Bubble Bubble - Swirl and Trouble

Swirls in Mare Ingenii, far side of the Moon (LROC: The Swirls of Mare Ingenii, Brett Denevi, June 22, 2012.)  [NASA/GSFC/Arizona State University].

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

The Moon, unlike Earth, has no global magnetic field but many surface locales of limited extent (tens of kilometers across) are magnetized.  In many instances, these small areas of high magnetic intensity are associated with unusual patterns of surface brightness (albedo, or degree of reflectance) that occur in curved, blotchy or other strange “swirl-like” shapes.  First observed by telescope, lunar scientists have been puzzled by the possible origin of what they imaginatively named “swirls.”

An example of a lunar swirl is a feature named Reiner γ (pronounced “Reiner gamma”), a bright splotch in southern Oceanus Procellarum, the dark mare region of the western near side.  The name indicates that initially this feature was thought to be an isolated peak of highland material that juts up through the mare (lowercase Greek letters were assigned to such prominences in the old nomenclature.)  However, even at very low sun elevations, close examination shows that this bright patch does not cast a shadow.  It is simply a bright patch on the surface, one with diffuse and nebulous edges, yet clearly more reflective than the surrounding dark mare material.  It does not appear to be associated with any crater or other surface feature.  It’s as though someone smudged a finished painting of the lunar surface.

During later Apollo missions, orbiting vehicles released “sub-satellites” (small spacecraft that continued to orbit the Moon long after the crews had left for home) carrying instruments to measure the Moon’s magnetic field.  Interestingly, they found a very strong magnetic field enhancement around the Reiner γ feature.  Moreover, numerous other swirls were found elsewhere on the Moon, especially on the floor of the huge South Pole-Aitken (SPA) basin in Mare Ingenii on the far side, and on the eastern limb of the Moon near Mare Marginis.  Each newly seen swirl was found to be associated with a magnetic anomaly.  However, the converse statement is not true – not all magnetic anomalies have associated swirls.

Two principal models emerged to explain these relations.  One model held that the swirls and the magnetism were contemporaneous – the swirls were surficial deposits caused by the scouring of the surface during the impact of a comet.  In this model, the cometary coma (i.e., the dense gaseous “atmosphere” surrounding the icy nucleus) struck the Moon at high velocity, scouring the surface and increasing its brightness while at the same time embedding the soil with a strong magnetic field caused by the creation of an impact-generated plasma (high temperature, low density matter).

The other model suggested that the magnetic anomalies pre-dated and were the cause of the swirls.  The lunar surface darkens and becomes redder with time owing to exposure to the solar wind (the stream of energetic particles – mostly protons – from the Sun).  Strong, localized magnetic fields serve as protective “bubbles” that caused the incident solar wind to flow around these tiny areas, darkening the edges of the field bubbles with enhanced flow but preserving the inner zones (which were shielded from the solar wind) as bright patches.  Thus, the bright parts of the swirls are areas that have not undergone “weathering” by the solar wind while the dark parts are zones that have experienced excessive space weathering.

Magnetic bubble created in the laboratory [RAL/Univ. York].

It remained uncertain whether this postulated “magnetic bubble” effect would actually work but recent experiments suggest that these bubbles might well operate on the Moon.  Scientists from the UK’s Rutherford Appleton Laboratory, creating a “solar wind tunnel” to observe the interactions of streaming plasma and confined magnetic bubbles, successfully produced a magnetic bubble under simulated space conditions.  They have compared the flow field around the laboratory magnetic bubble with the observations from orbiting spacecraft of lunar surface magnetism and find that the solar wind would be diverted around these magnetic anomalies on the Moon.  If solar wind darkening is the primary process that darkens the surface, we may have an explanation for the creation of the bright swirls.

