In the cold depths of space, interactions between gas and dust can produce a range of complex molecules. Everything from water and alcohol to the basic building blocks of life. While much of this chemistry occurs in cold molecular clouds, molecules can also be produced in the warm regions surrounding a young star, in what is known as a hot molecular core. A few hot molecular cores have been observed in our galaxy, but recently one was discovered in the Large Magellanic Cloud. Somewhat surprisingly, the molecular composition of this extragalactic hot molecular core is strikingly different from the ones seen in our galaxy. 

The young star in question is known as ST11, and it was recently observed by the ALMA radio telescope array. ALMA is particularly suited to observe complex molecules in space, because it is able to view them at the kind of sub-millimeter wavelengths these molecules often emit. ALMA was not only able to observe the warm dust around ST11, but also molecules such as formaldehyde and nitrous oxide. The region is lacking other molecules such as methanol, which are common in cold molecular clouds. Since the formation of different molecules depends not only on the available elements but also temperature and cloud density, the study of such hot molecular cores allows us to better understand complex molecular interactions in space, which can give us clues about how complex chemistry and even life formed on Earth.

One key difference between the Large Magellanic Cloud (LMC) and our own Milky Way galaxy is that the LMC has a much lower metallicity. This means it has a lower fraction of heavier elements such as silicon, oxygen and iron. These elements are common building blocks of interstellar dust, which is why the LMC has a lower fraction of such dust. A great deal of complex chemistry can happen on the surface of dust grains as it interacts with surrounding gases, and a lower metallicity means such interactions are less common. We see this in the types of molecules forming around ST11. Given the density of ST11’s hot molecular core, the levels of molecules such as formaldehyde and isocyanic acid are a tenth to a thousandth of levels seen in the Milky Way. This demonstrates the central role of dust surface chemistry to the formation of these molecules.

It’s a powerful insight into just how young stars can seed the cosmos with some of the complex molecules we see around us.

Paper: Takashi Shimonishi, et al. The detection of a hot molecular core in the Large Magellanic Cloud with ALMA. The Astrophysical Journal, Volume 827, Number 1 (2016)

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It’s flu shot season, which means an annual popup of anti-vax memes in my social media feeds. Most of the memes this year are of the “OMG! The flu shot contains mercury!” variety. While it’s true that some versions of the flu vaccine do contain trace amounts of mercury, such a statement is largely meaningless. 

Thimerosal, the organic compound used as a preservative in some vaccines, breaks down in the body into ethyl mercury. Since our bodies can remove ethyl mercury from our bodies, it doesn’t bioaccumulate. This is very different from methyl mercury, found in trace amounts in certain fish like tuna. Methyl mercury is hard for our bodies to remove, and can bioaccumulate. It’s the buildup of mercury over time that can be dangerous, which is why the FDA recommends limiting consumption of certain varieties of fish. While both compounds contain mercury, the two molecules are structurally different and behave differently in our bodies. It’s similar to the difference between ethyl alcohol and methyl alcohol. The former is found in beer and wine and used as a social lubricant, while the latter is used in things like antifreeze and is highly toxic. Simply stating some vaccines contain mercury is like saying “OMG! Beer contains antifreeze!”

The glossing over of these kinds of details is depressingly common in popular science writing. For example, a while back there were posts about how there is evidence of life found in some meteorites, supporting the idea that life came from outer space. What was actually found was that some meteorites, such as the Murchison meteorite, contain more than 70 types of amino acids, which are sometimes referred to as the building blocks of life. Since the fall of the Murchison meteorite was observed, and the meteorite was recovered soon after it reached Earth, we can be confident that those amino acids are not due to terrestrial contamination. It’s in the details, however, where things get interesting.

