By cabinsinthewoods

Saturn Rings and Moons: From left, the moons are Janus, Pandora, Enceladus, Mimas and Rhea. Following the images below, Enceladus and Tethys, Titan, Rhea and Mimas. Enceladus and Tethys.

by Gordan Ugarkovic

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Characteristics of the moons of Saturn

Saturn has 62 natural satellites. Here are some features of some of its moons, with mountains, valleys, and striking marks on their surfaces, often marked by asteroid bombardments causing small, huge craters.

Iapetus -  Equatorial ridge

Iapetus’s equatorial ridge was discovered when the Cassini spacecraft imaged Iapetus on 31 December 2004. Peaks in the ridge rise more than 20 km above the surrounding plains, making them some of the tallest mountains in the Solar System. The ridge forms a complex system including isolated peaks, segments of more than 200 km and sections with three near parallel ridges. 

Tethys - Odysseus crater

Odysseus is the largest crater on Saturn’s moon Tethys. It is 445 km across, more than 2/5 of the moon’s diameter, and is one of the largest craters in the Solar System.

Tethys - Ithaca Chasma

Ithaca Chasma is a valley (graben) on Saturn’s moon Tethys, named after the island of Ithaca, in Greece. It is up to 100 km wide, 3 to 5 km deep and 2,000 km long, running approximately three-quarters of the way around Tethys’ circumference, making it one of the longer valleys in the Solar System. Ithaca Chasma is approximately concentric with Odysseus crater. 

Tethys - Red arcs

Unusual arc-shaped, reddish streaks cut across the surface of Saturn’s ice-rich moon Tethys in this enhanced-color mosaic. The red streaks are narrow, curved lines on the moon’s surface, only a few miles (or kilometers) wide but several hundred miles (or kilometers) long.

Rhea - Inktomi crater

Inktomi, also known as The Splat, is a prominent rayed impact crater 47.2 kilometres (29.3 mi) in diameter located in the southern hemisphere of Saturn’s moon Rhea.

Mimas - Herschel Crater

Herschel is a huge crater in the leading hemisphere of the Saturnian moon Mimas, on the equator at 100° longitude. It is so large that astronomers have expressed surprise that Mimas was not shattered by the impact that caused it. It measures 139 kilometres (86 miles) across, almost one third the diameter of Mimas. If there were a crater of an equivalent scale on Earth it would be over 4,000 km (2,500 mi) in diameter – wider than Canada – with walls over 200 km (120 mi) high.

Enceladus - Surface with fractures

Close up of one of the ‘tiger stripes” or fissures called Baghdad Sulcus. Both heat and occasional geysers issue from this formidable crack. Some of the material coating the landscape may be snow condensed from vapor. This closeup of the surface of Enceladus on November 21, 2009, viewed from approximately 1,260 miles (2,028 kilometers) away. 

Dione - Contrasts

This image from NASA’s Cassini spacecraft shows a part of Dione’s surface that is covered by linear, curving features, called chasmata. One possibility is that this stress pattern may be related to Dione’s orbital evolution and the effect of tidal stresses over time. This view looks toward the trailing hemisphere of Dione. 

Learn more: Iapetus, Tethys, Rhea, Mimas, Enceladus and Dione.

Images: NASA/JPL-Caltech

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Stars and Dust in Corona Australis (NASA)

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Halloween hike/drive

October 31st, 2018

Front Royal, VA

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#Cool

What’s Enceladus?

Before we tell you about Enceladus, let’s first talk about our Cassini spacecraft…

Our Cassini mission to Saturn is one of the most ambitious efforts in planetary space exploration ever mounted. Cassini is a sophisticated robotic spacecraft orbiting the ringed planet and studying the Saturnian system in detail.

Cassini completed its initial four-year mission to explore the Saturn System in June 2008. It has also completed its first mission extension in September 2010. Now, the health spacecraft is making exciting new discoveries in a second extension mission!

Enceladus

Enceladus is one of Saturn’s many moons, and is one of the brightest objects in our solar system. This moon is about as wide as Arizona, and displays at least five different types of terrain. The surface is believed to be geologically “young”, possibly less than 100 million years old.

Cassini first discovered continually-erupting fountains of icy material on Enceladus in 2005. Since then, the Saturn moon has become one of the most promising places in the solar system to search for present-day habitable environments.  

Scientists found that hydrothermal activity may be occurring on the seafloor of the moon’s underground ocean. In September, it was announced that its ocean –previously thought to only be a regional sea – was global!

Since Cassini is nearing the end of its mission, we are able to make a series of three close encounters with Enceladus, one of Saturn’s moons.

Close Encounters

On Oct. 14, Cassini performed a mid-range flyby of Enceladus, but the main event will take place on Oct. 28, when Cassini will come dizzyingly close to the icy moon. During this flyby, the spacecraft will pass a mere 30 miles above the moon’s south polar region!

This will be the deepest-ever dive through the moon’s plume of icy spray, where Cassini can collect images and valuable data about what’s going on beneath the frozen surface.

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Black holes

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like an ideal black body, as it reflects no light.  

The idea of a body so massive that even light could not escape was briefly proposed by astronomical pioneer and English clergyman John Michell in a letter published in November 1784. Michell’s simplistic calculations assumed that such a body might have the same density as the Sun, and concluded that such a body would form when a star’s diameter exceeds the Sun’s by a factor of 500, and the surface escape velocity exceeds the usual speed of light.

At the center of a black hole, as described by general relativity, lies a gravitational singularity, a region where the spacetime curvature becomes infinite. For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity that lies in the plane of rotation. In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution. The singular region can thus be thought of as having infinite density. 

How Do Black Holes Form?

Scientists think the smallest black holes formed when the universe began.

Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.

Scientists think supermassive black holes were made at the same time as the galaxy they are in.

Supermassive black holes, which can have a mass equivalent to billions of suns, likely exist in the centers of most galaxies, including our own galaxy, the Milky Way. We don’t know exactly how supermassive black holes form, but it’s likely that they’re a byproduct of galaxy formation. Because of their location in the centers of galaxies, close to many tightly packed stars and gas clouds, supermassive black holes continue to grow on a steady diet of matter.

If Black Holes Are “Black,” How Do Scientists Know They Are There?

A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. 

Scientists can study stars to find out if they are flying around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.

On 11 February 2016, the LIGO collaboration announced the first observation of gravitational waves; because these waves were generated from a black hole merger it was the first ever direct detection of a binary black hole merger. On 15 June 2016, a second detection of a gravitational wave event from colliding black holes was announced. 

Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background 

Animated simulation of gravitational lensing caused by a black hole going past a background galaxy. A secondary image of the galaxy can be seen within the black hole Einstein ring on the opposite direction of that of the galaxy. The secondary image grows (remaining within the Einstein ring) as the primary image approaches the black hole. The surface brightness of the two images remains constant, but their angular size varies, hence producing an amplification of the galaxy luminosity as seen from a distant observer. The maximum amplification occurs when the background galaxy (or in the present case a bright part of it) is exactly behind the black hole.

Could a Black Hole Destroy Earth?

Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.

Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now.

The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.

More posts about black holes

Source 1, 2 & 3