Existence of Earth Trojan Asteroid Confirmed – Could Become “Ideal Bases” for Advanced Exploration of the Solar System

Trojan Asteroid 2020 XL5

Using the 4.1-meter SOAR (Southern Astrophysical Research) Telescope on Cerro Pachón in Chile, astronomers have confirmed that an asteroid discovered in 2020 by the Pan-STARRS1 survey, called 2020 XL5, is an Earth Trojan (an Earth companion following the same path around the Sun as Earth does) and revealed that it is much larger than the only other Earth Trojan known. In this illustration, the asteroid is shown in the foreground in the lower left. The two bright points above it on the far left are Earth (right) and the Moon (left). The Sun appears on the right. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine, Acknowledgment: M. Zamani (NSF’s NOIRLab)

Data from NSF’s NOIRLab Show Earth Trojan Asteroid Is the Largest Found

The SOAR Telescope, part of NOIRLab’s Cerro Tololo Inter-American Observatory, has helped astronomers refine the size and orbit of the largest known Earth Trojan companion.

By scanning the sky very close to the horizon at sunrise, the SOAR Telescope in Chile, part of Cerro-Tololo Inter-American Observatory, a Program of NSF’s NOIRLab, has helped astronomers confirm the existence of only the second-known Earth Trojan asteroid and reveals that it is over a kilometer wide — about three times larger than the first.

Astronomers have confirmed the existence of the second known Earth Trojan asteroid and found that it is much bigger than the first. An Earth Trojan is an asteroid that follows the same path around the Sun as Earth does, either ahead of or behind Earth in its orbit. Called 2020 XL5 the asteroid was discovered by the Pan-STARRS1 survey telescope in 2020, but astronomers were not sure then whether it was an Earth Trojan. The SOAR Telescope operated by NOIRLab in Chile helped confirm that it is an Earth Trojan and found that it is over a kilometer across — almost three times bigger than the other Earth Trojan known.

Using the 4.1-meter SOAR (Southern Astrophysical Research) Telescope on Cerro Pachón in Chile, astronomers led by Toni Santana-Ros of the University of Alicante and the Institute of Cosmos Sciences of the University of Barcelona observed the recently discovered asteroid 2020 XL5 to constrain its orbit and size. Their results confirm that 2020 XL5 is an Earth Trojan — an asteroid companion to Earth that orbits the Sun along the same path as our planet does — and that it is the largest one yet found.

“Trojans are objects sharing an orbit with a planet, clustered around one of two special gravitationally balanced areas along the orbit of the planet known as Lagrange points,”[1] says Cesar Briceño of NSF’s NOIRLab, who is one of the authors of a paper published today in Nature Communications reporting the results, and who helped make the observations with the SOAR Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF’s NOIRLab, in March 2021.

Several planets in the Solar System are known to have Trojan asteroids, but 2020 XL5 is only the second known Trojan asteroid found near Earth.[2]

Five Lagrange Points for the Earth-Sun System

Lagrange points are places in space where the gravitational forces of two massive bodies, such as the Sun and a planet, balance out, making it easier for a low-mass object (such as a spacecraft or an asteroid) to orbit there. This diagram shows the five Lagrange points for the Earth-Sun system. (The size of Earth and the distances in the illustration are not to scale.) Credit:
NOIRLab/NSF/AURA/J. da Silva, Acknowledgment: M. Zamani (NSF’s NOIRLab)

Observations of 2020 XL5 were also made with the 4.3-meter Lowell Discovery Telescope at Lowell Observatory in Arizona and by the European Space Agency’s 1-meter Optical Ground Station in Tenerife in the Canary Islands.

Discovered on December 12, 2020, by the Pan-STARRS1 survey telescope in Hawai‘i, 2020 XL5 is much larger than the first Earth Trojan discovered, called 2010 TK7. The researchers found that 2020 XL5 is about 1.2 kilometers (0.73 miles) in diameter, about three times as wide as the first (2010 TK7 is estimated to be less than 400 meters or yards across).

When 2020 XL5 was discovered, its orbit around the Sun was not known well enough to say whether it was merely a near-Earth asteroid crossing our orbit, or whether it was a true Trojan. SOAR’s measurements were so accurate that Santana-Ros’s team was then able to go back and search for 2020 XL5 in archival images from 2012 to 2019 taken as part of the Dark Energy Survey using the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter Telescope located at CTIO in Chile. With almost 10 years of data on hand, the team was able to vastly improve our understanding of the asteroid’s orbit.

