June 21, 2011

Diviner observes cooling during June 15 total eclipse

Preliminary results from the Diviner Lunar Radiometer show that dayside surface temperatures on the Moon cooled significantly during the June 15th total eclipse.

The following plot shows data taken during successive orbits over a unit of lunar mare situated between 32 and 33 degrees north. The orbit path progressed from east to west (right to left), with each orbit separated by roughly two hours. The first two data swaths were taken before the eclipse, the three center swaths were taken during the eclipse, and the last two swaths were taken after the Moon had reemerged from Earth’s shadow. The data show an average decrease in surface temperature during the eclipse of around 100K, with some locations remaining warmer than others.

Channel 7 brightness temperature plot of mid-latitude maria terrain.

Channel 7 brightness temperature plot of mid-latitude maria terrain.

The fact that some parts of the lunar surface remained warmer than others during the eclipse could be for a number of reasons - degree of cooling is dependent on factors such as how rocky the surface is, how densely packed the soil is, and which minerals it is composed of. The challenge now for the Diviner science team is to deconvolve the eclipse data into useful information that can be used to map each of these properties.

Their job is made more difficult by the fact that not all areas on the Moon’s surface receive equal illumination. At the lunar poles especially, topography plays a big role in determining the amount of illumination a location receives, with low-lying terrain such as the interiors of impact craters typically receiving little to no illumination while slopes that face the sun can receive almost constant illumination.

In the following animation, which shows data taken from seven consecutive orbits over a fresh, rocky impact crater near the lunar north pole, it’s clear that the parts of the surface that were illuminated by the sun prior to the eclipse, such as the crater rim, were the locations that experienced the greatest cooling during the eclipse.

Animation depicting surface cooling during the total lunar eclipse on June 15 2011. The data were taken during seven consecutive orbits over a fresh, rocky impact crater in the lunar north pole (-70E, 82.5N). The white arrow indicates location of the plotted temperatures.

Animation depicting surface cooling during the total lunar eclipse on June 15 2011. The data were taken during seven consecutive orbits over a fresh, rocky impact crater in the lunar north pole (-70E, 82.5N). The white arrow indicates location of the plotted temperatures.

Diviner is one of seven instruments aboard NASA’s Lunar Reconnaissance Orbiter, which is currently orbiting 50 km (30 mi) above the Moon’s surface. It is the first infrared instrument to observe lunar eclipses from orbit. The next chance to observe an eclipse will be in December, 2011.

June 14, 2011

Diviner to observe temperatures during June 15th total eclipse

On June 15th, 2011, sky-watchers across much of the world will be treated to one of nature’s most impressive spectacles – a total lunar eclipse. The eclipse is set to be one of the longest and darkest of the 21st century, lasting just over 100 minutes.

Although it will not be visible in North America, the eclipse provides a rare opportunity for the Diviner Lunar Radiometer to gather valuable information about the lunar surface.

Figure 1. Projection of the lunar north pole showing solar illumination and predicted orbit tracks of NASA's Lunar Reconnaissance Orbiter during the eclipse on June 15, 2011.

Figure 1. Projection of the lunar north pole showing solar illumination and predicted orbit tracks of NASA's Lunar Reconnaissance Orbiter during the eclipse on June 15, 2011.

Figure 2. Projection of the lunar south pole showing solar illumination and predicted orbit tracks of NASA's Lunar Reconnaissance Orbiter during the eclipse on June 15, 2011.

Figure 2. Projection of the lunar south pole showing solar illumination and predicted orbit tracks of NASA's Lunar Reconnaissance Orbiter during the eclipse on June 15, 2011.

Lunar eclipses occur when the Sun, Moon and Earth are aligned so that the Earth is positioned between the Sun and Moon in such a way that it blocks the Sun’s rays, casting a shadow over the Moon. In the outer part of the shadow or ‘penumbra’ the Sun’s rays are only partially blocked, but in the center of the shadow, the ‘umbra’, there is no direct sunlight at all. A total lunar eclipse occurs when the Moon travels completely into the umbra.

Figure 2 shows the Moon’s near-central path through the penumbra and umbra on June 15. The times of each stage of the eclipse are displayed in the upper right-hand corner. The penumbral eclipse (“P1”) begins when the Moon first enters the Earth’s penumbra. This is followed by a partial eclipse (“U1”), as the Moon first enters the umbra. The total eclipse (“U2”) will begin as soon as the Moon travels completely into the umbra, and the point of greatest eclipse will occur when the Moon reaches the center of this darkest region. U3, U4 and P4 indicate the ends of the total, partial and penumbral eclipse, respectively. Source: http://eclipse.gsfc.nasa.gov/eclipse.html

