I am excited to find out what is between the stars and galaxies. Do scientists have any theories?
35 years on Voyager 1 is heading for spaceSave this story to read later
THIRTY-FIVE years after leaving Earth, Voyager 1 is reaching for the stars.
- by: By Alicia Chang, AP Science Writer
- From: AAP
Sooner or later, the workhorse spacecraft will bid adieu to the solar system and enter a new realm of space - the first time a man made object will have escaped to the other side.
Perhaps no one on Earth will relish the moment more than 76-year-old Ed Stone, who has toiled on the project from the start.
"We're anxious to get outside and find what's out there," he said.
When NASA's Voyager 1 and Voyager 2 first rocketed out of Earth's grip in 1977, no one knew how long they would live. Now, they are the longest-operating spacecraft in history and the most distant, at billions of miles from Earth but in different directions.
Wednesday marks the 35th anniversary of Voyager 1's launch to Jupiter and Saturn. It is now flitting around the fringes of the solar system, which is enveloped in a giant plasma bubble. This hot and turbulent area is created by a stream of charged particles from the sun.
Outside the bubble is a new frontier in the Milky Way - the space between stars. Once it plows through, scientists expect a calmer environment by comparison.
When that would happen is anyone's guess. Voyager 1 is in uncharted celestial territory. One thing is clear: The boundary that separates the solar system and interstellar space is near, but it could take days, months or years to cross that milestone.
Voyager 1 is currently more than 11 billion miles from the sun. Twin Voyager 2, which celebrated its launch anniversary two weeks ago, trails behind at 9 billion miles from the sun.
They're still ticking despite being relics of the early Space Age.
Each only has 68 kilobytes of computer memory. To put that in perspective, the smallest iPod - an 8-gigabyte iPod Nano - is 100,000 times more powerful. Each also has an eight-track tape recorder. Today's spacecraft use digital memory.
The Voyagers' original goal was to tour Jupiter and Saturn, and they sent back postcards of Jupiter's big red spot and Saturn's glittery rings. They also beamed home a torrent of discoveries: erupting volcanoes on the Jupiter moon Io; hints of an ocean below the icy surface of Europa, another Jupiter moon; signs of methane rain on the Saturn moon Titan.
Voyager 2 then journeyed to Uranus and Neptune. It remains the only spacecraft to fly by these two outer planets. Voyager 1 used Saturn as a gravitational slingshot to catapult itself toward the edge of the solar system.
"Time after time, Voyager revealed unexpected - kind of counterintuitive - results, which means we have a lot to learn," said Stone, Voyager's chief scientist and a professor of physics at the California Institute of Technology.
These days, a handful of engineers diligently listen for the Voyagers from a satellite campus not far from the NASA Jet Propulsion Laboratory, which built the spacecraft.
The control room, with its cubicles and carpeting, could be mistaken for an insurance office if not for a blue sign overhead that reads "Mission Controller" and a warning on a computer: "Voyager mission critical hardware. Please do not touch!"
There are no full-time scientists left on the mission, but 20 part-timers analyse the data streamed back. Since the spacecraft are so far out, it takes 17 hours for a radio signal from Voyager 1 to travel to Earth. For Voyager 2, it takes about 13 hours.
Cameras aboard the Voyagers were turned off long ago. The nuclear-powered spacecraft, about the size of a subcompact car, still have five instruments to study magnetic fields, cosmic rays and charged particles from the sun known as solar wind. They also carry gold-plated discs containing multilingual greetings, music and pictures - in the off chance that intelligent species come across them.
Since 2004, Voyager 1 has been exploring a region in the bubble at the solar system's edge where the solar wind dramatically slows and heats up. Over the last several months, scientists have seen changes that suggest Voyager 1 is on the verge of crossing over.
When it does, it will be the first spacecraft to explore between the stars. Space observatories such as the Hubble and Spitzer space telescopes have long peered past the solar system, but they tend to focus on far-away galaxies.
As ambitious as the Voyager mission is, it was scaled down from a plan to send a quartet of spacecraft to Jupiter, Uranus, Neptune and Pluto in what was billed as the "grand tour" of the solar system. But the plan was nixed, and scientists settled for the Voyager mission.
American University space policy expert Howard McCurdy said it turned out to be a boon.
They "took the funds and built spacecraft robust enough to visit all four gas giants and keep communicating" beyond the solar system, McCurdy said.
The double missions so far have cost $US782.15 million ($A764.48 million) in 1977 dollars, which translates to $US2.94 billion now. The spacecraft have enough fuel to last until around 2020.
