The Jet Propulsion Laboratory (JPL) has announced that NASA has its sights set on visiting a mysterious giant asteroid –about 173 miles (280 kilometers) at its widest point–a mystery object about the size of Massachusetts named Psyche that may be the frozen remains of the molten core of a world long gone –the only known object of its kind in the solar system. It appears to be the exposed nickel-iron core of a protoplanet, one of the building blocks of the Sun’s planetary system –an alien panorama sculpted by “ferrovolcanism,” eruptions of liquid iron. NASA’s mission to seek iron-spewing volcanoes at Psyche could help rewrite early chapters of the solar system’s history.
This strange object is the 16th minor planet to be discovered — hence its formal designation, 16 Psyche. The asteroid was found in 1852 by Italian astronomer Annibale de Gasparis, who named it for the Greek mythological figure Psyche. Using data gathered from Earth-based radar and optical telescopes, scientists believe that Psyche is a relic made largely of metal that could be part or all of the iron-rich interior of an early planetary building block that was stripped of its outer rocky shell as it repeatedly collided with other large bodies during the early formation of the solar system.
It Could be a Primordial Relic
Or, could also be something else entirely –the leftover remnant of a completely different kind of iron-rich body that formed from metal-rich material somewhere in the solar system.
NASA’s Psyche mission hopes to find out. Set for an August 2022 launch, the spacecraft will for two years orbit the asteroid it was named after, taking pictures, mapping the surface, and looking for evidence of an ancient magnetic field. Psyche also will study the neutrons and gamma rays coming from the asteroid’s surface to help determine its elemental composition.
At NASA’s Jet Propulsion Laboratory, an engineer inspects the gamma ray and neutron spectrometer as it is integrated into the agency’s Psyche spacecraft. The instrument will help determine the elements that make up its target.
At NASA’s Jet Propulsion Laboratory, an engineer inspects the gamma ray and neutron spectrometer as it is integrated into the agency’s Psyche spacecraft. The instrument will help determine the elements that make up its target. Credit: NASA/JPL-Caltech Full Image Details
The first mission to explore an asteroid with a surface that contains substantial amounts of metal rather than rock or ice, Psyche seeks to better understand iron cores, an unexplored building block of planet formation. The mission also potentially provides the first opportunity to directly examine the inside of a rocky planet by offering a look at the interior of a previously layered planetary body that otherwise could never be seen. What scientists learn could shed additional light on how Earth and other rocky planets formed.
“There are a lot of basic questions about Psyche that are unanswered,” said the mission’s principal investigator, Lindy Elkins-Tanton of Arizona State University. “And with every detail that gets added from data we can collect from Earth, it just becomes harder to make a sensible story. We really don’t know what we’re going to see until we visit, and we’re going to be surprised.”
For instance, previous ground-based observations led scientists to believe that the asteroid was as much as 90% metal. Recent research led by Elkins-Tanton used updated density measurements to estimate that the asteroid is more likely between 30% and 60% metal.
And scientists are puzzled why Psyche appears to be low in iron oxides, which are chemical compounds made of iron and oxygen. Mars, Mercury, Venus, and Earth all have them. “So if we’re correct that Psyche is a mixture of metal and rock, and the rock has very little iron oxide, then there’s got to be a strange story about how it was created – because it doesn’t fit the standard stories of planetary creations,” Elkins-Tanton said.
Scientists also don’t know where Psyche formed. It might have originated inside the main asteroid belt, but it’s also possible that it was born in the same zone as the inner planets like Earth – or in the outer solar system, where giant planets like Jupiter now reside. Neither origin story follows a simple path to where Psyche lives now, 280 million miles (450 million kilometers) from the Sun.
Asteroids in general can offer insight into planet formation and how the early solar system worked 4.6 billion years ago. But Psyche is particularly interesting to scientists because of how unusual it is, with its metal content, high density, and low concentration of iron oxides.
Lindy Elkins-Tanton on Psyche’s Formation
“We are working toward being able to explain how Psyche was formed, that is, is it a part of a differentiated body (metal core separated from rocky exterior), or is it material that never melted?,” Elkins-Tanton wrote in an email to The Daily Galaxy. “Knowing what it is made of and what kind of body that material came from will give clues on whether it originated in the inner or outer solar system, but we may never know that with certainty.
“Rocky material that is very low in iron oxides is rare.” Elkins-Tanton explained. “Psyche’s reflected spectra indicate that its rocky constituents are low in iron-oxide, we’ll see once we get there! But at the moment there are three ideas for how to create low-iron-oxide rock.
“One is that Psyche captures only the first minerals solidified from a planetesimal magma ocean (the first minerals in a fractional solidification series are always lowest in iron oxide); perhaps the rest of the rock was lost to impacts. A second is that Psyche’s surface is covered with the same material that CB chondrite meteorites are made of: Metal, plus chondrules that are very low in iron oxide. Finally,” Elins-Tanton concluded in her email, “perhaps Psyche formed in very hot or otherwise highly reducing conditions, and almost all its iron was reduced to a metallic phase and entered the core. None of these are high-likelihood scenarios, which only makes Psyche more mysterious and interesting. No doubt, when we get there, we’ll discover it’s something else entirely!”
