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The Cassini spacecraft, which has been observing the Saturn system from up close since 2004, gave us yet another ringside view of an event that had never been directly seen before. It recorded the northern summer solstice on Saturn, which happens once about every 15 Earth years, and the associated changes that happen on the gas giant, its rings, and moons

The giant storm that formed a ring around the planet’s northern hemisphere from late 2010 to 2011 was one of the most remarkable features observed by Cassini during its Solstice Mission. Another observation was that of hazes forming in the far north during the Saturn spring, leading to the disappearance of bluer hues in that region of the planet.

SaturnStorm
SaturnStorm

During its seven-year Solstice Mission, Cassini watched as a huge storm erupted and encircled Saturn. Scientists think storms like this are related, in part, to seasonal effects of sunlight on Saturn's atmosphere. Photo: NASA/JPL/Space Science Institute

The formation of the hazes was found to be linked to the seasonal changes in temperature and chemical composition of the planet’s upper atmosphere. Some compounds in those parts of the atmosphere were seen to react quickly to the changing amount of sunlight as Saturn and its many companions went along their orbit around the sun. The changes were also found to be sudden, instead of gradual shifts, and occurring at specific latitudes in the planet’s layered atmosphere.

“Eventually a whole hemisphere undergoes change, but it gets there by these jumps at specific latitude bands at different times in the season,” Robert West, a Cassini imaging team member at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement Thursday.

SaturnSolstice

These natural color views from Cassini show how the color of Saturn’s north-polar region changed between June 2013 and April 2017, as the northern hemisphere headed toward summer solstice. Photo: NASA/JPL-Caltech/SSI/Hampton University

Large-scale seasonal changes were also seen on Titan, Saturn’s largest moon. Some methane clouds have begun to appear in the moon’s northern hemisphere since 2010, when Cassini saw giant storms around the equator, having moved there from around the south pole, where the spacecraft had seen them on its arrival in 2004. Scientists had expected the shift to the northern hemisphere to have started much longer ago.

A sudden, rapid buildup of trace hydrocarbons and haze — previously seen only in the high northern regions of Titan — was observed by Cassini in 2013 in the moon’s south, suggesting a seasonal reversal of direction for Titan’s atmospheric circulation.

“Observations of how the locations of cloud activity change and how long such changes take to give us important information about the workings of Titan’s atmosphere and also its surface, as rainfall and wind patterns change with the seasons too,” Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said.

Titan

Following Saturnian equinox in 2009, Cassini observed cloud activity on Titan shift from southern latitudes toward the equator, and eventually to the high north. Such observations have provided evidence of seasonal shifts in Titan's weather systems. Photo: NASA/JPL/Space Science Institute

The observations of Enceladus, Saturn’s icy moon with a global subsurface ocean, also changed due to the solstice. As the moon’s southern half sunk into the winter darkness, Cassini could monitor the internal heat emanating from within Enceladus, without any interference by the heat from the sun.

As the planet moved toward the solstice, the position of the gradually became higher in relation to the angle of the rings, allowing more light to penetrate into them and heating them to the warmest temperatures recorded by Cassini.

The light allowed Cassini to better observe how the particles of Saturn’s rings clump together and the differences in the properties of the particles that make up the different rings. As the angle of the rings changed, it also allowed for the spacecraft’s radio signals to pass more easily and cleanly through the densest of the rings, allowing scientists on Earth to capture high-quality data about the ring particles.

SaturnCRing

Various regions of Saturn's C ring, with varying degrees of brightness, can be seen in this image captured by the Cassini spacecraft, Jan. 9, 2017. Photo: NASA/JPL-Caltech/Space Science Institute

“During Cassini’s Solstice Mission, we have witnessed — up close for the first time — an entire season at Saturn. The Saturn system undergoes dramatic transitions from winter to summer, and thanks to Cassini, we had a ringside seat,” Linda Spilker, Cassini project scientist at JPL, said in the statement.

