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

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

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.

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

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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Protoplanetary Disks Throw Out More Material Than Gets Turned Into Planets

When a young solar system gets going it’s little more than a young star and a rotating disk of debris. Accepted thinking says that the swirling debris is swept up in planet formation. But a new study says that much of the matter in the disk could face a different fate.

It may not have the honour of becoming part of a nice stable planet, orbiting placidly and reliably around its host star. Instead, it’s simply discarded. It’s ejected out of the young, still-forming solar system to spend its existence as interstellar objects or as rogue planets.

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Astronomers see an Accretion Disk Where Planets are About to Form

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.

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