Tag Archives: Formation

Planet forming.

Astronomers capture first images of an exoplanet forming

Astronomers have snapped the first pictures of a planet forming.

Planet forming.

This is the first clear image of a planet forming around the dwarf star PDS 70.
Image credits ESO / Müller et al., 2018, A&A.

Researchers led by a group at the Max Plank Institute for Astronomy in Heidelberg, Germany, are spying on a baby planet. The object of their attention is a still-forming planet that orbits around PDS 70, a young dwarf star. This is the first time we’ve captured clear images of a forming planet and its travels through the dust cloud surrounding young stars.

Far-away spheres

The images were captured using the SPHERE instrument installed on Unit Telescope 3 of the European Southern Observatory (ESO’s) Very Large Telescope (VTL) array in Chile. SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is one of the most powerful planet-finding tools astronomers have at their disposal today. What makes SPHERE stand out in the field of exoplanet exploration is that, unlike the majority of its contenders, it relies on direct imaging — SPHERE takes actual photographs of planets millions or billions of kilometers away.

SPHERE relies on a technique known as high-contrast imaging to produce such amazing shots. The device uses complex observation techniques and powerful data processing algorithms to tease out the faint traces of light incoming from planets around bright stars. Astronomers draw on the Earth’s rotation to help them better observe such planets — SPHERE continuously takes images of the star over a period of several hours, while keeping the instrument as stable as possible. This creates images of a certain planet taken from slightly different angles and at different points in the stellar halo, giving the impression that it’s slowly rotating or moving about. The stellar halo, meanwhile, appears immobile. The last step is to combine all the images and filter out all the parts that do not appear to move — blocking out signals that don’t originate from the planet itself.

The new planet, christened PDS 70b, stands out very clearly in the images SPHERE recorded. It appears as a bright point to the right of that blackened blob in the middle of the image. That blob is a coronagraph — a mask that researchers apply directly onto the star, lest its light blocks out everything else in the image.

Polarimetric Differential Imaging

Some examples of how such images from different angles helps astronomers tease out the light incoming from exoplanets.
Image credits Müller et al., 2018, A&A.

PDS 70b is a gas giant with a mass several times that of Jupiter. It’s about as far from its host star as Uranus is to the Sun. Currently, PDS 70d is busy carving a path through the planet-forming material surrounding the young star, the researchers note, making it instantly stand out.

“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” explains Miriam Keppler, who lead the team behind the discovery of PDS 70’s still-forming planet. “The problem is that until now, most of these planet candidates could just have been features in the disc.”

PDS 70d is already drawing a lot of attention from astronomers. A second paper, which Keppler also co-authored, has followed-up on the initial observations with a few months of study. The data from SPHERE also allowed the team to measure the planet’s brightness over different wavelengths — based on which they estimated the properties of its atmosphere. The planet is blanketed in thick clouds, the team explained, and its surface is currently revolving around a crisp 1000°C (1832°F), which is much hotter than any planet in the Solar System.

The findings also helped researchers make heads and tails of a structure known as a transition disc. This is a ring-like protoplanetary (meaning it is involved in early planetary formation) structure. Transitional disks roughly resemble a stadium, with a clean area in the middle (from which planets drew their matter), surrounded by a ring of dust and gas. While these gaps have been known for several decades now and speculated to be produced by the interaction between forming planets and its host star’s disk, this is the first time we’ve actually seen them.

“These objects represent […] disks whose inner regions are relatively devoid of distributed matter, although the outer regions still contain substantial amounts of dust,” explains a paper published by Strom et al. in 1989.

All this data helps flesh out our understanding of the early stages of planetary evolution — which are quite complex and, up to now, “poorly-understood”, according to André Müller, leader of the second team to investigate the young planet.

“We needed to observe a planet in a young star’s disc to really understand the processes behind planet formation,” he explains.

The findings further help improve our overall knowledge of how planets form. By determining PDS 70d’s atmospheric and physical properties, astronomers now have a reliable data point from which to extrapolate — which will help improve the accuracy of our planetary formation models.

Not bad for a bunch of photographs.

The first paper, “Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70” has been published in the journal Astronomy & Astrophysics.

