Earlier this year I was lucky enough to get to go over to California for a few days all in the name of science. We stayed up in the hills behind Berkeley, a short walk away from the instrument we were using. The view from our hotel room was pretty amazing with views across San Francisco, the Golden Gate Bridge and the Pacific Ocean.
The Moon formed in a Giant Impact of a planet called Theia with Earth (Figure 1). You can find a nice simulation of this event at the end of this post or watch the orginal here. In a post a few weeks back I mentioned that there are some problems with the details of this theory and that I would write about that soon.
As a paper published last week in Science  is exactly about that topic, I thought it is time to follow up on this promise. The mentioned paper shows that technology has developed far enough to allow science to tackle the problems lurking within the Giant Impact Theory. Responses in the media (e.g. here, or for german speakers here) about the paper seem to focus on the fact that the paper supports/confirms the Giant Impact Theory.
Yes, the results are in agreement with the theory and therefor support/confirm it!
But to focus on this, implies that the main question we are facing, when it comes to the Moons origin, is:
Was there a giant impact?
Of course one is allowed to ask this question. However, in science this question is only taken seriously if you`ll offer an alternative hypothesis, that works equally well or better in hindsight of the known facts. When it comes to the origin of the Moon, all other origin hypotheses have already been discarded for various reasons and to my knowledge there are no rival hypotheses to the giant impact left.1 The Giant Impact is a fact, and was one before this paper!2
The question is not: Did it happen?
The question is: How did it happen?
The Giant Impact Theory came a long way since it was first proposed in 1975 . It solved a lot of problems regarding chemical similarities and differences between Earth and Moon. But in recent years it got stuck in a bottleneck.
What had happened?
Measurements of the elements oxygen, chromium, titanium, tungsten and silicon had shown that the ratios between the isotopes of those elements were the same in the Earth and the Moon. 
Why was that a problem?
Those ratios are fundamentally different in other rocky bodies in our solar system like the asteroids and – more important – Mars. Therefor it is likely that Theia and the Proto-Earth (the Earth before the Giant Impact) differed in these isotopic signatures as well. If that was the case, the standard model of the Giant Impact would predict that those ratios would be different in the Earth and the Moon (Figure 2).
Different changes in the model were proposed to achieve the similarity in isotopic ratios, but all of them require very special conditions, such as a fast spinning Proto-Earth or Theia being the same size as Earth (Figure 2) or complex processes following the impact [3-5].
Or maybe Theia didn`t had a similar isotopic signature to the Proto-Earth? For that line of thinking we would have to revise what we assume about the distribution of isotopic signatures in the solar system. That would be a great and enlightening thing to do, but would require samples from a rocky planet other than Mars – preferentially our twin planet Venus. 
So what`s the great news?
Actually, the great news are small – very small. That best describes the differences between the isotopic signatures of Earth and Moon rocks which now were uncovered.
But didn`t I said above that there were no such differences?
Indeed, but I should have added “within error”. The error is used to describe the area of uncertainty around a measured result. For example, I know I`m 185 cm tall. But I have never measured that very accurately, so it could easily be that I`m actually 1 cm taller or smaller. The 1 cm is the error on the measurement of my height. If I now meet a person who has measured his or her height (equally lax) to be 185 cm, we would have to conclude that we are equally tall (within error), even though he or she might be 186 cm and I only 184 cm. How can we find out? We have to measure more precise, let’s say with a mm-scaled tape.
In a nutshell, that is what the new study did – measured more precise. They found that when you compare 1 million oxygen atoms on Earth to 1 million oxygen atoms on the Moon, you`ll find that 123 of those atoms are different isotopes4.
This means a great relief, for some reasons:
a.) It means there is a difference in those isotopic signatures and we don`t have to invoke very special conditions5 for the Giant Impact.
b.) It promises that we`ll find similar differences in the other isotope systems apart from oxygen.6
c.) When we know how the Earth and the Moon differ, we can infer more on the nature of Theia, the Proto-Earth and the details of the impact.7
And that is much more, than just to confirm that there was a Giant Impact!
A simulation showing the Giant Impact.
1 That doesn`t mean someone might come up with a new one in the future.
2 Imagine the media would title every article about new advances in evolutionary biology with “Evolution Confirmed!” – Technically true, but still missing the point.
4 Don`t worry about the isotopes. It basically is like two boxes filled with 1 million red and blue balls, where one box has 12 more of the blue balls. Even finding that out, would be hard. Now imagine that on an atomic scale, where you can`t “see” the atoms and where the difference between the balls is the equivalent of blue and very-slightly-darker blue.
