Sonda Cassini fotografa uma das luas de Saturno em resolução inédita

Esta é a imagem com maior resolução até hoje da região polar norte da Encélado, uma das luas de Saturno. A sonda Cassini fez a foto a uma distância de 35.000 quilômetros do satélite. (Foto: Nasa)

Cassini Flies Through Watery Plumes of Saturn Moon

NASA’s Cassini spacecraft performed a daring flyby of Saturn’s moon Enceladus on Wed., March 12, flying about 15 kilometers per second (32,000 mph) through icy water geyser-like jets. The spacecraft snatched up precious samples that might point to a water ocean or organics inside the little moon.

Scientists believe the geysers could provide evidence that liquid water is trapped under the icy crust of Enceladus. The geysers emanate from fractures running along the moon’s south pole, spewing out water vapor at approximately 400 meters per second (800 mph).

The new data provide a much more detailed look at the fractures that modify the surface and will give a significantly improved comparison between the geologic history of the moon’s north pole and south pole.

New images show that compared to much of the southern hemisphere on Enceladus–the south polar region in particular–the north polar region is much older and pitted with craters of various sizes. These craters are captured at different stages of disruption and alteration by tectonic activity, and probably from past heating from below. Many of the craters seem sliced by small parallel cracks that appear to be ubiquitous throughout the old cratered terrains on Enceladus.

“These new images are showing us in great detail how the moon’s north pole differs from the south, an important comparison for working out the moon’s obviously complex geological history,” said Carolyn Porco, Cassini imaging team leader, Space Science Institute, Boulder, Colo. “And the success of yesterday’s daring and very low-altitude flyby means this coming summer’s very close encounter, when we get exquisitely detailed images of the surface sources of Enceladus’ south polar jets, should be an exciting ‘next big step’ in understanding just how the jets are powered.”

This week’s flyby and another one planned for Oct. 9, 2008, were designed so that Cassini’s particle analyzers could dissect the “body” of the plume for information on the density, size, composition and speed of the particles. Among other things, scientists will use the data gathered this week to figure out whether the gases from the plume match the gases that make up the halo of particles around Enceladus. This may help determine how the plumes formed.

During Cassini’s closest approach, two instruments were collecting data–the Cosmic Dust Analyzer and the Ion and Neutral Mass Spectrometer. An unexplained software hiccup with Cassini’s Cosmic Dust Analyzer instrument prevented it from collecting any data during closest approach, although the instrument did get data before and after the approach. During the flyby, the instrument was switching between two versions of software programs. The new version was designed to increase the ability to count particle hits by several hundred hits per second. The other four fields and particles instruments on the spacecraft, in addition to the ion and neutral mass spectrometer, did capture all of their data, which will complement the overall composition studies and elucidate the unique plume environment of Enceladus.

Cassini’s instruments discovered evidence for the geyser-like jets on Enceladus in 2005, finding that the continuous eruptions of ice water create a gigantic halo of ice dust and gas around Enceladus, which helps supply material to Saturn’s E-ring.

This was the first of four Cassini flybys of Enceladus this year. During Wednesday’s flyby, the spacecraft came within 50 kilometers (30 miles) of the surface at closest approach, 200 kilometers (120 miles) while flying through the plume. Future trips may bring Cassini even closer to the surface of Enceladus. Cassini will complete its prime mission, a four-year tour of Saturn, in June. From then on, a proposed extended mission would include seven more Enceladus flybys. The next Enceladus flyby would take place in August of this year.

For more images and more information, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Sol engolirá a Terra em 7,6 bi de anos, diz astrônomo

Um novo cálculo realizado por astrônomos afirma que a Terra será “engolida” pelo Sol em 7,6 bilhões de anos, segundo um estudo publicado pela revista científica Monthly Notices of the Royal Astronomical Society. A previsão quer terminar com um longo debate sobre a capacidade do nosso planeta de resistir ou não à atração gravitacional solar.

Outras teorias dizem que a Terra vai “fritar” no momento que o Sol se expandir. Mas o tempo estimado varia em bilhões de anos. “Ainda que esse problema tenha sido abordado antes, nós acreditamos que esta é a melhor abordagem sobre o assunto”, disse o astrônomo britânico Robert Smith, da Universidade de Sussex.

