15. October 2021
NASA asteroid mission with entirely new destinations

To the Tro­jans and Greeks with Lucy

More:
Space
NASA's Lucy spacecraft at the Trojan asteroids
NASA's Lucy space­craft at the Tro­jan as­ter­oids
Image 1/8, Credit: Southwest Research Institute

NASA's Lucy spacecraft at the Trojan asteroids

With the Lucy mis­sion, as­ter­oids of the 'Jo­vian Tro­jans' fam­i­ly will be ex­plored for the first time. These are plan­e­toids that have ac­cu­mu­lat­ed at two points in front of and be­hind the gas gi­ant, where the grav­i­ty of Jupiter and the Sun can­cel each oth­er out – re­ferred to as La­grange points. Af­ter launch­ing on 16 Oc­to­ber 2021, NASA's space­craft will ar­rive at the L4 point along Jupiter’s or­bit in 2027 and ob­serve five Tro­jan as­ter­oids in suc­ces­sion at close range un­til 2028, as an­tic­i­pat­ed in this artist's im­pres­sion. Af­ter a re­turn to the in­ner So­lar Sys­tem, Lucy will fi­nal­ly study a sys­tem of two bi­na­ry as­ter­oids at the L5 point in 2033.
'Trojans' and 'Greeks' along the orbit of Jupiter
'Tro­jans' and 'Greeks' along the or­bit of Jupiter
Image 2/8, Credit: NASA/JPL-Caltech

'Trojans' and 'Greeks' along the orbit of Jupiter

Ob­ser­va­tions in re­cent years have shown that the 'Tro­jan as­ter­oids' or­bit­ing the Sun in the same or­bit as Jupiter have uni­form, very dark sur­faces with a hint of a red tinge and com­par­a­tive­ly dull sur­faces that re­flect lit­tle sun­light. The re­sults are cap­tured in this artist's im­pres­sion, which shows both the as­ter­oids ahead of Jupiter, the 'Greeks', and the as­ter­oids trail­ing the gi­ant plan­et in the 'Tro­jan camp'. The red colour­ing is rem­i­nis­cent of ni­troge­nous com­pounds that have been de­tect­ed on some bod­ies in the out­er So­lar Sys­tem – tholins. Ob­ser­va­tions made as part of the WISE project al­so con­firmed the ear­li­er sug­ges­tion that there are more as­ter­oids in the lead­ing group of Tro­jans (vis­i­ble in the dis­tance) than in the trail­ing group.
500 watts for Lucy
500 watts for Lucy
Image 3/8, Credit: Lockheed Martin

500 watts for Lucy

At dis­tances of 700 to 800 mil­lion kilo­me­tres from the Sun – Jupiter's or­bit, like the or­bits of all plan­ets, is not per­fect­ly cir­cu­lar but el­lip­ti­cal – the pow­er den­si­ty of so­lar ra­di­a­tion av­er­ages on­ly 12.6 watts per square me­tre. By com­par­i­son, Earth re­ceives 1361 watts per square me­tre, ap­prox­i­mate­ly 100 times more so­lar en­er­gy. In or­der for a space­craft like Lucy to still be able to op­er­ate us­ing so­lar pow­er at these dis­tances from the Sun (which was tech­ni­cal­ly im­pos­si­ble two decades ago), it needs two very large so­lar pan­els, each 7.3 me­tres in di­am­e­ter. At the mis­sion’s fur­thest dis­tance from the Sun, they can sup­ply the space­craft with 504 watts of pow­er.
A trajectory like never before
A tra­jec­to­ry like nev­er be­fore
Image 4/8, Credit: Southwest Research Institute/DLR

