According to the Planetary Science and Astrobiology Decadal Survey, “Origins, Worlds, and Life,” planetary science and astrogeology are multidisciplinary activities involving members of the geology, geophysics, geochemistry, astronomy, atmospheric science and space physics communities. That’s in tune with our EXPLORER readers.
In the November issue, we reported on the exciting OSIRIS REx asteroid sample return from the near Earth asteroid Bennu. The NASA team responsible for sample curation reports that they have extracted and gathered 70.3 grams of material from Bennu within the capsule, exceeding mission requirements. Remarkably, this material is solely from the sample collector’s head, which holds much more asteroid sample, and hasn’t been opened yet. Special new equipment is needed to remove two stubborn screws.
Meanwhile, Lucy and Psyche are ongoing missions to asteroids orbiting beyond Mars. The Lucy and Psyche asteroid missions were chosen by NASA in 2017 as Discovery Program Missions recommended by the 2013–22 Decadal Survey, “Vision and Voyages.”
The $10 Quintillion Asteroid
On Oct. 13, 2023, a Falcon Heavy rocket carried NASA’s Psyche mission into space, embarking on a six-year journey to reach asteroid 16 Psyche in the main asteroid belt between the orbits of Mars and Jupiter. This mission holds unique historic significance as it marks the first exploration of an asteroid composed, not of rock or ice, but of metal, with a diameter of 136 miles. Notably, asteroid 16 Psyche is recognized as the heaviest known M-type asteroid and is speculated to be the exposed iron core of a protoplanet – a relic from a tumultuous collision, billions of years ago, that stripped away its mantle and crust.
Characterized by an abundance of iron, nickel and other precious metals like gold and platinum, Psyche has been called the “$10 quintillion asteroid.” This label reflects an estimate suggesting that its metal resources could theoretically be valued at around ten million trillion dollars if extracted. The astronomical estimated worth surpasses the entire global economy. Lindy Elkins-Tanton, the lead scientist of the Psyche mission, said the mission presents exciting prospects for the emerging asteroid mining industry.
The Psyche mission is led by Arizona State University, while mission management, operations and navigation are handled by NASA’s Jet Propulsion Laboratory.
What sets the Psyche asteroid apart is its resemblance to an exposed nickel-iron core from the early stages of a planet’s formation, representing one of the fundamental components of our solar system.
While metallic cores are theorized to exist deep within rocky planets, including Earth, they remain inaccessible beneath the planets’ rocky silicate exteriors. Psyche provides an exclusive opportunity to gain insights into the tumultuous history of collisions and accretion that shaped the development of terrestrial planets, as the asteroid’s composition allows for a direct examination of what lies beneath the rocky mantles and crusts of planets like Earth.
The mission seeks to understand a previously unexplored building block of planet formation: iron cores. To achieve this, the mission will determine whether the Psyche asteroid is the core of a once melted, differentiated protoplanet, or if it is unmelted material. The mission will ascertain the relative ages of regions of Psyche’s surface and map its topography. The probe will map the asteroids elemental composition to investigate whether metallic asteroids include comparable light elements as anticipated in the Earth’s high-pressure core. This should also reveal whether the Psyche asteroid was formed under more oxidizing or more reducing conditions than Earth’s core.
Psyche Scientific Instruments and Operations
The Psyche spacecraft is equipped with a multispectral imager designed to capture high-resolution images, utilizing filters to distinguish between the metallic and silicate components of 16 Psyche. This instrument uses a pair of identical cameras aimed at acquiring geological, compositional and topographic data. The gamma ray and neutron spectrometer will identify, measure and map the elemental composition of 16 Psyche. The magnetometer is tailored to detect and measure the remanent (residual) magnetic field of the asteroid. The X-band gravity science investigation will utilize the X-band radio telecommunications system to precisely measure Psyche’s gravity field. When combined with topography information derived from onboard imagery, this will offer insights into the interior structure of the Psyche asteroid.
Psyche’s Itinerary
Currently in the beginning stage of its voyage, the Psyche spacecraft is now executing an initial 100-day checkout phase before initiating its thrusters. Roughly 2.5 years post-launch, the spacecraft will conduct a gravity-boosting flyby of Mars. As the cruise period concludes about 5.5 years into the mission, around June 2029, the spacecraft’s imagers will capture images of the asteroid Psyche. Subsequently, in August 2029, the spacecraft will enter the first of its planned 26-month orbits around the metal-rich asteroid. Once the spacecraft arrives at the asteroid, plans call for it to perform science operations from four staging orbits, which become successively closer, down to an altitude of 47 miles.
Since the spacecraft’s launch, Psyche mission controllers have confirmed the full acquisition of the signal from the spacecraft, and the solar arrays are now fully deployed. Propelled by solar electric propulsion, the five-panel, cross-shaped solar arrays offer approximately 800 square feet of solar-collecting surface, rendering the spacecraft similar in size to a singles tennis court.
