Voyager Set to Enter Interstellar Space
Article By: Dr. Tony Phillips - NASA's Goddard Space Flight Center - 4-29-2011
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More than 30 years after they left Earth, NASA's twin Voyager probes are now at the edge of the solar system. Not only that, they're still working. And with
each passing day they are beaming back a message that, to scientists, is both unsettling and thrilling.
The message is, "Expect the unexpected."
"It's uncanny," says Ed Stone of Caltech, Voyager Project Scientist since 1972. "Voyager 1 and 2 have a knack for making discoveries."
Today, April 28, 2011, NASA held a press conference to reflect on what the Voyager mission has accomplished -- and to preview what lies ahead as the
probes prepare to enter the realm of the Milky Way itself.
The adventure began in the late 1970s when the probes took advantage of a rare alignment of outer planets for an unprecedented Grand Tour. Voyager 1
visited Jupiter and Saturn, while Voyager 2 flew past Jupiter, Saturn, Uranus and Neptune. (Voyager 2 is still the only probe to visit Uranus and Neptune.)
When pressed to name the top discoveries from those encounters, Stone pauses, not for lack of material, but rather an embarrassment of riches. "It's so hard
to choose," he says.
Stone's partial list includes the discovery of volcanoes on Jupiter's moon Io; evidence for an ocean beneath the icy surface of Europa; hints of methane rain
on Saturn's moon Titan; the crazily-tipped magnetic poles of Uranus and Neptune; icy geysers on Neptune's moon Triton; planetary winds that blow faster and
faster with increasing distance from the sun.
"Each of these discoveries changed the way we thought of other worlds," he says Stone.
In 1980, Voyager 1 used the gravity of Saturn to fling itself slingshot-style out of the plane of the Solar System. In 1989, Voyager 2 got a similar assist from
Neptune. Both probes set sail into the void.
Sailing into the void sounds like a quiet time, but the discoveries have continued.
Stone sets the stage by directing our attention to the kitchen sink. "Turn on the faucet," he instructs. "Where the water hits the sink, that's the sun, and the
thin sheet of water flowing radially away from that point is the solar wind. Note how the sun 'blows a bubble' around itself."
There really is such a bubble, researchers call it the "heliosphere," and it is gargantuan. Made of solar plasma and magnetic fields, the heliosphere is about
three times wider than the orbit of Pluto. Every planet, asteroid, spacecraft, and life form belonging to our solar system lies inside.
The Voyagers are trying to get out, but they're not there yet. To locate them, Stone peers back into the sink: "As the water (or solar wind) expands, it gets
thinner and thinner, and it can't push as hard. Abruptly, a sluggish, turbulent ring forms. That outer ring is the heliosheath -- and that is where the Voyagers
are now."
The heliosheath is a very strange place, filled with a magnetic froth no spacecraft has ever encountered before, echoing with low-frequency radio bursts
heard only in the outer reaches of the solar system, so far from home that the sun is a mere pinprick of light.
"In many ways, the heliosheath is not like our models predicted,” says Stone.
In June 2010 Voyager 1 beamed back a startling number: zero. That's the outward velocity of the solar wind where the probe is now. No one thinks the solar
wind has completely stopped; it may have just turned a corner. But which way? Voyager 1 is trying to figure that out through a series of "weather vane"
maneuvers, in which V1 turns itself in a different direction to track the local breeze. The old spacecraft still has some moves left, it seems.
No one knows exactly how many more miles the Voyagers must travel before they "pop free" into interstellar space. Most researchers believe, however, that
the end is near. "The heliosheath is 3 to 4 billion miles in thickness," estimates Stone. "That means we'll be out within five years or so."
There is plenty of power for the rest of the journey. Both Voyagers are energized by the radioactive decay of a Plutonium 238 heat source. This should keep
critical subsystems running through at least 2020.
After that, he says, "Voyager will become our silent ambassador to the stars."
Each probe is famously equipped with a Golden Record, literally, a gold-coated copper phonograph record. It contains 118 photographs of Earth; 90 minutes
of the world's greatest music; an audio essay entitled Sounds of Earth (featuring everything from burbling mud pots to barking dogs to a roaring Saturn 5
liftoff); greetings in 55 human languages and one whale language; the brain waves of a young woman in love; and salutations from the Secretary General of
the United Nations. A team led by Carl Sagan assembled the record as a message to possible extraterrestrial civilizations that might encounter the spacecraft.
