Science

More than 150 years have passed since novelist Jules Verne wrote “Journey to the Center of the Earth,” but reality has yet to catch up with that science fiction adventure. While humans can’t bore a path to our planet’s metallic core, NASA’s Psyche mission will visit a giant asteroid that may be the solidified remains of the molten core of a bygone world.

The asteroid Psyche orbits the Sun in the main asteroid belt between Mars and Jupiter. Using data gathered from Earth-based radar and optical telescopes, scientists hypothesize that Psyche is a metal-rich asteroid. It could be part or all of the iron-rich interior of a planetesimal, 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.

The asteroid, which is about 173 miles (280 kilometers) at its widest point, could also be the leftover piece of a completely different kind of object that formed from metal-rich material somewhere in the solar system.

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 will be the first to directly examine the interior of a previously layered planetary body, which they expect will shed additional light on how Earth and other rocky planets formed.

Science Goals and Objectives

Each NASA mission has a set of science goals – larger areas of knowledge that it must contribute to – and a set of science objectives, which are specific, measurable actions to complete.

The science goals for Psyche are to:

• Understand iron cores, a previously unexplored building block of planet formation.
• Look inside terrestrial planets, including Earth, by directly examining the interior of a differentiated (layered) body, which otherwise could not be seen.
• Explore a new type of world – one made not of rock and ice, but significant amounts of metal.

Psyche’s more specific science objectives are:

• Determine whether the asteroid Psyche is a planetary core or if it is unmelted material.
• Determine the relative ages of regions of Psyche’s surface.
• Determine whether small metal bodies incorporate the same light chemical elements (including sulfur, potassium, and silicon) that are expected to be present in Earth’s high-pressure core.
• Determine whether Psyche was formed under conditions more oxidizing or more reducing than Earth’s core. In Psyche’s case, these terms refer to whether there is a lot of oxygen present in the asteroid’s metal compounds (oxidized) or little to no oxygen (reduced). Answering this question will help to determine the conditions of the environment in which Psyche formed.
• Characterize Psyche’s topography.

What Do We Know About the Asteroid Psyche?

Until recently, the scientific consensus was that the asteroid Psyche consisted mostly of metal. New information on density, radar properties, and spectral signatures indicate that the asteroid is possibly a mix of metal and silicate minerals. There are still contradictions in the data, but the best analysis indicates that Psyche is likely made of a mixture of rock and metal, with metal composing 30% to 60% of its volume. The asteroid’s metal content is estimated based on its density, how much visible light and radar are reflected by the asteroid, and by the measurements of the asteroid’s thermal inertia (how quickly it gains or re-radiates heat). 

By combining radar and optical observations, scientists have generated a 3D model of Psyche that gives us an idea of the general shape of the asteroid and even shows evidence of two craterlike depressions. The data also suggest that there is significant variation in the metal content and color of the asteroid over its surface. But until this mission sees the asteroid Psyche up close for the first time, we will not know what it looks like in detail.

How was the asteroid formed?

Scientists think Psyche may consist of significant amounts of metal from the core of a planetesimal, one of the building blocks of our solar system. The asteroid is most likely a survivor of multiple violent hit-and-run collisions, common when the solar system was forming. Thus, Psyche may be able to tell us how Earth’s core and the cores of the other rocky, or terrestrial, planets came to be.

What is its size, shape, density, and gravity?

The shape of the asteroid Psyche is irregular and potatolike. If it were sliced in half horizontally at the equator – picture a squished oval – the asteroid would measure 173 miles (280 kilometers) across at its widest point and 144 miles (232 kilometers) long. Its surface area is 64,000 square miles (165,800 square kilometers).

Psyche is dense, estimated at about 212 to 256 pounds per cubic foot (3,400 to 4,100 kilograms per cubic meter). The surface gravity on Psyche is much less than it is on Earth or even the Moon. On Psyche, lifting a car would feel like lifting a large dog.

What kind of orbit is the asteroid Psyche in?

