Touchdown! Rosetta’s Philae probe lands on comet

Still image from animation of Philae separating from Rosetta and descending to the surface of comet 67P/Churyumov-Gerasimenko in November 2014. Credit: ESA/ATG medialab

ESA's Rosetta mission has soft-landed its Philae probe on a comet, the first time in history that such an extraordinary feat has been achieved.

After a tense wait during the seven-hour descent to the surface of Comet 67P/Churyumov-Gerasimenko, the signal confirming the successful touchdown arrived on Earth at 16:03 GMT (17:03 CET).

The confirmation was relayed via the Rosetta orbiter to Earth and picked up simultaneously by ESA's ground station in Malargüe, Argentina and NASA's station in Madrid, Spain. The signal was immediately confirmed at ESA's Space Operations Centre, ESOC, in Darmstadt, and DLR's Lander Control Centre in Cologne, both in Germany.

The first data from the lander's instruments were transmitted to the Philae Science, Operations and Navigation Centre at France's CNES space agency in Toulouse.

"Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet's surface," noted Jean-Jacques Dordain, ESA's Director General.

"With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today."

"After more than 10 years travelling through space, we're now making the best ever scientific analysis of one of the oldest remnants of our Solar System," said Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"Decades of preparation have paved the way for today's success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration."

"We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander," said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

"In the next hours we'll learn exactly where and how we've landed, and we'll start getting as much science as we can from the surface of this fascinating world."

Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.

"Rosetta's journey has been a continuous operational challenge, requiring an innovative approach, precision and long experience," said Thomas Reiter, ESA Director of Human Spaceflight and Operations.

"This success is testimony to the outstanding teamwork and the unique knowhow in operating spacecraft acquired at the European Space Agency over the decades."

The landing site, named Agilkia and located on the head of the bizarre double-lobed object, was chosen just six weeks after arrival based on images and data collected at distances of 30-100 km from the comet. Those first images soon revealed the comet as a world littered with boulders, towering cliffs and daunting precipices and pits, with jets of gas and dust streaming from the surface.

Following a period spent at 10 km to allow further close-up study of the chosen landing site, Rosetta moved onto a more distant trajectory to prepare for Philae's deployment.

Five critical go/no-go decisions were made last night and early this morning, confirming different stages of readiness ahead of separation, along with a final preseparation manoeuvre by the orbiter.

Deployment was confirmed at 09:03 GMT (10:03 CET) at a distance of 22.5km from the centre of the comet. During the seven-hour descent, which was made without propulsion or guidance, Philae took images and recorded information about the comet's environment.

"One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander's descent trajectory," said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.

"Furthermore, we're performing these operations in an environment that we've only just started learning about, 510 million kilometres from Earth."

Touchdown was planned to take place at a speed of around 1 m/s, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.

At the same time, two harpoons fired and locked the probe onto the surface.

But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface. The conditions of landing -- including whether or not the thruster performed -- along with the exact location of Philae on the comet are being analysed.

The first images from the surface are being downlinked to Earth and should be available within a few hours of touchdown.

Over the next 2.5 days, the lander will conduct its primary science mission, assuming that its main battery remains in good health. An extended science phase using the rechargeable secondary battery may be possible, assuming Sun illumination conditions allow and dust settling on the solar panels does not prevent it. This extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.

Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet's surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.

The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.

The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the orbiter covering the whole comet.

"Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?" said Matt Taylor, ESA Rosetta project scientist.

"Today's successful landing is undoubtedly the cherry on the icing of a 4 km-wide cake, but we're also looking further ahead and onto the next stage of this ground-breaking mission, as we continue to follow the comet around the Sun for 13 months, watching as its activity changes and its surface evolves."

While Philae begins its close-up study of the comet, Rosetta must manoeuvre from its post-separation path back into an orbit around the comet, eventually returning to a 20 km orbit on 6 December.

Next year, as the comet grows more active, Rosetta will need to step further back and fly unbound 'orbits', but dipping in briefly with daring flybys, some of which will bring it within just 8 km of the comet centre.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow it throughout the remainder of 2015, as they head away from the Sun and activity begins to subside.

"It's been an extremely long and hard journey to reach today's once-in-a-lifetime event, but it was absolutely worthwhile. We look forward to the continued success of the great scientific endeavour that is the Rosetta mission as it promises to revolutionise our understanding of comets," said Fred Jansen, ESA Rosetta mission manager.

More about Rosetta

Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta is the first mission in history to rendezvous with a comet. It is escorting the comet as they orbit the Sun together, and has deployed a lander to its surface.Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission should become the key to unlocking the history and evolution of our Solar System.

Source: European Space Agency

Still hot inside the Moon: Tidal heating in the deepest part of the lunar mantle

This is an artist's conception of internal structure of the Moon based on this science result.
Credit: Image courtesy of National Astronomical Observatory of Japan

An international research team, led by Dr. Yuji Harada from Planetary Science institute, China University of Geosciences, has found that there is an extremely soft layer deep inside the Moon and that heat is effectively generated in the layer by the gravity of Earth.

The results were derived by comparing the deformation of the Moon as precisely measured by Kaguya (SELENE, Selenological and Engineering Explorer) and other probes with theoretically calculated estimates. These findings suggest that the interior of the Moon has not yet cooled and hardened, and also that it is still being warmed by the effect of Earth on the Moon. This research provides a chance to reconsider how both Earth and the Moon have been evolving since their births through mutual influence until now.

