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Getting Excited for an Asteroid Expedition


A spacecraft consisting of a bright central box and two cross-shaped solar panels flies above the jagged landscape of a large asteroid.

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In the classic Star Trek TV show, Captain Kirk and the USS Enterprise crew searched for M-class planets – celestial bodies made of rock and metal with atmospheres similar to Earth. Psyche, a NASA mission slated for launch on October 5th, is embarking on a journey to an M-class asteroid, breaking new ground for spacecraft exploration.

If all goes according to plan, the spacecraft will circle around the asteroid, known as Psyche, for over 2 years. Researchers stated that its findings will provide insight into the beginnings of the solar system, such as the creation of Earth and the other planets closer to the sun.

Lindy Elkins-Tanton, a professor at Arizona State University and lead researcher for the Psyche mission, described it as a completely new world. She admitted that the true nature of Psyche is still uncertain. Unlike Mars, which we are familiar with, Psyche presents a unique challenge due to our lack of information and context.

Studying metallic asteroids can provide us with the most accurate insight on the inner cores of planets similar to Earth.

Psyche, also known as 16 Psyche as it was the sixteenth asteroid to be discovered, is a sizable asteroid with high concentrations of metal (indicated by the “M” in M-type). It has an average diameter of approximately 222 kilometers and resides in the main asteroid belt between the orbits of Jupiter and Mars. On average, it orbits the Sun at three times the distance between Earth and the Sun. This will be the first opportunity to observe a metal-rich asteroid up close, as all previous encounters with asteroids have been with rocky bodies, including three missions that returned samples.

Zoe Landsman, a planetary scientist at the University of Central Florida who specializes in studying asteroid surfaces, stated that Psyche is considered the epitome of M-type asteroids. She also mentioned that the data collected from getting a closer look at Psyche will be incredibly valuable.

Rhonda Stroud, a professor at Arizona State University (not involved with the mission), stated that each asteroid provides a distinct glimpse into the process of planet formation. She also noted that studying metal asteroids will provide valuable insights into the inner cores of planets such as Earth.

Enhanced Observations, Novel Models

Ten years ago, when the Psyche mission was created, researchers believed they had a good understanding of its objective. Data from radar scans indicated that Psyche was remarkably luminous, indicating a composition primarily made of metal. Observations using optical instruments showed a spectrum similar to that of iron meteorites.

The structure proposed that Psyche is the remaining central part of a separated body – one of significant size that would have melted and formed layers, with denser elements like iron and nickel settling in the center. This means that observing Psyche up close would be similar to examining the core of Earth or another inner planet, potentially revealing insights into the formation of metallic cores.

“We are interested in exploring the Earth’s core, however, it is currently inaccessible,” stated Bill Bottke, the director of the science directorate at Southwest Research Institute in Boulder, Colorado and a scientist for the Psyche mission. “To overcome this obstacle, we can instead seek out a location where the core is naturally exposed,” he explained. “This is one potential option that piques our curiosity.”

Subsequent studies on Psyche, partially motivated by NASA’s endorsement of the project, challenged the initial theory of its creation. These investigations offered a more comprehensive understanding of the asteroid, with improved data on its surface makeup, structure, and mass.

Several small, irregularly shaped gray-white objects show asteroid Psyche from different angles.

Some potential surface characteristics of the asteroid Psyche can be seen in some high-quality images taken by the Very Large Telescope in Chile as it rotates. Photo credit: ESO/LAM

I prefer to view it as being shaped like an avocado instead of a potato, which is how many people describe it.

“It has a somewhat circular shape with slight indentations,” stated Stroud. “I prefer to envision it as resembling an avocado rather than a potato, as many people often describe it. It must possess a certain texture, and it boasts a high level of brightness and reflectivity, similar to that of an avocado which is shinier than a potato.”

