Lucy: NASA's mission to Jupiter's Trojans
Jupiter's swarms of Trojan asteroids may be remnants of the primordial material that formed the outer planets, and serve as time capsules from the birth of our Solar System more than 4 billion years ago. The Trojans orbit in two loose groups that orbit the Sun, with one group always ahead of Jupiter in its path, the other always behind. At these two Lagrange points the bodies are stabilized by the Sun and Jupiter in a gravitational balancing act. 1) 2)
Lucy is a Discovery class mission led by principal investigator Harold "Hal" Levison from SwRI (Southwest Research Institute) in Boulder, Colorado, who, with a team of scientists and engineers, will address key science questions about the solar system. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will provide overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space Systems in Denver will build the spacecraft. Instruments will be provided by Goddard, the JHU/APL ( Johns Hopkins University/ Applied Physics Laboratory) in Laurel, Maryland, and Arizona State University. Discovery missions are overseen by the Planetary Missions Program Office at NASA's Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Planetary Science Division.
Figure 1: During the course of its mission, Lucy will fly by six Jupiter Trojans. This time-lapsed animation shows the movements of the inner planets (Mercury, brown; Venus, white; Earth, blue; Mars, red), Jupiter (orange), and the two Trojan swarms (green) during the course of the Lucy mission [image credit: Astronomical Institute of CAS/Petr Scheirich (used with permission)]
These primitive bodies hold vital clues to deciphering the history of the solar system, and perhaps even the origins of life and organic material on Earth.
Lucy will be the first space mission to study the Trojans. The mission takes its name from the fossilized human ancestor (called “Lucy” by her discoverers) whose skeleton provided unique insight into humanity's evolution. Likewise, the Lucy mission will revolutionize our knowledge of planetary origins and the formation of the solar system.
Lucy will launch in October 2021 and, with boosts from Earth's gravity, will complete a 12-year journey to seven different asteroids — a Main Belt asteroid and six Trojans, the last two members of a “two-for-the-price-of-one” binary system. Lucy’s complex path will take it to both clusters of Trojans and give us our first close-up view of all three major types of bodies in the swarms (so-called C-, P- and D-types).
The dark-red P- and D-type Trojans resemble those found in the Kuiper Belt of icy bodies that extends beyond the orbit of Neptune. The C-types are found mostly in the outer parts of the Main Belt of asteroids, between Mars and Jupiter. All of the Trojans are thought to be abundant in dark carbon compounds. Below an insulating blanket of dust, they are probably rich in water and other volatile substances.
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. Lucy’s discoveries will open new insights into the origins of our Earth and ourselves.
Figure 2: This diagram illustrates Lucy's orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape. After launch in October 2021, Lucy has two close Earth flybys before encountering its Trojan targets. In the L4 cloud Lucy will fly by (3548) Eurybates (white), (15094) Polymele (pink), (11351) Leucus (red), and (21900) Orus (red) from 2027-2028. After diving past Earth again Lucy will visit the L5 cloud and encounter the (617) Patroclus-Menoetius binary (pink) in 2033. As a bonus, in 2025 on the way to the L4, Lucy flies by a small Main Belt asteroid, (52246) Donaldjohanson (white), named for the discoverer of the Lucy fossil. After flying by the Patroclus-Menoetius binary in 2033, Lucy will continue cycling between the two Trojan clouds every six years (image credit: Southwest Research Institute)
Some background: In January 2017, NASA selected a mission that will perform the first reconnaissance of the Trojans, a population of primitive asteroids orbiting in tandem with Jupiter. The Lucy mission will launch in 2021 to study six of these exciting worlds. 3)
“This is a unique opportunity,” said Dr. Harold F. Levison, Lucy principal investigator from SwRI (Southwest Research Institute) in Boulder, Colorado. “Because the Trojans are remnants of the primordial material that formed the outer planets, they hold vital clues to deciphering the history of the solar system. Lucy, like the human fossil for which it is named, will revolutionize the understanding of our origins.”
The Lucy spacecraft and a remote-sensing instrument suite will study the geology, surface composition, and bulk physical properties of these bodies at close range. The payload includes three complementary imaging and mapping instruments, including a color imaging and infrared mapping spectrometer from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, a high-resolution visible imager from the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, and a thermal infrared spectrometer from Arizona State University, Tempe. In addition, Lucy will perform radio science investigations using its telecommunications system to determine the masses and densities of the Trojan targets.
“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,” said Dr. Catherine Olkin, the mission’s deputy principal investigator from SwRI.