When it comes to clarifying how a celestial body like a planet or a natural satellite is born and grows, it is necessary to know as precisely as possible its internal structure and thermal state. How can we know the internal structure of a celestial body far away from us? We can get clues about its internal structure and state by thoroughly investigating how its shape changes due to external forces. The shape of a celestial body being changes by the gravitational force of another body is called tide. For example, the ocean tide on Earth is one tidal phenomenon caused by the gravitational force between the Moon and the Sun, and Earth. Sea water is so deformable that its desplacement can be easily observed. How much a celestial body can be deformed by tidal force, in this way, depends on its internal structure, and especially on the hardness of its interior. Conversely, it means that observing the degree of deformation enables us to learn about the interior, which is normally not directly visible to the naked eye.

The Moon is no exception; we can learn about the interior of our natural satellite from its deformation caused by the tidal force of Earth. The deformation has already been well known through several geodetic observations (*1). However, models of the internal structure of the Moon as derived from past research could not account for the deformation precisely observed by the above lunar exploration programs.

Therefore, the research team performed theoretical calculations to understand what type of internal structure of the Moon leads to the observed change of the lunar shape.
What the research team focused on is the structure deep inside the Moon. During the Apollo program, seismic observations (*2) were carried out on the Moon. One of the analysis results concerning the internal structure of the Moon based upon the seismic data indicates that the satellite is considered to consist mainly of two parts: the "core," the inner portion made up of metal, and the "mantle," the outer portion made up of rock. The research team has found that the observed tidal deformation of the Moon can be well explained if it is assumed that there is an extremely soft layer in the deepest part of the lunar mantle. The previous studies indicated that there is the possibility that a part of the rock at the deepest part inside the lunar mantle may be molten. This research result supports the above possibility since partially molten rock becomes softer. This research has proven for the first time that the deepest part of the lunar mantle is soft, based upon the agreement between observation results and the theoretical calculations.

Furthermore, the research team also clarified that heat is efficiently generated by the tides in the soft part, deepest in the mantle. In general, a part of the energy stored inside a celestial body by tidal deformation is changed to heat. The heat generation depends on the softness of the interior. Interestingly, the heat generated in the layer is expected to be nearly at the maximum when the softness of the layer is comparable to that which the team estimated from the above comparison of the calculations and the observations. This may not be a coincidence. Rather, the layer itself is considered to be maintained as the amount of the heat generated inside the soft layer is exquisitely well balanced with that of the heat escaping from the layer. Whereas previous research also suggests that some part of the energy inside the Moon due to the tidal deformation is changed to heat, the present research indicates that this type of energy conversion does not uniformly occur in the entire Moon, but only intensively in the soft layer. The research team believes that the soft layer is now warming the core of the Moon as the core seems to be wrapped by the layer, which is located in the deepest part of the mantle, and which efficiently generates heat. They also expect that a soft layer like this may efficiently have warmed the core in the past as well.

Concerning the future outlook for this research, Dr. Yuji Harada, the principle investigator of the research team, said, "I believe that our research results have brought about new questions. For example, how can the bottom of the lunar mantle maintain its softer state for a long time? To answer this question, we would like to further investigate the internal structure and heat-generating mechanism inside the Moon in detail. In addition, another question has come up: how has the conversion from the tidal energy to the heat energy in the soft layer affected the motion of the Moon relative to the Earth, and also the cooling of the Moon? We would like to resolve those problems as well so that we can thoroughly understand how the Moon was born and has evolved."

Another investigator, Prof. Junichi Haruyama of Institute of Space and Aeronautical Science, Japan Aerospace Exploration Agency, mentioned the significance of this research, saying, "A smaller celestial body like the Moon cools faster than a larger one like the Earth does. In fact, we had thought that volcanic activities on the Moon had already come to a halt. 

Therefore, the Moon had been believed to be cool and hard, even in its deeper parts. However, this research tells us that the Moon has not yet cooled and hardened, but is still warm. It even implies that we have to reconsider the question as follows: How have the Earth and the Moon influenced each other since their births? That means this research not only shows us the actual state of the deep interior of the Moon, but also gives us a clue for learning about the history of the system including both the Earth and the Moon."

The scientific paper on which this article is based appears in the Nature Geoscience.

Strong tidal heating in an ultralow-viscosity zone at the core-mantle boundary of the Moon.
Note:
*1: Geodetic observation. (This is also called "selenodetic" observation as it is for the Moon.)
Observational results on gravity and rotation of the Moon are used in this research. Precise measurements of the lunar gravity and rotation enable us to know how our natural satellite is deformed by tidal forces.

The gravity of the Moon can be measured by tracking the motion of a satellite orbiting the Moon. This is because the motion of the satellite is influenced by lunar gravity. The motion of the satellite orbiting the Moon can be determined by using radio waves between the Earth and the satellite, and between multiple satellites around the Moon. The gravity of the Moon changes when it deforms due to tidal forces. The change in gravity caused by the lunar deformation due to the tidal force is extremely small, but when the change in location of the orbiter can be determined precisely enough, it is possible to accurately detect the change in lunar gravity caused by the deformation due to the tidal force. During the last several years, the degree of the lunar deformation caused by the tidal forces has been determined by several orbiters, for example, Kaguya from Japan, Chang'e-1 from China, and Lunar Reconnaissance Orbiter (LRO) and Gravity Recovery and Interior Laboratory (GRAIL) from the USA.