Observing the solstice and the seasonal changes in the Saturn system was one of the primary objectives for the spacecraft’s Solstice Mission — the name given to Cassini’s second extended mission that began in 2010. The first extended mission, from 2008 to 2010, was called the Equinox Mission.

Cassini is a collaboration between NASA, the European Space Agency, and the Italian Space Agency. During its ongoing Grande Finale Mission, the spacecraft is making 22 dives through Saturn’s rings, one every week, till Sept. 15. On that day, Cassini will plunge into the gas giant’s atmosphere and burn up, bringing the mission to an end. Its fate has been planned to avoid possible contamination of Enceladus, which may be potentially habitable.

Source: This article was published ca.news.yahoo.com By Himanshu Goenka

Categorized in Science & Tech

Why do the other planets, like Venus (shown above) have a different atmosphere than Earth? Credit: ESA

Here on Earth, we tend to take our atmosphere for granted, and not without reason. Our atmosphere has a lovely mix of nitrogen and oxygen (78% and 21% respectively) with trace amounts of water vapor, carbon dioxide and other gaseous molecules. What’s more, we enjoy an atmospheric pressure of 101.325 kPa, which extends to an altitude of about 8.5 km.

In short, our atmosphere is plentiful and life-sustaining. But what about the other planets of the Solar System? How do they stack up in terms of atmospheric composition and pressure? We know for a fact that they are not breathable by humans and cannot support life. But just what is the difference between these balls of rock and gas and our own?

For starters, it should be noted that every planet in the Solar System has an atmosphere of one kind or another. And these range from incredibly thin and tenuous (such as Mercury’s “exosphere”) to the incredibly dense and powerful – which is the case for all of the gas giants. And depending on the composition of the planet, whether it is a terrestrial or a gas/ice giant, the gases that make up its atmosphere range from either the hydrogen and helium to more complex elements like oxygen, carbon dioxide, ammonia and methane.

Mercury’s Atmosphere:

Mercury is too hot and too small to retain an atmosphere. However, it does have a tenuous and variable exosphere that is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10-14 bar (one-quadrillionth of Earth’s atmospheric pressure). It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.

Mercury's Horizon
A High-resolution Look over Mercury’s Northern Horizon. Credit: NASA/MESSENGER

Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences considerable variations in temperature. Whereas the side that faces the Sun can reach temperatures of up to 700 K (427° C), while the side in shadow dips down to 100 K (-173° C).

Venus’ Atmosphere:

Surface observations of Venus have been difficult in the past, due to its extremely dense atmosphere, which is composed primarily of carbon dioxide with a small amount of nitrogen. At 92 bar (9.2 MPa), the atmospheric mass is 93 times that of Earth’s atmosphere and the pressure at the planet’s surface is about 92 times that at Earth’s surface.

Venus is also the hottest planet in our Solar System, with a mean surface temperature of 735 K (462 °C/863.6 °F). This is due to the CO²-rich atmosphere which, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the Solar System. Above the dense CO² layer, thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets scatter about 90% of the sunlight back into space.

Another common phenomena is Venus’ strong winds, which reach speeds of up to 85 m/s (300 km/h; 186.4 mph) at the cloud tops and circle the planet every four to five Earth days. At this speed, these winds move up to 60 times the speed of the planet’s rotation, whereas Earth’s fastest winds are only 10-20% of the planet’s rotational speed.

Venus flybys have also indicated that its dense clouds are capable of producing lightning, much like the clouds on Earth. Their intermittent appearance indicates a pattern associated with weather activity, and the lightning rate is at least half of that on Earth.

Earth’s Atmosphere:

Earth’s atmosphere, which is composed of nitrogen, oxygen, water vapor, carbon dioxide and other trace gases, also consists of five layers. These consists of the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. As a rule, air pressure and density decrease the higher one goes into the atmosphere and the farther one is from the surface.