Location of Trojan Asteroid 2020 XL5 in the Sky at Sunrise

This graphic shows where the Earth Trojan asteroid 2020 XL5 would appear in the sky from Cerro Pachón in Chile as the asteroid orbits the Earth-Sun Lagrange point 4 (L4). The arrows show the direction of its motion. The SOAR Telescope appears in the lower left. The asteroid’s apparent magnitude is around magnitude 22, beyond the reach of anything but the largest telescopes. Credit: NOIRLab/NSF/AURA/J. da Silva

Although other studies have supported the Trojan asteroid’s identification,[3] the new results make that determination far more robust and provide estimates of the size of 2020 XL5 and what type of asteroid it is.

“SOAR’s data allowed us to make a first photometric analysis of the object, revealing that 2020 XL5 is likely a C-type asteroid, with a size larger than one kilometer,” says Santana-Ros. A C-type asteroid is dark, contains a lot of carbon, and is the most common type of asteroid in the Solar System.

The findings also showed that 2020 XL5 will not remain a Trojan asteroid forever. It will remain stable in its position for at least another 4000 years, but eventually it will be gravitationally perturbed and escape to wander through space.

2020 XL5 and 2010 TK7 may not be alone — there could be many more Earth Trojans that have so far gone undetected as they appear close to the Sun in the sky. This means that searches for, and observations of, Earth Trojans must be performed close to sunrise or sunset, with the telescope pointing near the horizon, through the thickest part of the atmosphere, which results in poor seeing conditions. SOAR was able to point down to 16 degrees above the horizon, while many 4-meter (and larger) telescopes are not able to aim that low.[4].

“These were very challenging observations, requiring the telescope to track correctly at its lowest elevation limit, as the object was very low on the western horizon at dawn,” says Briceño.

Nevertheless, the prize of discovering Earth Trojans is worth the effort of finding them. Because they are made of primitive material dating back to the birth of the Solar System and could represent some of the building blocks that formed our planet, they are attractive targets for future space missions.

“If we are able to discover more Earth Trojans, and if some of them can have orbits with lower inclinations, they might become cheaper to reach than our Moon,” says Briceño. “So they might become ideal bases for an advanced exploration of the Solar System, or they could even be a source of resources.”


  1. Lagrange points are gravitationally balanced regions around two massive bodies, such as the Sun and a planet. The Earth-Sun system has five Lagrange points: L1 is between Earth and the Sun; L2 is on the opposite side of Earth from the Sun; L3 is on the opposite side of the Sun from Earth; and L4 and L5 are along Earth’s orbit, one 60 degrees ahead of our planet along its orbit and the other 60 degrees behind it. (The image in the middle of this article illustrates their positions.) Trojan asteroids are found at L4 and L5. The two Earth Trojans found so far are at L4.
  2. Jupiter has over 5000 known Trojan asteroids, and a NASA spacecraft called Lucy has recently launched on a mission to explore them. Venus, Mars, Uranus, and Neptune are also known to have Trojan asteroids.
  3. Man-To Hui (Macau University of Science and Technology) and collaborators published observations in the Astrophysical Journal Letters in December 2021 supporting the Trojan nature of 2020 XL5.
  4. These kinds of observations low in the sky are also the ones that will be most affected by the increasing number of satellite constellations.

More information

This research is presented in a paper titled “Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5” published on 1 February 2022 in Nature Communications.

Reference: “Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5” by T. Santana-Ros, M. Micheli, L. Faggioli, R. Cennamo, M. Devogèle, A. Alvarez-Candal, D. Oszkiewicz, O. Ramírez, P.-Y. Liu, P. G. Benavidez, A. Campo Bagatin, E. J. Christensen, R. J. Wainscoat, R. Weryk, L. Fraga, C. Briceño and L. Conversi, 1 February 2022, Nature Communications.
DOI: 10.1038/s41467-022-27988-4