5 Special conditions are often a sign that there`s something wrong with your theory.
6 Oxygen isotopes were the first to indicate the similarity-problem , it`s good that they make up by showing a way out.
7 In the presented paper, the authors speculate on the basis of their data, that Theia might have had a enstatite chondrite composition, which is material we find in the asteroid belt. But we have to see what the future (and other isotopic systems) will bring.
1. Herwartz, D., et al., Identification of the giant impactor Theia in lunar rocks. Science, 2014. 344(6188): p. 1146-1150.
2. Hartman, W.K. and R.D. Davis, Satellite-Sized Planetesimals and Lunar Origin. Icarus, 1975. 24: p. 504-515.
3. Canup, R., Lunar conspiracies. Nature, Vol. 504, 2013(7478): p. 27.
4. Elkins-Tanton, L.T., Planetary science: Occam’s origin of the Moon. Nature Geoscience, 2013. 6(12): p. 996-998 (2013).
5. Clery, D., Impact Theory Gets Whacked. Science, 2013. 342(6155): p. 183-185.
6. Wiechert, U., et al., Oxygen isotopes and the moon-forming giant impact. Science, 2001. 294(5541): p. 345-348.
It happens at least once every month. Sometimes, rarely, it happens twice a month. It’s when lunatics roam the streets and when drivers get distracted by what they see up there in the sky. It’s a bird. It’s a plane. No, it’s a FULL MOON.
Yesterday, inspired by the beautiful sight of the Moon outside my window and soon after reading Thomas’s post about impact craters on the different hemispheres of the Moon, I wanted to find out if there were others around the world who were also thinking about the Moon. It turned out there were lots of people tweeting about the Moon (hashtag analysis suggested atleast hundreds of tweets per hour). Historical statistics suggested the around this time of each month, the webosphere goes wild about the Moon and so I began digger deeper. I plotted data from Google Trends and noticed how periodic peaks in searches for the keywords “Big Moon” coincided with the days around a full moon. Over the last few years, since social media took over the world, annual Supermoon events sparked the most interest with about 4 times as many Google searches than a typical day in the year.
A new report in Science  is dealing with a striking and so far mysterious feature of the lunar surface:
An asymmetric distribution of large lunar basins.
Large in this case means, that the basins diameter exceeds 200 km and that the formation of the basin thinned the crust to an extend that could be picked up by NASA`s GRAIL mission which measured the thickness of the lunar crust.
If you count these large basins on the nearside and the farside of the Moon you`ll find 12 of them on each side (excluding the very old and very big South Pole-Aitkin basin). And that is what you expect for a Moon that is getting hit randomly by impactors like asteroids and comets.
So where is the asymmetry? It shows up when you look at the size of these basins:
The basins on the nearside are (in average) bigger than those on the farside (Fig. 1). Eight basins on the nearside are bigger than 320 km in diameter whereas there is only one of this kind on the farside.
A possible explanation is that bigger (or faster) impactors favourably hit the nearside. But there is no reasonable mechanism which could explain this behaviour of the impactors. So it could only happen by chance. A chance that is lower than 2%. And that is not a very satisfactory scientific explanation.
As the impactor properties couldn`t provide an answer the team that published the paper had a look on the target properties, meaning the surface of the Moon. And once again, another striking feature of the Moon’s surface, the Procellarum KREEP Terrain (PKT) on the nearside, plays a major role. The origin of the PKT itself is still not a closed issue (I wrote about that here). However it already existed at the time when most of the big basins were formed. And one of the PKT`s main properties is that it is enriched in heat-producing elements (due to their radioactivity). The presence of these elements might have warmed the nearside crustal and upper-mantle rocks (or at least big parts of it) considerably compared to their farside counterparts.
What effect would that have on basin forming impact events?
In the modelling on which the report is based, the team found that in the initial stage of the basin forming impact there is little effect caused by the target temperature. This stage, which is mainly characterized by growing of the crater and ejection of material from within the growing crater, is mainly affected by the impactor properties (speed and mass).
However the target rock properties come into play in the next stage, when the formed crater is modified by subsequent processes. In this stage the mantle below the crater is uplifted (as there is no or much less crust above it, holding it down). On the warm nearside this uplift is much stronger and occurs over a wider area. The basic principle behind this is that warmer rocks can be more
easily elastically deformed than colder rocks. The uplifting mantle prevents the crater rim and surrounding crustal material from collapsing into the crater (“This is my spot!”). On the farside, where this isn`t the case, a lot of crustal material
collapses into the crater. Therefor those basins look much smaller for the GRAIL mission as it detects the thickness of the crust and it cannot distinguish between normal crustal material and crustal material that fell back into the basin. If one accounts for this target related effects on the crater formation the size distributions of the lunar basins look pretty similar on the near- and farside (Fig. 2).
