Amazing voyager: 25 years of exploring space. (Earth science: solar system/interstellar space).
1 Cape Canaveral, Florida
August 20 and September 5, 1977 The launches are timed to meet a rare planetary alignment in order to travel the most distance using the least amount of time and energy. Voyager 1 (blue) launches last, but flies on a shorter and faster trajectory.
March and July 1979 The probes snap more than 33,000 images of the solar system's largest planet and five of its moons. Some cool finds: Jupiter's mysterious Great Red Spot is actually a huge, counterclockwise hurricane; the moon Io contains many active volcanoes; a vast ocean may lie beneath the moon Europa's icy surface.
November 1980 And August 1981 Voyager discovers that Saturn's mammoth ring--made of specks to house-size pieces of ice and rock--has thousands of ripples. Close-ups show some rings are narrow and others broad and diffuse. And colors indicate different chemical compositions. After Saturn, Voyager 1 heads northward of the planets' orbital plane.
January 1986 Voyager 2 becomes the planet's first visitor and discovers 10 of its 15 moons. On the moon Miranda the probe captures a geological mishmash of grooves and canyons as deep as 20 km (12 mi), along with young and old terrain. Scientists aren't sure what caused the patchwork landscape. One theory: The moon was once shattered by impact with space objects--and somehow, the pieces reassembled back together.
August 1989 Voyager 2 remains the only spacecraft to visit the windiest planet in the solar system: Near the Great Dark Spot, hurricane winds rage over 2,000 km (1,500 mi) per hour. The probe also finds six of Neptune's eight moons.
6 Far Out!
February 17, 1998 Voyager 1 surpasses an older spacecraft to become the most distant human-made object in space.
Each 1-ton probe--containing 65,000 parts--is powered by decaying plutonium, a human-made element. To communicate with Voyager, giant antennas on Earth track faint signals (their power 20 billion times weaker than a digital watch) emitted by the spacecraft's antennas and 23-watt transmitters. Today it takes 12 hours to transmit or receive a radio signal traveling at the speed of light (186,355 miles per second) between Voyager 1 and Earth, about 9 hours for Voyager 2.
Approaching the Unknown
Today, Voyager 1 continues to travel upward of the planets orbital plane. Voyager 2 is venturing downward, Both probes are speeding at nearly 1,5 million km (930,000 mi) per day to reach where no human-made object has ever gone: interstellar space, or space between stars, The voyage continues ...
Like a proud father. Dr. Edward Stone has kept a watchful eye on Voyager 1 and 2 for 30 years. As the mission's chief scientist, he guided the two sturdy robotic probes from the drawing board to a wealth of lunar and planetary discoveries. Now he's leading the mission into a new era. The twin probes are soaring where no human-made object has ever ventured: interstellar space. Dr. Stone talked to Science World's Mona Chiang about his amazing "babies."
Q Did you ever imagine these spacecraft would accomplish anything close to this magnitude?
A think we all expected that there would be a lot of discoveries, but we were really not prepared for the wealth of discovery. That's because there are so many diverse bodies in the solar system. All the moons, the ring systems [like Saturn's rings], and the magnetic fields of the planets are different. So, it's the diversity that really gave us so much to learn.
Q Wasn't the Voyager mission supposed to end a lot earlier?
A You have to remember, when the two Voyager spacecraft were launched, the space age was only 20 years old. There was no basis to predict a spacecraft could last 25 years. So we took it step-by-step. The first commitment from NASA was a four-year mission to Saturn. And at that time, it was a bold venture to go 10 times farther from the Sun than Earth. When that was successful, we took the next step to go to Uranus, which is about 19 times farther front the Sun than Earth. And when that was successful, NASA committed to go to Neptune, which is 30 times as far from the Sun. After that, we got approval to continue to interstellar space.
Q So, the probes were preprogrammed for a potential long haul?
A Oh, yes, we had planned the mission so we would have the option to do this. But Voyager 2 actually had two possibilities: Had Voyager 1 not succeeded to Saturn, Voyager 2 was to repeat the mission after Voyager 1. And that would have meant Voyager 2 wouldn't have flown by Uranus and Neptune, because Voyager 1 was to head above the plane of the planets' orbits.
Q Didn't a rare planetary alignment also help speed up their trips?
A Yes. Every 176 years, Jupiter, Saturn, Uranus, and Neptune are all on the same side of the Sun. That makes it possible for a single spacecraft to fly by all four. But more importantly, each flyby actually gave the spacecraft a big boost. It's like a slingshot. When you fly by Jupiter, the planet is orbiting the Sun. So Jupiter has motion. And Jupiter's gravity--like your arm--just flips the spacecraft in the direction it's moving. So this speeds up the spacecraft. Using this boost, we made it to Neptune in 12 years.
When we launched from Cape Canaveral, Florida, a launch rocket big enough to get us to Saturn didn't exist. But even if there had been a large enough rocket to launch Voyager onto a direct trajectory to Neptune, it would have taken 30 years to get there.
Q It must have been really exciting to see the very first fly-by images.
A Oh yes. Right away we knew that we were seeing things that we hadn't even imagined we'd be finding. During the encounters, which would last typically a week, the images and other science data were coming back continuously. And people were working around the clock to try to understand what we were seeing. It was a very intense period of discovery. Many people brought in sleeping bags and didn't go home.
Q What are you looking for now?
A We monitor these spacecraft for 8 to 10 hours every day. And what we're looking for is a sign that we're approaching the edge of interstellar space.
Q Where are they today?
A They're still in the heliosphere [see diagram, above]. There's a wind of about 1 million miles per hour that blows radially outward from the Sun. That wind is the Sun's atmosphere expanding out to create a bubble around the star. And that bubble is the heliosphere. Actually, it's more of a comet shape than a sphere.