70 kilometer-wide field of view LROC Wide Angle Camera (WAC) mosaic swept up from two orbital passes in May 2010. (The yellow box show a roughly 2.5 km-wide LROC Narrow Angle Camera (NAC) field of view in the image below. Something is allowing the radiation-linked maturation of lunar regolith in the dark lanes of Reiner Gamma while continuing to keep dust at the surface of its bright albedo lanes fresh and optically immature. Though the local magnetic field is probably strong enough to refract solar radiation, it's not sufficient for repelling more energetic (and admittedly less frequent) cosmic rays. The latter should have sufficient time to redden (darken) or "mature" the bright regions over about 900 million years [NASA/GSFC/Arizona State University].

The astute reader will note that while this bubble model might account for the origin of the swirls, it begs the question about what caused the magnetic field anomalies in the first place.  That remains a mystery.  It was noted many years ago by my colleague Lon Hood of the University of Arizona that many of the magnetic anomalies on the Moon are at the antipodes (i.e., 180° away from the center) of some of the youngest, large impact basins on the Moon.  The largest concentration of both surface magnetic anomalies and swirls are on the floor of the large SPA basin, near Mare Ingenii on the lunar far side.  This area is directly antipodal to the large, young Imbrium basin on the near side.  Likewise, the Mare Marginis swirls and magnetic fields are antipodal to the Orientale basin on the western limb (the last of the large lunar multi-ring impact basins).  Furthermore, as basins tend to cover the entire Moon, one can find a basin near the antipodes of almost any given feature (note well: the swirl that started all this hubbub, Reiner γ, isn’t antipodal to anything in particular).  But an even more significant issue is that while the basin antipodal association of many swirls is intriguing, it does not explain why we should see a zone of enhanced magnetization at such locations.  Igneous intrusion, concentration of impact-generated plasmas and converging ballistic ejecta have all been proposed but no specific mechanism seems to emerge as the magnetic field creating event.

We are left with a continuing and highly unsatisfactory situation – a possible explanation for the development of surface swirls on the Moon and of their association with magnetic field bubbles, but we still don’t understand the origins of these fields, the cause of their shapes and intensities and how they fit into the continually vexing problem of lunar magnetism in general.  Two steps forward and one step back.   Lunar science marches on.

Originally published at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average. 

Moon in UV sheds light on maturation and materials

One of four "enigmatic" domes singled out in a segment of an LROC Wide Angle Camera (WAC) color mosaic released at the European Planetary Science Congress and the American Astronomical Society's Division for Planetary Sciences on October 7. Long suspected of being a separate species from more common volcanic features, like those of the Marius Hills, the Darney C 3 domes ("D" on the second image following) on the border of Mare Cognitum with Oceanus Procellarum (11.22°S, 333.5°E) may, instead, be fragments of a long obliterated lunar crust or islands, once high places now nearly buried  by the flows that created the nearside's basins. LRO orbits 4559 and 4560, June 22, 2010; from 44.9 km altitude, resolution ~ 62.5 meters per pixel [NASA/GSFC/Arizona State University].

Editors Note: Fairly reliable elemental maps of the Moon have been around since the Apollo era, becoming more detailed as planetary scientists continue to comb through data obtained by Clementine (1994) and Lunar Prospector (1998-1999) (along with those of the flotilla of probes dispatched by ESA, Japan, India and China). The highest-resolution direct observations of the Moon are still being swept up by the record-shattering Lunar Reconnaissance Orbiter, now well into a third year in low lunar orbit and only beginning to show a degree of age after the loss of Mini-RF operations and a redundant gyro this past year.

In December LRO will be raised to a more stable 100 km-high orbit to save fuel after orbiting the Moon 11,000 times since arriving in lunar orbit in June 2009, and long after becoming the longest lasting lunar mission as well, returning more data than all previous Deep Space missions put together.

LRO teams continue to use earlier abaselines to map confirm the abundance of a variety of strategic elements on the lunar surface, and in unprecedented detail.A promise made for delivering such comprehensive high-resolution color maps and elemental surveys of the Moon is being fulfilled.

What follows is "value-added" detail from a widely-circulated press release about presentations made by the Lunar Reconnaissance Orbiter Camera (LROC) investigators to a joint meeting of the European Planetary Science Congress and the American Astronomical Society's Division for Planetary Sciences on October 7. Along with the elusive original demonstration images we've added a number of mosaics of images already released to the Planetary Data System.

