Seeing the Moment Planets Start to Form

ALMA captured this high-resolution image of the protoplanetary disk surrounding DG Taurus at a 1.3 mm wavelength. The young star is still embedded in its disk, and the smooth appearance, absent of ring-like structures, indicates a phase shortly before planets form. Credit: ALMA (ESO/NAOJ/NRAO), S. Ohashi, et al.

Nature makes few duplicates, and planets are as distinct from one another as snowflakes are. But planets all start out in the same circumstances: the whirling disks of material surrounding young stars. ALMA’s made great progress imaging these disks and the telltale gaps excavated by young, still-forming planets.

But new images from ALMA (Atacama Large Millimeter/submillimeter Array) show a star and disk so young that there are no telltale gaps in the disk. Is this the moment that planets start to form?

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Clumps Around a Young Star Could Eventually Turn Into Planets Like Jupiter

The young star V960 Mon and its surrounding dusty material, seen by SPHERE (left) and ALMA (right). Credit: ESO/ALMA (ESO/NAOJ/NRAO)/Weber et al

From the dust, we rise. Vortices within the disks of young stars bring forth planets that coalesce into worlds. At least that’s our understanding of planetary evolution, and new images from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Telescope’s Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) further support this.

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Astronomers Directly Image Debris Disk and find a Jupiter-Sized Planet Orbiting a Sunlike Star

Astronomers with the SHINE collabortion observed a debris disk containing a Super-Jupiter around a young star. Credit: ALMA (ESO/NAOJ/NRAO); M. Weiss (NRAO/AUI/NSF)

According to the most widely-accepted theory, planetary systems form from large clouds of dust and gas that form disks around young stars. Over time, these disks accrete to create planets of varying size, composition, and distance from their parent star. In the past few decades, observations in the mid- and far-infrared wavelengths have led to the discovery of debris disks around young stars (less than 100 million years old). This has allowed astronomers to study planetary systems in their early history, providing new insight into how systems form and evolve.

This includes the SpHere INfrared survey for Exoplanets (SHINE) consortium, an international team of astronomers dedicated to studying star systems in formation. Using the ESO’s Very Large Telescope (VLT), the SHINE collaboration recently directly imaged and characterized the debris disk of a nearby star (HD 114082) in visible and infrared wavelengths. Combined with data from NASA’s Transiting Exoplanet Space Satellite (TESS), they were able to detect a gas giant many times the size of Jupiter (a “Super-Jupiter”) embedded within the disk.

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Ceres Probably Formed Farther out in the Solar System and Migrated Inward

This image of Ceres was taken by NASA's Dawn spacecraft on May 7, 2015, from a distance of 8,400 miles (13,600 kilometers). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

When Sicilian astronomer Giuseppe Piazzi spotted Ceres in 1801, he thought it was a planet. Astronomers didn’t know about asteroids at that time. Now we know there’s an enormous quantity of them, primarily residing in the main asteroid belt between Mars and Jupiter.

Ceres is about 1,000 km in diameter and accounts for a third of the mass in the main asteroid belt. It dwarfs most of the other bodies in the belt. Now we know that it’s a planet—albeit a dwarf one—even though its neighbours are mostly asteroids.

But what’s a dwarf planet doing in the asteroid belt?

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Astronomers See the Wreckage Where Planets Crashed Into Each Other in a Distant Star System

This illustration depicts the result of a collision between two large asteroid-sized bodies. NASA's Spitzer saw a debris cloud block the star HD 166191, giving scientists details about the smashup that occurred. Credit: NASA/JPL-Caltech

Our Solar System was born in chaos. Collisions shaped and built the Earth and the other planets, and even delivered the building blocks of life. Without things smashing into each other, we might not be here.

Thankfully, most of the collisions are in the past, and now our Solar System is a relatively calm place. But frequent collisions still occur in other younger solar systems, and astronomers can see the aftermath.

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Even More Complex Organic Molecules Have Been Found in a Protoplanetary Disc. Was Life Inevitable?

This artist's concept a protoplanetary disk around a young star. Researchers at the Leiden Observatory found the large organic molecule dimethyl ether in a protoplanetary disk for the first time. Credit: NASA/JPL-Caltech

Will we ever understand life’s origins? Will we ever be able to put our finger on the exact moment and circumstances that lead to living matter? Will we ever pinpoint the spark? Who knows.