The second paper, “Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk,” has also been published in the journal Astronomy & Astrophysics

We can’t grow new neurons in adulthood after all, new study says

Previous research has suggested neurogenesis — the birth of new neurons — was able to take place in the adult human brain, but a new controversial study published in the journal Nature seems to challenge this idea.

a. Toluidine-blue-counterstained semi-thin sections of the human Granule Cell Layer (GCL) from fetal to adult ages. Note that a discrete cellular layer does not form next to the GCL and the small dark cells characteristic of neural precursors are not present.

Scientists have been struggling to settle the matter of human neurogenesis for quite some time. The first study to challenge the old theory that humans did not have the ability to grow new neurons after birth was published in 1998, but scientists had been questioning this entrenched idea since the 60’s when emerging techniques for labeling dividing cells revealed the birth of new neurons in rats. Another neurogenesis study was published in 2013, reinforcing the validity of the results from 1998.

Arturo Alvarez-Buylla, a neuroscientist at the University of California, San Francisco, and his team conducted a study to test the neurogenesis theory using immunohistochemistry — a process that applies various fluorescent antibodies on brain samples. The antibodies signal if young neurons as well as dividing cells are present. Researchers involved in this study were shocked by the findings.

“We went into the hippocampus expecting to see many young neurons,” says senior author Arturo Alvarez-Buylla. “We were surprised when we couldn’t find them.”

In the new study, scientists analyzed brain samples from 59 patients of various ages, ranging from fetal stages to the age of 77. The brain tissue samples came from people who had died or pieces were extracted in an unrelated procedure during brain surgery. Scientists found new neurons forming in prenatal and neonatal samples, but they did not find any sustainable evidence of neurogenesis happening in humans older than 13. The research also indicates the rate of neurogenesis drops 23 times between the ages one and seven.

But some other uninvolved scientists say that the study left much room for error. The way the brain slices were handled, the deceased patients’ psychiatric history, or whether they had brain inflammation could all explain why the researchers failed to confirm earlier findings.

The 1998 study was performed on brains of dead cancer patients who had received injections of a chemical called bromodeoxyuridine while they were still alive. The imaging molecule — which was used as a cancer treatment — became integrated into the DNA of actively dividing cells. Fred Gage, a neuroscientist involved in the 1998 study, says that this new paper does not really measure neurogenesis.

“Neurogenesis is a process, not an event. They just took dead tissue and looked at it at that moment in time,” he adds.

Gage also thinks that the authors used overly restrictive criteria for counting neural progenitor cells, thus lowering the chances of seeing them in adult humans.

But some neuroscientists agree with the findings. “I feel vindicated,” Pasko Rakic, a longtime outspoken skeptic of neurogenesis in human adults, told Scientific American. He believes the lack of new neurons in adult primates and humans helps preserve complex neural circuits. If new neurons would be constantly born throughout adulthood, they could interfere with preexisting precious circuits, causing chaos in the central nervous system.

“This paper not only shows very convincing evidence of a lack of neurogenesis in the adult human hippocampus but also shows that some of the evidence presented by other studies was not conclusive,” he says.

Dividing neural progenitors in the granule cell layer (GCL) are rare at 17 gestational weeks (orthogonal views, inset) but were abundant in the ganglionic eminence at the same age (data not shown). Dividing neural progenitors were absent in the GCL from 22 gestational weeks to 55 years.

Steven Goldman, a neurologist at the University of Rochester Medical Center and the University of Copenhagen, said, “It’s by far the best database that has ever been put together on cell turnover in the adult human hippocampus. The jury is still out about whether there are any new neurons being produced.” He added that if there is neurogenesis, “it’s just not at the levels that have been presumed by many.”

The debate still goes on. No one really seems to know the answer yet, but I think that’s a positive — the controversy will generate a new wave of research on the subject.

The Types of Fossils and Other Rock-solid Fossil Facts

There are several ways of classifying fossils, depending on the process by which they form, the mineral and the underlying processes, but in the largest sense, fossils can be:

  • Body fossils
  • Trace fossils

Ah, fossils

Not as dramatic as an earthquake or as awe-inspiring as a volcano, but instrumental in shaping our understanding of the Earth. They are our only link to millions and millions of years of life that came before us. Almost everything we know about dinosaurs, ancient plants and countless other species of organisms we’ve learned from fossils. Geologists can use fossils to determine the age of rocks, to understand climate and environmental types from millions of years ago, and get an understanding of plate tectonics.

