LRO Mini-RF spends month mapping lunar poles

The Mini-RF radar instrument on-board the Lunar Reconnaissance Orbiter has just completed its first month of systematic polar mapping. These mosaics cover from 70° to the pole for both the north (top) and south (bottom) polar regions. The left-hand images show radar brightness whilst the right-hand color images also show the circular polarization ratio. These data will be analyzed to search for ice deposits in the floors of the permanently shadowed craters, as well as to learn more about the impact cratering process on the Moon.

In this close-up of the full-size mosaic released by NASA August 7, most of the resolution is drained of the very granularity investigators are looking for, and have found at these highest northern latitudes, indications of changes in the polarity of radar signals returned to the spacecraft consistent with, among very few other things, hydrogen in a bound state with oxygen, as frozen water. Lost in this hazy reproduction also is a small crater singled last month showing a exceptionally strong indication. (See Potentially ice-rich' crater in Rozhdestvenskiy, Friday, July 2, 2010).

Familiar relief is obscured in Mini-RF (and in representations of data returned by the somewhat less sensitive but proven valuable Mini-SAR instrument flown on India's Chandrayaan-1), but the information obtained is like nothing else. Mapping and narrowing the possible composition of the lunar surface must be an exceptionally interesting study in images not yet available to the public [NASA/GSFC].

This nighttime temperature map, shown for reference, assembled from LRO Diviner data closely matches the field of view further up. (Left center, along the western interior of Hermite is an area unseen until LRO, within a permanently shadowed region now known to host the coldest temperatures yet detected in the entire solar system, during long lunar night only 25 degrees K.) [NASA/GSFC]

'Potentially ice-rich' crater in Rozhdestvenskiy

NASA Radar returns first high-resolution view of an unusual crater near Moon’s north pole

Investigators for Mini-RF, the synthetic aperture radar on-board NASA’s Lunar Reconnaissance Orbiter (LRO), recently imaged a potentially ice-rich crater near the north pole of the Moon.

Located at 85°N, 193.4°E, this permanently shadowed crater, about 8 km in diameter, is on the floor of the larger, more degraded 177 km Rozhdestvenskiy. With no sunlight to warm the crater floor and walls, ice brought to the Moon by comets or formed through interactions with solar wind appears to have collected there.

The crater was first identified as a region of interest during India's (ISRO) Chandrayaan-1 mission in2009, when it was seen to exhibit unusual radar properties consistent with the presence of ice.

With a resolution 10x better than the radar aboard Chandrayaan-1, LRO's Mini-RF allows NASA to see details of the crater’s interior.

In particular the circular polarization ratio (CPR) measures polarization characteristics of radar echoes, which give clues to the nature of the surface materials.

The inset figure shows a colorized CPR image of the crater. Red pixels have CPR values greater than 1.2. The CPR values inside the crater are almost all greater than 1, while CPR values outside the crater are generally low (much less than 1).

Regions with CPR greater than 1 are relatively rare in nature, but are commonly seen in regions with thick deposits of ice, such as Martian polar caps or the icy Galilean satellites. These are also seen in rough, blocky ejecta around fresh, young craters but in that occurrence scientists also observe high CPR outside the crater rim.

This crater has high CPR inside but low CPR outside. The Mini-RF team plans to examine data from the other LRO instruments, particularly temperature and topographic measurements, to better characterize the environment and setting of these unusual features near the poles of the Moon.

Global context map (Virtual Moon Atlas v.4) shows the location of recently noted lunar north pole craters. Nearby, permanently shadowed region (PSR) within Hermite may feature the coldest temperatures yet recorded in the entire Solar System. Goldshmidt, at a relatively lower latitude, has demonstrated a unusually high water signature in daylight.

The Four Flavors of Lunar Water

From Lunar Pioneer

Earth over the watery north polar regions of the Moon, as viewed from NASA/DOD platform Clementine (1994) [USGS].

Paul D. Spudis
The Once and Future Moon
Smithsonian Air & Space Blogs

The Moon is constantly bombarded by the solid debris of the Solar System. Comets, asteroids and interplanetary dust, all containing varying amounts of water, have pounded the lunar surface for billions of years. Yet until recently, the Moon was considered to be barren and bone-dry. Rock and soil samples returned by the Apollo missions lacked any hydrous mineral phases or water-bearing weathering products. Since water is not stable on the Moon under ordinary conditions, what happens to it?

New studies of lunar samples, along with results from several missions in recent years, have given us a revolutionary new picture of water on the Moon. Study of volcanic glass from the Apollo 15 landing site in 2008 demonstrated that tiny amounts of water (about 50 parts per million) are present in the interiors of these glasses, suggesting that the lunar mantle (whence they came) contains about ten times this amount. This was a startling result, considering the extreme dryness of other lunar samples.