"A billion years from now, when everything on Earth we've ever made has crumbled into dust, when the continents have changed beyond recognition and our
species is unimaginably altered or extinct, the Voyager record will speak for us," wrote Carl Sagan and Ann Druyan in an introduction to a CD version of the
record.
Some people note that the chance of aliens finding the Golden Record is fantastically remote. The Voyager probes won't come within a few light years of
another star for some 40,000 years. What are the odds of making contact under such circumstances?
On the other hand, what are the odds of a race of primates evolving to sentience, developing spaceflight, and sending the sound of barking dogs into the
cosmos?
Expect the unexpected, indeed.
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Breakthrough Study Confirms Cause Of Short Gamma-Ray Bursts
Article By: NASA News Release - 4/8/2011
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A new supercomputer simulation shows the collision of two neutron stars can naturally produce the magnetic structures thought to power the high-speed
particle jets associated with short gamma-ray bursts (GRBs). The study provides the most detailed glimpse of the forces driving some of the universe's most
energetic explosions.
The state-of-the-art simulation ran for nearly seven weeks on the Damiana computer cluster at the Albert Einstein Institute (AEI) in Potsdam, Germany. It
traces events that unfold over 35 milliseconds -- about three times faster than the blink of an eye. GRBs are among the brightest events known, emitting as
much energy in a few seconds as our entire galaxy does in a year. Most of this emission comes in the form of gamma rays, the highest-energy form of light.
"For the first time, we've managed to run the simulation well past the merger and the formation of the black hole," said Chryssa Kouveliotou, a co-author of
the study at NASA's Marshall Space Flight Center in Huntsville, Ala. "This is by far the longest simulation of this process, and only on sufficiently long
timescales does the magnetic field grow and reorganize itself from a chaotic structure into something resembling a jet."
GRBs longer than two seconds are the most common type and are widely thought to be triggered by the collapse of a massive star into a black hole. As
matter falls toward the black hole, some of it forms jets in the opposite direction that move near the speed of light. These jets bore through the collapsing star
along its rotational axis and produce a blast of gamma rays after they emerge. Understanding short GRBs, which fade quickly, proved more elusive.
Astronomers had difficulty obtaining precise positions for follow-up studies.
That began to change in 2004, when NASA's Swift satellite began rapidly locating bursts and alerting astronomers where to look. "For more than two
decades, the leading model of short GRBs was the merger of two neutron stars," said co-author Bruno Giacomazzo at the University of Maryland and NASA's
Goddard Space Flight Center in Greenbelt, Md. "Only now can we show that the merger of neutron stars actually produces an ultrastrong magnetic field
structured like the jets needed for a GRB."
A neutron star is the compressed core left behind when a star weighing less than about 30 times the sun's mass explodes as a supernova. Its matter reaches
densities that cannot be reproduced on Earth -- a single spoonful outweighs the Himalayan Mountains.
The simulation began with a pair of magnetized neutron stars orbiting just 11 miles apart. Each star packed 1.5 times the mass of the sun into a sphere just
17 miles across and generated a magnetic field about a trillion times stronger than the sun's.
In 15 milliseconds, the two neutron stars crashed, merged and transformed into a rapidly spinning black hole weighing 2.9 suns. The edge of the black hole,
known as its event horizon, spanned less than six miles. A swirling chaos of superdense matter with temperatures exceeding 18 billion degrees Fahrenheit
surrounded the newborn black hole. The merger amplified the strength of the combined magnetic field, but it also scrambled it into disarray.
Over the next 11 milliseconds, gas swirling close to the speed of light continued to amplify the magnetic field, which ultimately became a thousand times
stronger than the neutron stars' original fields. At the same time, the field became more organized and gradually formed a pair of outwardly directed funnels
along the black hole's rotational axis.
This is exactly the configuration needed to power the jets of ultrafast particles that produce a short gamma-ray burst. Neither of the magnetic funnels was
filled with high-speed matter when the simulation ended, but earlier studies have shown that jet formation can occur under these conditions.
"By solving Einstein's relativity equations as never before and letting nature take its course, we've lifted the veil on short GRBs and revealed what could be
their central engine," said Luciano Rezzolla, the study's lead author at AEI. "This is a long-awaited result. Now it appears that neutron star mergers inevitably
produce aligned jet-like structures in an ultrastrong magnetic field."
The study is available online and will appear in the May 1 edition of The Astrophysical Journal Letters.
