Is asteroid Psyche actually a planetary core? James Webb Space Telescope results cast doubt

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NASA's Psyche mission arrives at the asteroid in 2029, when it will get the chance to solve the mystery.

A box-shaped spacecraft with large solar wings swoops in toward a metal-looking asteroid in space.
An artist's visualization video showing the Psyche spacecraft getting closer to the asteroid. (Image credit: NASA/JPL-Caltech/ASU)

Hydrated minerals have paradoxically been found by the James Webb Space Telescope (JWST) on the surface of 16 Psyche, a metallic asteroid that's the target of a NASA mission that launched in October 2023. Hydroxyl and possibly water were identified on Psyche, and the substances may originate from impacts — but if such hydration came from inside the asteroid instead, that would change everything. It would mean we were wrong about Psyche.

16 Psyche, sometimes simply called Psyche, is a dense, metallic asteroid that is 280 kilometers (173 miles) across at its widest point and moves in a 378 million to 497-million-kilometer (235-million- to 309-million- mile) orbit around the sun. This places Psyche in the asteroid belt between Mars and Jupiter, between 2.5 and 3.3 times further from the sun than Earth is.

Psyche was chosen as a destination for NASA's mission because its high iron content flags the asteroid as a potential remnant core of a protoplanet that was smashed apart by collisions billions of years ago. It was protoplanets such as this that eventually accreted more mass and evolved into worlds such as Earth — so, by studying Psyche and asteroids of similar ilk, we can learn more about the beginnings of our own planet.

However, the JWST's discovery of hydrated minerals containing the molecule hydroxyl (OH, meaning one oxygen atom and one hydrogen atom) and possibly water (H20, or two hydrogen atoms and one oxygen atom) has added an extra layer of complexity to Psyche's history. The presence of hydroxyl within minerals is often a strong indicator that water is present, too.

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One possibility is that these minerals were brought to Psyche by impacts with smaller carbonaceous chondrite asteroids that are known to contain substantial quantities of water. The other possibility, however, is that the hydration comes from within Psyche – and if that's the case, it changes everything we thought we knew about Psyche.

"Asteroids are leftovers from the planetary formation process, so their compositions vary depending on where they formed in the solar nebula," said Anicia Arredondo of the Southwest Research Institute in a statement. "Hydration that is endogenous [i.e. internal] could suggest that Psyche is not the remnant core of a protoplanet."

Instead, it might indicate that Psyche migrated to its current location from farther out, beyond what is called the "snow line." The solar system formed out of a protoplanetary disk, or a frisbee shaped disk around the young sun filled with dust, gas and ice. The snow line is a certain distance from the sun in this disk where temperatures would have been low enough for volatile gases, such as water and carbon dioxide, to freeze out as ice and become incorporated into the structure of any small bodies that formed out there. If true, this calls into question the true nature of Psyche — including how metallic it really is and whether it actually is a core remnant of a protoplanet.

An artist's impression showing an impact on the asteroid 16 Psyche that could have left hydrated minerals found by the JWST. (Image credit: SwRI)

However, the observations with the JWST's Near-Infrared Spectrometer (NIRSpec) indicate that the hydrated minerals are not evenly spread across the surface of Psyche. If the hydration was coming from inside the asteroid, we might expect its distribution to be more homogenous. So, that patchiness does suggest that random impacts may be the cause.

It will be up to the Psyche spacecraft to discover the final answer when it arrives at the asteroid in 2029. Ultimately, the findings could have a huge impact on our picture of how the planets formed.

Related Stories:

— NASA shuts down NEOWISE asteroid hunter after almost 15 years in space

— NASA's DART asteroid impact mission revealed ages of twin space rock targets (images)

— Saturn threw a comet out of the solar system at 6,700 mph. Here's how

"Our understanding of solar system evolution is closely tied to interpretations of asteroid composition, particularly the M-class [metallic] asteroids that contain higher concentrations of metal," said Stephanie Jarmak of the Harvard–Smithsonian Center for Astrophysics.

The analysis of the JWST's observations of Psyche are currently available as a pre-print and will be published in a future issue of the Planetary Science Journal.