The rotation of the Moon can be observed by monitoring the change in position of a kind of mirror placed in several locations on the lunar surface. The same side of the Moon is almost always facing the Earth, but strictly speaking, it changes by a slight amount according to the lunar orbit around the Earth. This means that the locations of the mirrors with respect to the Earth also changes over time. If this change in position is precisely measured, it can also be determined how the direction of the lunar axis changes. This slight change of direction also depends on the deformation caused by the tidal force. It can be seen, therefore, how the Moon deforms due to the tidal force once the change in the axis is measured precisely. Some of the above-mentioned mirrors have been left on the surface of the Moon in the framework of the lunar exploration programs led by the USA or the former USSR several decades ago, such as the Apollo program. The degree of change in the location of each mirror on the Moon can be determined by using laser beams emitted from the Earth. This experiment still continues to be carried out even today.

*2: Seismic observation. (Quakes on the Moon are also called "moonquakes." )

There are seismic activities not only on the Earth, but also on the Moon. As part of the Apollo program in the past, seismometers were placed on the lunar surface for seismological measurements. Waves induced by quakes measured with seismometers suggest what the internal structure of a celestial body is like. The behavior of the seismic waves is very important for understanding how the hardness inside the celestial body will change in accordance with the depth. In particular, the present research considered the following two previous analysis results in order to theoretically calculate the lunar deformation caused by the tidal force.

The first one is the existence of the area deep inside the Moon where the seismic waves become drastically weaker. It is generally known that the energy of the seismic waves tends to reduce more in softer solids, especially when they contain liquids. Therefore, the deepest part of the lunar mantle is softer than the shallower part. Also, a portion of the rocks is thought to be melted.

The second one is the existence of areas deep inside the Moon whose interfaces reflect the 
seismic waves. Three boundaries are considered to exist. Two of them are like the ones in the Earth: one separating the solid inner core and the liquid outer core, and the other one separating the outer core and the mantle. The last boundary is considered to correspond to the one in the mantle separating the solid area and the partially molten area mentioned above.

Source: National Astronomical Observatory of Japan

Moon mission: Images of LADEE's impact crater captured

LRO has imaged the LADEE impact site on the eastern rim of Sundman V crater. The image was created by ratioing two images, one taken before the impact and another afterwards. The bright area highlights what has changed between the time of the two images, specifically the impact point and the ejecta. Credit: NASA/Goddard/Arizona State University

NASA'S Lunar Reconnaissance Orbiter (LRO) spacecraft has spied a new crater on the lunar surface; one made from the impact of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) mission.

"The Lunar Reconnaissance Orbiter Camera (LROC) team recently developed a new computer tool to search Narrow Angle Camera (NAC) before and after image pairs for new craters, the LADEE impact event provided a fun test, said Mark Robinson, LROC principal investigator from Arizona State University in Tempe. "As it turns there were several small surface changes found in the predicted area of the impact, the biggest and most distinctive was within 968 feet (295 meters) of the spot estimated by the LADEE operations team. What fun!"

The LADEE mission ended on April 18, 2014, with the spacecraft's planned impact into the eastern rim of Sundman V crater on the far side of the moon.

LRO has imaged the LADEE impact site on the eastern rim of Sundman V crater. The image was created by ratioing two images, one taken before the impact and another afterwards. 

The bright area highlights what has changed between the time of the two images, specifically the impact point and the ejecta.

LADEE's engines fired April 11, 2014, to perform a final orbital maintenance maneuver and adjust to guarantee it would impact on the farside of the moon and away from the Apollo landing sites. Over a seven-day period, LADEE's orbit decreased and the spacecraft orbited very low to the surface and close to the walls of lunar craters and mountain ridges to give the team a chance to collect valuable science data. Finally, LADEE impacted the eastern rim of Sundman V crater on April 18. The impact site is about half a mile (780 meters) from the crater rim with an altitude of about 8,497 feet (2,590 meters) and was only about two tenths of a mile (300 meters) north of the location mission controllers predicted based on tracking data.

The impact crater is small, less than ten feet (three meters) in diameter, barely resolvable by the LROC NAC. The crater is small because the spacecraft -- compared to most celestial impacts -- was not traveling very fast, approximately 3,800 miles per hour (1,699 meters per second) and had a low mass and a low density. The size of the impact crater made it hard to identify among the myriad of small fresh craters on the lunar surface. Images acquired of the impact region before the impact, were compared with images obtained after the impact to identify the crater.

Since the NAC images are so large (250 mega-pixels) and the new crater is so small, the LROC team co-registered the before and after images (called a temporal pair) and then divided the before image by the after image. By doing this, changes to the surface become evident.

The ejecta from the impact forms a triangular pattern primarily downrange to the west, extending about 656-984 feet (200-300 meters) from the impact site. There is also a small triangular area of ejecta up range but it extends only about 66-98 feet (20-30 meters). The ejecta pattern is oriented northwest, consistent with the direction the spacecraft was traveling when it impacted the surface.

"I'm happy that the LROC team was able to confirm the LADEE impact point," said Butler Hine, LADEE project manager at Ames Research Center in Moffett Field, California. "It really helps the LADEE team to get closure and know exactly where the product of their hard work wound up."

LADEE launched Sept. 6, 2013 from Pad 0B at the Mid-Atlantic Regional Spaceport, at NASA's Wallops Flight Facility, Wallops Island, Virginia. LADEE gathered detailed information about the structure and composition of the thin lunar atmosphere and determining whether dust is being lofted into the lunar sky.