Fossils, scaring naughty children since millions of years before there were naughty children. Image credits albertr / Pixabay.

Fossils, scaring naughty children since millions of years before there were any naughty children.
Image credits albertr / Pixabay.

In other words, they’re incredibly useful even though they’re technically just a bunch of rocks. So how do they form? What kinds of fossils are there? Can you lick them?

The answer to that last question is yes. You should probably wash them first but still yes. The other two questions need more elaborate answers, so put on your hardhats and get those notebooks out because it’s paleontology time.

First thing first, how do they form?

A fossil represents the preserved remains or impressions of either whole or parts of ancient organisms. For the most part, they’re found in sedimentary rocks, although under certain conditions they could be preserved in metamorphic or igneous rocks — volcanic tufts, for example, a rock formed by volcanic ash.

Now, not every critter gets to become a fossil — else the world would be choke full of them, which it evidently is not. Certain conditions have to be met for organic matter to become fossilized, and the most important one is for the remains to be buried before they decompose. The faster this happens, the more features of the animal will be preserved. For example, if an animal dies in the sea and its body is slowly covered with sediment, we’ll probably find its fossilized bones. For an animal that got caught in quicksand, however, we may even see things such as impressions of skin and soft tissue.

The fish’s soft tissue can be clearly seen in this fossil, unlike the dinosaur from earlier.
Image credits The High Fin Sperm Whale / Wikimedia.

So to get a fossil you need the remains of an organism and some sediment to cover it before it fully decomposes. Most fossils we find today are formed in either marine environments or land areas with lots of water (such as swamps,) because they have high rates of sediment deposition and mobility. Year after year, new layers of material deposits over the animal’s remains — and in millions, even tens of millions of years, they get buried pretty deep. During this time, the sedimentary layer follows its natural cycle of lithification and, compressed by the weight of sediment above it, starts turning to stone, encasing the remains. By this point, some fossils rot away leaving behind a mold-like cavity which is them filled with new sediment in the shape of the former animal.

If the fossil doesn’t rot away, the huge pressure involved in lithification squashes the particles of sediment into each other, generating heat that cooks the remains enriching them in carbon — that’s why plant fossils usually take on brown or blackish hues. More resilient tissue such as shells, bone or wood can stand this pressure and remain inside the rock. Here one of two things happens — interstitial solutions either fill their pores with rock-forming minerals or dissolve them completely and fill the space with minerals that crystallize — that’s why I said fossils are technically just rocks.

The fossil and the rock that houses it can remain buried or, through various geological processes — mountain formation, for example — get pushed back up to the surface where the rock gets eroded, leaving behind the cast, ready to be found by enthusiastic paleontologists.

What can they expect to find?

All fossils are created through those three processes. They can be mold and cast, carbonized, or form through permineralization/replacement. So it might seem a bit weird that paleontologists categorize them in two “flavors,” but it actually makes sense.

The first type, known as body fossils, are the remains of an animal or plant — like bones, shells, and leaves. These can be mold and cast fossils, like the big dinosaur skeletons you can see in a museum, replacement fossils like petrified wood or whole body fossils — from insects caught in amber to mammoths encased in ice.

Fossil Coleoptera, Elateridae (Click beetles) in Baltic amber.
Image credits Manukyan Andranik / Wikimedia

The second type, known as trace fossils (or ichnofossils,) are records of organism’s lives but not parts of their body — these include footprints, track-ways, and coprolites.

Possitive ichinofosiil (worm tracks) in the Bright Angel Formation, Grand Canyon, USA. Image credits Grand Canyon National Park / Flickr

Positive ichnofossil (worm tracks) in the Bright Angel Formation, Grand Canyon, USA.
Image credits Grand Canyon National Park
/ Flickr

In geology, body fossils are used to determine the age of rocks — because we know the time-frames during which different animals or plants lived, we can estimate the age of the rocks based on what organisms we find. Trace fossils are very useful to determine the foot and the roof of a layer, in other words, which part was up and which was down as it sedimented. Imagine a worm wiggling over the sea floor, leaving a tiny dent behind it as it does. When the sand turns into sandstone, that little ditch will become a negative ichnofossil on the rock’s roof and a positive ichnofossil on the next layer’s foot.

