Question of the Week

Jan 042016
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In the history of mankind, the sky above us has always fascinated and inspired. Many investigations with different scientific questions have led to great progress towards better understanding of the universe and our Solar System. But many questions are still waiting to be answered – not only in the distant universe, but also in our direct neighborhood. One such question is about the origin of the Moon.

Astronomers have presented several hypothesis how the satellite of the Earth could have been formed. Most likely, the Moon has not been captured and is also not the result of a fission process [1]. Nowadays, most scientists agree on the giant impact hypothesis: Another celestial object named Theia collided with the proto-Earth about 4.5 billion years ago [2]. After the impact, matter in the orbit around our planet could have accumulated to form the Moon. Compared to other planet and satellite pairs, the Moon is peculiarly large. To explain the corresponding angular momentum, Theia must have been as large as Mars [3]. But this hypothesis does not explain all characteristics of the Moon. Whereas the density differs between the Earth and the Moon, the chemical composition, mainly investigated in terms of abundances of some element isotope ratios (e.g. oxygen, titanium or tungsten), is rather similar. This is odd, because most other objects in our Solar System show significant differences that represent their different origin in the Solar System. Therefore, the Moon’s chemical composition should resemble the one of Theia – at least for the assumed impact angle and velocity and mass ratios [3].

One possible solution: coincidence! The composition of proto-Earth and Theia as collision partners must have been similar. Earlier this was thought to be too unlikely, but new investigations and simulations show that there is a certain probability of about 20% for this incident to happen [1]. Subtle differences in isotope ratios may be the result of a late accretion following the impact [4,5]. But why this accretion led to the isotope ratios astronomers observe nowadays, still remains a riddle.

-Nicola Reusch

[1] A. Mastrobuono-Battisti, H. B. Perets, S. N. Raymond, A primordial origin for the compositional similarity between the Earth and the Moon, Nature 520 (2015), 212–215.
[2] R. M. Canup, E. Asphaug, Origin of the Moon in a giant impact near the end of the Earth’s formation, Nature 412 (2001), 708–712.
[3] R. M. Canup, Simulations of a late lunar-forming impact, Icarus 168 (2004), 433–456.
[4] M. Touboul, I. S. Puchtel, R. J. Walker, Tungsten isotopic evidence for disproportional late accretion to the Earth and Moon, Nature 520 (2015), 530–533.
[5] T. S. Kruijer, T. Kleine, M. Fischer-Goedde, P. Sprung, Lunar tungsten isotopic evidence for the late veneer, Nature, 520 (2015), 534–537.

Nov 292015
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Mainz sports an unusually busy sky given its close proximity to Frankfurt International Airport. And quite often, maybe even every few minutes during the day, one just has to look up and see airplanes zipping across. In their wake, these vehicles leave behind long and wispy trails. Trails, not unlike those, of boats against the turquoise of the ocean. But if one patiently keeps on watching, he/she will be able to make out these trails combining to form cirrus clouds.

These trails are the ejected exhaust crystallizing under a supercooled condition and forming ice. In other words, they are very aptly named as condensation trails or contrails for short. Subsequently, these clouds then act as a blanket and trap the heat radiating from the surface…an impromptu greenhouse effect…and just like a greenhouse they prevent the sun’s rays from reaching the surface also.

Contrails : Benign or Not ?

A 1999 report by the IPCC revealed an inconvenient truth – a 15 percent increase in global warming within the next 5 decades from aircraft carbon emissions [1]. Several international think-tanks including NASA over the last fifteen years have tried to promote zero-emission flights but results have not been commercially viable for long-haul flights yet. Still it remains one of the big challenges going forward [2]. So one must really take stock and think about where are we flying to.

Fortunately, not all is lost just yet. Researchers, after meticulously combing through 20 years of flight data over the busy North Atlantic flight route, have shown from calculations that even a small detour for long haul flights of around 100 km can lead to something quite unexpected [3]. Their predictions indicate it would not only reduce the formation of a serpentine mile long contrails which would trap more heat but also at no added cost to the environment compared to CO2 emissions from the jets themselves.

So yes, we may have 10 year old statistics stating the obvious misuse of our carbon footprint [4] but hey, those ethereal formations may yet have a silver lining.

– Soham Roy

[3] E.A. Irvine et al., “A simple framework for assessing the tradeoff between the climate impact of aviation carbon dioxide emissions and contrails for a single flight”, Environ. Res. Lett., 2014, 9, 064021.
[4] D.S. Lee et al., “International Emissions”, UNEP ‘Bridging the emissions gap’, 2011, 4, 40.