This gives a neat explanation of the observed asymmetry of the large lunar impact basins and similar process might account for weird basin size variations on other planets, especially Mars. It also might mean that we have overestimated the impact flux recorded in the lunar surface as the production of the big nearside basins can be explained with smaller impactors than previously thought.
“P.S.: I came across the paper through a fairly new blog. The site adds (on a daily basis) links to recently published papers that are related to cosmochemistry. So if you are interested in that field it might be worthwile checking it out: http://cosmochemistry-papers.com/ ”
 Miljkovic et al., 2013. Asymmetric Distribution of Lunar Impact Basins Caused by Variations in Target Properties. Science 342, 724-726.
On the 6th of September NASA launched their LADEE mission (Lunar Atmosphere and Dust Environment Explorer) into space (Fig. 1). You might have heard of the launch as a frog photo-bombed a picture of the start (Fig. 2). So far the mission is fully on track. The mission will take about 30 days to travel to the Moon, 30 days for checkout and then around 100 days for science operations (Fig. 3).
So what`s hidden in that featureless term “science operations”?
The LADEE spacecraft contains three science instruments: The Ultraviolet and Visible Light Spectrometer (UVS), the Neutral Mass Spectrometer (NMS) and the Lunar Dust Experiment (LDEX). The instruments will analyse the light signatures of atmospheric materials, the variations in the composition of the lunar atmosphere in different heights over the Moon and dust particles in the atmosphere.
Furthermore LADEE carries the Lunar Laser Communications Demonstration (LLCD) which will not be used to investigate the lunar atmosphere. The purpose of the LLCD is to demonstrate the possibility to use lasers for communication with satellites and spacecrafts instead of the conventionally used radio transmitters. This will allow broadband speed in the communications between future satellites/spacecrafts and Earth. LADEE therefore does not only have research goals but also aims to make a major improvement in space flights from the engineering point of view. Continue reading “LADEE and the Lunar Atmosphere”→
The Moon has many mysteries. One of the biggest is the Procellarum KREEP Terrain (PKT) (see Fig. 1) in the north west of the lunar nearside (the one you can see from Earth).
This areas main characteristic is that it has high concentrations in iron, thorium and the so called KREEP components (potassium (K), rare earth elements (REE) and phosphorous (P)). It also contains a lot of the lunar maria (the dark patches you can see on the Moon) which are basalts that flooded big impact basins. The KREEP components are incompatible elements, which means, if you have a crystallizing magma they tend to stay in the residual magma. This is because they do not fit very well in the first crystallizing minerals (such as olivine or plagioclase) due to their size and/or electron configuration. Continue reading “Hidden connections on the moon”→
We begin this week with what might seem to be a collection of random videos and stories that lead us from earthly elements to stellar spectacles. Individually, they are all interesting but there is also a common thread… Can you identify the “periodic” feature in all the stories?
The NEW Periodic Table Song (In Order)
You have probably heard the Elements song by Tom Lehrer or heard a rendition of that song by Daniel Radcliffe (Harry Potter). There have been a number of other interesting takes on it but this new attempt by ASAP SCIENCE to sing the Period Table in order of the elements for the 21st century audience is awesome!
I have always wondered if there will ever be a day when we shall be able to control time and space. You know, fast forward things we experience, then slow them down… Zoom into our world and then zoom back out simply with a two-finger pinch? For the time being at least, such control of our everyday experience seems to be in the realms of science fiction. But I recently discovered three new web-based visualization apps that can give us a feel for how useful such control would be for scientists.
Apologies for the ridiculously late notice, but at this very moment, there is a solar eclipse occurring. It’s visible only from the Southern Hemisphere, particularly from northern Australia.
For safety reasons, please don’t rush outside now and look at the sun. You can safely watch the eclipse occurring anywhere in the world, live on the internet. Log on to sloosh.com or click here to see the live feed.
Now before we all resort to name calling, I realise that a giant rose wasn’t actually discovered on Saturn on Monday. What was discovered however, is a giant hurricane centred on the planet’s north pole – an equally as exciting discovery!
