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Lucy in the Sky

Extended operations at multiple targets, as Dawn showed us, are possible with ion propulsion. But we still learn much from flybys, something New Horizons reminded us with its spectacular success at Pluto/Charon, and again reminds us as it closes on MU69. Likewise, a mission called Lucy will visit multiple objects, using traditional chemical propulsion with gravity assist to achieve flybys of seven different targets. The destination: Jupiter’s trojan asteroids. With launch scheduled for 2021, Lucy’s will study six Jupiter trojans and one asteroid in the Main Belt.

Image: Jupiter’s extensive trojan asteroids, divided into ‘Trojans’ and ‘Greeks’ in a nod to Homer, but all trojans nonetheless. Credit: “InnerSolarSystem-en” by Mdf at English Wikipedia – Transferred from en.wikipedia to Commons. Licensed under Public Domain via Commons.

The trojans are interesting bodies orbiting at the L4 and L5 Lagrange points 60° ahead and behind the gas giant. Jupiter’s trojans are the best known but the term is generic — Neptune has trojans, as does Mars, Uranus and even the Earth (2010 TK7). In fact, some Solar System moons themselves have trojans, as we saw recently when discussing Saturn’s moon Dione, which has the trojans Helene and Polydeuces. Saturn’s moon Tethys also has two trojans.

But as befits Jupiter’s massive size, it’s associated with over 6000 trojans already identified, and a larger population perhaps reaching as high as one million objects over a kilometer in diameter. 617 Patroclus is a particularly intriguing object, a D-type asteroid thought to have water ice in its interior. This object is actually a binary, with a moon named Menoetius slightly smaller than the primary. But we have C- and P- type asteroids in these Lagrange points as well, and Lucy will give us a view of each type as it makes its way into both clusters of Trojans.

The assumption is that the Jupiter trojans are remnants of primordial planet-building material, with clues to the Solar System’s formation and possibly the origins of organic material on Earth. While C-type asteroids are primarily found in the outer regions of the Main Belt, the darker P- and D-type objects have similarities to Kuiper Belt objects beyond the orbit of Neptune. Evidently abundant in dark carbon compounds, all are thought to be rich in volatiles.

Image: 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. Credits: Southwest Research Institute.

The Lucy mission has just passed the milestone known as Key Decision Point C, a confirmation review that authorizes continuation of the project into its development phase and sets its cost and schedule. This means as well that the confirmation review panel has approved the instrument suite, budget and risk factor analysis for the overall mission. Up next comes the Critical Design Review, which thoroughly vets all aspects of the system design.

Lucy, in other words, is well on its way, says principal investigator Hal Levison (SwRI):

“Up until now this mission has entirely been on paper. Now we have the go ahead to actually cut metal and start putting this spacecraft together.”

Emphasizing the connection with the origins of the Solar System and the possible delivery of organics to Earth, PI Levison named the mission after Lucy, the fossil remains of a three million year old hominid. But he’s enough of a Beatles fan to see a connection there as well, as noted in an older quote on the mission:

“These asteroids really are like diamonds in the sky in terms of their scientific value for understanding how the giant planets formed and the solar system evolved.”

Including imaging and mapping instruments — a color imaging and infrared mapping spectrometer, a high-resolution visible imager, and a thermal infrared spectrometer — the science instrument package is similar to what flew on New Horizons and OSIRIS-REx. Lucy should reach its first targets, the L4 trojans, in 2025, followed by a return to Earth and gravity assist there to move on to the L5 trojan cluster in 2033, The craft will also make a flyby of Main Belt asteroid 52246 Donaldjohanson, which was named for the discoverer of the Lucy fossil.


Comments on this entry are closed.

  • Alex Tolley November 12, 2018, 14:50

    Any information on the spacecraft specifications? E.g. what are the course correction engines – hydrazine? Solar array power output?
    Instruments seem to be those already flown. As LM is building the craft, there must be info on this somewhere, but I cannot seem to find any links.

    • Paul Gilster November 12, 2018, 15:26

      I’m having the same problem, but have some emails in that may help clarify things.

      • steven Torry Rappolee November 13, 2018, 15:18

        Please be sure to ask about extended missions, what objects are possible to be targeted?

  • Rob Flores November 12, 2018, 16:44

    This is fantastic. Among the unknowns about space colonization is what is an acceptable gravity to maintain human physical health. Hollowing out asteroids and spining them up is a viable fallback if it turns out that even Mars gravity is hazardous. Cataloging and characterizing them is vital. We need to see what the smallest (1km) ones are like and how common they are. Even if 15% gravity is ok for humans the raw materials will make the belt an important economic center soon after Mars is colonized.

    • Alex Tolley November 15, 2018, 13:19

      I’m skeptical about spinning up asteroids for gravity as this requires ensuring the asteroid is fully fused rock and has no structural weakness that could cause a blowout. It also requires a full reworking of the asteroid at the outset. Instead, why not hollow it out slowly, adding membranes to hold in an atmosphere and have carousels to provide the g forces? This is an incremental approach than would eventually become an O’Neill habit of preferred configuration with asteroidal “slag” material as the radiation shield. This will be more structurally sound, yet have the same benefits when complete of a hollowed out, spinning asteroid. I would go for a carbonaceous asteroid for the carbon needed for the structure and biomass, as well as the accompanying volatiles.

      Where we agree is that there is more scope to tailor the habitat to human needs than any arbitrary planetary or moon surface. The ability to fully utilize the asteroids using this approach would indeed create far more habit for humans and life than the paltry collection of planetary surfaces, even if covered in mile high buildings. The ease of quarantining ensures no possible “global” pandemic or diseases, as well as a wider diversity of polities.