“The Lucy mission is one of those rare moments where a single mission can have a major impact on our understanding of such fundamental questions,” added Dr. Keith Noll, Lucy project scientist from Goddard.
SwRI in Boulder, Colorado is the principal investigator institution and will lead the science investigation. NASA’s Goddard Space Flight Center, Greenbelt, Maryland will provide overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space Systems in Denver, Colorado will build the spacecraft.
Discovery Program class missions like these are relatively low-cost, their development capped at about $450 million. They are managed for NASA’s Planetary Science Division by the Planetary Missions Program Office at Marshall Space Flight Center in Huntsville, Alabama. The missions are designed and led by a principal investigator, who assembles a team of scientists and engineers, to address key science questions about the solar system.
Figure 3: Artist's rendition of the Lucy spacecraft at a Trojan asteroid (image credit: NASA)
The Lucy spacecraft will be over 13 m from tip to tip, but most of that is the huge solar panels (each over 6 meters) in diameter needed to power the spacecraft as it flies out to the orbit of Jupiter. All of the instruments, and the 2 m-high gain antenna needed to communicate with Earth, will be located on the much smaller spacecraft body. 4)
Figure 4: Illustration of the Lucy spacecraft (image credit: SwRI)
• April 19, 2021: On Jan. 9, 2020, NASA’s Lucy mission officially announced that it would be visiting not seven, but eight asteroids. As it turns out, Eurybates, one of the asteroids along Lucy’s path, has a small satellite. 5)
Figure 5: On Jan. 9, 2020, the Lucy Mission officially announced that it would be visiting not seven, but eight asteroids. As it turns out, Eurybates, one of the asteroids along Lucy’s path, has a small satellite. Shortly after the Lucy team discovered the satellite, both it and Eurybates moved behind the Sun, preventing the team from observing it further. However, the asteroids emerged from behind the Sun in July 2020, and since then, the Lucy team has been able to observe the satellite with Hubble on multiple occasions, allowing the team to precisely define the satellite’s orbit and allowing the little satellite to finally get an official name – Queta (video credit: NASA Goddard Space Flight Center)
- Though searching for satellites is one of the mission’s central goals, finding these tiny worlds before Lucy is launched gives the team the opportunity to investigate their orbits and plan for more detailed follow-up observations with the spacecraft. Without searching for these asteroid companions before launch, Lucy could also run the risk of encountering an unexpected binary pair. Seeing two asteroids when the spacecraft is expecting only one could confuse its autonomous tracking system.
- Fortunately, the Lucy science team is already familiar with the perfect tool to use. “One of the ways that you can try to look for satellites is to use Hubble. And that’s something that I’ve done a lot with the Kuiper Belt,” says Keith Noll, the mission’s project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and one of the discoverers of Eurybates’ satellite. “We know more than 100 binaries in the Kuiper Belt, and the vast majority of those were found with Hubble.”
Figure 6: Hubble images of Eurybates and its satellite on Jan. 3, 2020, when the satellite was visible (circled in green), and on Dec. 11, 2019, when the satellite was too close to Eurybates to be seen (image credits: NASA/Hubble, K. Noll/SwRI)
- And understandably so. The orbiting telescope, 13.3 meters long, which has a primary mirror with a diameter of 2.4 meters, is unencumbered by the normal blurring effects of Earth’s atmosphere, since it resides comfortably above the atmosphere. Though some of the larger earthbound telescopes are sometimes able to observe the heavens with similar clarity, Hubble can detect a small, dim satellite orbiting very close to a larger, brighter asteroid that a telescope on Earth might miss.
- To know where to look for satellites, the science team had to calculate the Hill spheres of the asteroids they wanted to examine. The Hill sphere is an imaginary sphere around a body, inside of which the body has the dominant gravitational influence. In other words, all stable satellites of a body orbit within its Hill sphere. Earth’s Hill sphere, for instance, has a radius of nearly 1.5 million km (930,000 miles), and the Moon orbits safely inside at approximately 380,000 km (236,000 miles).
- Noll’s team submitted a proposal to use Hubble to search for satellites and made their first round of observations in the fall of 2018. They then scoured the images for evidence of satellites. This process is difficult, since raw images from Hubble can be messy. “It’s got a lot of bumps and blobs, it’s not a clean thing,” remarks Noll. For instance, raw images of bright objects often show diffraction spikes, the bright X-shapes that resemble cartoon four-pointed stars. Hubble’s cameras are also susceptible to cosmic rays (particles traveling at close to the speed of light) which can appear as bright dots on the images. “So when you look at [the images], you say, ‘Well, is that blob a satellite, or is it just part of… the way that the light gets scattered from the entire optical assembly throughout the telescope?’” Except for a brief false alarm when it appeared that another Lucy target, Orus, might be a binary, the team saw no new evidence of satellites.