Chiral molecules come in left-handed and right-handed versions. Credit: Wikipedia

Amino acids are chiral molecules. This means they come in two different forms that are mirror images of each other. Each type of amino acid has a left handed and right handed version. Terrestrial organisms mainly use left-handed proteins (of which amino acids are the building blocks) and right-handed sugars. The amino acids on the Murchison meteorite were found to be roughly equal parts left and right handed. This means they were likely produced by a nonbiological process. We know from other studies that complex molecules can form in deep space. So the Murchison meteorite actually contradicts the idea that terrestrial life began in space. Cosmic amino acids may have played a role, but likely some mechanism on Earth gave rise to the handedness of biology we see today.

Often in science it’s the smallest of details that make all the difference. Some evidence can’t be reduced to a catchy headline, and doing so can often lead to headlines that are downright misleading.

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Our atmosphere is about 78% nitrogen and 21% oxygen, with traces of other things like water and carbon dioxide. It’s an odd mix compared to the atmospheres of other planets. Jupiter and Saturn are dominated by hydrogen and helium, The thick atmosphere of Venus is about 96% carbon dioxide, and only 3% nitrogen, which is about the same ratio as the thin atmosphere of Mars. So why is our atmosphere so dominated by nitrogen? 

It wasn’t always this way. Like most planets Earth’s earliest atmosphere was dominated by hydrogen and helium. These two elements are by far the most abundant in the Universe. About 92% of the atoms created by the big bang were hydrogen, and most of the rest were helium. All the other elements on the periodic table are formed through astrophysical processes such as nuclear fusion in the heart of a star. To this day they make up only a small trace of cosmic elements. When planets initially form, their composition is mostly hydrogen and helium. Some of the hydrogen bonds with other elements, but most of it remains free hydrogen. Both hydrogen and helium are light elements, so they will tend to evaporate into space over time. A large planet such as Jupiter has enough gravity to hold on to most of its hydrogen and helium, which is why these elements dominate the atmospheres of gas giants. But the gravity of Earth isn’t strong enough, so Earth’s early atmosphere of helium and free hydrogen evaporated into space.

The relative abundances of elements on Earth. Credit: Gordon B. Haxel, Sara Boore, and Susan Mayfield from USGS

Of the remaining elements, carbon, nitrogen, and oxygen are the most abundant. This is due to the fact that the main fusion reaction in large stars is the CNO cycle, which produces these elements as a by-product. These react easily with other elements, and produce gasses like water (H₂O), carbon dioxide (CO₂), and ammonia (NH₃). Young Earth was much more geologically active than it is today, and volcanic activity released large quantities of these gases, and over time they came to dominate Earth’s atmosphere.

So why are the atmospheres of Venus and Mars dominated by CO₂, while Earth’s is not? It all comes down to water. Earth’s vulcanism driven atmosphere was likely dominated by carbon dioxide like Venus and Mars, but Earth also has vast oceans of liquid water. Carbon dioxide dissolves easily in water, so our oceans absorbed much of the atmospheric CO₂, leaving an atmosphere dominated by ammonia. It turns out that ammonia is unstable in Earth’s atmosphere. When struck by ultraviolet light from the Sun, it breaks apart into nitrogen and hydrogen. The liberated hydrogen evaporated into space, leaving nitrogen behind. Venus’ atmosphere likely followed a similar process, but without vast oceans to pull CO₂ out of its atmosphere. While Venus’ atmosphere is mostly carbon dioxide, it is much thicker than Earth’s, and contains four times the nitrogen.

Even with it’s vast oceans, Earth’s atmosphere would likely have been dominated by carbon dioxide were it not for the appearance of life. Early cyanobacteria used sunlight and the carbon dioxide dissolved in Earth’s oceans to produce energy, and released oxygen as a by-product. Early oxygen bonded with iron to form a layer of rust, but eventually began to build up in Earth’s atmosphere. As carbon dioxide was broken down by cyanobacteria, more CO₂ could be dissolved into the ocean. This gave rise to our modern atmosphere dominated by nitrogen and oxygen.