Closest to the Earth is the Troposphere, which extends from the 0 to between 12 km and 17 km (0 to 7 and 10.56 mi) above the surface. This layer contains roughly 80% of the mass of Earth’s atmosphere, and nearly all atmospheric water vapor or moisture is found in here as well. As a result, it is the layer where most of Earth’s weather takes place.

The Stratosphere extends from the Troposphere to an altitude of 50 km (31 mi). This layer extends from the top of the troposphere to the stratopause, which is at an altitude of about 50 to 55 km (31 to 34 mi). This layer of the atmosphere is home to the ozone layer, which is the part of Earth’s atmosphere that contains relatively high concentrations of ozone gas.

Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere.[1] (The shuttle is actually orbiting at an altitude of more than 320 km (200 mi), far above all three layers.) Credit: NASA
Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere. Credit: NASA

Next is the Mesosphere, which extends from a distance of 50 to 80 km (31 to 50 mi) above sea level. It is the coldest place on Earth and has an average temperature of around -85 °C (-120 °F; 190 K). The Thermosphere, the second highest layer of the atmosphere, extends from an altitude of about 80 km (50 mi) up to the thermopause, which is at an altitude of 500–1000 km (310–620 mi).

The lower part of the thermosphere, from 80 to 550 kilometers (50 to 342 mi), contains the ionosphere – which is so named because it is here in the atmosphere that particles are ionized by solar radiation.  This layer is completely cloudless and free of water vapor. It is also at this altitude that the phenomena known as Aurora Borealis and Aurara Australis are known to take place.

The Exosphere, which is outermost layer of the Earth’s atmosphere, extends from the exobase – located at the top of the thermosphere at an altitude of about 700 km above sea level – to about 10,000 km (6,200 mi). The exosphere merges with the emptiness of outer space, and is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide

The exosphere is located too far above Earth for any meteorological phenomena to be possible. However, the Aurora Borealis and Aurora Australis sometimes occur in the lower part of the exosphere, where they overlap into the thermosphere.

This photo of the aurora was taken by astronaut Doug Wheelock from the International Space Station on July 25, 2010. Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center
Photo of the aurora taken by astronaut Doug Wheelock from the International Space Station on July 25, 2010. Credit: NASA/Johnson Space Center

The average surface temperature on Earth is approximately 14°C; but as already noted, this varies. For instance, the hottest temperature ever recorded on Earth was 70.7°C (159°F), which was taken in the Lut Desert of Iran. Meanwhile, the coldest temperature ever recorded on Earth was measured at the Soviet Vostok Station on the Antarctic Plateau, reaching an historic low of -89.2°C (-129°F).

Mars’ Atmosphere:

Planet Mars has a very thin atmosphere which is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates that measure 1.5 micrometers in diameter, which is what gives the Martian sky a tawny color when seen from the surface. Mars’ atmospheric pressure ranges from 0.4 – 0.87 kPa, which is equivalent to about 1% of Earth’s at sea level.

Because of its thin atmosphere, and its greater distance from the Sun, the surface temperature of Mars is much colder than what we experience here on Earth. The planet’s average temperature is -46 °C (51 °F), with a low of -143 °C (-225.4 °F) during the winter at the poles, and a high of 35 °C (95 °F) during summer and midday at the equator.

The planet also experiences dust storms, which can turn into what resembles small tornadoes. Larger dust storms occur when the dust is blown into the atmosphere and heats up from the Sun. The warmer dust filled air rises and the winds get stronger, creating storms that can measure up to thousands of kilometers in width and last for months at a time. When they get this large, they can actually block most of the surface from view.

Mars, as it appears today, Credit: NASA
Mars, as it appears today, with a very thin and tenuous atmosphere. Credit: NASA

Trace amounts of methane have also been detected in the Martian atmosphere, with an estimated concentration of about 30 parts per billion (ppb). It occurs in extended plumes, and the profiles imply that the methane was released from specific regions – the first of which is located between Isidis and Utopia Planitia (30°N 260°W) and the second in Arabia Terra (0°N 310°W).