A trajectory like never before

Af­ter launch, Lucy will first gain mo­men­tum for its jour­ney through the as­ter­oid belt to its des­ti­na­tion, the Tro­jans in Jupiter's or­bit, by per­form­ing two close fly-bys of Earth, re­ferred to as swing-by ma­noeu­vres. Be­fore that, Lucy will pass and in­ves­ti­gate the as­ter­oid Don­ald­jo­han­son in April 2025. In 2027, the space­craft will ar­rive at the Tro­jan as­ter­oids, which pre­cede Jupiter at La­grange point 4, the 'Greek camp'. Four close-up stud­ies of as­ter­oids will take place there. In 2028, Lucy's path leads back to Earth, where the space­craft will be steered by the plan­et's grav­i­ty to­wards the Tro­jans at La­grange Point 5, the gath­er­ing point of the 'Tro­jans' be­sieged by the Greeks. Here, in March 2033, Lucy will fly past the Greek 'spies' in the Tro­jan camp, the as­ter­oid Pa­tro­clus and its bi­na­ry com­pan­ion Me­noetius. Af­ter­wards, Lucy will be on a hun­dred-thou­sand-year sta­ble, high­ly el­lip­ti­cal or­bit around the Sun be­tween Earth and Jupiter. If suf­fi­cient re­sources are avail­able, the space­craft could even be steered once more to the L4 Tro­jans us­ing an­oth­er close fly­by of Earth. Lucy's or­bit is loop-shaped or S-shaped in this rep­re­sen­ta­tion, which is fixed rel­a­tive to Jupiter. In re­al­i­ty, how­ev­er, the or­bits be­tween the in­ner So­lar Sys­tem and Jupiter's or­bit are el­lip­ti­cal.
Seven of Lucy's eight targets
Sev­en of Lucy's eight tar­gets
Image 5/8, Credit: Southwest Research Institute

Seven of Lucy's eight targets

NASA's Lucy mis­sion will in­ves­ti­gate eight plan­e­toids at close range be­tween 2025 and 2033, sev­en of which are shown here as artist's im­pres­sions. They are: an as­ter­oid in the Main Belt be­tween Mars and Jupiter (Don­ald­jo­han­son, Ø ap­prox­i­mate­ly four kilo­me­tres), then four Tro­jan as­ter­oids at La­grange point 4 along Jupiter's or­bit – Eu­ry­bates (Ø 64 kilo­me­tres, Au­gust 2027) with its moon Que­ta (Ø es­ti­mat­ed at one kilo­me­tre), dis­cov­ered on­ly in 2020 (and not shown here), Poly­mele (Ø 21 kilo­me­tres, Septem­ber 2027 ), Leu­cus (Ø 40 kilo­me­tres, April 2028) and Orus (Ø 51 kilo­me­tres, Novem­ber 2028). In the last cur­rent­ly planned mis­sion seg­ment, Lucy will ob­serve the as­ter­oid Pa­tro­clus (Ø 113 kilo­me­tres) with its bi­na­ry com­pan­ion Me­noetius (Ø 104 kilo­me­tres) at the L5 point in the 'Tro­jan Camp' (March 2033).
Surprise! One of the Trojans has a moon
Sur­prise! One of the Tro­jans has a moon
Image 6/8, Credit: Southwest Research Institute (J. Spencer)

Surprise! One of the Trojans has a moon

Mem­bers of the Lucy sci­ence team, in­clud­ing DLR plan­e­tary sci­en­tist Ste­fano Mot­to­la (to the right of the pil­lar, be­hind team lead­er Harold Lev­i­son, with beard) dis­cov­ered a bare­ly kilo­me­tre-sized satel­lite of the tar­get as­ter­oid Eu­ry­bates with tele­scop­ic ob­ser­va­tions on 4 Jan­uary 2020, which was named Que­ta. The small Tro­jan moon was im­me­di­ate­ly added to the mis­sion plan­ning as an ad­di­tion­al, eighth ob­serv­ing tar­get. Que­ta was the nick­name of Mex­i­can track and field ath­lete Nor­ma En­ri­que­ta ('Que­ta') Basilio Sote­lo (1948-2019), the first wom­an to have the hon­our of light­ing the Olympic flame. She did this as part of the open­ing cer­e­mo­ny at the 1968 Olympic Games in Mex­i­co City.
Lucy during integration in 2020
Lucy dur­ing in­te­gra­tion in 2020
Image 7/8, Credit: Lockheed Martin

