Cassini

Cassini, Voyager missions suggest new picture of Sun’s interaction with galaxy

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NASA's Cassini, Voyager missions suggest new picture of Sun's interaction with galaxy
New data from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions show that the heliosphere — the bubble of the sun’s magnetic influence that surrounds the inner solar system — may be much more compact and rounded than previously thought. The image on the left shows a compact model of the heliosphere, supported by this latest data, while the image on the right shows an alternate model with an extended tail. The main difference is the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. This tail is shown in the old model in light blue. 

New data from NASA’s Cassini mission, combined with measurements from the two Voyager spacecraft and NASA’s Interstellar Boundary Explorer, or IBEX, suggests that our sun and planets are surrounded by a giant, rounded system of magnetic field from the sun—calling into question the alternate view of the solar magnetic fields trailing behind the sun in the shape of a long comet tail.

The sun releases a constant outflow of magnetic solar material—called the —that fills the inner solar system, reaching far past the orbit of Neptune. This solar wind creates a bubble, some 23 billion miles across, called the . Our entire solar system, including the heliosphere, moves through interstellar space. The prevalent picture of the heliosphere was one of comet-shaped structure, with a rounded head and an extended . But  covering an entire 11-year solar activity cycle show that may not be the case: the heliosphere may be rounded on both ends, making its shape almost spherical. A paper on these results was published in Nature Astronomy on April 24, 2017.

“Instead of a prolonged, comet-like tail, this rough bubble-shape of the heliosphere is due to the strong —much stronger than what was anticipated in the past—combined with the fact that the ratio between particle pressure and magnetic pressure inside the heliosheath is high,” said Kostas Dialynas, a space scientist at the Academy of Athens in Greece and lead author on the study.

An instrument on Cassini, which has been exploring the Saturn system over a decade, has given scientists crucial new clues about the shape of the heliosphere’s trailing end, often called the heliotail. When charged  from the inner solar system reach the boundary of the heliosphere, they sometimes undergo a series of charge exchanges with neutral gas atoms from the interstellar medium, dropping and regaining electrons as they travel through this vast boundary region. Some of these particles are pinged back in toward the inner solar system as fast-moving , which can be measured by Cassini.

NASA's Cassini, Voyager missions suggest new picture of Sun's interaction with galaxy
Many other stars show tails that trail behind them like a comet’s tail, supporting the idea that our solar system has one too. However, new evidence from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions suggest that the trailing end of our solar system may not be stretched out in a long tail. From top left and going counter clockwise, the stars shown are LLOrionis, BZ Cam and Mira. 

“The Cassini instrument was designed to image the ions that are trapped in the magnetosphere of Saturn,” said Tom Krimigis, an instrument lead on NASA’s Voyager and Cassini missions based at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, and an author on the study. “We never thought that we would see what we’re seeing and be able to image the boundaries of the heliosphere.”

 Cassini’s new measurements of these neutral atoms revealed something unexpected—the particles coming from the tail of the heliosphere reflect the changes in the solar cycle almost exactly as fast as those coming from the nose of the heliosphere.

“If the heliosphere’s ‘tail’ is stretched out like a comet, we’d expect that the patterns of the solar cycle would show up much later in the measured neutral atoms,” said Krimigis.

NASA's Cassini, Voyager missions suggest new picture of Sun's interaction with galaxy
New data from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions show that the heliosphere — the bubble of the sun’s magnetic influence that surrounds the inner solar system — may be much more compact and rounded than previously thought. This illustration shows a compact model of the heliosphere, supported by this latest data. The main difference between this and previous models is Credit: Dialynas, et al.the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. 

But because patterns from solar activity show just as quickly in tail particles as those from the nose, that implies the tail is about the same distance from us as the nose. This means that long, comet-like tail that scientists envisioned may not exist at all—instead, the heliosphere may be nearly round and symmetrical.