Ammonia was also tentatively detected on Mars by the Mars Express satellite, but with a relatively short lifetime. It is not clear what produced it, but volcanic activity has been suggested as a possible source.

Jupiter’s Atmosphere:

Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere create a light show that is truly spectacular.

Jupiter also experiences violent weather patterns. Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s. The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear.

Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. These clouds are located in the tropopause and are arranged into bands of different latitudes, known as “tropical regions”. The cloud layer is only about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region.

There may also be a thin layer of water clouds underlying the ammonia layer, as evidenced by flashes of lightning detected in the atmosphere of Jupiter, which would be caused by the water’s polarity creating the charge separation needed for lightning. Observations of these electrical discharges indicate that they can be up to a thousand times as powerful as those observed here on the Earth.

Saturn’s Atmosphere:

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The gas giant is also known to contain heavier elements, though the proportions of these relative to hydrogen and helium is not known. It is assumed that they would match the primordial abundance from the formation of the Solar System.

Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion.

Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter and wider near the equator. As with Jupiter’s cloud layers, they are divided into the upper and lower layers, which vary in composition based on depth and pressure. In the upper cloud layers, with temperatures in range of 100–160 K and pressures between 0.5–2 bar, the clouds consist of ammonia ice.

Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in an aqueous solution.

On occasion, Saturn’s atmosphere exhibits long-lived ovals, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice.

These spots can be several thousands of kilometers wide, and have been observed in 1876, 1903, 1933, 1960, and 1990. Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed enveloping Saturn, which was spotted by the Cassini space probe. If the periodic nature of these storms is maintained, another one will occur in about 2020.

The winds on Saturn are the second fastest among the Solar System’s planets, after Neptune’s. Voyager data indicate peak easterly winds of 500 m/s (1800 km/h). Saturn’s northern and southern poles have also shown evidence of stormy weather. At the north pole, this takes the form of a hexagonal wave pattern, whereas the south shows evidence of a massive jet stream.

The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images. The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior.

The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope. These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter.

Uranus’ Atmosphere:

As with Earth, the atmosphere of Uranus is broken into layers, depending upon temperature and pressure. Like the other gas giants, the planet doesn’t have a firm surface, and scientists define the surface as the region where the atmospheric pressure exceeds one bar (the pressure found on Earth at sea level). Anything accessible to remote-sensing capability – which extends down to roughly 300 km below the 1 bar level – is also considered to be the atmosphere.

Diagram of the interior of Uranus. Credit: Public Domain
Diagram of the interior of Uranus. Credit: Public Domain

Using these references points, Uranus’  atmosphere can be divided into three layers. The first is the troposphere, between altitudes of -300 km below the surface and 50 km above it, where pressures range from 100 to 0.1 bar (10 MPa to 10 kPa). The second layer is the stratosphere, which reaches between 50 and 4000 km and experiences pressures between 0.1 and 10-10 bar (10 kPa to 10 µPa).

The troposphere is the densest layer in Uranus’ atmosphere. Here, the temperature ranges from 320 K (46.85 °C/116 °F) at the base (-300 km) to 53 K (-220 °C/-364 °F) at 50 km, with the upper region being the coldest in the solar system. The tropopause region is responsible for the vast majority of Uranus’s thermal infrared emissions, thus determining its effective temperature of 59.1 ± 0.3 K.

Within the troposphere are layers of clouds – water clouds at the lowest pressures, with ammonium hydrosulfide clouds above them. Ammonia and hydrogen sulfide clouds come next. Finally, thin methane clouds lay on the top.

In the stratosphere, temperatures range from 53 K (-220 °C/-364 °F) at the upper level to between 800 and 850 K (527 – 577 °C/980 – 1070 °F) at the base of the thermosphere, thanks largely to heating caused by solar radiation. The stratosphere contains ethane smog, which may contribute to the planet’s dull appearance. Acetylene and methane are also present, and these hazes help warm the stratosphere.

