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Take a tour of the Moon

USING ELEVATION AND IMAGE DATA returned by NASA’s Lunar Reconnaissance Orbiter (LRO), this animation takes the viewer on a virtual tour of the Moon.

Unfortunately there’s no narration or music track, but the visuals are stunning enough. Try zooming the YouTube window to full screen to get the best view.

The tour visits a number of interesting sites chosen to illustrate a wide variety of lunar terrain features. Some are on the near side and are familiar to both professional and amateur observers on Earth, while others can only be seen clearly from space.

Some are large and old (Orientale, South Pole-Aitken), others are smaller and younger (Tycho, Aristarchus, Shackleton).

Constantly shadowed areas near the poles are hard to photograph but easier to measure with altimetry, while several of the Apollo landing sites, all relatively near the equator, have been imaged at resolutions as high as 25 centimetres per pixel.

The shape of the terrain in this animation is based primarily on data from LRO’s laser altimeter (LOLA), supplemented by stereo image data from its wide-angle camera (LROC WAC) and from Japan’s Kaguya mission. The global surface colour is from the Clementine mission.

Adapted from information issued by NASA / Goddard Space Flight Centre Scientific Visualization Studio.

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In the astronauts’ footsteps

LRO image of Apollo 12 landing site

LRO's image of the Apollo 12 landing site, showing the lunar module, Surveyor III probe (see image below) and the astronauts' tracks.

NASA’S LUNAR RECONNAISSANCE ORBITER (LRO) has captured the sharpest images ever taken from space of the Apollo 12, 14 and 17 landing sites. The images show the twists and turns of the paths made when the astronauts explored the lunar surface.

At the Apollo 17 site, the tracks laid down by the lunar rover are clearly visible, along with the last foot trails left on the Moon. The images also show where the astronauts placed some of the scientific instruments that provided the first insight into the Moon’s environment and interior.

“We can retrace the astronauts’ steps with greater clarity to see where they took lunar samples,” said Noah Petro, a lunar geologist at NASA’s Goddard Space Flight Centre and member of the LRO project science team.

All three images show distinct trails left in the Moon’s thin soil when the astronauts exited the lunar modules and explored on foot.

Apollo image of Apollo 12 lunar module and Surveyor III

The Apollo 12 crew intentionally landed near the Surveyor III probe, which has soft-landed on the Moon to test its surface some years prior to the first manned missions.

In the Apollo 17 image, the foot trails, including the last path made on the Moon by humans, are easily distinguished from the dual tracks left by the lunar rover, which remains parked east of the lander.

A sharper view

“The new low-altitude Narrow Angle Camera images sharpen our view of the Moon’s surface,” said Arizona State University researcher Mark Robinson, principal investigator for the Lunar Reconnaissance Orbiter Camera (LROC).

“A great example is the sharpness of the rover tracks at the Apollo 17 site. In previous images the rover tracks were visible, but now they are sharp parallel lines on the surface.”

LRO image of Apollo 17 landing site

LRO image of the Apollo 17 landing site. Apollo 17 was the final manned mission to the Moon.

At each site, trails also run to the west of the landers, where the astronauts placed the Apollo Lunar Surface Experiments Package (ALSEP) to monitor the Moon’s environment and interior. This equipment was a key part of every Apollo mission.

It provided the first insights into the Moon’s internal structure, measurements of the lunar surface pressure and the composition of its atmosphere. Apollo 11 carried a simpler version of the science package.

One of the details that shows up is a bright L-shape in the Apollo 12 image. It marks the locations of cables running from ALSEP’s central station to two of its instruments. Although the cables are much too small for direct viewing, they show up because they reflect light very well.

In a perfect position

The higher resolution of these images is possible because of adjustments made to LRO’s orbit, which is slightly oval-shaped or elliptical.

“Without changing the average altitude, we made the orbit more elliptical, so the lowest part of the orbit is on the sunlit side of the Moon,” said Goddard’s John Keller, deputy LRO project scientist.

“This put LRO in a perfect position to take these new pictures of the surface.”

LRO image of Apollo 14 landing site

LRO image of Apollo 14 landing site showing the location of the lunar module as well as the astronaut's tracks.

