Two Full Days of Saturn’s Aurora

Saturn’s aurora shimmers and shines over the course of two full days in a new movie and images from Cassini orbiter. In an ongoing study compiling thousands of these images, scientists are beginning to decipher what drives the celestial light show.

Much like Earth’s northern and southern lights, Saturn’s aurora is triggered when charged particles from solar winds are channeled toward the poles by the planet’s magnetic field. At the poles, these particles interact with charged gas or plasma in the upper atmosphere and emit light. Saturn’s aurora can also be caused by electromagnetic waves generated when its moons move through its magnetosphere.

Cassini has already delivered some gorgeous examples of these colorful curtains of light.

“But to understand the overall nature of the auroral region we need to make a huge number of observations — which can be difficult because Cassini observation time is in high demand,” said astronomer Tom Stallard of the University of Leicester in the UK in a press release.

Rather than snapping photos of the aurora directly, Stallard and his colleagues are sifting through 7,000 images from Cassini’s VIMS (Visual and Infrared Mapping Spectrometer) instrument to piece together fragments of aurora into a more complete picture.

“As a whole, this wide set of observations will allow us to understand the aurora in general,” Stallard said. Stallard will present preliminary results at the European Planetary Science Congress in Rome on September 24.

The movie shows how the aurora vary over the course of a Saturnian day (about 10 hours and 47 minutes). On the noon (left) and midnight (right) sides, the aurora brighten significantly for several hours at a time, suggesting the brightening is connected with the direction of the Sun. Other features rotate with the planet below, reappearing at the same time and the same place on the second day. This suggests that these features are directly controlled by the direction of Saturn’s magnetic field.

So far, Stallard and his colleagues have made it through about 1,000 out of 7,000 VIMS images of Saturn’s auroral region.

Fuente: Wired Science

Here Comes Jupiter: Gas Giant Makes Closest Approach

Jupiter is cozying up to Earth this month. At its closest approach, the giant planet will swing closer and shine brighter than at any time between 1963 and 2022.

You can already see Jupiter twinkling low in the east after twilight, and higher in the southeast as the evening wears on. But it will be brightest in the second half of September. The gas giant’s closest approach will be at a distance of 368 million miles on Monday, September 20. Its previous swing-by in August 2009 was 2 percent farther, and the next approach in October 2011 will be a little less than 1 percent more distant.

Jupiter is also brighter than usual by about 4 percent because one of its brown cloud belts is hidden.

Uranus will be visible in the same part of the sky until September 24, though you’ll need binoculars or a telescope to see it. The full moon will appear right above Jupiter on September 22, which is coincidentally the fall equinox.


Fuente: Wired Science

Mercury Flyby Maps New Territory

The results from the Messenger spacecraft’s third and final flyby of Mercury are finally in and cover ground never before mapped. But they leave scientists wanting more.

NASA’s orbiter swung around Mercury on Sept. 29, 2009 to get a gravitational boost before settling into orbit in March 2011. The snapshots it took as it flew past provide tantalizing glimpses of young volcanic vents, violent magnetic storms and mysterious concentrations of calcium in the atmosphere. But the view was cut short by the spacecraft going into safe mode just before its closest approach.

Planetary scientists are now anxious for the main event.

“It will be so great when we go into orbit,” said planetary scientist Brett Denevi of Arizona State University, co-author of a new paper describing the new view of Mercury’s surface. “This is all just a teeny snapshot. Going into orbit will be like two flybys every day.”

Three papers published online July 15 in Science Express describe what Messenger saw on its last flyby. Scientists have now mapped 98 percent of the planet by combining the new observations with the first two flybys in January and October 2008, plus the Mariner 10 mission in the ’70s, Denevi said. The latest flyby filled in a 360-mile-wide gap that had never been imaged before.