      By all means colonize Mars if desired, but perhaps the main thrust of our expansion should be to use the more accessible resources of the solar system for habitation.

      • Rob Flores November 15, 2018, 22:11

        To save on mass transfer costs, an insitu process wherein
        the asteroids own material can be use to create a carousel, and
        yes eventually these carousels could be duplicated adjacently to the original one, and so on… until a great percentage of the asteroid is carousel living space. I am not sure I would want full conversion to oneill habitat, because you are in hazard zone (belt) and the extra layers of rock are a good protection.

  • AlexT November 13, 2018, 2:44

    These asteroids really are like diamonds in the sky

    I suppose that word – “diamonds” is the key word to explain why this project exists. This explains also increased interest to asteroids exploration, that we can see in present time.
    The new – space “gold fever” ,has just began.

  • Michael C. Fidler November 13, 2018, 10:25

    Interesting that this is like the sailing ships of old using the currents of the oceans to cross great distances. The interplanetary superhighway of the L4 to L5 sounds similar to the strange attractors of chaos theory. Just imagine in 200 years planet size dyson spheres, Gerard K. O’Neill L5 tubes and Niven ringworld’s in those locations with giant cruise ships sailing between L4 to L5. With all that material easily available in the asteroids belt to make dream vacation islands enroute…

  • ljk November 13, 2018, 10:45

    Jason Davis

    November 8, 2018

    Here’s (almost) everything you need to know about Israel’s Moon lander

    An Israeli spacecraft is gearing up for a 2019 Moon mission that features unique partnerships, investigation of the Moon’s origin, and closure for an 11-year-old contest designed to spur commercial lunar activities.

    Full article here:


  • ljk November 13, 2018, 10:48

    What to Expect When InSight Lands on Mars

    Emily Lakdawalla

    November 12, 2018

    If all goes well, anxious space fans on Earth will learn of a successful InSight landing on Mars on Monday, 26 November 2018, at 19:53 UTC. Here’s a preview of all the landing day events.


  • ljk November 20, 2018, 13:43

    Mars moon got its grooves from rolling stones, study suggests

    November 20, 2018 Media contact: Kevin Stacey

    Computer models developed by Brown University researchers shine a light on the origin of the Mars moon Phobos’ distinctive grooves.

    PROVIDENCE, R.I. [Brown University] — A new study bolsters the idea that strange grooves crisscrossing the surface of the Martian moon Phobos were made by rolling boulders blasted free from an ancient asteroid impact.

    The research, published in Planetary and Space Science, uses computer models to simulate the movement of debris from Stickney crater, a huge gash on one end of Phobos’ oblong body. The models show that boulders rolling across the surface in the aftermath of the Stickney impact could have created the puzzling patterns of grooves seen on Phobos today.

    “These grooves are a distinctive feature of Phobos, and how they formed has been debated by planetary scientists for 40 years,” said Ken Ramsley, a planetary science researcher at Brown University who led the work. “We think this study is another step toward zeroing in on an explanation.”

    Full article here:


  • ljk February 21, 2019, 10:44

    Where’s Lucy Going? Studying Asteroid Mission Targets

    By Astrobites on 12 February 2019

    Title: Light Curves of Lucy Targets: Leucus and Polymele

    Author: Marc W. Buie, Amanda M. Zangari, Simone Marchi, Harold F. Levison, Stefano Mottola

    First Author’s Institution: Southwest Research Institute

    Status: Published in AJ

    Asteroids, meteoroids, meteors, meteorites. Usually when we talk about these small chunks of debris and rock in the solar system, it’s about another possible apocalypse scenario. Studies of rocky objects that may pass near Earth’s orbit (near-Earth objects, or NEOs) are of obvious importance for the safety of humanity, but they are only one minor subset of the small bodies in our solar system. Most of the asteroids in our neighborhood live in the Asteroid Belt, a region between the orbits of Mars and Jupiter, and they’re referred to as “main-belt asteroids”. There are also large populations trailing Jupiter in its orbit (the Trojan asteroids) and floating out in the outer solar system near Neptune (the Centaur asteroids).

    But apart from the potential threat posed by NEOs, why study these plentiful, seemingly uninteresting hunks of rock and metal that we will likely never encounter on Earth? It turns out that they actually serve as an important window into the formation of the solar system, providing us with information on how the planets formed and what our early solar system was made of. Since we have the chance to get up close and personal with the planets and asteroids nearest to us with rovers and other probes, scientists use this information to infer how other planetary systems form as well. In recent history, we’ve visited most of the major planets with satellites, such as Voyager or Cassini, or rovers, such as Curiosity on Mars; however, the smaller debris is still largely unexplored. The New Horizons mission provided a glimpse into icy debris in the outer solar system when it imaged Pluto and a Kuiper-Belt object (2014 MU69) in detail for the first time, and both NASA’s OSIRIS-REx and JAXA’s Hayabusa missions are working on returning samples from near-Earth asteroids.

    A new asteroid mission has begun preparation as well, targeting multiple asteroids in the further-out Trojan group near Jupiter. The Lucy Discovery mission plans to visit multiple Trojans (actually, the largest number of independently orbiting objects ever visited by a single probe), including Leucus and Polymele, whose flybys are scheduled for September 2027 and April 2028 respectively. Until that date, though, astronomers are busy preparing for the mission and trying to gather all the data on these objects that we can from Earth. The authors specifically investigate Leucus and Polymele, using their light curves to tease out information about their color, composition, orbit, and reflectivity.