Apollo 14 image showing the lunar module on the surface of the Moon

Apollo 14 image showing the lunar module on the surface of the Moon. The shiny tracks are impressions left in the dust by a hand-drawn equipment cart, which the astronaut's nicknamed the "rickshaw".

The manoeuvre lowered LRO from its usual altitude of approximately 50 kilometres to an altitude that dipped as low as nearly 21 kilometres as it passed over the Moon’s surface.

The spacecraft has remained in this orbit for 28 days, long enough for the Moon to completely rotate. This allows full coverage of the surface by LROC’s Wide Angle Camera. The cycle ended yesterday when the spacecraft was returned to its 50km orbit.

Adapted from information issued by NASA.

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Our damaged, wrinkly Moon

Surface of the Moon

The ups and downs of the Moon's battered surface hint at the processes that have shaped it for eons.

WRITTEN ON THE MOON’S WEARY FACE are signs of the damage it has endured for the past 4.5 billion years. From impact craters to the dark plains or ‘maria’ left behind by volcanic eruptions, the scars are all that remain to tell the tale of the past.

But these features only hint at the processes that once acted—and act today—to shape the surface.

To get more insight, Meg Rosenburg and her colleagues at the California Institute of Technology have put together the first comprehensive set of maps revealing the slopes and roughness of the Moon’s surface, based on detailed data collected by the Lunar Orbiter Laser Altimeter (LOLA) on NASA’s Lunar Reconnaissance Orbiter.

Like wrinkles on skin, the roughness of craters and other features on the Moon’s surface can reveal their age.

“The key is to look at the roughness at both long and short scales,” says Rosenburg, who is the first author on the paper describing the results, published in the Journal of Geophysical Research earlier this year.

The roughness depends on the subtle ups and downs of the landscape, a quality that the researchers get at by measuring the slope at locations all over the surface.

A lunar maria

The lunar maria are smooth regions of solidified lava.

To put together a complete picture, the researchers looked at roughness at a range of different scales—the distances between two points—from 17 metres to as much as 2.7 kilometres.

“Old and young craters have different roughness properties—they are rougher on some scales and smoother on others,” says Rosenburg. That’s because the older craters have been pummelled for eons by meteorites that pit and mar the site of the original crater, changing its shape.

“Because this softening of the terrain hasn’t happened at the new impact sites, the youngest craters immediately stand out,” says Gregory Neumann, a co-investigator on LOLA at NASA’s Goddard Space Flight Centre.

By looking at where and how the roughness changes, the researchers can get important clues about the processes that shaped the Moon.

A roughness map of the material surrounding Orientale basin, for example, reveals subtle differences in the ejecta, or debris, that was thrown out when the crater was formed by a giant object slamming into the Moon.

That information can be combined with a contour map that shows where the high and low points are.

“By looking at both together, we can say that one part of Orientale is not just higher or lower, it’s also differently rough,” Rosenburg says. “That gives us some clues about the impact process that launched the ejecta and also about the surface processes that later acted to modify it.”

The smooth plains of the maria, which were created by volcanic activity, have a different roughness “signature” from the Moon’s highlands, reflecting the different origins of the two terrains. Maria is Latin for “seas,” and they got that name from early astronomers who mistook them for actual seas.

Adapted from information issued by Elizabeth Zubritsky, NASA’s Goddard Space Flight Centre.

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Lunar rock and roll

Crater Tycho

The 85-kilometre-wide crater Tycho on the Moon. The arrow marks the location of the huge boulder shown in detail below.

THE 85-KILOMETRE-WIDE CRATER Tycho is one of the standout features of the side of the Moon that faces Earth.

Named after the 16th century Danish astronomer Tycho Brahe, it is thought to have formed 108 million years ago when an asteroid smashed into the lunar surface.

Southern region of the Moon

Like the spokes of a wheel, rays of lighter-coloured ejected rock stretch away from the crater Tycho (the prominent crater near centre, with the central peak). Photo by Joe Huber, sourced from Wikipedia.

The impact formed the crater, and also flung out huge amounts of molten rock—called ejecta— in all directions.

That ejecta can still be seen today, in the form of bright ‘rays’ stretching away from Tycho.

Astronauts of the final Apollo mission, Apollo 17, managed to collect samples of Tycho ejecta from their landing site in the Taurus-Littrow valley, thousands of kilometres away.