Nov 252015
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White Christmas, open air events without rain or in agriculture – the weather is important in many aspects of our daily life. From time to time, we would like to change it. But can we specifically influence it?
If we aim to control weather, we first have to understand the correlation between different weather phenomena. But, actually, weather forecasts only indicate a probability about how the weather will most likely be on the next day. These forecasts are based upon numerical simulations, because weather phenomena are the result of nonlinear dynamics. They cannot be described by analytic solutions, but rather have to be described by means of chaos theory.[1] The most prominent example is the so called “butterfly effect”: A small change in the initial conditions (e.g. the flapping of a butterfly’s wings) leads to a big difference in the outcome. In this case, the result is not a compulsory consequence – not to be mixed up with the snowball effect! But if forecasts are already difficult, can we succeed in controlling the weather?
For example, lightning rods are a tool to influence the weather. It also seems possible that silver iodide can be used for cloud seeding and, therefore, to induce rain or suppress hail. But scientific evidence is still missing.[2, 3] Several ideas to prevent hurricanes have been gathered in a documentary in 2007.[4] They include the removal of electrical charge by means of lasers or the cooling of the surface of the ocean with liquid nitrogen to deprive the heat energy of an oncoming hurricane.
In spite of several interesting applications, we are far away from controlling the weather. Mostly, we neither understand the complete outcome of such interventions, nor can we calculate them quantitatively. The future will show whether we can specifically influence the weather some day with all its chaotic effects.

-Nicola Reusch

[1] J. Slingo, T. Palmer, Uncertainty in weather and climate prediction, Philosophical transactions Series A, Mathematical, physical, and engineering sciences, 369, 2011.
[2] B. A. Silverman, A Critical Assessment of Hygroscopic Seeding of Convective Clouds for Rainfall Enhancement, Bull. Amer. Meteor. Soc., 84, 2003.
[3] Z. Levin, N. Halfon, P. Alpert, Reassessment of rain enhancement experiments and operations in Israel including synoptic considerations, Atmospheric Research, 97, 2010.

Sep 012015
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Among the building blocks of life there are molecules that behave like mirror images to one another. They are called enantiomers, which means that the atoms are connected in the same way, but in three dimensions they have another arrangement – just as the right hand differs from the left hand. To distinguish between two of such so-called chiral molecules we add L- or D- to their names. Though many properties of two enantiomers are similar, in biological systems they can show a rather different behavior. One example is the odor of carvone: one enantiomer smells like spearmint while the other one smells like caraway. [1] Furthermore, in nature we almost only find L-amino acids whilst sugars appear in their D-form – a phenomenon we call homochirality. [2]

Despite intensive research on this topic, we still do not know why nature chose to favor the corresponding configuration. There are several hypothesis on the origin of homochirality. Some state that it is a result of necessity, others explain it on a “by chance”-basis. In each case, an initially small excess of one enantiomer could have been amplified until only the D- or the L-form dominated.

One possibility is that asymmetric photochemistry led to an enantiomer enrichment in space that meteorites could have brought down to earth. Currently, the Rosetta mission investigates the question on enantiomer excesses on comets. [2] In some cases also the crystallization conditions can lead to a symmetry breaking. Furthermore, there is a really small energy difference due to parity violation (calculated to be on the order of 10-12 – 10-15 J/mol) between two enantiomers and by now we cannot exclude that this also could be the origin of homochirality. [2, 3]

Either way, to understand where homochirality stems from would also improve our knowledge of the origin of life itself.

Nicola Reusch

[1] Theodore J. Leitereg, Dante G. Guadagni, Jean. Harris, Thomas R. Mon, Roy., J. Agric. Food Chem., 1971, 19 (4), 785–787.
[2] Iuliia Myrgorodska, Cornelia Meinert, Zita Martins, Louis Le Sergeant d’Hendecourt, Uwe J. Meierhenrich, Angew. Chem., 2015, 127: 1420–1430.
[3] Martin Quack, Angew. Chem., 2012, 114: 4812–4825.

Aug 252015
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When you sleep, the brain subconsciously processes a lot of information gathered during the day. This is often reflected in the fact that we dream. But besides processing an overflow of information, the accumulation of cellular waste products in our brain is happening during sleep. A mis-accumulation of these metabolic by-products plays an important role in the development of neurodegenerative diseases. For example, the accumulation and aggregation of β-amyloid proteins is hypothesized to be one major cause for Alzheimer’s disease. Generally, the body has developed its ways to eliminate toxic metabolic by-products from the system. In other parts of the body than the brain, our lymphatic system is responsible for waste removal. Since it would be fatal if any compound were able to freely diffuse between the brain and the rest of the body, the blood-brain-barrier prevents the unhindered exchange very effectively. As a consequence, it is plausible that there must be a separate “garbage truck” exclusively for the brain. This system has been identified by a group of researchers in 2013 and called the glymphatic pathway.1 In very simple terms, regulated by an expansion and contraction of the brain’s extracellular space during sleep, solutes between the incoming fluid, called the cerebrospinal fluid and the interstitial lymphatic fluid in our brain are exchanged. In this way, metabolic waste is drained from the brain.