Figure 3 shows the Moon’s near-central path through the penumbra and umbra on June 15. The times of each stage of the eclipse are displayed in the upper right-hand corner. The penumbral eclipse (“P1”) begins when the Moon first enters the Earth’s penumbra. This is followed by a partial eclipse (“U1”), as the Moon first enters the umbra. The total eclipse (“U2”) will begin as soon as the Moon travels completely into the umbra, and the point of greatest eclipse will occur when the Moon reaches the center of this darkest region. U3, U4 and P4 indicate the ends of the total, partial and penumbral eclipse, respectively. SOURCE: http://eclipse.gsfc.nasa.gov/eclipse.html

As the Moon passes into Earth’s shadow on June 15th, its dayside will be plunged into darkness, resulting in a rapid cooling of its surface. However, not all parts of the Moon’s surface will cool equally; rocks and boulders for example, because of their smaller surface area relative to their mass, will cool more slowly than fine-grained dust and sand.

The Diviner Lunar Radiometer, which will be measuring lunar surface temperatures continuously throughout the entire eclipse period, will be able to observe this difference in cooling rate, allowing scientists to deduce what lies just beneath the surface.

Animation showing predicted lunar surface temperatures during the June 15th eclipse

“This is an unprecedented opportunity to learn more about the uppermost few millimeters of the Moon,” says David Paige, principal investigator for Diviner. “Unlike on Earth, which takes 24 hours to rotate through one full day, the typical day-night cycle on the Moon lasts around 29 Earth days, so lunar dusk and dawn usually extend over a number of days.”

“During a total lunar eclipse, the Moon is essentially experiencing a day-night cycle that lasts only a matter of hours, so it’s going to be interesting to see how the surface responds.”

“You might imagine how it will respond if you’ve ever walked into the shadow of a building on a warm, sunny day - as you walk into the shadow, you are effectively walking into an eclipse, and as the building blocks the Sun’s rays you can usually notice a marked drop in temperature.”

“This effect is much more pronounced on the Moon, where there is no atmosphere to insulate the surface, so heat is lost much more rapidly into space. And of course, unlike in the case of the building on a sunny day, during a real eclipse there is no surrounding sunlit area to act as a heat source.”

During the eclipse, Diviner will target ten specific regions on the lunar surface. These regions were chosen because they represent a wide range of lunar terrains, from seemingly smooth areas, to regions that appear to be relatively rocky; and from dark, iron-rich locations in the lunar maria to light, iron-poor locales in the lunar highlands. The rest of the instruments on LRO will be switched off to conserve energy.

October 21, 2010

Diviner results indicate presence of widespread ice on the Moon

Scientists from NASA’s Diviner Lunar Radiometer Experiment team published research in this week’s issue of Science that points to the widespread presence of water ice in large areas of the lunar south pole.

The Diviner Lunar Radiometer aboard NASA’s Lunar Reconnaissance Orbiter (LRO) has made the first-ever infrared measurements of temperatures in the permanently shadowed craters at the lunar poles. In October 2009, Diviner also made the first infrared observations of a controlled planetary impact when LCROSS, the companion spacecraft to LRO, slammed into one of the coldest of these craters in an experiment to confirm the presence or absence of water ice.

David Paige, Principal Investigator of the instrument, and lead author of one of two Science papers based on its observations, used temperature measurements of the lunar south pole obtained by Diviner to model the stability of water ice both at and near the surface.

“The temperatures inside these permanently-shadowed craters are even colder than we had expected. Our model results indicate that in these extreme cold conditions, surface deposits of water ice would almost certainly be stable,” says Paige, “but perhaps more significantly, these areas are surrounded by much larger permafrost regions where ice could be stable just beneath the surface.”

This lunar ‘permafrost’ would be analogous to the high-latitude terrain found on the Earth and on Mars, where sub-freezing temperatures persist below the surface throughout the year.

“These permafrost regions may receive direct sunlight at certain times of the year, but they maintain annual maximum subsurface temperatures that are sufficiently cold to prevent significant amounts of ice from vaporizing,” says Paige.

Given that these lunar permafrost regions are not in permanent shadow, surface lighting and thermal conditions in these locations would be far more hospitable for humans, which makes them of prime interest for future manned missions to the moon. Subsurface water ice deposits are also likely to be more stable than surface deposits of water ice because they are protected from bombardment by ultraviolet radiation and energetic cosmic particles.

“We conclude that large areas of the lunar south pole are cold enough to trap not only water ice, but other volatile compounds (substances with low boiling points) such as sulphur dioxide, carbon dioxide, formaldehyde, ammonia, methanol, mercury and sodium.”

LRO Diviner Lunar Radiometer Experiment surface temperature map of the south polar region of the Moon. The data were acquired during September and October, 2009 when south polar temperatures were close to their annual maximum values. The map shows the locations of several intensely cold impact craters that are potential cold traps for water ice as well as a range of other icy compounds commonly observed in comets. The approximate maximum temperatures at which these compounds would be frozen in place for more than a billion years is shown next to the scale on the right. The LCROSS spacecraft was targeted to impact one of the coldest of these craters, and many of these compounds, including water, were observed in the LCROSS ejecta plume.  Credit: UCLA/JPL/GSFC/NASA.

