With a long and accomplished career as prelude, Richard Binzel is just getting started—with an impressive four new NASA missions set to explore our asteroid neighbors.
Richard Binzel, Professor of Planetary Sciences and Margaret MacVicar Faculty Fellow in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), is one of the world’s leading scientists in the study of asteroids and Pluto. As the inventor of the Torino Scale, a method for categorizing the impact hazard associated with near-Earth objects such as asteroids and comets, his ongoing telescopic research includes the spectral characterization of asteroids posing a potential hazard to Earth as well as those that may be most easily reachable by future robotic and human missions.
Binzel’s Pluto-mapping efforts in the 1980s revealed a diverse surface entreating for exploration, finally achieved in 2015 as a co-investigator on NASA’s hugely successful New Horizons mission. However, with Pluto now firmly in the rear-view mirror—so to speak, although Binzel and the New Horizons team remain engaged in work to prepare for an encounter with a secondary Kuiper Belt target—this latter-day one-man Lewis and Clark remains occupied with a dizzying array of solar system exploration.
Bound for Bennu
NASA’s OSIRIS-REx spacecraft blasted off from Cape Canaveral in Florida in September 2016 carrying MIT’s first student-built science instrument bound for interplanetary space. The SUV-sized spacecraft is hurtling towards the asteroid Bennu carrying MIT’s innovative REgolith X-ray Imaging Spectrograph (REXIS). It took five years and a great deal of ingenuity and fortitude from Binzel and his ever-changing roster of around 60 students from MIT and Harvard to overcome many technical setbacks and perfect their instrument in time for launch. REXIS will analyze the interaction of the Sun’s X-rays with the soil, or regolith, to identify chemical elements on Bennu’s surface. The objective of the OSIRIS-REx mission is to alight briefly—“like a mosquito”—on the surface of Bennu to suck up a dust sample that will be sealed in a capsule and dropped back to Earth in 2023 for analysis. A mission goal for REXIS is to help determine the best locations for the robotic arm to reach out and grab its sample.
NASA technicians carefully mount MIT’s student-designed REXIS instrument to the OSIRIS-REx spacecraft, which took off for asteroid Bennu in 2016. Image credits: NASA
Asteroids are remnants from the formation of our solar system more than 4.5 billion years ago and, based on telescopic measurements by Binzel and other astronomers, asteroids like Bennu are thought to have been a source of the water and organic molecules for the early Earth and other planetary bodies. NASA is optimistic that precise analyses of the asteroid sample from Bennu will yield results far beyond what can be achieved by spacecraft-based instruments or by studying meteorites.
Psyched About Psyche
It was again Binzel’s asteroid composition expertise that brought him onto the roster of the Psyche mission announced in January 2017. Led by principal investigator Lindy Elkins-Tanton ’87, SM ’87, PhD ’02—former EAPS faculty member and now director of Arizona State University’s School of Earth and Space Exploration (SESE)—the mission to visit a giant metal asteroid is expected to launch in 2023, arriving at the asteroid in 2030, where the spacecraft will spend 20 months in orbit, mapping and studying its properties.
16 Psyche, an asteroid orbiting the Sun between Mars and Jupiter, is made almost entirely of nickel-iron metal. As such, it offers a unique look into the violent collisions that created Earth and the other terrestrial planets. Binzel performed a detailed telescopic analysis in 1994 showing all sides of Psyche were stripped bare of its overlying crust, literally opening the window for a future investigation.
“Visiting the asteroid Psyche will be the first time humans will ever be able to see a planetary core,” says Elkins-Tanton. “The Psyche mission will help us gain invaluable insights into the metal interior of all rocky planets in our solar system, including Earth.”
“This is an opportunity to explore a new type of world—not one of rock or ice, but of metal,” says Elkins-Tanton. “[The asteroid] 16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space.”
On the same day NASA revealed its selection of Psyche, a second mission involving Professor Binzel was also announced. The Lucy Mission, which will launch in 2021, is set to perform the first reconnaissance of the Trojans, a population of primitive asteroids orbiting in tandem with Jupiter. Binzel performed pathfinding observations on the shapes and spins of Trojan asteroids in the 1980s, noting, “I put my very first UROP student to work on these in 1989.” These exciting worlds are remnants of the primordial material that formed the outer planets, and therefore hold vital clues to deciphering the history of the solar system. Scientists hope that Lucy, like the human fossil for which the mission is named, will revolutionize the understanding of our origins.
The mission sees Binzel reunited with New Horizons co-investigator and EAPS alumna Catherine Olkin ’88, PhD ’96, who is serving as a deputy principal investigator for Lucy. “Understanding the causes of the differences between the Trojans will provide unique and critical knowledge of planetary origins, the source of volatiles and organics on the terrestrial planets, and the evolution of the planetary system as a whole,” says Olkin.
The Trojans orbit in two loose groups around the Sun, with one group always ahead of Jupiter in its path, the other always behind. At these two so-called Lagrange points, the bodies are stabilized by a gravitational balancing act between the Sun and Jupiter. Lucy’s complex path will take it to both clusters. Over 12 years, with boosts from Earth’s gravity, the spacecraft will journey to seven different asteroids in total—six Trojans and one from the Main Belt.
“No other space mission in history has been launched to as many different destinations in independent orbits around our Sun. Lucy will show us, for the first time, the diversity of the primordial bodies that built the planets, opening up new insights into the origins of our Earth and ourselves,” says Binzel.
Richard Binzel and graduate student Alissa Earle witness the first images transmitted back to Earth from Pluto during the historic New Horizons mission flyby. Image credit: NASA/Bill Ingalls/EPA
Apophis is Coming
On April 13, 2029, the asteroid Apophis will pass by Earth at approximately 1/10 the distance separating the Earth from the moon. This once-in-a-thousand-year event will provide planetary scientists with a direct experiment revealing how asteroid surface and interiors hold up to tidal stress. Binzel began studying the colors and composition of Apophis in 2006, research made possible thanks to MIT’s Magellan telescopes.
The asteroid Apophis is named after the Egyptian god of chaos and evil who was thwarted by the god Set sailing a solar boat. Like Set, the MIT SET Mission will be propelled by sunlight (though in this case solar electric propulsion) to meet Apophis where the spacecraft will characterize the asteroid inside and out before and after the Earth flyby event. Binzel gives the mission design credit to students who worked together in a joint class between EAPS and AeroAstro, with EAPS graduate student Alissa Earle working as the Chief Scientist.
Launching in August 2026, the six-year mission has three principle objectives: to understand the bulk physical properties of Apophis, determining internal structural changes on Earth flyby, and finally tracking the Yarkovsky Effect, the force on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. Perhaps surprisingly, the MIT student mission is the first significant attempt to take on Apophis, which is 350 meters across with a mass of 20 million metric tons.
Focusing on the surface properties and orbital characteristics of the asteroid are intended to help improve the scientific community’s understanding of asteroids as well as inform planetary defense strategies. Measuring the internal structure of Apophis before and after an Earth close encounter will allow for a better understanding of not only how asteroids are constructed, but also how tidal stresses affect them. And following Apophis to measure the thermal emissions and orbital characteristics, the components of the Yarkovsky Effect can be decoded, improving our ability to track and one day potentially change the course of a hazardous asteroid bound for Earth.
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