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Interstellar cloud baffles scientists
25 December 2009
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Remember the early planetary spaceships, Voyager 1 and 2? They were launched in summer, 1977, to explore the outer planets - Jupiter to Neptune. Their discoveries and photographs from those systems were among the most exciting events in science in our lifetimes. And they continue to surprise us.
Voyager 1 reached Jupiter in March, 1979, and went on to visit Saturn in November, 1980. The gravity of Saturn's moon, Titan, bent the craft's trajectory and it was flung outside the plane of the ecliptic, heading towards interstellar space. It is now more than 16.7 billion km, (10.4 billion miles) from the Sun, and still has several instruments functioning, and transmitting data back to Earth. It has almost reached the heliopause, the boundary of the solar system. Signals from Voyager 1 take almost 31 hours to make the round trip to Earth and back.*
Voyager 2 arrived at Jupiter not much later - July, 1979 - and then reached Saturn in August, 1981. Voyager 2 continued its grand tour, coming within 81,500 kms (50,600 miles) of Uranus occurred in January, 1986. It passed by Neptune in August, 1989, and headed out of the solar system. V2 passed through the termination shock into the heliosheath, at the end of August, 2007. It is currently more than 13.5 billion km (8.5 billion miles), or more than twice as far from the Sun as Pluto.**
These puppies are moving fast. Voyager 1 travels 520 million kilometers (320 million miles) a year, heading above the plane o the ecliptic. Voyager 2, a little slower, travels about 470 million kilometers (290 million miles) a year, diving below the ecliptic plane. V1 will reach the heliopause in 2015, and be more than 19 billion kms away then (or 133.15 AU - V2 will be more than 16 billion kms distant).
Both spacecraft are expected to keep transmitting radio messages until at least 2025, when there won't be enough power left for any single instrument. That's pretty amazing - more than 48 years since they were launched, and using technology that is older than a Commodore Pet computer.*** Not all the instruments continue to function- hardly surprising given the environment and their age.
But if you think these are merely techno-dinosaurs of the space age with nothing important to report, think again. They are making discoveries that are still rocking science.
This week, NASA announcedV2 had discovered "an interstellar cloud that physics says should not exist."
The big deal here is that this cloud - called the Local Fluff by astronomers - is magnetized.
Exciting stuff. The universe as we knew it in 1977 has changed, thanks in part to the continuing discoveries made by these spacecraft.
~~~~~
* Signals from V1 take over 15.6 hours to reach Earth. In comparison, a radio signal from the Moon takes about 1.4 seconds, a signal from the Sun about 8.5 minutes, and a signal from Pluto would take 5.5 hours. Light from the nearest star takes 4.3 years to reach us.
** There are other spacecraft headed outside the solar system, including the two Pioneer vehicles, launched in the early 1970s, and New Horizons, launched in 2006. You can find where they are at Heavens Above. The Pioneer craft are no longer operating.
*** I purchased my first computer - a Radio Shack TRS-80, in fall, 1977.
**** A microgauss is one millionth of a Gauss, a unit of magnetic field strength. Earth's magnetic field is about 0.5 gauss or 500,000 microgauss. Some Neodymium rare earth magnets, grade N42, can have ahuge 13,000 Gauss. Even a small, .75" x .125" rare earth magnet, has a Gauss rating of of 2,400 to 2,600, which translates into a direct pull force of 22 lb. or almost 50 kg! Merav Opher is an associate professor at George Mason University. [/indent]
Voyager 1 reached Jupiter in March, 1979, and went on to visit Saturn in November, 1980. The gravity of Saturn's moon, Titan, bent the craft's trajectory and it was flung outside the plane of the ecliptic, heading towards interstellar space. It is now more than 16.7 billion km, (10.4 billion miles) from the Sun, and still has several instruments functioning, and transmitting data back to Earth. It has almost reached the heliopause, the boundary of the solar system. Signals from Voyager 1 take almost 31 hours to make the round trip to Earth and back.*
Voyager 2 arrived at Jupiter not much later - July, 1979 - and then reached Saturn in August, 1981. Voyager 2 continued its grand tour, coming within 81,500 kms (50,600 miles) of Uranus occurred in January, 1986. It passed by Neptune in August, 1989, and headed out of the solar system. V2 passed through the termination shock into the heliosheath, at the end of August, 2007. It is currently more than 13.5 billion km (8.5 billion miles), or more than twice as far from the Sun as Pluto.**
These puppies are moving fast. Voyager 1 travels 520 million kilometers (320 million miles) a year, heading above the plane o the ecliptic. Voyager 2, a little slower, travels about 470 million kilometers (290 million miles) a year, diving below the ecliptic plane. V1 will reach the heliopause in 2015, and be more than 19 billion kms away then (or 133.15 AU - V2 will be more than 16 billion kms distant).