- That is, until November 2019. The night before a large science team meeting, Noll was preparing a presentation on searching for satellites. In looking for photos to demonstrate the difficulties of distinguishing between satellites and other bright blobs, he came across one of his team’s Hubble photos from Sept. 12, 2018. After experimenting with the brightness and contrast, he saw one peculiar bright spot near Eurybates. “I said, ‘Gosh, that one really looks like what I would expect a satellite to look like.’” Realizing it was getting late, he circled the object and finished making the presentation. In his talk the next day, he pointed out the object’s striking resemblance to a satellite. In the audience was Mike Brown, one of the mission’s science co-investigators. Brown interrupted to ask Noll if he had looked at the data from the other observation on Sept. 14, but Noll admitted that he had not had a chance yet. According to Noll, before he finished presenting, Brown examined the data from Sept. 14 and exclaimed, “I see it there too!”
- Everyone crowded around Brown’s laptop. Had they actually discovered a satellite of Eurybates? The team noticed that as they compared the two photos, the object appeared to have moved a little, like a satellite might. A check revealed that the object’s observed positions fit many possible orbits. From a planetary dynamics perspective, it also made sense that Eurybates might have a satellite. Eurybates is one of a massive set of fragments created by the same asteroid collision, so the idea that one of these fragments might be orbiting Eurybates is not far-fetched. These were all steps in the right direction, but not conclusive evidence. The team had only two observations so far, and according to Noll, “You never really believe anything until you’ve seen it the third time, so we had to get more data.” They submitted an urgent proposal to use Hubble again, which was approved quickly enough that the team was able to get their observations about a month later. They requested 12 chances to observe the satellite, but they were granted three. If they could see the satellite again on at least one of the three, they would be given the other nine.
- Their first chance was on Dec. 11. The satellite was a no-show. The team wasn’t worried – yet – because they knew there was a good chance that it might be simply too close to Eurybates, and lost in the glare. They tried a second time on Dec. 21, but much to their consternation, the shy little rock was nowhere to be found. The team began to doubt that their so-called satellite even existed. “Maybe we’re just kidding ourselves. Maybe it’s not real,” Noll remembers thinking.
- Finally, on Jan. 3, they found it. The tiny, dim satellite was clearly visible on the new images. As they’d suspected, in the previous two observations it was too close to Eurybates (which is over 6,000 times brighter than its companion) to be seen. The difference in brightness suggests that the satellite is probably less than 1 km in diameter, puny compared to Eurybates (64 km).
- Shortly after the Lucy team discovered the satellite, both it and Eurybates moved behind the Sun, preventing the team from observing it further. However, the asteroids emerged from behind the Sun in July 2020, and since then, the Lucy team has been able to observe the satellite with Hubble on multiple occasions, allowing the team to precisely define the satellite’s orbit and allowing the little satellite to finally get an official name – Queta.
Figure 7: The Lucy science team examines images of the satellite. Co-discoverer Keith Noll and Mike Brown sit opposite each other in front of the screen as other science team members look on (image credit: SwRI, J. Spencer)
- Queta is the first Trojan asteroid named under a newly revised naming convention for Trojan asteroids. Though the Trojans were previously only named for heroes from Homer’s Iliad, smaller Trojans are now named after Olympic and Paralympic athletes, in recognition of these modern day heroes. Queta is named in honor of Mexican track and field athlete Norma Enriqueta “Queta” Basilio Sotelo. At the 1968 Summer Olympics, she became the first woman in history to light the Olympic cauldron. The name “Queta” was selected for Eurybates’ satellite because Basilio’s role is similar to that of Eurybates, a Greek herald. In ancient Greece, heralds were messengers in the service of kings or governments, an occupation that sometimes involved running long distances. According to the ancient Greek historian Herodotus, a herald named Pheidippides ran 260 km from Athens to Sparta to request the Spartans’ aid in the Battle of Marathon. (It is from this legend that we get the word “marathon.”) Heralds were also tasked with announcing the start of the ancient Olympic Games, similar to how the torch ceremony announces the start of the modern Olympic Games. Though the torch ceremony was not a part of the ancient Olympics, it is inspired by an ancient Greek tradition called the lampadedromia, a relay race in which the runners pass a torch while trying to keep its sacred fire burning. Several other members of the Eurybates family, a group of asteroids that are actually fragments formed by the same collision, have been named after heroes of the 1968 Olympic and Paralympic Games. As a fellow trailblazer of the 1968 Games, Queta fits right in.
