Millimeter-wavelength emissions reveal the temperature of the asteroid Psyche as it rotates through space. Credit: California Institute of TechnologyA close examination of the millimeter-wavelength emissions from the asteroid Psyche, which NASA intends to visit in 2026, has produced the first temperature map of the object, providing new insight into its surface properties. These findings were published in Planetary Science Journal (PSJ), August 5, and are a first step towards solving the mystery surrounding the origin of this strange object. Some believe it to be part of a fragment of a ill-fated protoplanet's core.Psyche orbits Jupiter in the asteroid Belt, a region between Earth and Jupiter with more than a million rocky bodies. It is a donut-shaped area of space that houses more than a million rocky objects ranging in size from 10 to 946 km in diameter.Psyche has a diameter greater than 200 km and is the largest M-Type asteroids. This mysterious class of asteroids are metal rich, so they may possibly be fragments from the cores of protoplanets that were lost as the solar system was formed.Caltech's Katherine de Kleer is assistant professor of planet science and astronomy at Caltech and the lead author of the PSJarticle. We believe that fragments from the cores, mantles and crusts of these objects are still present today as asteroids. This is our only chance to study the cores planet-like objects.It is difficult to study such tiny objects so far from Earth (Psyche drifts at a distance of between 179.5 million and 329,000,000 km from Earth). NASA plans to send a probe up to Psyche to investigate it closer. Thermal observations from Earth, which measure the light emitted from an object rather than the sun's reflected light, are limited to 1-pixel images. However, that one pixel can reveal a lot of information. For example, it can be used for studying the asteroid’s thermal inertia. This is how quickly it heats up under sunlight and cools off in darkness."Low thermal energy is often associated with layers of dust. However, high thermal inertia could indicate rocks on the surface," said Saverio Cambioni of Caltech, a postdoctoral scholar of planetary science and coauthor of the PSJ article. It is not easy to distinguish one type of landscape from another. The data from multiple times of the day allows for more detailed observations, which leads to more accurate interpretations and a better prediction of the type of landscape before a spacecraft arrives.De Kleer and Cambioni, together with co-author Michael Shepard of Bloomsburg University in Pennsylvania, took advantage of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which became fully operational in 2013, to obtain such data. The team was able to map the thermal emissions of Psyche at a resolution 30 km. Each pixel is 30km by 30km. This enabled them to generate an image of the asteroid consisting of approximately 50 pixels.ALMA was able to observe Psyche at millimeter wavelengths. These wavelengths are much longer than infrared wavelengths (5-30 microns). Researchers were able to combine data from 66 telescopes to make a larger telescope. The telescope's size determines the quality of the images.The study revealed that Psyche's thermal resistance is much higher than that of asteroid. This indicates that Psyche may have a dense or conductive surface. Shepard, de Kleer, and Cambioni also analysed the data. They found that Psyche's heat emission-the amount it emits-is only 60 percent of what is expected for a surface with this thermal inertia. Their findings indicate that Psyche has a surface of at least 30 percent metal, as surface emission can be affected by the presence or absence of metal. The researchers were able to determine the form of this metal by analysing the polarization of the emission. A well-organized polarized beam of light is emitted from a smooth surface. However, the scattered light emitted in Psyche suggests that the surface may be covered with metallic grains.De Kleer states, "We know for years that objects of this class aren't solid metal. But what they are and how it formed is still an enigma." These findings support alternative theories for Psyche’s surface composition. They include the possibility that Psyche could have formed closer to sun than it is now, instead of a core from a fragmented protoplanet.This study provides a fresh perspective on the surface compositions of asteroid surfaces. This team is expanding their scope to include large objects in the asteroid Belt.A related project led by Michael Shepard, Bloomsburg University, enabled the study. This used de Kleer data along with data from other telescopes including Arecibo Observatory, Puerto Rico, in order to determine the size, shape and orientation of Psyche. This allowed researchers to identify which pixels actually represented the surface of the asteroid. Shepard's team was due to again observe Psyche at the end 2020. However, damage to the cable network prevented the telescope from being used for the observation.The paper is titled "The surface of (16) psyche from thermal emission and polarization mapping."Continue reading Study provides a more comprehensive view of the massive asteroid PsycheMore information: Katherine de Kleer et., The Surface of (16), Psyche From Thermal Emission And Polarization Mapping. The Planetary Science Journal (2021). Information from The Planetary Science Journal Katherine de Kleer et., The Surface of (16), Psyche From Thermal Emission And Polarization Mapping (2021). DOI: 10.3847/PSJ/ac01ec
