LROC images reveal intricate details of lunar impacts

March 17, 2015

The moon is pelted with cosmic debris all the time, but the largest explosion on its surface that we’ve actually recorded occurred two years ago today. On March 17, 2013, an object the size of a small boulder hit the surface in Mare Imbrium and exploded in a flash of light nearly 10 times as bright as anything ever recorded before.

Images acquired of the surface before and after the impact by NASA’s Lunar Reconnaissance Orbiter Camera (LROC), overseen by a team at Arizona State University, reveal intricate details of the resulting impact crater and help calibrate models of crater formation. March 17 crater Download Full Image

Since 2005, astronomers have monitored the moon for signs of explosions caused by meteoroids hitting its surface. When a meteoroid strikes the moon, a large portion of the impact energy goes into heat and excavating a crater; however, a small fraction goes into generating visible light, which results in a brilliant flash at the point of impact.

The brightest flash recorded by researchers at NASA’s Marshall Space Flight Center occurred on March 17, 2013 with coordinates 20.6°N, 336.1°E. The team predicted the crater’s size based on the energy, and they eagerly awaited LROC’s next pass over the location to confirm their calculations.

Being able to get observations before, during and after the impact is a valuable opportunity to understand impact events better. Comparing the actual size of the crater to the brightness of the flash helps validate impact models.

The hunt for the March 17 crater

LROC’s first set of post-impact flash images acquired on May 21, 2013 by the Narrow Angle Camera were targeted on the Marshall-reported coordinates, and numerous small surface disturbances (“splotches”) were detected by comparing the pre- and post-flash images, but no new crater was found.

A second set of Narrow Angle Camera images was acquired on July 1, 2013 showing three faint, ray-like features and several chains of splotches and asymmetric splotches that generally pointed to a common area west of the Marshall coordinates. A Narrow Angle Camera pair was targeted on that convergence point for July 28, 2013; comparison of this third set of images with preexisting coverage revealed a new crater.

The crater itself is small, measuring 18.8 meters (61.7 feet) in diameter, but its influence large; debris excavated by the sudden release of energy flew for hundreds of meters. More than 200 related surficial changes up to 30 kilometers (19 miles) away were noted.

Not only did the LROC images reveal intricate details of ejecta distribution, but they also offered a valuable opportunity to study the structure of the top meter of the regolith. Regolith is a term that refers to a soil that is lacking organic material.

The soil on the moon is formed slowly over time as micrometeorites impact the surface and slowly grind rocks into a fine powder. As the fresh soil grains sit on the surface, they are exposed to radiation and slowly become darker and redder (mostly due to reduction of iron in minerals to iron metal – reverse of rusting that happens on Earth). This slow change in reflectance and color is generally referred to as space weathering; fresh soil is referred to as immature, and weathered soil is mature. The longer a soil sits on the surface, the more mature it becomes.

Several surprises were revealed in the before and after image pairs around the new crater. Conventional thought predicted that the new crater should be surrounded by a high reflectance ejecta blanket out to about a crater diameter with some patchy ejecta spreading out two or three diameters.

“The high reflectance was there, but three other zones were discovered. At the edge of the high reflectance ejecta was a low reflectance zone, then, beyond that, another high reflectance zone, and beyond that, another low reflectance zone,” reports Mark Robinson, a professor in ASU’s School of Earth and Space Exploration and LROC’s principal investigator.

The results are published in the Jan. 31 edition of the journal Icarus.

Finding new impact craters

It’s not easy to find new impact craters because most of them are very small. The only way to really do this is to have a before image and an after image to compare.

LROC began systematically mapping the moon in the summer of 2009. Now, the team is going back to images taken in the first year or two and comparing them to recent images. Called temporal pairs, these before/after images enable the search for a range of surface changes, including new impact craters formed between the time the first and second image were acquired.

As of Jan. 1, 2015, LROC has acquired about 10,000 before and after image pairs. Manual scanning of all these pairs is impractical so Robinson’s team developed a computer program that automatically identifies suspected changes from each temporal pair.

With the help of the automated tool, the team has identified 225 new impact craters ranging in size from 1.5 meters to 43 meters (4.9 feet to 140 feet) and over 25,000 small changes known as “splotches” (likely unresolved primary and secondary craters).

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

Experimental filmmaker to headline ASU lecture on indigenous time-keeping

March 17, 2015

Multimedia producer Victor Masayesva, Jr. (Hopi) is the featured speaker in the spring 2015 installment of the Simon Ortiz and Labriola Center Lecture on Indigenous Land, Culture, and Community. He will present "Indian Time," a talk, discussion and film screening at 7 p.m., March 19 at the Heard Museum in Phoenix.

Masayesva’s transdisciplinary work addresses the subject of calendars and time-keeping in modern and ancient eras. “Calendars are not only tools to measure time; they can also be magnificent instruments to connect cosmic time with human time,” he said. Victor Masayesva Download Full Image

“They are doors that allow men to access the mystery of the cosmos and, at the same time, to correlate the activities of men with the rhythm of the stars. Indigenous peoples from the Americas have been tracking time since their arrival.”

According to Masayesva, the term “Indian Time” has been used to denigrate native people’s way of being and to keep them from inclusion in the dominant culture. But, he says, the notion of being “part of a larger order” of cosmic time-keeping can instead help indigenous youth celebrate their place within society.

“Over seven thousand years, [indigenous] lunar calendars have accurately determined ecosystems and agricultural cycles,” said Masayesva. “Their precise recordings of Venus as morning and evening star affirmed their ever-cyclic relationship with the cosmos above them and the underworld beneath. By reinvigorating the sense of cosmic time, we can initiate the dialogue that our individual existences are a part of the larger planetary consciousness and reclaim ‘Indian Time.’”

A member of the Hopi Tribe from Hotevilla, Arizona, Masayesva has been a life-long advocate for the ascendancy of the indigenous aesthetic in multimedia productions. He has promoted this aesthetic by curating programs at the Museum of Modern Art in New York City and serving as artist-in-residence at the School of Art Institute of Chicago, Walker Art Center, and Banff Centre for the Arts, and featured director and jurist at the Yamagata International Film Festival and the CLACPI Festival in La Paz, Bolivia.

Honored with the American Film Institute’s Maya Deren Award, Masayesva has been at the forefront of independent, experimental filmmaking in the Native American media community. His publications include “Husk of Time” from the University of Arizona Press, and his media work is included in the permanent collections at the Center for Creative Photography in Tucson, Arizona; the Museum of Modern Art in New York City; the Houston Museum of Art in Houston, Texas; and the Corcoran Gallery in Washington, D.C.

The Simon Ortiz and Labriola Center Lecture on Indigenous Land, Culture, and Community at Arizona State University addresses topics and issues across disciplines in the arts, humanities, sciences and politics. Underscoring indigenous American experiences and perspectives, this series seeks to create and celebrate knowledge that evolves from an inclusive indigenous worldview and that is applicable to all walks of life.

ASU sponsors include the American Indian Policy Institute; American Indian Studies Program; Department of English; School of Historical, Philosophical, and Religious Studies; Women and Gender Studies in the School of Social Transformation (all units in the College of Liberal Arts and Sciences); Indian Legal Program in the Sandra Day O’Connor College of Law; School of Art in the Herberger Institute for Design and the Arts; and Labriola National American Indian Data Center. The Heard Museum is our community partner.

Kristen LaRue-Sandler

senior marking & communications specialist, Department of English