Like many craters, it has a central peak that rises high above the crater floor. This peak was formed as the molten rock splashed back upwards immediately after the impact…just as a central splash back occurs when an object is dropped into a glass of milk.

Tycho’s central peak rises 1.6 kilometres above the floor.

Along with the rest of the lunar surface, Tycho has been imaged in detail by NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft, currently still operating.

Large boulder in crater Tycho

A 320-metre-long block of ejected rock sits near the rim of Tycho. It has a smooth top, thought to be a veneer of solidified molten rock droplets.

One of LRO’s most startling images of Tycho shows a huge boulder, 320 metres long, perched near the crater’s rim.

This boulder is thought to have been blasted out of the lunar surface when the impactor that formed the crater, struck.

It has a smooth top, which scientists think is the result of a rain of molten rock droplets settling on it and solidifying.

Images courtesy of NASA / GFSC / Arizona State University.

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Huge new Moon image

The Moon

A huge new mosaic image of the Moon's nearside has been produced from 1,300 images taken by NASA's Lunar Reconnaissance Orbiter spacecraft. This is a screenshot of the LRO Camera nearside online browse web page, where you can zoom in and pan around the lunar surface.

A TEAM USING the Wide Angle Camera aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft has produced a huge new mosaic image of the nearside of the Moon.

Because the Moon rotates on its own axis in the same amount of time as it takes to circle the Earth, it always keeps the same face toward us…known as the lunar nearside.

LRO, carrying a suite of instruments, has been in orbit around the Moon since June 2009.

For a fortnight in December 2010, mission controllers kept the spacecraft pointed straight down at the lunar surface, and collected around 1,300 individual images with which to make the mosaic.

The image will become the new standard for geologists studying the Moon.

The entire image can be downloaded from the LRO Camera website, or you can zoom in and pan around on an online version here.

LRO’s Wide Angle Camera (WAC) is remarkably small, with a mass of only 900 grams and easily able to fit in a person’s hand. As LRO orbits the Moon, the WAC builds up an almost complete picture of lunar surface every month. It was designed and built by Malin Space Science Systems (MSSS) in San Diego, a firm which has produced many imaging systems for scientific spacecraft, including many ones on spacecraft sent to Mars.

Story by Jonathan Nally, Images courtesy NASA / GSFC / Arizona State University.

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Moon’s buried treasure uncovered

  • LCROSS and LRO missions crashed into lunar south pole
  • Detected water ice plus a suite of other useful chemicals
  • Could be a good place for future lunar base

Nearly a year after announcing the discovery of water molecules on the Moon, scientists Thursday revealed new data uncovered by NASA’s Lunar CRater Observation and Sensing Satellite, or LCROSS, and Lunar Reconnaissance Orbiter, or LRO.

The missions found evidence that the lunar soil within shadowy craters is rich in useful materials, and the Moon is chemically active and has a water cycle. Scientists also confirmed the water was in the form of mostly pure ice crystals in some places.

The results are featured in six papers published in the October 22 issue of Science.

“NASA has convincingly confirmed the presence of water ice and characterised its patchy distribution in permanently shadowed regions of the Moon,” said Michael Wargo, chief lunar scientist at NASA Headquarters in Washington. “This major undertaking is the one of many steps NASA has taken to better understand our Solar System, its resources, and its origin, evolution, and future.”

The twin impacts of LCROSS and a companion rocket stage in the Moon’s Cabeus crater on October 9, 2009, lifted a plume of material that might not have seen direct sunlight for billions of years.

Artist's impression of LCROSS about to impact the Moon

Artist's impression of LCROSS studying the plume of lunar soil flung up by the impact of the spent Centaur rocket booster.

As the plume travelled nearly 15 kilometres above the rim of Cabeus, instruments aboard LCROSS and LRO made observations of the crater and debris and vapour clouds. After the impacts, grains of mostly pure water ice were lofted into the sunlight in the vacuum of space.

“Seeing mostly pure water ice grains in the plume means water ice was somehow delivered to the Moon in the past, or chemical processes have been causing ice to accumulate in large quantities,” said Anthony Colaprete, LCROSS project scientist and principal investigator at NASA’s Ames Research Centre.

