ASU spectrometer working perfectly as it flies past Earth on way to asteroid

NASA's OSIRIS-REx spacecraft now halfway on the journey to its target, an asteroid named Bennu

September 28, 2017

Shortly after NASA's OSIRIS-REx spacecraft flew past Earth at a distance of about 11,000 miles on Sept. 22, an ASU-built spectrometer onboard looked at Earth and detected methane, ozone, carbon dioxide and water vapor. Taken together these gases in our atmosphere set Earth apart from other planets.

While hardly a discovery, the findings helped scientists calibrate the ASU-built instrument and show that it is working perfectly after a year in space. When NASA's OSIRIS-REx spacecraft flew past Earth on Sept. 22, the OSIRIS-REx Camera Suite (OCAMS) looked back at our planet about two hours after closest approach. The Pacific Ocean and clouds filled most of the view; Australia is visible at lower left. At the same time, the ASU-built OSIRIS-REx Thermal Emission Spectrometer (OTES) took a series of spectral measurements so scientists could calibrate the instrument. OCAMS image from NASA/Goddard Space Flight Center/University of Arizona Download Full Image

The OSIRIS-REx spacecraft was launched Sept. 8, 2016, from the Kennedy Space Center in Florida. It is now about halfway on the journey to its target, a primitive carbonaceous asteroid named Bennu. The gravity assist the spacecraft received in the Earth flyby changed its trajectory so that it is now on track to arrive at Bennu in August 2018.

OSIRIS-REx stands for Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer. The mission's goals are to return a sample of surface rocks, soil and dust from Bennu, map the asteroid's global properties, document the surface at the sample site down to centimeter scales, characterize its type of asteroid for comparison with meteorites, and measure a subtle effect of sunlight that can alter an asteroid's orbit.

The latter two goals are the main scientific tasks for the ASU-built OSIRIS-REX Thermal Emission Spectrometer, or OTES for short. Philip Christensen, Regents’ Professor of geological sciences in Arizona State University’s School of Earth and Space Exploration, designed the instrument, which was constructed on ASU's Tempe campus.

"OTES is the first complex space instrument to be designed and built entirely at ASU," Christensen said. "We're very proud that this instrument is on its way and operating as designed."

With an orbit that comes inside Earth's orbit, Bennu is the most accessible asteroid rich in organic materials from the early solar system. It reflects only 3 percent of the sunlight falling on it, making it about as dark as charcoal.

When OSIRIS-REx arrives at Bennu, OTES will make a global mineral map of the asteroid, which is roughly spherical and about 1,600 feet (500 meters) across. The map will help mission scientists decide the best place to collect surface samples for eventual return to Earth.

Little pushes, little shoves

Given its Earth-crossing orbit, Bennu is also a space rock scientists want to keep an eye on. They estimate that it has a 1-in-2,700 chance of hitting Earth in the year 2170.

Which directly leads to OTES' other major task: measuring the temperature and heat emission over Bennu's surface as it spins through its 4.3-hour-long day. This is to help scientists gauge the strength of the Yarkovsky effect on Bennu.

The Yarkovsky effect is a weak but steady thrust produced by sunlight as it falls on a spinning object. The effect comes from the fact that sunlit ground is warmer in the afternoon than the same ground is in the morning, because sunlight has had longer to heat it.

This means that the afternoon side of a rotating object radiates more heat than the morning side, thus producing an extremely small thrust. The effect is negligible for massive objects like planets, but for small bodies like Bennu the effect could shift its orbit.

Using OTES data, OSIRIS-REx will help scientists assess how fast Bennu's orbit is changing and gather information useful for future generations, which may have to take action to deflect the asteroid.

OSIRIS-REx will remain at Bennu until 2021. Then with the sample of rocks and dust safely packed into a sealed re-entry capsule, the spacecraft will fire its engine and go into an orbit to meet with Earth in 2023.

After releasing the sample return capsule, OSIRIS-REx will fly past Earth and continue in its solar orbit. The capsule with the samples will enter the atmosphere behind a heat shield and land under a parachute in Utah.

Flyby yields first OTES results

Christensen said, "This Earth flyby gave us our first real data. Up to now we have just looked at an onboard test target. It's exciting to collect spectral data on a real solar-system body. OTES has performed exactly as we hoped."

The spectrometer works by examining infrared (heat) wavelengths.

"The infrared is great for identifying minerals," Christensen explained. "Rocks and minerals may look similar to the eye, but they show unique spectra when studied in the infrared, where their 'colors' stand out differently."

Showing almost entirely ocean and clouds, planet Earth (upper left) appears misnamed in this view taken by OSIRIS-REx on Sept. 22, two hours after its closest approach to Earth. The circles, each about 500 miles in diameter, indicate where the OTES spectrometer made its observations. The peaks and valleys in the spectral curves show absorption of solar energy by methane, ozone, carbon dioxide, and water vapor in Earth’s atmosphere. OTES also took the temperature of the ocean surface (red curve, 55 °F) and the stratosphere (blue, -38 °F). Image by NASA/Goddard Space Flight Center/University of Arizona (Earth image) and Arizona State University (OTES spectrum)

As it happened, the flyby trajectory gave OTES a view of Earth dominated by the Pacific Ocean. Almost no land areas came within the instrument's field of view, which saw clouds and seawater.