But what we can do is find out how widespread the conditions for life are and how widespread the molecular constituents for life are.

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A Star Passed too Close and Tore Out a Chunk of a Protoplanetary Disk

Scientists have captured an intruder object disrupting the protoplanetary disk—birthplace of planets—in Z Canis Majors (Z CMa), a star in the Canis Majoris constellation. This artist’s impression shows the perturber leaving the star system, pulling a long stream of gas from the protoplanetary disk along with it. Observational data from the Subaru Telescope, Karl G. Jansky Very Large Array, and Atacama Large Millimeter/submillimeter Array suggest the intruder object was responsible for the creation of these gaseous streams, and its “visit” may have other as yet unknown impacts on the growth and development of planets in the star system. Credit: ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)

When it comes to observing protoplanetary disks, the Atacama Large Millimetre/sub-millimetre Array (ALMA) is probably the champion. ALMA was the first telescope to peer inside the almost inscrutable protoplanetary disks surrounding young stars and watch planets forming. ALMA advanced our understanding of the planet-forming process, though our knowledge of the entire process is still in its infancy.

According to new observations, it looks like chaos and disorder are part of the process. Astronomers using ALMA have watched as a star got too close to one of these planet-forming disks, tearing a chunk away and distorting the disk’s shape.

What effect will it have on planetary formation?

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Rings in the Early Solar System Kept our Planet From Becoming a Super-Earth

A protosolar disk is the disk of material around a young stellar object that isn't yet a star. It's called a protoplanetary disk once the star has formed and begun fusion. Planetesimals are the building blocks of planets and are present in both stages of a disk's evolution. Image Credit: NASA/JPL

To date, a total of 4,884 extrasolar planets have been confirmed in 3,659 systems, with another 8,414 additional candidates awaiting confirmation. In the course of studying these new worlds, astronomers have noted something very interesting about the “rocky” planets. Since Earth is rocky and the only known planet where life can exist, astronomers are naturally curious about this particular type of planet. Interestingly, most of the rocky planets discovered so far have been many times the size and mass of Earth.

Of the 1,702 rocky planets confirmed to date, the majority (1,516) have been “Super-Earths,” while only 186 have been similar in size and mass to Earth. This raises the question: is Earth an outlier, or do we not have enough data yet to determine how common “Earth-like” planets are. According to new research by an international team led by Rice University, it may all have to do with protoplanetary rings of dust and gas in an early solar system.

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This is How You Get Moons. An Earth-Sized World Just got Pummeled by Something Huge.

An MIT-led team has discovered evidence of a giant impact in the nearby HD 17255 star system, in which an Earth-sized terrestrial planet and a smaller impactor likely collided at least 200,000 years ago, stripping off part of one planet’s atmosphere. Credits:Image: Mark A. Garlick

Titanic collisions are the norm in young solar systems. Earth’s Moon was the result of one of those collisions when the protoplanet Theia collided with Earth some 4.5 billion years ago. The collision, or series of collisions, created a swirling mass of ejecta that eventually coalesced into the Moon. It’s called the Giant Impact Hypothesis.

Astronomers think that collisions of this sort are a common part of planet formation in young solar systems, where things haven’t settled down into predictability. But seeing any of these collisions around other stars has proved difficult.

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The Early Solar System Had a Gap Where the Asteroid Belt is Today

An MIT study suggests that a mysterious gap existed within the solar system’s protoplanetary disk around 4.567 billion years ago, and likely shaped the composition of the solar system’s planets. This image shows an artist’s interpretation of a protoplanetary disk. Image Credit: National Science Foundation, A. Khan

Wind the cosmic clock back a few billion years and our Solar System looked much different than it does today. About 4.5 billion years ago, the young Sun shone much like it does now, though it was a little smaller. Instead of being surrounded by planets, it was ensconced in a swirling disk of gas and dust. That disk is called a protoplanetary disk and it’s where the planets eventually formed.

There was a conspicuous gap in the early Solar System’s protoplanetary disk, between where Mars and Jupiter are now, and where the modern-day asteroid belt sits. What exactly caused the gap is a mystery, but astronomers think it’s a sign of the processes that governed planet formation.

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