LRO Diviner Lunar Radiometer Experiment surface temperature map of the south polar region of the Moon. The data were acquired during September and October, 2009 when south polar temperatures were close to their annual maximum values. The map shows the locations of several intensely cold impact craters that are potential cold traps for water ice as well as a range of other icy compounds commonly observed in comets. The approximate maximum temperatures at which these compounds would be frozen in place for more than a billion years is shown next to the scale on the right. The LCROSS spacecraft was targeted to impact one of the coldest of these craters, and many of these compounds, including water, were observed in the LCROSS ejecta plume. Credit: Based on a figure in the journal Science (UCLA/JPL/GSFC/NASA).

A representative cross-section of these substances was detected by the LCROSS near-infrared spectrometers when its upper stage rocket impacted into Cabeus crater, ejecting a host of material that was previously buried beneath its surface.

The impact site was situated within a permanently-shadowed part of Cabeus with an average annual temperature of 37 K (-393 °F), making it one of the coldest locations near the lunar south pole. Temperature data from Diviner played a key role in the selection of Cabeus as the target for LCROSS, and when it came time for impact, Diviner scientists and engineers made sure that the instrument had a front row seat: Diviner targeted the impact site for 8 orbits spaced roughly 2 hours apart, the closest of which was timed to pass by 90 seconds after impact. It observed an enhanced thermal signal on this and two subsequent orbits.

Paul Hayne, UCLA graduate student and lead author of the second paper appearing in Science, was monitoring the data in real-time as it was sent back from Diviner.

“During the fly-by 90 seconds after impact, all seven of Diviner’s infrared channels measured an enhanced thermal signal from the crater. The more sensitive of its two solar channels also measured the thermal signal, along with reflected sunlight from the impact plume. Two hours later, the three longest wavelength channels picked up the signal, and after four hours only one channel detected anything above the background temperature.”

Diviner brightness temperature measurements of the lunar surface near the LCROSS impact site in Cabeus crater. (A) Before and after images of the LCROSS impact site in each of five different Diviner channels, with the thermal emission from the impact circled in the right-hand column, taken approximately 90 seconds after the Centaur impacted the lunar surface. (B) Pre-impact surface temperatures in Cabeus crater recorded by Diviner indicate the LCROSS impact site ('x') was only 40 degrees Celsius above absolute zero just before the impact. Credit: The Journal Science.

Diviner brightness temperature measurements of the lunar surface near the LCROSS impact site in Cabeus crater. (A) Before and after images of the LCROSS impact site in each of five different Diviner channels, with the thermal emission from the impact circled in the right-hand column, taken approximately 90 seconds after the Centaur impacted the lunar surface. (B) Pre-impact surface temperatures in Cabeus crater recorded by Diviner indicate the LCROSS impact site ('x') was only 40 degrees Celsius above absolute zero just before the impact. Credit: The journal Science.

Scientists were able to learn two things from these measurements: firstly, they were able to constrain the mass of material that was ejected outwards into space from the impact crater; secondly, they were able to infer the initial temperature and make estimates about the effects of ice in the soil on the observed cooling behavior.

“Diviner’s solar channel measured scattered sunlight from the impact plume over an area of 140 km2 (54 sq mi). Using this measurement we were able to place constraints on the mass of the cloud at between 1,200 kg and 5,800 kg (2,700 - 12,800 lbs), which is consistent with measurements by the LCROSS Shepherding Spacecraft,” says Hayne. “This is important because the cloud mass is used to estimate the abundance of water observed by the LCROSS spectrometers.”

“In addition, we determined that in order to agree with the data from each of Diviner’s channels, the impact must have heated a region of 30 to 200 m2 (320 – 2150 ft2) to at least 950 K (1250 °F). This concentrated region was surrounded by a larger, lower temperature component that would have included the surrounding blanket of material excavated by the impact.”

Given that ice within soil pore spaces influences cooling because it uses up heat energy in the process of sublimating, and conducts heat more efficiently than lunar soil does, scientists were able to use Diviner’s measurements of cooling at the impact site to place constraints on the proportion of volatiles present.

“The fact that heated material was still visible to Diviner after four hours indicates LCROSS did not hit a skating rink; the ice must have been mixed within the soil,” says Hayne, “we estimate that for an area of 30 to 200 m2, the steaming crater could produce more than enough water vapor to account for what was observed by LCROSS over a four minute period.”

“Although Cabeus crater is typical of the coldest areas on the moon today, we have determined that billions of years ago, smaller craters with steeper walls would have made more favorable cold-traps,” says Paige, “it is therefore possible that the craters which have accumulated the most ice are not the coldest ones.”