Telling Us a New Story About Our Solar System
“The fact that it’s so unusual is telling us a new story that we haven’t seen before about how asteroids evolved,” said Bill Bottke, Psyche mission scientist of the Southwest Research Institute in Boulder, Colorado. “That’s a piece of the story we don’t have right now. By getting that piece together with all the others we have, we continue to refine our story of how the solar system formed and evolved early on.”
Bill Bottke –“Composition will be a Major Factor”
“The composition of materials on the surface will give us insights into the temperatures that had to exist in the region where Psyche was formed. From that information, we can try to determine its formation location in the solar nebula,” Bill Bottke wrote in an email to The Daily Galaxy. “As an example, consider that the Dawn mission showed that the dwarf planet Ceres — within the asteroid belt today — is rich in ammonium (NH4+) bearing phyllosilicates. That suggests that Ceres likely formed somewhere in the giant planet zone much further than we see it today.
“As for Psyche being low in iron oxides,” Bottke continued, “there are enough unknowns that I cannot provide a good answer for you. Perhaps this is useful. The meteorite evidence suggests some iron meteorites came from inner solar system planetesimals while others came from outer solar system materials (i.e., they probably formed in the same region as the giant planets). The origin of the iron-rich outer solar system planetesimals is still murky, so perhaps Psyche will give us insights into those kinds of parent bodies — and how iron oxide behaves in outer system planetesimals that are capable of differentiation.”
To help figure out the asteroid’s origins, the mission’s science investigation will rely on a magnetometer, a gamma ray and neutron spectrometer, and a multispectral imager. Scientists know that the asteroid doesn’t generate a magnetic field the way Earth does, but if Psyche had a magnetic field in the past, it could still be recorded in the asteroid’s material today. With sensors mounted onto a 6-foot (2-meter) boom, the magnetometer can determine whether Psyche is still magnetized. If so, that would confirm that the asteroid is part of the core of an early planetesimal, the building block of an early planet.
Gamma Ray and Neutron Analysis
The orbiter’s gamma ray and neutron spectrometer instrument will help scientists determine the asteroid’s chemical elements. As cosmic rays and high-energy particles impact Psyche’s surface, the elements that make up the surface material absorb the energy. The neutrons and gamma rays they emit in response can be detected by the spectrometer, allowing scientists to match their properties to those emitted by known elements to determine what Psyche is made of.
Meanwhile, a pair of color cameras make up the multispectral imager. The imager is sensitive to light just beyond what humans can see, using filters in the ultraviolet and near-infrared wavelengths. The light reflected in these filters could help determine the mineralogy of any rocky material that may exist on Psyche’s surface.
The spacecraft’s telecommunications system will help with the science as well. The X-band radio system is primarily used to send commands to the spacecraft and receive engineering and science data from it. But scientists can also analyze subtle changes in these radio waves to measure the body’s rotation, wobble, mass, and gravity field, providing additional clues about the composition and structure of Psyche’s interior.
Imager Team On Deck
But before any of this science analysis gets underway, there will be pictures. By late 2025, three years after launch, Psyche will be within sight of the asteroid, and the imager team will be on high alert.
“Even before we get into orbit, we’ll start getting much better pictures than we can from telescopes on Earth. We’ll start to resolve features, see big craters, crater basins – maybe mountain ranges. Who knows what we’ll see?” said Jim Bell of Arizona State University, deputy principal investigator of Psyche and imager team lead. “All we know is that the reality of Psyche is going to be even weirder and more beautiful than we can imagine.”
“Will be Weirder and More Beautiful than We can Imagine”
In an email to The Daily Galaxy Bell wrote: “Indeed, one of our goals is to try to determine whether (16) Psyche formed where it is now in the Main Asteroid Belt, or in the inner solar system, or in the outer solar system. Our mission and our science payload are designed to provide important clues. For example, measuring the abundance of chemical elements like Nickel on the asteroid will allow us to test models for the origin of the asteroid. As well, mapping of the interior of the asteroid using gravity science techniques can help us understand if it is more porous or layered or not, more properties that can be related to models of its place of origin.”
“There is debate not only about the presence and abundance of iron oxides,” Bell noted in his email, “but of the iron-rich versus silicate-rich composition of (16) Psyche in general. Is the asteroid a mixed iron and silicate body, comparable to meteorites that come from the ancient core-mantle boundaries of shattered protoplanets? Or is it primarily a metal-rich body, comparable to meteorites that come from the ancient cores of shattered protoplanets, but with silicate added to the surface by later impacts of rocky asteroids? Or… something else entirely? We can’t wait to get there and try to find out!”