It has been known for a number of years that a strange hexagonal shaped weather phenomenon was located on Saturn’s north pole. However, the orientation of the planet relative to the sun has meant that this feature has remained in darkness since its discovery in 2004. In August of 2009, Saturn finally transitioned into spring, bathing this weather anomaly in light for the first time, allowing the Cassini spacecraft, which is currently orbiting the planet, to properly study it. Continue reading “Giant rose discovered on Saturn!”→
Private exploration of space is becoming all the rage now a days, after cutbacks to agencies like NASA have stifled government based programs. On Thursday, Dennis Tito (a former astronaut himself when he paid is way to space back in 2001) announced an ambitious plan to send a couple to rocket to Mars and back to Earth during an optimal orbital alignment in 2018. The plan does not include landing on Mars (which I find unfortunate), but it perhaps is the only way to bring the people back with the gravity assist of slingshotting past the planet. Most plans to land people on Mars do not involve a return trip, due to the inability to carry enough fuel to get back. As it stands, Tito’s plan is to send a married couple, with the assumption that they will have a better chance of getting along during the five year trip. For more information, here is a link to the mission’s website.
Tito compared the trip to the Lewis and Clark Expedition (which lasted over two years). I think a more apt comparison might be the Franklin expedition. That mission was truly in an isolated environment through the Canadian Arctic, and was expected to take several years (they had five years worth of food supplies). The last known note from the Franklin Expedition was dated nearly 3 years after it started, after the crew became stranded after their boats became stuck in ice. A slingshot mission to Mars will be a test of the resilience of the human spirit in isolated conditions, with the very real possibility of disaster (over half of the missions to Mars have ended in failure). It would take a very sound mind to tackle this long journey, and I have to say it would be very difficult for just two people to do this. I will be excited to see this happen, though. If successful, I think it will lead to future missions, and possibly a landing on the planet. I think you would need an armada of unmanned ships to build a base with adequate supplies for years if the were to do this.
Ah meteors, the great pieces of rock that fall from the heavens to wreck havoc on the world (rarely). Just a week after a study came out about to confirm the role of a massive impact wiping out the non-avian dinosaurs 66 million years ago, we are reminded that we are not immune to meteors, and they are always a threat. The meteor that exploded above the Russian city of Chelyabinsk caused injuries of over 1000 people, probably caused when people went to their windows to see what had happened, only to find them shattering due to the blast. Russia Today has a great compilation of videos of the blast (I was informed most Russian cars have dashboard cameras to record road rage incidents, which ended up being beneficial to capture some great views of the explosion):
The National Post has put up some of the latest ESA pictures that reveal Mars’ glacial past. Included is a large, 7 km wide river valley, and what appears to be a cirque, a mountain scooped out by a glacier. The river valley shows evidence of braided streams, which are common in glaciated regions. As noted by some of the commentators, this feature is relatively young on the Martian surface, and there are few craters that have damaged the geomorphology.
NASA has just released a series of images taken by one of NASA’s satellites of the Earth at night.
The images show a network of city lights, wild fires, gas flares and fishing boats, illustrating the pattern of human settlement across the Earth.
The images were taken using the day-night band of the Visible Infrared Imaging Radiometer Suite (VIIRS), which is sensitive enough to detect the nocturnal glow produced by Earth’s atmosphere and the light from a single ship in the sea. These images have been stitched together to produce a composite image of the planet, titled “The Black Marble“.
Tomorrow, the 14th November 2012, Australia will be in a prime position to view a solar eclipse, occurring as the moon passes between the Earth and the Sun.
While solar eclipses are relatively common – occurring somewhere on Earth every 18 months or so, they are limited to specific geographical areas, meaning they are not often visible from Australia.
The best place to view the full solar eclipse is Carins, Australia. Other parts of Australia will be able to see a partial eclipse throughout the morning.
It is very important to remember not to look directly into the sun when trying to view the eclipse!! The simplest way to see the eclipse is to poke a small hole in a piece of cardboard, and project the image of the sun onto a piece of paper.
RSES’s very own Joe Cali is organising the eclipse viewing site in Cairns. He has a whole lot of information available on his website, so check it out.
If you happen to be in Canberra tomorrow, Mount Stromlo will have telescopes set up to allow you to safely view the eclipse. Check out their website for details.
In recent days, Curiosity has been busy with self-inspections and calibration of its instrument suite. It has clocked about 150 meters and continues to work in good health.
You might have already seen some photos of the red planet from this or past missions but prepare to be amazed by this impressive panorama.
The Mars Science Laboratory might only sport a 2 Mega Pixel camera (so that it can send it photos in a reasonable time frame back to Earth), but thanks to the clever people at NASA and photographers like Andrew Bodrov, we can get a taste for what it might be like to stand on Mars and look around.