Planetary Nebula

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Geminid Meteors over Chile

Image Credit & Copyright: Yuri Beletsky (Las Campanas Observatory, Carnegie Institution)

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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.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

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Ocean on the moon Europa

Scientists' consensus is that a layer of liquid water exists beneath Europa's surface, and that heat from tidal flexing allows the subsurface ocean to remain liquid.

Europa's surface temperature averages about 110 K (−160 °C; −260 °F) at the equator and only 50 K (−220 °C; −370 °F) at the poles, keeping Europa's icy crust as hard as granite. The first hints of a subsurface ocean came from theoretical considerations of tidal heating (a consequence of Europa's slightly eccentric orbit and orbital resonance with the other Galilean moons). Galileo imaging team members argue for the existence of a subsurface ocean from analysis of Voyager and Galileo images.

The most dramatic example is "chaos terrain", a common feature on Europa's surface that some interpret as a region where the subsurface ocean has melted through the icy crust.

The thin-ice model suggests that Europa's ice shell may be only a few kilometers thick. However, most planetary scientists conclude that this model considers only those topmost layers of Europa's crust that behave elastically when affected by Jupiter's tides.

The Hubble Space Telescope acquired an image of Europa in 2012 that was interpreted to be a plume of water vapour erupting from near its south pole The image suggests the plume may be 200 km (120 mi) high, or more than 20 times the height of Mt. Everest.

Life?

So far, there is no evidence that life exists on Europa, but Europa has emerged as one of the most likely locations in the Solar System for potential habitability. Life could exist in its under-ice ocean, perhaps in an environment similar to Earth's deep-ocean hydrothermal vents. Even if Europa lacks volcanic hydrothermal activity, a 2016 NASA study found that Earth-like levels of hydrogen and oxygen could be produced through processes related to serpentinization and ice-derived oxidants, which do not directly involve volcanism.

In 2015, scientists announced that salt from a subsurface ocean may likely be coating some geological features on Europa, suggesting that the ocean is interacting with the seafloor. This may be important in determining if Europa could be habitable. The likely presence of liquid water in contact with Europa's rocky mantle has spurred calls to send a probe there.

Missions

Europa Clipper is an interplanetary mission in development by NASA comprising an orbiter. Set for a launch in October 2024, the spacecraft is being developed to study the Galilean moon Europa through a series of flybys while in orbit around Jupiter.

The Europa Lander is a proposed astrobiology mission concept by NASA to Europa, an icy moon of Jupiter. If funded and developed as a large strategic science mission, it would be launched in 2027 to complement the studies by the Europa Clipper orbiter mission and perform analyses on site. NASA's budget for fiscal year 2021 neither mandates nor allocates any funds to the mission leaving its future uncertain.

The objectives of the mission are to search for biosignatures at the subsurface ≈10 cm, to characterize the composition of non-ice near-subsurface material, and determine the proximity of liquid water and recently erupted material near the lander's location.

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Astronomers Detect Matter Falling into Black Hole

University of Leicester’s Professor Ken Pounds and co-authors report the detection of matter falling into a black hole at 30% of the speed of light.

It is now well established that a supermassive black hole lies in the center of most galaxies, and further that it accretes matter through a disk.

With sufficient matter (interstellar gas clouds or even isolated stars) falling into the black hole, these can become extremely luminous, and are seen as a quasar or active galactic nucleus (AGN).

The orbit of matter around the black hole is often assumed to be aligned with the rotation of the black hole, but there is no compelling reason for this to be the case. In fact, the reason we have summer and winter is that the Earth’s daily rotation does not line up with its yearly orbit around the Sun.

Until now it has been unclear how misaligned rotation might affect the in-fall of matter. This is particularly relevant to the feeding of supermassive black holes since matter can fall in from any direction.

Using data from ESA’s XMM-Newton X-ray Observatory, Professor Pounds and colleagues looked at X-ray spectra from PG1211+143, a Seyfert galaxy (characterized by a very bright AGN resulting from the presence of the massive black hole at its nucleus) located in the constellation Coma Berenices, about one billion light-years away.

The team found the spectra to be strongly red-shifted, showing the observed matter to be falling into PG1211+143’s black hole at the enormous speed of 30% of the speed of light, or around 62,000 miles per second (100,000 km per second).

The gas has almost no rotation around the black hole, and is detected extremely close to it in astronomical terms, at a distance of only 20 times the black hole’s size (its event horizon, the boundary of the region where escape is no longer possible).

“The galaxy we were observing with XMM-Newton has a 40-million-solar-mass black hole which is very bright and evidently well fed,” Professor Pounds said.

“Indeed some 15 years ago we detected a powerful wind indicating the black hole was being over-fed. While such winds are now found in many active galaxies, PG1211+143 has now yielded another ‘first,’ with the detection of matter plunging directly into the black hole itself.”

“We were able to follow an Earth-sized clump of matter for about a day, as it was pulled towards the black hole, accelerating to a third of the velocity of light before being swallowed up by the hole.” source

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