el nucleo de la tierra gira mas lento de lo q se creia

Un grupo de geofísicos ha descubierto que el núcleo de la tierra rota mucho más despacio de lo que se creía previamente afectando a nuestro campo magnético, según un artículo publicado en la revista 'Nature Geoscience'.

El estudio desarrollado por el Departamento de Ciencias de la Tierra de la Universidad de Cambridge, indica que el núcleo de la tierra gira mucho más despacio del grado anual que se pensaba, ya que en realidad la velocidad de rotación es menor de un grado cada millón de años.

El núcleo interno de la Tierra crece muy despacio a medida que el fluido exterior se va solidificando sobre la superficie del núcleo externo, afirma la investigación firmada por Lauren Waszek, y la diferencia en la velocidad hemisférica este-oeste de este proceso queda congelada en la estructura del núcleo interno.

"Hemos descubierto que la velocidad de rotación proviene de la evolución de la estructura hemisférica, y así demostramos que los hemisferios y la rotación son compatibles", explica Waszek. Hasta ahora, señala el geofísico de la Universidad de Cambridge, este era un importante problema de la geofísica "ya que las rápidas velocidades de rotación eran incompatibles con los hemisferios observados en el núcleo interno, puesto que no permitían tiempo suficiente para que las diferencias se congelasen la estructura".

Flujos de calor

Para obtener estos resultados, los científicos utilizaron ondas sísmicas que atravesaron el núcleo interno, 5.200 kilómetros bajo al superficie de la tierra, y las compararon con el tiempo de viaje de las ondas reflejadas en la superficie del núcleo. Posteriormente, observaron las diferencias en la rotación de los hemisferios este y oeste, y comprobaron que giran de manera consistente en dirección este y hacia dentro, por lo que la estructura más profunda es más vieja.

Estos hallazgos son importantes porque el calor producido durante la solidificación y el crecimiento del núcleo interno dirige la convección del fluido en las capas externas del núcleo. Estos flujos de calor son los que crean los campos magnéticos, que protegen a la superficie terrestre de la radiación solar, y sin los que la vida en la Tierra no podría darse. Waszek resalta que estos resultados "nos aportan una perspectiva adicional para comprender la evolución de nuestro campo magnético".

Dead Spacecraft Walking

Oct. 27, 2010:  A pair of NASA spacecraft that were supposed to be dead a year ago are instead flying to the Moon for a breakthrough mission in lunar orbit.
"Their real names are THEMIS P1 and P2, but I call them 'dead spacecraft walking,'" says Vassilis Angelopoulos of UCLA, principal investigator of the THEMIS mission. "Not so long ago, we thought they were goners. Now they are beginning a whole new adventure."

An artist's concept of THEMIS-P1 and P2 (since renamed ARTEMIS-P1 and P2) in lunar orbit. [larger image]

The story begins in 2007 when NASA launched a fleet of five spacecraft into Earth's magnetosphere to study the physics of geomagnetic storms. Collectively, they were called THEMIS, short for "Time History of Events and Macroscale Interactions during Substorms." P1 and P2 were the outermost members of the quintet.
Working together, the probes quickly discovered a cornucopia of previously unknown phenomena such as colliding auroras, magnetic spacequakes, and plasma bullets shooting up and down Earth’s magnetic tail. These findings allowed researchers to solve several longstanding mysteries of the Northern Lights.

In their previous life, THEMIS-P1 and P2 were on a mission to study Northern Lights. [more]

The mission was going splendidly, except for one thing: Occasionally, P1 and P2 would pass through the shadow of Earth. The solar powered spacecraft were designed to go without sunlight for as much as three hours at a time, so a small amount of shadowing was no problem. But as the mission wore on, their orbits evolved and by 2009 the pair was spending as much as 8 hours a day in the dark.
"The two spacecraft were running out of power and freezing to death," says Angelopoulos. "We had to do something to save them."
The team brainstormed a solution. Because the mission had gone so well, the spacecraft still had an ample supply of fuel--enough to go to the Moon. "We could do some great science from lunar orbit," he says. NASA approved the trip and in late 2009, P1 and P2 headed away from the shadows of Earth.
With a new destination, the mission needed a new name. The team selected ARTEMIS, the Greek goddess of the Moon. It also stands for "Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun."
The first big events of the ARTEMIS mission are underway now. On August 25, 2010, ARTEMIS-P1 reached the L2 Lagrange point on the far side of the Moon. Following close behind, ARTEMIS-P2 entered the opposite L1 Lagrange point on Oct. 22nd. Lagrange points are places where the gravity of Earth and Moon balance, creating a sort of gravitational parking spot for spacecraft.

