The long road to ALSEP data recovery

The human presence on the Moon did not end with Gene Cernan’s final footsteps, nor with Jack Schmitt’s final words before the Apollo 17 lunar module launched from the lunar surface on December 14th, 1972. The remnants of the six Apollo endeavors will, of course, remain on the lunar surface indefinitely as monuments of 20th Century space exploration. But for five years after Apollo 17, a human presence on the Moon was maintained through a collection of experiments at each landing site called the ALSEP program.

Down-Sun picture of the Lunar Mass Spectrometer with the main hub and antenna in the background. (Image from the Apollo Lunar Surface Journal)

Over 5000 ARCSAV tapes were produced during the years of ALSEP data collection, and today most of these are missing

When the Apollo Lunar Surface Experiments Package (ALSEP) program was terminated on September 30th, 1977, it brought an end to 8 years of continuous data collection on a planetary body – a record that would stand (I believe) until Opportunity rolled past 3000 sols in 2012. And, much like Opportunity, ALSEP experiments long outlived their nominal one-year lifetimes. The ALSEP program relayed real-time data on seismicity (natural and astronaut-made), solar wind strength, ion flux, shallow surface heat flow and more to the distributed Manned Space Flight Network on Earth. Analog magnetic tapes (14-track range tapes) from the distributed network were collected at the Johnson Space Center (JSC) for further processing and re-recording. Range tapes made between November 1969 and February 1973 were to be permanently archived at Goddard Space Flight Center. Between 1973 and February 1976, a day’s worth of data from each site were stored onto separate magnetic tapes (7-track digital ARCSAV tapes) so range tapes could be recycled. Data processing was moved offsite (1976-1977) to the University of Texas, where the use of ARCSAV tapes were replaced by 9-track digital tapes (work tapes). And throughout this eight year period, numerous tapes were made for preliminary reports by PIs (PI tapes). Well over 5000 ARCSAV tapes were produced during the years of ALSEP data collection, and today most of these are missing.

In fact, if this tape rack represented the entirety of the ALSEP data collection, we would only have about three tapes (Image by fastlizard4 on Flickr)

The extended-mission life of ALSEP operations created some unanticipated issues for PIs. For example, the six passive seismic experiments recorded data 24-hours a day, enough to fill over one thousand range tapes per year for each site. The ever-growing volume of data tapes were increasingly difficult for PIs to work with, though this was abated somewhat by transferring to higher data-density tapes. The sharp decline in post-Apollo funding – NASA’s budget dropped by a third in the 1970′s – meant some PIs could not devote the hours necessary for data processing and maintenance. Although PIs were instructed to archive tapes with the Washington National Record Center (WNRC), the requirements were vague and poorly enforced and so only an estimated 50% of the PI data were archived. In some cases this was only a subset of processed, “scientifically important” data as selected by PI teams.

Records show something like 3270 ARCSAV tapes made between April 1973 to February 1976 were sent to WNRC. Records also show a massive withdrawal of analog tapes from WNRC, prompted by the tape shortage in 1980, which included ~2800 ARCSAV tapes as Goddard Space Flight Center staff searched high and low for reusable/recyclable tapes. Fortunately, the 7-track digital tapes were not their target (the Apollo 11 landing footage tapes were probably not as fortunate), but instead of returning them to WNRC the ARCSAV tapes were stored in the basement of GSFC. Many of these were later destroyed in a 1990 building flood, and the trail of surviving tapes goes cold after they were removed from the basement of GSFC during cleanup.

Modern computers could do so much more with the ALSEP tapes than was previously possible, if only the data were available. The potential was highlighted in the 1990′s when the University of Texas ’76-’77 tapes were reprocessed and made available on the National Space Science Data Center. But a concerted effort to find the missing tapes wouldn’t get off the ground until 2004, when the presidential mandate for space exploration sparked a resurgence in lunar research in terms of both interest and funds. With practically zero ground-truth characterization of the lunar surface (apart from returned samples and meteorites) and lunar atmosphere, the ALSEP program was a natural target for reevaluation. Suddenly there was a call for these tapes that were nowhere to be found. The NLSI Recovery of Missing Data Focus Group was formally convened in 2007 and is a multi-institutional, (mostly) volunteer-run effort led by some of the original ALSEP PIs.