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Since matter is made of atoms, it’s fairly common for materials to form into crystal lattices. Table salt, quartz, diamonds, etc. are all crystal formations. The arrangement of atoms in such crystals are regular and periodic, but there are some materials where the atoms are arranged in a crystal-like structure, but their patterns are not periodic. These quasicrystals follow patterns similar to Penrose tiles, where there is some broad sense of symmetry, but not a rigid repeating arrangement. 

Crystals can be identified by their overall symmetry, and follows the way different shapes can tile on a flat surface. Since lines, triangles, squares and hexagons can all tile a plane, crystals must have an n-fold symmetry of 2, 3, 4, or 6. But in 1982 Dan Shechtman found that aluminium-manganese alloys could form a 5-fold symmetry, like some Penrose tiles, hence the origin of quasicrystals.

Most quasicrystals are manufactured in the lab. It’s tricky to get them to form, since the tendency for atoms to arrange in regular patterns is so strong. But there are a couple of cases where quasicrystals formed natural, and it’s a bit of a mystery as to how they occurred. New work suggests that they could have formed through the collision of rare asteroids.

There are only two examples of natural quasicrystals, both from the same meteorite. This particular meteorite also has evidence of shock fractures, indicating it had undergone a collision at some point in its history. This led a team to suspect that meteor collisions could produce quasicrystals through a rapid succession of compression, heating, and cooling. So they devised an experiment where a bullet-speed projectile was fired at small sample of the meteorite. Since the natural quasicrystals are formed of aluminum, copper, and iron, they used a sample that contained a copper-aluminum alloy. They found that impact with the projectile did indeed form quasicrystal structures.

So it seems that quasicrystals do form naturally through asteroid collisions, but are still likely to be quite rare.

Paper: Paul D. Asimow, et al. Shock synthesis of quasicrystals with implications for their origin in asteroid collisions. PNAS (2016) DOI: 10.1073/pnas.1600321113

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The first elements to appear in the Universe were hydrogen and helium, created soon after the big bang. Other elements on the periodic table are produced through nuclear interactions within stars. Lighter elements such as carbon, nitrogen and oxygen are formed through nuclear fusion in a star’s core, but heavier elements such as gold are formed through catastrophic events such as a supernova explosion or the collision of neutron stars. It’s known as r-process nucleosynthesis (due to the rapid neutron interactions) and is still a bit of a mystery. 

We can distinguish r-process elements not only by their presence in stars, gas and dust, but also by their relative abundances. The r-process abundances are distinctly different from other nucleosynthesis methods such as the s-process (slow neutron) that occurs in the late stage fusion of large stars. So we know that heavier elements can are produced through r-process events, but one of the big debates has been over which type of events create the most heavy elements.

There’s basically been two schools of thought. One is that core-collapse supernova are the main factor. These are fairly common on a cosmic scale, but the amount of heavy elements released in a particular supernova is relatively low. In this model a galaxy would be seeded with a low but steady flow of heavy elements. The other idea is that stellar collisions create most heavy elements. The collision of two neutron stars, for example, is fairly rare, but the amount of heavy elements released from such an explosion would be quite high. In this model heavy elements are seeded into a galaxy in bursts every now and then. The challenge is to determine which model is right.

Recently astronomers found evidence that the collision model seems to be the right one. They looked at the abundance of elements in a dwarf galaxy known as Reticulum II. They found that the 9 brightest stars in this galaxy have heavy element abundances 100 to 1,000 times greater than seen in other similar galaxies. This would imply that the abundance of r-process elements was unusually high during their formation, which is what you would expect if they are produced at high quantities in rare events. It seems clear, then that stellar collisions play a major role in the production of heavy elements.

Since gold is one of those heavy elements, you could say that the collision of neutron stars causes a galaxy to enter a gilded age.