Uranus. Image credit: Hubble
Uranus, as imaged by the Hubble Space Telescope. Image credit: NASA/Hubble

The outermost layer, the thermosphere and corona, extend from 4,000 km to as high as 50,000 km from the surface. This region has a uniform temperature of 800-850 (577 °C/1,070 °F), although scientists are unsure as to the reason. Because the distance to Uranus from the Sun is so great, the amount of sunlight absorbed cannot be the primary cause.

Like Jupiter and Saturn, Uranus’s weather follows a similar pattern where systems are broken up into bands that rotate around the planet, which are driven by internal heat rising to the upper atmosphere. As a result, winds on Uranus can reach up to 900 km/h (560 mph), creating massive storms like the one spotted by the Hubble Space Telescope in 2012. Similar to Jupiter’s Great Red Spot, this “Dark Spot” was a giant cloud vortex that measured 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles).

Neptune’s Atmosphere:

At high altitudes, Neptune’s atmosphere is 80% hydrogen and 19% helium, with a trace amount of methane. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune’s is darker and more vivid. Because Neptune’s atmospheric methane content is similar to that of Uranus, some unknown constituent is thought to contribute to Neptune’s more intense coloring.

Neptune’s atmosphere is subdivided into two main regions: the lower troposphere (where temperature decreases with altitude), and the stratosphere (where temperature increases with altitude). The boundary between the two, the tropopause, lies at a pressure of 0.1 bars (10 kPa). The stratosphere then gives way to the thermosphere at a pressure lower than 10-5 to 10-4 microbars (1 to 10 Pa), which gradually transitions to the exosphere.

Neptune’s spectra suggest that its lower stratosphere is hazy due to condensation of products caused by the interaction of ultraviolet radiation and methane (i.e. photolysis), which produces compounds such as ethane and ethyne. The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide, which are responsible for Neptune’s stratosphere being warmer than that of Uranus.

In this image, the colors and contrasts were modified to emphasize the planet’s atmospheric features. The winds in Neptune’s atmosphere can reach the speed of sound or more. Neptune’s Great Dark Spot stands out as the most prominent feature on the left. Several features, including the fainter Dark Spot 2 and the South Polar Feature, are locked to the planet’s rotation, which allowed Karkoschka to precisely determine how long a day lasts on Neptune. (Image: Erich Karkoschka)
A modified color/contrast image emphasizing Neptune’s atmospheric features, including wind speed. Credit Erich Karkoschka)

For reasons that remain obscure, the planet’s thermosphere experiences unusually high temperatures of about 750 K (476.85 °C/890 °F). The planet is too far from the Sun for this heat to be generated by ultraviolet radiation, which means another heating mechanism is involved – which could be the atmosphere’s interaction with ion’s in the planet’s magnetic field, or gravity waves from the planet’s interior that dissipate in the atmosphere.

Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours, which is slower than the 16.1-hour rotation of the planet’s magnetic field. By contrast, the reverse is true for the polar regions where the rotation period is 12 hours.

This differential rotation is the most pronounced of any planet in the Solar System, and results in strong latitudinal wind shear and violent storms. The three most impressive were all spotted in 1989 by the Voyager 2 space probe, and then named based on their appearances.

The first to be spotted was a massive anticyclonic storm measuring 13,000 x 6,600 km and resembling the Great Red Spot of Jupiter. Known as the Great Dark Spot, this storm was not spotted five later (Nov. 2nd, 1994) when the Hubble Space Telescope looked for it. Instead, a new storm that was very similar in appearance was found in the planet’s northern hemisphere, suggesting that these storms have a shorter life span than Jupiter’s.

Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL

The Scooter is another storm, a white cloud group located farther south than the Great Dark Spot – a nickname that first arose during the months leading up to the Voyager 2 encounter in 1989. The Small Dark Spot, a southern cyclonic storm, was the second-most-intense storm observed during the 1989 encounter. It was initially completely dark; but as Voyager 2 approached the planet, a bright core developed and could be seen in most of the highest-resolution images.