Psyche follows an orbit in the outer part of the main asteroid belt, between Mars and Jupiter, at an average distance from the Sun of 3 astronomical units, or AU (about 280 million miles, or 450 million kilometers). Earth orbits at 1 AU (about 93 million miles, or 150 million kilometers). Because Psyche and Earth orbit at different speeds, the distance from Earth to Psyche varies over a large range, from less than 2 AU to greater than 4 AU.

Where is asteroid Psyche now?

Track the asteroid’s location with NASA’s Eyes on Asteroids.

Is NASA mining Psyche or other asteroids?

No, NASA is not mining asteroids. Psyche is a fundamental science research mission that is looking to understand more about asteroids.

Science Team Leadership

Psyche is a science-led mission helmed by Principal Investigator Lindy Elkins-Tanton of Arizona State University (ASU) in Tempe. The deputy principal investigator is Ben Weiss of the Massachusetts Institute of Technology (MIT) in Cambridge.

Science Instruments and Investigations

Multispectral Imager

Psyche’s multispectral imager consists of a pair of identical cameras equipped with filters and telescopic lenses to photograph the surface of the asteroid in different wavelengths of light. The cameras can take pictures in the part of the spectrum visible to the human eye, as well as in near-infrared wavelengths of light beyond what humans can see. The images will help the science team learn about the mineral composition of Psyche; map the distribution of craters, valleys, cliffs, and other geologic features; and enable the creation of 3D topographic maps – all of which will provide clues to Psyche’s history.

The imager operations team is based at ASU. Jim Bell is the imager team lead, David Williams is the deputy lead, and Michael Walworth is the imager operations lead.

A video about the instrument can be found at https://bit.ly/46eVJ1s.

Gamma-Ray and Neutron Spectrometer

The orbiter’s gamma-ray and neutron spectrometer (GRNS) will help scientists determine the chemical elements that make up the asteroid’s surface material. As cosmic rays and high energy particles bombard the asteroid Psyche’s surface, the elements there absorb the energy. In response, they emit neutrons and gamma rays of varying energy levels. The spectrometer can detect these emissions, enabling scientists to match them to properties of known elements to determine what Psyche is made of.

The team is based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. David Lawrence is the GRNS lead, and Michael Cully is the GRNS project manager.

A video about the instrument can be found at https://bit.ly/45cOvK9.

Magnetometer

The orbiter’s magnetometer will look for evidence of an ancient magnetic field at the asteroid Psyche. Unlike Earth and other rocky planets that generate a magnetic field in their liquid metallic cores, small bodies like asteroids do not generate one because they are frozen. If the magnetometer detects an intrinsic field around the asteroid, it would be from remanent, or residual, magnetization – electrons that were aligned in Psyche’s materials when they cooled in an ancient field generated in the body’s molten core billions of years ago before that core cooled. Confirmation of a remanent magnetic field would be strong evidence that the asteroid formed from the core of a planetary body.

The instrument’s team is based at MIT in Cambridge, where Ben Weiss is the magnetometry investigation lead, and Technical University of Denmark (DTU) in Lyngby, where José Merayo is the chief magnetometer designer and co-investigator at DTU Space.

A video about the instrument can be found at https://bit.ly/48B0mVn.

Gravity Science

The Psyche science team will rely on the telecommunications system, used to send commands to and receive data from the spacecraft, to conduct gravity science also. By analyzing the X-band radio waves the spacecraft communicates with, scientists can measure how Psyche affects the spacecraft’s orbit. From that information, scientists can determine the body’s rotation, mass, and gravity field, providing additional clues about the composition and structure of Psyche’s interior. Unlike Earth, Psyche is far from round. Measuring the gravity field is important so that the navigation team can safely fly the spacecraft close to the surface and provide detailed and accurate scientific measurements.

The team is based at MIT and NASA’s Jet Propulsion Laboratory in Southern California. Maria Zuber of MIT is the gravity science investigation lead, and Ryan Park of JPL is the deputy lead.

A video about the instrument can be found at https://bit.ly/3ZIdGmX.