Q Why a comet shape?
A There's an interstellar wind blowing from a particular direction that deforms the bubble. Want to see what a heliosphere looks like?
A First, turn the running faucet in your kitchen sink so that the water hits the sink bottom rather than runs directly down the drain. You'll notice a circle around the running water on the sink bottom. Inside the circle the water is very thin, fast, and flows radially outward in all directions. But it gets thinner as it spreads into a larger circle. Right now the Voyagers are inside this thin fast flow of the wind coming from the Sun. And at some point you'll see there's a sudden slowdown, where the water gets much thicker. This jump is called termination shock. We're looking for this first shock, which is where the wind will abruptly slow down. We may be within a couple of years from reaching that.
Q Sounds intense. Will the spacecraft survive out there?
A Yes. Turns out, it s a very diluted environment. And we know because we have very sensitive instruments that measure it.
Q What happens after that?
A The spacecraft then go through a region where the wind is slow and hot, like where the water is thicker. But, eventually, the solar wind will run into the interstellar wind--where the water turns around and goes down the drain. That's the end of the heliosphere called the heliopause.
We're in a race to see if we can get through the heliopause and truly into interstellar space while the craft still have the electrical power to observe what's out there. We're very confident that we have about 20 years of power left.
Q Will you be sad the moment you lose contact with Voyager?
A Certainly. This is our only chance in several decades to reach interstellar space. So it would be most disappointing if we lose contact before Voyager gets there.
For more, visit: voyager.jpl.nasa.gov
interstellar space space between stars
ED'S FAVE IMAGE
Q Do you have a favorite image?
A One fine favorite is of Jupiter with the Great Rod Spat and two of its moans-lo and Europa-suspended in front. It captures the size of the giant outer planet, and we saw the two moons up close for the first time.
VOYAGER 1 SNAPPED IT ON 2/13/79. IO IS ABOUT 350,000 KM (220,000 MI) ABOVE JUPITER'S STORMY RED SPOT. EUROPA IS AROUND 600,000 KM (375,000 MI) ABOVE THE PLANET'S CLOUDS.
THE VOYAGE CONTINUES
Today, Voyager 1 and 2 are exploring the fringes of the solar system, navigating toward interstellar space. But will they be able to traverse the heliosphere (bubble of solar wind surrounding the Sun) and send back landmark data before they run out of power? Follow the journey.
The wave of interstellar wind that forms as it encounters the oncoming solar system. It's similar to water plowed aside by the bow of a moving ship.
Considered the boundary of the solar system, where the declining pressure of the solar wind balances incoming pressure of interstellar wind. Here, solar wind turns backward. Estimated arrival: ID to 15 years after passing termination shack.
Solar wind abruptly slows from a supersonic speed of 1 million mph to about 250,000 mph! Estimated arrival: three years.
Did You Know?
* The radiation level Voyager encountered when flying by Jupiter is 1,000 times the lethal amount for humans.
* After the Neptune fly-by, the bits of scientific data that both Voyager spacecraft returned to Earth totaled 5 trillion. That's enough information to encode more than 6,000 complete sets of the Encyclopedia Britannica, or approximately 1,000 bits of information for each person on Earth.
* The electronics and heaters on each Voyager spacecraft operate on approximately 400 watts of power, or about the amount of energy it takes to power a personal computer.
Language Arts: In case of a possible encounter with an alien, each Voyager spacecraft carries a golden disk containing images and sounds to showcase Earth. If you had to create your own disk to describe what your home planet is like, what would you include? Devise a list and write a short essay on why you made the selections.
Imagine a world in which space exploration did not exist. Would it impact everyday life? Why or why not?
Directions: Read the article on the Voyager mission. Then write two short essays using the following words.
1. You're Dr. Edward Stone's assistant at voyager's mission control during an early fly-by. Describe the work atmosphere as scientists observe the transmission of data and images. (176 years, direct trajectory, sleeping bags, lo)
2. You're in a sci-fi movie. And you're flying a spacecraft toward interstellar space. Signal your findings back to NASA. (Cape Canaveral, Neptune, heliosphere, termination shock, Interstellar space)
Answers will vary, but may contain the following definitions.
1. Every 176 years, Jupiter, Saturn, Uranus, and Neptune are all on the same side of the Sun, which make it possible for a single spacecraft to fly by all four. More important, 25 years ago NASA did not possess a launch rocket powerful enough to launch Voyager directly to Saturn. During each fly-by, Voyager got a slingshot-like boost thanks to the gravitational pull and motion of the planets. A direct trajectory to Neptune would have taken 30 years. But the boosts shortened the trip to just 12 years. During the encounters, many people worked around the clock to process unprecedented data and images. Many brought in sleeping bags and didn't go home. lo is one of Jupiter's moons.
2. The Voyager mission was launched from Cape Canaveral, Florida. Neptune, the windiest planet in the solar system, is the most-distant planet visited by Voyager. Right now, the spacecraft is still in the heliosphere, a bubble of wind of about 1 million miles per hour that blows radially outward from the Sun. That wind is the Sun's atmosphere expanding out to create a bubble around the star. One part of the heliosphere is called termination shock, which is where the solar wind abruptly slows down to about 250,000 miles per hour. Estimated arrival: three years. Voyager must traverse the heliosphere to reach Interstellar space, or space between stars.
Voyager's Web site is located at voyager The Planetary Society's special coverage on the 25th anniversary of Voyager: www.planetary.org/voyater25/Index.html
Check out: spacelink.nas.gov/instructional.Materials/ for free and reproducible instructional and educational support materials developed by NASA. Information covers Earth, life, physical and space sciences. CD-ROMs, videotapes, and slides are also available to educators for a minimal fee.
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|Date:||Nov 29, 2002|
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