The team is composed of T. Santana-Ros (Departamento de Fisica, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante; Institut de Ciències del Cosmos, Universitat de Barcelona), M. Micheli (ESA NEO Coordination Centre), L. Faggioli (ESA NEO Coordination Centre), R. Cennamo (ESA NEO Coordination Centre), M. Devogèle (Arecibo Observatory; University of Central Florida), A. Alvarez-Candal (Instituto de Astrofísica de Andalucía, CSIC; Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante; Observatório Nacional / MCTIC), D. Oszkiewicz (Faculty of Physics, Astronomical Observatory Institute), O. Ramírez (Solenix Deutschland), P.-Y. Liu (Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante), P.G. Benavidez (Departamento de Fisica, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante; Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante), A. Campo Bagatin (Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante; Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante), E.J. Christensen (Lunar and Planetary Laboratory, University of Arizona,), R. J. Wainscoat (Institute for Astronomy, University of Hawaii), R. Weryk (Department of Physics and Astronomy, University of Western Ontario), L. Fraga (Laboratório Nacional de Astrofísica LNA/MCTI), C. Briceño (Cerro Tololo Inter-American Observatory/NSF’s NOIRLab), and L. Conversi (ESA NEO Coordination Centre; ESA ESRIN).

8 Comments on "Existence of Earth Trojan Asteroid Confirmed – Could Become “Ideal Bases” for Advanced Exploration of the Solar System"

  1. Babu G. Ranganathan | February 2, 2022 at 6:35 am | Reply

    Babu G. Ranganathan*
    (B.A. Bible/Biology)


    In the Earth’s past there were powerful volcanic explosions propelling millions of tons of earth soil and rock into space (many of which are now asteroids and meteors and which may contain organic molecules and organisms). Read my popular Internet article, ANY LIFE ON MARS CAME FROM EARTH. The article explains how millions of tons of Earth soil may exist on Mars, and how debris we call asteroids, meteors, and comets (some even containing the chemical building blocks of life) could have originated from Earth.

    According to a Newsweek article of September 21, 1998, p. 12 that quotes a USC professor and scientist, there may be SEVEN MILLION tons of Earth soil on Mars!

    Even if the right chemicals exist, life cannot arise by chance. The molecules that make-up life have to be in a sequence, just like the letters found in a sentence.

    Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    Regarding comets, scientist and creationist, Dr. Brian Thomas explains:

    “Astronomers measure comets’ masses and erosion rates to calculate potential lifespans. Sun grazing comets last fewer than 100,000 years.2 They thus confront secular astronomy which maintains that comets formed with the rest of the solar system billions of years ago. A solar system that old should have no remaining comets.

    How do secularists solve this dilemma?

    Reporting on Ison, The Independent said, “Comet Ison has taken millions of years to reach us travelling from the so-called Oort cloud – a reservoir of trillions and trillions of chunks of rock and ice, leftovers from the birth of the planets.”3

    Unfortunately, nobody has yet witnessed a single one of those “trillions and trillions of chunks.” Going strictly with observational science, the “so-called Oort cloud” may exist only in the reservoir of the human mind.

    Clearly, secular astronomers invented the Oort cloud to rescue their billions-of-years dogma from a disintegration process that limits a comet’s age—and thus the age of the Solar System—to thousands of years. When Ison becomes visible later this year, perhaps it will remind thoughtful viewers that the universe is quite young, just as Scripture teaches” (Brian Thomas, M.S., Science Writer at the Institute for Creation research).

    Read scientist and creationist Brian Thomas’ Internet article, EXOCOMETS: EVIDENCE OF RECENT CREATION

    Check out my most recent Internet articles and sites: THE SCIENCE SUPPORTING CREATION and WAR AMONG EVOLUTIONISTS (2nd Edition)


    *I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.

    • Not a Bible Scientist | February 2, 2022 at 7:59 am | Reply

      Sounds like a lot of “evidence” that you have gathered to support a conclusion you had already made.

      If God created humans and the only life in the entire universe was made on Earth, why then is the universe so enormous. There’s billions and billions of worlds out there, many the same size if not much larger than Earth. We are only now starting to see the first grains of sand on this beach that is the universe.

      You’re telling me God created all of that just to create one form of sentient life on one planet. Sounds pretty inefficient and wasteful.

      Not saying there is no God, I honestly don’t know. But I do know that the god that is preached about in the bible is contradictory. It’s getting to the point where you “Bible Scientists” are having to stretch things pretty far to try and get science to even remotely line up with what the bible teaches. Can’t wait until we detect sentient life from another star system just so I can watch the bible scientists try and scramble to explain how it came from Earth.

      • Torbjörn Larsson | February 2, 2022 at 3:29 pm | Reply

        Goo response! I’m thinking of just posting TalkOrigins responses to old creationist questions, in case someone is seriously confounded by their strawmen.

