Solar system born amid flood of ultraviolet light, say ASU astrophysicists

April 6, 2018

The sun is made almost entirely of hydrogen and helium. Earth, on the other hand, is made mostly of oxygen packed into various compounds. So are its rocky planet neighbors. The giant planets, such as Jupiter and Saturn, have compositions more like the sun's, but still are notably different from it.

Here's the puzzle. The sun and planets formed at the same time from the same cloud of gas and dust. But the material that made the planets had a composition different from the sun's. How did that happen? The sun is a strong source of ultraviolet light, as seen in this image from NASA's Solar Dynamics Observatory satellite. Ultraviolet light, either from the young sun itself or from a powerful nearby star, may have given the planets a different composition than the sun. NASA image. Download Full Image

A team led by Arizona State University scientists has found an explanation for this long-standing question and published it recently in the journal Nature Communications.

"Our goal is to determine the starting composition for the solar system," said James Lyons, associate research professor of astrophysics and cosmochemistry in ASU's School of Earth and Space Exploration and lead author on the paper. His co-authors are Ehsan Gharib-Nezhad of ASU's School of Molecular Sciences, and Thomas Ayres of the University of Colorado.

The team studied carbon and oxygen, common among the terrestrial planets, but not in their standard elemental form. Instead, they used these elements' isotopes, varieties of an element that have an extra neutron or two.

"We're most interested in the light, stable isotopes," Lyons said.

These are the isotopes of elements that do not decay radioactively. He explains that isotopes such as those of carbon, nitrogen, oxygen and sulfur should reflect the original bulk composition of the molecular cloud from which the solar system formed.

To determine the abundances of these isotopes, the researchers started with infrared spectroscopic data on carbon monoxide in the sun's atmosphere. This was collected by the Atmospheric Trace Molecule Spectroscopy (ATMOS) spectrometer, which flew in Earth orbit aboard the space shuttleScott Parazynski, the astronaut who tended the ATMOS instrument on that flight, went on to become a professor at the School of Earth and Space Exploration from 2014 to 2017. (STS-66) in 1994.

The ATMOS data were compared to measurements of solar oxygen from the Genesis mission (2001–2004), which collected and returned to Earth samples of the solar wind, which is in effect the sun's outermost atmosphere. The comparisons showed that Earth and (by analogy) the inner planets are 5 percent enriched in both carbon-13 and oxygen-18 compared to the sun.

"When talking about isotope ratios, a 5 percent difference is massive," Lyons said. He added that it implies that the carbon and oxygen that formed part of Earth and the inner solar system experienced a different history than these elements did in the sun.

What caused that difference remains partly unknown, say the scientists, but they point to a likely culprit: ultraviolet light.

As Lyons noted, "One possible explanation for the isotope difference is that carbon monoxide was blasted by ultraviolet light in the early stages of forming the planets."

Irradiation by UV would have attacked both elemental carbon and oxygen and their compounds. This would break up compounds and change the isotope ratios, gradually moving the overall composition away from that of the sun.

The source for the ultraviolet light could have been either a vigorously active young sun or — more likely, says the team — a hot, massive star that was close to the gas and dust cloud from which the sun and planets formed. The radiation from such powerful stars can affect a large volume of space within giant molecular clouds.

In this scenario, the proto-sun is a massive body unaffected by those isotope effects, and therefore still carries the isotope composition of the starting material from which the solar system formed. Yet the thin disk of material from which the planets formed would have been affected much more, leading to a difference in isotopic composition between the sun and planets.

"If this explanation is correct," Lyons said, "then we have a strong constraint on the UV radiation present when the solar system formed."

Such a constraint would help astronomers understand the degree of UV processing of organic molecules in the nascent solar system.

It would also, he said, "help us characterize the role of ultraviolet radiation in the formation of other stars' solar systems with Earth-like planets."

It is likely, the team adds, that UV radiation processed organic materials on ancient Earth, contributing to the prebiotic chemistry that led to the origin of life.

Lyons said, "We now see that this UV processing actually began in the solar nebula, even before Earth formed, and it must have occurred in some exoplanet systems as well."

Robert Burnham

Science writer, School of Earth and Space Exploration


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A snide remark, a spark of inspiration and a life forever changed

April 6, 2018

ASU's Zócalo Public Square celebrates 15 years of innovative journalism

Fifteen years ago, when Gregory Rodriguez first conceived of the idea that would become Zócalo Public Square, he could not have imagined what it would become.

In 2002, a tasteless remark by a guest at a “snooty” L.A. gathering of his writing peers would spark inspiration in Rodriguez that would change the direction of his life.

While attending the networking event — a rare activity for the otherwise solitary writer — Rodriguez was jokingly asked in front of a collection of strangers, not about the book he was writing or his latest intellectual pursuits, but whether he had been invited "under the Mexican quota.”

He left the event that afternoon frustrated by the experience and determined to create a space where people from diverse backgrounds, experiences and intellectual disciplines could come together to discuss ideas and make connections.

That space would become known as Zócalo Public Square. “The name Zócalo was meant to convey that the organization would be all about openness and generosity and inclusion,” Rodriguez noted. “I felt the symbolism of a grand, all-embracing central plaza — the type of public space many of us long for in America.”

It would operate under a specific set of tenets: events would be free to the public and everyone would be welcome to participate; ideas would be exchanged rather than advocated for; receptions would include complimentary refreshments and engaging speakers; and there would always be music.

What began as a simple lecture series — supported by Rodriguez and his traveling boom box, poster and reservation list — has blossomed into a thriving, innovative journalism and media organization, now a creative unit of Arizona State University.

Since its founding in 2003, Zócalo has presented 565 events, featuring 2,230 speakers in 23 cities, seven states and six countries. In addition to convening intellectually engaging events, Rodriguez and his staff publish over 500 original articles a year and syndicate to 280 media outlets worldwide, including USA Today, the Chicago Tribune, the Houston Chronicle, Smithsonian Magazine and The Singapore Straits Times.

The organization also presents an annual book prize to the authorThis year’s 8th annual Zócalo Book Prize was awarded to Michael Ignatieff, author of “The Ordinary Virtues: Moral Order in a Divided World.” Ignatieff will accept his award and give a lecture at an event in Los Angeles on May 22. whose book best enhances our understanding of community and the forces that strengthen or undermine human connectedness.

The Zócalo model of ideas journalism — examining essential questions in an accessible, open-minded and democratic spirit — has allowed the organization to thrive in an increasingly turbulent media landscape within a politically polarized world. The innovative organization seeks to cut through perceived geographic, social and intellectual boundaries to create experiences and knowledge that reflect the true diversity of the country.

“Amid these increasingly divisive times, Zócalo has created a space where people from all walks of life can come together and engage in thoughtful dialogue and the civil exchange of ideas,” said ASU President Michael Crow. “They join ASU as a place to share knowledge, challenge assumptions and find common ground on the important issues facing our world.”

In 2011, ASU and Zócalo entered into a formal partnership. Seven years later, Zócalo is now a creative unit of ASU, and together, the organizations are leveraging their strengths in support of a shared vision of inclusion, discovery and the pursuit of knowledge.

On Friday, April 6, Zócalo celebrated its 15th anniversary in Los Angeles, with, appropriately, a party. And while Rodriguez didn't bring the boom box along, the event’s principles remained the same: everyone was welcome, judgment was left at the door, and the drinks and music were free.

Top photo: Gregory Rodriguez at a Zócalo Public Square event. 

Katherine Reedy

Senior Media Relations Officer , Media Relations & Strategic Communications