Monday, September 15, 2014

Watching craters "as they happen"

A new crater on the Moon, "found among so many." The bright flash of formation for this approximately 34 meter diameter crater was captured simultaneously by two Earthbound telescopes in Spain on September 11, 2013. From LRO, before-image LROC NAC observation M1119014742L, orbit 17116, March 27, 2013; incidence 23.66° resolution 82 cm from 84.41 km, After-image LROC NAC M1149637354L, LRO orbit 21423, March 16, 2014; incidence 23.18° resolution 91 cm from 89.12 km  [NASA/GSFC/Arizona State University].
Mark Robinson
Principal Investigator
Lunar Reconnaissance Orbiter Camera (LROC)
Arizona State University

On 11 September 2013 the "Moon Impacts Detection and Analysis System" (MIDAS) camera captured a bright 8-second long flash on the central nearside of the Moon.

This was the brightest event captured so far by the MIDAS team, and they estimated that the crater should be between 46 and 56 meters in diameter.

The LROC team targeted the reported coordinates (17.2°S, 339.5°E) of the flash and acquired several images over a few months until the crater was found in images acquired on 16 March 2014 and 13 April 2014.

Strictly speaking, the 11 Sept. 2013 event was visible to the naked eye, though at nearly First Quarter the idealized reproduction above fails to account for the discriminating human eye. The illuminated east hemisphere would tend to have washed out Earthshine for all but those with the steadiest eyes. Fortunately, for at least ten years the unlit portion of the Nearside "visible" at night has been carefully monitored systematically, improving our understanding of hazards in the Near-Earth environment [NASA/GSFC/SVS].
Video sequence recording impact on the Moon's nearside in Mare Nubium. The magnitude of the explosion is estimated to have been roughly equal to that of Polaris, the North Star, and the recorded light curve following after lasted a remarkable eight seconds. Madiedo, et al. (2014) [IAA-CSIC/Universidad de Huelva].

Fortunately there was a NAC image of the target area acquired before the impact, so finding the new crater was relatively easy once an "after" image with comparable lighting to the "before" image was acquired.

As it turns out the new crater is ~34 meters (112 feet) in diameter and is located at 17.167°S, 339.599°E, only 2 kilometers (1.2 miles) from the original telescope-based prediction. In the before-after animation you can see ejecta effects from the crater extend out more than 500 meters in all directions!

See also LROC NAC image M1149637354L (16 March 2014).

Impact flash recorded on the unlit Nearside by Prof. Jose M. Madiedo, 11 Sept. 2013. North is to the right (note the visibility of Grimaldi, top center - the 173 km-wide walled plain is often the last recognizable feature on portion of the Nearside lit by Earthshine as the Moon waxes Full). The Moon was shy of First Quarter. This video was produced on the occasion of the publication (in Feb. 2014) in Monthly Notices of the Royal Astronomical Society (MNRAS) of the paper entitled "A large lunar impact blast on 2013 September 11," by J.M. Madiedo, J.L. Ortiz, N. Morales and J. Cabrera-Caño.

A longer, more instructive version was uploaded by the authors HERE

Wide Angle Camera morphology basemap overlaid with color-coded LROC GLD100 topography centered on the 11 September 2013 impact crater. The large crater just visible in the lower left is 60 kilometer diameter crater Bullialdus [NASA/GSFC/Arizona State University].
Revisit the LROC NAC image of new crater formed on 17 March 2013, HERE.

Read the paper describing the 11 September 2013 observation (Madiedo et al., 2014)

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