Interestingly, the same group of researchers found in a follow-up study in rats that body posture during sleep exhibits an effect on the clearance rate of metabolic waste.2 Using different techniques including dynamic-contrast-enhanced magnetic resonance imaging (MRI) and fluorescence spectroscopy, the researchers concluded that waste removal was more efficient in the lateral position (laying on the side) compared to the prone (laying on the stomach) or supine position (laying on the back).

These findings combined may first of all explain, why sleep is essential for our survival. Second, even if there may be no simple explanation why one body posture during sleep improves the glymphatic transport compared to others, this research certainly goes in the right direction concerning fully understanding the molecular causes for neurodegenerative diseases and, thus, maybe finding a way to prevent Alzheimer’s disease.

– Kristina Klinker

Read more:

1 M. Nedergaard, Science, 2013, 340, 1529–30.

2  H. Lee, L. Xie, M. Yu, H. Kang, T. Feng, R. Deane, J. Logan, M. Nedergaard and H. Benveniste, J Neurosci, 2015, 35, 11034–11044.

Aug 242015
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I am sure you all spend some time at the beach when you were a kid. And I am also sure that your started digging holes in the sand when you were there. Or maybe you did something like that in your backyard. Anyhow, have you ever wondered how deep you would be able to dig? If you maybe could dig through the whole world? And if yes, why hasn’t anyone done this, yet?
Russian scientists tried this out for real between 1970 and 1994. They dug a hole, the Kola Superdeep Borehole, which got 12.2 km deep in the end.[1] Only being about one third of the thickness of the earth’s mantle, this is even deeper than the deepest point on earth, the Mariana Trench southeast of Japan, which is “only” 11.0 km deep. So why did they stop, when they already bested the Mariana Trench? Well, it just became too hot. The temperature in these depths is around 180 °C and this was obviously too much for the drilling equipment. So they just sealed up the hole and left it.
Is the story over here? No! Just recently the so called 2012 MoHole to the Mantle Project was started. It supposedly costs about one billion dollars. They adventurous plan: starting to dig at the bottom of the Mariana Trench, so the mantle to dig through would be thinner already in the beginning.[2] There weren’t any news after 2012. So, if the project was stopped, I cannot tell, but maybe the diggers just need to collect some courage (and more money).

Andreas Neidlinger

[1] (last access 23.08.2015)
[2] (last access 23.08.2015)

Jul 092015
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Almost one year ago Facebook and Apple announced that they will cover the cost of egg freezing for their female employees [1]. Egg freezing is seen as a way to improve the success of a potential future in-vitro fertilization (IVF) procedure by using an egg that is years, even decades, younger than the mother. However, this approach is based on a not yet solid assumption: That a woman’s eggs are produced during fetal development and, as direct consequence, gain in age (and loose in fertility) with the woman that carries them [2, 3]. The age of first-time parents is rising in our time, which entails growth of the IVF industry that seeks to ensure fertility of women that are rather at the end of their reproductive age [4].

What if IVF could be circumvented by letting the body generate new eggs? This process would require appropriate stem cells that are able to divide. Whether such cells exist is still a matter of debate. In 2005 the group of Jonathan L. Tilly identified bone marrow transplantation as source for stem cells that restore fertility in sterilized mice [5]. The same group claimed to have identified actively dividing germ cells in the ovaries of reproductive age women, that were capable to develop into eggs [6].

The hoped-for natural substitute of IVF seemed found at last, but was soon challenged by Zhang et al., who could disprove the existence of dividing stem cell precurors in mice [7]. In fact another paper confirmed that mouse oogenesis originates from cells that are already formed at birth [8]. Thus the debate remains open, with some scientists claiming that “absence of evidence is not evidence of absence” [9]. Current evidence arguing for or against non-renewable ovary stores in mammals is reviewed in [10].