The results presented in both papers represent strong evidence in support of the theory that volatiles have been delivered to the moon by impacts by icy bodies from the outer solar system and then ‘cold-trapped’ at the lunar poles.

The research covered here is from two of six papers published in Science by scientists from LCROSS and LRO. The research was funded by NASA.

Full text versions of the articles published in Science can be found here:

Diviner Lunar Radiometer Observations of the LCROSS Impact
Diviner Lunar Radiometer Observations of Cold Traps in the Moon’s South Polar Region

September 16, 2010

Diviner Data Reveal Complex Lunar Geology

Using data from the Diviner Lunar Radiometer, an instrument uniquely capable of identifying common lunar silicate minerals, scientists are finding that the Moon is more geologically complex than previously thought. The data have revealed previously unseen compositional differences in the crustal highlands, and have confirmed the presence of anomalously silica-rich material in five distinct regions.

Every mineral, and therefore every rock, absorbs and emits energy with a unique spectral signature that can be measured to reveal its identity. For the first time ever, the Diviner Lunar Radiometer is providing scientists with global, high-resolution infrared maps of the Moon, which are enabling them to make a definitive identification of silicates commonly found within its crust. “Diviner is literally viewing the Moon in a whole new light” says Benjamin Greenhagen of NASA’s Jet Propulsion Laboratory, lead author of one of two papers on the research appearing in the next issue of Science.

Lunar geology can be roughly broken down into two categories – the anorthositic highlands, rich in calcium and aluminum, and the basaltic maria, which are abundant in iron and magnesium. Both of these crustal rocks are what’s deemed by geologists as ‘primitive’; that is, they are the direct result of crystallization from lunar mantle material.

Diviner’s observations have confirmed that most lunar terrains have spectral signatures consistent with compositions that fall into these two broad categories. However they have also revealed that the lunar highlands may be less homogenous than previously thought.

In a wide range of terrains, Diviner revealed the presence of lunar soils with compositions more sodium rich than that of the typical anorthosite crust. The fact that these soils are found in distinct locations around the surface implies that when the early lunar crust formed, there may have been variations in the chemistry and cooling rate of the molten material that it crystallized from.

Most impressively, in several locations around the Moon, Diviner has detected the presence of highly silicic minerals such as quartz, potassium-rich feldspar and sodium-rich feldspar - minerals that are only ever found in association with highly evolved lithologies (rocks that have undergone extensive magmatic processing).

Map showing locations (in purple) where the anorthositic crust exhibits compositional anomalies. The iron and magnesium-rich maria appear red while the calcium-rich highlands appear blue green. The five anomalous silicic features are labelled. (credit: The journal Science)

Map showing locations (in purple) where the anorthositic crust exhibits compositional anomalies. The iron and magnesium-rich maria appear red while the calcium-rich highlands appear blue green. The five anomalous silicic features are labelled. (credit: The journal Science)

The detection of silicic minerals at these locations is a significant finding for scientists, as they occur in areas previously shown to exhibit anomalously high abundances of the element thorium, another proxy for highly evolved lithologies.

“The silicic features we’ve found on the Moon are fundamentally different from the more typical basaltic mare and anorthositic highlands,says Timothy Glotch of Stony Brook University, lead author of the second paper based on this research, “The fact that we see this composition in multiple geologic settings suggests that there may have been multiple processes producing these rocks.”

Some of the silicic features, such as the Gruithiusen Domes, possess steep slopes and rough surfaces suggesting that they may be lava domes created by the slow extrusion of viscous lava on the lunar surface (similar to the dome which formed on Mt. St. Helens after its eruption).

In other regions, such as Aristarchus, the silicic spectral signatures are confined to impact craters and their ejecta blankets. This suggests that excavation of the subsurface caused by these impacts has exposed portions of plutons, which are magma bodies that solidified underground before reaching the surface.

Diviner data superimposed on a Lunar Orbiter IV mosaic of Aristarchus crater. Red and orange colors depict silicic compositions.

Diviner data superimposed on a Lunar Orbiter IV mosaic of Aristarchus crater. Red and orange colors depict silicic compositions. (credit: The journal Science)

So how did such highly silicic lithology form on a Moon that is dominated by calcium-rich anorthosite highlands, and iron and magnesium-rich basaltic maria?

Most of the silicic features occur in the Procellarum KREEP Terrane (PKT), an area on the lunar nearside known for its extensive basaltic volcanism. This has led scientists to believe that the silica-rich material present in this region is a result of hot basaltic magma intruding into and re-melting the lunar crust.

However, one of the regions, Compton Belkovich, occurs on the farside of the Moon, far from the PKT and its associated volcanism. The location of the Compton Belkovich anomaly suggests that the conditions that led to sustained heat production and volcanism within the PKT may have been present at much smaller scales on the far side of the Moon.