Figure 8: Illustration of the Lucy Trojan asteroid target Eurybates and its satellite, Queta (image credit: NASA's Goddard Space Flight Center)
• February 9, 2021: With less than a year to launch, NASA’s Lucy mission’s third and final scientific instrument has been integrated onto the spacecraft. 6)
- The spacecraft, which will be the first to explore the Trojan asteroids — a population of small bodies that share an orbit with Jupiter — is in the final stages of the assembly process. Just five months ago, at the beginning of the Assembly, Testing and Launch operations (ATLO) process, the components of the Lucy spacecraft were being built all over the country. Today, a nearly assembled spacecraft sits in the high bay in Lockheed Martin Space in Littleton, Colorado.
- “A bit over a year and a half ago, I was excited to hold the first small pieces of metal that were destined to travel to the Trojan asteroids,” says Hal Levison, principal investigator from the Southwest Research Institute. “Now there is an actual spacecraft, nearly ready to go. It is incredible.”
- The final instrument, L’Ralph, was built by NASA’s Goddard Space Center in Greenbelt, Maryland, and was received at Lockheed Martin on January 21 and integrated on to the spacecraft on January 26. L’Ralph is the most complicated instrument that will fly on Lucy, as it is actually two instruments in one. The Multispectral Visible Imaging Camera (MVIC), will take visible light color images of the Trojan asteroids. The Linear Etalon Imaging Spectral Array (LEISA), will collect infrared spectra of the asteroids. Both of these components will work together to allow Lucy to determine the composition of the Trojan asteroids and provide insight into the early history of our solar system.
- The L’Ralph instrument experienced significant COVID-19 related delays, particularly when construction had to be halted when Goddard was placed under stage 4 COVID restrictions in April of last year. However, both the L’Ralph team at Goddard and the ATLO team at Lockheed Martin rose to the challenge and developed a new schedule that allowed everyone to work safely while keeping the spacecraft on track for its originally planned October 16, 2021 launch.
- “The L’Ralph team has done an outstanding job to deliver a fantastic instrument,” says Dennis Reuter, L’Ralph instrument principal investigator, from Goddard. “Doing what they did under normal conditions would have been remarkable. Doing it under the actual conditions that had to be dealt with is amazing.”
Figure 9: Two engineers work on L’Ralph, the most complicated instrument that will fly on the Lucy mission to Jupiter's Trojan asteroids. It is actually two instruments in one. The Multispectral Visible Imaging Camera (MVIC), will take visible light color images. The Linear Etalon Imaging Spectral Array (LEISA), will collect infrared spectra (image credits: NASA/Goddard/Barbara Lambert/Desiree Stover)
- L’Ralph has been installed on Lucy’s Instrument Pointing Platform. This platform provides the spacecraft significant flexibility during the encounters — the instruments can point at the Trojan asteroids during the high-speed flybys while the high gain antenna remains pointed at Earth — as well as carrying out fine adjustments and out-of-plane pointing to get the best data possible on these elusive objects.
- Lucy’s other two scientific instruments, L’TES and L’LORRI, designed and built at Arizona State University, and Johns Hopkins Applied Physics Laboratory, respectively, as well as the two Terminal Tracking Cameras have already been installed on the platform. Now that L’Ralph is installed, the platform itself will be installed onto the spacecraft bus — making Lucy one step closer to ready for her 12-year-long journey to the Trojans.
- “Lucy ATLO has been tremendously successful and having L’Ralph delivered and integrated onto the Instrument Pointing Platform is a great start to the new year,” said Donya Douglas-Bradshaw, mission project manager from Goddard.
- Southwest Research Institute’s Hal Levison and Cathy Olkin are the principal investigator and deputy principal investigator of the Lucy Mission. Goddard provides overall mission management, systems engineering and safety and mission assurance. Lockheed Martin Space is building the spacecraft. Lucy is the 13th mission in NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Discovery Program for the agency’s Science Mission Directorate in Washington, D.C.
• January 5, 2021: In addition to L’TES, Lucy’s High Gain Antenna, which will enable spacecraft communication with the Earth for navigation and data collection, as well as precise measurement of the masses of the Trojan asteroids, was recently installed. It joined L’LORRI, Lucy’s highest resolution camera, built by the Johns Hopkins Applied Physics Laboratory, which was installed in early November. Lucy’s remaining scientific instrument, L’Ralph, the mission’s color imaging camera and infrared spectrometer, is scheduled to be delivered in early 2021 (Ref. 15).