Apollo 12 dust detector PI tape of days 465-468 (Source: Prof. Brian J. O’Brien PI and SpectrumData)

It is through the efforts of the ALSEP focus group that most of what we know of the tapes has come to light. Every year at the Lunar & Planetary Science Forum (in March) and Lunar Science Forum (in July), the group has a side meeting where they share their successes and frustrations. And there have been successes. In 2010, ~450 ARCSAV tapes made between April and June of 1975 were recovered from WNRC. And at some point, a large quantity of ALSEP data was condensed onto microfiche and microfilm, and also backed up on paper. For LPSC this year, an abstract from the group announced the complete restoration of seven lunar data sets. Another eight data sets are in the final stages and will likely be completed by LPSC, with a promise of more to come. In short, many raw data tapes have been recovered…and also some processed data tapes, and reprocessed tapes of processed data tapes, and prints of raw and processed data…now what?

Hopefully “restoration” should hint at something more involved than slapping an ARCSAV tape in a reader and ripping it onto a hard drive like a CD. Well…OK, that is part of it. But unsurprisingly, such tape readers in working condition are increasingly rare, and at least some of the ARCSAV data recovery was outsourced to data recovery/conversion companies or citizens. Prof. Brian J. O’Brien (Australian government) was an original PI for the Early Apollo Surface Experiments Package (EASEP) and ALSEP Dust Detectors (Apollo 11, 12, 14, and 15) and the Charged Particle Lunar Environment experiment (Apollo 14). He maintained possession of a number of original tapes (including the one pictured above), and is working with SpectrumData to recover quality data.

And quality is the other main issue here. Tape quality degrades over time. Converting tape formats can introduce transcription errors. Processed data might be missing metadata on conversion programs, units, calibrations, random transcription errors, or whatever “corrections” the PI deemed necessary. Even in raw data tapes, anomalies occasionally occur because, after all, they came from the Moon.

It’s all the way past those trees and everything. (Photo by poikiloblastic)

Without relevant metadata (including telemetry to assess transmission quality), the tapes would be worse than useless because any product would rest on a flawed foundation. That remains a major obstacle to data restoration. Significant progress in terms of tapes acquired and metadata resolved has been via cooperation with PI teams and their universities, with one PI even lending an ALSEP experiment notebook to scan for use in calibrating a data set. Prior to archiving with the Planetary Data System, data sets undergo peer review. The ALSEP-recovered-data-related abstracts submitted to LPSC this year are a promising sign of the science return we can expect to see from these important datasets in the years to come.

References:

Almost all of the details above are collected from focus group meetings at the NLSI Lunar Science Forum (2011 & 2012), as well as ALSEP Data Recovery Focus Group progress abstracts submitted to the Lunar and Planetary Science Conference (2011 & 2013). My contribution to the focus group thus far has been to introduce myself at the beginning of said meetings.

ALSEP system and experiment reports are available from the LPI website.

Recovered EASEP and ALSEP data sets are archived in the Planetary Data System Geoscience Node.

Related: Lunar Orbiter Image Recovery Program (LOIRP)

Remove a carbon coat from thin sections with methanol

tl;dr: methanol is great but don’t let it kill you

Thin sections, oh glorious thin sections! They are little slices of truth, windows into the processes that shape all rocks. And for a variety of reasons, geologists do terrible things to them. Thin sections are subjected to staining, acid etching, laser beams and more. In my case, my samples are all subjected to the electron microprobe for in-situ mineral analysis. The first step in this process is to coat each thin section in carbon. Samples are placed in a carbon evaporator, which creates a vacuum (down to at least ~10^-4 torr) and coats the sample in a ~20nm thick carbon layer. This is great for analytical work, but it dulls everything in plane polarized light, can mask birefringence colors, and just forget about trying reflect light microscopy.

