by the sun -- at least not yet. �The LAT sees the sun because cosmic rays -- nuclei traveling close to the speed of light -- strike the sun�s gas and the light it emits. These collisions produce gamma rays,� Hays explained. The LAT will sense the sun directly when a sufficiently powerful solar eruption occurs, but the sun is now in a quiet portion of its activity cycle.

Another striking aspect of the movie is that, even far from the brightest gamma-ray sources, the sky is not dark. �We see a general background of gamma rays over the whole sky,� Hays said. Some of this glow is the result of cosmic rays colliding with gas and light in our own galaxy and producing gamma rays. But some of this emission originates from beyond our galaxy. �Although we don't know exactly where all of these gamma rays are coming from, we know that some of them must be the collective radiation from galaxies we are not detecting directly,� she explained. It�s possible that something more exotic could also be contributing to this background glow, and Fermi is making measurements to test such ideas.

One galactic source lies far enough from the Milky Way�s plane that it stands out in the movie. �That�s PSR J1836+5925, one of the new class of pulsars discovered by Fermi,� Hays said. The pulsar is a fast-spinning neutron star that sends a broad fan of gamma rays toward us with each rotation. Neutron stars pack twice the mass of the sun into a sphere the size of Manhattan and can spin thousands of times in one second. �It looks steady in the movie because we have to add up gamma rays from many rotations to see the pulses,� she noted.

Most of the other bright sources in the movie are actually distant galaxies. Each of these active galaxies, called blazars, hosts a central black hole with a mass of a million suns. Somehow, the black hole produces extremely fast-moving jets of matter, and with blazars we�re looking almost directly down the jet. �The strong variations in brightness that you see during the movie tell us that something about these jets has changed,� Hays said.

One example is the blazar AO 0235+164, located 7.5 billion light-years away in the constellation Aries. �The flares we are seeing happened when the universe was about half of its current age,� she explained. �The LAT sees a very strong flare. The gamma rays increase by 30 to 40 times in a single day. On that day, AO 0235 became one of the brightest gamma-ray sources in the sky.�

Fermi�s LAT became the first gamma-ray telescope to see the blazar called PKS 1502+106. The galaxy, located 10 billion light-years away in the constellation Bo�tes, appeared suddenly, flared in brightness for a few days, and then faded away.

Such rapid and dramatic change underscores one of the most valuable things the Fermi team does. �We watch the sky all the time and alert other telescopes, in space and on the ground, when something interesting is going on,� Hays said. This gives other astronomers the chance to watch these events at other wavelengths, such as visible light, infrared, radio, ultraviolet, X-ray, and even gamma rays above the energy the LAT can detect.

�The broader the wavelength coverage, the better our understanding of the event will be,� Hays adds. �We have to be quick to catch these flares before they fade away.�

Hubble Celebrates the International Year of Astronomy With the Galaxy Triplet ARP 274

Tue, 07 Apr 2009 08:38:33 GMT

On April 1-2, the Hubble Space Telescope photographed the winning target in the Space Telescope Science Institute�s �You Decide� competition in celebration of the International Year of Astronomy (IYA).

The winner is a group of galaxies called Arp 274. The striking object received 67,021 votes out of the nearly 140,000 votes cast for the six candidate targets.

Arp 274, also known as NGC 5679, is a system of three galaxies that appear to be partially overlapping in the image, although they may be at somewhat different distances. The spiral shapes of two of these galaxies appear mostly intact. The third galaxy (to the far left) is more compact, but shows evidence of star formation.

Two of the three galaxies are forming new stars at a high rate. This is evident in the bright blue knots of star formation that are strung along the arms of the galaxy on the right and along the small galaxy on the left.

The largest component is located in the middle of the three. It appears as a spiral galaxy, which may be barred. The entire system resides at about 400 million light-years away from Earth in the constellation Virgo.

Hubble�s Wide Field Planetary Camera 2 was used to image Arp 274. Blue, visible, and infrared filters were combined with a filter that isolates hydrogen emission. The colors in this image reflect the intrinsic color of the different stellar populations that make up the galaxies. Yellowish older stars can be seen in the central bulge of each galaxy. A bright central cluster of stars pinpoint each nucleus. Younger blue stars trace the spiral arms, along with pinkish nebulae that are illuminated by new star formation. Interstellar dust is silhouetted against the starry population. A pair of foreground stars inside our own Milky Way are at far right.

The International Year of Astronomy is the celebration of the 400th anniversary of Galileo�s first observations with a telescope. People around the world are coming together to participate in the IYA�s 100 Hours of Astronomy, April 2 to 5. This global astronomy event is geared toward encouraging as many people as possible to experience the night sky.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA) and is managed by NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Md. The Space Telescope Science Institute (STScI) conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington, D.C.

NASA Updates TV Coverage of Next Soyuz Landing

Mon, 06 Apr 2009 08:43:51 GMT

NASA Television will air the landing of the Expedition 18 crew and a visiting spaceflight participant on Wednesday, April 8. Russian managers on Friday postponed the Soyuz landing one day and switched to a more southerly landing site in Kazakhstan because of soggy conditions at the original site.

Expedition 18 Commander E. Michael Fincke, Flight Engineer and Soyuz Commander Yury Lonchakov and Spaceflight Participant Charles Simonyi will return to Earth at 2:15 a.m. CDT, which is 1:15 p.m. local time in Kazakhstan. The landing will take place near the town of Dzhezkazgan, which is west of Karaganda and southeast of the usual landing zone near Arkalyk. Fincke and Lonchakov have been aboard the orbiting laboratory since October 2008 and will land in the Soyuz TMA-13 spacecraft that carried them into orbit.