Lucy during integration in 2020

Lucy, shown here in an im­age from late 2020, is the 13th mis­sion of NASA's Dis­cov­ery class. The space­craft is ap­prox­i­mate­ly four me­tres high when stowed in launch con­fig­u­ra­tion and has a launch mass of 1550 kilo­grams, about half of which is pro­pel­lant. Dur­ing the mis­sion phase, Lucy will de­ploy to a width of 14 me­tres with two large so­lar pan­els. The di­am­e­ter of the main an­ten­na is two me­tres. Lucy car­ries three sci­en­tif­ic in­stru­ments and two nav­i­ga­tion cam­eras, which will be used to im­age the tar­get as­ter­oids and de­ter­mine their chem­i­cal-min­er­alog­i­cal com­po­si­tion and phys­i­cal pa­ram­e­ters us­ing var­i­ous spec­trom­e­ters.
L'Ralph – camera and spectrometer in one
L'Ralph – cam­era and spec­trom­e­ter in one
Image 8/8, Credit: NASA/Goddard Space Flight Center

L'Ralph – camera and spectrometer in one

One of Lucy's two sci­en­tif­ic cam­era sys­tems is L'Ralph. It con­sists of the Mul­ti­spec­tral Vis­i­ble Imag­ing Cam­era (MVIC), with colour chan­nels for vis­i­ble light wave­lengths up to near in­frared (0.38-0.92 mi­crons), and the Lin­ear Etalon Imag­ing Spec­tral Ar­ray (LEISA), an in­frared spec­trom­e­ter for near to mid-in­frared (1.0-3.6 mi­crons). LEISA can iden­ti­fy ab­sorp­tion lines that re­veal sil­i­cate min­er­als, ice and or­gan­ic car­bon and hy­dro­car­bon com­pounds sus­pect­ed to be present on the sur­faces of the Tro­jan as­ter­oids. L'Ralph, named af­ter Ralph Kram­den of the 'Hon­ey­moon­ers', is a fur­ther de­vel­op­ment of the Ralph cam­era sys­tem on the New Hori­zons mis­sion, which trans­mit­ted ra­zor-sharp im­ages of Plu­to and its com­pan­ion Charon to Earth in 2015.
  • Lucy will launch from Cape Canaveral at 11:34 CEST on Saturday 16 October 2021.
  • The mission will visit eight asteroids in 12 years.
  • Lucy will be the first spacecraft to visit the 'Trojans', asteroids in Jupiter's orbit.
  • The DLR Institute of Planetary Research is involved in the mission's scientific activities.
  • Focus: Solar System exploration and origins, space and spaceflight

On Saturday 16 October 2021, at 11:34 CEST, an unusual NASA mission will set off from Cape Canaveral on an Atlas launch vehicle, beginning its journey across the Solar System. The targets of the Lucy mission are the Trojan asteroids, which share Jupiter's orbit around the Sun. Scientists suspect that they are very different from the planetoids in the Main Asteroid Belt between Mars and Jupiter. Asteroids are considered to be witnesses of the formation of the planets in the Solar System and can provide information about their development. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is involved in the mission's scientific activities.

After a journey lasting several years, Lucy will be the first spacecraft to visit members of the 'Trojan asteroids'. The Trojans are small planetoids that found their place in the Solar System, two regions on the orbit of Jupiter, over four billion years ago. Unlike the many hundreds of thousands of celestial bodies in the Main Asteroid Belt, these bodies are more than 700 million kilometres from the Sun and are believed to be asteroids that originated beyond Jupiter's orbit. "This makes these 'time capsules' very interesting for closer study," says Stefano Mottola of the DLR Institute of Planetary Research, who is involved in Lucy's scientific activities. "We hope to gain new and significant knowledge about the Solar System's earliest period and the formation of the planets."