- Southwest Research Institute’s Hal Levison and Cathy Olkin are the principal investigator and deputy principal investigator of the Lucy Mission. NASA’s Goddard Space Flight Center provides overall mission management, systems engineering and safety and mission assurance. Lockheed Martin Space is building the spacecraft. Lucy is the 13th mission in NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Discovery Program for the agency’s Science Mission Directorate in Washington, D.C.
• August 28, 2020: NASA’s first mission to explore the Trojan asteroids is one step closer to launch. The Discovery Program’s Lucy mission passed a critical milestone and is officially authorized to transition to its next phase. 7)
- NASA’s first mission to explore the Trojan asteroids is one step closer to launch. The Discovery Program’s Lucy mission passed a critical milestone and is officially authorized to transition to its next phase.
- This major decision was made after a series of independent reviews of the status of the spacecraft, instruments, schedule and budget. The milestone, known as Key Decision Point-D (KDP-D), represents the official transition from the mission’s development stage to delivery of components, testing, assembly and integration leading to launch. During this part of the mission’s life cycle, known as Phase D, the spacecraft bus (the structure that will carry the science instruments) is completed, the instruments are integrated into the spacecraft and tested, and the spacecraft is shipped to NASA's Kennedy Space Center in Florida for integration with the launch vehicle.
- “Each phase of the mission is more exciting than the last,” says Lucy Principal Investigator Hal Levison of Southwest Research Institute in Boulder, CO. “While, of course, Lucy still has several years and a few billion miles to go before we reach our real goal – exploring the never-before-seen Trojan asteroids – seeing this spacecraft come together is just incredible.”
- Assembly, Testing and Launch Operations (ATLO) began on schedule last week at Lockheed Martin Space in Littleton, Colorado, despite many unforeseen challenges related to the coronavirus pandemic. The schedule was revised to allow for later integration of components that were delayed due to COVID-19 restrictions.
- “This team has been truly incredible,” says Lucy Project Manager Donya Douglas-Bradshaw, from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Building a spacecraft is never easy, but seeing the team persevere through all of the challenges that they have encountered is inspiring. We now have a spacecraft structure in the Lockheed Martin high bay and a team ready to install the instruments and components.”
- The oxidizer tank has already been integrated with the spacecraft, and the instrument integration starts in October. All spacecraft assembly and testing will be completed by the end of July 2021, when the spacecraft will be shipped to Kennedy Space Center in Cape Canaveral, Florida in preparation for the launch window opening on October 16, 2021. After launch, Lucy will have a long cruise phase before it arrives at its first target. Lucy is flying out to the distance of Jupiter to make close fly-bys past a record-breaking number of asteroids, encountering the first of eight targets in April 2025 and the final binary pair of asteroids in March 2033.
- The next major milestone is the Mission Operation Review, scheduled in October 2020, which assesses the project's operational readiness and its progress towards launch.
- Southwest Research Institute in Boulder, Colorado, is the principal investigator institution for Lucy. NASA Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space near Denver is building the spacecraft and will perform spacecraft flight operations. Instruments will be provided by Goddard, the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and Arizona State University.
Figure 10: Engineers install Lucy’s oxygen propellant tank into the spacecraft structure in a high-bay clean room at Lockheed Martin (image credit: Lockheed Martin Space)
• August 3, 2020: Last week marked the completion of a major milestone on the path to spacecraft assembly, test, and launch operations for NASA’s Lucy mission. 8)
- The Systems Integration Review ensured segments, components, and subsystems, scientific instrumentation, electrical and communication systems, and navigation systems are on schedule to be integrated into the system. It confirmed that facilities, support personnel, and plans and procedures are on schedule to support integration.
- The four-day meeting took place from July 27-30. On July 31, the standing review board briefed the team on the results. Due to Covid-19, the review occurred virtually.
Figure 11: This video highlights the Lucy mission's four main science objectives, and the instruments aboard the spacecraft that will be utilized for the data collection (video credit: NASA/GSFC/Scientific Visualization Studio)
- In order to keep the team safe during the pandemic, NASA and the partner institutions delayed construction on some of the instruments and components. The Lucy assembly, test and launch operations (ATLO) team developed a new schedule to allow the team to reorder the assembly and testing timeline to give components and subsystems the flexibility they need and still get the spacecraft ready for an on-schedule launch in October 2021.
- "No one anticipated that we would be building a spacecraft under these circumstances," said Lucy Principal Investigator, Hal Levison, "but I once again have been impressed by this team's creativity and resiliency to overcome any challenge placed before them."