The authors note the ultimate proof of the merger model will have to await the detection of gravitational waves -- ripples in the fabric of space-time predicted
by relativity. Merging neutron stars are expected to be prominent sources, so the researchers also computed what the model's gravitational-wave signal would
look like. Observatories around the world are searching for gravitational waves, so far without success because the signals are so faint.
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NASA Spacecraft Reveal Mysteries Of Jupiter And Saturn Rings
Article By: NASA 4/2/2011
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PASADENA, Calif. -- In a celestial forensic exercise, scientists analyzing data from NASA's Cassini, Galileo and New Horizons missions have traced telltale
ripples in Saturn and Jupiter's rings to specific collisions with cometary fragments that occurred decades, not millions of years, ago.
Jupiter's ripple-producing culprit was comet Shoemaker-Levy 9. The comet's debris cloud hurtled through the thin Jupiter ring system on a collision course
into the planet in July 1994. Scientists attribute Saturn's ripples to a similar object - likely another cloud of comet debris - plunging through the inner rings in
1983. The findings are detailed in two papers published Thursday in the journal Science.
"We're finding evidence that a planet's rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million
years ago," said Matthew Hedman, a Cassini imaging team associate, lead author on one of the papers, and a research associate at Cornell University in
Ithaca, N.Y. "The solar system is a much more dynamic place than we gave it credit for."
Scientists learned about the patchy patterns in Jupiter's rings in the late 1990s from Galileo's visit to Jupiter. Unfortunately, the images from that mission were
fuzzy, and scientists didn't understand why such patterns would occur. Not until Cassini entered orbit around Saturn in 2004 and started sending back
thousands of images did scientists have a better picture of the activity. A 2007 science paper by Hedman and colleagues first noted corrugations in Saturn's
innermost ring, dubbed the D ring.
A group including Hedman and Mark Showalter, a Cassini co-investigator based at the SETI Institute in Mountain View, Calif., saw that the grooves in the D
ring appeared to wind together more tightly over time. Playing the process backward, Hedman demonstrated the pattern originated when something tilted the
D ring off its axis by about 300 feet (100 meters) in late 1983. The scientists found Saturn's gravity on the tilted area warped the ring into a tightening spiral.
Cassini imaging scientists received another clue around August 2009 when the sun shone directly along Saturn's equator and lit the rings edge-on. The
unique lighting conditions highlighted ripples not previously seen in another part of the ring system. Whatever happened in 1983 was big - not a small,
localized event.
The collision tilted a region more than 12,000 miles (19,000 kilometers) wide, covering part of the D ring and the next outermost ring, called the C ring.
Unfortunately, spacecraft were not visiting Saturn at that time, and the planet was on the far side of the sun out of sight from ground or space-based
telescopes.
Hedman and Showalter, the lead author on the second paper, wondered whether the long-forgotten pattern in Jupiter's ring system might illuminate the
mystery. Using Galileo images from 1996 and 2000, Showalter confirmed a similar winding spiral pattern by applying the same math they had applied to
Saturn and factoring in Jupiter's gravitational influence. Galileo was launched on a space shuttle in 1989 and studied Jupiter until 2003.
Unwinding the spiral pinpointed the date when Jupiter's ring was tilted off its axis between June and September 1994. Shoemaker-Levy plunged into the
Jovian atmosphere in late July. The Galileo images also revealed a second spiral, which was calculated to have originated in 1990. Images taken by New
Horizons in 2007, when the spacecraft flew by Jupiter on its way to Pluto, showed two newer ripple patterns, in addition to the fading echo of the Shoemaker-
Levy impact.
"We now know that collisions into the rings are very common – a few times per decade for Jupiter and a few times per century for Saturn," Showalter said.
"Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later."
Launched in Oct. 15, 1997, Cassini began orbiting Saturn in 2004 and sends back data daily.
"Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system," said Linda Spilker, Cassini
project scientist, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Cassini's long sojourn around Saturn has helped us tease out subtle clues
that tell us about the history of our origins."
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by JPL
for NASA's Science Mission Directorate in Washington. The imaging team is based at the Space Science Institute in Boulder, Colo. For more information
about Cassini, visit: http://www.nasa.gov/cassini
Pluto New Horizons launched in 2006 on the first mission to study Pluto and the Kuiper Belt. The mission is managed by the Johns Hopkins Applied Physics
Laboratory in Laurel, Md., for NASA. The mission is part of the New Frontiers program managed at the agency's Marshall Space Flight Center in Huntsville,
Ala. For more information about Pluto New Horizons.
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