Ahuna Mons is a volcano that rises 13,000 feet high and spreads 11 miles wide at its base. This would be impressive for a volcano on Earth. But Ahuna Mons stands on Ceres, a dwarf planet less than 600 miles wide that orbits the sun between Mars and Jupiter. Even stranger, Ahuna Mons isn't built from lava the way terrestrial volcanoes are — it's built from ice.

"Ahuna is the one true 'mountain' on Ceres," said David A. Williams, associate research professor in Arizona State University's School of Earth and Space Exploration. "After studying it closely, we interpret it as a dome raised by cryovolcanism." Volcanic dome Ahuna Mons rises above a foreground impact crater, as seen by NASA's Dawn spacecraft with no vertical exaggeration. Eruptions of salty, muddy water built the mountain by repeated eruptions, flows and freezing. Streaks from falls of rocks and debris run down its flanks, while overhead views show fracturing across its summit.

This is a form of low-temperature volcanic activity, where molten ice — water, usually mixed with salts or ammonia — replaces the molten silicate rock erupted by terrestrial volcanoes. Giant mountain Ahuna is a volcanic dome built from repeated eruptions of freezing salty water.

Williams is part of a team of scientists working with NASA's Dawn mission who have published papers in the journal Science this week. His specialty is volcanism, and that drew him to the puzzle of Ahuna Mons.

"Ahuna is truly unique, being the only mountain of its kind on Ceres," he said. "It shows nothing to indicate a tectonic formation, so that led us to consider cryovolcanism as a method for its origin."

Dawn scientist Ottaviano Ruesch, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, is the lead author on the Science paper about Ceres volcanism. He says, "This is the only known example of a cryovolcano that potentially formed from a salty mud mix, and which formed in the geologically recent past."

Williams explained that "Ahuna has only a few craters on its surface, which points to an age of just couple hundred million years at most."

According to the Dawn team, the implications of Ahuna Mons being volcanic in origin are enormous. It confirms that although Ceres' surface temperature averages almost 40° (Celsius or Fahrenheit; the scales converge at this temperature), its interior has kept warm enough for liquid water or brines to exist for a relatively long period. And this has allowed volcanic activity at the surface in recent geological time.

Ahuna Mons is not the only place where icy volcanism happens on Ceres. Dawn's instruments have spotted features that point to cryovolcanic activity that resurfaces areas rather than building tall structures. Numerous craters, for example, show floors that appear flatter than impacts by meteorites would leave them, so perhaps they have been flooded from below. In addition, such flat-floored craters often show cracks suggesting that icy "magma" has pushed them upward, then subsided.

A few places on Ceres exhibit a geo-museum of features. "Occator Crater has several bright spots on its floor," said Williams. "The central spot contains what looks like a cryovolcanic dome, rich in sodium carbonates." Other bright spots, he says, occur over fractures that suggest venting of water vapor mixed with bright salts.

"As the vapor has boiled away," he explained, "it leaves the bright 1salts and carbonate minerals behind. "

Dawn's Framing Camera looks down on the fractured summit of Ahuna Mons, tallest mountain on dwarf planet Ceres. The cracks on top suggest Ahuna grew by inflation: Icy freezing water pushed up inside the mountain, making a dome. 

Researchers draped a digital terrain model over a shaded image of Ahuna, placing contour lines at 100-meter (330-foot) elevation intervals. Key spot elevations are shown in meters.

The geological map of the major units at Ahuna Mons will be filled in with more details as scientists continue to study this small world shaped by icy volcanism.
Photo courtesy of Dawn Science Team and NASA/JPL-Caltech/GSFC

Although volcanic-related features appear across the surface of Ceres, for scientists perhaps the most interesting aspect is what these features say about the interior of the dwarf world. Dawn observations suggest that Ceres has an outer shell that's not purely ice or rock, but rather a mixture of both.

Recently, Williams was involved in research that discovered that large impact craters are missing, presumably erased by internal heat, but smaller craters are preserved.

"This shows that Ceres' crust has a variable composition — it's weak at large scales but strong at smaller scales," he said. "It has also evolved geologically."

In the big picture, said Williams, "Ceres appears differentiated internally, with a core and a complex crust made of 30 to 40 percent water ice mixed with silicate rock and salts." And perhaps pockets of brine still exist in its interior.

"We need to continue studying the data to better understand the interior structure of Ceres," said Williams.

Ceres is the second port of call for the Dawn mission, which was launched in 2007 and visited another asteroid, Vesta, from 2011 to 2012. The spacecraft arrived at Ceres in March 2015. It carries a suite of cameras, spectrometers and gamma-ray and neutron detectors. These were built to image, map and measure the shape and surface materials of Ceres, and they collect information to help scientists understand the history of these small worlds and what they can tell us of the solar system's birth.

NASA plans for Dawn to continue orbiting Ceres and collecting data for another year or so. The dwarf planet is slowly moving toward its closest approach to the sun, called perihelion, which will come in April 2018. Scientists expect that the growing solar warmth will produce some detectable changes in Ceres' surface or maybe even trigger volcanic activity.

"We hope that by observing Ceres as it approaches perihelion, we might observe some active venting. This would be an ideal way to end the mission," said Williams.

The Daily Galaxy via Arizona State University

Image credits: Courtesy of Dawn Science Team and NASA/JPL-Caltech/GSFC

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Scientists are exploring are proposing transplanting life to planets outside our solar system that are not permanently inhabitable. a Genesis mission could be achieved within a few decades with the aid of interstellar unmanned micro-spacecraft that could be accelerated and slowed down passively. On arrival, an automated gene laboratory on board the probe would synthesize a selection of single-cell organisms with the aim of establishing an ecosphere of unicellular organisms on the target planet. This could subsequently develop autonomously into complex life forms.