LRO launched September 18, 2009. LRO continues to bring the world astounding views of the lunar surface and a sizable collection of lunar data for research.

LRO recently received a second two-year extended mission. Under the extended mission, LRO will study the seasonal volatile cycle; determine how many small meteorites are currently hitting the moon and their effects; characterize the structure of the lunar regolith; investigate the moon's interaction with the space environment; and reveal more about the lunar interior using observations of the moon's surface.

"With LRO, NASA will study our nearest celestial neighbor for at least two more years," said John Keller, LRO project scientist from NASA's Goddard Space Flight Center in Greenbelt, Maryland. "LRO continues to increase our understanding of the moon and its environment."

Source: nasa

Every full moon, Landsat looks to the moon

Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting information on Earth.
Credit: NASA's Goddard Space Flight Center

Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting land-cover information of the sunny side of Earth below.

These monthly lunar scans are key to ensuring the land-imaging instrument aboard Landsat 8 is detecting light consistently. For this, engineers need a consistent source of light to measure. And while there are some spots on Earth -- like the Sahara Desert or other arid sites -- that reflect a relatively stable amount of light, nothing on our planet beats the moon, which lacks an atmosphere and has an unchanging surface, barring the odd meteorite.

We really wanted something we could trust for Landsat 8," said Brian Markham, leader of the calibration team for Landsat 8, which was built and launched by NASA and is now operated by the U.S. Geological Survey. "We do have Earth sites we look at for calibration. But the precision with which you can track things by using the Earth, because of the atmosphere, is not as good as the moon."

Landsat 8's Operational Land Imager, or OLI, collects information on the visible, near infrared and shortwave-infrared light reflecting off Earth's surface. Each wavelength of light provides information about the ground surface below. OLI has 14 detector modules, each of which contains hundreds of individual detectors that record different spectral bands. The calibration team at Goddard and the U.S. Geological Survey's EROS facility in South Dakota is tasked with making sure each of those detectors register light consistently over time.

Aboard the spacecraft, lamps provide light to calibrate OLl's detectors, but the lamps aren't perfect. On the Landsat 7 satellite, the lamps started to fade before the detectors did. Another option, solar diffusers, which use indirect sunlight, can darken as well.

"Everything else we've tried to use to monitor the stability of our instruments has often not been as good as the instruments themselves," Markham said. But the moon is a steady, not-too-bright light in the sky. "As long as we know what its illumination conditions are, we can trend our instrument performance to it because we trust its stability."

So Landsat 8 planners designed this latest satellite to image the moon as a baseline calibration. If, during these lunar tests, the OLI detectors indicate that the moon is getting slightly duller or brighter, then the Goddard scientists will know the instrument -not the moon -- is off. With that data, they can adjust the algorithms that calculate land cover information during Landsat's regular Earth-observation orbits.

It's a fairly complicated operation to scan the moon each month, said Susan Good, a flight dynamics engineer at Goddard who works with Landsat 8.

"There are 14 detector modules," Good said, "each of these has to scan the same path along the moon, so that you collect exactly the same data on each sensor."

The flight dynamics software determines precisely where the spacecraft will need to point during a lunar calibration. The timing is set for just after the moon is completely full. Then, as Landsat 8 passes over Antarctica and heads north in Earth's shadow, the spacecraft maneuvers to the precise location to start the first scan across the lunar surface.

It executes tiny and precise scans to take seven or eight passes across the moon -- each one angled so that a different detector is centered on the moon. This takes about 18 minutes, by which time the spacecraft has almost reached the Arctic. So it maneuvers back to point at 

Earth, and complete its day-lit imaging. Then, Landsat 8 pivots to face the moon again, completing additional passes to test the remaining detectors. After two orbits, the lunar calibration is complete.

In Landsat 8's first year, the lunar calibration tests show that the detectors are stable, Markham said, within a fraction of a percent. If the lunar calibrations and other tests show the detectors are off, the scientists can adjust the calculations that turn the raw Landsat data into information on land cover brightness, maintaining their accuracy.

Since the regular checks on Landsat 8's performance, Good jokes that she will never look at the full moon the same. "I think oh, we're having a lunar calibration," she said. "I always know what Landsat' 8's doing when the moon is full."

Source: Nasa

Solar photons drive water off the moon

Lunar sample in vacuum. A lunar sample in a ultra-high vacuum system is hit with ultraviolet (157 nm) photons to simulate conditions in space. Credit: Image courtesy of Georgia Institute of Technology

Water is thought to be embedded in the moon's rocks or, if cold enough, "stuck" on their surfaces. It's predominantly found at the poles. But scientists probably won't find it intact on the sunlit side.

New research at the Georgia Institute of Technology indicates that ultraviolet photons emitted by the sun likely cause H2O molecules to either quickly desorb or break apart. The fragments of water may remain on the lunar surface, but the presence of useful amounts of water on the sunward side is not likely.

The Georgia Tech team built an ultra-high vacuum system that simulates conditions in space, then performed the first-ever reported measurement of the water photodesorption cross section from an actual lunar sample. The machine zapped a small piece of the moon with ultraviolet (157 nm) photons to create excited states and watched what happened to the water molecules. They either came off with a cross section of ~ 6 x 10−19 cm2 or broke apart with a cross section of ~ 5 x 10−19 cm2.. According to the team's measurements, approximately one in every 1,000 molecules leave the lunar surface simply due to absorption of UV light.