Because the Moon’s spin axis is nearly perpendicular (1.5° from vertical) to the ecliptic plane, the Sun is always on the horizon at the poles, keeping the floors of deep craters in permanent shadow. These dark areas only receive heat from the interior of the Moon and are extremely cold; recent measurements by the DIVINER instrument on the Lunar Reconnaissance Orbiter (LRO) spacecraft indicate temperatures as cold as 25-35° C above absolute zero. Water molecules are trapped by the cold as soon as they find their way into these craters. Over the more than 4.5 billion years of lunar history, significant amounts of water could accumulate in many of these crater “cold traps” at the Moon’s poles.

"The Moon is on the critical path to human expansion into the Solar System."

The first hint of water ice in these polar cold traps came from a radio experiment aboard the 1994 Clementine mapping mission orbiting the Moon. The polarization characteristics of echoes from the south pole were consistent with the presence of ice in the crater Shackleton. Four years later, the Lunar Prospector (LP) spacecraft carried an instrument designed to measure the amount and energy of neutrons given off the Moon’s surface. Hydrogen absorbs neutrons, so when LP investigators saw a decrease in the flux of medium-energy neutrons near the lunar poles, they concluded that excess amounts of hydrogen were present there. Although this observation is consistent with the presence of polar ice, neutron data alone do not tell us what form the hydrogen is in, and it was alternatively postulated that this enhancement was caused by excess solar wind hydrogen.

The Moon Mineralogy Mapper (M3) instrument on the 2008-09 Indian Chandrayaan-1 mission collected reflectance spectra for most of the Moon. It found both water (H2O) and hydroxyl (OH) molecules, present either as a monolayer on lunar dust grains or bound into the mineral structures in surface materials, poleward of about 65° latitude at both poles. Moreover, the abundance of this surface water varies with time, being present in greater quantity in both local early morning and late evening and it increases in abundance with increasing latitude. These results were verified by observations from the Cassini and EPOXI spacecraft during separate flybys of the Moon. The new observations indicate significant quantities of water moving towards areas with lower mean surface temperatures and increasing in abundance with latitude. Taken all together, the results mean that water is being deposited (e.g., by comet impact) and/or created (e.g., by reduction of metal oxides in the surface by solar wind protons) and then transported to the poles. By this process, significant quantities of water ice could accumulate at the poles over geological time.

Last October, the companion satellite to LRO, LCROSS, slammed the upper stage of its launch vehicle into the Moon’s south pole and observed the ejected material. Results show that both water vapor and ice particles were ejected from the LCROSS impact crater; initial analyses indicate that water is present at about the 5-10 wt.% level. The LCROSS impact site exhibits no anomalous radar behavior, suggesting that such an amount of water ice cannot be detected by radar. However, the results do indicate that significant amounts of lunar polar water may be present even in the absence of specific radar evidence for it. Spectra from this impact event show evidence for other volatile substances, including ammonia and simple carbon compounds. The presence of such material may indicate a cometary source for these volatile materials.

Both poles were covered by radar images from the Mini-SAR instrument on Chandrayaan-1. Much of the north polar region displays backscattering properties typical for the ordinary Moon, but one group of craters in the region show elevated polarization enhancements in their interiors, but not in deposits exterior to their rims. Almost all of these anomalous craters are in permanent sun shadow and correlate with proposed locations of ice modeled on the basis of the Lunar Prospector neutron data. These relations suggest that the interiors of these craters contain nearly pure water ice, with approximately 600 million metric tonnes of ice present in over 40 small craters within 10 degrees of the pole. The south polar region shows similar relations, except that it has fewer anomalous craters than the north pole. Small areas of polarization enhancement are found in some craters, notably Shoemaker, Haworth and Faustini; these areas might be deposits of water ice.

So water on the Moon is present in large quantity in at least four different “flavors.” Water was in the deep lunar interior 3.3 billion years ago, at concentration levels of a few hundred parts per million. This water would have been released during the eruption of lunar magma and could have made its way into the polar cold traps. Water is either being made or being deposited nearly continuously by impact all over the Moon. Most of this water is subsequently lost to space (e.g., by sputtering, ionization or thermal escape) but some is retained on the Moon. Any water arriving at a cold trap near the pole will be captured. Water, once in the polar areas, is stable as ice in the permanent darkness or where sublimation is prevented when buried by a thin layer of soil. Significant quantities of water may accumulate there; the LCROSS results suggest several to tens of weight percent water ice may exist in the polar soils. Finally, some of this migrating water apparently collects at rates high enough so that significant soil cannot mix with it during normal impact bombardment, as shown by the presence of relatively “pure” water ice deposits in selected lunar craters imaged by radar.