When near Earth, the solar arrays generate more than 20 kilowatts of power, but this output decreases to just over 2 kilowatts when the spacecraft reaches the 16 Psyche. Despite the reduced power, it is more than sufficient to meet the spacecraft’s needs during its journey. This includes running science instruments, telecommunications, equipment controlling the spacecraft’s temperature and the highly efficient solar electric propulsion engines.
The spacecraft employs ion propulsion, featuring four SPT-140 engines, Hall-effect thrusters using solar electric propulsion. In this system, electricity generated from solar panels powers an electric rocket engine, which is distinct from chemically-powered engines. The thrusters utilize electromagnetic fields to accelerate and expel charged atoms (ions) of the neutral gas xenon. These expelled ions emit a distinctive blue glow and provide thrust continuously accelerating the Psyche spacecraft. With no atmospheric drag impeding its progress, the spacecraft will accelerate to speeds of up to 124,000 miles per hour relative to Earth during its journey to the asteroid belt.
On Nov. 8, Lindy Elkins-Tanton reported, “The Psyche spacecraft successfully tested our electric propulsion thrusters!”
Launched in 1998, the Deep Space 1 Mission to asteroid 9969 Braille and comet 19P/Borrelly was the first NASA spacecraft to use ion propulsion. In 2022, the DART mission, to binary asteroid Didymos and Dimorphos, tested NASA’s Xenon Thruster-Commercial (NEXT-C), a solar-powered, ion-propulsion system.
NASA’s DSOC (Deep Space Optical Communications) demonstration, hosted by the Psyche spacecraft, will perform data transmission and reception tests using an unseen near-infrared laser. This laser technology has the capability to transmit data at a bandwidth ranging from 10- to 100-times greater than that of traditional radio wave systems currently employed on spacecraft. DSOC is set to showcase its operations for almost two years following the launch of NASA’s Psyche mission, as the spacecraft journeys toward its Mars flyby scheduled for 2026. The experiment will not be used to relay Psyche mission data.
Fossil Asteroids
Launched in 2021, NASA’s 12-year Lucy Mission will explore more asteroids than any other spacecraft, flying by two asteroids in the main asteroid belt in 2023 and 2025, and by eight trojan asteroids near the L4 and L5 Lagrange points of Jupiter’s orbit from 2027 to 2033. The Lagrange points are positions of gravitational stability 60 degrees ahead of and behind Jupiter in its orbit. The complicated mission trajectory will require several Earth flyby gravity assists.
From measured spectra, the Jupiter trojans are mostly D-type asteroids, common in the outer regions of the asteroid belt. They have a very low albedo (reflectivity) and a reddish spectrum with an assumed composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors. As such, they are similar to C-type asteroids like Bennu and Ryugu.
The Lucy mission takes its name from the early hominin Lucy fossil, which offered distinctive insights into the evolution of humans. Through the exploration of Jupiter trojan asteroids, Lucy aims to enhance our understanding of the origins of planets.
“The trojan asteroids are leftovers from the early days of our solar system, effectively the fossils of planet formation,” said Lucy mission principal investigator Harold Levison of the Southwest Research Institute.
For us as resource explorers, the D-type trojan asteroids could have water ice interiors with implications for future deep space commerce. The primary driver is water, the deep space resource analog of oil on Earth. Astronauts and settlers will need water to drink. Electrolysis of water yields oxygen and hydrogen. Oxygen is obviously valuable to breathe and both oxygen and hydrogen are valuable rocket propellants.
Lucy will fly by and carry out remote sensing on two main belt asteroids and eight Jupiter trojan asteroids to achieve its science objectives:
Lucy will map surface geology characterizing asteroid albedo, shape, spatial and size-frequency distributions of craters. Lucy will analyze asteroid crustal structure and layering, and map the composition of surface units, and their relative ages. Mapping will entail defining the asteroid surface color, composition and regolith properties. Details of this will include mapping organics, minerals and ice.
The mission will assess asteroid interior and bulk properties. Mass and density can be determined by measuring their effect on the spacecraft trajectory and by using the Doppler shift of the high-gain radio signal. Sub-surface composition will be gleaned in exposed bedding, fractures, craters excavation and ejecta blankets.
Lucy will look for and analyze possible binary companions and rings of the asteroids it visits. The 617 Patroclus-Menoetius binary is a planned flyby. Lucy’s first target flyby was on Nov. 1, 2023, testing its instruments and systems on main belt asteroid 152830 Dinkinesh, which turned out to be a binary as described below.
Lucy’s Instruments and Operations
The Lucy spacecraft instrument pointing platform will conduct remote-sensing science with the following instruments:
L’Ralph serves as both the color visible imager (MVIC, 0.4-0.85 microns) and the infrared imaging spectrometer (LEISA, 1-3.6 microns). LEISA enables the identification of absorption lines, acting as unique markers for various silicates, ices and organics likely present on the trojan asteroids’ surfaces. MVIC captures color images of the targets, aiding in assessing their activity levels.