“Also, the diversity and abundance of certain materials called volatiles in the plume, suggest a variety of sources, like comets and asteroids, and an active water cycle within the lunar shadows.”

Volatiles are chemical compounds that freeze and are trapped in the cold lunar craters and vaporise when warmed by the Sun. The suite of LCROSS and LRO instruments determined that as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.

Silver lining

The instruments also discovered relatively large amounts of light metals such as sodium, mercury and possibly even silver. Scientists believe the water and mix of volatiles that LCROSS and LRO detected could be the remnants of a comet impact.

According to scientists, these volatile chemical by-products are also evidence of a cycle through which water ice reacts with lunar soil grains.

LRO’s Diviner instrument gathered data on water concentration and temperature measurements, and LRO’s Lunar Exploration Neutron Detector mapped the distribution of hydrogen. This combined data led the science team to conclude the water is not uniformly distributed within the shadowed cold traps, but rather is in pockets, which may also lie outside the shadowed regions.

Location of Cabeus crater

False-colour image showing the location of the impact point in Cabeus crater.

The proportion of volatiles to water in the lunar soil indicates a process called “cold grain chemistry” is taking place. Scientists also theorise this process could take as long as hundreds of thousands of years and may occur on other frigid, airless bodies, such as asteroids; the moons of Jupiter and Saturn, including Europa and Enceladus; Mars’ moons; interstellar dust grains floating around other stars and the polar regions of Mercury.

“The observations by the suite of LRO and LCROSS instruments demonstrate the Moon has a complex environment that experiences intriguing chemical processes,” said Richard Vondrak, LRO project scientist at NASA’s Goddard Space Flight Centre. “This knowledge can open doors to new areas of research and exploration.”

By understanding the processes and environments that determine where water ice will be, how water was delivered to the Moon and its active water cycle, future mission planners might be better able to determine which locations will have easily-accessible water.

The existence of mostly pure water ice could mean future human explorers won’t have to retrieve the water out of the soil in order to use it for valuable life support resources. In addition, an abundant presence of hydrogen gas, ammonia and methane could be exploited to produce fuel.

LCROSS launched with LRO aboard an Atlas V rocket from Cape Canaveral on June 18, 2009, and used the Centaur upper stage rocket to create the debris plume. The research was funded by NASA’s Exploration Systems Missions Directorate at the agency’s headquarters. LCROSS was managed by Ames and built by Northrop Grumman. LRO was built and is managed by Goddard.

Adapted from information issued by NASA.

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Moon’s face is a history book

Artist's impression of LRO

Artist's impression of the NASA's Lunar Reconnaissance Orbiter spacecraft, which has been mapping the Moon with unprecedented precision.

  • Moon’s craters came from bombardment by impactors
  • Now, first comprehensive map of craters has been made
  • Shows the bombardment changed dramatically at a certain stage

Take a cursory look at the Moon, and it can resemble a pockmarked golf ball. The dimples and divots on its surface are testament that our satellite has withstood a barrage of impacts from comets, asteroids and other space matter throughout much of its history.

Because the geological record of that pummelling remains largely intact, scientists have used the Moon to help reconstruct the history of the chaotic early days of the inner Solar System.

Now a team led by Brown University planetary geologists has produced the first uniform, comprehensive catalogue of large lunar craters…which could help shed light on the full-scale, planetary bombardment suffered by the planets of the inner Solar System more than 4 billion years ago.

In a paper appearing in the journal Science, the team used data from the Lunar Orbiter Laser Altimeter (LOLA), one of a suite of instruments aboard NASA’s Lunar Reconnaissance Orbiter, to identify and map 5,185 craters that are 20 kilometres in diameter or larger.

Map of craters on the Moon

A research team mapped nearly 5,200 craters on the Moon, the first global catalogue of large craters on the lunar surface. The analysis could shed light on planetary bombardment in the inner Solar System more than 4 billion years ago.

From the crater count and analysis, the team (which includes scientists from the Massachusetts Institute of Technology and the NASA Goddard Space Flight Centre) determined the Moon’s oldest regions are the southern near side and the north-central far side.

The group also confirmed that the South Pole–Aitken Basin is the oldest basin, meaning that any samples from there could be invaluable to further understanding the Moon and other bodies of the inner Solar System.