“It wasn’t a huge amount of real estate, but there was a lot of really interesting stuff there,” Denevi said. The most exciting features include a 180-mile-wide basin filled with hardened lava, and a crooked bowl surrounded by glass and magma that may be the largest volcanic vent ever identified on Mercury. Together, these features suggest that Mercury had active volcanoes later in its history than scientists had suspected.

“After Mariner 10, it was thought that if Mercury had volcanism at all, it probably shut off really early in the planet’s history, earlier than the other planets,” Denevi said. Earlier flybys showed this view to be totally wrong: 40 percent of Mercury’s surface was formed by volcanoes, some of it recently. And the new basin, dubbed Rachmaninoff, shows that Mercury may have been volcanically active well into the second half of its life.

The smooth plains that fill Rachmaninoff were likely once molten magma that welled up from below. Although Denevi says we can’t be certain exactly how old the terrain is without analyzing samples, it could be less than a billion years old, “which is young on a planetary scale.”

To Rachmaninoff’s north is an irregular depression surrounded by bright material that looks yellow in false color images (right). This feature was spotted from Earth-based telescopes, but had been labeled an impact crater. It wasn’t until the third flyby that scientists recognized the bowl for what it is: a volcanic vent.

That was surprising. Because Mercury is so close to the sun, scientists expected all the volatile gases that could burst out in explosive volcanism would have been driven off. But at least in this one spot, there were enough gases to drive fiery plumes of magma to the surface.

There’s still more to see of Mercury’s surface, and better angles to see it from, Denevi said. “We’ll have to wait until orbit to get a really good look.”

Another surprise came from Mercury’s magnetosphere, the region above the planet’s surface where the magnetic field butts against charged particles and plasma from the solar wind. Besides Earth, Mercury is the only terrestrial planet that has a magnetic field generated by a liquid core. Both planets’ magnetospheres are deformed by the solar wind, leaving a bulge of magnetic field on the planet’s sunward side and a long tail like a comet’s extending away from the sun (below, left).

On Earth, the solar wind sometimes breaks the lines of magnetic force on the sunward side and pulls them back into the tail, resulting in a massive buildup and subsequent dissipation of energy (below, center and right). This “loading” and “unloading” of the tail causes space weather disturbances called magnetic substorms, which last around an hour on Earth. The energy from these storms accelerates charged particles through the Earth’s upper atmosphere, creates the Northern Lights and wreaks havoc on communications satellites.

Mercury’s weak magnetic field supports substorms, too — 10 times stronger and 20 times faster than Earth’s. Messenger recorded four storms, each of which took only two or three minutes. On Earth, the amount of energy in the tail increases by only 10 or 20 percent, but on Mercury, the energy doubled or tripled.

“The loading and unloading was extreme, it was huge,” said NASA space physicist James A. Slavin, lead author of a paper describing the magnetic observations.

But weirdly, despite the intensity of the substorms, Messenger didn’t detect a single accelerated particle.

“It’s a conundrum,” Slavin said. “For some reason in this little magnetosphere, none of that energy is making it into energetic particles.”

The only solution is to wait for more data. “We’re really looking forward to the orbit phase,” Slavin said. “It might be quite a treasure trove.”

The link between the surface and the magnetic field is Mercury’s tenuous and changeable atmosphere, called the exosphere. Everything in the exosphere was knocked off the surface by ions, photons or dust.

“You get definitive fingerprints of things coming off the surface,” said planetary scientist Ron Vervack of Johns Hopkins’ Applied Physics Lab, lead author of the paper that deals with the exosphere. “It gives the best picture of composition until we can have hard samples in the lab.”

And charged particles in the exosphere can be carried around and away from the planet by the magnetic field. “Our extreme tail loading may be important for maintaining Mercury’s exosphere,” Slavin said.

The third flyby made the first detailed measurements of sodium, calcium and magnesium over Mercury’s poles. Messenger also made the first measurement of an ion, positively charged calcium, in the exosphere. These measurements can help understand how materials move around the planet, Vervack said.