Paper: Alexander P. Ji, et al. R-process enrichment from a single event in an ancient dwarf galaxy. Nature 531, 610–613 (2016) doi:10.1038/nature17425

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The origin of Earth’s water is a bit of a mystery. While water is common in our solar system, it’s much more common in the outer solar system, such as Jupiter’s moon Europa or Saturn’s moon Enceladus. Most of the worlds of the inner solar system are fairly dry. So how did Earth come to have large oceans on its surface?

There are two main ideas on the origin of Earth’s water. One is that Earth’s water was locked up in the original rocks and dust that formed our planet. As the material collapsed under its own gravitational weight, water was released and eventually formed the oceans we have now. The other idea is that any water in the original material escaped early on, and the current water of Earth came to our planet through the bombardment by asteroids and comets. Evidence that Venus and Mars were also wet in their early history points toward a formation origin of water, but there has generally been more evidence to support the bombardment model.

Three isotopes of atomic hydrogen. Credit: Dirk Hünniger, CC BY-SA 3.0.

This evidence comes through what’s known as the deuterium/hydrogen (D/H) ratio of Earth’s water. Deuterium is an isotope of hydrogen that has a nucleus of a proton and neutron, rather than the single proton of regular hydrogen. Chemically it reacts in the same way as hydrogen, but since it is heavier than regular hydrogen there are slight differences. For example, when a deuterium atom is part of a water molecule, the extra mass means it doesn’t evaporate as readily as regular water. Deuterium water is more likely to form in space than in the gravitational field of a planet, so the D/H ratio of water tells us about the origin of that water.

The D/H ratio for Earth’s oceans is about 150 parts per million, which is similar to that of chondrite asteroids. This would seem to support the bombardment model. But a new paper argues that such a conclusion is too simplistic. Our oceans cycle between the surface and interior of Earth, which could affect the D/H ratio. In this paper the team looked at rocks from Earth’s mantle, and they found that the water contained within these rocks has a much lower D/H ratio than that of our oceans. This suggests that mantle water formed locally rather than through astroid bombardment.

There’s still a number of unanswered questions. This latest work doesn’t disprove the bombardment model, and it’s possible that our water came from a number of sources. Further study on both fronts is needed to resolve this mystery.

Paper: Lydia J. Hallis, et al. Evidence for primordial water in Earth’s deep mantle. Science, Vol. 350 no. 6262 pp. 795-797 (2015) DOI: 10.1126/science.aac4834

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Comets are frozen remnants from the formation of our solar system. They live on the outer edges of our solar system until some gravitational perturbation causes them to sweep near the Sun. Because they have been relatively undisturbed for most the Sun’s history, they provide an excellent window into the chemistry and composition of the early solar system. Which is why it’s interesting that ethyl alcohol has been observed in the tail of comet Lovejoy.

Lovejoy is a long-period comet, which means it’s probably originates from the Oort cloud, and hasn’t had time to become contaminated by material of the inner solar system. Finding ethyl alcohol streaming off such a comet is somewhat surprising. We’ve long known that alcohol is plentiful in space, but much of it is in the form of methyl alcohol, which is a simpler molecule than ethyl alcohol. In this case, it seems the more complex alcohol formed through surface chemistry interacting with ultraviolet light. The team also found quantities of glycolaldehyde, which is a simple sugar-like molecule, which also supports the surface chemistry idea.

Compounds such as these are necessary ingredients for life on Earth, so its possible that comets similar to Lovejoy could have seeded Earth with these molecules through early impacts. That’s still a bit speculative, but it now seems clear that both comets and meteorites contain such molecules, so its within the realm of possibility that they seeded Earth with the building blocks of life.

At the very least the observations of Lovejoy show that these molecules formed in our solar system early in its history.

Paper: Nicolas Biver, et al. Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy). Science Advances, 23 Oct 2015

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Tholins are a broad class of complex organic molecules. They are typically formed when ultraviolet light strikes simple organic molecules such as methane. They were first categorized by Carl Sagan when reproducing the Miller-Urey experiment. While tholins don’t exist naturally on Earth since our high-oxygen atmosphere tends to prevent them from forming, they are very common on the cold worlds of the outer solar system.

