Present technology does not enable us to view images of these kilometer-sized infalling bodies, but the evaporation of gaseous products liberated from exocomets that occurs close to a star can potentially cause small disruptions in the ambient circumstellar disk plasma. For circumstellar disks that are viewed “edge-on” this evaporating material may be directly observed through transient (night-to-night and hour-to-hour) gas absorption features seen at rapidly changing velocities.
Using high resolution spectrographs mounted to large aperture ground-based telescopes, we have discovered 15 young stars that harbor swarms of exocomets. In this lecture we briefly describe the physical attributes of comets in our own solar system and the instrumental observing techniques to detect the presence of evaporating exocomets present around stars with ages in the 10 – 100 Myr range.
We note that this work has particular relevance to the dramatic fluctuations in the flux recorded towards “Tabby’s star” by the NASA Kepler Mission, that may be explained through the piling up of swarms of exocomets in front of the central star.
Here is an interview with Chris Lewicki, chief of the asteroid mining company Planetary Resources:
As Humans venture out far away from the Earth into the solar system, they will need material resources to keep us going. Where do we get those from? One for-profit company, Planetary Resources, wants to be the one to make it happen.
We had a chance to speak with the company’s President and CEO, Chris Lewicki about the company’s plans to survey, prospect, and exploit near-Earth asteroids. The company has a lot of financial backing and has plans to send its first satellite to an asteroid in 2020.
This interview was originally broadcast as part of our ongoing Facebook Live segment, The Convo: www.facebook.com/PCMag/videos…
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Jason Dunn, CTO of Made In Space, talks about the role of 3d printing in space development:
NASA intern turned Silicon Valley entrepreneur, Jason Dunn, saw what was holding humans back from colonizing outer space…and decided to do something about it. With his company Made in Space’s cutting-edge 3D printer, astronauts can break their reliance on costly resupply missions from Earth and—for the first time ever—build new supplies for themselves in space. Dunn and his team believe their invention will usher in a new era of dramatic progress in space.
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Craig Clark, CEO of Clyde Space in Scotland, talks about their smallsat projects:
Comet landing site: Sequence of images captured by Rosetta during its descent to the surface of Comet 67P/C-G on 30 September.
ESA’s historic Rosetta mission has concluded as planned, with the controlled impact onto the comet it had been investigating for more than two years.
Confirmation of the end of the mission arrived at ESA’s control centre in Darmstadt, Germany at 11:19 GMT (13:19 CEST) with the loss of Rosetta’s signal upon impact.
Rosetta carried out its final manoeuvre last night at 20:50 GMT (22:50 CEST), setting it on a collision course with the comet from an altitude of about 19 km. Rosetta had targeted a region on the small lobe of Comet 67P/Churyumov–Gerasimenko, close to a region of active pits in the Ma’at region.
The descent gave Rosetta the opportunity to study the comet’s gas, dust and plasma environment very close to its surface, as well as take very high-resolution images.
Pits are of particular interest because they play an important role in the comet’s activity. They also provide a unique window into its internal building blocks.
The information collected on the descent to this fascinating region was returned to Earth before the impact. It is now no longer possible to communicate with the spacecraft.
This video shows the trajectory that led the spacecraft into the comet:
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Here is a video preview of Rosetta’s final act from TMRO.tv:
TMRO Astronomer Jared Head gives us a review of the incredible Rosetta mission from the European Space Agency, and then gives us a preview of what to expect in it’s final days ahead at the end of the mission.
The European Space Agency’s Rosetta mission to the Comet 67P/Churyumov-Gerasimenko will end soon with the spacecraft touching down onto the icy rock sometime around September 29-30, 2016.
This video animation of Rosetta’s mission end was created with BINARY SPACE’s SpaceTraveller™, “the ultimate Solar System & Space Missions Simulator”:
The SpaceTraveller™ is a 3D Solar System & Space Missions Simulator designed for the Microsoft® Windows® platform (Microsoft® Windows® 7 or higher only). Download it and have a try for free: http://www.binary-space.com/products….
A lonely 3-mile-high (5-kilometer-high) mountain on Ceres is likely volcanic in origin, and the dwarf planet may have a weak, temporary atmosphere. These are just two of many new insights about Ceres from NASA’s Dawn mission published this week in six papers in the journal Science.
Ceres’ lonely mountain, Ahuna Mons, is seen in this simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Images taken using blue (440 nanometers), green (750 nanometers) and infrared (960 nanometers) spectral filters were combined to create the view. The spacecraft’s framing camera took the images from Dawn’s low-altitude mapping orbit, from an altitude of 240 miles (385 kilometers) in August 2016. The resolution of the component images is 120 feet (35 meters) per pixel.Chris Russell, principal investigator of the Dawn mission, based at the University of California, Los Angeles, said
“Dawn has revealed that Ceres is a diverse world that clearly had geological activity in its recent past”
Ahuna Mons as a Cryovolcano
Ahuna Mons is a volcanic dome unlike any seen elsewhere in the solar system, according to a new analysis led by Ottaviano Ruesch of NASA’s Goddard Space Flight Center, Greenbelt, Maryland, and the Universities Space Research Association. Ruesch and colleagues studied formation models of volcanic domes, 3-D terrain maps and images from Dawn, as well as analogous geological features elsewhere in our solar system. This led to the conclusion that the lonely mountain is likely volcanic in nature. Specifically, it would be a cryovolcano — a volcano that erupts a liquid made of volatiles such as water, instead of silicates.