One thing not apparent in the data is evidence for pristine lunar mantle material, which previous studies have suggested may be exposed at some places on the lunar surface. Such material, rich in iron and magnesium, would be readily detected by Diviner.

However, even in the South Pole Aitken Basin (SPA), the largest, oldest, and deepest impact crater on the Moon - deep enough to have penetrated through the crust and into the mantle - there is no evidence of mantle material.

The implications of this are as yet unknown - perhaps there are no such exposures of mantle material, or maybe they occur in areas too small for Diviner to detect.

However it’s likely that if the impact that formed this crater did excavate any mantle material, it has since been mixed with crustal material from later impacts inside and outside SPA. “The new Diviner data will help in selecting the appropriate landing sites for future missions to return samples from SPA.   We want to use these samples to date the SPA-forming impact and potentially study the lunar mantle, so it’s important to use Diviner data to identify areas with minimal mixing. ” says Greenhagen.

greenhagen_webcast1

Full text versions of the articles published in Science can be found here:

Global Silicate Mineralogy of the Moon from the Diviner Lunar Radiometer
Highly Silicic Compositions on the Moon

December 15, 2009

Diviner Observes Extreme Polar Temperatures

The Diviner lunar radiometer has been mapping the temperature of the
Moon since July, 2009. During this period, temperatures in the lunar
polar regions have changed gradually as the lunar seasons have evolved.
The tilt of the moon’s spin axis is only 1.54 degrees and as a
consequence, lunar seasons are barely noticeable in most locations on
the Moon. However, at the north and south poles, the height of the sun
above the horizon varies by more than 3 degrees over the course of the
year. This affects the percentage of sunlit regions and surface
temperatures at the poles.

During October, 2009, Diviner observed the passage of summer solstice in
the southern hemisphere and winter solstice in the northern hemisphere.
The LRO launch date was chosen so that its orbital plane passed
through the noon to midnight plane in October, allowing Diviner to
measure the extremes of polar temperatures.  Figure 1 illustrates the
configuration of the LRO orbit and the lunar seasons.

polar_viewing_geometry_sm

Figure 1. The configuration of the LRO orbit during October 2009 allowed Diviner to measure maximum temperatures near summer solstice in the south polar region, and minimum temperatures near winter solstice in the north polar region. (NASA/GSFC/UCLA)

Figure 2 shows a Diviner Channel 8 thermal image of the south polar
region acquired between October 3-30, 2009. The mapping period overlaps
with the LCROSS impact on October 9, 2009. Figure 3 shows an annotated
version of the image, including the location of the LCROSS impact. The
rugged south polar topography  makes it one of the most picturesque
regions on the planet. Diviner’s thermal measurements allow us to “see”
both the warm sunlit and cold shadowed regions in striking
clarity and detail. Even at their warmest, the permanently shadowed areas
in the south polar region are extremely cold. The coldest areas are
located in doubly shadowed regions inside small craters that themselves
lie within the permanently shadowed regions of larger craters. Diviner
measured minimum channel 9 brightness temperatures as low as 35K (-238C
or -397F) in these areas, even at noon on the warmest day of the year.

 Figure 2. Diviner Channel 8 thermal image of the south polar region.

Figure 2. Diviner Channel 8 thermal image of the south polar region. (NASA/GSFC/UCLA)

Figure 3. Annotated version of Figure 2 including the location of the LCROSS impact.

Figure 3. Annotated version of Figure 2 including the location of the LCROSS impact. (NASA/GSFC/UCLA)

On the opposite side of the planet, Diviner mapped the north polar
region at winter solstice. Figure 4 shows a nighttime false-color
channel 9 map of the region that reveals the presence of areas with
temperatures as low as 25K (-258C or -415F).  The coldest spot on the Moon
that Diviner has detected thus far is located on the south western edge of
the floor of Hermite Crater. There are also regions on the southern
edges of the floors of Peary and Bosch Craters that are almost as cold.
To put these cold temperatures in perspective, one would have to travel
to a distance well beyond the Kuiper belt to find objects with surfaces
this cold. Diviner measures the temperature of the top millimeter of the
lunar surface. We would expect temperatures below the surface to be
warmer due to heat retention from the spring and summer seasons.

Figure 4. Diviner channel 9 nighttime brightness temperature map of the north polar region acquired close to winter solstice.

Figure 4. Diviner channel 9 nighttime brightness temperature map of the north polar region acquired close to winter solstice. (NASA/GSFC/UCLA)

Figure 5 shows an animated flyover of the north polar region that
terminates at the coldest measured areas inside of Hermite Crater.

flyover

Figure 5. Animated nighttime flyover of the north polar region during the mid-winter season. (NASA/GSFC/UCLA)

Figure 6 shows a histogram of measured daytime and nighttime Channel 9
brightness temperatures in both polar regions. The results show that
there are large regions at both poles with temperatures colder than
~106K, the temperature necessary to prevent significant loss of water
ice over billion-year timescales.  The Diviner data show that The LCROSS
impact successfully sampled one of the coldest lunar cold traps - a fact
that may help put the results of the LCROSS mission into context.

