SOFIA provides insights into the metallic characteristics of asteroid Psyche

by Haygen Warren

On Oct. 12, 2023, NASA’s Psyche mission and spacecraft will launch out into the asteroid belt to research asteroid 16 Psyche. Psyche, the asteroid, is thought to be metal-rich and is one of the largest asteroids within the asteroid belt. However, the true nature of the asteroid is largely unknown, and new research from NASA’s now-retired Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope and NASA’s Ames Research Center is helping scientists predict what to expect at Psyche when the spacecraft arrives.

Throughout the last few years, especially as Psyche teams began planning the mission and its goals, scientists have hypothesized the asteroid’s characteristics. One of the leading theories behind the asteroid’s origins is that Psyche was once the iron-rich interior of a planetesimal or a forming planet.

The surface of the planetesimal is believed to have been blown away by the near-constant collisions between it and other planetary material that existed in the early solar system. Once the surface of the asteroid had been blown away, just the core of the asteroid was left, and this left-over core is thought to be what is presently known as Psyche.

However, even with this hypothesis and data to support the hypothesis, scientists are still largely unsure of the nature of Psyche and its features. To try and learn more about the asteroid, a group of scientists, led by Psyche’s principal investigator Maggie McAdam of Ames and lead author Anicia Arredondo of the Southwest Research Institute, used SOFIA to observe Psyche in February 2022. SOFIA, when in operation, was a reflecting telescope that was integrated into a Boeing 747SP airplane. The unique setup allowed scientists to observe astronomical objects from above Earth’s lower atmosphere and from any location on Earth, even oceans.

SOFIA’s observations of Psyche are the first to gather data from every part of the asteroid’s surface. The observations allowed scientists to research and analyze the materials that make up the surface of the asteroid — information that is crucial to understanding the asteroid, and information that could have never been collected by telescopes on Earth’s surface.

To determine the exact compounds and elements that makeup Psyche’s surface, Arrendondo et al. analyzed different wavelengths of light that were reflected off of the surface of the asteroid using a mid-infrared camera on SOFIA. More specifically, the team measured the emissivity, the amount of energy the asteroid radiates into space, and the porosity, the amount of small holes or openings in the asteroid’s surface.

So, what did the team find from SOFIA’s observations?

Arrendondo et al. found that Psyche’s emissivity and spectra data are flat. While this may initially not seem like an interesting data point, it should be noted that flat emissivity and spectra data are often associated with mid-infrared instruments that are used to observe metal objects. This means that Psyche is likely a metallic body — which aligns with scientists’ expectations.

Another interesting data point from the emissivity and spectra data was that a spectral feature called the 10-micron plateau was not observed in the data. Typically, the 10-micron plateau is found in the spectra data of objects that have “fluffy” surfaces that are similar to lunar regolith. Interestingly, previous studies into Psyche’s characteristics featured the 10-micron plateau in their data, which means that Psyche’s surface likely varies in composition. These previous studies investigated the south pole of the asteroid while Arrendondo et al.’s study investigated the north pole.

Psyche (the asteroid) as imaged by the Very Large Telescope in northern Chile. (Credit: ESO/LAM)

Scientists are currently investigating why these surface differences could exist, but one theory suggests that the surface material at the south pole could have been ejected from a collision that occurred elsewhere on the asteroid. Previous observations of the asteroid’s surface support this theory, as it is known that Psyche’s surface is littered with massive craters and depressions.

Scientists, unfortunately, won’t know the exact nature of the surface differences on the asteroid until Psyche (the spacecraft) arrives at the asteroid in 2029. For now, the teams will just have to use the SOFIA data and other observational data for analysis. Their remaining questions can only be answered when the mission arrives at the asteroid and takes up-close imagery and observations of the asteroid.

“With this analysis and the previous studies of Psyche, we have reached the limit of what astronomical observations can teach us about this fascinating asteroid. Now we need to physically visit Psyche to study it up close and learn more about what appears to be a very unique planetary body,” said McAdam.

These unique characteristics and theorized history of Psyche (the asteroid) are exactly why scientists selected Psyche (the mission) to be the 14th mission of NASA’s Discovery Program. The asteroid, if scientists’ current predictions are true, could answer some of planetary science’s greatest questions about planet formation. What’s more, the cores of Earth, Mars, and Mercury are all metallic, and if Psyche is indeed the left-over metallic core of a planetesimal, scientists could learn more about the formation of rocky planets and the interiors of Earth and Mars than ever before.

Psyche’s potential past as a planetary core isn’t the only characteristic that makes it similar to Earth. Psyche is the largest M-type, or metallic, asteroid in our solar system, and its immense size means it’s more likely to show differentiation — the process by which materials within an object separate and the heavier materials sink to the middle and form cores.

“Every time a new study of Psyche is published, it raises more questions. Our findings suggest the asteroid is very complex and likely holds many other surprises. The possibility of the unexpected is one of the most exciting parts of a mission to study an unexplored body, and we look forward to gaining a more detailed understanding of Psyche’s origins,” Arrendondo said.

As mentioned, NASA’s Psyche mission is set to launch on Oct. 12, 2023, atop a SpaceX Falcon Heavy rocket from Launch Complex 39A at the Kennedy Space Center in Florida. Both NSF and NASA will broadcast the launch on YouTube and other social media sites.

(Lead image: An artist’s depiction of Psyche (the asteroid). Credit: NASA/JPL-Caltech/ASU)

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