The formation of tholins on Titan. Credit: NASA-JPL

Tholins recently hit the news during the flyby of Pluto. The reddish brown coloring of the dwarf planet is likely caused by tholins on its surface. The molecules also give Titan’s atmosphere its brown coloring. They are suspended in the Saturnian moon’s atmosphere like smog. We’ve found tholins on comets and asteroids, and there’s even some evidence of tholins on planets orbiting other stars.

Tholins may have been common on Earth before the rise of free oxygen in our atmosphere about 2.3 billion years ago. There is some speculation that tholins may have played a role in the appearance of life on Earth. We know, for example, that many soil bacteria can feed off tholins as a source of carbon. Since tholins absorb ultraviolet light, they could also have played a role in protecting young Earth from UV rays that can tend to harm fragile living organisms.

Paper: M. Köhler, et al. Complex Organic Materials in the HR 4796A Disk? The Astrophysical Journal 686 L95 (2008)

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There are buckyballs in space. More formally known as fullerenes, these carbon molecules such as C₆₀ have long been known to exist in space due to the complex chemistry that can occur between gas and dust in interstellar clouds. But we now know fullerenes can help explain one of the nagging mysteries of astronomy known as diffuse interstellar bands.

Diffuse interstellar bands are absorption features seen in stellar spectra. While many absorption lines can be identified with particular atoms or molecules, DIBs don’t have a clear identification. But two bands in the infrared (at 958 and 963 nanometers) were thought to be caused by C₆₀. Now a paper in Nature confirms this hypothesis. In this work, the team looked at the spectra of buckyballs when cooled to about 6 Kelvin (a common temperature for interstellar clouds). They observed absorption bands 963.27 ± 0.1 and 957.75 ± 0.1 nanometers, in good agreement with the interstellar bands.

So that’s two DIBs identified, and a few hundred more with origins yet to be discovered.

Paper: E. K. Campbell, et al. Laboratory confirmation of C₆₀⁺ as the carrier of two diffuse interstellar bands. Nature 523, 322–323 (2015)

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This week in Nature it was announced that complex organic molecules were observed in a young planetary system. This isn’t the first time such molecules have been observed in space, nor is this result particularly surprising, but the result does confirm some of our suspicions about the chemistry of the early solar system.

The team looked at a star known as MWC 480. It is about a million years old, and has a protoplanetary disk surrounding it. By analyzing the spectra from this star they found evidence of methyl cyanide and hydrogen cyanide in the region equivalent to the Kuiper belt of our solar system. This means that as the star’s planetary system forms, these organics will become locked up in cometary bodies.

We’ve long known that cyanide molecules can exist in comets. In fact, one of the first detections of an organic molecule in space was the discovery of cyanogen in Halley’s comet in 1910. What this new work shows is that the comets of other planetary systems are likely to have similar organics.

One of the reasons cyanides in space are interesting is that they are the types of molecules necessary to build amino acids and eventually proteins. We know that these “building blocks” of life have been found in meteors, and there is speculation that these kinds of molecules could have helped jump start the formation of life on Earth. Since they appear common to other planetary systems as well, they might help jumpstart life across the cosmos.

At this point we can’t be sure, but it does appear that the conditions of the one planetary system where we know life exists are not particularly unusual.

Paper: Karin I. Öberg, et al. The comet-like composition of a protoplanetary disk as revealed by complex cyanides. Nature 520, 198–201 (2015)

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One of the big unsolved questions in chemistry and biology concerns the origin of life on Earth. One of the more speculative ideas on the matter is known as panspermia, or idea that life arose elsewhere and was seeded (either intentionally or through comets or meteors) on Earth. Thus, we came from outer space. It’s an idea that has been approached with both serious research and wild “ancient aliens” pseudoscience, so it doesn’t always get much respect in the field of astronomy. 