Carbon coated lunar basalt 70135,64 looks mostly “normal” in plane-polarized light (though a bit dim). Most major phases are easily identifiable (plag = plagioclase; px = pyroxene), but reflected light is necessary to identify opaques…

Same area of lunar basalt 70135,64 shown in reflected light. Not only can you still not identify the opaque phases, but you’ve lost the boundaries between plagioclase and pyroxene!

It’s just a big gray mass of cracks. If you need to take a second look at your sample, that carbon coat will just have to go! Despite being only 20nm thick, the coating is surprisingly resilient. You must also take care not to damage the thin section, so what do you do? There are various ways to approach carbon coat removal, and I thought it would be useful to highlight two common methods: grit and methanol

Removing a carbon coating with Al-polish

Use a fine grit Al-oxide powder and water to polish off the carbon coat. This quote from a mineral forum post suggests several ways to remove a carbon coat, including:

The simplest way to remove a carbon coat or a gold coat is via a 1 micron Al2O3-H2O slurry (1 part Al2O3 to 8 parts H2O) on a Buehler Polishing Cloth ( Catalog No. 40-7218 Microcloth with adhesive for a 8 inch wheel) aka “moleskin”. Gentle rubbing of the thin section or grain mount by hand on the mole skin polishing cloth (on a flat surface) with a generous amount of the slurry will completely remove the coating both on the surface of the mineral grains as well as in between the cracks and grain boundaries. This is due to the the action of the very fine short hairs of the moleskin. The Al2O3 can be easily removed under a running tap (preferably distilled water) or else (if fussy) in distilled water for five minutes under ultrasound. Afterwards the thin section or grain mount should be dried using a soft cloth or a kleenex wipe.

I really like the idea of using a polishing cloth, as it is rather difficult to remove carbon from low areas (e.g., cracks) with only a kimwipe. Removing Al2O3 buildup in these areas can also prove difficult. In addition, this method gets messy, and I am always worried about over-polishing and losing the sample. That is why I prefer to use methanol.

Removing a carbon coating with methanol

Methanol is also an effective carbon coat remover, with one caveat: Methanol is extremely toxic! You should already be wearing gloves during cleaning to prevent your gross human oils from transferring to the thin sections, but in the case of methanol it is an absolute necessity to have proper hand protection. I also prefer to work under a fume hood to prevent inhalation (and because it smells wicked strong). Methanol is my preferred method because it is clear and evaporates rapidly, making for an easy assessment of the status of carbon removal and leaves almost nothing to clean up.

Before, during, and after carbon coat removal. Methanol preferentially removed carbon from the sample, so it was cleaned before the surrounding epoxy. The thin section is 1″ diameter.

How I removed this carbon coat with methanol:

1. Wear safety gloves
2. Place the thin section on a flat surface
3. Moisten a kimwipe with a drop or two of methanol
4. Hold the thin section in place and rub the kimwipe in a variably circular motion, applying gentle pressure
5. Regularly change the face of the kimwipe being rubbed on the thin section. This minimizes the risk of loosened material scratching the surface.
6. Keep the kimwipe moist but not too juicy with methanol
7. Check your progress in reflected light. The image below is the nearly-cleaned thin section, with a couple trouble spots to finish up. Checking your progress early and often is the best way to get your eye in on carbon coat removal. You won’t know when it’s all gone if you have no idea what it looked like before you started!

A couple of minutes work on 70135,64 and the carbon coat is nearly gone. Now we can see the opaque phases in 70135,64 are mostly ilmenite, with some exsolution troilite (and unlabeled Fe-metal and possible melt inclusions) popping out that we would have missed previously.