Georgia Tech's cross section values can now be used by scientists attempting to find water throughout the solar system and beyond.

"The cross section is an important number planetary scientists, astrochemists and the astrophysics community need for models regarding the fate of water on comets, moons, asteroids, other airless bodies and interstellar grains," said Thomas Orlando, the Georgia Tech professor who led the study.

The number is relatively large, which establishes that solar UV photons are likely removing water from the moon's surface. This research, which was carried out primarily by former Georgia Tech Ph.D. student Alice DeSimone, indicates the cross sections increase even more with decreasing water coverage. That's why it's not likely that water remains intact as H2O on the sunny side of the moon. Orlando compares it to sitting outside on a summer day.

"If a lot of sunlight is hitting me, the probability of me getting sunburned is pretty high," said Orlando, a professor in the School of Chemistry and Biochemistry and School of Physics. "It's similar on the moon. There's a fixed solar flux of energetic photons that hit the sunlit surface, and there's a pretty good probability they remove water or damage the molecules."

The result, according to Orlando, is the release of molecules such as H2O, H2 and OH as well as the atomic fragments H and O. The research is published in two companion articles in the Journal of Geophysical Research: Planets. The first discusses the water photodesorption. The second paper details the photodissociation of water and the O(3PJ) formation on a lunar impact melt breccia.

Orlando is the associate director of Georgia Tech's Center for Space Technology and Research (C-STAR). C-STAR is an interdisciplinary research center that serves to organize, integrate and facilitate the impact of Georgia Tech's space science and space technology research activities. The center brings together a wide range of Georgia Tech faculty, active in space science and space technology research, and functions as the Institute's focal point for growth of the space industry in the state of Georgia.

Source: Georgia Institute of Technology

Water in moon rocks provides clues and questions about lunar history

This shows secondary electron image of pits left by ion microprobe analyses of a heterogeneous apatite grain in Apollo sample 14321, 1047. Water has now been detected in apatite in many different lunar rock types. Credit: Katharine L. Robinson, University of Hawaii, HIGP

A recent review of hundreds of chemical analyses of Moon rocks indicates that the amount of water in the Moon's interior varies regionally -- revealing clues about how water originated and was redistributed in the Moon. These discoveries provide a new tool to unravel the processes involved in the formation of the Moon, how the lunar crust cooled, and its impact history.

This is not liquid water, but water trapped in volcanic glasses or chemically bound in mineral grains inside lunar rocks. Rocks originating from some areas in the lunar interior contain much more water than rocks from other places. The hydrogen isotopic composition of lunar water also varies from region to region, much more dramatically than in Earth.

The present consensus is that the Moon formed as the result of a giant impact of an approximately Mars-sized planetesimal with the proto-Earth. The water in the Moon is a tracer of the processes that operated in the hot, partly silicate gas, partly magma disk surrounding Earth after that impact.

The source of the Moon's water has important implications for determining the source of Earth's water, which is vital to life. There are two options: either, water was inherited by the Moon from Earth during the Moon-forming impact, or it was added to the Moon later by comets or asteroids. It might also be a combination of these two processes.

"Basically, whatever happened to the Moon also happened to the Earth," said Katharine Robinson, lead author of the study and Graduate Assistant at the University of Hawai'i -- Mānoa (UHM) School of Ocean and Earth Science and Technology.

Robinson and Researcher G. Jeffrey Taylor, both at the UHM Hawai'i Institute of Geophysics and Planetology, compiled water measurements from lunar samples performed by colleagues from around the world, as well as their own. Specifically, they measured hydrogen and its isotope, deuterium (hydrogen with an extra neutron in its nucleus) with ion microprobes, which use a focused beam of ions to sputter ions from a small rock sample into a mass spectrometer. The ratio of hydrogen to deuterium can indicate the source of the water or trace magmatic processes in the lunar interior.

When water was first discovered in lunar samples in 2008, it was very surprising because from the time Apollo astronauts brought lunar samples, scientists thought that the Moon contained virtually no water.

"This was consistent with the idea that blossomed during the Origin of the Moon conference in Kona in 1984 -- that the Moon formed by a giant impact with the still-growing Earth, leading to extensive loss of volatile chemicals. Our work is surprising because it shows that lunar formation and accretion were more complex than previously thought," said Robinson.

The study of water in the Moon is still quite new, and many rocks have not yet been studied for water. The HIGP researchers have a new set of Apollo samples from NASA that they will be studying in the next few months, looking for additional clues about the early life of Earth and the Moon.

Source: University of Hawaii ‑ SOEST

First broadband wireless connection ... to the moon: Record-shattering Earth-to-Moon uplink

The ground terminal, with the sun reflecting off of the solar windows of the uplink telescopes, is shown. Credit: Robert LaFon, NASA/GSFC

If future generations were to live and work on the moon or on a distant asteroid, they would probably want a broadband connection to communicate with home bases back on Earth. They may even want to watch their favorite Earth-based TV show. That may now be possible thanks to a team of researchers from the Massachusetts Institute of Technology's (MIT) Lincoln Laboratory who, working with NASA last fall, demonstrated for the first time that a data communication technology exists that can provide space dwellers with the connectivity we all enjoy here on Earth, enabling large data transfers and even high-definition video streaming.