Felix Spenkuch

Read more:

[1] (called at 8.07.2015)
[2] S. Zuckerman (1951) The number of oocytes in the mature ovary. Recent Prog. Horm. Res. 6, 63-108.
[3] S. Zuckerman, T. G. Baker (1977) The development of the ovary and the process of oogenesis. The Ovary, Academic Press, New York, 41-67.
[4] (called at 8.07.2015)
[5] J. Johnson et al. (2005) Oocyte Gerneration in Adult Mammalian Ovaries by Putative Germ Cells in Bone Marow and Peripheral Blood. Cell. 122, 303-315.
[6] Y. A. R. White et al. (2012) Oocyte formation in mitotically active germ cells purified from ovaries of reproductive-age women. Nature Medicine, 18, 413-421.
[7] Zhang et al. (2012) Experimental evidence showing that no mitotically active female germline progenitors exits in postnatal mopuse ovaries. Proc Natl Acad Sci USA, 109, 12580-12858.
[8] Lei Lie and A. C. Spradling (2013) Female mice lack adult germ-line stem cells but sustain oogenesis using stable primordial follicles. Proc Natl Acad Sci USA, 8585-8590.
[9] D. Bhatiya et a. (2013) Ovarian stem cells: absence of evidence is not evidence of absence. J Ovarian Res, 6:65.
[10] C. B. Hanna, J. D. Hennebold (2014) Fertility and Sterility, 101, 20-30.

May 262015
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The Younger Dryas Event (YDE) is a climatological phenomenon that happened roughly 13,000 years ago. In a span of a few years, the temperature in Western Europe and North America dropped sharply and stayed low for over a millennium. The effect was more diffuse in northern America and less pronounced in the southern hemisphere.
Nonetheless, the YDE is associated with the mass extinction of large mammals in North America. At this time, humans had already spread around the globe and started civilizations. One of these civilizations was the so called Clovis culture that also vanished during the YDE. It is entirely possible that the extinctions coinciding with the YDE are not due to climatological changes, but rather human overkill [1]. The decline in mammal population in turn led to the decline of the Clovis. But as life is complicated, the activity of humans likely conspired with the changing climate to cause the extinction and the downfall of the Clovis.
In contrast to our current civilization, the people 13,000 years ago did not have the means to affect such dramatic climatic changes (going far beyond even our current level of climate change).

The question now is: what caused the YDE in the first place? A widely held belief is that the melting of the North American ice caps disrupted the thermohaline circulation (the ocean circulation that nowadays brings warm water from the Gulf of Mexico to Western Europe), by dumping large quantities of fresh water into the north Atlantic. In 2007 Firestone et al. proposed an interesting trigger for the melting of the ice caps [2]: An impact of an asteroid, or rather the explosion of an asteroid in the atmosphere. This would have been much stronger version of the 2013 Chelyabinsk meteor. Support for this hypothesis comes from the presence of nanodiamonds in the geological layers associated with the YDE. The only other strata where these diamonds are present is the K-T boundary that marks the global extinction event that killed the dinosaurs [3].

The impact hypothesis is however hotly debated [4]. Many of the original markers used to determine that an impact took place have later been discredited, as it turned out they can also be produced by earthly phenomena, e.g. volcanism. The markers left over on the other hand could not be consistently reproduced by other research groups. One problem is that different groups include different kinds of nanodiamonds in their analysis or use different calibration scales for the dating of samples. The uncertainty in the dating is often several hundreds of years so that it is not clear if potential impact markers have been deposited at the same time or in independent events. Additionally the uncertainty in the age of the samples makes it hard to pin them to the relatively narrow time frame for the beginning of the YDE. The impact event might thus have happened significantly before or after the onset of the YDE, or it might not have happened at all. After all new climate models suggest that the melting of the North American ice sheets could have occurred without a specific trigger such as the proposed impact.

So where are we left if the impact is not necessary to explain the behavior of the climate and the evidence for an impact is disputed? There is certainly the possibility that an impact took place without changing the climate, but the main question seems to be if the impact ever occurred.

Stephan Koehler

Read more:
[1] Samdom et al., Proceedings of the Royal Society B 281, 20133254 (2014).
[2] Firestone et al., PNAS 104(41), 16016-16021 (2007).
[3] Kinzie et al., Journal of Geology 122(5), 475-505 (2014).
[4] van Hoesel et al., Quaternary Science Reviews 83, 95-114 (2014).

May 122015
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Have you ever felt vertigo after a ride on a merry-go-round? Why can we feel this acceleration so intensively, while we do not notice at all that our very world does rotate around itself and rotate around the sun the entire time? This seems odd, considering that the Earth is travelling around the sun with a speed of approx. 30 km/s[1], while a merry-go-round is comparably slow with 8 m/s (see below).