A significant amount of water at the poles of the Moon is present, with many billions of metric tonnes at each pole (detailed estimates of the water reserves are in progress). Such an amount is more than enough to support both permanent, sustainable human presence on the Moon and for export to cislunar space. Water is useful as rocket fuel and energy storage (hydrogen and oxygen are the two most powerful chemical propellants known) and for life support (water and oxygen) in space. These new discoveries fundamentally alter our understanding of the Moon’s processes and history and highlight both it’s scientific value and utilization potential. The Moon is on the critical path to human expansion into the Solar System.

Addendum. In Comments, below Dr. Spudis original post, Pradeep Mohandas reminded the author of the findings of the Moon Impact Probe, released from Chandrayaan-1, which discovered water vapor in very small concentrations in the space just above the Moon during its descent to the south pole. "This exospheric water (i.e., water in extremely small concentrations) may be related to the time-variable water seen in the spectral data from M3, Cassini, and EPOXI — in other words, it may represent water molecules in motion, migrating toward the poles. Work on the nature and processes of the lunar hydrosphere continues, and I will keep you up to date on the latest research results on this new and exciting subtopic of lunar science."

LRO Mini-RF: Asymmetric crater in Mare Nubium

Mini-RF has imaged this unusual crater in Mare Nubium that shows a bright pattern of ejecta around the crater, but with and excluded zone in one sector. We know from laboratory experiments that this is caused by a very low-angle, oblique impact, coming from the direction of the excluded zone (south). The large crater at bottom is Kies C (26° S 26.1° W; 5 km diameter). Area shown is about 12 km wide by 25 km long [View large version of the Nubium Crater (1.3 MB) NASA/GSFC/LRO-Mini-RF].

LRO's Mini-RF Serenitatus Swath

LRO Mini-RF S-band zoom synthetic aperture radar (SAR) image strip through central Mare Serenitatis on the near side of the Moon (approximate longitude of strip ~ 18° E; center latitude ~ 20° N). (Full Image HERE.)

The radar strip runs through the crater Bessel (inset; 17 km (10 mile) diameter; center at 21.8° N, 17.9° E) and covers the highlands of the Haemus Mts. (rim of Serenitatis basin) in its southern (bottom) third. The full-resolution SAR data are 30 m (90 feet). The streaks of bright and dark material in the walls of Bessel probably reflect the blockiness of landslides within the crater, brighter streaks having more blocks of the 10-cm (4-inch) scale. The radar strip covers a major geological boundary in Mare Serenitatis; the darker, lower maria has higher titanium content than central Serenitatis. We see this geological boundary in the Mini-RF radar image, caused by higher absorption of RF energy by the high content of the iron-titanium oxide mineral ilmenite. Thus, Mini-RF SAR images can be used to map the titanium content of the lunar maria. The background image is part of the Clementine global mosaic [NASA/GSFC].

For no particular reason, a notional view of the interior of Bessel as seen within the Apollo corridor, the high-definition digital elevation model supported in all current versions of the Moon as seen in Google Earth application. Bessel stands out in minimal telescopes from Earth. It's easy to spot, just south of the basin's center, though there is some question whether the 17 km crater actually lies inside a prominent ray of Tycho, running north from Menelaus. That ray does seem to originate at Tycho, though it is slightly "off" when traced all the way back to the more famous ~109 year old crater 2100 km away in the southern highlands. But this "discontinuity" may just be a matter of perspective, an optical illusion, since the ray lines up well with Tycho when viewed from directly overhead.

Strong hints of lunar H2O stirs excitement

This Mini-RF image from NASA's powerful Lunar Reconnaissance Orbiter shows radar imagery of the lunar south pole, a potential reservoir for hidden water ice, in new images released Sept. 17, 2009. [NASA/APL/LPSI]

Leonard David
Space.com

Earth's aged, crater-pocked and seemingly bone-dry moon may well sport a wet look.

That outlook is gaining momentum via a wealth of new scientific measurements gleaned by an international armada of moon-orbiting scientific scouts, including a report last week that craters near the lunar poles, always in shadow, may harbor water ice.

Such a prospect could fuel those eager to send human explorers back to the moon, to establish a base camp there, and to hone talent and hardware for jumping off to other destinations.

Locating, mining and processing polar deposits of water ice on the moon, it is reasoned, would add up to a useful resource for future lunar inhabitants.

The idea of ice in the floors of sunlight-shy polar lunar craters was first aired in 1961 by Caltech researchers Kenneth Watson, Bruce Murray and Harrison Brown. In the late 1970s, James Arnold of the University of California, San Diego, suggested that comets and water-rich asteroids crashing into the moon could deposit water to the lunar surface.