Upcoming NASA TV Soyuz landing programming events (all times CDT):

April 7, Tuesday
7:30 p.m. -- Coverage of the crew's farewell and hatch closure
10:30 p.m. -- Coverage of the undocking of Soyuz TMA-13 from the International Space Station

April 8, Wednesday
1 a.m. -- Coverage of the deorbit burn and landing of Soyuz TMA-13 (deorbit burn at 1:24 a.m.; landing at 2:15 a.m.)
12:30 p.m. � Video File feed of landing site activities and the crew's welcoming ceremony in Kazakhstan
2 p.m. -- Video File feed of the crew's return to Star City, Russia and a post-landing interview with Expedition 18 Commander Mike Fincke.

For NASA TV streaming video, downlink and schedule information, visit:

http://www.nasa.gov/ntv

For more information about the space station, visit:

http://www.nasa.gov/station

Hubble Finds Hidden Exoplanet in Archival Data

Sat, 04 Apr 2009 09:44:56 GMT

A powerful, newly refined image-processing technique may allow astronomers to discover extrasolar planets that are possibly lurking in over a decade's worth of Hubble Space Telescope archival data.

David Lafreni�re of the University of Toronto, Ontario, Canada, has successfully demonstrated this new strategy for planet hunting by identifying an exoplanet that went undetected in Hubble images taken in 1998 with its Near Infrared Camera and Multi-Object Spectrometer (NICMOS). In addition to illustrating the power of new data-processing techniques, this finding underscores the value of the Hubble data archive, on which those new techniques can be used.

The planet, estimated to be at least seven times Jupiter's mass, was originally discovered in images taken with the Keck and Gemini North telescopes in 2007 and 2008. It is the outermost of three massive planets known to orbit the dusty young star HR 8799, which is 130 light-years away. NICMOS could not see the other two planets because its coronagraphic spot -- a device which blots out the glare of the star -- also interferes with observing the two inner planets.

"We've shown that NICMOS is more powerful than previously thought for imaging planets," says Lafreni�re. "Our new image-processing technique efficiently subtracts the glare from a star that spills over the coronagraph's edge, allowing us to see planets that are one-tenth the brightness of what could be detected before with Hubble." Lafreni�re adapted an image reconstruction technique that was first developed for ground-based observatories.

Using the new technique, he recovered the planet in NICMOS observations taken 10 years before the Keck/Gemini discovery. The Hubble picture not only provides important confirmation of the planet's existence, it provides a longer baseline for demonstrating that the object is in an orbit about the star. "To get a good determination of the orbit we have to wait a very long time because the planet is moving so slowly (it has a 400-year period)," says Lafreni�re. "The 10-year-old Hubble data take us that much closer to having a precise measure of the orbit."

NICMOS's view provided new insights into the physical characteristics of the planet, too. This was possible because NICMOS works at near-infrared wavelengths that are severely blocked by Earth's atmosphere due to absorption by water vapor.

NASA Sets Briefings for Upcoming Shuttle Mission to Hubble

Thu, 02 Apr 2009 08:00:48 GMT

NASA will hold briefings Thursday, April 23, to update reporters about the space shuttle's fifth and final servicing mission to the Hubble Space Telescope. NASA Television and the agency's Web site will provide live coverage of the briefings from NASA's Johnson Space Center in Houston and from NASA Headquarters in Washington. Questions also will be taken from other participating NASA locations.

Shuttle Atlantis' 11-day flight, designated STS-125, is targeted for launch May 12 from NASA's Kennedy Space Center in Florida and will include five spacewalks to refurbish and upgrade the telescope with state-of-the-art science instruments. As a result, Hubble's capabilities will be expanded and its operational lifespan extended through at least 2014.

U.S. journalists planning to attend the briefings at Johnson must contact the Johnson newsroom at 281-483-5111 by April 21 to arrange for credentials. All reporters who are foreign nationals must contact Johnson by April 6.

Scott Altman will command Atlantis' crew, which includes Pilot Gregory C. Johnson and Mission Specialists Andrew Feustel, Michael Good, John Grunsfeld, Megan McArthur and Mike Massimino. The spacewalkers are Good, Grunsfeld, Feustel and Massimino. McArthur is the flight engineer and lead for robotic arm operations.

The briefings will include a crew news conference, but the crew will not be available for round robin interviews.

The schedule of activities is (times CDT):

7 a.m. -- Video B-roll feed from Johnson Space Center
8 a.m. -- Shuttle Program overview briefing from Johnson
9:30 a.m. -- Hubble Program and science overview from NASA Headquarters
11 a.m. -- NASA TV Video File
2 p.m. -- STS-125 crew news conference from Johnson

Altman and Grunsfeld will be available for satellite interviews on NASA TV from 3:30 p.m. to 5:30 p.m. To arrange an interview via satellite, contact the Johnson newsroom at 281-483-5111 no later than April 21.

For NASA TV streaming video, schedules and downlink information, visit:

http://www.nasa.gov/ntv

For the latest information about the STS-125 mission and its crew, visit:

http://www.nasa.gov/shuttle

For more information about the Hubble Space Telescope, visit:

http://www.nasa.gov/hubble