In recent years, the search for exoplanets has identified very different types. "It is therefore certain that we will discover a large number of exoplanets that are inhabitable intermittently but not permanently. Life would, indeed, be possible on these planets, but it would not have the time to grow and develop independently," says Claudius Gros from the Institute of Theoretical Physics at Goethe University Frankfurt.

"In this way, we could jump the approximately four billion years that had been necessary on Earth to reach the Precambrian stage of development out of which the animal world developed about 500 million years ago," explains Gros. In order not to endanger any life that might already be present, Genesis probes would only head for uninhabited exoplanets.

The mission's actual duration played no role in the Genesis project, since the time scales for the subsequent geo-evolutionary development of the target planet lies in the range between a few tens of millions and a hundred million years.

The Genesis project therefore has no direct benefit for people on Earth. "It would, however, enable us to give life something back," says Gros. In this context, he is also discussing whether biological incompatibilities would have to be expected in the case of colonization of a second Earth fully developed in terms of evolution. "That seems at present to be highly unlikely," says the physicist, dampening any excessive expectations.

The image at the top of the page is artist's conception depicting an Earth-like planet orbiting an evolved star that has formed a stunning planetary nebula. Earlier in its life, this planet may have been like one of the eight newly discovered worlds orbiting in the habitable zones of their stars.  David A. Aguilar (CfA)

More information: Claudius Gros; Developing Ecospheres on Transiently Habitable Planets: The Genesis Project; Astrophysics and Space Science (in press); DOI: arxiv.org/abs/1608.06087

The Daily Galaxy via Goethe University Frankfurt am Main

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Two years ago, the XMM-Newton X-ray satellite radioed data back to Earth which fired up great hopes with astrophysicists. It had picked up weak radiation from several galaxy clusters at an energy of around 3.5 kiloelectronvolts (keV) which the researchers were not immediately able to explain with the aid of the known X-ray spectra.

Speculation quickly arose that they could be signals of decaying particles of dark matter this would have been the first concrete trace of the long-sought form of matter. Hope was soon dampened, however: The regions in which XMM-Newton observed the X-ray radiation did not match the spatial distribution which astrophysical analyses predicted for dark matter.

In addition, there are still a large number of physical processes for which astronomers do not know the corresponding fingerprints in X-ray spectra, and so cannot yet be excluded as the possible cause of the mysterious signal. Fact is, the spectral data in the collection of tables which researchers use to evaluate astronomical spectra are still incomplete. They are sometimes based on theoretical assumptions and are correspondingly unreliable.

In order to help answering this question, physicists at the Max Planck Institute for Nuclear Physics in Heidelberg checked an alternative explanation. Accordingly, the search for this form of matter, which is difficult to detect, must go on, as the mysterious X-ray signal seems to originate from highly charged sulfur ions that capture electrons from hydrogen atoms.

Highly charged ions can frequently be found between the galaxies. Physicists working with José Crespo, leader of a research group at the Max Planck Institute for Nuclear Physics, have now closed one gap in the X-ray data with their experiments. According to computations done by researchers from SRON, Netherlands Institute for Space Research, the mysterious line could be caused by bare sulfur nuclei (S16+), i.e. sulfur atoms that have lost all their electrons, each of which picks up one electron from a hydrogen atom.

Highly charged ions can often be found in the hot medium between the galaxies of a cluster, and sufficient completely ionized sulfur is present as well. “Explained in illustrative terms, the charge exchange operates like this,” says José Crespo in explanation of the process: “The high charge of the S16+ ion sort of sucks in the electron of the H atom. It then releases energy in the form of X-rays.”

The physicists used an electron beam ion trap for the measurements. First, they injected an extremely thin beam of a volatile sulfur compound into the vacuum of the apparatus. The electrons with which they then bombarded the molecules fragmented the molecules and knocked the electrons out of the atoms how many depends on the energy of the electron beam. They can thus specifically produce the highly charged sulfur ions desired.

The researchers then switched off the electron beam for a few seconds in order to be able to observe how bare sulfur ions suck electrons from molecules which have not yet been destroyed. The electrons initially have a large amount of energy when they are captured by the S16+ ions, but release this energy in the form of X-rays. The most energetic of these emissions was at around 3.47 kiloelectronvolts i.e. quite near the mysterious line which XMM-Newton had recorded.

“In order to support our interpretation, our colleagues from the Netherlands have carried out model computations on the charge exchange, and they can explain our data very well,” says Chintan Shah, who made crucial contributions to the experiments.

The fact that the bare sulfur ions removed the electrons from intact molecules of the volatile sulfur compound and not from hydrogen atoms in the experiments carried out in Heidelberg, is not important for the X-ray spectrum, as X-rays are only generated when the electrons in the sulfur lose energy.

“If the inaccuracies of the astrophysical measurements and the experimental uncertainties are taken into account, it becomes clear that the charge exchange between bare sulfur and hydrogen atoms can outstandingly explain the mysterious signal at around 3.5 keV,” explains José Crespo, in summary of the result. The search for dark matter must therefore go on.

The image at the top of the page shows 1/1000 of a Bolshoi cosmological simulation, zooming in on a region centered on the dark matter halo of a very large cluster of galaxies. (NASA Ames Research Center)

The Daily Galaxy via Max Planck Institute

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