From a partial map of the nearside lunar surface centered on the colorful contact zone bordering Mare Serenitatis and Mare Tranquillitatis, combining observations in visible and ultraviolet wavelengths and showing a 'treasure trove' of areas rich in titanium oxide. Titanium is a valuable element, key to helping scientists unravel mysteries of the Moon's interior. LROC investigators Mark Robinson and Brett Denevi presented the results at the European Planetary Science Congress and the American Astronomical Society's Division for Planetary Sciences on October 7. The relative blue color of the Tranquillitatis mare is due to a higher abundances of the titanium-bearing mineral ilmenite. Direct study of samples gathered by Cernan and Schmitt (Taurus Littrow, Apollo 17, December 1972) aided in establishing baselines for comparable elemental signatures. Enhanced color formed as 689 nm filter image in red, 415 nm in green, and 321 nm in blue. See the full size demonstration image HERE [NASA/GSFC/Arizona State University].

Titanium relative abundance mapped
by Clementine (1994).

From: EPSC/ASA Joint Meeting 2011 Press Notice - October 7
 

Subtly Shaded Map of Moon Reveals Titanium Treasure Troves

"Looking up at the Moon, its surface appears painted with shades of grey -- at least to the human eye. But with the right instruments, the Moon can appear colorful," said Mark Robinson, of Arizona State University. "The maria appear reddish in some places and blue in others. Although subtle, these color variations tell us important things about the chemistry and evolution of the lunar surface. They indicate the titanium and iron abundance, as well as the maturity of a lunar soil."

The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) is imaging the surface in seven different wavelengths at a resolution of between 100 and 400 metres per pixel. Specific minerals reflect or absorb strongly certain parts of the electromagnetic spectrum, so the wavelengths detected by LROC WAC help scientists better understand the chemical composition of the lunar surface.

Robinson and his team previously developed a technique using Hubble Space Telescope images to map titanium abundances around a small area centred on the Apollo 17 landing site. Samples around the site spanned a broad range of titanium levels.  By comparing the Apollo data from the ground with the Hubble images, the team found that the titanium levels corresponded to the ratio of ultraviolet to visible light reflected by the lunar soils.

“Our challenge was to find out whether the technique would work across broad areas, or whether there was something special about the Apollo 17 area,” said Robinson.

Robinson’s team constructed a mosaic from around 4000 LRO WAC images collected over one month. Using the technique they had developed with the Hubble imagery, they used the WAC ratio of the brightness in the ultraviolet to visible light to deduce titanium abundance, backed up by surface samples gathered by Apollo and Luna missions.

The new map shows that in the mare titanium abundances range from about one percent to a little more than ten percent. In the highlands, everywhere TiO2 is less than one percent. The new titanium values match those measured in the ground samples to about one percent.

From a full-resolution LROC Wide Angle Camera three-color composite (566 nm filter image in red, 360 nm in green, and 321 nm in blue), "Figure 2" accompanying the October 7 press release, highlighting regions with varying mare compositions and certain of the more "enigmatic" small volcanic domes. The area shown is a familiar nearside territory, west longitude from around 340° to 320° and from the equatorial landing sites of Apollo 12 and 14 down to 21° south. View the full size image accompanying the October 7 press release HERE  [NASA/GSFC/Arizona State University].

Designated by the letter "H" in 'Figure 2' immediately above is 'the Helmet," apparently the official designation for the enigmatic dome previously known as Agatharchides 1 (and "the Fireman's Hat) for the associated crater group, may be an island of ancient crust 60 km wide floating northeast of Mare Humorum (18.2°S, 328.9°E). Mosaic of three LROC WAC observations in the 643 nm band, January 27, 2011 [NASA/GSFC/Arizona State University].

“We still don’t really understand why we find much higher abundances of titanium on the Moon compared to similar types of rocks on Earth.  What the lunar titanium-richness does tell us is that the interior of the Moon had less oxygen when it was formed, knowledge that geochemists value for understanding the evolution of the Moon,” said Robinson.