70135,64 after methanol removal of the carbon coat. Notice the change from the previous picture – we uncovered a new exsolution feature in the lower left ilmenite grain. The ugly methanol droplets are also almost all gone, and the remaining “bubbles” are melt inclusions.

A few swipes with a methanol-dipped kimwipe is also a quick way to remove all those annoying loose particles surrounding laser ablation pits.

Wedge Fifty: The Catskills Conundrum

The following mystery was written for Accretionary Wedge #50, hosted by Evelyn of Georneys. This month we are invited to:

Share a fun moment from geology field camp or a geology field trip. You can share a story, a picture, a song, a slogan, a page from your field notebook– anything you like!

On to the story…

The Brunton Compass is a field geology staple. Image from the Brunton website (click to visit).

Every geologist worth their rock salt recognizes – and hopefully knows how to use – a Brunton Compass (Evelyn gave them their due in B is for Brunton). Housing a compass (with adjustable declination), clinometer and mirror at less than 10 ounces, the Brunton is important as much for its form as its function. One of the more common uses of a Brunton is to take strike and dip measurements of strata. Strike indicates the compass direction of the originally horizontal bedding plane (i.e. the orientation). Dip is the angle relative to horizontal in the downward direction of the bedding plane, measured with a simple adjustable bubble level.

Visualizing strike and dip can be tough at first, and it’s easier done than said. That’s why, on an undergraduate class trip to the Catskills, our first task of the day was to warm up with some Brunton practice – and we needed some warming up. It was crisp late September morning, and many of us were sporting geology club hoodies, warm hats and gloves. Fortunately the Catskills record a smorgasbord of interesting geologic events to get the blood flowing, and our first stop of the day was a doozy.

The “Taconic Unconformity” near Catskill, NY. Steeply dipping Ordovician sandstone interbedded with shale (right) lies unconformibly below a not-quite-as-steeply dipping Silurian-age limestone and medium-grained sandstone (left).

There is no evidence of deformation on the discontinuity (it is an angular unconformity), but there is a fault zone as well, with slickenlines. Ron Schott’s gigapan of the area shows the broader context, though I couldn’t find any slickenlines. Anyway, Bruntons in hand, we spread out over the outcrop to measure the strike and dip of the surfaces with slickenlines. Some of the not-quite-awake students worked in pairs.

It is not difficult to persuade geologists to climb. Here the structures class swarms an outcrop in the Catskills to practice using a Brunton in taking strike and dip measurements.

After our Professor had made the rounds to see everyone had the general idea, we collected together and reached a general consensus of strike and dip measurements. The slickenlines were striking towards the west-northwest and were dipping around 45 degrees south…I think. My notes from this trip aren’t very good, but everyone seemed to be in agreement. Well, almost everyone.

One student spoke up about some wonky strike measurements she had recorded. Sometimes they would be striking west, but then other areas seemed to say the slickenlines were striking north or southwest. Her dip measurements were spot on, but she was getting no consistency with strike. It wasn’t a method issue, as she demonstrated she used the normal strike-taking steps. We had a mystery on our hands! A nice little brain teaser to start the morning. The Prof started running through a process of elimination to find the source of error.

It is possible for magnetic minerals in rocks to mess with the compass and give erroneous strike measurements, but that was ruled out as the rest of us were getting consistent results. The Prof took strike in one area, then had her measure the same location and it was way off. They swapped Bruntons with the same result. A little frustrated, the student took off her fingerless mittens to get a better feel when taking strike measurements. She remeasured the strike and finally read a west-northwest strike. The Prof gave her back her Brunton, and the needle once again pointed west-northwest. Things seemed back to normal…but what caused the slew of mis-measurements that morning?