        Speaking of which, while I don’t care to bother about the details of various superstitions, the 2018 Planck observatory (and later massive data sets) confirmation of the Lambda-Cold Dark Matter cosmology convinced me that we now know beyond reasonable doubt that the universe is a 100 % natural process of expansion. The corollary is that magic agency doesn’t exist.

        But of course the corollary isn’t cosmology, it’s just an investigation into superstitious claims on nature and how they totally not apply.

    • Torbjörn Larsson | February 2, 2022 at 3:22 pm | Reply

      Superstition, posting of irrelevant pseudoscience links – creationism is superstition of religion, not science.

      Speaking of actual science, it now explicitly rejects creationism claims of life evolving by mechanisms involving variation and contingence (“chance”).

      “Our earliest, ‘half-alive’ ancestor needed little boost from heat
      Life on Earth assembled itself in warm, mildly alkaline conditions, study says”
      [ https://www.science.org/content/article/our-earliest-half-alive-ancestor-needed-little-boost-heat ]

      These suoerstitious makes up rules of likelihood that doesn’t apply to biology as a process of evolutionary change, and rules of ‘observational science’ or ‘forensic science’ that doesn’t apply to observation in science as a method involving observation and tests. All strawman arguments in the face of facts such as existence of comets, and that cosmology rejects existence of magic without contemplating creationism in particular.

      By the way, these are decades old answered false claims on science. From TalkOrigins [and see references there]:

      “Claim CE261.1:
      The Kuiper Belt and Oort Cloud have never been observed. They have been proposed merely as an ad hoc explanation for a source of comets.

      As of June 2000, more than 250 objects in the Kuiper Belt have been observed directly (Buie 2000), and it alone can be the source of short-term comets. …”

      “Claim CB010:
      The proteins necessary for life are very complex. The odds of even one simple protein molecule forming by chance are 1 in 10113, and thousands of different proteins are needed to form life. (See also Primitive cells arising by chance.)

      The calculation of odds assumes that the protein molecule formed by chance. However, biochemistry is not chance, making the calculated odds meaningless. Biochemistry produces complex products, and the products themselves interact in complex ways. For example, complex organic molecules are observed to form in the conditions that exist in space, and it is possible that they played a role in the formation of the first life (Spotts 2001).

      The calculation of odds assumes that the protein molecule must take one certain form. However, there are innumerable possible proteins that promote biological activity. Any calculation of odds must take into account all possible molecules (not just proteins) that might function to promote life.

      The calculation of odds assumes the creation of life in its present form. The first life would have been very much simpler.

      The calculation of odds ignores the fact that innumerable trials would have been occurring simultaneously.”

  2. We know we have no intuition or everyday understanding of cosmic distances. Nor do we have an apprehension of Deep Time. That lack gives us posts such as the above. It also fails to appreciate the sheer scale of the space and time outside our little bubble of everyday life on Earth’s surface. Creationists are simply not humble enough. Their hubris is all too human. They have not found a shortcut.

    Scientists may work and contend on details and processes of evolution, but not the reality of it in Deep Time. Especially the more profound understandings coming through genetics. The train has left the station on a wonderful journey. Sad for someone left on the platform.

    Genetics has shown us a unity in the examples of life accessible to us. We are related to the humble yeast and share processes required for life with them. All life could have been created ten minutes ago incorporating all the evidence for evolution, but there is no reason to think up such a deception, nor understanding, nor profit in doing so. Indeed, medicine increasingly depends on genetics and Evolution and is seeing only successes in doing so.

    Creationists are concerned to imprison the mind, not liberate it as they represent.

    • Torbjörn Larsson | February 2, 2022 at 3:33 pm | Reply

      Maybe I misunderstand in my reading, but FWIW biology do span 4 billion years of deep time by dated phylogenetic trees as do geology by dated rocks (they are related) – but that is nothing to the 14 billion years of cosmology dated by redshift distance.

  3. Daniel J Barber | February 2, 2022 at 8:50 am | Reply

    can you tell us about spaceships too?

  4. Torbjörn Larsson | February 2, 2022 at 2:45 pm | Reply

    Good confirmation, good uses.

    The hope that L4/L5 could contain building blocks to Earth is endearing, as is the hope that it could have collected some early hypervelocity impactor ejecta. There is a lot of history there to know more of!

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