Astronomy has confirmed the passage of two notable interstellar objects that crossed Sistema Solar before the recent discovery of 3I/Atlas. The first, called 1I/Oumuamua, was identified in 2017 by telescopes at Havaí, while the second, 2I/Borisov, appeared in 2019, spotted by an amateur astronomer at Crimeia. Ambos celestial bodies followed hyperbolic trajectories, a clear indication of their external origin, coming from distant star systems.
These events, although they seem rare, occur with certain frequency due to the gravitational attraction exerted by Sol, which temporarily captures these cosmic travelers from Via Láctea. Cientistas estimate that hundreds of similar objects could enter our neighborhood annually, but detection capacity is still limited, resulting in only three being monitored so far. Confirming their origins depends on advanced observatories, capable of calculating their orbits and speeds with high precision.
The main characteristic that defines these bodies as visitors from outside our system is their orbital eccentricity greater than 1, which means that their trajectories are open and do not keep them tied to the gravity of Sol. Suas entry velocities, much higher than those of native asteroids and comets, reinforce the conclusion that they are nomads coming from other stars, offering a unique opportunity to study matter from other parts of the galaxy.
The unique characteristics of Oumuamua
Identified in October 2017, 1I/Oumuamua intrigued the scientific community due to its extremely elongated shape, similar to a cosmic cigar, measuring around 400 meters in length. Sua detection was carried out by the Pan-STARRS observatory when the object was already moving away, close to the orbit of Vênus. The name “Oumuamua” means “messenger from afar who arrives first” in Hawaiian, a tribute to the location of its discovery.
The object exhibited an unusual variation in brightness, indicating that it rotated on itself every eight hours. Mais was mysterious in its non-gravitational acceleration, a slight impulse that could not be explained by the attraction of Sol alone. Although outgassing was the most likely hypothesis, no coma or tail was visible, leading to speculation that was later discarded in favor of natural processes not yet fully understood.
Borisov: a comet coming from far away
In August 2019, amateur astronomer Gennadiy Borisov detected the second visitor, 2I/Borisov, using a telescope he built himself. Diferente than its predecessor, Borisov displayed characteristics of a classic comet, with a clearly visible coma (diffuse atmosphere) and tail. Essa’s familiar appearance has allowed scientists to study it with more traditional techniques.
Analysis of its composition revealed a high concentration of carbon monoxide, much higher than that found in comets from our Sistema Solar. Essa chemical peculiarity suggests that it formed in an extremely cold region of its home star system, possibly around a red dwarf star. The Telescópio Espacial Hubble was able to capture detailed images of the object during its passage.
Borisov’s trajectory took it to a distance of approximately two astronomical units from Sol, allowing for an observation period of several months. Esse time was crucial to collect detailed spectroscopic data, which confirmed its cometary nature and provided valuable clues about the chemical diversity existing in other planetary systems in the galaxy.
The challenge of identifying space travelers
The rarity of detections of interstellar objects is not due to a lack of them, but rather to the immense technical challenges involved in finding them. The vast majority of these bodies are small, with diameters less than a kilometer, and have a very faint glow. Isso makes them extremely difficult to see against the dark vastness of space, requiring large, highly sensitive telescopes.
In addition to their small size, these objects travel at very high speeds. Sua passage through the inner Sistema Solar, where our telescopes have the greatest chance of detecting them, is a fleeting event. The observation window may last just a few weeks or months, requiring a rapid response from the global astronomical community to coordinate tracking before the visitor disappears into deep space again.
Another complicating factor is the presence of giant planets like Júpiter, which act as a kind of gravitational “bodyguard”. The immense gravity of Júpiter can drastically alter the trajectories of these visitors, often ejecting them from Sistema Solar before they even get close enough to be detected by observatories based on Terra or its orbit.
Finally, the long journey through the interstellar medium degrades these bodies. Over millions or billions of years, continuous exposure to cosmic radiation and collisions with interstellar dust erodes their surfaces. Esse process can change their characteristics and further reduce their reflectivity, making them even more difficult targets to locate with current instruments.
Distinct routes and impressive speeds
The journeys of Oumuamua and Borisov were markedly different, providing two distinct case studies. Oumuamua approached our system from the direction of the Lyra constellation, with an entry speed of 26 km/s. Sua passage was quick and close, limiting data collection to just a few weeks. Sua orbit, with an eccentricity of 1.2, was the first definitive proof of an object not bound to our Sol, opening a new field in astronomy. Sua trajectory did not allow for prolonged observations, leaving many of its properties shrouded in mystery.
In contrast, Borisov arrived from the direction of the constellation Cassiopeia at a speed of 32 km/s, which increased to 44 km/s at its point of closest approach to Sol. Sua trajectory was more favorable for observation, allowing astronomers to follow it for more than six months. Essa’s long window enabled detailed spectroscopic analyses, which revealed a tail about 160,000 kilometers long and the release of compounds such as cyanogen and water, confirming its active cometary nature and offering a clear counterpoint to the apparently inert behavior of Oumuamua.
Windows for the formation of other systems
The scientific importance of these interstellar visitors is immeasurable, as they represent the first direct physical samples of other planetary systems that humanity has ever been able to study. Cada object carries with it the chemical and geological “fingerprint” of its birthplace, providing crucial clues about planet formation processes elsewhere in the galaxy. By analyzing their composition, astronomers can infer the conditions of temperature, pressure and materials available in the protoplanetary disks where these bodies were formed. The discovery that the composition of Borisov differs from that of comets in our system, for example, suggests a great diversity in planet formation environments. Essas observations are key to refining theoretical models about how solar systems form and evolve, as well as inspiring the development of new technologies and space missions designed to intercept and analyze future cosmic messengers.
The future of interstellar observation
The detection of Oumuamua and Borisov marked just the beginning of a new era in astronomy. The next generation of observatories, like the Observatório Vera C. Rubin on the Chile, are poised to revolutionize the search for these objects. With its wide field of view and ability to quickly scan the sky, Rubin is expected to identify dozens of interstellar visitors per year, turning a rarity into a routine.
In parallel, space agencies are developing proactive missions. The Comet Interceptor mission, from Agência Espacial Europeia (ESA), is a notable example. Ela will be positioned at a strategic point in space, awaiting the discovery of an interstellar object or a long-period comet with a favorable trajectory. Upon receiving the alert, the probe will be sent to perform a close flyby, collecting data with unprecedented precision.
Frequency of annual visitors
Based on available data and statistical models, scientists calculate that Sistema Solar receives between 10 and 100 interstellar objects larger than 100 meters in diameter annually. The vast majority, however, go unnoticed as they traverse the outer regions of the system, far beyond the orbit of Netuno and far from the reach of our most powerful telescopes. Aumentar the detection rate is one of the great challenges for the next decade.