L’LORRI, or the long-range reconnaissance imager, is a high-resolution visible imager covering wavelengths from 0.35 to 0.85 microns. This panchromatic camera provides detailed surface images of asteroids.
L’TES, the thermal emission spectrometer, operates in the infrared range (6-75 microns), similar to instruments on OSIRIS-REx and the Mars Global Surveyor. It enables the Lucy team to gather more information about asteroid properties, including thermal inertia, providing insights into surface composition and structure.
Lucy utilizes its high gain antenna to determine target masses through the Doppler shift of the radio signal. The terminal tracking camera (T2CAM) captures wide-field images of the asteroids, contributing to a better understanding of their shapes. T2CAM was successfully tested during the Dinkinesh asteroid flyby.
Following its launch in October 2021, Lucy operations will conduct two close flybys of Earth for gravity assist before reaching its main belt and trojan targets. In 2025, en route to the L4, Lucy will encounter another main belt asteroid, (52246) Donaldjohanson, named after the discoverer of the Lucy fossil. Within the L4 cloud, Lucy will encounter (3548) Eurybates, (15094) Polymele, (11351) Leucus and (21900) Orus from 2027-28. After the subsequent Earth gravity assist, Lucy will proceed to the L5 cloud and engage with the (617) Patroclus-Menoetius binary in 2033.
Dinkinesh Flyby
Asteroid 152830 Dinkinesh was the first flyby target for NASA’s Lucy mission, passing the asteroid from a distance of 264 miles on Nov. 1, 2023. This binary main-belt asteroid, with a diameter of approximately 2,600 feet, was initially identified by the Lincoln Near-Earth Asteroid Research (LINEAR) survey in Socorro, New Mexico, on Nov. 4, 1999. The Lucy spacecraft revealed that Dinkinesh possesses a natural satellite measuring 720 feet in diameter. Notably, Dinkinesh stands as the smallest main-belt asteroid to be explored by a spacecraft.
Lucy’s flyby of Dinkinesh was a crucial test for the spacecraft’s autonomous tracking capabilities. Lucy began capturing images of Dinkinesh between Sept. 3–5, 2023, when the asteroid was 14 million miles away from the spacecraft. Despite its small size, Lucy utilized optical navigation to image Dinkinesh from a distance, enhancing preparations for the flyby.
“Dinkinesh really did live up to its name; this is marvelous,” said Hal Levison, Lucy principal investigator, Southwest Research Institute.
The name “Dink’inesh” is the Ethiopian name for the fossil Lucy, and it means “you are wonderful” in the Ethiopian Amharic language.
Researchers working on the spacecraft had suspected that Dinkinesh might be a binary pair because of the way its brightness changed with time. When the team downlinked additional images, captured in the minutes after the flyby, the companion asteroid was revealed to be a contact binary. “It is puzzling, to say the least,” said Levison. “I would have never expected a system that looks like this. In particular, I don’t understand why the two components of the satellite have similar sizes. This is going to be fun for the scientific community to figure out.”
“This is an awesome series of images,” said Tom Kennedy, a guidance and navigation engineer at Lockheed Martin in Colorado, in a news release. “They indicate that the terminal tracking system worked as intended, even when the universe presented us with a more difficult target than we expected.”
Detailed surface features of Dinkinesh were only resolved on the day of the flyby, during which Lucy, moving at a speed of 2.8 miles per second relative to Dinkinesh, captured 2 meters per pixel images with the panchromatic L’LORRI imager, 15 meters per pixel color images with the L’Ralph imager, and 24 meters per pixel near-infrared spectra and thermal measurements with the L’TES spectrometer. Post-flyby, Lucy’s L’LORRI instrument continued observing Dinkinesh for four days to analyze the asteroid’s light curve.
Research teams conducted visible light spectroscopy on Dinkinesh in November and December of 2022. The results revealed that Dinkinesh is categorized as an S-type asteroid, indicating a composition primarily composed of rocky silicates with limited metal content. Spectral analysis from the 10-meter Keck I telescope at Mauna Kea, Hawaii, specifically identified Dinkinesh as belonging to the Sq subclass of S-type asteroids. This classification is attributed to the presence of the 1 μm olivine and pyroxene spectral absorption band, a characteristic feature observed in Q-type asteroids.
Upcoming Missions
The next exciting deep space exploration mission out of the gate will be the Europa Clipper Mission, planned for launch on Oct. 10, 2024, with Jupiter orbit insertion in April 2030. The Europa Clipper mission aims to extensively study Jupiter’s moon Europa, analyzing whether subsurface regions might provide conditions conducive to life.
The Jupiter Icy Moons Explorer (Juice) spacecraft launched on April 14, 2023, by the European Space Agency to study Jupiter moons Ganymede, Callisto and Europa. These moons are believed to harbor substantial liquid water beneath their icy exteriors, suggesting the possibility of habitable conditions. Juice is set to enter orbit around Ganymede, in December 2034, coinciding with the operational phase of NASA’s Europa Clipper mission.