The name Lucy is not an abbreviation, as is so often the case with NASA missions. It refers to one of the most important discoveries in anthropological research – that of the 3.2-million-year-old partial skeleton of Australopithecus afarensis in Ethiopia, known as an 'early human'. Palaeontologist Donald Johanson, who co-discovered Lucy, celebrated by throwing a party with his team on the evening of that November day in 1974. As the night wore on, the Beatles' perennially popular song Lucy in the Sky with Diamonds played repeatedly on the tape recorder. There is still some speculation over the initial letters of the three title nouns, but the skeleton needed a name. In Ethiopia, the skeleton is also referred to as 'Dinkinesh', which means 'you are marvellous' in the Amharic language. With her bones, scientists were able to decipher the origins of humankind. The NASA spacecraft is also intended to help, in a figurative sense, decode the origins of the Solar System.

The 14-member core scientific team will require a great deal of patience. After launch, Lucy will not reach the Trojan asteroids until 2027, following a tortuous path through the inner Solar System. But before that, in April 2025, it will pass the four-kilometre, main-belt asteroid Donaldjohanson, named after one of Lucy's discoverers. The spacecraft, which will weigh approximately one and a half tonnes at launch, carries three scientific instruments with which the target asteroids will be imaged and have their chemical-mineralogical compositions and physical parameters determined using spectrometers. Lucy is the 13th member of NASA's highly successful Discovery class – highly specialized, comparatively small and organisationally 'lean' space missions. Harold Levison and Cathy Olkin from the Southwest Research Institute in Boulder, Colorado, USA, are the mission's Principal Investigator and Deputy Principal Investigator, respectively. The mission will be controlled by NASA's Goddard Spaceflight Center in Greenbelt, Maryland.

DLR's involvement includes Stefano Mottola from the Institute of Planetary Research in Berlin, who is a member of the Lucy science team. Mottola was also significantly involved in the Rosetta, Dawn and Hayabusa2/MASCOT missions. "During the mission preparations for Lucy, I studied the target asteroids with Earth-based telescopes and obtained light curves for them," Mottola explains. "Using these observations, we can optimise the flybys." Over the course of his career, Mottola has been involved in the telescopic discovery of hundreds of asteroids. "We will also support the mission upon arrival via calculations of body shapes, creation of image mosaics and atlases, and mapping luminosities and composition. The exact shape of the asteroids will be derived from the data obtained using the navigation cameras." In addition, Martin Pätzold of the University of Cologne, supported by the German Space Agency at DLR, will investigate the mass and composition of the asteroids by analysing the redshift and blueshift of reflected radio signals – the stretching and compression of the radio waves caused by the Doppler effect.

Jupiter, its Trojans and Greeks

The Trojans are a special group of asteroids, small bodies with diameters of up to 250 kilometres, located in regions that precede or follow the planet Jupiter at a constant distance along its orbit around the Sun. These are the points in a two-body system – such as the Sun and Jupiter in this case – at which gravitational and centrifugal forces balance one another out. The total of five points at which this occurs, from Lagrange-1 (L1) to Lagrange-5 (L5), are named after the Italian-French astronomer and mathematician Joseph-Louis de Lagrange (1736-1813).