Lunar titanium is mostly found in the mineral ilmenite, a compound containing iron, titanium and oxygen. Future miners living and working on the Moon could break down ilmenite to liberate these elements.  In addition, Apollo data shows that titanium-rich minerals are more efficient at retaining particles from the solar wind, such as helium and hydrogen. These gases would also provide a vital resource for future human inhabitants of lunar colonies.

“The new map is a valuable tool for lunar exploration planning. Astronauts will want to visit places with both high scientific value and a high potential for resources that can be used to support exploration activities. Areas with high titanium provide both – a pathway to understanding the interior of the Moon and potential mining resources,” said Denevi, from John Hopkins University.

Based on it's spectacular rays and highly reflective deeper anatomy Giordano Bruno (35.9°N, 102.8°E) had once been believed the result of a very recent event, perhaps even a famous 12th century phenomena witnessed and recorded by European monks. Though that theory fell by the wayside some time ago, LROC Wide Angle Camera UV imagery has shown optical maturity by solar UV radiation occurs more rapidly than previously understood. In the LROC WAC UV mosaic below, more or less matching the area shown above of global lunar albedo mosaic from the 1994 Clementine mission, the wider area affected by the G. Bruno event is far less dramatic [NASA/DOD/VMA6].

On the other hand, in the LROC global UV mosaic (Figure 3 from the Oct. 7 press release: Color Ratio 321 nm / 415 nm), the full extent of the Goddard/Mare Marginis albedo swirl, contrasts with it's background quite well. The coincident crustal magnetic anomaly is antipodal to Mare Orientale, which, though the youngest of the classic impact basins is still estimated at over 3 billion years old. This image adds evidence to the theory that lunar swirls associated with fossil magnetic fields must result from a more dynamic phenomena than merely deflection of solar radiation by magnetic fields. Shedding and retaining charged sub-micron regolith must, in no small part, be linked with the Moon's "daily" dusty atmospheric cycles [NASA/GSFC/Arizona State University].

The new maps also shed light on how space weather changes the lunar surface. Over time, the lunar surface materials are altered by the impact of charged particles from the solar wind and high-velocity micrometeorite impacts. Together these processes work to pulverize rock into a fine powder and alter the surface’s chemical composition and hence its colour.  Recently exposed rocks, such as the rays that are thrown out around impact craters, appear bluer and have higher reflectance than more mature soil. Over time this ‘young’ material darkens and reddens, disappearing into the background after about 500 million years.

“One of the exciting discoveries we’ve made is that the effects of weathering show up much more quickly in ultraviolet than in visible or infrared wavelengths.  In the LROC ultraviolet mosaics, even craters that we thought were very young appear relatively mature. Only small, very recently formed craters show up as fresh regolith exposed on the surface,” said Robinson.

SCIENCE CONTACTS:

Mark Robinson 
Arizona State University
School of Earth and Space Exploration
E-mail: robinson@ser.asu.edu
http://ser.sese.asu.edu/
Brett Denevi
The Johns Hopkins University
Applied Physics Laboratory
Brett.Denevi@jhuapl.edu 

Figure 4 from the October 7 press release compares the familiar Reiner Gamma swirl in the visual with the UV (right), as seen in LROC WAC mosaics. Nearside swirls differ from those on the farside. They are fewer and none are linked with basin-forming impacts on the opposite side of the Moon. The beauty of the swirl at Reiner Gamma and the much more vague bright albedo of the Descartes Formation are associated with the strongest crustal magnetic anomalies yet mapped. Reiner Gamma is almost certainly linked geologically with the Marius Hills. Regardless, in ultra-violet, Reiner y seems too fresh and too superficial for an airless body whose surface is gardened every 2 million years. The Moon's dusty surface may be migrating very slowly, but it is surely on the move [NASA/GSFC/Arizona State University].