Despite the occasional claims, such as the red rain incident that was claimed to contain extraterrestrial organisms, or the application of Moore’s law to the complexity of organisms to argue that life is older than Earth, there is no solid evidence that extraterrestrial organisms seeded life on Earth. And although abiogenesis is an unsolved problem, there is no indication that life couldn’t have originated on Earth.

That said, we also know that the building blocks of life, such as amino acids, sugars and fatty acids, have formed in space, and could have been brought to Earth. Perhaps the most famous example comes from a meteorite that fell near Murchison, Victoria, in Australia. Commonly known as the Murchison meteorite, it was observed to fall in 1969, and its fragments total more than 100 kilograms. It is a carbonaceous chondrite meteorite, which means it formed in the early solar system when dust grains began coalescing into small asteroids, and was never heated to its melting point.

Because samples were gathered soon after impact, the amount of possible contamination from terrestrial organics is minimal, so we can be confident that building block materials aren’t due to contamination. We’ve also found, for example that the sugars and amino acids from the asteroid are a mix of left and right handed molecules. Terrestrial organisms mainly use left-handed proteins (of which amino acids are the building blocks) and right-handed sugars. This would imply that the Murchison organics have a non-biological origin.

By 2010, more than 70 amino acids and 14,000 other molecular compounds have been detected in the meteorite. We also now know that complex molecules can form in interstellar clouds, and these molecules could have survived through the formation of the solar system. So while life probably didn’t begin “out there,” it’s possible that organic material brought to Earth by meteors similar to Murchison could have helped jump start the rise of life by providing useful raw materials.

Paper: Kvenvolden, Keith A., et al. Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite. Nature 228 (5275): 923–926. (1970)

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For an inner planet, Earth is bountiful with water. The origin of that water has been a matter of some debate. One idea is that a combination of Earth’s strong magnetic field and distance from the Sun allowed Earth to retain much of the water emitted from rocks as the planet cooled. Another is that water came to Earth through cometary or asteroid bombardment. But now it seems the origin of Earth’s water is more complex and more interesting that we’ve thought.

Last month an article in Science showed that much of Earth’s water existed before the formation of the solar system. The authors demonstrated this by looking a levels of deuterium in terrestrial water. Deuterium is an isotope of hydrogen that has a proton and neutron in its nucleus, rather than just a proton. As a result, it’s almost twice as heavy as regular hydrogen, and this means the way it chemically reacts is slightly different from regular hydrogen.

Deuterium isn’t very common compared to hydrogen, and exists at about 26 parts per million. When the team measured levels of deuterium in the water of Earth and other solar system bodies, they found the water contained deuterium at about 150 parts per million. This is interesting, because deuterium water is more likely to form in interstellar space. Water formed in the heat of a young solar system isn’t likely to produce much deuterium water. Given measured deuterium levels, the authors calculate that about half of Earth’s water was produced in the depths of space, before the solar system was formed.

This month another paper in Science found that water arrived on Earth earlier than expected. In this paper the team compared chondrite minerals on Earth with chondrite asteroids, specifically ones that likely originated from Vesta. Chondrite asteroids have a high quantity of water chemically bound to them, and one idea is that they could have been the source of Earth’s water. When they looked at the chemical makeup of terrestrial chondrites, they found them to be remarkably similar. This likely means terrestrial chondrites were themselves the source of Earth’s water. If that’s the case, then Earth was likely a water world a hundred million years earlier than the bombardment model predicts.

So it seems that Earth’s seas are more ancient both in origin and composition than we once thought.

Paper: Cleeves, L. I., et al. The ancient heritage of water ice in the solar system. Science, 345 (6204), p. 1590 – 1593 (2014)

Paper: Sarafian et al. Early accretion of water in the inner solar system from a carbonaceous chondrite–like source. Science, 346 (6209) p. 623-626 (2014)

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