Over on Planet Four Talk moderator wassock found this Martian double crater in the HiRise images:
which can only have been created by 2 simultaneous impacts.
He messaged me to ask if we had found anything similar on the Moon and also sent a further image of a laboratory test of a high velocity simultaneous impact by 2 objects:
Here are some lunar doubles:
Messier A (on the left – most likely created by separate events)
None of these examples has the distinctive “equatorial” ejecta pattern of first 2 images which I have never seen on the Moon. Why might that be? Well, we know that Mars and the Moon differ geologically so maybe the type of impacted surface and bedrock plays a role. Did the impact take place when Mars was much wetter/ muddier than it is now? Mars also has a more dynamic atmosphere. Would any of these differences account for the distinctive formation of the Martian doubles and ejecta pattern? Maybe the angle and velocity of impact is relevant here too and these double craters form only from high velocity overhead impacts. Wassock says he has found more Martian examples. On a quick look at ACT-REACT quick map I can’t find any lunar equivalents. Can you?
The Lunar Reconnaissance Orbiter will soon have been orbiting the Moon for 4 years. Here’s a reminder of ten cool things it “saw” in its first year.
From NASA’s mission pages.
|The coldest place in the solar system
Astronauts first steps on the Moon
Apollo14 and the near miss of cone crater
Lukhnod 1 found
LOLA’s Lunar farside
Craters and boulders with Moon Zoo
Pits and skylights
Areas of Near Constant Sunlight at the South Pole
Kaguya – NASA
Forum regular JJ went hunting for the Japanese lunar explorer Kaguya impact site. Kaguya (or SELENE: SELenological and ENgineering Explorer) was launched 14 September 2007. Once in lunar orbit Kaguya released two smaller satellites into separate elliptical polar orbits: Okina (a relay satellite for communications) and Ouna (a Very Long Baseline Interferometry (VLBI) radio source satellite for supporting radio measurements). As well as its 2 sub-satellites Kaguya carried 13 scientific instruments including a lunar Magnetometer, a Gamma ray spectrometer, a Lunar Radar Sounder and an Earth-looking Upper Atmosphere and Plasma Imager. the mission lasted 18 months after which Kayuya was sent into a series of lunar orbits prior to a controlled impact on 10 June 2009. The impact site was conveniently in darkness at the time allowing the impact flash to be seen from Earth. Okina impacted on the far side on February 12 2009. Ouna is still in orbit.
The Kaguya mission amongst other things has improved lunar global topography maps (also used by Google to make Google Moon 3D), a detailed gravity map of the far side, and the first optical observation of the permanently shadowed interior of south pole Shackleton crater.
The Kaguya impact coordinates are well documented but we couldn’t recall seeing a high resolution view of the impact site from LRO. What JJ was looking for was a small fresh impact which would have exposed some fresh lunar regolith leaving a white scar with a blackened centre where debris may remain.
The Kaguya website gives the impact coordinates as E80.4, S65.5. Here’s the location:
This indicates an impact site on the wall of an unnamed crater near crater Gill. Part of crater Gill is top left of this image provided by ESA:
Using the ACT-REACT Quick Map tool JJ located the unnamed crater.
And found a likely impact site on the rim of a smaller crater within the unnamed crater.
And finally – a potential impact site with a centre geodetic diameter of 23m:
We think it’s definitely a contender.