Both spacecraft are expected to keep transmitting radio messages until at least 2025, when there won't be enough power left for any single instrument. That's pretty amazing - more than 48 years since they were launched, and using technology that is older than a Commodore Pet computer.*** Not all the instruments continue to function- hardly surprising given the environment and their age.
But if you think these are merely techno-dinosaurs of the space age with nothing important to report, think again. They are making discoveries that are still rocking science.
This week, NASA announcedV2 had discovered "an interstellar cloud that physics says should not exist."
The big deal here is that this cloud - called the Local Fluff by astronomers - is magnetized.
Quote
Astronomers call the cloud we're running into now the Local Interstellar Cloud or "Local Fluff" for short. It's about 30 light years wide and contains a wispy mixture of hydrogen and helium atoms at a temperature of 6000 C. The existential mystery of the Fluff has to do with its surroundings. About 10 million years ago, a cluster of supernovas exploded nearby, creating a giant bubble of million-degree gas. The Fluff is completely surrounded by this high-pressure supernova exhaust and should be crushed or dispersed by it.
"The observed temperature and density of the local cloud do not provide enough pressure to resist the 'crushing action' of the hot gas around it," says Opher.
So how does the Fluff survive? The Voyagers have found an answer.
"Voyager data show that the Fluff is much more strongly magnetized than anyone had previously suspected—between 4 and 5 microgauss," says Opher.**** "This magnetic field can provide the extra pressure required to resist destruction."
<snip>
The fact that the Fluff is strongly magnetized means that other clouds in the galactic neighborhood could be, too. Eventually, the solar system will run into some of them, and their strong magnetic fields could compress the heliosphere even more than it is compressed now. Additional compression could allow more cosmic rays to reach the inner solar system, possibly affecting terrestrial climate and the ability of astronauts to travel safely through space. On the other hand, astronauts wouldn't have to travel so far because interstellar space would be closer than ever. These events would play out on time scales of tens to hundreds of thousands of years, which is how long it takes for the solar system to move from one cloud to the next.
"The observed temperature and density of the local cloud do not provide enough pressure to resist the 'crushing action' of the hot gas around it," says Opher.
So how does the Fluff survive? The Voyagers have found an answer.
"Voyager data show that the Fluff is much more strongly magnetized than anyone had previously suspected—between 4 and 5 microgauss," says Opher.**** "This magnetic field can provide the extra pressure required to resist destruction."
<snip>
The fact that the Fluff is strongly magnetized means that other clouds in the galactic neighborhood could be, too. Eventually, the solar system will run into some of them, and their strong magnetic fields could compress the heliosphere even more than it is compressed now. Additional compression could allow more cosmic rays to reach the inner solar system, possibly affecting terrestrial climate and the ability of astronauts to travel safely through space. On the other hand, astronauts wouldn't have to travel so far because interstellar space would be closer than ever. These events would play out on time scales of tens to hundreds of thousands of years, which is how long it takes for the solar system to move from one cloud to the next.
Exciting stuff. The universe as we knew it in 1977 has changed, thanks in part to the continuing discoveries made by these spacecraft.
~~~~~
* Signals from V1 take over 15.6 hours to reach Earth. In comparison, a radio signal from the Moon takes about 1.4 seconds, a signal from the Sun about 8.5 minutes, and a signal from Pluto would take 5.5 hours. Light from the nearest star takes 4.3 years to reach us.
** There are other spacecraft headed outside the solar system, including the two Pioneer vehicles, launched in the early 1970s, and New Horizons, launched in 2006. You can find where they are at Heavens Above. The Pioneer craft are no longer operating.
*** I purchased my first computer - a Radio Shack TRS-80, in fall, 1977.
**** A microgauss is one millionth of a Gauss, a unit of magnetic field strength. Earth's magnetic field is about 0.5 gauss or 500,000 microgauss. Some Neodymium rare earth magnets, grade N42, can have ahuge 13,000 Gauss. Even a small, .75" x .125" rare earth magnet, has a Gauss rating of of 2,400 to 2,600, which translates into a direct pull force of 22 lb. or almost 50 kg! Merav Opher is an associate professor at George Mason University. [/indent]
