3 posts tagged “astrophysics”
What's Wrong with the Sun? (Nothing) |
07.11.2008
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+ Play Audio | + Download Audio | + Email to a friend | + Join mailing list July 11, 2008: Stop the presses! The sun is behaving normally. So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle." This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise. But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."
Above: The solar cycle, 1995-2015. The "noisy" curve traces measured sunspot numbers; the smoothed curves are predictions. Credit: D. Hathaway/NASA/MSFC. [more] During Solar Max, huge sunspots and intense solar flares are a daily occurance. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001. During Solar Minimum, the opposite occurs. Solar flares are almost non-existant while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.
"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then. Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values." In summary, "the current minimum is not abnormally low or long." The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.
For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again. The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally." What's next? Hathaway anticipates more spotless days1, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012. Stay tuned to Science@NASA for updates. Author: Dr. Tony Phillips | Credit: Science@NASA
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13 May 2008
Is something lurking just over the sun's eastern limb? Yesterday's impressive display suggests the answer is yes. Amateur astronomers in Europe and North America witnessed fountains of hot, magnetized gas surging over the eastern edge of the sun. "My hard drive is full of movies," says Didier Favre of Brétigny sur Orge, France, who counted no fewer than seven eruptions.
Veteran observer Pete Lawrence of Selsey, UK, took the picture above. "This is the first time I've ever seen material moving visually away from the surface of the Sun," he says. "What a treat!"
Readers, if you have a solar telescope, train it on the eastern edge of the sun. "The area," says Lawrence, "appears full of promise."
UPDATE: Observers are reporting a sunspot (or proto-sunspot) emerging from the direction of yesterday's prominence: #1, #2, #3.
more images: from Britta Suhre of Dortmund, Germany; from Monty Leventhal of Sydney, Australia; from Les Cowley of eastern England; from Stephen Ames of Hodgenville, Kentucky; from Cai-Uso Wohler of Bispingen, Germany; from C. Miller and J. Stetson of South Portland, Maine; from Malcolm Park of London, England.By Dave Mosher - Space.com
Staff Writer
28 February 2008
Venus is made of the same stuff of Earth, but is bone-dry, hot enough to melt lead and has a chokingly thick atmosphere. It even spins backwards.
Astronomers have spent decades trying to explain Venus' mysterious properties. Now one scientist thinks the planet's formation may explain all: Two huge, protoplanetary bodies collided head-on and merged to form our planetary neighbor, but obliterated nearly all water in the process.
"The probability that two protoplanets collided to form Venus is not at all implausible," said John Huw Davies, a geodynamicist at Cardiff University in the U.K. who developed the idea.
A majority of scientists think Earth's moon formed when a protoplanet about the size of Mars smacked into the planet at an angle. Davies thinks Venus was born of a far worse cosmic train wreck.
"What if the moon-Earth collision isn't that big in planetary terms?" Davies told SPACE.com. "A head-on blow between two similarly sized bodies would have been about twice as energetic."
Astronomers have had little time to react to Davies' proposition, which is detailed in recent issue of the journal Earth and Planetary Science Letters, but already some are wary. Despite the cautionary responses from other scientists, Davies thinks his idea is worth exploring.
Over-baked
Earth harbors an enormous volume of water, even in its searing interior. The life-giving molecule emerges as a vapor with molten lava, carrying with it a radioactive gas known as argon-40. The isotope is generated from radioactive potassium deposits inside of our planet, as well as in Venus.
Davies thinks the relatively low amount of such argon detected in Venus' atmosphere — about 400 times scarcer than on Earth — is a sign that water never really seeped out of the parched, volcano-covered planet.
"The only way water could have out-gassed is very early in Venus' history," Davies said. "The argon-40 gives us a timescale of water leaving the ground because it's produced over time, and only a little of it has been released."
A mega-collision between two bodies of roughly equal size could have provided the energy necessary to rip water, which is made of two hydrogen and one oxygen, into pieces. The hydrogen would escape into space while oxygen would bond with iron and sink to the planet's core.
Although the Earth suffered a catastrophic impact that formed the moon, Davies explained that the process did not dry out the two bodies.