- Successful completion of this System Integration Review means that the project can proceed with assembling and testing the spacecraft in preparations for launch. The spacecraft is on track to begin ATLO next month at the Lockheed Martin Space Systems facilities in Littleton.
- Another upcoming milestone is the Key Decision Point-D (KDP-D), which occurs after the project has completed a series of independent reviews that cover the technical health, schedule and cost of the project. Lucy’s KDP-D is currently scheduled for late August of this year.
- Lucy will be the first space mission to study the Trojan asteroids, a population of small bodies orbiting the Sun “leading” and “trailing” Jupiter, at the same distance from the Sun as the gas giant. With flyby encounters past eight different asteroids – one in the Main Asteroid Belt and seven in the Trojan swarms, Lucy will be the first space mission in history to explore so many different destinations in independent orbits around our Sun.
- SwRI (Southwest Research Institute) in Boulder, Colorado, is the principal investigator institution for Lucy. NASA Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space Systems in Denver is building the spacecraft.
• January 9, 2020: NASA’s Lucy mission team is seeing double after discovering that Eurybates, the asteroid the spacecraft has targeted for flyby in 2027, has a small satellite. This “bonus” science exploration opportunity for the project was discovered using images taken by the Hubble Space Telescope’s Wide Field Camera 3 in September 2018, December 2019, and January 2020. 9)
- Launching in October 2021, Lucy will be the first space mission to study the Trojan asteroids, a population of small bodies orbiting the Sun “leading” and “trailing” Jupiter, at the same distance from the Sun as the gas giant. With flyby encounters past seven different asteroids – one in the Main Asteroid Belt and six in the Trojans, Lucy will be the first space mission in history to explore so many different destinations in independent orbits around our Sun.
- “This newly discovered satellite is more than 6,000 times fainter than Eurybates, implying a diameter less than 1 km,” said Southwest Research Institute’s Hal Levison, principal investigator of the mission. “If this estimate proves to be correct, it will be among the smallest asteroids visited.”
- Eurybates was first observed with Hubble in a search for small satellites in 2018, but it wasn’t until this past November when a Lucy team member noticed something in the data indicating a possible satellite.
- “We asked for more Hubble time to confirm, and they gave us three tries,” said Keith Noll, Lucy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a co-discoverer of the satellite.
- The team was quick to make the first set of confirmation observations in December and early January. The possible satellite was hard to see and moving on an unknown orbit around the much brighter Eurybates. There was no guarantee that it would be visible in the new images. “In the first two observations in December we didn’t see anything, so we began to think we might be unlucky. But on the third orbit, there it was,” said Noll.
- The team is working with Hubble schedulers to decide when to make the next observations after Eurybates becomes observable again. Due to the orbits of Earth and Eurybates, and because Hubble cannot be pointed toward the Sun, further observations are not possible until June. In the meantime, the team is using current observation data to study the satellite’s orbit around the asteroid, which will help scientists determine the best times for observations.
- While there is no impact to the spacecraft architecture or schedule, the project team is carefully planning how to safely examine the new satellite while ensuring the mission’s requirement to study Eurybates is fully met.
- Trojan asteroids have been trapped on orbits associated with the stable Lagrange Points for billions of years due to the combined gravitational influences of the Sun and Jupiter. Lucy will explore the diversity of these ancient leftover building blocks of the giant planets and will open new insights into the origins of our planet and the solar system.
- “There are only a handful of known Trojan asteroids with satellites, and the presence of a satellite is particularly interesting for Eurybates,” said Thomas Statler, Lucy Program Scientist at NASA Headquarters in Washington. “It’s the largest member of the only confirmed Trojan collisional family – roughly 100 asteroids all traceable to, and probably fragments from, the same collision.”
- The opportunity to study a prospective collisional satellite at close range will help our fundamental understanding of collisions, which Statler says may be responsible for the formation of satellites in other small body populations.
- Southwest Research Institute in Boulder, Colorado, is the principal investigator institution for Lucy. Goddard provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space Systems in Denver is building the spacecraft.
- Discovery Program class missions like Lucy are relatively low-cost, with development capped at approximately $450 million. They are managed for NASA’s Planetary Science Division by the Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama. The missions are led by a principal investigator who assembles a team of scientists and engineers to design and conduct the mission to address key science questions about the solar system.