At CLEO: 2014, being held June 8-13 in San Jose, California, USA, the team will present new details and the first comprehensive overview of the on-orbit performance of their record-shattering laser-based communication uplink between the moon and Earth, which beat the previous record transmission speed last fall by a factor of 4,800. Earlier reports have stated what the team accomplished, but have not provided the details of the implementation.

"This will be the first time that we present both the implementation overview and how well it actually worked," says Mark Stevens of MIT Lincoln Laboratory. "The on-orbit performance was excellent and close to what we'd predicted, giving us confidence that we have a good understanding of the underlying physics," Stevens says.

The team made history last year when their Lunar Laser Communication Demonstration (LLCD) transmitted data over the 384,633 kilometers between the moon and Earth at a download rate of 622 megabits per second, faster than any radio frequency (RF) system. They also transmitted data from Earth to the moon at 19.44 megabits per second, a factor of 4,800 times faster than the best RF uplink ever used.

"Communicating at high data rates from Earth to the moon with laser beams is challenging because of the 400,000-kilometer distance spreading out the light beam," Stevens says. "It's doubly difficult going through the atmosphere, because turbulence can bend light -- causing rapid fading or dropouts of the signal at the receiver."

To outmaneuver problems with fading of the signal over such a distance, the demonstration uses several techniques to achieve error-free performance over a wide range of optically challenging atmospheric conditions in both darkness and bright sunlight. A ground terminal at White Sands, New Mexico, uses four separate telescopes to send the uplink signal to the moon. Each telescope is about 6 inches in diameter and fed by a laser transmitter that sends information coded as pulses of invisible infrared light. The total transmitter power is the sum of the four separate transmitters, which results in 40 watts of power.

The reason for the four telescopes is that each one transmits light through a different column of air that experiences different bending effects from the atmosphere, Stevens says. This increases the chance that at least one of the laser beams will interact with the receiver, which is mounted on a satellite orbiting the moon. This receiver uses a slightly narrower telescope to collect the light, which is then focused into an optical fiber similar to fibers used in terrestrial fiber optic networks.

From there, the signal in the fiber is amplified about 30,000 times. A photodetector converts the pulses of light into electrical pulses that are in turn converted into data bit patterns that carry the transmitted message. Of the 40-watt signals sent by the transmitter, less than a billionth of a watt is received at the satellite -- but that's still about 10 times the signal necessary to achieve error-free communication, Stevens says.

Their CLEO: 2014 presentation will also describe how the large margins in received signal level can allow the system to operate through partly transparent thin clouds in Earth's atmosphere, which the team views as a big bonus.

"We demonstrated tolerance to medium-size cloud attenuations, as well as large atmospheric-turbulence-induced signal power variations, or fading, allowing error-free performance even with very small signal margins," Stevens says.

While the LLCD design is directly relevant for near-Earth missions and those out to Lagrange points -- areas where the forces between rotating celestial bodies are balanced, making them a popular destination for satellites -- the team predicts that it's also extendable to deep-space missions to Mars and the outer planets.

Presentation SM4J.1, titled "Overview and On-orbit Performance of the Lunar Laser Communication Demonstration Uplink," will take place Monday, June 9.

Source: The Optical Society

NASA completes LADEE mission with planned impact on moon's surface

An artist's concept of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft seen orbiting near the surface of the moon. Credit: NASA Ames/Dana Berry

Ground controllers at NASA's Ames Research Center in Moffett Field, Calif., have confirmed that NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the surface of the moon, as planned, between 9:30 and 10:22 p.m. PDT Thursday, April 17.

LADEE lacked fuel to maintain a long-term lunar orbit or continue science operations and was intentionally sent into the lunar surface. The spacecraft's orbit naturally decayed following the mission's final low-altitude science phase.

During impact, engineers believe the LADEE spacecraft, the size of a vending machine, broke apart, with most of the spacecraft's material heating up several hundred degrees -- or even vaporizing -- at the surface. Any material that remained is likely buried in shallow craters.

"At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour -- about three times the speed of a high-powered rifle bullet," said Rick Elphic, LADEE project scientist at Ames. "There's nothing gentle about impact at these speeds -- it's just a question of whether LADEE made a localized craterlet on a hillside or scattered debris across a flat area. It will be interesting to see what kind of feature LADEE has created."

In early April, the spacecraft was commanded to carry out maneuvers that would lower its closest approach to the lunar surface. The new orbit brought LADEE to altitudes below one mile (two kilometers) above the lunar surface. This is lower than most commercial airliners fly above Earth, enabling scientists to gather unprecedented science measurements.

On April 11, LADEE performed a final maneuver to ensure a trajectory that caused the spacecraft to impact the far side of the moon, which is not in view of Earth or near any previous lunar mission landings. LADEE also survived the total lunar eclipse on April 14 to 15. This demonstrated the spacecraft's ability to endure low temperatures and a drain on batteries as it, and the moon, passed through Earth's deep shadow.

In the coming months, mission controllers will determine the exact time and location of LADEE's impact and work with the agency's Lunar Reconnaissance Orbiter (LRO) team to possibly capture an image of the impact site. Launched in June 2009, LRO provides data and detailed images of the lunar surface.

"It's bittersweet knowing we have received the final transmission from the LADEE spacecraft after spending years building it in-house at Ames, and then being in constant contact as it circled the moon for the last several months," said Butler Hine, LADEE project manager at Ames.