By that time, scientists hope Voyager will already be floating between the starsThe space between galaxies, the intergalactic medium, is much emptier. Nonetheless, it too is a "soup", although more of a "watery consommé" when compared to the "minestrone" of the ISM. At least that's what the IGM appears to be like in the local, nearby universe. At redshifts above 2 — that is, at a time when the Universe's volume was about three percent of what it is at present — astronomers have not had a way to probe its nature.
But now Ojha et al. have used the ISM &mdash the "minestrone" in our Galaxy — as a special kind of filter to distinguish between distant compact radio sources — quasars — on the basis of their angular size. And above a redshift of 2, the angular size of the sources appears to increase. Ojha et al. argue that this apparent increase in size is not due to the intrinsic nature of the sources or some trick of cosmology, but rather that it is the result of the quasars' radio emission being scattered by a turbulent and ionized IGM.
How does one use the interstellar medium as a filter? In the 1980s, certain extragalactic radio sources, the quasars, were found to vary on extremely short time scales, their radio flux strength rising and falling drastically in just a few hours. After a bit of sleuthing, this "intraday variability" was traced to the ISM, which was causing the quasars to scintillate, or "twinkle", just as Earth's atmosphere causes stars to twinkle. Radio telescope sky surveys then followed to establish how widespread these rapidly scintillating sources were.
The largest of these surveys to date, MASIV (Micro-Arcsecond Scintillation-Induced Variability), was carried out using the National Science Foundation's Very Large Array radio telescope at Socorro, New Mexico, by Jim Lovell and colleagues. MASIV detected 500 flat-spectrum radio sources at a frequency of 5 GHz: 56% of these showed scintillation. Ojha et al. obtained redshifts for 190 of the 500 sources in the MASIV survey: 150 came from the literature, while 40 were new measurements made with the 2.6-m Nordic Optical Telescope in La Palma, Spain. The entire dataset was then used to look for any difference in the redshift distribution of scintillating and non-scintillating sources. The researchers found, to a 98% confidence level, a redshift dependence on the scintillators, with a striking deficit of scintillating sources above z~2.
Scintillation occurs only if the radio sources are below a certain angular size, which is around 100 millionths of an arcsecond — a level of detail that would allow us to see an ant in Albuquerque, New Mexico while sitting in downtown Sydney, Australia! This is almost 10 times finer than the angular size that astronomers can currently observe by other techniques. The drop-off at z~2 implies that, at higher redshifts, the sources are either intrinsically or apparently larger in angular size. While an intrinsically larger angular size at higher redshifts cannot be completely ruled out, there are a number of reasons why this is not very likely. Current theories of galaxy formation tell us that quasars should appear smaller at higher redshifts. Also, the sources for the MASIV survey were selected in a manner that tended to bias the survey towards finding smaller sources at high redshifts.
The most likely explanation of these results is that an ionized IGM is diffusing the radio emissions from the quasars, causing them to appear larger than the angular size below which they can twinkle. A terrestrial analogy would be the way fog or heavy snowfall diffuses the headlights of distant oncoming cars at night. At z>2 the Universe was much smaller than it is today, so the intergalactic medium must have been much denser, overall, than it is now. Hot young stars, radio galaxies, and quasars, all present in abundance at this epoch, would have been "ionization factories" pumping out both ionizing radiation and charged particles. "We believe, therefore, that we're seeing the effect of the radio signals being scattered by the ionized intergalactic medium," said Dr. Jauncey. "But to confirm this result, we really need to get more redshifts, particularly for weaker sources, so that we can rule out any possible selection effects," said Dr. Pursimo.
Given enough radio sources of the right kind, the scientists say, they might be able to trace how the scattering properties of the intergalactic medium changed through time at higher redshifts. The degree of inhomogeneity, or lumpiness, in the intergalactic medium could be established by taking optical spectra along the lines of sight to quasars from the survey
Edited by The Ratiocinator, 04 September 2012 - 04:31 PM.
"These are the things to keep in mind. These are not just academic exercises. We're not analyzing the media on Mars or in the eighteenth century or something like that. We're dealing with real human beings who are suffering and dying and being tortured and starving because of policies that we are involved in, we as citizens of democratic societies are directly involved in and are responsible for, and what the media are doing is ensuring that we do not act on our responsibilities, and that the interests of power are served, not the needs of the suffering people, and not even the needs of the American people who would be horrified if they realized the blood that's dripping from their hands because of the way they are allowing themselves to be deluded and manipulated by the system."
Jesus didn’t say yes to everyone. I mean Jesus knew that there was a place for everything and it is not necessarily everyone’s place to come to Australia
Tony Abbott......Current Australian PM