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Keith Cooper
Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

19 Comments Comment from the forums
  • What is to stop Psyche forming in a metal rich gaseous zone of the disc (and sweeping up/ absorbing water elements) as temperatures cool, to be left as an entity in its own right?
    Reply
  • Torbjorn Larsson
    Here'smythought said:
    What is to stop Psyche forming in a metal rich gaseous zone of the disc (and sweeping up/ absorbing water elements) as temperatures cool, to be left as an entity in its own right?
    Nothing, but such an element sorting in the disk is less likely,

    Gravitational sorting in rocky planets with metal cores is ubiquitous, and we expect many protoplanets in the early system. C,f. how the Venus massed Tellus and Mars massed Theia collided to form Earth and Moon, and how Uranus may have gotten its tilt from an Earth massed impactor.

    But the question of what Psyche is is still open.
    Reply
  • Unclear Engineer
    Given the mass of Psyche and the local environment, it would not surprise me if an exposed planetary core would accumulate some surface materials that were not from the core, but rather from other debris from its own collision and/or other collisions in the asteroid belts.

    The density is the main indicator. How well do we really know the density value for Psyche?
    Reply
  • Torbjorn Larsson said:
    Nothing, but such an element sorting in the disk is less likely,

    Gravitational sorting in rocky planets with metal cores is ubiquitous, and we expect many protoplanets in the early system. C,f. how the Venus massed Tellus and Mars massed Theia collided to form Earth and Moon, and how Uranus may have gotten its tilt from an Earth massed impactor.

    But the question of what Psyche is is still open.
    With respect - why would sorting of metals within the disk be less likely than something that might have occurred later. The article posits sorting wrt water elements in the disk.

    " The solar system formed out of a protoplanetary disk, or a frisbee shaped disk around the young sun filled with dust, gas and ice. The snow line is a certain distance from the sun in this disk where temperatures would have been low enough for volatile gases, such as water and carbon dioxide, to freeze out as ice and become incorporated into the structure of any small bodies that formed out there."

    At higher and cooling temperatures would there not have been a "snow line" for eg iron, resulting from gas to liquid to solid?
    Reply
  • billslugg
    It is possible to do some amount of sorting of elemental iron in the solar nebula. The freeze line of iron would be very close to the Sun. The amount of volume available for sorting purposes is very small. There is not enough volume to do enough separation to explain the amount of separated out iron in the Solar System.
    Reply
  • billslugg said:
    It is possible to do some amount of sorting of elemental iron in the solar nebula. The freeze line of iron would be very close to the Sun. The amount of volume available for sorting purposes is very small. There is not enough volume to do enough separation to explain the amount of separated out iron in the Solar System.
    Thanks. Can you support those statements?
    Reply
  • Unclear Engineer
    When theorists calculate temperatures in the various locations of the protoplanetary disk, how do they account for shadowing of disk material from solar energy by intervening disk material, and heat transfer by radiation out of the disk, more or less perpendicular to the plane of the disk? Doesn't that depend strongly on the thickness and density of the disk, and how that changes over time as planets form? And is the transfer of kinematic energy to heat energy of particles and protoplanets in the disk accounted for? This seems like it would need to be quite complicated, and have some substantial levels of uncertainty.

    And, with the models showing that the major planets may have migrated towards and away from the Sun as the planets evolved, why would that not have scattered the asteroids that we seen in a belt inside Jupiter now, unless they formed after Jupiter went through the current asteroid belt for the last time?

    I wonder if the asteroids formed "late" in the process, with Jupiter effectively demolishing some protoplanets whose debris eventually coalesced into the various asteroid belt objects we see now. Perhaps much of the debris ended up in Jupiter, and what we see is a fraction of what was initially in that distance from the Sun.
    Reply
  • billslugg
    Here'smythought said:
    Thanks. Can you support those statements?
    No, I can't cite where I read it. I've seen the explanation twice in the last couple of weeks though. Just ignore me.
    Reply
  • Unclear Engineer
    These 2 links provide some better discussion of formation locations and migrations:

    https://en.wikipedia.org/wiki/Frost_line_(astrophysics)
    https://www.universetoday.com/155028/the-building-blocks-of-earth-could-have-come-from-farther-out-in-the-solar-system/
    And iron in the planets' formations is discussed here:

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8713747/

    Iron in the protoplanetary disk seems to have been present in molecules of various sorts, rather than in reduced form. So, its volatility is not what you would expect by looking at the properties of the pure metal. It is probably best thought of as non-volatile dust until it gets into a very hot accreting protoplanet.
    Reply
  • billslugg said:
    No, I can't cite where I read it. I've seen the explanation twice in the last couple of weeks though. Just ignore me.
    No worries billslugg, you might well be right - I'm just imagining different scenarios so they can be scrutinised here.
    Reply