"It wasn't as energetic, limiting the reaction of iron and water," he said.
Diabolical deuterium
Tobias Owens, a planetary scientist at the University of Hawaii, thinks Davies has "swept deuterium under the rug." This form of hydrogen gas, Owens explained, can form high in a planet's atmosphere when ultraviolet sunlight breaks apart a water molecule.
"When a Venus probe sent back readings of deuterium on the planet, everybody was astonished," Owens said of a Russian Venus lander mission. "There was a huge fraction of deuterium 150 times greater than you see on Earth. You have to explain that."
Owens and other scientists argue that at 836 degrees F (447 degrees C), Venus' surface would have instantly baked water into vapor and pushed it into the upper atmosphere, where sunlight is two times more intense than at Earth. Over time, he said, the water would degrade.
Davies, however, said a lack of molecular oxygen — the same type we breathe — produced by the photo-degradation process does not support such an origin of deuterium.
"Venus has virtually no oxygen, whereas Earth's atmosphere is about 20 percent oxygen," Davies said. "If not trapped in the atmosphere, then rocks would have to absorb it." And evidence from Venus, he said, does not suggest that this is the case.
Spin factor
Another clue that Davies said gives his theory legs is the odd rotation of Venus. The planet rotates in a clockwise or retrograde direction, which is the opposite spin of every planet in the inner solar system. "Another peculiarity is that it has no moon," Davies said. "If the head-on impact I've hypothesized was a little off of the mark, it could explain Venus' retrograde rotation without making a moon."
Alan Boss, a scientist at the Carnegie Institution in Washington, D.C., thinks massive collisions — including head-on mergers — were the norm for terrestrial plants early in their histories and could explain our sinister twin's backwards habits.
"Venus must have suffered a giant impact during its formation, as did all the terrestrial planets. That is how the final phase of terrestrial planet formation occurs," Boss said in an e-mail. "This could have been a head-on impact, which might not have produced a moon, or it could have been an off-center impact, like the impact that led to Earth's moon."
If the latter was the case, then where is Venus' moon? Boss explained that if a Venusian moon formed via a giant impact, its orbit could have decayed and spiraled the body into the planet's surface.
Davies thinks the simpler explanation is his own.
"Of course it is possible, but it is unclear whether it is probable," Davies said. Whatever the case, Davies, Boss and most other scientists think big collision events were common in the solar system's formative years.
New Venusian visitor?
Aside from planning to create a detailed computer model for the hypothesized mega-collision, as has been done for moon formation theory, Davies said another way to test his idea is to send a new spacecraft to Venus.
Russia's space program successfully landed nearly 10 spacecraft on Venus' surface in the 1970s and 1980s. But Davies said none of them scouted for water-containing minerals such as mica — evidence that would challenge his hypothesis.
"They made remote chemical measurements of the surface," Davies said, but none indicated hydrated rocks. "If a new spacecraft finds a lot of hydrated minerals, it would show there is still abundant water on Venus. Then my hypothesis would be out."
Spacecraft that have recently encountered Venus can't detect such minerals from space, he said, because of a layer of reflective hydrogen sulfide in the atmosphere.
"A rover of some sort could scout for such minerals before it fails from the intense heat, or maybe a satellite below the hydrogen sulfide [layer]," he said.
Boss, however, said even detecting such minerals might not rule out a collision.
"Water can always be added as a 'late veneer' by ... icy planetesimals that helped finish building the planet," Boss said, although Davies thinks comets and other such bodies could only deliver a small amount of water to the planet.
Even if hydrated rocks on Venus' surface could rule out a cataclysmic formation, other data could provide better clues to the planet's origins, Francis Nimmo of the University of California Santa Cruz thinks.
"There a lot of things that would be very nice to do on Venus, like put a seismometer on the surface," said Nimmo, a planetary scientist. "The reason we know anything about Earth's interior is from such devices."
Whether or not someone launches a new spacecraft to scout out Venus' surface, and whatever its scientific mission is, Davies said it will have to investigate quickly.
"You have to take all of your measurements before the lander, or whatever it is, quite literally burns up," Davies said. "The longest any spacecraft has lasted is less than two hours."