Even so, the instrument worked as designed. In addition to identifying minerals, the infrared also excels at detecting gases such as methane, ozone, carbon dioxide and water vapor, which are common in our atmosphere.

"We measured them with OTES and got good 'ground truth' results," Christensen explained.

"Earth isn't our prime target, however," Christensen said. "That will come about a year from now. But the Earth flyby was a great test for OTES and the other instruments on the spacecraft.

NASA’s Goddard Space Flight Center provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space Systems in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the agency’s New Frontiers Program for its Science Mission Directorate in Washington.

Robert Burnham

Science writer, School of Earth and Space Exploration


3 ASU students to attend Clinton Global Initiative University in Boston

September 29, 2017

In June 2017, three Arizona State University students received a very exciting email — they had been selected to attend the Clinton Global Initiative University (CGI U) later this year.

The students had submitted a global change idea proposal for a special graduate research conference they will be hosting, Feb. 1-2, 2018. Larissa Gaias, Michelle Pasco and Chanler Hilley — who are all enrolled in the Family and Human Development Doctoral program in ASU's T. Denny Sanford School of Social and Family Dynamics — are committee members of the Diversity and Inclusion Science Initiative (DISI) Graduate Research Conference. Their conference idea led to their invitation to this year’s CGI U. Picture of conference stage with a filled room of attendees Image from CGIU (2016) website

The CGI U, launched in 2007 by former President Bill Clinton, engages over 1,000 college students yearly to discuss and take action on pressing global challenges. Over 8,700 college students from 150 countries have attended the CGI U meetings over the past ten years. To be eligible to attend, each student or student group must establish and submit a Commitment to Action. The CGI U commitments aim to address challenges in the CGI U’s five focus areas: education, environment and climate change, poverty alleviation, peace and human rights, and public health.

Of the five CGI U focus areas, Gaias, Pasco, and Hilley’s submission was in the area of education. The DISI Graduate Research Conference at ASU aims to address issues of diversity and inclusion through scholarship, which can help create and promote an inclusive society that enhances compassion, equity and empowerment, while reducing prejudice, stereotyping and exclusion. The interdisciplinary nature of this conference will bring together ASU graduate students with diverse academic backgrounds to collaborate by sharing research, teaching strategies and personal experiences that incorporate and address diversity and inclusion.

Picture of ASU DISI committee members

DISI committee members from left (Annabelle Atkin, Bobbi Bromich, Kenton Woods, Michelle Pasco, Chanler Hilley, Arlyn Moreno Luna and Larissa Gaias)

Gaias is the steering committee chair for the conference. Originally from Southampton, New York, Gaias obtained her Bachelor of Science in psychology and environmental studies from Bowdoin College in Brunswick, Maine before receiving her Master of Science in family and human development from ASU. Her current research focuses on educational equity and how schools can better support marginalized youth.

“Getting accepted to the GCI U was very encouraging as it affirmed that this work is of broader interest beyond our team and our school,”  Gaias said. “I am looking forward to getting a global perspective on diversity and inclusion and bringing back ideas to our own conference.”

Michelle Pasco, conference steering committee chair elect, was also thrilled by the special invitation to attend the CGI U: “I was really excited and happy that the goals and objectives we have for the graduate research conference was being recognized and valued at a broader level.”

An Azusa, California native, Pasco earned a Bachelor of Arts in psychology with a minor in Asian American studies from UCLA, and hopes the CGI U will provide some valuable insights.

“I hope to learn tools and skills to help promote the (DISI) conference to a larger and broader audience so we incorporate even more disciplines to the conference,” Pasco said.

In the meantime, Pasco will continue her study of adolescent development, particularly Latino adolescents, living in ethnically and racially concentrated neighborhoods.

Chanler Hilley sits as the logistics committee chair for the conference. Hailing from Calhoun Falls, South Carolina, Hilley obtained his Bachelor of Science in health promotion from Coastal Carolina University before going on to receive his Master of Education in higher and postsecondary education from ASU. His research focus is on adolescence and the transition to adulthood.

“I was excited and overwhelmed to learn we were accepted to CGI U,” Hilley said. “CGI U focuses on global issues, and the acceptance reinforces the impact we can make through this conference (DISI).”

“I hope to meet other students who are interested or engaged in the type of work we’re doing at ASU," he said. "I hope we are able to continue to strengthen the conference and learn about ways to sustain our efforts through participation in CGI U.”

ASU is part of the CGI U network and hosted a meeting in 2014. This year, the CGI U will be hosted by Northeastern University in Boston, Massachusetts from Oct. 13-15. Over $750,000 in funding will be available to select CGI U 2017 students to help them turn their ideas into action. 

Click here to register for the DISI Graduate Research Conference (must be an ASU graduate student in Spring 2018).

John Keeney

Media Relations Coordinator, T. Denny Sanford School of Social and Family Dynamics