A seventy kilometer-wide field of view LROC WAC mosaic swept up during two orbital passes last May. The yellow box show the roughly 2.5 km-wide Narrow Angle Camera field of view shown in the last image, below. Something is allowing the radiation-linked maturation of lunar regolith in the dark lanes of Reiner Gamma and continually keeping the dust at the surface of its bright albedo fresh and optically (and UV) "immature." The intense crustal magnetism closely incidental with this very long but very superficial swirl anomaly may be linked to sub-surface flows of melt and remelted materials originating in the Marius Hills, where the swirl has a clear terminus, 200 kilometers to the northeast. Though the local magnetic field may be intense enough to refract solar radiation it is insufficient at repelling more energetic (or, admittedly less frequent) cosmic rays. Though less frequent, the latter would have had sufficient time to mature the brighter regions over the last 900 million years. Instead, it was proposed in 2008 by one of us (and more recently by Carle Pieters, et.al.) that a far more dynamic, seasonal and daily cycle of lunar dust formation, charging, discharging and relentless migration is being disrupted at these locations [NASA/GSFC/Arizona State University].

LROC Narrow Angle Camera (NAC) observation M114342150L, LRO orbit 1984, December 1, 2009 [NASA/GSFC/Arizona State University].

Juxtaposed LROC WAC mosaics of the Lassell dome formation designated with the letter "L" in the third image from the top in this posting, Figure 2 from the October 7 press release. From LRO orbital observations under different angles of incidence.  M129350040CE, orbit 4195, May 24, 2010 (phase angle 55.94°) and M147041474CE, orbit 6803, December 15, 2010 (phase angle 76.89°) [NASA/GSFC/Arizona State University].

How to make gif

UK laser locates LRO within 10 cm

As spotlighted on August 12 ("Laser ranging and LRO") NASA's Goddard Space Flight Center is using the Lunar Reconnaissance Orbiter laser altimeter ("LOLA") for more than just determining the distance and anatomy of the lunar surface. Routed through the vehicle's high-gain antenna, LOLA is also being used to make more accurate measurements of the distance between its transient location in lunar orbit and fixed points on Earth. The method used for "reflecting" laser light pulses from Earth is not passive, as with decades of counting photons being reflected back to Earth by the laser "retro-reflector" mirror arrays left on the Moon by Apollo. Instead, LRO collects photons after a one-way trip, at the vehicle, and then tags the data before returning detailed information back to Earth. Eventually, this method may aid in resolving some hairy cosmic questions, such as whether expansion of the Cosmos varies locally from what is observed at great distances. On July 12, the United Kingdom's Space Geodesy Facility located LRO within 10 centimeters, using a 13 Hz timed laser pulse from its SLR . The UK's SGF is managed by the National Environmental Research Council, which announced the results on their website "Planet Earth."

Goddard takes advantage of STEREO A & B ride through L4 & L5 to gather evidence of Earth Trojans

Join STEREO and Explore Gravitational "Parking Lots" That May Hold Secret of Moon's Origin

Goddard Space Flight Center

Two places on opposite sides of Earth may hold the secret to how the moon was born. NASA's twin Solar Terrestrial Relations Observatory (STEREO) spacecraft are about to enter these zones, known as the L4 and L5 Lagrangian points, each centered about 93 million miles away along Earth's orbit.

As rare as free parking in New York City, L4 and L5 are among the special points in our solar system around which spacecraft and other objects can loiter. They are where the gravitational pull of a nearby planet or the sun balances the forces from the object's orbital motion. Such points closer to Earth are sometimes used as spaceship "parking lots", like the L1 point a million miles away in the direction of the sun. They are officially called Libration points or Lagrangian points after Joseph-Louis Lagrange, an Italian-French mathematician who helped discover them.

L4 and L5 are where an object's motion can be balanced by the combined gravity of the sun and Earth. "These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago," said Michael Kaiser, Project Scientist for STEREO at NASA's Goddard Space Flight Center in Greenbelt, Md. "According to Edward Belbruno and Richard Gott at Princeton University, about 4.5 billion years ago when the planets were still growing, this hypothetical world, called Theia, may have been nudged out of L4 or L5 by the increasing gravity of the other developing planets like Venus and sent on a collision course with Earth. The resulting impact blasted the outer layers of Theia and Earth into orbit, which eventually coalesced under their own gravity to form the moon."