A rounded heliosphere could come from a combination of factors. Data from Voyager 1 show that the interstellar magnetic field beyond the heliosphere is stronger than scientists previously thought, meaning it could interact with the solar wind at the edges of the heliosphere and compact the heliosphere’s tail.

The structure of the heliosphere plays a big role in how particles from interstellar space—called cosmic rays—reach the inner solar system, where Earth and the other planets are.

“This data that Voyager 1 and 2, Cassini and IBEX provide to the scientific community is a windfall for studying the far reaches of the solar wind,” said Arik Posner, Voyager and IBEX program scientist at NASA Headquarters in Washington, D.C., who was not involved with this study. “As we continue to gather data from the edges of the heliosphere, this data will help us better understand the interstellar boundary that helps shield the Earth environment from harmful cosmic rays.”

Why NASA is going to vaporize one of its best spacecraft.

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Artist illustration of Cassini preparing to dip its toes into Saturn’s atmosphere. The spacecraft will meet a violent end as it plummets through the atmosphere on September 15, 2017.

All good things must come to an end. On April 23, Cassini will begin its final quest into oblivion.

Flying at over 76,000 miles per hour, the spacecraft will zip through an uncharted gap between Saturn and its rings, where no spacecraft has flown before. In September, after 22 laps through this region, the spacecraft will dive into the gas giant’s atmosphere, where it will “break apart, melt, vaporize, and become a part of the very planet it left Earth 20 years ago to explore,” Cassini project manager Earl Maize said in a press conference on Tuesday.

It’ll be a sad ending for a mission that brought us amazing views of Saturn and its rings and moons. Cassini revealed the geysers of Enceladus, which hint at a subsurface ocean, and showed scientists just how how Earthlike—yet alien—Titan is. Why does the spacecraft have to die?

 Some space probes are allowed to keep orbiting their targets in perpetuity after their mission ends—like the Dawn spacecraft at the dwarf planet Ceres. But things are a lot more complicated around Saturn.

Whereas Ceres is essentially just a really big rock with no moons, Saturn has 62 satellites, at last count. The gravitational push and pull from those moons—especially the largest, Titan—wreak havoc on Cassini’s trajectory, which it normally corrects by burning fuel.

But the spacecraft’s fuel is running out, and ultimately its fate is sealed by its own discoveries; scientists don’t want to risk the spacecraft crashing into Titan and Enceladus, which may be capable of supporting life.

cassini grand finale trajectories

In April, Cassini will begin the first of 22 dives through the relatively narrow, 1200-mile gap between Saturn and its rings.

 “[Without fuel], the orbit would become less and less predictable,” Cassini project scientist Linda Spilker told Popular Science. “Cassini’s orbit would slowly change enough to eventually risk crashing into one of the moons.”

Although Cassini launched 20 years ago, experiments on the Space Station have suggested microbes can survive for years in the extreme temperatures, radiation, and airless vacuum of space. If NASA were to accidentally put water bears on Enceladus, the tiny Earthlings could potentially wipe out any native lifeforms that the moon may harbor, and/or complicate the search for those alien organisms later. This is why Cassini must die now, while NASA can still control its last swan dive.

But scientists are hoping to get some new information from the mission’s dramatic ending. They hope to learn more about the composition of Saturn’s atmosphere and rings, and figure out how big the planet’s core is, and how fast it’s rotating. Cassini will also get the closest view ever of the auroras and strange hexagonal storm at the north pole.

 Cassini will continue to beam back data until the very end, when atmospheric drag severs the spacecraft’s connection with Earth. That’s expected to happen about three minutes into Cassini’s dive on September 15.

“Once the signal is lost,” said Spilker at Tuesday’s press conference, “that heartbeat of Cassini is gone.”

Source:popsci.com

Cassini Gets Final, Stunning View of Saturn’s Moon Hyperion

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On Sunday, May 31, 2015, NASA’s Cassini spacecraft made its latest and final flyby of Hyperion, Saturn’s spongy moon. At around 9:36 a.m. EDT Cassini came within 21,000 miles (34,000 km) of Hyperion’s surface — not its closest approach ever but certainly close enough to grab some fantastic images of this porous and punched-in world.

