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Nasa LRO - The fractured floor of Compton

Published by Matt on Mon Jul 13, 2009 7:05 pm
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(NASA) – Orbit 136 took LRO over the Imbrian-aged Compton Crater (162 km diameter) at an altitude of 172 kilometers. At this height, large boulders can be seen casting shadows, especially on the rims of the numerous secondary impacts that cover this ancient surface. But there is more to this image than craters and boulders.

In the upper part, the western edge of Compton’s huge central peak is visible. The wide, sloping flat floored trough (or graben) records a period of uplift of the crater floor. The uplift caused the floor to break and pull apart, forming the graben. The cause of the uplift and fracture of crater floors is not yet fully understood. One possibility is the slow readjustment of the crust after the crater-forming impact. Asteroids and comets strike the Moon at speeds greater than 15 km/second. So much energy is released that rock behaves as a plastic for a brief instant – the crust is pushed down. Over time the crust relaxes and uplifts towards its original position, fracturing lava flows that were erupted and hardened after the impact. Another idea concerns the intrusion of lava into the shallow subsurface. As this magma follows existing cracks, it exerts pressure on the surrounding rock causing uplift and more fracturing. Unraveling the origin of lunar tectonic features like this one is a primary focus of LROC science team.

LROC is now officially in the instrument commissioning phase.  The LROC team has begun the process of analyzing the data, and are still making small adjustments to the instruments as the LRO mission continues.

The central peak and fractured floor of Compton crater as imaged by the LROC Narrow Angle Camera at dawn, image width is ~1720 meters Credit: NASA/GSFC/Arizona State University

The central peak and fractured floor of Compton crater as imaged by the LROC Narrow Angle Camera at dawn, image width is ~1720 meters Credit: NASA/GSFC/Arizona State University

LROC Commissioning Phase Operations

LRO will remain in a 30 km by 199 km (19 mile by 124 mile) orbit with a periapsis above the South Pole during the commissioning phase. This orbit requires very little in the way of station-keeping, thus it saves fuel while the spacecraft and instruments are running through their checkout procedures. For LROC we have two types of checkout observations. First, there are sequences that require the spacecraft to maneuver to a special orientation to support our observations. For example, we will image stars and Jupiter to check the geometric and radiometric calibrations we performed on the ground.

Second, there will be other calibration sequences that are taken while the spacecraft is in its nominal nadir (looking straight down at the Moon) position. There are seven instruments on LRO, and each has its own specific requirements for calibration and checkout. Some of the calibration sequences prevent other instruments from acquiring data at the same time, so there is a bit of planning that takes place so all of the instrument teams can get the observations they need within the commissioning phase. Of course, not everything goes exactly as planned, so each instrument team must remain flexible in terms of adjusting the timelines.

We hope to have all of the LROC checkout and calibration sequences completed by mid-August so we can begin systematic data acquisition with the NACs and WAC. Of course, we will post images from the commissioning phase soon after receipt on the ground to allow everybody to follow our progress. Right now, the spacecraft is still performing a series of maneuvers to get LRO into the commissioning orbit by the end of this week.

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