суббота, 14 декабря 2019 г.

New study finds the mix that makes Titan's lakes spew nitrogen bubbles


New research explains how bubbles erupt in frigid hydrocarbon lakes on Saturn's largest moon Titan, potentially creating fizz intense enough to form geologic features on the moon.

New study finds the mix that makes Titan's lakes spew nitrogen bubbles
Artist’s depiction of Winnipeg Lacus, a hydrocarbon lake close to Titan’s north pole
[Credit: NASA/JPL-Caltech]
Titan is covered in hydrocarbon lakes made up of methane and ethane. Scientists have noticed bright spots in these lakes, which appeared in some pictures from NASA's Cassini spacecraft and mysteriously vanished in others. They later theorized these "magic islands" might be outbursts of nitrogen bubbles.

In the new study published in AGU's journal Geophysical Research Letters, researchers simulated Titan's lakes in a pressurized chamber. They found the right combination of methane, ethane and nitrogen crucial for bubbles to form.

Under conditions most like those on Titan, the researchers found ethane had to flow into pools of methane to produce vigorous bubbles. It is possible these bubble outbreaks are strong enough to shape river deltas in bodies of liquid on the moon, according to the new research.


Explaining how bubbles form in Titan's lakes now allows scientists to begin probing fundamental questions about how liquids behave on the moon. Of all the bodies in our solar system, few are more Earth-like than Titan, and it is one of the few places scientists think might have conditions necessary for extraterrestrial life.

The results also hint at scenarios an exploratory submarine might face in Titan's lakes, if the spacecraft were to give off heat and potentially spark an explosion of bubbles.

"The more we learn about Titan, the more we learn that we can't ignore the lakes," said Kendra Farnsworth, a planetary scientist at the University of Arkansas in Fayetteville and lead author of the new study. "And we find fun things like bubbles. Maybe a little bit more violent than we'd expected, but definitely fun to watch."

Making bubbles

Titan is the only moon in our solar system to have an atmosphere. Its air is composed mainly of nitrogen—an element that also forms the bulk of Earth's atmosphere—and hydrocarbons, which form a thick, hazy layer obscuring many of the features across its surface.

New study finds the mix that makes Titan's lakes spew nitrogen bubbles
These images from the Radar instrument aboard NASA’s Cassini spacecraft show the evolution of a transient feature,
informally known as a “magic island”, in the large hydrocarbon sea named Ligeia Mare
on Saturn’s moon Titan [Credit: NASA/JPL-Caltech/ASI/Cornell]
Titan's clouds deliver hydrocarbon rain in the form of methane and ethane. On Earth, methane is a gas used for heating, cooking and electricity, while ethane gas is a precursor for polyethylene plastic.

Temperatures on Titan, however, are cold enough for these compounds to be liquids. There, hydrocarbons cycle through the atmosphere much like water does on Earth. Liquid methane and ethane lakes sprinkle Titan's surface—making it the only other body in our solar system besides Earth to host stable fluids.


Previous work found nitrogen gas from Titan's atmosphere could readily dissolve into cold pools with high concentrations of methane—like when carbon dioxide dissolves into soda. Upon heating, the liquid released nitrogen gas in the form of fizzing bubbles.

But these earlier experiments didn't fully mimic the natural environment on Titan. They also didn't explain what conditions could make the lakes foam, although researchers suspected it happens during heavy rainfall or when a stream flows into a lake.

"Titan's lakes have very interesting dynamics," Farnsworth said. "They're not just static bodies of liquid."

Titan, but on Earth

To determine how ethane, methane and nitrogen might burst into bubbles on Titan, Farnsworth and her colleagues conducted experiments in a six-foot tall, pressurized chamber simulating conditions on the moon. Inside, they set the atmospheric pressure to 1.5-bar—which is 1.5 times higher than Earth's at sea level—and temperatures ranged from a brisk 83 degrees Kelvin (-190 Celsius or -310 Fahrenheit) to a balmy 94 degrees Kelvin (-179 Celsius or -290 Fahrenheit).

The researchers allowed one liquid to flow into a sample dish containing a pool of the other. The researchers then cooled the inside of the chamber until it was either above or below 86 degrees Kelvin (-187 Celsius or -305 Fahrenheit) to let nitrogen dissolve. In one set of experiments, ethane flowed into ponds of methane. In another, methane flowed into ethane. The team then gradually warmed up the chamber and waited for bubbles to erupt.