• October 21, 2019: NASA’s Lucy mission successfully completed its Critical Design Review on Oct. 18. During this review, Lucy team members presented the completed mission design, demonstrating that the team has met all the technical challenges of the mission and is ready to begin building hardware. After the review completion, NASA's independent review board provided a green light for proceeding into the fabrication/manufacturing stage of the mission. 10)
- The Lucy Critical Design Review began on Oct. 15 at Lockheed Martin in Littleton, Colorado. This major mission milestone marks the culmination of months of reviews of all of the mission systems and subsystems. Over four days, the independent review board, comprised of reviewers from NASA and several external organizations, heard presentations on all aspects of the mission design. All aspects of the mission were addressed, including the Lucy spacecraft and its instrument payload, system-level test plans for flight hardware and software, systems engineering, mission assurance, the ground system, and science.
Figure 12: Beyond the asteroid belt are "fossils of planet formation" known as the Trojan asteroids. These primitive bodies share Jupiter's orbit in two vast swarms, and may hold clues to the formation and evolution of our solar system. NASA is preparing to explore the Trojan asteroids for the first time with a mission called Lucy (video credit: NASA's Goddard Space Flight Center)
- "This is a very exciting time for us because we are moving beyond the design phase and a really starting to build the spacecraft, said Hal Levison, Lucy principal investigator from Southwest Research Institute in Boulder, Colorado. “It is finally becoming real!"
- Lucy will be the first space mission to study the Trojan asteroids, which orbit the Sun at a distance of Jupiter. The mission will launch in October 2021. With boosts from Earth's gravity, the spacecraft will complete a 12-year journey to seven different asteroids — a Main Belt asteroid and six Trojan asteroids.
- “I am constantly amazed at the dedication and diversity of skills that our team brings to this project," said Keith Noll, Lucy project scientist from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. ”Day by day the mission comes into clearer focus and the mission critical design review is the latest milestone in our journey to launch just two years from now.”
• February 1, 2019: NASA has selected United Launch Alliance’s Atlas 5 rocket to dispatch the Lucy spacecraft on a mission from Cape Canaveral in October 2021 to fly by seven unexplored asteroids, including six objects locked in orbits leading and trailing Jupiter, where scientists expect swarms of miniature worlds could hold clues about the formation of the solar system. 11)
• January 5, 2017: Lockheed Martin has been selected to design, build and operate the spacecraft for NASA's Lucy mission. One of NASA's two new Discovery Program missions, Lucy will perform the first reconnaissance of the Jupiter Trojan asteroids orbiting the sun in tandem with the gas giant. The Lucy spacecraft will launch in 2021 to study six of these exciting worlds. 12)
Launch: The Lucy mission will be launched in October 2021. NASA has selected United Launch Services LLC (ULS) of Centennial, Colorado, to provide launch services for the agency’s first-ever mission to explore Trojan asteroids. The launch is on an an Atlas V 401 rocket from Launch Complex 41 at Cape Canaveral Air Force Station in Florida. With boosts from Earth’s gravity, the spacecraft will embark on a 12-year journey to study primitive asteroids orbiting the Sun in tandem with Jupiter. 13)
In 2025 it will fly by the inner main-belt asteroid 52246 Donaldjohanson, which was named for the discoverer of the Lucy hominin fossil. In 2027 it will arrive at the L4 Trojan cloud (a group of asteroids that orbits about 60° ahead of Jupiter), where it will fly by four Trojans, 3548 Eurybates, 15094 Polymele, 11351 Leucus, and 21900 Orus. After these flybys, Lucy will return to the vicinity of the Earth whereupon it will receive a gravity assist to take it to the L5 Trojan cloud (which trails about 60° behind Jupiter), where it will visit the binary Trojan 617 Patroclus with its satellite Menoetius in 2033.
Table 1: Lucy targets with their flyby dates include 14)
Sensor complement (L' Ralph, L'LORRI, L' TES, T2CAM)
Lucy’s instrument platform will carry four instruments for remote-sensing science.
L’Ralph is Lucy's color visible imager (the Multi-spectral Visible Imaging Camera, MVIC, 0.4-0.85 µm) and infrared imaging spectrometer (Linear Etalon Imaging Spectral Array, LEISA, 1-3.6 µm). LEISA will allow us to look for the absorption lines that serve as the fingerprints for different silicates, ices and organics that likely will be on the surface of the Trojan asteroids. MVIC will take color images of the Trojan asteroid targets, and help determine how active they are.
L' LORRI (LOng Range Reconnaissance Imager)
L' LORRI is the high spatial resolution visible imager. It is panchromatic, covering the wavelengths 0.35-0.85 µm. This camera will provide the most detailed images of the surface of the Trojans.
L' TES (Thermal Emission Spectrometer)
L' TES is similar to instruments flying on OSIRIS-REx and Mars Global Surveyor. This infrared spectrometer (6-75 µm) will allow the Lucy team to learn much more about the properties of the Trojans such as their thermal inertia, how well the bodies retain heat, which teaches us about the composition and structure of material on the surface of the asteroids.