Rethinking the Moon’s bombardment

A major finding deals with the stream of projectiles pinballing throughout the inner Solar System in its earliest days.

For years, the prevailing wisdom was that the Moon was buffeted by a volley of space matter that held a steady ratio between larger and smaller objects, which planetary scientists refer to as “size-frequency distribution.”

The bombardment activity has never been questioned. But in 2005, the size-frequency distribution part of it was challenged. In a paper in Science, a group led by University of Arizona geologist Robert Strom hypothesised that the ratio of larger and smaller objects striking the Moon had differed during its first billion years of existence.

The Brown-led team’s crater analysis lends added credence to that hypothesis.

The researchers studied impact craters formed early in the Moon’s history (when major basins were created by large projectiles striking the surface) and compared them with those they knew were formed later (when objects struck lava flows that had covered these basins).

Craters on the Moon

Scientists have found differences in the size range of craters on the lunar highlands compared to the lowlands.

They found that the oldest surfaces (located in the lunar highlands) bore crater markings indicating a greater ratio of larger impactors. The group looked in particular at Orientale Basin, formed by a massive impactor about 3.8 billion years ago, and determined that this is approximately when the era of larger projectiles versus smaller projectiles ended.

Much more to do

The finding opens a set of intriguing questions for what was going on in the inner Solar System leading up to roughly the time that Orientale Basin was formed.

“We know the asteroid belt has been spinning off projectiles at a relatively constant rate for three and a half billion years,” said Caleb Fassett, a postdoctoral researcher at Brown. “But now we go back earlier in the Solar System’s history, and suddenly things are completely different.”

The scientists think the change may have been caused by the gravitational pull on the asteroid belt exerted by larger planets such as Jupiter and Saturn as they settled into their orbits…or it could have been a temporary abundance of comets, an unexplained change in the size of impactors emanating from the asteroid belt, or something else.

The Lunar Orbiter Laser Altimeter measures the Moon’s surface topography with a vertical precision of 10 centimetres using laser pulses bounced off the lunar surface just 25 metres apart.

In all, the findings “are telling us something about the infancy of the Solar System,” said James W. Head III, a planetary geologist at Brown and the paper’s lead author. “It is clear we can find out and learn so much more from future missions, robotic or otherwise. There is so much to do.”

Adapted from information issued by NASA / LRO / LOLA / GSFC / MIT / Brown.

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A bridge too far(side)

Rock bridge on the Moon

NASA's Lunar Reconnaissance Orbiter spacecraft snapped this image of a natural rock bridge on the far side of the Moon. The bridge spans what appears to be two cave-ins in an underground lava tube.

An image taken by the main camera aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft—currently orbiting the Moon—has revealed a natural bridge of rock that apparently crosses two holes in the lunar crust.

The bridge appears to be about 20 metres long and 7 metres wide.

On Earth, natural rock bridges are usually formed from long-term erosion by wind and flowing water.

But the Moon has neither of those phenomena, so how did the bridge form?

The answer seems to be a collapsed lava tube.

Images of Moon, going all the way back to the Apollo days of the 1960s, have shown that numerous lava tubes can be found across its face.

Lava tubes are where a stream of molten rock moves across a surface. The outside of the stream cools and solidifies, insulating the still-moving lava within and forming a tunnel. Eventually the lava flow is depleted and an empty tube or tunnel is left behind.

Two views of a rock bridge on the Moon

What a difference an angle can make. The image on the left shows the bridge with sunlight slanting in from a 42-degree angle. The image on the right is with the sunlight at 82 degrees, or almost overhead.

Occasionally parts of the tunnel roof collapses, sometimes leaving a bridge or arch where the roof was a bit thicker or stronger.

This is what seems to have happened in the case of the newly-discovered bridge on the Moon.

But instead of the lava coming from a volcano, in this instance it appears to have been a flow of rock that formed when a large meteoroid hit the lunar surface and melted everything around it.

The location in question is called King Crater, and the bridge is found on the floor of the crater, where a large pool of molten rock would have been formed after the meteoroid struck.

Story by Jonathan Nally, editor

Images courtesy NASA / Goddard / ASU.