Two scenarios resulted in bubbles. At temperatures below 86 degrees Kelvin, ethane layered on top of nitrogen-rich methane, no matter what order they were poured into the petri dish. As the temperature warmed, the methane underneath began to foam and when the layers dissolved, bubbles reached the surface.


If the chamber was above 86 degrees Kelvin when the researchers added the liquids, methane flowing into ethane didn't yield any foam. Only ethane flowing into methane pools produced bubbles—and did so forcefully.

"The most surprising thing was how violent the explosions were," Farnsworth said. During one experiment, the outburst of bubbles was so strong, it affected the equipment. "All of a sudden, I look over and the bubbles literally blew up and hit my camera," she recalled.

Fun fizz

The new results suggest changes in both temperature and composition are crucial for bubbles to form in Titan's lakes.

Bubbles erupt when flowing ethane mixes with methane supersaturated with nitrogen—meaning the methane contains more dissolved nitrogen than normal conditions allow. When the methane warms, it can hold less dissolved nitrogen, which escapes as gas. The mixture must also have between 40 and 95 percent methane to make bubbles, according to the study.

It's almost like making rock candy. When boiling water is supersaturated with sugar—or contains more sugar than can normally be dissolved—crystals will form on a piece of sugar-coated wood as the liquid cools.

Experiments at warmer temperatures most likely mimic what is happening on Titan's surface because the moon's coldest temperatures dip down to only 89 degrees Kelvin (-184 Celsius or-299 Fahrenheit), Farnsworth said.

"[The new study] is a nice piece of work that adds to what we are learning about Titan's lakes and emphasizes how important laboratory work is," said Michael Malaska, a planetary scientist at NASA's Jet Propulsion Laboratory in California who was not involved in the work. "It's like 'welcome to the weird' and is a different way of thinking about something that's not water."

Author: Erin I. Garcia De Jesus | Source: American Geophysical Union [December 04, 2019]



* This article was originally published here

First giant planet around white dwarf found


Researchers using ESO's Very Large Telescope have, for the first time, found evidence of a giant planet associated with a white dwarf star. The planet orbits the hot white dwarf, the remnant of a Sun-like star, at close range, causing its atmosphere to be stripped away and form a disc of gas around the star. This unique system hints at what our own Solar System might look like in the distant future.

First giant planet around white dwarf found
This illustration shows the white dwarf WDJ0914+1914 and its Neptune-like exoplanet. Since the icy giant orbits the
hot white dwarf at close range, the extreme ultraviolet radiation from the star strips away the planet's atmosphere.
While most of this stripped gas escapes, some of it swirls into a disc, itself accreting onto the white dwarf
[Credit: ESO/M. Kornmesser]
"It was one of those chance discoveries," says researcher Boris Gansicke, from the University of Warwick in the UK, who led the study, published today in Nature. The team had inspected around 7000 white dwarfs observed by the Sloan Digital Sky Survey and found one to be unlike any other. By analysing subtle variations in the light from the star, they found traces of chemical elements in amounts that scientists had never before observed at a white dwarf. "We knew that there had to be something exceptional going on in this system, and speculated that it may be related to some type of planetary remnant."


To get a better idea of the properties of this unusual star, named WDJ0914+1914, the team analysed it with the X-shooter instrument on ESO's Very Large Telescope in the Chilean Atacama Desert. These follow-up observations confirmed the presence of hydrogen, oxygen and sulphur associated with the white dwarf. By studying the fine details in the spectra taken by ESO's X-shooter, the team discovered that these elements were in a disc of gas swirling into the white dwarf, and not coming from the star itself.

"It took a few weeks of very hard thinking to figure out that the only way to make such a disc is the evaporation of a giant planet," says Matthias Schreiber from the University of Valparaiso in Chile, who computed the past and future evolution of this system.


The detected amounts of hydrogen, oxygen and sulphur are similar to those found in the deep atmospheric layers of icy, giant planets like Neptune and Uranus. If such a planet were orbiting close to a hot white dwarf, the extreme ultraviolet radiation from the star would strip away its outer layers and some of this stripped gas would swirl into a disc, itself accreting onto the white dwarf. This is what scientists think they are seeing around WDJ0914+1914: the first evaporating planet orbiting a white dwarf.

Combining observational data with theoretical models, the team of astronomers from the UK, Chile and Germany were able to paint a clearer image of this unique system. The white dwarf is small and, at a blistering 28 000 degrees Celsius (five times the Sun's temperature), extremely hot.


By contrast, the planet is icy and large--at least twice as large as the star. Since it orbits the hot white dwarf at close range, making its way around it in just 10 days, the high-energy photons from the star are gradually blowing away the planet's atmosphere. Most of the gas escapes, but some is pulled into a disc swirling into the star at a rate of 3000 tonnes per second. It is this disc that makes the otherwise hidden Neptune-like planet visible.

