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Planet formation is notoriously difficult to study.  Not only does the process take millions of years, making it impossible to observe in real time, there are myriad factors that play into it, making it difficult to distinguish cause and effect.  What we do know is that planets form from features known as protoplanetary disks, which are made up of gas and dust surrounding young stars.  And now a team using ALMA have found a star system that has a protoplanetary disk and enough variability to help them nail down some details of how exactly the process of planet formation works.

The research is described in two new papers in The Astrophysical Journal.  They describe the star system Elias 2-27, which is located about 400 light years from Earth in Ophiuchus, the Serpent Bearer.  It has attracted the attention of astronomers for the last 5 years, first being studied in 2016 when it revealed a pinwheel of dust surrounding the star.

Visualization from NASA of planets forming in a protoplanetary disk.
Credit – NASA

Usually protoplanetary disks don’t take the shape of a pinwheel, which is more commonly found in galactic formations such as the Pinwheel Galaxy.  Researchers speculated that the two pinwheel arms visible around the star were caused by gravitational instabilities, which could also contribute to planetary formation processes.  But they needed further data to prove their idea.

That is where the new papers come in.  Data that was collected over the last 5 years proved the existence of gravitational instabilities, but also found a few things that weren’t caught in the first round of data.  It appears there may have been more material accreting to the disk itself, causing more gravitational chaos. More surprisingly, some parts of the protoplanetary disk were much taller than others.

Traces of dynamic gas patterns in the Elias 2-27 system.
Credit – ALMA (ESO / NAOJ / NRAO) / T. Penque-Carreño (Universidad de Chile), B. Saxton (NRAO)

This type of “vertical asymmetry” had never been observed before in a protoplanetary disk, and allowed the researchers to take a step forward in one of the computational hurdles that block the path to fully understanding planetary formation.  Computational members of the team had predicted that gravitational instabilities might cause the huge pillars of matter that appear to tower over the disk.  Those towers also open up the possibility of calculating the actual quantity of material present in the disk itself – a measurement that has eluded planetary scientists so far.  

“Knowing the amount of mass present in planet-forming disks allows us to determine the amount of material available for the formation of planetary systems, and to better understand the process by which they form.” said Venedetta Veronesi, lead author of one of the papers and a graduate student at the University of Milan.  

Map of Elias 2-27 system showing why causes of gravitational instabilities are important in causing planetary formation.
Map of Elias 2-27 system showing why causes of gravitational instabilities are important in causing planetary formation.
Credit – ALMA (ESO / NAOJ / NRAO) / T. Penque-Carreño (Universidad de Chile), B. Saxton (NRAO)

Even with the possibility of finally being able to calculate a protoplanetary disk’s size, there is still a lot of work to be done to fully flesh out the entire planetary formation process.  Luckily, there are plenty more star systems out there to study, and some of them undoubtedly have planets at every stage of that formation process.  With tools like ALMA, scientists will continue searching for them, and help draw an even more complete picture of where planets come from.

Learn More:
NRAO – Study of Young Chaotic Star System Reveals Planet Formation Secrets
UT – How Was the Solar System Formed? – The Nebular Hypothesis
UT – Planets Form in Just a Few Hundred Thousand Years

Lead Image:
Different images of the Elias 2-27 star system showing dust (blue) and various gases (red & yellow).
Credit – ALMA (ESO / NAOJ / NRAO) / T.
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Frontier Adventure

Review: Himali Limitless Grid Fleece Hoodie

Hooded Fleece Jacket
Himali Limitless Grid Fleece Hoodie
$160, 9.2 oz./261g (men’s medium)
Sizes: men’s S-XXL

The evolution of fleece has traced an arc toward efficiency and versatility that now seems to be reaching its apex in lightweight fleece hoodies, perfectly exemplified by Himali’s Limitless Grid Fleece Hoodie. The breadth of activities, conditions, and environments where I’ve worn it just this fall speak to my point, from a 13-hour, four-summit dayhike in Utah’s Wasatch Range to a short hike in southern New Hampshire, backpacking in southern Utah’s Escalante region, camping and climbing in Idaho, and a local trail run in the chilly, fading daylight of a November afternoon.