Launched in September 2013 from NASA's Wallops Flight Facility in Virginia, LADEE began orbiting the moon Oct. 6 and gathering science data Nov. 10. The spacecraft entered its science orbit around the moon's equator on Nov. 20, and in March 2014, LADEE extended its mission operations following a highly successful 100-day primary science phase.

LADEE also hosted NASA's first dedicated system for two-way communication using laser instead of radio waves. The Lunar Laser Communication Demonstration (LLCD) made history using a pulsed laser beam to transmit data over the 239,000 miles from the moon to the Earth at a record-breaking download rate of 622 megabits-per-second (Mbps). In addition, an error-free data upload rate of 20 Mbps was transmitted from the primary ground station in New Mexico to the Laser Communications Space Terminal aboard LADEE.

LADEE gathered detailed information about the structure and composition of the thin lunar atmosphere. In addition, scientists hope to use the data to address a long-standing question: Was lunar dust, electrically charged by sunlight, responsible for the pre-sunrise glow seen above the lunar horizon during several Apollo missions?

"LADEE was a mission of firsts, achieving yet another first by successfully flying more than 100 orbits at extremely low altitudes," said Joan Salute, LADEE program executive, at NASA Headquarters in Washington. "Although a risky decision, we're already seeing evidence that the risk was worth taking."

A thorough understanding of the characteristics of our nearest celestial neighbor will help researchers understand other bodies in the solar system, such as large asteroids, Mercury and the moons of outer planets.

NASA also included the public in the final chapter of the LADEE story. A "Take the Plunge" contest provided an opportunity for the public to guess the date and time of the spacecraft's impact via the internet. Thousands submitted predictions. NASA will provide winners a digital congratulatory certificate.

NASA's Science Mission Directorate in Washington funds the LADEE mission. Ames was responsible for spacecraft design, development, testing and mission operations, in addition to managing the overall mission. NASA's Goddard Space Flight Center in Greenbelt, Md., managed the science instruments, technology demonstration payload and science operations center, and provided mission support. Goddard also manages the LRO mission. 

Wallops was responsible for launch vehicle integration, launch services and operations. NASA's Marshall Space Flight Center in Huntsville, Ala., managed LADEE within the Lunar Quest Program Office.

Source: NASA

Stretching forces shaped Jupiter moon's surface, laboratory model suggests

An image of a tabletop-size analog model (left) shows details of fault systems created by extension that visually match an image by spacecraft Galileo of faulted terrain on Ganymede (right). Credit: Image courtesy of Southwest Research Institute

Processes that shaped the ridges and troughs on the surface of Jupiter's icy moon Ganymede are likely similar to tectonic processes seen on Earth, according to a team of researchers led by Southwest Research Institute (SwRI). To arrive at this conclusion, the team subjected physical models made of clay to stretching forces that simulate tectonic action. The results were published in Geophysical Research Letters.

Physical analog models simulate geologic structures in laboratory settings so that the developmental sequence of various phenomena can be studied as they occur. The team -- including researchers from SwRI, Wheaton College, NASA's Jet Propulsion Laboratory and NuStar Energy LP -- created complex patterns of faults in their models, similar to the ridge and trough features seen in some regions of Ganymede. The models consisted of a "wet clay cake" material possessing brittle characteristics to simulate how the icy moon's lithosphere, the outermost solid shell, responds to stresses by cracking.

The laboratory models suggest that characteristic patterns of ridges and troughs, called grooved terrain on Ganymede, result from its surface being stretched. "The physical models showed a marked similarity to the surface features observed on Ganymede," said co-author Dr. Danielle Wyrick, a senior research scientist in the SwRI Space Science and Engineering Division. "From the experiments, it appears that a process in which the crust breaks into separate blocks by large amounts of extension is the primary mechanism for creating these distinct features."

"Physical analog modeling allows us to simulate the formation of complex three-dimensional geologic structures on Ganymede, without actually going to Ganymede," said co-author Dr. David Ferrill, director of the Earth, Material and Planetary Sciences 

Department in the SwRI Geosciences and Engineering Division. "These scaled models are able to reproduce the fine geometric details of geologic processes, such as faulting, and to develop and test hypotheses for landscape evolution on planetary bodies."

SwRI researchers previously have used physical analog models to examine the process by which pit crater chains -- a series of linear pits, or depressions -- develop on Mars, and how magma in the Martian subsurface deforms the surface of the Red Planet.

Source: Southwest Research Institute.

Losing air: Barrage of small impacts likely erased much of the Earth’s primordial atmosphere

Today's atmosphere likely bears little trace of its primordial self: Geochemical evidence suggests that Earth's atmosphere may have been completely obliterated at least twice since its formation more than 4 billion years ago. Credit: Image courtesy of NASA

Today's atmosphere likely bears little trace of its primordial self: Geochemical evidence suggests that Earth's atmosphere may have been completely obliterated at least twice since its formation more than 4 billion years ago. However, it's unclear what interplanetary forces could have driven such a dramatic loss.

Now researchers at MIT, Hebrew University, and Caltech have landed on a likely scenario: A relentless blitz of small space rocks, or planetesimals, may have bombarded Earth around the time the moon was formed, kicking up clouds of gas with enough force to permanently eject small portions of the atmosphere into space.

Tens of thousands of such small impacts, the researchers calculate, could efficiently jettison Earth's entire primordial atmosphere. Such impacts may have also blasted other planets, and even peeled away the atmospheres of Venus and Mars.