The strangest thing found in the exosphere was a persistent smear of neutral calcium near the edge of night and day. This extra clump of calcium was in the same spot in all three flybys, which, in an ever-changing exosphere, is profoundly weird.

“We don’t understand where it’s coming from, or why it’s so consistent,” Vervack said. Concentrations of magnesium and sodium both changed between the flybys, so some unknown surface process must work on calcium alone.

Like the rest of the Messenger team, “we need more observations at this point,” Vervack said. “It’s a puzzle, but we don’t have all the pieces yet.”


Fuente: Wired Science

La Luna se sigue alejando

Concretamente, cuatro centímetros cada año como consecuencia del debilitamiento gravitacional provocado por la diferencia de velocidades de la Tierra y la Luna.
Este es el resultado de las mediciones obtenidas desde hace 40 años mediante unos espejos reflectores que la misión Apolo dejó en la superficie lunar.

Efectos aunque a muy largo plazo: nuestros días se harán más largos, las mareas más suaves y el eje de la Tierra más inestable. También dejará de haber eclipses totales, ya que el tamaño del satélite será insuficiente para tapar con completo al Sol. Esto puede suceder dentro de 400 millones de años.

De hecho, la Luna se aleja de la Tierra desde siempre, provocando cambios importantes en nuestro planeta. En un remoto pasado, nuestros días apenas duraban seis horas, las mareas eran 1.000 veces mayores y los vientos alcanzaban normalmente los 160 km/h


Fuente: DDG

Solsticio de verano: hoy es el día más largo del año en el hemisferio norte

Solsticio es un término astronómico que tiene relación con la posición del Sol en el ecuador celeste y se refieren a aquellos momentos del año en que alcanza su máxima posición meridional o boreal.

En el solsticio de verano del hemisferio norte el Sol alcanza el cenit (la intersección entre una línea recta imaginaria vertical desde el punto de vista del observador y la esfera celeste) al mediodía sobre el Trópico de Cancer.

La razón por la cual existen solsticios es porque la Tierra está inclinada sobre el plano de su órbita y la forma en que el planeta enfrenta al Sol varía a lo largo que cumple su órbita alrededor de este.

Por lo tanto en el solsticio de verano se da el día más largo y la altura máxima del Sol en el hemisferio norte, asi misom, durante el solsticio de invierno es el día más corto y altura del Sol es la mínima.

El día del solsticio también corresponde al cambio de estación. En España, por ejemplo, el verano oficialmente empieza hoy a las 13:28 horas y durará 93 días. El otoño empezará el 23 de septiembre. En el hemisferio sur hoy también se cambia de estación de otoño a invierno.


Fuente: ALT1040

El Hubble nos desvela las incógnitas tras el terrible impacto sufrido por Júpiter

Si nos ponemos a estudiar la historia de la ciencia rápidamente veremos que las serendipias están muy presentes. Muchos grandes descubrimientos de todos a los que hemos asistido a lo largo de la historia se han producido en parte fruto de la casualidad, y especialmente presentes están estas en determinadas ramas de la ciencia como puede ser la observación astronómica. El último caso más sonado de “descubrimiento casual” fruto de la observación astronómica tuvo lugar por el mes de julio del año pasado cuando el astrónomo aficionado Anthony Wesley detectó un impacto masivo en la superficie de Júpiter, sobre el cual ahora un grupo de científicos, con el Hubble como aliado, han echado luz.

El impacto que recibió Júpiter en el mes de julio no fue ninguna tontería, lo que más o menos ya se sabía pero ahora ha confirmado este grupo de investigadores de la NASA. Según comenta la propia agencia espacial estadounidense en un comunicado oficial el golpe que sufrió el planeta fue equivalente a la explosión de varios miles de bombas atómicas, lo que dejó como resultado una enorme “cicatriz” que tiene aproximadamente el tamaño del Océano Pacífico. ¿Y qué fue exactamente lo que le atizó al mayor planeta de nuestro sistema solar y de dónde vino?

