The period known as "Cosmic Noon," which took place roughly 2 to 3 billion years after the Big Bang, was characterized by the rapid formation of new stars and planetary systems. Naturally, objects dated to this period are coveted by scientists hoping to learn more about the processes that led to the formation of planets and the emergence of life itself. This includes asteroids and comets, which are known to be composed of material leftover from the formation of entire star systems and their planets. And with the detection of three interstellar objects (ISOs) in the Solar System since 2017, there could be multiple opportunities to do so.
This includes 3I/ATLAS, which was detected on July 1st by researchers at the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile. Since then, astronomers have conducted ongoing observations to learn as much as they can about this object before it is beyond the range of our telescopes. According to a new study by an international team of astrophysicists, several active missions could rendezvous with this object before it leaves the Solar System. Any one of these missions could provide detailed information on a period when star formation was prolific in our galaxy, and the building blocks of life likely emerged.
The research was led by T. Marshall Eubanks, the Chief Scientist at Space Initiatives Inc. He was joined by researchers from the Institute for Interstellar Studies (i4is), the Interdisciplinary Center for Security, Reliability and Trust (SnT) at the University of Luxembourg, the Laboratory for Instrumentation and Research in Astrophysics (LIRA) at the Observatiore de Paris, the French-Chilean Laboratory for Astronomy, the Technical University of Munich (TU Munich), and NASA's Jet Propulsion Laboratory. The paper detailing their findings recently appeared online.
Observations of 3I/ATLAS have already revealed much about the object's trajectory, composition, and where it may have come from. The kinematics of the object revealed that it is likely to be an object from the galactic thick disk, where 85% of the stars in our galaxy are located. It is also where the oldest stars in the galaxy reside, most being older than 10 billion years, which means they formed during the "Galactic Noon" period. As Andreas told Universe Today via email:
Stars in the galactic thick disk have formed billions of years earlier than those in the thin disk, which includes our Sun. If 3I has been ejected from a thick disk star system, it means that we could get insights into it without flying to it, something which we will not be able to do for the foreseeable future. Hence, observing 3I is a literal example of: If the prophet cannot go to the mountain, let the mountain come to the prophet.
As they explain, the formation of 3I in the thick disk can be tested observationally as it transits through the Solar System. If 3I can be traced to the galactic thick disk, it will provide a means to explore the formation process of stars and planets and the possible origins of life during this early period. However, 3I will reach its closest point to the Sun (perihelion) when Earth is on the opposite side, making observations using ground-based telescopes virtually impossible. This is unfortunate, since 3I will experience its most intense outgassing while at perihelion, and the composition of its tail will provide detailed information on its internal composition.
A mission that could study it up close would be able to obtain spectra from its outgassing before it is no longer observable. Eubanks and his colleagues theorize that 3I could have originated from the galactic thick disk because of its galactic orbit, as well as its velocity and direction, which takes it 3,000 light-years out of the galactic plane. Said Andreas:
3I/ATLAS flew in from outside the solar system almost at the same angle as the solar system plane. This is surprising. The solar system is traveling through the Milky Way in a direction perpendicular to the plane of its planets. Now, you would expect that interstellar objects would fly into the solar system from that direction if they have similar trajectories as our Solar System. In other words, they would fly into the solar system at a steep angle to the Solar System plane. And in fact, this is exactly what we observed for the first two interstellar objects 'Oumuamua and Borisov. They flew into the solar system at steep angles. What makes 3I/ATLAS unusual is that it flew in almost parallel to the plane of the Solar System.
The trajectory of 3I/ATLAS through the Solar System. Credit: NASA
"We seek to confirm this hypothesis through an analysis of 3I's chemical nature. One prediction is that the planet formation would occur at a higher temperature in the 'Cosmic Noon' period, which makes 3I appear to be 'dynamically old,' with fewer easily evaporated supervolatiles," Eubanks added. "Early indications are that 3I does appear to be dynamically old (unlike 2I/Borisov, which appeared to the dynamically new). It is much too early to say that this issue is resolved, but we are hopeful that it will be by the time all the 3I data is analyzed."
Based on its trajectory, 3I is expected to pass inside the orbit of Mars, bringing it relatively close to several interplanetary spacecraft that have already launched. To determine which could conduct observations of this ISO, the team examined 15 missions in heliocentric orbits or currently active around Mars. Of these, they found that the Mars Reconnaissance Orbiter (MRO) and the ESA's Trace Gas Orbiter (TGO), which could view 3I with their instruments on October 2nd and 3rd, respectively. Tianwen-1 and Hope also present opportunities for observations.
The ESA's JUpiter ICy moons Explorer (JUICE) and NASA's Europa Clipper and Psyche will also be in a good position to conduct observations for even longer. Said Eubanks:
During the JUICE spacecraft close approach (a period near 3I's perihelion when it will be hard to observe from Earth), the Juice spacecraft will observe 3I with five of its instruments November 2-25, 2025, just after 3I's perihelion, including its closest approach on November 4, while the Europa Clipper will use its magnetometer and plasma instruments to observe possible passages through 3I's cometary tail, more or less continuously from now into November. In addition, several solar observatories and probes will attempt remote monitoring of 3I from late October through mid-November 2025, as it passes through their instrumental fields of view (FOV).
While none of the missions profiled allow for a direct intercept with the interstellar comet, some of the spacecraft may pass through the tail before it is beyond our reach. For instance, the Europa Clipper, Hera, and even the more distant Lucy spacecraft may pass through 3I's cometary tail in the period after its perihelion passage, potentially directly observing the conditions and composition there. "Finally, three heliophysics space observatories (SOHO, Solar Orbiter, and the Parker Solar Probe) will have 3I pass through their instruments' fields of view (FOV) in this period; the Parker Solar Probe and even the solar coronagraphs may be able to monitor 3I at intervals in the period from late September through mid-November in 2025," said Andreas.
The Gemini South Observatory captured this image of the interstellar comet 3L/ATLAS on August 27th. It shows the object's fuzzy coma and tail, made of volatiles released by the Sun's heat. Image Credit: By International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the Scientist, CC BY 4.0
Above all, the observations these missions could perform would yield data that is impossible to obtain using Earth-based instruments. Even when Earth observations are possible, the different angles of the different spacecraft will provide valuable data on the nature of the dust and ejecta from 3I. In addition to testing the thick disk origin of this latest ISO, these observations could also confirm how hot its formation region was by analyzing the spectra emissions of its gas and dust tail and the rate of outgassing. All this information would shed light on star systems that existed at a crucial time in cosmic history.
The team also notes that while astronomers will benefit from a combination of Earth and space-based observations, the spacecraft they considered would provide the only source of spectral and imaging data during the 3I perihelion passage. More information is expected shortly, thanks to images captured by the James Webb Space Telescope (JWST) and other observations. However, spacecraft currently operational in deep space could provide some of the most important data yet. "If 3I is really from the thick disk, it may be one of the oldest objects we have ever observed in the solar system," said Andreas. "It is like an eon-old fridge, which will open during the next months to release some of its content."
Further Reading: arXiv