The ARTEMIS spacecraft are currently located at the L1 and L2 Earth-Moon Lagrange points. [more]

"We're exploring the Earth-Moon Lagrange points for the first time," says Manfred Bester, Mission Operations Manager from the University of California at Berkeley, where the mission is operated. "No other spacecraft have orbited there."
Because they lie just outside Earth's magnetosphere, Lagrange points are excellent places to study the solar wind. Sensors onboard the ARTEMIS probes will have in situ access to solar wind streams and storm clouds as they approach our planet—a possible boon to space weather forecasters. Moreover, working from opposite Lagrange points, the two spacecraft will be able to measure solar wind turbulence on scales never sampled by previous missions.
"ARTEMIS is going to give us a fundamental new understanding of the solar wind," predicts David Sibeck, ARTEMIS project scientist at the Goddard Space Flight Center. "And that's just for starters."
ARTEMIS will also explore the Moon's plasma wake—a turbulent cavity carved out of the solar wind by the Moon itself, akin to the wake just behind a speedboat. Sibeck says "this is a giant natural laboratory filled with a whole zoo of plasma waves waiting to be discovered and studied."

 

A Youtube video (http://science.nasa.gov/science-news/science-at-nasa/2010/27oct_artemis/)describes the complex orbits of the two Artemis spacecraft.

Another target of the ARTEMIS mission is Earth's magnetotail. Like a wind sock at a breezy airport, Earth's magnetic field is elongated by the action of the solar wind, forming a tail that stretches to the orbit of the Moon and beyond. Once a month around the time of the full Moon, the ARTEMIS probes will follow the Moon through the magnetotail for in situ observations.
"We are particularly hoping to catch some magnetic reconnection events," says Sibeck. "These are explosions in Earth's magnetotail that mimic solar flares--albeit on a much smaller scale." ARTEMIS might even see giant 'plasmoids' accelerated by the explosions hitting the Moon during magnetic storms.
These far-out explorations may have down-to-Earth applications. Plasma waves and reconnection events pop up on Earth, e.g., in experimental fusion chambers. Fundamental discoveries by ARTEMIS could help advance research in the area of clean renewable energy.
After six months at the Lagrange points, ARTEMIS will move in closer to the Moon—at first only 100 km from the surface and eventually even less than that. From point-blank range, the spacecraft will look to see what the solar wind does to a rocky world when there's no magnetic field to protect it.
"Earth is protected from solar wind by the planetary magnetic field," explains Angelopolous. "The Moon, on the other hand, is utterly exposed. It has no global magnetism."
Studying how the solar wind electrifies, alters and erodes the Moon's surface could reveal valuable information for future explorers and give planetary scientists a hint of what's happening on other unmagnetized worlds around the solar system.
Orbiting the Moon is notoriously tricky, however, because of irregularities in the lunar gravitational field. Enormous concentrations of mass (mascons) hiding just below the surface tug on spacecraft in unexpected ways, causing them over time to veer out of orbit. ARTEMIS will mitigate this problem using highly elongated orbits ranging from tens of km to 18,000 km.
"We'll only be near the lunar surface for a brief time each orbit (accumulating a sizable dataset over the years)," explains Angelopoulos. "Most of the time we'll linger 18,000 km away where we can continue our studies of the solar wind at a safe distance."
The Dead Spacecraft Walking may have a long life, after all.

Siembra de nubes reflectoras

Rociando desde el mar gotas de agua salada del tamaño de un micrón (una milésima parte de un milímetro) a través de unas pequeñas embarcaciones, un grupo de científicos modifica las nubes para ayudar a revertir el calentamiento global.

La reflectividad solar de las nubes depende de la distribución del tamaño de las gotas de agua presentes en ellas. Ante esta premisa, dos científicos estudian la posibilidad de modificar la concentración de los núcleos de condensación de las nubes marinas para hacerlas más reflectantes y así devolver los rayos solares hacia el espacio.

Las nubes son acumulaciones de pequeñas gotas de agua o de partículas de hielo que se mantienen en suspensión en la atmósfera y que forman una masa de vapor acuoso de color variable según su densidad o según la luz.

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