January 2021: NASA’s Lucy mission is one step closer to launch as L’TES, the Lucy Thermal Emission Spectrometer, has been successfully integrated on to the spacecraft. 15)
“Having two of the three instruments integrated onto the spacecraft is an exciting milestone,” said Donya Douglas-Bradshaw, Lucy project manager from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The L’TES team is to be commended for their true dedication and determination.”
Lucy will be the first space mission to study the Trojan asteroids, leftover building blocks of the Solar System’s outer planets orbiting the Sun at the distance of Jupiter. The mission takes its name from the fossilized human ancestor (called “Lucy” by her discoverers) whose skeleton provided unique insight into humanity’s evolution. Likewise, the Lucy mission will revolutionize our knowledge of planetary origins and the birth of our solar system more than 4 billion years ago.
L’TES, developed by a team at Arizona State University (ASU), is effectively a remote thermometer. It will measure the far infrared energy emitted by the Trojan asteroids as the Lucy spacecraft flies by an unprecedented seven of these objects during this first ever mission to this population.
The instrument arrived at Lockheed Martin Space on December 13 and was successfully integrated on to the spacecraft on December 16. By measuring the Trojan asteroids’ temperatures, L’TES will provide the team with important information on the material properties of the surfaces. As the spacecraft will not be able to touch down on the asteroids during these high speed encounters, this instrument will allow the team to infer whether the surface material is loose, like sand, or consolidated, like rocks. In addition, L’TES will collect spectral information using thermal infrared observations in the wavelength range from 4 to 50 µm.
“The L’TES team has used our experienced designing, manufacturing, and operating similar thermal emission spectrometers on other missions such as OSIRIS-REx and the Mars Global Surveyor as we built this instrument,” said Instrument Principal Investigator, Phil Christensen. “Each instrument has its own challenges, but based on our experience we expect L’TES to give us excellent data, as well as likely some surprises, about these enigmatic objects.”
Despite the challenges surrounding the COVID-19 pandemics, Lucy is on schedule to launch in October 2021 as originally planned.
“I am constantly impressed by the agility and flexibility of this team to handle any challenges set before them,” said mission Principal Investigator, Hal Levison of Southwest Research Institute. “Just five years ago this mission was an idea on paper, and now we have many major components of the spacecraft and payload assembled, tested, and ready to go.”
Figure 13: Photo of the L'TES instrument in the cleanroom at Arizona State University (image credit: NASA/ASU)
T2CAM (Terminal Tracking Camera)
Additionally, Lucy will be able to use its High Gain Antenna to determine the masses of the targets using the Doppler shift of the radio signal. Lucy will be able to use its T2CAM to take wide-field images of the asteroids to better constrain the asteroids shapes.
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3) Nancy Neal Jones, ”NASA Selects Mission to Study Jupiter’s Trojan Asteroids,” NASA, 4 January 2017, URL: https://www.nasa.gov/feature/goddard/2017/nasa-selects-mission-to-study-jupiter-s-trojan-asteroids
David Dezell Turner, ”Hide and Seek – How NASA’s Lucy
Mission Team Discovered Eurybates' Satellite,” NASA Feature, 19
April 2021, URL: https://www.nasa.gov/feature/goddard/2021
”NASA’s First Mission to the Trojan Asteroids Installs its
Final Scientific Instrument,” NASA Feature, 9 February 2021, URL:
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”NASA’s Lucy Mission Confirms Discovery of Eurybates
Satellite,” NASA Solar System and Beyond, 9 January 20220, URL: https://www.nasa.gov/feature/
10) ”NASA’s Lucy Mission Clears Critical Milestone,” NASA, 21 October 2019, URL: https://www.nasa.gov/feature/goddard/2019/lucy-mission-clears-critical-milestone
Stephen Clark, ”ULA wins contract to launch NASA’s Lucy
mission to visit unexplored asteroids,” Spaceflight Now, 1
February 2019, URL: https://spaceflightnow.com/2019/02/01
”Lockheed Martin to Build NASA's Lucy Spacecraft, a Mission to
Trojan Asteroids,” Lockheed Martin, 5 January 2017, URL: https://news.lockheedmartin.com/
13) ”NASA Awards Launch Services Contract for Lucy Mission,” NASA Contract Release C19-001, 31 January 2019, URL: https://www.nasa.gov/press-release/
”NASA’s First Mission to the Trojan Asteroids Integrates
its Second Scientific Instrument,” NASA Feature, 5 January 2021,
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).