The Prof figured it out first. He asked to see a mitten, which had a flap that could be folded back to make a fingerless glove. The student had been using it in the fingerless configuration, with the flap held securely to the back of the mitten. The Prof folded the flap near the back of the mitten and smiled as several small but powerful hidden magnets pulled the flap back into place with a dull thud.

Sampling Gruithuisen

The following is an abstract I wrote for – but never submitted to – the 2011 micro-symposium on The Importance of Solar System Sample Return Missions to the Future of Planetary Science. Because of time constraints I had to limit myself to a single presentation on how and why we sample crater ejecta (PDF of that abstract here).

Introduction:  The case for planetary differentiation has been well established for inner Solar System planets. Samples from meteoritic material and robotic and manned missions have contributed to current models of planetary evolution. A key early finding of the Apollo missions was evidence for a lunar magma ocean (LMO) and the early differentiation of terrestrial planets [1, 2]. This model was later applied to other rocky planets such as the Earth, Mars, and Venus.

Silicic volcanism represents a compositional end-member of planetary differentiation. As late-stage products, these evolved magmas may be used to place constraints on mantle sources and processes. Silicic magma in sufficient quantities may also play a role in early planetary mantle dynamics, magmatism and crustal evolution.

Non-terrestrial silicic volcanism is potentially identified on Venus (e.g., Pancake Volcanoes) and the Moon (e.g., Gruithuisen Domes) [3, 4]. Of these locations, the Moon is both uniquely preserved and accessible to robotic and manned missions. The Gruithuisen Domes were a Constellation region of interest, and much work has been done to characterize the area.

Samples to determine the extent and range of products of differentiation are among the highest lunar science priorities [5, 6]. Silicic volcanic terranes are rare in the current lunar sample collection. Those that have been identified are of uncertain provenance [4]. Origins as the products of silica-liquid immiscibility or basaltic underplating have been proposed for non-mare domes, but it is unclear whether they are volumetrically minor late stage residual melt or form large intrusive (and extrusive) bodies [7, 8].

Image and caption from [NASA/GSFC/Arizona State University]: “All three of the Gruithuisen domes and the surrounding terrain are shown in WAC frame M117752970. Image width is 64 km and illumination is from the left.” Click the photo to visit the post on the LROC website.

Gruithuisen Domes:  Located on the northeast margin of Oceanus Procellarum, the Gruithuisen Domes area contains three dome structures: Gruithuisen Delta (27 km diameter), Gruithuisen Gamma (19 km), and Gruithuisen Northwest (7.5 km) [4]. As nearside non-mare volcanic features, they represent an accessible and valuable scientific site. Spectral observations indicate the domes are low in iron and titanium compared to mare and are also enriched in thorium (~20-40 ppm), similar in nature to rhyolite domes on Earth [7,9]. Emplacement and rheology models also indicate similarities with rhyolite [10]. Elevation profiles of central summit craters are consistent with non-impact origin [6].

The Gruithuisen Domes are located in a geologically complex region proximal to highland and mare units. On the basis of crater counts and geologic mapping, the timing of dome emplacement has been calculated as 3.85-3.72 Ga (Late Imbrian), earlier than the ≤3.55 Ga surrounding mare units [7, 11]. A significant contribution of sample return would be the establishment of an absolute age for these units and the association with the surrounding mare and underlying highlands. [Click here to visit the featured post on the Gruithuisen Domes at the LROC website.]

Sample Missions:  Scientific potential is significant for a stationary lander, and only increases if mobile rovers and manned missions are also considered.

Automated Sample Return.  There are several potentially key areas of focus for a sample return mission from the Gruithuisen Domes. The summits of larger domes are plateaus large enough to target for automated landing. Targeting the plateaus may avoid issues associated with landing on mare or highland terrane. Flank slopes (11-18 degrees [6]) may present problems for a lander, but are manageable by rover. A single sample return from the Gruithuisen Domes would likely yield rock types currently lacking in the lunar sample collection.