In sum, the planet’s of our Solar System all have atmospheres of sorts. And compared to Earth’s relatively balmy and thick atmosphere, they run the gamut between very very thin to very very dense. They also range in temperatures from the extremely hot (like on Venus) to the extreme freezing cold.

And when it comes to weather systems, things can equally extreme, with planet’s boasting either weather at all, or intense cyclonic and dust storms that put storms here n Earth to shame. And whereas some are entirely hostile to life as we know it, others we might be able to work with.

We have many interesting articles about planetary atmosphere’s here at Universe Today. For instance, he’s What is the Atmosphere?, and articles about the atmosphere of MercuryVenusMarsJupiterSaturnUranus and Neptune,

For more information on atmospheres, check out NASA’s pages on Earth’s Atmospheric LayersThe Carbon Cycle, and how Earth’s atmosphere differs from space.

Astronomy Cast has an episode on the source of the atmosphere.

Source: This article was published universetoday.com By Matt Williams

Categorized in Science & Tech

NASA’s Cassini spacecraft is currently conducting a series of elaborate dives in which it repeatedly comes closer to Saturn than ever before. But during its slower periods, NASA is still using the craft’s fantastic photography equipment to grab images of Saturn’s nearby bodies, such as the moon Titan. The latest photo from the agency shows Titan in all its glory, complete with some very volatile cloud cover.

The new images, which were captured by Cassini on May 7th but not released immediately, show Titan in impressive detail, with long, feathery streaks of clouds obscuring portions of the landscape. But unlike the clouds we’re used to here on Earth — which are made of extremely tiny water droplets or bits of crystalized ice — the clouds you see in the Titan photos are actually made of methane.

In addition to Titan’s wealth of atmospheric methane, the planet also has vast lakes thought to be primarily made up of liquid ethane and methane, along with nitrogen. That’s an extremely hostile combination, at least in terms of Earth-like life. However, NASA isn’t ruling out the possibility that there may actually be methane-based life on the large moon, and even has some theories as to how it might survive.

According to NASA, these new photos were snapped at a distance of about 316,000 miles, which means that each pixel of the image equals roughly 2 miles. With that scale in mind, take a look at the dark splotches dotting the top of the image. Those are the huge methane-filled seas, which may or may not be home to huge, methane-filled whales.

Source : This article was published bgr news By Mike Wehner

Categorized in Science & Tech
This illustration shows Cassini above Saturn's northern hemisphere prior to one of its 22 Grand Finale dives. Credit: NASA/JPL-Caltech
 

The Cassini spacecraft is nearing the end of its lifespan. This September, after spending the past twenty years in space – twelve and a half of which were dedicated to studying Saturn and its system of moons – the probe will be crash into Saturn’s atmosphere. But between now and then, the probe will be making its “Grand Finale” – the final phase of its mission where it will dive between the planet and its rings 22 times.

In addition to exploring this region of Saturn (something no other mission has done), the probe will also be using this opportunity to study Saturn’s hexagonal polar jet stream in greater detail. This persistent storm, which rages around Saturn’s northern polar region, has been a subject of interest for decades. And now that it enjoys full sunlight, Cassini will be able to directly image it with every pass it makes over Saturn’s north pole.

This persistent storm was first noticed in images sent back by the Voyager 1and 2 missions, which flew by Saturn in 1980 and 1981, respectively. As storms go, it is extremely massive, with each side measuring about 13,800 km (8,600 mi) in length – longer than the diameter of the Earth. It also rotates with a period of 10 hours 39 minutes and 24 seconds, which is assumed to be equal to the rotation of Saturn’s interior.

