Archive | June 2012

Linné Crater

Linné crater is a young, well preserved impact crater on the western edge of Mare Serenitatis, at coordinates: latitude = 27.7, longitude = 11.8. It is 2.2 km in diameter and bowl-shaped and is often cited as a good example of a fresh impact crater. Its actual age is unknown but thought to be less than 10 million years.

It has been used to investigate how cratering occurs in mare basalts and the report from the 42nd Lunar and Planetary Science Conference (2011) has a very good description of the crater and compares it to the terrestrial Barringer Crater (aka Meteor Crater). The report can be found here: Linne: Simple Lunar Mare Crater Geometry from LRO Observations

There is some controversy about Linné crater to do with ‘transient lunar phenomena’ (TLP) maybe caused by outgassing. In the nineteenth century some astronomers believed that they had seen changes around the crater, in some cases they said that the crater had vanished leaving only a mound behind. This is discussed here: The Linné Crater Controversy

NAC Strips:  Left – M139836046LE Right – M139836046RE

[NASA/GSFC/Arizona State University]

Colour coded shaded relief map of Linné crater created from an LROC NAC stereo topographic model. The colours represent elevations; cool colours are lowest and hot colours highest.

Useful Links

NASA – Linné Crater

LROC NAC Image of Linné Crater

ACT-REACT Overview

The following site contains a movie of a “fly around” Linné crater:

Barnstorming Linné Crater

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A Field Guide To Lunar “Black Stuff”

This week forum regular kodemunkey has chosen to highlight the lunar “black stuff” we have been looking for since Dr Tony Cook asked us to post examples.  Often difficult to distinguish from shadows this black deposit might be volcanic in origin or just a dark albedo feature. Whatever it is we now have quite a collection to study.  Over to kodemunkey to explain further.

Hello once again moon fans, this week I have a strange one for you, Lunar “Black Stuff.”

Of all the sub-topics on the forum, I think this one is the most mysterious and it’s certainly caught my attention.

To quote Anthony Cook on the subject:

“Description: Dark slightly branching features, often on the shaded side of slopes. Boulders associated with these. Also appears as an exposed strata layer in a nearby rill rim.

Interest: Is this “dark stuff” an exposed dark material black volcanic glass, a deep branching crack with shadow, dark boulders, or a combination? Either way we need to find more of these and their geographical distribution. Could be worth monitoring these from orbit and at different sun angles to see if the darkness is related to shadow.”

I, like many people, enjoy both a good mystery and a chance to be nosey, so this was one project that suited me down to the ground (or regolith if you prefer!)

(Obsidian)

Where has it been found so far?

During my time on the forum, I’ve found examples of “Black stuff” in the following locations:

Marius Hills (Perhaps ejecta from Aristarchus / Kepler?)

Schroter, Fauth, Bode, Sommering and Gambart (Ejecta from Copernicus perhaps?)

Vallis Alpes.

As well as various dark haloed craters and other unnamed crater ejecta blankets.

This section is a guide to where you might find examples of Black stuff:

On the edges of rille systems

Vallis Alpes Rille


Rimae Marius

On crater rims

Unamed impact, Taurus-Littrow region

Crater floors

Unnamed far side impact

Occasionally in the ejecta blankets of small impacts

Minor impact within Michelson crater on the far side.


Unnamed near side impact

Covering the landscape

Marius Region


Schroter Region

Question time:
Taking into account the number of impacts, both large and small, why isn’t there more black stuff laying around, and why is it seemingly more prevalent on the near side more than the far side?

Sources used:

WMS Browser: http://wms.lroc.asu.edu/lroc#damoon
Act – React tool: http://target.lroc.asu.edu/da/qmap.html
Moon Zoo Thread “TLP – Black Stuff”: http://forum.moonzoo.org/index.php?topic=264.0
Special mentions go to forum moderators Jules, Geoff, Ireneant and forum members Astrostu and Tom128, who i imagine i drove to insanity badgering them with my own inane ramblings on the subject.

