Tag: protoplanetary disk

New Insights Into How Earth Got Its Nitrogen

An artist’s conception shows a protoplanetary disk of dust and gas around a young star. New research by Rice University shows that Earth’s nitrogen came from both inner and outer regions of the disk that formed our solar system, contrary to earlier theory.  (NASA/JPL-Caltech)

Scientists have long held that many of the important compounds and elements that make life possible on Earth arrived here after the planet was formed and was orbiting the sun.  These molecules came via meteorites and comets, it was thought,  from the colder regions beyond Jupiter.

But in a challenge to that long-accepted view, a team from Rice University has found isotopic signatures of nitrogen from both the inner and the outer disk in iron meteorites that fell to Earth.  What this strongly suggests is that the seeds of rocky, inner solar system planets such as Earth were bathed in  dust that contained nitrogen and other volatiles, and the growing planet kept some of that “local” material.

“Our work completely changes the current narrative,” said Rice University graduate student and lead author Damanveer Grewal. “We show that the volatile elements were present in the inner disk dust, probably in the form of refractory (non-gaseous) organics, from the very beginning. This means that contrary to current understanding, the seeds of the present-day rocky planets — including Earth — were not volatile-free.”

The solar protoplanetary disk was separated into two reservoirs, with the inner solar system material having a lower concentration of nitrogen-15 and the outer solar system material being nitrogen-15 rich. The nitrogen isotope composition of present-day Earth lies in between, according to a new Rice University study that shows it came from both reservoirs. (Credit: Illustration by Amrita P. Vyas)

This work helped settle a prolonged debate over the origin of life-essential volatile elements — such as hydrogen, water, carbon dioxide, methane, nitrogen, ammonia — on Earth and other rocky bodies in the solar system.

“Researchers have always thought that the inner part of the solar system, within Jupiter’s orbit, was too hot for nitrogen and other volatile elements to condense as solids, meaning that volatile elements in the inner disk were only in the gas phase,” Grewal said.

Because the seeds of present-day rocky planets, also known as protoplanets, grew in the inner disk by accreting locally sourced dust, he said it appeared they did not contain nitrogen or other volatiles because of the high temperatures, necessitating their delivery from the outer solar system.… Read more

Planets Still Forming Detected in a Protoplanetary Disk

An artist rendering of infant star HD 163296 with three protoplanets forming in its disk  The planets were discovered using a new mode of detection — identifying unusual patterns in the flow of gas within a protoplanetary disk. (NRAO/AUI/NSF; S. Dagnello)

Just as the number of planets discovered outside our solar system is large and growing — more than 3,700 confirmed at last count — so too is the number of ingenious ways to find exoplanets ever on the rise.

The first exoplanets were found by measuring the “wobble” in their host stars caused by the gravitational pull of the planets, then came the transit technique that measured dips in the light from stars as planets passed in front of them, followed by the direct imaging of moving objects deemed to be planets, and numerous more.

A new technique can now be added to the toolkit, one that is useful only in specific galactic circumstances but is nonetheless ingenious and intriguing.

By detecting unusual patterns in the flow of gas within the protoplanetary disk of a young star, two teams of astronomers have confirmed the distinct, telltale hallmarks of newly formed planets orbiting the infant star.

In other words, the astronomers found planets in the process of being formed, circling a star very early in its life cycle.

These results came thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), and are presented in a pair of papers appearing in the Astrophysical Journal Letters.

Richard Teague, an astronomer at the University of Michigan and principal author on one of the papers, said that his team looked at “the localized, small-scale motion of gas in a star’s protoplanetary disk. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images coming from ALMA.”

ALMA image of the protoplanetary disk surrounding the young star HD 163296 as seen in dust. ( ALMA: ESO/NAOJ/NRAO; A. Isella; B. Saxton NRAO/AUI/NSF.

To make their respective discoveries, each team analyzed the data from various ALMA observations of the young star HD 163296, which is about 4 million years old and located about 330 light-years from Earth in the direction of the constellation Sagittarius.

Rather than focusing on the dust within the disk, which was clearly imaged in an earlier ALMA observation, the astronomers instead studied the distribution and motion of carbon monoxide (CO) gas throughout the disk.

As explained in a release from the National Radio Astronomy Observatory, which manages the American operations of the multi-national ALMA, molecules of carbon monoxide naturally emit a very distinctive millimeter-wavelength light that ALMA can observe.

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