Figure 6. Histograms of Diviner Channel 9 brightness daytime and nighttime temperatures acquired in in the north and south polar regions (square regions to +/- 80 degrees latitude) during their respective winter and summer solstice seasons. The measured pre-impact daytime and nighttime summer solstice brightness temperatures for LCROSS impact site  are also indicated.

Figure 6. Histograms of Diviner Channel 9 brightness daytime and nighttime temperatures acquired in in the north and south polar regions (square regions to +/- 80 degrees latitude) during their respective winter and summer solstice seasons. The measured pre-impact daytime and nighttime summer solstice brightness temperatures for LCROSS impact site are also indicated. (NASA/GSFC/UCLA)

October 9, 2009

Diviner Observes LCROSS Impact

The LRO Diviner instrument obtained infrared observations of the LCROSS impact this morning. LRO flew by the LCROSS Centaur impact site 90 seconds after impact at a distance of ~80 km. Diviner was commanded to observe the impact site on eight successive orbits, and obtained a series of thermal maps before and after the impact at approximately two hour intervals at an angle of approximately 48 degrees off nadir. In this viewing geometry, the spatial footprint of each Diviner detector was roughly 300 by 700 meters.

Figure 1. Diviner thermal map of the LCROSS impact sites.

Figure 1. Diviner thermal map of the LCROSS impact sites (NASA/GSFC/UCLA).

Figure 1 shows the locations of the Diviner LCROSS impact swaths overlain on a grayscale daytime thermal map of the Moon’s south polar region. Diviner data were used to help select the final LCROSS impact site inside Cabeus Crater, which sampled an extremely cold region in permanent shadow that can serve as an effective cold trap for water ice and other frozen volatiles. Figure 2 shows preliminary, uncalibrated Diviner thermal maps of the impact site acquired two hours before the impact, and 90 seconds after the impact. The thermal signature of the impact was clearly detected in all four Diviner thermal mapping channels. Since the LCROSS impact feature is predicted to be significantly smaller than a Diviner footprint, its detection is consistent with the notion that the LCROSS  impact resulted in significant local heating of the lunar surface.

Figure 2. Diviner thermal maps in four infrared channels acquired before and after the LCROSS Centaur impact.

Figure 2. Uncalibrated Diviner thermal maps of the LCROSS impact region acquired before and after the LCROSS Centaur impact (NASA/GSFC/UCLA).

September 17, 2009

Diviner Commissioning Observations

Overview

The Diviner Lunar Radiometer Experiment is mapping the temperature of the surface of the Moon in unprecedented detail. Diviner is one of seven instruments aboard NASA’s Lunar Reconnaissance Orbiter (LRO) http://lunar.gsfc.nasa.gov/ which launched June 18, 2009.

The Moon’s surface temperatures are among the most extreme of any planetary body in the solar system. Noontime surface temperatures near the lunar equator are hotter than boiling water, whereas nighttime surface temperatures on the Moon are almost as cold as liquid oxygen. It has been estimated that near the lunar poles, in areas that never receive direct sunlight, temperatures can dip to within a few tens of degrees of absolute zero. During the course of LRO’s mapping mission, Diviner will map the entire surface of the Moon at a resolution of better than 500 meters to create the first global picture of the current thermal state of the moon and its daily and seasonal variability.

The Moon’s extreme temperature environment is of interest to future human and robotic explorers, especially if they plan on visiting the Moon for extended periods. Detailed thermal maps of the Moon can also yield information regarding the locations of rocky areas that may be hazardous to landing vehicles, and for mapping compositional variations in lunar rocks and soils. In the Moon’s polar regions, temperature maps also point to the locations of cold traps where water ice and other volatile materials may have accumulated. Mapping the locations of these lunar cold traps and searching for the presence of frozen water is one of the main goals of the LRO mission.

Diviner is designed, built, and operated by the California Institute of Technology Jet Propulsion Laboratory (JPL) in Pasadena, CA. Prof. David A. Paige of the University of California, Los Angeles (UCLA) is the Principal Investigator.

How Diviner Works

Diviner determines the temperature of the Moon by measuring the intensity of infrared radiation emitted by the lunar surface. The hotter the surface, the greater the intensity of emitted infrared radiation. Diviner measures infrared radiation in seven infrared channels (Channels 3-9) that cover a wavelength range from 7.6 to 400 microns. Diviner is the first instrument designed to measure the full range of lunar surface temperatures, from the hottest to the coldest. Diviner also includes two solar channels (Channels 1-2) that measure the intensity of reflected solar radiation.