I must gather these fossils for myself! Where can I find them?

First, you have to understand that each and every fossil is a miracle of chance – or rather, a statistical outlier. So many things have to go just right, over millions of years (the right animal has to die in the right spot, followed by the right climate and sedimentary influx to the area, burial, exondation, and erosion at the right moment) for you to find one that the mind just boggles. The first time I found a fossil I was literally jumping up and down with joy even though it was only one fish vertebra as tiny as the frontal camera on an iPhone.

That being said, if there’s one thing that life hasn’t lacked for it is numbers — the sheer quantity of animals and plants that have ever lived on Earth means that there’s a decent quantity of fossils to be found and more are created all the time. As a general rule, search for fossils in areas of erosion. Mary Anning, probably the most important fossil finder that you’re never heard of, did much of her fossil hunting in the sheer cliffs beside the English Channel.

For more detailed fossiliferous sites in the US, Fossilguy.com has a pretty extensive guide set up that’s definitely worth your attention.

How caves form and the different types of caves

Ahh, the cave, cradle of humanity since time immemorial. Early humans sought them for shelter, plastered their walls with paintings, made them into the first temples. And even after we’ve moved out, they still captivate and terrify us — unknown, but somehow familiar.

Without caves, our life might have been very different now. So how did they come about? How does a cave form? Well, in a lot of different ways, really. Caves come in different sizes and shapes, and the way they’re created depends on the type of cave. Most often, they form when water dissolves limestone, but they can also be shaped by waves, even lava.

So don your hardhats and pull your learning pants on, because I’m going to tell you all about:

The Types of Caves

Solutional caves

Son Doong Cave in Vietnam, the largest cave ever found, is a solutional cave. It’s big enough to have its own ecosystem.
Image credits Doug Knuth

These are the structures people most readily associate with the idea of a cave, and for good reason. They’re the most numerous, the largest and most often-encountered structures. If you’ve ever been spelunking or seen a cave in a movie chances are it was a solutional cave. The secret to their abundance is two-fold: for starters, the rocks that house them are found throughout the globe, and the chemical elements required to shape them are abundant. As Andrei wrote:

“Solutional caves are generally formed in limestone or other similar rock such as gypsum or dolomite. They form when acidic water dissolves the rock, seeping through the bedding planes.”

Let’s consider a geological environment of soil over a bedrock of limestone, as solutional caves are most frequently found in this type of rock. Limestone is a carbonatic rock, formed over millions of years from the remains of coral, zooplankton, shells or bones, all mashed up together. This material gets bunched up and subjected to huge pressure, fusing into solid rock.

The main mineral found in limestone is calcium carbonate, or CaCO3, a mixture of calcium and carbon trioxide, an unstable compound. While limestone is pretty resilient and nice to look at, it tends to be relatively brittle and fractures a lot due to tectonic stress. Its chemical makeup also makes it susceptible to attack by acids which break up the calcium carbonate into calcium compounds (Ca + the non-metal that forms the acid), carbon dioxide (CO2), and water (H2O).

Limestone cave in Australia.
Image credits Andrew McMillan

[panel style=”panel-info” title=”Fun geology fact” footer=””]Rubbing a diluted solution of acid onto a geological sample is still the easiest way to determine if there are any carbonatic compounds in the rock. If so, the solution will bubble and foam quite vigorously.[/panel]

These conditions work together to make limestone an ideal place for cave formation. In nature water invariably becomes acidic by mixing with carbon dioxide molecules (H2O+CO2=H2CO3) forming a solution of carbonic acid. Part of this can happen in the atmosphere as rain pours down, but most of the mixing takes place in the soil which is rich in CO2 left over from decaying organic matter.

This solution trickles down through the soil and cracks in the limestone until it reaches the water table. Here it starts to eat through the rock, forming channels. In an almost cruel twist of geological fate, while limestone dissolves it releases the exact components needed to make more carbonatic acid. This chain reaction and the extra acids that seep in from the surface keep expanding the cavern until the water table level drops. If this happens, water with dissolved calcium compounds will trickle down to the new area of dissolution, forming stalactites and stalagmites.