Image of Saturn’s hexagonal polar jet stream, taken by Cassini on Jan. 22nd, 2017. Credit: NASA/JPL-Caltech/Space Science Institute
 

When the Cassini spacecraft arrived around Saturn in 2004 to conduct the first part of its mission, this region was in shadow. This was due to the fact that the northern hemisphere was still coming out of winter, and was hence tilted  away from the Sun. However, since Saturn began its summer solstice in May of 2017, the northern polar region is now fully illuminated – at least by Saturn’s standards.

In truth, between its distance from the Sun (an average of 9.5549 AU) and its axial tilt (26.73°), the northern polar region only gets about 1% as much sunlight as Earth does. And from the perspective of the north pole, the Sun is very low in the sky. Nevertheless, the sunlight falling on the north pole at this point is enough to allow the Cassini mission to directly image the region by capturing its reflected light.

Images of the hexagonal jet stream (like the one above) will be taken by Cassini’s wide-angle camera, which uses special filters that admit wavelengths of near-infrared light. Already, Cassini has captured some impressive imagery during its first plunge between Saturn and its rings (which took place on April 26th, 2017). The rapid-fire images acquired by one of Cassini’s cameras were then stitched together to create a movie (posted below).

As you can see, the movie begins with a view of the vortex at the center of the hexagon, then heads past the outer boundary of the jet stream and continues further southward. Toward the end of the movie, the spacecraft reorients itself to direct its saucer-shaped antenna in the direction of the spacecraft’s motion, which is apparent from the way the camera frame rotates.

The images that make up this movie were captured as the Cassini spacecraft dropped in altitude from 72,400 to 6,700 km (45,000 to 4,200 miles) above Saturn’s cloud tops. As this happened, the features which the camera could resolve changed drastically – going from 8.7 km (5.4 mi) per pixel to 810 meters (0.5 mi) per pixel.

The movie was produced by Kunio Sayanagi and John Blalock – an associate of the Cassini imaging team and a  graduate research assistant (respectively) at Hampton University in Virginia – who collaborated with the Cassiniimaging team. And thanks to this video, new insights are already being made into the hexagonal jet stream and the mechanisms that power it.

For example, as Sayanagi indicated in a NASA press release, the video captured the boundary regions of the jet stream rather nicely, which allowed him to note an interesting fact about them. “I was surprised to see so many sharp edges along the hexagon’s outer boundary,” he said. “Something must be keeping different latitudes from mixing to maintain those edges.”

Andrew Ingersoll, a member of the Cassini imaging team based at Caltech, expressed how similar movies will result from future plunges taken as part of the Grand Finale. “The images from the first pass were great, but we were conservative with the camera settings,” he said. “We plan to make updates to our observations for a similar opportunity on June 29th that we think will result in even better views.”

Between now and the end of the mission, who knows what we might learn about this mysterious storm? The next plunge – aka. Grand Finale Dive No. 4 – will take place on Sunday, May 15th at 4:42 p.m. UTC (12:42 p.m EDT; 9:42 a.m. PDT). A total of 22 dives will be made on a weekly basis before the probe takes the final plunge – the one that will cause it to breakup in Saturn’s atmosphere – on Friday, September 15th, 2017.

For more information, consult Cassini’s Grand Finale Orbit Guide. And be sure to enjoy this video of the final phase of the probe’s mission, courtesy of NASA:

Source: This article was published on universetoday.com by 

Categorized in Science & Tech

The latest images from the Cassini probe orbiting Saturn have been sent back to Earth.

The probe has successfully completed the second of 22 planned 'death dives' through the rings of the gigantic gas planet. NASA is threading the distant spacecraft through the rings as it comes to the end of its life in an effort to understand more about the planet.

These latest pictures were received by the space agency on May 3, and show the dust and debris that make up the rings. 

Cassini was originally launched in 1997 and arrived at Saturn in 2004. Since then it has been exploring not just the planet, but also its moons: Enceladus and Titan.

It is responsible for the discovery of deep oceans underneath the surface ice of Enceladus. Scientists believe this could be one of the best places in the solar system for potentially discovering alien life.