Pues a esas dos preguntas también ha dado respuesta las nuevas investigaciones. Gracias a las imágenes tomadas por el Hubble con una de las nuevas cámaras que le instalaron recientemente y a otras imágenes tomadas en 1994 -de esto hablaré luego- se ha llegado a la conclusión de que lo que impactó contra Júpiter fue un asteroide de aproximadamente 500 metros de diámetro, el cual probablemente vino (y esto lo han descubierto científicos españoles de la Universidad del País Vasco) del cinturón de asteroides Hilda, el cual está formado por uno 1.100 cuerpos estelares de este tipo.

El dato curioso del caso que nos ocupa, a pesar de que se sabe que este tipo de fenómeno es bastante habitual (hablando en términos de astronomía), es que otro mes de julio, pero de 1994, en la misma semana que se ha producido este impacto, Júpiter sufrió otro de características similares que también fue visto, que no descubierto, por Anthony Wesley y otros aficionados y profesionales de la astronomía (la diferencia fundamental de este último suceso respecto al más reciente es que en el primero lo que colisionó contra Júpiter fue un cometa y no un asteroide).

Y poco más puede añadir servidor ante tanta investigación y datos interesantes, que me llevan a plantearme la pregunta que siempre ronda por mi cabeza tras escribir de estas cosas: ¿Cómo puede ser que los grandes medios no le den más cobertura a la ciencia en general y a la astronomía en particular? Hay muchas posibles respuestas a esa pregunta, que cada uno le de vueltas y se quede con la que más le guste.


Fuente: ALT1040

Venus Orbiter Finds Potential Active Volcanoes

The Venus Express spacecraft has found convincing evidence that Earth is not the only geologically active planet in the solar system.

Infrared emissions from lava flows on the surface of Venus indicate that they are relatively young, which means the planet may still be capable of volcanic eruptions.

“The solidified lava flows, which radiate heat from the surface, seem hardly weathered. So we can conclude that they are younger than 2.5 million years old — and the majority are probably younger than 250,000 years,” Jörn Helbert of the DLR Institute of Planetary Research in Germany, co-author of a study published April 8 in Science, said in a press release. “In geological terms, this means that they are practically from the present day.”

The results could explain why there are fewer asteroid impacts than expected on the planet’s surface. Volcanism has been the prime suspect, because lava flows can fill in and obscure craters. But scientists were unsure whether a major episode of volcanic activity resurfaced much of the planet all at once in the past, or if intermittent activity has slowly filled in craters over time. The existence of a recent flow suggests the latter is more likely, and that volcanism may be ongoing.

Venus is shrouded in a thick cloud cover which obscures the visible light emissions form the surface. So a team led by Suzanne Smrekar of NASA’s Jet Propulsion Laboratory studied the thermal emissions of the surface using the Visible and Infrared Thermal Imaging Spectrometer on the Venus Express orbiter. Older surfaces tend to be smoothed by weathering over time, while younger surfaces are more rough and have higher thermal emissions.

Several areas on the surface had been identified as potential volcanic centers by radar imagery data from the Magellan mission, which ended in 1994 when the spacecraft was intentionally crashed into the surface. Smrekar’s team targeted three of these areas and found they had higher thermal emissions than the surrounding areas.

“Now we have strong evidence right at the surface for recent eruptions,” Smrekar said in a press release.

Because Venus is similar in size and internal structure to Earth, comparisons between the two planets can help scientists understand our own planet’s evolution. If volcanism on Venus is also similar to Earth, as the new study indicates, that narrows the factors that could have sent the planets on such different paths that ended with Earth being habitable and Venus being bone dry and hellishly hot.

In order to determine what the young rock is made of, Helbert plans to build a lab that can heat various rock types to around 900 degrees Fahrenheit, the planet’s surface temperature, and study their thermal emission signatures to compare to the Venus Express readings.

Fuente: Wired Science