And looking awesome.
Image via pixabay

If on the other hand water remains mobile throughout dissolution, the caves take on the appearance of an underground drainage system, a landscape known as karst.

Something like this, but underground.
Image credits Jonathan Wilkins

It takes a few million years for a solutional cave to form.

Lava caves

While dissolution caves are formed by hollowing out preexistent packets of rock, lava caves form at the same time as the geological environment around them — and so, they’re considered to be primary caves. They’re centered around areas of volcanic activity and resemble huge underground rock pipes.

Lava River Cave in Arizona.
Image credits Volkan Yuksel

And in a way, that’s just what they are. Molten rock that reaches the surface (called lava) can form sprawling cave networks while it flows down the path of least resistance. The material is very hot initially, but as the outer layer of lava starts to cool it solidifies into a shell of rock. This process insulates the lava within and starts at the base of the flow (because the rock it’s pouring over is a better thermal conductor than air,) forming a through-like structure through which the hot lava at the center keeps on flowing. Over time, material clings to the edges of this through and solidifies, eventually closing into a pipe-like structure.

Because this shell of rock is solidified from a flowing material its inner walls are neat, almost polished, with horizontal conduits on the inner side that channel the flow. Once the lava supply starts to dwindle the cave cools down and thermal constriction starts fragmenting the walls. The pressure of volcanic gasses in the cave, however, support the roof from collapsing. As these gasses mix with air from vents in the roof resulting oxidation processes sometimes generate enough heat to re-fuse the ceiling, solidifying it. Sometimes, this process can lead to the formation of stalactites as molten material drips from the ceiling.

Long exposure picture of a lava tube near Bend, OR. The lighting is artificial. Image credits to Michael Harms.

Long exposure picture of a lava tube near Bend, Oregon. The lighting is artificial.
Image courtesy of Michael Harms.

These structures are called lava tubes, and it’s important to note that they form on the surface and are later covered with sediments. They often have lava streams solidified along their floors. The most common access points into these caves are areas with collapsed ceiling.

Similar processes form inflationary caves or vertical conduits underground, which can be big enough to qualify as caves. The former are areas where lava pushed on neighboring rock then receded, leaving domes of solid rock behind. The latter are formed in areas where lava escaped to the surface.

Sea caves

Erosion is the process by which soil or rock is removed from their original structures by surface factors. Dissolution can be viewed as a particular case of erosion, but we’ve already talked about those.

Sea caves are also formed by water. But, while dissolution caves get hollowed out through chemical reactions, sea caves are constructed by wave-powered erosion, either above or below the waterline. They can be found on the shoreline, as the name implies, but also inland, in areas that were once close to the sea but have since dried up — in parts of Norway, for example. They can form in all types of rock: igneous, metamorphic or sedimentary.

This Minecrafty beauty is named Fingal’s Cave, Scotland. It is a sea cave formed through basalt pillars.
Image via reddit user narwalmart

Waves form these structures by sheer attrition, throughout millions of years of battering with particle-rich water. As such, they tend to form in weaker areas of the rock, such as fault lines in igneous or metamorphic rocks or bedding plane contacts in sedimentary rocks. Once waves open a fissure through the rocks, the process becomes much faster — confined to a narrower space, the water and suspended particles exert more pressure on the walls and pressurize the gasses within, acting like a wedge.

Their walls are usually chunky and jagged, as erosion breaks off irregular slabs of rock from them. Some sea caves, however, have circular shapes with smooth walls and are filled with pebbles. This is caused by the waves taking on a circular motion inside the caves as they wash in and out, grinding the pebbles against the walls and smoothing them down.

Such as this beautiful cave in the Algarve region, Portugal.
Image via Imgur

Because erosion is a continuous process, removing rock bit by bit, sea caves are prone to collapse, leaving behind a “littoral sinkhole.”

Caving in

There are many other kinds of caves, each one with its own story to tell. Each one tells of how an area’s geology interacts with the world above it, being shaped by it over countless centuries. But, the paintings our ancestors adorned them with, the lines of sooth they burned into their walls stand testament to how they can, in turn, shape the world around them.