Cassini has twenty more dives to make through the rings of Saturn, before it plunges into the planet's atmosphere.

"No spacecraft has ever gone through the unique region that we’ll attempt to boldly cross 22 times,’ said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington.

NASA explains the ending of Cassini on its website: "The spacecraft will repeatedly climb high above Saturn’s poles, flying just outside its narrow F ring 20 times. After a last targeted Titan flyby, the spacecraft will then dive between Saturn’s uppermost atmosphere and its innermost ring 22 times.

"As Cassini plunges past Saturn, the spacecraft will collect rich and valuable information far beyond the mission’s original plan, including measuring Saturn’s gravitational and magnetic fields, determining ring mass, sampling the atmosphere and ionosphere, and making the last views of Enceladus."

Source: This article was published on mirror.co.uk BY

Categorized in Science & Tech

This is a view of Enceladus, Saturn's sixth-largest moon, taken by the Cassini spacecraft.

New research from NASA’s Cassini mission has all eyes on Enceladus, Saturn’s sixth-largest moon. The research, recently published in Science magazine, indicates that plumes of vapor escaping from cracks in the moon’s icy shell are full of molecular hydrogen, the fuel for microbial life.

As Scott Bolton, a co-author and mission co-investigator from the Southwest Research Institute, explains: “Hydrogen’s the most common element in the whole universe, but we don’t expect a lot of it sitting on Enceladus.” That’s because Enceladus is too small to trap large reserves of hydrogen in its gravity field, he says.

The inference, of course, is that hydrogen is being produced somewhere on the Saturnian moon. But how? Bolton and his colleagues have an idea — one that could link the global ocean beneath Enceladus’ ice shell with the life-sustaining deep oceans of Earth.

“The idea that we’ve proposed — and we’ve researched a lot of different ideas trying to come up with an alternative theory — is that actually there’s hydrothermal activity going on deep in the ocean on Enceladus, and it may be producing white and black smokers, kind of like what we see on Earth,” Bolton says.

He explains that on Earth, smokers are deep hydrothermal vents that put out white or black “smoke” underwater, depending on their sulfur content: “Basically, what you have is you have minerals that are very rich in iron interacting with water.” That chemical process forms new minerals, he says — and releases hydrogen.

“In other words, under the deep sea, the water meets the rock, and some chemistry occurs, and hydrogen is released,” he explains. At least, that’s how it happens on Earth — and Cassini data has already shown that the ocean on Enceladus lies above a rocky core.

On Earth, scientists believe that hydrothermal vents were an early source of life. Today, the areas around deep sea vents teem with species that we’re still discovering.

“You don’t need any sunlight at all,” Bolton says. “You just have the microbes basically feeding off of this hydrogen, and that’s its energy source. And around that region on the Earth in these hydrothermal vents, you find little spider crabs, little shrimp, all kinds of different kinds of mussels.”

To find a shrimp in Enceladus’ ocean would take a submarine, but Bolton says there’s another place we can look for life: in the water vapor spewing through cracks in the moon’s ice hull.

“If you can fly a spacecraft through that water mist, you can go in and measure whether there’s microbes, and amino acids, and other kinds of things that might be present in that water,” he says.

Bolton says that a follow-up probe to Enceladus hasn’t yet been approved, but a mission to one of Jupiter’s moons, Europa, is currently in the works. “It would, hopefully, fly through these plumes,” Bolton says.

“We’ve seen some plumes coming out of the ice of Europa through Hubble telescope images. And so we would look for something similar as to what we just saw on Enceladus, and even more.”

UPDATE: A previous version of this story incorrectly stated Europa was a moon of Saturn, it is a moon of Jupiter.

This article is based on an interview that aired on PRI's Science Friday. Watch a video about the discovery here.

Source : This article was published in ijpr.org By  JULIA FRANZ, CHRISTIE TAYLOR

Categorized in Science & Tech

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