Manned Sample Return.  Adding a human element enhances the diversity and quality of collected samples. Mobile missions are currently restricted to a 10km radius around the lunar module on slopes of less than 25 degrees. Within these architectural constraints, a single mission could fully explore one dome or sample the flanks of two domes and the surrounding mare.

References:

1. J. A. Wood et al. (1970) Lunar anorthosites and a geophysical model of the Moon. Proceedings of the 11th Lunar Science Conference, 965-988.
2. P. H. Warren (1985) The magma ocean concept and lunar evolution. Annual Reviews of Earth & Planetary Science 13, 201-240.
3. J. H. Fink et al. (1993) Shapes of Venusian “pancake’ domes imply episodic emplacement and silicic composition. Geophysical Research Letters 20, 261-264.
4. J. W. Head and T. B. McCord (1978) Imbrian-Age Highland Volcanism on the Moon: The Gruithuisen and Mairan Domes. Science 199, 1433-1436.
5. NRC (2007) The Scientific Context for Exploration of the Moon, 107p.
6. S. E. Braden et al. (2010) Morphology of Gruithuisen and Hortensius Domes: Mare vs nonmare volcanism (PDF). Lunar and Planetary Science Conference XXXXI, #2677.
7. S. D. Chevrel et al. (1999) Gruithuisen domes region: A candidate for an extended nonmare volcanism unit on the Moon. Journal of Geophysical Research 104, 16515-16529.
8. S. E. Braden et al. (2007) Unexplored Areas of the Moon: Nonmare Domes. Planetary Science Decadal Survey, 2013-2022.
9. J. J. Hagerty et al. (2006) Refined thorium abundances for lunar red spots: Implications for evolved, nonmare volcanism on the Moon. Journal of Geophysical Research 111, E06002.
10. L. Wilson and J. W. Head (2003) Deep generation of magmatic gas on the Moon and implications for pyroclastic eruptions. Journal of Geophysical Research 108, 5012.
11. R. Wagner et al. (2002) Stratigraphic sequence and ages of volcanic units in the Gruithuisen region of the Moon. Journal of Geophysical Research 107(E11), 5104.

Flippin’ Rocks

click to view Flickr group

Thanks to this post by Rebecca in the Woods, I found out that today is International Rock Flipping Day! The purpose of IRFD from the main post at Wanderin’ Weeta:

It’s a day set aside to explore a too-often forgotten part of our world, one we walk past every day, and rarely are aware of; our nearest neighbours, the vibrant life under our feet.

I needed to take a walk, so I grabbed my phone and headed out with a friend to circle St. Mary’s Lake on the Notre Dame campus. Unfortunately the college landscapers apparently decided against leaving any rocks of size lying about for passerby’s to trip on. Instead we headed home and I had to settle for some concrete rip-rap near an apartment complex.

The “rock” in its natural state

It became unusually blurry and overexposed when flipped (a defense mechanism?)

The “rock”, flipped

Getting closer, there was a slug that didn’t seem to perturbed to being exposed. His buddy the worm schlooped underground when I got too close:

Mr. Snail and The Worm hanging out

And bonus creature, clinging to the underside of the “rock” was this guy:

Spider chilling out

I placed the rock back in place, being careful not to crush the slug. Happy International Rock Flipping Day!

Six days in the crater, day three

Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6

This post is part of a slowly unfolding saga of my experience at the Meteor Crater Field Camp that was held from October 17-23, 2010. The field camp was run under the NASA Lunar Science Institute and headed by Dr. David Kring of the Lunar and Planetary Institute.
This post also doubles as my entry into Accretionary Wedge #49: Out of This World, which focuses on extraterrestrial geology and terrestrial analogues. Thanks to Dana at En Tequila Es Verdad for hosting this month’s Wedge!

Tuesday, October 19, 2010.