Ainda que 7,6 bilhões de anos pareça muito tempo, não é aconselhável deixar de lado o fato de que o clima do nosso planeta vai esquentar ainda mais, acompanhando o ritmo do Sol. “Depois de cerca de um bilhão de anos a Terra não terá atmosfera nem água, e a temperatura na superfície chegará a centenas de graus Celsius”, disse Smith.

Apesar de provavelmente não estarmos mais aqui, os cientistas estão curiosos sobre o episódio final da Terra. Estudos recentes do próprio Smith indicam que, quando o Sol envelhecer e se tornar uma gigante vermelha, ele vai perder massa e força gravitacional. Isso pode fazer com que a Terra seja capaz de se “desprender” da órbita da estrela.

Mas esse cenário não considera as forças relativas, como as exercidas pelas suas camadas externas. Os campos gravitacionais menores do Sol não são completamente insignificantes em relação à órbita da Terra – eles fazem com que o lado do Sol voltado para o nosso planeta acumule mais massa, ficando mais “inchado”.

“Ao mesmo tempo em que a Terra faz o Sol ‘inchar’, o Sol atrai a Terra, e faz com que o nosso entre vagarosamente em sua órbita”, disse Smith. “No final, vamos acabar dentro do Sol”. Além disso, o gás que a estrela expele vai arrastar a Terra à morte, sentenciou o cientista ao site Space.com.

Earth’s Final Sunset Predicted

“Some say the world will end in fire, Some say in ice,” wrote the poet Robert Frost. Astronomers, it turns out, are in the former camp.

A new calculation predicts that Earth will be swallowed up by the sun in 7.6 billion years, capping off a longstanding debate over whether the sun’s gravitational pull will have weakened enough for Earth to escape final destruction or not.

Other theorists have predicted that our planet will fry as the sun expands in its old age. But the time estimates have varied by a couple billion years.

“Although people have looked at these problems before, we would claim this is the best attempt that’s been made to date, and probably the most reliable,” said astronomer Robert Smith, emeritus reader at the U.K.’s University of Sussex, who made the new calculations with astronomer Klaus-Peter Schroeder of the University of Guanajuato in Mexico. “What we’ve done is to refine existing models and to put the best calculations we can at each point in the model.”

If 7.6 billion years doesn’t sound like an urgent death sentence, don’t relax yet. Regardless of whether Earth will ultimately be vaporized, as the sun heats up, our planet will become too hot to live on before then.

“After a billion years or so you’ve got an Earth with no atmosphere, no water and a surface temperature of hundreds of degrees, way above the boiling point of water,” Smith told SPACE.com. “The Earth will become dry basically. It will become completely impossible for life of any kind to exist. It’s a pretty gloomy forecast.”

Nonetheless, scientists are curious about the ultimate fate of our planet after we are gone (like all previous hominids and more than 99 percent of all species that have lived on Earth, humans will probably go extinct, and it will likely happen sooner than a billion years).

Smith’s earlier studies found that Earth would narrowly escape being engorged. As the sun ages and expands into a red giant star, it will shed its outer gaseous layers, thus losing mass and weakening its gravitational pull. Previous calculations found that this let-up would allow the Earth’s orbit to shift outward, enabling the planet to slip free of the smoldering sun.

But this scenario doesn’t account for tidal forces, and the drag of the sun’s outer layers. As the Earth orbits the sun, its smaller gravitational pull isn’t completely negligible — it actually causes the side of the sun closest to our planet to hoard more mass and bulge out toward us.

“Just as the Earth is pulling on the sun’s bulge, it’s pulling on the Earth, and that causes the Earth to slow in its orbit,” Smith said. “It will spiral back and finally end up inside the sun.”

In addition, the gas that the sun expels will also drag Earth inward toward its demise.

Smith’s previous calculations had ignored these effects.

“We didn’t think it mattered, but it turns out it does,” he said. “You might say our previous models had a gap.”

There may even be hope for Earth. Some scientists have proposed a scheme for down the road to use the gravity of a passing asteroid to budge Earth out of the way of the sun toward cooler territory, assuming there is life around at the time that is intelligent enough to engineer this solution.

“It sounds like science fiction, but there’s a group of people who have quite seriously suggested that it might be possible,” Smith said. “If it’s done right, that would just keep the Earth moving fast enough to keep it out of harm’s way. Maybe life could go on for as much as 7 billion years.”