"This is the first time we can measure the amounts of gases like oxygen and sulphur in the disc, which provides clues to the composition of exoplanet atmospheres," says Odette Toloza from the University of Warwick, who developed a model for the disc of gas surrounding the white dwarf. "The discovery also opens up a new window into the final fate of planetary systems," adds Gansicke.


Stars like our Sun burn hydrogen in their cores for most of their lives. Once they run out of this fuel, they puff up into red giants, becoming hundreds of times larger and engulfing nearby planets. In the case of the Solar System, this will include Mercury, Venus, and even Earth, which will all be consumed by the red-giant Sun in about 5 billion years.


Eventually, Sun-like stars lose their outer layers, leaving behind only a burnt-out core, a white dwarf. Such stellar remnants can still host planets, and many of these star systems are thought to exist in our galaxy. However, until now, scientists had never found evidence of a surviving giant planet around a white dwarf. The detection of an exoplanet in orbit around WDJ0914+1914, located about 1500 light years away in the constellation of Cancer, may be the first of many orbiting such stars.

First giant planet around white dwarf found
The Sun will evolve into a white dwarf in about 6 billion years from now. Mars and the outer gas giants of our solar system
will survive this metamorphosis. For the first few million years after its formation the white dwarf will be extremely hot
 and its strong EUV emission will evaporate gas from the outer atmospheres of the gas giants. A fraction of this gas
will be accreted by the white dwarf and produce atmospheric lines detectable for future generations
of alien astronomers [Credit: Mark Garlick]
According to the researchers, the exoplanet now found with the help of ESO's X-shooter orbits the white dwarf at a distance of only 10 million kilometres, or 15 times the solar radius, which would have been deep inside the red giant. The unusual position of the planet implies that at some point after the host star became a white dwarf, the planet moved closer to it. The astronomers believe that this new orbit could be the result of gravitational interactions with other planets in the system, meaning that more than one planet may have survived its host star's violent transition.

"Until recently, very few astronomers paused to ponder the fate of planets orbiting dying stars. This discovery of a planet orbiting closely around a burnt-out stellar core forcefully demonstrates that the Universe is time and again challenging our minds to step beyond our established ideas," concludes Gansicke.

The research was presented in a paper to appear in Nature.

Source: ESO [December 04, 2019]



* This article was originally published here

Looking for exoplanet life in all the right spectra


A Cornell University senior has come up with a way to discern life on exoplanets loitering in other cosmic neighbourhoods: a spectral field guide.

Looking for exoplanet life in all the right spectra
While astronomers don’t know what the Earth-like exoplanet Proxima b looks like, this artistic impression presents
a view of the possible surface. New, upcoming large telescopes on Earth will soon explore atmospheres
on exoplanets – like Proxima b – for signatures of life [Credit: ESO/M. Kornmesser]
Zifan Lin has developed high-resolution spectral models and scenarios for two exoplanets that may harbor life: Proxima b, in the habitable zone of our nearest neighbor Proxima Centauri; and Trappist-1e, one of three possible Earth-like exoplanet candidates in the Trappist-1 system.

The paper, co-authored with Lisa Kaltenegger, associate professor of astronomy and director of Cornell's Carl Sagan Institute, published in Monthly Notices of the Royal Astronomical Society.


"In order to investigate whether there are signs of life on other worlds, it is very important to understand signs of life that show in a planet's light fingerprint," Lin said. "Life on exoplanets can produce a characteristic combination of molecules in its atmosphere -- and those become telltale signs in the spectra of such planets.

"In the near future we will be seeing the atmosphere of these worlds with new, sophisticated ground-based telescopes, which will allow us to explore the exoplanet's climate and might spot its biota," he said.

In the search for habitable worlds, "M dwarf" stars catch astronomers' eyes, since the local universe teems with these suns, which make up 75% of the nearby cosmos, according to Lin.


Throughout the Milky Way, our home galaxy, astronomers have discovered more than 4,000 exoplanets, some in their own suns' habitable zone -- an area that provides conditions suitable for life.

To explore the atmosphere of these places, scientists need large next-generation telescopes, such as the Extremely Large Telescope (ELT), which is currently under construction in northern Chile's Atacama Desert and expected to be operational in 2025. Scientists can aim the mammoth eyepiece -- with a flawless primary mirror about half the size of a football field -- at Proxima b and Trappist-1e. The future telescope will have more than 250 times the light-gathering power of the Hubble Space Telescope.