From above, our deluge of sun hats would appear to run into and froth against the tourist rope corral for a moment before spilling over and around into the area of No Trespassing. Rapidly arriving at a flattened part of the rim, we diffuse and come to rest, idly shifting for something in our backpacks and maybe a better view into the crater. David starts speaking of the plans for the day, and it takes us a few moments to realize we’re looking in the wrong direction. We turn around and he points at a small hill near the side of an access road. Pondering aloud, he wonders What do you suppose that boulder is doing on top of that hill?

Hint: It’s not a geocache.

The plains surrounding Meteor Crater are afflicted with an excess of flatness. Aside from the crater itself, the only relief is from scattered blocks, mounds and low rises of Coconino Sandstone and Kaibab Dolostone. They are blemishes on the otherwise flat patchwork terrain surrounding the crater. Like the boulder on the hill, many large coherent blocks of ejecta excavated during impact were thrown out of the crater and now rest upwards of 300 feet above where they ought to. Three days in, we were no longer tourists; It was time for science. We started work to answer a few relatively simple questions: Where in the crater did those blocks originate? How big are they? What would it take to launch them tens and hundreds of meters to their current position?

To answer those questions, the group split in two. One team examined the ejecta blocks, recording their dimensions and lithology. The other team measured the distance from crater to ejecta, using a physical measuring tape and recording map position and GPS coordinates to cross-check calculations. It was a rather straightforward assignment that also got us thinking in terms of cratering processes. The furthest blocks we studied were a solid five minute walk from the crater. It is easy to lose sight of something that is no longer present, but after the initial impact we would have been scrambling over several additional meters of ejecta the whole trip.

The measuring group stands on the rim of Meteor Crater as the tape is prepared for the trek to ejecta block E-3. Some members of the lithology group are visible on the white block of Kaibab (limestone) in the distance.

Team Tape and Team Lithology knocked out six profiles over the course of the day, including an assessment of the famous three-story-tall House Rock (a.k.a. Monument Rock). Six blocks is a small sample set to be sure, but one that lays the groundwork for a more thorough and complete ejecta study to be conducted over a number of Meteor Crater Field Camps. With a few simplifying assumptions – radial path, ballistic trajectory, 45 degree angle of ejection^† – our results indicated flight times for these boulders of three to fifteen seconds at ~60-360 km/hr [~15-100 m/s]. These velocities get well above hurricane force winds (though they pale in comparison to the ~12 km/s impact velocity). And we’re not talking about shingles and trees flying around – these are multi-ton boulders getting hucked out in all directions. Given enough force, ejecta can go anywhere. House Rocks might not get very far, but there are loads of examples of ejecta traveling hundreds of kilometers, into the atmosphere, or even off-planet. We only have fragments of Mars as a result of a few impacts into the martian surface sending material into space and eventually to Earth. Simon Wellings (@metageologist) wrote a bit more about the evidence of impacts in his contribution to the Wedge, What came from outer space.

The Apollo Era really brought to light the importance of impact processes on the evolution of planetary surfaces. Apollo missions also proved a challenge to geologists. No lunar material was collected in-situ, which means the provenance of many samples is uncertain. The provenance of regolith (soil) and impact breccia fragments is still the subject of intense debate. Many of these fragments likely have origins in basin forming events (e.g., the Sea of Tranquility). Boulders like those surrounding Camelot Crater in the above photo, are a bit easier to reconcile with their source. Mapping the distribution of ejecta lithology around terrestrial and lunar craters is the ground-truth to theoretical distribution models. Gravity and atmospheric conditions may differ between the Earth and Moon, but the results of an impact are similar across the solar system.

Top: Boulder field at Camelot Crater from the Apollo 17 mission. Panorama compiled by Warren Harold of NASA/JSC. Bottom: Looking outward from the rim of Meteor Crater. Both images are in color.

^†Learn more about impact cratering processes with the Lunar & Planetary Institute Impact Cratering Lab

Cosmic Stopover?