The image above is a color composite made from images acquired in optical wavelengths (i.e., Cassini’s red, green, and blue color filters) with some contrast enhancement and a bit of color saturation boosting as well. This is about what Hyperion would look like to an astronaut’s eyes, if she happened to have been riding along with Cassini last Sunday.

At 255 x 163 x 137 miles (410 x 262 x 220 kilometers), Hyperion is the largest of Saturn’s irregularly-shaped moons and its eighth-largest overall. Scientists think it could be what’s left over from a larger moon that was blown apart in the distant past.

Because of its porosity and low density, impacts on Hyperion tend to create punched-in craters with little to no ejecta, giving it its strange spongelike appearance.

Discovered in 1848 Hyperion is four times as far from Saturn as our moon is from us yet completes an orbit every 21 days, getting gravitational tugs and nudges from its inner neighbor Titan as it passes.

In fact some of Hyperion’s reddish coloration may come from Titan, as hydrocarbons from its atmosphere get blown into orbit by the solar wind and eventually fall on Hyperion, where they concentrate in low spots and impact craters.

Hyperion on May 31, 2015

Cassini will not come this close to Hyperion again for the remainder of its mission, which will come to an end in September 2017 when it makes a final dive between the rings and down into Saturn’s atmosphere.

Source: Cassini mission site

Plastic ingredient spied on Titan.

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Cassini probe sees plastic ingredient on Titan moon

 

Titan

 

 

The Cassini probe has detected propene, or propylene, on Saturn’s moon Titan.

 

On Earth, this molecule, which comprises three carbon atoms and six hydrogen atoms, is a constituent of many plastics.

 

It is the first definitive detection of the plastic ingredient on any moon or planet, other than our home world, says the US space agency (Nasa).

 

The discovery, made by Cassini‘s infrared spectrometer, is reported in Astrophysical Journal Letters.

 

“This chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene,” said Conor Nixon, a Nasa planetary scientist from the agency’s Goddard Space Flight Center. A classic example would be the plastic boxes used to store food in kitchens worldwide.

 

Titan is dominated by hydrocarbons – principally methane, which after nitrogen is the most common component of the atmosphere.

 

Sunlight drives reactions that break apart the methane, allowing the fragments to join up and form even bigger molecules.

 

Other common species seen at the moon as a result are propane, which on Earth is used in portable cooking equipment, and ethane, which is the raw material for another ubiquitous plastic – polyethylene.

 

But the likes of methane, propene, propane and ethane are dwarfed by some truly colossal hydrocarbons that have been detected in Titan’s atmosphere.

 

When the effects of ultraviolet light are combined with the bombardment from particles driven in Saturn’s magnetic field, it becomes possible to cook up some very exotic chemistry.

 

Cassini’s plasma spectrometer has seen evidence for hydrocarbons with an atomic mass thousands of times heavier than a single hydrogen atom.

Shadow Dance: Cassini Captures Dramatic Panorama of Saturn Backlit by the Sun.

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cassiniThe giant planet Saturn looks a bit like a delicate Christmas ornament in a new photomosaic released by NASA.

The Cassini orbiter, currently exploring Saturn and its moons, snapped the 60 images that would become the mosaic in October, as the spacecraft swung through the planet’s shadow. At the time Cassini was beneath the plane of the rings. The result is an enhanced-color panorama of the giant world and its rings, backlit by the sun against the blackness of space. The shadow of Saturn itself can be seen as a dark crescent shape cast across the plane of the rings. Just below and to the left of the rings are two white dots: Saturn’s moons Enceladus and Tethys.

“Of all the many glorious images we have received from Saturn, none are more strikingly unusual than those taken from Saturn’s shadow,” Cassini’s imaging team lead Carolyn Porco of the Space Science Institute in Boulder, Colo., said in a prepared statement.

Source: Scientific American