Lin and Kaltenegger said the high-resolution spectrographs from the ELT can discern water, methane and oxygen for both Proxima b and Trappist-1e, if these planets are like our own pale blue dot.

"Zifan has generated a database of light fingerprints for these worlds, a guide to allow observers to learn how to find signs of life, if they are there," Kaltenegger said. "We are providing a template on how to find life on these worlds, if it exists."

Author: Blaine Friedlander | Source: Cornell University [December 04, 2019]



* This article was originally published here

Hubble Views Galaxy’s Dazzling Display













NASA - Hubble Space Telescope patch.

Dec. 13, 2019


NGC 3175 is located around 50 million light-years away in the constellation of Antlia (the Air Pump). The galaxy can be seen slicing across the frame in this image from the NASA/ESA Hubble Space Telescope, with its mix of bright patches of glowing gas, dark lanes of dust, bright core, and whirling, pinwheeling arms coming together to paint a beautiful celestial scene.

The galaxy is the eponymous member of the NGC 3175 group, which has been called a nearby analog for the Local Group. The Local Group contains our very own home galaxy, the Milky Way, and around 50 others — a mix of spiral, irregular and dwarf galaxies. The NGC 3175 group contains a couple of large spiral galaxies — the subject of this image and NGC 3137 — and numerous lower-mass spiral and satellite galaxies. Galaxy groups are some of the most common galactic gatherings in the cosmos, and they comprise 50 or so galaxies all bound together by gravity.

This image comprises observations from Hubble’s Wide Field Camera 3.

Hubble Space Telescope (HST)

For more information about Hubble, visit:

http://hubblesite.org/

http://www.nasa.gov/hubble

http://www.spacetelescope.org/

Text Credits: ESA (European Space Agency)/NASA/Rob Garner/Image, Animation Credits: ESA/Hubble & NASA, D. Rosario et al.

Greetings, Orbiter.ch

* This article was originally published here

Production site of stone armour from Qinshihuang mausoleum discovered


A production site of the stone armour found in the Qinshihuang mausoleum was discovered in northwest China's Shaanxi Province, the Shaanxi Provincial Institute of Archaeology said Wednesday.

Production site of stone armour from Qinshihuang mausoleum discovered
Archaeological excavation at the Zhang Yuming site in the Qindu District of Xianyang, in China's
 northwest Shaanxi Province [Credit: Shaanxi Institute of Archaeology]


The site was found in a protection area in the Qindu District of Xianyang, with limestone unearthed that have the same characteristics as the stone armour of the mausoleum of the Emperor Qinshihuang of the Qin Dynasty (221 BC-207 BC), according to the institute.

Production site of stone armour from Qinshihuang mausoleum discovered
Stone fragments used in the production of the stone armour from the Qinshihuang mausoleum lying 
in situ at the Zhang Yuming site [Credit: China News]
Production site of stone armour from Qinshihuang mausoleum discovered
The stone fragments unearthed at the Zhang Yuming site have the same characteristics as the stone armour 
from the mausoleum of the Emperor Qinshihuang of the Qin Dynasty (221 BC-207 BC)
 [Credit: Shaanxi Institute of Archaeology]


Production site of stone armour from Qinshihuang mausoleum discovered
Threaded copper bars and iron tools unearthed at the Zhang Yuming in the Qindu District
of Xianyang 
[Credit: Shaanxi Institute of Archaeology]
Production site of stone armour from Qinshihuang mausoleum discovered
An archaeologist shows a fragment of stone armour found at the Zhang Yuming site 
[Credit: Xinhua/Li Yibo]


Ash pits, a house base, ditches and stone ash stacks were found at the site of over 100 square metres, as well as materials to make armour such as stones, workpieces and waste products and tools such as iron awls, drills and knives.

Production site of stone armour from Qinshihuang mausoleum discovered
Stone armour unearthed from the funeral pit of Qin Shihuang's Mausoleum
[Credit: Xian News]
A burial pit of stone armour of the Qinshihuang mausoleum was found in 1998, and a well which is believed to be one of the production bases of the stone armour was discovered in 2001, about 4.5 km north of the mausoleum, said Xu Weihong, a research of the institute.

Such remains were seen by researchers again in July this year in the area, which is 40 km away from the mausoleum, Xu added.

The new site has expanded the sources of burial items of the mausoleum and provides new materials for studying the functions of the northern part of the area, Xu said.

Source: Xinhua News Agency [December 05, 2019]



* This article was originally published here

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