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Shrinking moon starts to crack up

  • Cliffs or scarps suggest Moon has shrunk in the recent past
  • It could still be slowly shrinking today
  • Observations made by NASA’s Lunar Reconnaissance Orbiter spacecraft

Newly discovered cliffs in the lunar crust indicate the Moon shrank globally in the geologically recent past and might still be shrinking today, according to a team analysing new images from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft. The results provide important clues to the Moon’s recent geologic and tectonic evolution.

The Moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the Moon hot. The Moon cooled off as it aged, and scientists have long thought the Moon shrank over time as it cooled, especially in its early history.

Gregory Scarp on the Moon

A prime example of a lunar scarp is this one, called Gregory Scarp. The scale is in metres.

The new research reveals relatively recent tectonic activity connected to the long-lived cooling and associated contraction of the lunar interior.

“We estimate these cliffs, called lobate scarps, formed less than a billion years ago, and they could be as young as a hundred million years,” said Dr. Thomas Watters of the Centre for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum, Washington.

While ancient in human terms, it is less than 25 percent of the Moon’s current age of more than four billion years.

“Based on the size of the scarps, we estimate the distance between the Moon’s centre and its surface shrank by about 300 feet [100 metres],” said Watters, lead author of a paper on this research appearing in the August 20 issue of the journal Science.

The scarps are relatively small; the largest is about 100 metres high and extends for several kilometres or so, but typical lengths are shorter and heights are more in the tens of metres range.

Earth not to blame

The team believes they are among the freshest features on the Moon, in part because they cut across small craters.

Since the Moon is constantly bombarded by meteors, features like small craters (those less than about 400 metres across) are likely to be young because they are quickly destroyed by other impacts and don’t last long.

Diagram of a lunar scarp

Scarps on the Moon could be produced as the rocky world cools and contracts.

So, if a small crater has been disrupted by a scarp, the scarp formed after the crater and is even younger. Even more compelling evidence is that large craters, which are likely to be old, don’t appear on top any of the scarps, and the scarps look crisp and relatively un-degraded.

Because the scarps are so young, the Moon could have been cooling and shrinking very recently, according to the team.

Seismometers emplaced by the Apollo missions have recorded moonquakes. While most can be attributed to things like meteorite strikes, the Earth’s gravitational tides, and day/night temperature changes, it’s remotely possible that some moonquakes might be associated with ongoing scarp formation, according to Watters.

The team plans to compare photographs of scarps by the Apollo Panoramic Cameras to new images from LRO to see if any have changed over the decades, possibly indicating recent activity.

While Earth’s tides are most likely not strong enough to create the scarps, they could contribute to their appearance, perhaps influencing their orientation, according to Watters. During the next few years, the team hopes to use LRO’s high-resolution Narrow Angle Cameras (NACs) to build up a global, highly detailed map of the Moon.

This could identify additional scarps and allow the team to see if some have a preferred orientation or other features that might be associated with Earth’s gravitational pull.

Adapted from information issued by NASA.

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Portrait of Earth

LRO image of Earth from the Moon

Earth, as seen by NASA's Lunar Reconnaissance Orbiter from a distance of over 372,000 kilometres.

There’s a common misconception that certain manmade things on Earth, such as the Great Wall of China, can be seen from the Moon.

In fact, nothing manmade is visible from the Moon—it’s just too far away.

But that doesn’t mean the view isn’t worth taking in.

This image was taken on June 12, 2010, by the Narrow Angle Cameras aboard NASA’s Lunar Reconnaissance Orbiter (LRO) in orbit around the Moon.

It shows what our planet looks like from a distance of 372,334 kilometres.

Being mid-June, it is summer in Earth’s Northern Hemisphere and winter in the Southern Hemisphere.

The black and white image shows the bright polar ice cap over the Arctic Ocean, and cloud free skies over the Middle East.

Clouds stretch all the way from India on the left across to the northern parts of the Pacific Ocean on the right.

The image was taken to help with periodic calibration of LRO’s cameras.

There is a section missing near the bottom of the image due to a small miscalculation of the time when the Earth would be in the cameras’ field of view.

See the full-size, high-resolution image here (2MB, new window).

Adapted from information issued by Holli Riebeek / NASA / Goddard / Arizona State University.

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