In fact, the researchers found that small planetesimals may be much more effective than giant impactors in driving atmospheric loss. Based on their calculations, it would take a giant impact -- almost as massive as Earth slamming into itself -- to disperse most of the atmosphere. But taken together, many small impacts would have the same effect, at a tiny fraction of the mass.

Hilke Schlichting, an assistant professor in MIT's Department of Earth, Atmospheric and Planetary Sciences, says understanding the drivers of Earth's ancient atmosphere may help scientists to identify the early planetary conditions that encouraged life to form.
"[This finding] sets a very different initial condition for what the early Earth's atmosphere was most likely like," Schlichting says. "It gives us a new starting point for trying to understand what was the composition of the atmosphere, and what were the conditions for developing life."

Schlichting and her colleagues have published their results in the journal Icarus.
Efficient ejection

The group examined how much atmosphere was retained and lost following impacts with giant, Mars-sized and larger bodies and with smaller impactors measuring 25 kilometers or less -- space rocks equivalent to those whizzing around the asteroid belt today.

The team performed numerical analyses, calculating the force generated by a given impacting mass at a certain velocity, and the resulting loss of atmospheric gases. A collision with an impactor as massive as Mars, the researchers found, would generate a shockwave through Earth's interior, setting off significant ground motion -- similar to simultaneous giant earthquakes around the planet -- whose force would ripple out into the atmosphere, a process that could potentially eject a significant fraction, if not all, of the planet's atmosphere.

However, if such a giant collision occurred, it should also melt everything within the planet, turning its interior into a homogenous slurry. Given the diversity of noble gases like helium-3 deep inside Earth today, the researchers concluded that it is unlikely that such a giant, core-melting impact occurred.

Instead, the team calculated the effects of much smaller impactors on Earth's atmosphere. Such space rocks, upon impact, would generate an explosion of sorts, releasing a plume of debris and gas. The largest of these impactors would be forceful enough to eject all gas from the atmosphere immediately above the impact's tangent plane -- the line perpendicular to the impactor's trajectory. Only a fraction of this atmosphere would be lost following smaller impacts.

To completely eject all of Earth's atmosphere, the team estimated, the planet would need to have been bombarded by tens of thousands of small impactors -- a scenario that likely did occur 4.5 billion years ago, during a time when the moon was formed. This period was one of galactic chaos, as hundreds of thousands of space rocks whirled around the solar system, frequently colliding to form the planets, the moon, and other bodies.

"For sure, we did have all these smaller impactors back then," Schlichting says. "One small impact cannot get rid of most of the atmosphere, but collectively, they're much more efficient than giant impacts, and could easily eject all the Earth's atmosphere."

Runaway effect
However, Schlichting realized that the sum effect of small impacts may be too efficient at driving atmospheric loss. Other scientists have measured the atmospheric composition of Earth compared with Venus and Mars. These measurements have revealed that while each planetary atmosphere has similar patterns of noble gas abundance, the budget for Venus is similar to that of chondrites -- stony meteorites that are primordial leftovers of the early solar system. Compared with Venus, Earth's noble gas budget has been depleted 100-fold.
Schlichting realized that if both planets were exposed to the same blitz of small impactors, Venus' atmosphere should have been similarly depleted. She and her colleagues went back over the small-impactor scenario, examining the effects of atmospheric loss in more detail, to try and account for the difference between the two planets' atmospheres.

Based on further calculations, the team identified an interesting effect: Once half a planet's atmosphere has been lost, it becomes much easier for small impactors to eject the rest of the gas. The researchers calculated that Venus' atmosphere would only have to start out slightly more massive than Earth's in order for small impactors to erode the first half of the Earth's atmosphere, while keeping Venus' intact. From that point, Schlichting describes the phenomenon as a "runaway process -- once you manage to get rid of the first half, the second half is even easier."

Time zero
During the course of the group's research, an inevitable question arose: What eventually replaced Earth's atmosphere? Upon further calculations, Schlichting and her team found the same impactors that ejected gas also may have introduced new gases, or volatiles.

"When an impact happens, it melts the planetesimal, and its volatiles can go into the atmosphere," Schlichting says. "They not only can deplete, but replenish part of the atmosphere."

The group calculated the amount of volatiles that may be released by a rock of a given composition and mass, and found that a significant portion of the atmosphere may have been replenished by the impact of tens of thousands of space rocks.

"Our numbers are realistic, given what we know about the volatile content of the different rocks we have," Schlichting notes.

Jay Melosh, a professor of earth, atmospheric, and planetary sciences at Purdue University, says Schlichting's conclusion is a surprising one, as most scientists have assumed Earth's atmosphere was obliterated by a single, giant impact. Other theories, he says, invoke a strong flux of ultraviolet radiation from the sun, as well as an "unusually active solar wind."
"How the Earth lost its primordial atmosphere has been a longstanding problem, and this paper goes a long way toward solving this enigma," says Melosh, who did not contribute to the research. "Life got started on Earth about this time, and so answering the question about how the atmosphere was lost tells us about what might have kicked off the origin of life."
Going forward, Schlichting hopes to examine more closely the conditions underlying Earth's early formation, including the interplay between the release of volatiles from small impactors and from Earth's ancient magma ocean.

"We want to connect these geophysical processes to determine what was the most likely composition of the atmosphere at time zero, when the Earth just formed, and hopefully identify conditions for the evolution of life," Schlichting says.

Source:  Massachusetts Institute of Technology