Still, is the chatter about new lines of evidence supportive of water ice at the lunar poles a slam-dunk situation?

"If ice is found we have to further explore it with landers, rovers, coring drills to assess its distribution and composition," explained Bernard Foing, project scientist for the European Space Agency's now-defunct SMART-1 lunar orbiter. Foing is also the director of the International Lunar Exploration Working Group.

After such an assessment is made, the next task would be to figure out how ice could be partly exploited on the spot in some areas to ease the next steps of human exploration toward an international lunar base, Foing said.

Read the Article HERE.

Chandrayaan's orientation problematic during joint Mini-SAR survey of Erlanger with LRO

Chandrayaan-1 initial Mini-SAR portrait of a permanently shadowed portion of south pole crater Haworth, as released by NASA in January.

In the week prior to the August 28 premature shut-down of IRSO's Chandrayaan-1 it's NASA-built Mini-SAR side-glancing radar mapper continued to frustrate scientists correcting for earlier problems with India's first lunar orbiter.

Chandrayaan remained improperly aligned with its Mini-RF counterpart on-board NASA's Lunar Reconnaissance Orbiter (LRO).

On August 20 researchers worked to retrieve data from Chandrayaan-1 Mini-SAR using the LRO still undergoing commissioning, as its own near twin Mini-RF radar simultaneously gathered similar data from a slighly different angle of the same target, the permanently shadowed floor of 10 km Erlanger crater, near the Moon's north pole.

The maneuver brought Chandrayaan-1 and it's more recently arrived companion for the United State, LRO, "within kilometers" of one another in polar orbit of the Moon.

New Scientist reports "each spacecraft made it to its planned position, but programming problems on the US-built Mini-SAR instrument aboard Chandrayaan prevented the device from sending a radio pulse," according to NASA's Jason Crusan in Washington.

"Later analysis showed that even if Mini-SAR had released the pulse, the signal would not have reached its target because Chandrayaan-1's orientation was drifting more rapidly than anticipated," Crusan said.

Chandrayaan-1 has been orienting itself using spinning gyroscopes and the sun since its star-tracking system failed earlier this year.

To correct for the problem of the failed star-tracker, "the team found a way to correct Mini-SAR's programming and better estimate Chandrayaan-1's drift. Then ground controllers abruptly lost radio contact with Chandrayaan-1 on 28 August – a death knell for the mission."

"We were actually in the middle of planning to conduct the experiment at a future time," Crusan told New Scientist.

"Obviously with the termination of the Chandrayaan mission, that will not happen."

Stewart Nozette of the Lunar and Planetary Science Institute in Houston, who lead work on Mini-SAR's sister-instrument on LRO, called Mini-RF, said the joint experiment would have produced a very clear signal of water ice if it were present," a strategic goal of most of the recent series of lunar orbiters, and a top priority for NASA, beginning with LRO together with the LCROSS mission, still set for a shepherded kinetic explosion within one of six shadowed craters near the Moon's south pole on October 9.

"I think that it would have been the icing on the cake if we had been able to do that," Nozette told New Scientist. "It would have been the best thing you can do from the remote sensing perspective."

Even so, radar collected by LRO and Chandrayaan-1 individually could still reveal water ice – though not as clearly, Nozette said. Water ice, it is believed, should appear brighter at RF frequencies than rock viewed from above with star-lit equipment.

If such a signal appears only in areas that are permanently shaded – where free volatiles should stay protected from solar energy, it could suggest the presence of water.

It may not be long before new information on the ice question is revealed. Chandrayaan-1 flew over "a lot of little craters that looked like they had ice" and mapped 95 per cent of the polar regions before its mission ended," Nozette said.

The radar results are currently in review.

LRO & Chandrayaan to team up, Aug. 20

Nancy Atkinson
Universe Today

NASA's Lunar Reconnaissance Orbiter (LRO) and India's Chandrayaan-1 will team up on August 20 to perform a Bi-Static radar experiment to search for water ice in a crater on the Moon's north pole.

Both spacecraft will be in close proximity, approximately 200 km above the lunar surface, and both are equipped with radar instruments. The two instruments will look at the same location from different angles. Chandrayaan's radar will transmit a signal to be reflected off the interior of Erlanger crater and then received by LRO.

Scientists will then compare the signal that bounces straight back to Chandrayaan with the signal from a slightly different angle received by LRO and assemble unique information, particularly about any water ice that may be present inside Erlanger.

Both spacecraft are equipped with a NASA Miniature Radio Frequency (RF) instrument that functions as a Synthetic Aperture Radar (SAR), known as Mini-SAR on Chandrayaan-1 and Mini-RF on LRO.

Read the full story HERE.