As LRO orbits the Moon every two hours, Diviner maps a nearly continuous ~3.5 km-wide swath on the lunar surface. Diviner’s swath samples the full range of lunar longitudes once per month to create thermal maps. Diviner will acquire 24 thermal maps of the Moon over the course of a year - 12 daytime maps and 12 nighttime maps, each covering a different range of lunar local times.

Diviner Commissioning Orbit Operations

Diviner has been mapping the Moon continuously during the LRO commissioning phase. Since the instrument was first activated on July 5, 2009, it has acquired over 8 billion calibrated radiometric measurements, and has mapped almost 50% of the surface area of the Moon. “The performance of the instrument has been excellent, and closely matches our predictions” quotes Instrument Engineer Marc Foote at JPL. Says Principal Investigator David Paige of UCLA, “We have already accumulated an enormous amount of high-quality data”.

Diviner has obtained enough data during the LRO commissioning phase to characterize many aspects of the Moon’s current thermal environment. There are large gaps between Diviner’s individual ground tracks at the equator, but in the polar regions, the ground tracks overlap to create continuous high-resolution maps. The plane of the LRO orbit sampled from 5:40 am to 5:40 pm lunar local time at the start of commissioning and gradually drifted to sampling from 1:10 am to 1:10 pm by the end of commissioning. It will take about six months for LRO’s orbit to sample the full range of lunar local times.

In addition to mapping the Moon, Diviner executed a series of specialized calibration sequences to during the commissioning phase. These included scans of the limb of the Moon to better define the instruments fields of view, an infrared panorama of a portion of the LRO spacecraft (See Figures 1a-c), as well as infrared scans of the Earth from lunar orbit, which are presently being analyzed. “Diviner’s operations have run very smoothly” says JPL scientist and lead observational sequence designer Benjamin Greenhagen, “Diviner has been put through her paces and has executed our commands brilliantly”.

figure_1a5

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Figures 1a-c. Diviner acquired this infrared panorama of the LRO spacecraft between September 4 and 12, 2009. The panorama was constructed by combining over 7000 individual observations as Diviner used its azimuth and elevation actuators to raster across all areas of the LRO spacecraft within its field of regard.  To protect Diviner from pointing at the sun, the panorama was acquired over seven orbits while LRO was on the night side of the Moon. Diviner successfully imaged two other LRO instruments: Mini-RF and CRaTER, as well as portions of LOLA and LAMP.  The spacecraft panorama is useful for planning observation sequences and calibrations.

Figures 1a-c. Diviner acquired this infrared panorama of the LRO spacecraft between September 4 and 12, 2009. The panorama was constructed by combining over 7000 individual observations as Diviner used its azimuth and elevation actuators to raster across all areas of the LRO spacecraft within its field of regard. To protect Diviner from pointing at the sun, the panorama was acquired over seven orbits while LRO was on the night side of the Moon. Diviner successfully imaged two other LRO instruments: Mini-RF and CRaTER, as well as portions of LOLA and LAMP. The spacecraft panorama is useful for planning observation sequences and calibrations. (NASA/GSFC/UCLA)

First Global Temperature Maps

Figures 2a-b show the first global daytime and nighttime thermal maps of the Moon, created using Diviner data accumulated during August and the first-half of September, 2009. The maps show Channel 8 (50-100 micron wavelength range) brightness temperatures which approximate actual surface physical temperatures. Equatorial and mid-latitude daytime temperatures are close to 380K (224° F), and then decrease sharply poleward of 70° north latitude. Equatorial and mid-latitude nighttime temperatures are close to 95K (-298° F) and then decrease poleward of 80° north latitude. At low and mid-latitudes, there are isolated warmer regions with nighttime temperatures of 140K (-208° F). These correspond to the locations of larger fresh impact craters that have excavated rocky material that remains significantly warmer than the surrounding lunar soil throughout the long lunar night. The thermal behavior at high latitudes contrasts sharply with that of the equatorial and mid-latitudes. Close to the poles, both daytime and nighttime temperatures are strongly influenced by local topography and the thermal outlines of many partially illuminated impact craters are apparent. “Getting a look at the first global thermal maps of the lunar surface has been very exciting” says David Paige, “it’s a whole new way of seeing the Moon”.

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Figures 2a-b.  Diviner has acquired the first global daytime and nighttime thermal maps of the Moon. These maps were assembled using Diviner data obtained during August and the first half of September, 2009.