This theory is a modification of the "giant impact" theory of the moon's origin, which has become the dominant theory because it explains some puzzling properties of the moon, such as its relatively small iron core. According to giant impact, at the time of the collision, the two planets were large enough to be molten, so heavier elements, like iron, sank to their centers to form their cores.

The impact stripped away the outer layers of the two worlds, which contained mostly lighter elements, like silicon. Since the moon formed from this material, it is iron-poor.

Complete story HERE.

Northrop Grumman Integrating LCROSS Instruments; Mission to Seek Water Ice On Moon's South Pole - "on the fast track"

REDONDO BEACH Northrop Grumman Corporation is integrating the cameras, spectrometers and photometer comprising the nine instrument payload for the NASA's Lunar Crater Observation and Sensing Satellite (LCROSS) onto the spacecraft. LCROSS will impact the moon to determine the presence of water ice in one of its permanently shadowed craters at the lunar South Pole.

A photo accompanying this release is available at http://media.primezone.com/noc

The LCROSS payload is shown undergoing checkout following its arrival at Northrop Grumman's manufacturing facility in Redondo Beach, Calif. Built by NASA Ames, the payload consists of nine science instruments, weighs only 27.3 pounds (12.4 kilograms) and was designed to provide multiple complementary measurements. Eight of LCROSS' nine sensors are surrounded by a sunshade. The ninth LCROSS sensor views a perpendicular plane during the final impact and is located to the lower right outside the sunshade.

NASA Ames Research Center delivered all nine payload instruments to Northrop Grumman in mid-January, already assembled on a single, 30-by-40 inch spacecraft panel. The first step in integration, attaching electrical harnesses for power, telemetry and thermal control functions, has been completed, and the remaining steps will be completed over the next several weeks.

"Our entire approach to building, testing and integrating LCROSS was designed for speed," said Steve Hixson, vice president of Advanced Concepts for Northrop Grumman's Space Technology sector. "We're using innovative techniques to manage the LCROSS schedule, and this latest milestone is an outstanding example of the transparency between the government and industry teams that will be critical to our success. It's coming together very well, so we're already seeing the payoff in terms of schedule."

LCROSS is a fast track spacecraft development project. The Northrop Grumman-NASA team is utilizing streamlined acquisition and production processes to meet the mission's accelerated development schedule and cost constraints. Northrop Grumman expects to deliver the spacecraft about 26 months after the program start, less than half the time of a traditional spacecraft development program.

LCROSS and the Lunar Reconnaissance Orbiter, scheduled to launch at the end of the year aboard an Atlas V rocket, are the first American missions to return to the moon since the Lunar Prospector mission in 1999. LCROSS is the only current mission to the lunar surface. NASA scientists expect the impact plume will be visible from Earth with a medium-size (10-12 inch) amateur telescope.

LCROSS' nine science instruments, some of which were obtained commercially and qualified at NASA Ames, will analyze the plume from the impact for the presence of water ice or water vapor, hydrocarbons and hydrated materials. They consist of five cameras, operating in the visible, near infrared and mid-infrared light regimes; three spectrometers, operating in the ultraviolet, visible and near infrared; and one photometer operating in the visible light regime.

The LCROSS Spacecraft will ship to Florida late this summer for integration aboard the Atlas V launch vehicle. LCROSS will be launched as a secondary payload to NASA's Lunar Reconnaissance Orbiter from the NASA's Kennedy Space Center. Northrop Grumman is working under a $56 million contract to NASA Ames Research Center in Sunnyvale, Calif.

Northrop Grumman Corporation is a $32 billion global defense and technology company whose 120,000 employees provide innovative systems, products, and solutions in information and services, electronics, aerospace and shipbuilding to government and commercial customers worldwide.

CONTACT: Sally Koris
        Northrop Grumman Space Technology
        310.812.4721
        sally.koris@ngc.com