Here’s the first conclusion I drew about this fleece hoodie: It’s basically a warm, midweight jersey with a full front zipper and a hood. It replaced—and provided more versatility than—a midweight, long-sleeve top when I wore it over a synthetic T-shirt in the falling temperatures of an October evening hiking by headlamp in the dark for the last two hours of an 18-mile, 7,300-foot, partly off-trail dayhike in the Wasatch Range—when I needed warmth (and got a big boost from the hood) plus the ability to speedily dry my sweaty T-shirt.

Tet19 047 Me on Teton Crest Trail copy cropped
Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

The Himali Limitless Grid Fleece Hoodie.
” data-image-caption=”The Himali Limitless Grid Fleece Hoodie.
” data-medium-file=”″ data-large-file=”″ src=”″ alt=”The Himali Limitless Grid Fleece Hoodie.” class=”wp-image-61126″ srcset=” 1024w, 300w, 768w, 150w, 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />The Himali Limitless Grid Fleece Hoodie.

It served the same purpose in my layering system for three days in early October backpacking the 22-mile Boulder Mail Trail-Death Hollow-Escalante River Loop in the Grand Staircase-Escalante National Monument, shining especially in camp and for the first couple of hours hiking in shallow water down the shaded and cool canyon of Death Hollow on our second morning. Ditto on cool mornings and evenings in camp over a late-September weekend of climbing at Idaho’s City of Rocks National Reserve, pulling a down jacket over this hoodie in colder temps; and when I wore it as a middle layer under a rain shell on a 2.5-hour dayhike up a couple of wooded peaks along the Wapack Trail in southern New Hampshire on a rainy day with temps in the 40s Fahrenheit.

Lastly, it proved ideal worn over a lightweight, long-sleeve base layer on an hour-long trail run on a sunny day in mid-November,

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This Planet is Way Too Big for its Star

Scientists love outliers. Outliers are nature’s way of telling us what its boundaries are and where its limits lie. Rather than being upset when an outlier disrupts their understanding, scientists feed on the curiosity that outliers inspire.

It’s true in the case of a new discovery of a massive planet orbiting a small star. That goes against our understanding of how planets form, meaning our planet-formation model needs an update.

In a paper published in Science, researchers announced the discovery of a Neptune-mass exoplanet orbiting a low-mass star. The star is LHS 3154, an M-dwarf, or red dwarf star. It’s only 0.11 times as massive as the Sun, which is a normal mass for a red dwarf.

But what’s surprising is the size of the planet orbiting the star. The planet is called LHS 3154b, and it’s a monster compared to most planets orbiting red dwarfs. It has at least 13.2 Earth masses. That places it in the same range as Neptune, which has 17 Earth masses. LHS 3154b is also in a very close orbit, taking only 3.7 days to orbit the star.

“This discovery really drives home the point of just how little we know about the universe.”

Suvrath Mahadevan, Penn State University

The new paper is “A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models.” The lead author is Gudmundur Stefansson, NASA Sagan Fellow in Astrophysics at Princeton University. Stefansson was a graduate student at Penn State while working on this discovery.

“This discovery really drives home the point of just how little we know about the universe,” said Suvrath Mahadevan, a Professor of Astronomy and Astrophysics at Penn State and co-author of the paper. “We wouldn’t expect a planet this heavy around such a low-mass star to exist.”

Why is this discovery surprising? It’s all about stars and their protoplanetary disks.

When a star forms, it starts as a protostar in the center of a solar nebula. As the star forms, a rotating disk of gas and dust called a protoplanetary disk forms around the star. Dense knots form in the disk, and this is how planets and planetesimals form. It’s a detailed process and one we don’t entirely understand. But what scientists do know, or thought they knew, is that the more mass there is in the disk, the more massive the planets that can form. And the mass in the disk scales steeply with the mass of the star.