Two of these Lagrange points, L4 and L5, are always stable and each lie at one vertex of an equilateral triangle with the Sun and Jupiter at the other vertices. Today, just under 10,000 of these objects are known to exist in the vicinity of these two Lagrange points. They are not located exactly at these two points, but orbit them at different distances so that they form an asteroid 'cloud'. However, as in the Main Asteroid Belt, as many as one million similar bodies are suspected to exist. They are very difficult to detect with telescopes because of their dark surface and small size. The International Astronomical Union (IAU) has taken inspiration from the Iliad, Homer's famous ancient saga of the battle for Troy, for the naming of the asteroids. It refers to the asteroids moving ahead of Jupiter as the camp of the 'Greeks', which take the names of the Greek heroes. The asteroids moving behind Jupiter were named 'Trojans', and take the names of the heroes from the legendary city of Asia Minor. Since all the names appearing in the Iliad have now been given to Trojan asteroids, newly discovered bodies are being named by the IAU after modern 'heroes', great athletes who participated in the modern Olympic and Paralympic Games.

This will be the first time that bodies orbiting the Sun at Lagrange points along a planetary orbit have been visited by a spacecraft. Jupiter itself plays no role in the mission. It will be many hundreds of millions of kilometres away from Lucy during both phases of the mission. In planetary research, the Trojan asteroids have been a top priority as a new target for years. Researchers suspect that, in contrast to Main Belt asteroids, these Trojans have little in common with the bodies of the inner Solar System and more with the outer regions of the planetary system.

The realm of the gas giants and their icy moons begins with Jupiter. Even further away from the Sun, beyond Neptune, stretches the region in which the comets originate. These bodies of dust and ice also played an important role in the formation and evolution of the Solar System. This is the home of the 'transneptunian objects', to which Pluto also belongs. Just as the asteroids of the Main Belt are remnants of the formation of the four rocky planets, the Jovian Trojans are likely to be remnants of the source material of the outer planets, with origins at very different distances from the Sun. They may even contain organic molecules, which originated there before later reaching the inner Solar System, and thus Earth – substances that could have played an important role in the emergence of life almost four billion years ago.

Into the 'camp' of the Greeks, back to Earth and on to the Trojans

Arriving at its destination in the realm of the L4 asteroids, the 'Greek camp', Lucy will examine at close range the asteroids Eurybates (August 2027) and its small moon Queta, discovered by the Lucy team only last year, Polymele (September 2027), Leucus (April 2028) and Orus (November 2028). Then, Lucy will be steered back towards Earth and the inner Solar System – a first in the history of spaceflight. With the help of a 'gravity assist manoeuvre', the spacecraft will then be steered to the L5 point, where Lucy will reach the asteroid Patroclus and its binary companion Menoetius in the 'Trojan camp'. The nominal mission will then be over, but if fuel and resources necessary for mission operations are still available, the mission could be extended. Lucy would then return to Earth once again and be steered back towards the asteroid cloud at L4, arriving at the end of the decade.

Importance of asteroid research

The study of small bodies in the Solar System has become increasingly important in recent decades. Asteroids and comets are in most cases barely altered witnesses to the formation of planets a little more than four and a half billion years ago. The further away from the Sun they formed – and remain today – the less they have been exposed to the Sun's influence and therefore the less they have been altered. Four and a half billion years is a period of time so long that it is difficult to comprehend on human timescales, but planetary research has recently become increasingly successful in reconstructing the processes that took place in the first million years following the formation of the Sun 4.567 billion years ago. The planets formed surprisingly quickly at that time, in just a few million to tens of millions of years. This period was decisive for their further development, which is seen in the diversity of the planets and their moons. However, as they have all changed considerably since then, only asteroids and comets allow us to look back to that time and decipher the processes precisely.

Contact
  • Melanie-Konstanze Wiese
    Cor­po­rate Com­mu­ni­ca­tions, Berlin, Neustre­litz, Dres­den, Je­na and Cot­tbus/Zit­tau
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 30 67055-639
    Fax: +49 30 67055-102
    Rutherfordstraße 2
    12489 Berlin-Adlershof
    Contact
  • Stefano Mottola
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Plan­e­tary Geodesy
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact
Newsletter

Newslet­ter

Stay up to date and sub­scribe to the DLR newslet­ter with ar­ti­cles from the DLR ed­i­to­ri­al team in Ger­man and En­glish.

Main menu