The revised data indicates that regardless of one’s preferred food, Psyche is approximately 2/3 less dense than originally predicted, with a density of approximately 4,000 kilograms per cubic meter. Previous estimates had suggested a density of 6,000 kilograms per cubic meter. Despite this, Psyche remains the most dense asteroid known, with a volume of 30% to 60% being composed of metal. This could mean that the asteroid contains a significant amount of rocky material or that it is a “rubble pile” – a body that was broken apart and then reformed, resulting in empty spaces between pieces.

According to Bottke, this does not completely disprove the core remnant model, but rather decreases its likelihood. Instead, Psyche may have originated in its current form and composition from the solar nebula – the gas and dust cloud that created the Sun and its surrounding planets and bodies. If this theory is accurate, it could reveal the specific location and timing of Psyche’s birth for scientists.

Bottke explained that the solar nebula was in the process of creating planetesimals, which are the basic components of planets. Some areas may have had a higher concentration of metals, resulting in the formation of metal-rich planetesimals. It is possible that Psyche is one of these objects, created towards the end of the solar nebula’s existence, possibly as a final event.

Radar findings indicated that a majority of the surface of Psyche is coated with a layer of loose soil rich in iron, approximately 1 meter in depth. There are also a few bright areas that may be uncovered sections of nearly pure metal.

A large, round, grayish object with craters and two large depressions

This illustration depicts the possible appearance of Psyche, featuring significant impact craters and deposits of predominantly metallic material on its outer layer. Attribution: NASA/JPL-Caltech/ASU.

According to Michael Shepard, a planetary scientist at Bloomsburg University of Pennsylvania, our findings indicate that in the early stages, asteroids may have possessed a sufficient number of volcanoes to produce volcanic centers, where iron was being brought up from the interior.

According to Elkins-Tanton, the change in theories is not an issue for the Psyche mission, which was originally planned with a remnant core model in mind. In fact, this change may actually improve the scientific aspects of the mission.

A Lengthy Voyage to the Asteroid Belt

Psyche, the spacecraft, will finally launch on October 5th at 10:38 a.m. EDT after a 15-month delay due to software and other issues. There are also other potential launch dates until October 22nd.

The spacecraft will utilize an ion propulsion system, which has only been used in missions to the Moon, to assist in its journey to the asteroid Psyche. After traveling 3.6 billion kilometers, the spacecraft is expected to reach its destination in July 2029 and begin orbiting the asteroid one month later. Its main objective, lasting until November 2031, will involve gradually descending into lower orbits, with a final altitude of 75 kilometers above the asteroid’s surface.

Circles depict the orbits of the inner planets plus asteroid Psyche, with the path of the Psyche spacecraft as it travels around the Sun.

The spacecraft named Psyche will journey for approximately 6 years in order to cover a distance of 3.6 billion kilometers on its route to the asteroid Psyche. The journey will involve a gravitational boost from Mars. Attributed to NASA/JPL-Caltech.

The equipment on board includes a camera that can detect light in both visible and near-infrared ranges to create a map of the entire asteroid and analyze its mineral makeup. A device called a spectrometer will determine the chemical composition of the asteroid’s surface, while a magnetometer will measure its magnetic field. This data could potentially support the theory that the asteroid has a broken core. Additionally, scientists will utilize the spacecraft’s radio system to chart the asteroid’s gravitational field, providing more accurate measurements of its weight and density.

“We will utilize all of the available data sets to reconstruct the time and location of Psyche’s formation,” stated Elkins-Tanton. “Personally, I am focused on understanding the process of its formation. My greatest desire is for it to be revealed as something unexpected and unique, which would revolutionize our understanding of planetesimals.”

Shepard stated that it is a crucial element in completing the larger puzzle. He believes that Psyche will provide a clearer understanding of the diverse environment that makes up the asteroid belt.

“Damond Benningfield is a writer who covers science.”

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Reference: Benningfield, D. (2023), Preparing for an Asteroid Mission, Eos, 104, https://doi.org/10.1029/2023EO230376. Published on October 4, 2023.

Text © 2023. The authors. CC BY-NC-ND 3.0

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