The Transit of Venus – across the Moon!

NASA/ESA came up with a unique way to observe the recent transit of Venus using the Hubble space telescope. Hubble doesn’t have a solar filter as it was never designed to be a solar telescope so can’t be pointed at the Sun. However, as the Moon shines by reflecting sunlight from its surface Hubble was targeted on the Moon instead to observe this “second hand sunlight” including the tiny fraction of that light that passed through Venus’s atmosphere as it transited the Sun.

The point of the exercise was not to find out more about Venus’ atmosphere as that has already been extensively studied. Rather it was to use a local transit of an Earth-sized rocky planet as a convenient test bed. Venus and Earth have similar masses. The experiment will show whether the method used to analyse the bloated atmospheres of transiting giant exo-planets and super-Earths will be successful at detecting the atmosphere of a smaller Earth-sized planet. And as a sanity check whatever signature Hubble picked up can be checked against what we already know about Venus to see if it all makes sense.  Analysing the atmospheres of Earth-sized exo-planets is tricky. Even spotting Venus’ atmosphere, which involves looking at just 1/100,000th of the sunlight that bounces back off the Moon, is tricky.

On June 5th-6th Hubble observed the Moon for 7 hours both before and after the transit to establish a good baseline and also for the full transit to maximise the chances of filtering out the signature of Venus’ atmosphere. The only problem was that 40 minutes out of each 96-minute Hubble orbit was lost as Earth obscured Hubble’s view of the Moon. As part of the preparations for the observation and to make sure that after each 40-minute blackout Hubble was still pointing at the correct location this test image was taken of Tycho.


NASA

Hubble used its Advanced Camera for Surveys, Wide Field Camera 3 and Space Telescope Imaging Spectrograph to view the transit in several wavelengths from ultraviolet to near-infrared and took both spectra and photographs.

Results are expected in the next few weeks. Check the Hubble and NASA websites for details.

Astrophotographer Thierry Legault took this image of the transit of Venus. Look closely – he also captured a transit of the Hubble telescope too!


http://legault.perso.sfr.fr/venus_hst_transit.html

Taurus Littrow Safari

Forum regular kodemunkey has written this week’s Image of the Week . This time he has chosen to highlight the Taurus Littrow region which 40 years ago was the landing site of Apollo 17.

Hello again moon fans. Today I will be showing you some of the sites (but no sounds) of the Taurus Littrow valley,  made famous for a short while as the last place that some puny little hairless apes decided to visit for a short while.


One of the Apollo crew collecting rock samples

The valley is named (perhaps unsurprisingly) due to it being in the Taurus mountain range and south of Littrow crater.  Some of the other landing sites that were considered were Tycho crater, which was rejected due to the rough terrain found there. Copernicus crater was seen as a low priority, and Tsiolkovsky crater on the far side was also considered, but later rejected due to the additional cost of having to put communication satellites in orbit.

Apollo 17 landing site, imaged by the Lunar Reconnaissance Orbiter

The reason for Apollo 17 landing here, was so they could sample older material which makes up the area, and fresher material, which was ejected from the impact that created Tycho crater.

What else is there to see in the area?

Amongst all the craters and rocks in the area, I have found a few interesting sites and I hope they inspire you to explore the area yourself.

This rather prominent crater:

This rather interesting rille edge:

And this is my favourite find, particularly so because I don’t think it’s been documented here yet:

Sources: Nasa, Wikpedia and WMS Image Browser

Nac Frames:
http://wms.lroc.asu.edu/lroc/view_lroc/LRO-L-LROC-2-EDR-V1.0/M172696861LE
http://wms.lroc.asu.edu/lroc/view_lroc/LRO-L-LROC-2-EDR-V1.0/M109045942RE
http://wms.lroc.asu.edu/lroc/view_lroc/LRO-L-LROC-2-EDR-V1.0/M177433351LE