“This is the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past,” Ruesch said.
A surprising finding emerged in the paper led by Russell: Dawn may have detected a weak, temporary atmosphere. Dawn’s gamma ray and neutron (GRaND) detector observed evidence that Ceres had accelerated electrons from the solar wind to very high energies over a period of about six days. In theory, the interaction between the solar wind’s energetic particles and atmospheric molecules could explain the GRaND observations.
A temporary atmosphere would be consistent with the water vapor the Herschel Space Observatory detected at Ceres in 2012-2013. The electrons that GRaND detected could have been produced by the solar wind hitting the water molecules that Herschel observed, but scientists are also looking into alternative explanations.
“We’re very excited to follow up on this and the other discoveries about this fascinating world,” Russell said.
Ceres: Between a Rocky and Icy Place
While Ahuna Mons may have erupted liquid water in the past, Dawn has detected water in the present, as described in a study led by Jean-Philippe Combe of the Bear Fight Institute, Winthrop, Washington. Combe and colleagues used Dawn’s visible and infrared mapping spectrometer (VIR) to detect probable water ice at Oxo Crater, a small, bright, sloped depression at mid-latitudes on Ceres.
The small, bright crater Oxo (6 miles, 10 kilometers wide) on Ceres is seen in this perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Dawn’s visible and infrared mapping spectrometer (VIR) has found evidence of water ice at this crater. The results were published in the journal Science in Sept. 2016. Images taken using blue (440 nanometers), green (750 nanometers) and infrared (960 nanometers) spectral filters were combined to create the view. The spacecraft’s framing camera took the images from Dawn’s low-altitude mapping orbit, from an altitude of 240 miles (385 kilometers) in August 2016. The resolution of the component images is 120 feet (35 meters) per pixel.Exposed water-ice is rare on Ceres, but the low density of Ceres, the impact-generated flows and the very existence of Ahuna Mons suggest that Ceres’ crust does contain a significant component of water-ice. This is consistent with a study of Ceres’ diverse geological features led by Harald Hiesinger of the Westfälische Wilhelms-Universität, Münster, Germany. The diversity of geological features on Ceres is further explored in a study led by Debra Buczkowski of the Johns Hopkins Applied Physics Laboratory, Laurel, Maryland.
Impact craters are clearly the most abundant geological feature on Ceres, and their different shapes help tell the intricate story of Ceres’ past. Craters that are roughly polygonal — that is, shapes bounded by straight lines — hint that Ceres’ crust is heavily fractured. In addition, several Cerean craters have patterns of visible fractures on their floors.
Some, like tiny Oxo, have terraces, while others, such as the large Urvara Crater (106 miles, 170 kilometers wide), have central peaks. There are craters with flow-like features, and craters that imprint on other craters, as well as chains of small craters. Bright areas are peppered across Ceres, with the most reflective ones in Occator Crater. Some crater shapes could indicate water-ice in the subsurface.
The dwarf planet’s various crater forms are consistent with an outer shell for Ceres that is not purely ice or rock, but rather a mixture of both — a conclusion reflected in other analyses. Scientists also calculated the ratio of various craters’ depths to diameters, and found that some amount of crater relaxation must have occurred. Additionally, there are more craters in the northern hemisphere of Ceres than the south, where the large Urvara and Yalode craters are the dominant features.
“The uneven distribution of craters indicates that the crust is not uniform, and that Ceres has gone through a complex geological evolution,” Hiesinger said.
Distribution of Surface Materials
What are the rocky materials in Ceres’ crust? A study led by Eleonora Ammannito of the University of California, Los Angeles, finds that clay-forming minerals called phyllosilicates are all over Ceres. These phyllosilicates are rich in magnesium and also have some ammonium embedded in their crystalline structure. Their distribution throughout the dwarf planet’s crust indicates Ceres’ surface material has been altered by a global process involving water.
Although Ceres’ phyllosilicates are uniform in their composition, there are marked differences in how abundant these materials are on the surface. For example, phyllosilicates are especially prevalent in the region around the smooth, “pancake”-like crater Kerwan (174 miles, 280 kilometers in diameter), and less so at Yalode Crater (162 miles, 260 kilometers in diameter), which has areas of both smooth and rugged terrain around it. Since Kerwan and Yalode are similar in size, this may mean that the composition of the material into which they impacted may be different. Craters Dantu and Haulani both formed recently in geologic time, but also seem to differ in composition.
“In comparing craters such as Dantu and Haulani, we find that their different material mixtures could extend beneath the surface for miles, or even tens of miles in the case of the larger Dantu,” Ammannito said.
Looking Higher
Now in its extended mission, the Dawn spacecraft has delivered a wealth of images and other data from its current perch at 240 miles (385 kilometers) above Ceres’ surface, which is closer to the dwarf planet than the International Space Station is to Earth. The spacecraft will be increasing its altitude at Ceres on Sept. 2, as scientists consider questions that can be examined from higher up.
Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit: http://dawn.jpl.nasa.gov/mission
More information about Dawn is available at the following sites:
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