It looks like this: massive star = massive disk = massive planets. Naturally, we consider the obverse to be true, too. Small star = small disk = small planets. But LHS 3154b and its star don’t conform to this. There simply shouldn’t have been enough mass in the protoplanetary disk for the planet to form.

“The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to make this planet,” Mahadevan said. “But it’s out there, so now we need to reexamine our understanding of how planets and stars form.”

It took a special instrument to spot the massive planet, and Mahadevan led the team of scientists that built it. It’s called the Habitable Zone Planet Finder or HPF, a spectrograph built at Penn State. HPF is designed to detect planets orbiting cool stars that might have liquid surface water. Small planets can be very difficult to detect around large, bright stars like our Sun because the Sun’s light overpowers everything else.

But around smaller cooler stars, planets close enough to have liquid water are much easier to find.

“Think about it like the star is a campfire. The more the fire cools down, the closer you’ll need to get to that fire to stay warm,” Mahadevan said. “The same is true for planets. If the star is colder, then a planet will need to be closer to that star if it is going to be warm enough to contain liquid water. If a planet has a close enough orbit to its ultracool star, we can detect it by seeing a very subtle change in the colour of the star’s spectra or light as it is tugged on by an orbiting planet.”

This artist's illustration helps explain how small planets are easier to detect around stars that are smaller and cooler than the Sun. Image Credit: Penn State / Penn State. Creative CommonsDid you miss our previous article…

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Will Wide Binaries Be the End of MOND?

It’s a fact that many of us have churned out during public engagement events; that at least 50% of all stars are part of binary star systems. Some of them are simply stunning to look at, others present headaches with complex orbits in multiple star systems. Now it seems wide binary stars are starting to shake the foundations of physics as they question the very theory of gravity. 

General relativity has been part of the foundation of modern physics since it was published by Albert Einstein in 1915. One of the challenges though is that, along with normal matter (known by its official name baryonic matter) general relativity is unable to explain the current theories of the evolution of the universe without dark matter.  Alas dark matter has not been observed in any lab experiment or indeed directly in the sky. 

The idea for dark matter was developed in the early 1930’s to explain the movement of the galaxies in the Coma Cluster.  It was Fritz Zwicky who coined the phrase dark matter in 1933 to explain the unseen matter that was driving the movement.  Current theories suggest there is something like five times more dark matter in the Universe than there is normal matter but It’s a type of matter that we know little about other than it doesn’t interact with normal baryonic matter. 

Dark Flow
The Coma Galaxy Cluster. It appears to participate in the dark flow.

The standard model – that describes how the building blocks of matter interact – assumes that the current laws of gravity are all correct however a ‘tweak’ is required to explain certain observations and that tweak is called dark matter. In other words, we can see the effect of dark matter but we just haven’t actually directly detected it yet. In a paper published by J. W. Moffat, there is a bold suggestion that maybe it’s the gravitational model that is incorrect.

Enter MOND – ‘Modified Newtonian Dynamics’ – which proposes an adjustment to Newton’s second law (nicely encapsulated in the formula that force equals mass multiplied by acceleration) to explain the movement of galaxies without dark matter. The theory, proposed by M. Milgrom in 1983 suggests that the gravitational force exerted upon a star in the outer reaches of a galaxy was proportional to the square of its centripetal acceleration (instead of the centripetal acceleration itself).  Remember the existing models do not explain this without inserting dark matter which we have yet to discover.  

The paper by Moffat suggests that they should be able to detect the changes proposed by MOND but in applying the formulas correctly the galaxy constrains must be significantly affected. Wide binary data from Gaia (the Global Astrometric Interferometer) seems to conclude that any modified gravity theory must reliy upon scale and length rather than acceleration.  If this continues to be the case for future observations then it may well mark the demise of the MOND model for good. 

Source : Wide Binaries and Modified Gravity (MOG)

The post Will Wide Binaries Be the End of MOND? appeared first on Universe Today.

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