Mumford and Sons take the stage in Dixon after a long day full of great music http://t.co/O2BWGoWR

—
Jam Productions (@jamusa) August 19, 2012

After a long day full of fantastic and varied music, Mumford & Sons took the stage in Dixon, Illinois as part of their Gentlemen of the Road Stopover Tour. After warming up with a slow-paced lover’s lament, we jumped right in to Little Lion Man and just kept going. Hits and soon-to-be-new-releases were mixed in fair abundance, and will definitely go down as one of my favorite concerts. There was even some icing on the cake:

Mumford & Sons brought out Jerry Douglas (who would put on a separate show in Dixon later that evening) to play their cover of Simon & Garfunkel’s The Boxer. The stage lights began to dim as they played the opening licks. Between then and the opening lines, almost directly above the stage behind a thin veil of smoke and clouds, a fireball blazed from stage left to stage right. I heard a few “Wow!”s and “Did you see that?!”s, but crowd memory is short and the forces of nature on stage took rein. But I will remember, and I hope those people will, too.

I’m sorry to say I didn’t have a watch/phone to check the time – and didn’t think to ask those nearby – but as I said it started when The Boxer started. It appeared to travel N/NW, and was probably 45-60 degrees above the horizon, lasting less than 2 seconds. Because of the smoke and cloud cover, there is a small possibility that this was a firework. However, I did not see a smoke trail, no other fireworks were shot off, and it did seem to be behind actual clouds and not only smoke. Therefore I hope others will report their sightings, here or elsewhere so we can know for sure!

Have you seen this migmatite?

33 years ago on her first day of work at a hospital, my friend’s mother inherited, in her words, an “antique doorstop and/or paperweight …we think it is petrified wood”. It is fist-sized, shiny, and much heavier than it appears. It is stumpy and rhombohedral-ish, with many semi-parallel lines along the sides and curving bands along one face. It kind of looks like petrified wood…but it is not. Far from it.

The mystery migmatite. Dime for scale. Click for full resolution.

Petrified wood results from rapid burial and slow hydrous alteration into silicified casts (permineralization). Lying underground in a wet, mineral-rich environment, picking up hues of red and yellow and gray. Calmly, coolly, entirely without incident. A history about as far removed as possible from the sample that arrived in the mail over the weekend. Migmatites (from the Latin migma for mixture) are the product of intense heat and pressure that result both high-grade metamorphism and partial melting. Check out the Georneys post M is for Migmatite for fantastic coverage of all things migmatite.

“far side” of the migmatite from previous photo. Was there a vug/gap here that allowed free crystallization?

What’s missing from this story is the provenance (origin) of this fantastic rock. Not all migmatites look the same – some lack the leucosomes (light bands) seen here, and they are not all black-and-white – and my hope is that this sample is from the Pacific Northwest… maybe someone out there knows where. For the past three decades it was hanging out east of the Cascades in Central Washington, which is a good place to start. The crustal accumulation and volcanic history of the Pacific Northwest is a prime migmatite-forming environment. I’ve found references to the Okanogan dome/highlands and the Skagit migmatite as starting points, but detailed online photographic records are somewhat lacking. Now I reach out to the ether: Have you seen this migmatite?

Tolovana Beach sand

Quartz (white) and plagioclase (yellowish) dominate this sand collected from the edge of a tide-pool on Tolovana Beach near Arch Cape, Oregon. The regional geology is dominated by basalt overlying marine sediments.

Feathery Basalt

~1mm wide cross-polarized image of a portion of the groundmass in Apollo 17 high-Ti basalt 71157 (thin section ,8). The "feathery" texture results from the intergrowth of pyroxene (brown), plagioclase (white/gray/black), ilmenite (black), and some glass (black). The other major phase is olivine, which is present on the image borders and forms the plus-shaped cluster at right middle. There are several early literature (pre-1980s) references to feathery intergrowths, but the associated images have degraded in quality (many articles appear to be scans of photocopies).