Figures 2a-b. Diviner has acquired the first global daytime and nighttime thermal maps of the Moon. These maps were assembled using Diviner data obtained during August and the first half of September, 2009. (NASA/GSFC/UCLA)

High-Resolution North and South Polar Thermal Maps

Figures 3a-b, 4a-b and 5a-b show Diviner high-resolution daytime thermal maps of the north and south polar regions acquired between July 17 and August 14, which corresponds to 5 pm and 3 pm lunar local time. Because of the eccentricity of the LRO commissioning orbit, the north polar maps have a spatial resolution of 700 m and the south polar maps have a spatial resolution of 250 m. Figures 3a and 4a show Diviner Channel 3 (8 micron wavelength) brightness temperatures. Channel 3 is Diviner’s shortest wavelength infrared channel and is insensitive to extremely low temperatures in unilluminated areas. This property makes it useful for mapping the extent of shadowed regions, which appear black just as in a visible image. Figures 3b and 4b show Diviner Channel 8 (50-100 micron wavelength) brightness temperatures. Channel 8 is one of Diviner’s longest wavelength infrared channels and it has excellent capability to measure extremely low temperatures in unilluminated areas.

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Figures 3a-b. High-resolution thermal maps of the north polar region of the Moon. The maps cover the region to 80° north latitude and were assembled from Diviner observations obtained in July and August, 2009. Fig. 3a shows Diviner Channel 3 observations and Fig. 3b shows Diviner Channel 8 observations. Diviner’s Channel 3 observations map illuminated and unilluminated areas of the Moon as they appeared when the observations were acquired. Diviner’s observations provide the first measurements of temperatures inside permanently shadowed polar craters that may contain deposits of cold-trapped water ice.

Figures 3a-b. High-resolution thermal maps of the north polar region of the Moon. The maps cover the region to 80° north latitude and were assembled from Diviner observations obtained in July and August, 2009. Fig. 3a shows Diviner Channel 3 observations and Fig. 3b shows Diviner Channel 8 observations. Diviner’s Channel 3 observations map illuminated and unilluminated areas of the Moon as they appeared when the observations were acquired. Diviner’s observations provide the first measurements of temperatures inside permanently shadowed polar craters that may contain deposits of cold-trapped water ice. (NASA/GSFC/UCLA)

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Figures 4a-b. High-resolution thermal maps of the south polar region of the Moon. The maps cover the region to 80° south latitude and were assembled from Diviner observations obtained during July and August, 2009. Fig. 4a shows Diviner Channel 3 observations and Fig. 4b shows Diviner Channel 8 observations. Diviner’s Channel 3 observations map illuminated and unilluminated areas of the Moon as they appeared when the observations were acquired. Diviner’s observations provide the first measurements of temperatures inside permanently shadowed polar craters that may contain deposits of cold-trapped water ice.

Figures 4a-b. High-resolution thermal maps of the south polar region of the Moon. The maps cover the region to 80° south latitude and were assembled from Diviner observations obtained during July and August, 2009. Fig. 4a shows Diviner Channel 3 observations and Fig. 4b shows Diviner Channel 8 observations. Diviner’s Channel 3 observations map illuminated and unilluminated areas of the Moon as they appeared when the observations were acquired. Diviner’s observations provide the first measurements of temperatures inside permanently shadowed polar craters that may contain deposits of cold-trapped water ice. (NASA/GSFC/UCLA)

The Channel 8 maps reveal richly detailed thermal behavior throughout the north and south polar regions that extends to the limit of Diviner’s spatial resolution (see Figures 5 and 6). Most notable are the measurements of extremely cold temperatures within the permanently shadowed regions of large polar impact craters in the south polar region. Diviner has recorded minimum daytime brightness temperatures in portions of these craters of less than 35K (-397° F) in the coldest areas. These are to our knowledge, these super-cold brightness temperatures are among the lowest that have been measured anywhere in the solar system, including the surface of Pluto. According to science team member Ashwin Vasavada of JPL, “After decades of speculation, Diviner has given us the first confirmation that these strange, permanently dark and extremely cold places actually exist on our Moon. Their presence greatly increases the likelihood that water or other compounds are frozen there. Diviner has lived up to its name.”

Figure 5. Close-up view of Diviner Channel 8 high-resolution thermal maps of a portion of the south polar region

Figure 5. Close-up view of Diviner Channel 8 high-resolution thermal maps of a portion of the south polar region, including super cold areas in permanent shadow. (NASA/GSFC/UCLA)

Figure 6. Annotated version of Figure 5 showing the locations of named impact craters.

Figure 6. Annotated version of Figure 5 showing the locations of named impact craters.

The Diviner commissioning phase observations provide a snapshot in time of current polar temperatures that will evolve with the lunar seasons. However, it is safe to conclude that the temperatures in these super-cold regions are definitely low enough to cold-trap water ice, as well as other more volatile compounds for extended periods. The existence of such cold traps has been predicted theoretically for almost 50 years. Diviner is now providing detailed information regarding their spatial distribution and temperatures. Diviner’s thermal observations represent one component of LRO’s strategy for determining the nature and distribution of cold-trapped water ice in the lunar polar regions. Future comparisons between Diviner data, physical models, and other polar datasets may provide important scientific conclusions regarding the nature and history of the Moon’s polar cold traps, and any cold-trapped volatile materials they contain.

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