First of all: What is “vertigo”? It is the perception of a (mock-)motion of oneself against the environment. Responsible for such cognition is the vestibular system which is able to recognise acceleration. In the labyrinth of this organ in the inner ear tiny hair is arranged in two planes: horizontal and vertical. It is embedded in a heavy matrix, which remains as it is in case of linear acceleration. Thus the hair experiences deflection and it comes to a sensory stimulus.

Rotatory acceleration is also recognized by sensory hair, which arranged in semi-circular canals which are filled with lymphatic fluid. If it comes to a rotation, this fluid remains (due to inertia) in contrast to the cranial bone. Thus the sensory hair is deflected and again we have a sensory stimulus.

So, now as we know about that, we need to clarify how the movement of the Earth is affecting us. The Earth carries out two kinds of movement: It rotates around the sun and around itself. If we assume a speed of 30 km/s (which is quite fast) and 365 days as a time period the Earth needs to travel around the sun, we can calculate an acceleration of approx. 1 mm/s2, which is very small, in deed. (For this calculation we neglect the fact that the speed is fluctuating.)

For the rotation of the Earth around itself we assume a perimeter of 40000 km. Since the rotation of the Earth around itself takes one entire day we have a speed of approx. 0.5 m/s and an acceleration of 5 μm/s2, respectively. This figure is even smaller than the one we calculated for the travel around the sun.

If we assume a merry-go-round with a diameter of 15 m and a velocity of 30 km/h the acceleration which the body experiences is 1.5 m/s2. This value is much higher than the acceleration of the Earth that is resulting from the travel around the sun and the rotation around itself.

I don’t know if I considered all effects that are somehow important to answer the question why we do not feel dizzy on our planet. But I think if one keeps in mind that it is not the speed but the acceleration that causes dizziness, the answer that I can give sounds reasonable.

Katharina Stockhofe

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Apr 272015
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Covade syndrome can be defined as a psychosomatic phenomenon with little or no recognized physiological basis that affects male partners mainly during the first and third trimester of pregnancy and disappears early after the birth of the children. Determining the incidence rates of couvade syndrome has been problematic, as rates as low as 11% or as high as 97% have been reported which is in part attributed to a “Macho” culture in which men do not admit to symptoms to not appear weak. Also socio-demographic factors have been a matter of debate, as studies have reported a greater occurrence of the syndrome in men under 30, men over 30 and highly educated or working class men by different studies respectively. The matter is further complicated by the fact that different studies focused on different symptoms, physiological and psychological.

Infant holding fathers hand byClarence Goss (downloaded from

Infant holding fathers hand by Clarence Goss (downloaded from

Psychoanalytic, psychosocial as well as paternal theories have been put forward to explain the origins of Couvade syndrome. From psychoanalytic theories comes the idea that the man is envious of the ability of the woman to conceive children. The unconscious need to experience the woman’s pregnancy then manifests in psychosomatic pregnancy symptoms. Another view argues that the man fears to lose his partner to the baby and this might reactivate old sibling rivalry for the love of the mother. Psychosocial theories point out that men are often marginalized during pregnancy and birth, which might adversely affect the father’s health. Another theory postulates, that the pregnancy symptoms help the man prepare for his new father role in reinforcing the reality of the pregnancy. Paternal theories suggest that the emotional closeness to the unborn child is the cause of couvade syndrome. However, studies investigating the connection between couvade syndrome and either the involvement of the father in the pregnancy or anxiety levels in fathers have not shown clear results.

Physiological mechanisms underlying the syndrome might be connected to hormones, as men reporting Couvade symptoms showed higher prolactin and lower cortisol and testosterone levels.

But human males don’t seem to be the only ones experiencing pregnancy symptoms. Males in two species of monkeys (common marmosets and cotton-top tamarins), who are monogamous and caretakers of children gain up to 20% of their body weight during the pregnancy of their partners. While it is thought that the extra weight prepares the fathers for exhausting sleepless nights or carrying small children, it is not yet understood how the monkeys manage to gain weight.

Although numerous studies on how, where and why Couvade syndrome occurs, there is still not much we really know. Many of the studies are contradictory and the syndrome seems to be hard to pin down. We know that we are dealing with psychosomatic symptoms occurring during pregnancy, but for a deeper understanding, studies with large sample sizes investigating a multitude of physiological as well as psychological factors are needed.

— David Huesmann

Read more:

Brennan A, Ayers S, Ahmed H, Marshall-Lucette S. A critical review of the Couvade syndrome: The pregnant male. Journal of Reproductive and Infant Psychology, 2007, 25, 173 – 189

Ziegler TE, Prudom SL, Schultz-Darken NJ, Kurian AV, Snowdon CT. Pregnancy weight gain: marmoset and tamarin dads show it too. Biology Letters, 2006, 2, 181-183.