An interstellar visitor is an object that originates from outside our solar system and passes through it. The first confirmed interstellar object, 'Oumuamua, was discovered on October 19, 2017, by the Pan-STARRS1 telescope in Hawaii. Its hyperbolic orbit, with an eccentricity of 1.2, proved it came from another star system. A second object, Comet 2I/Borisov, was detected on August 30, 2019, by amateur astronomer Gennady Borisov. These two discoveries suggest that such objects may be more common than previously thought. This prediction market asks whether a third interstellar visitor will be confirmed before January 1, 2027. The interest in interstellar visitors stems from their potential to reveal information about other planetary systems. 'Oumuamua was elongated and cigar-shaped, about 800 meters long, with no visible coma or outgassing. 2I/Borisov was a more typical comet with a visible coma and tail, and it contained cyanogen gas. Their differences indicate a diversity of interstellar objects. Scientists have proposed that some interstellar objects could be fragments of exoplanets, comets from other star systems, or even artificial debris. Finding more of them would help answer questions about how planetary systems form and evolve. Recent developments include the construction of the Vera C. Rubin Observatory in Chile, which is expected to begin its Legacy Survey of Space and Time (LSST) in 2025. This survey will scan the entire southern sky every few nights, potentially detecting dozens of interstellar objects per year. The Pan-STARRS survey in Hawaii continues to scan the northern sky. In 2023, researchers proposed a mission called the Interstellar Object Explorer (IOE) to intercept future visitors. The European Space Agency has also studied concepts for a rapid-response spacecraft. These efforts depend on early detection, which requires continuous sky monitoring and data analysis. The prediction market reflects uncertainty about detection rates. Models based on 'Oumuamua and 2I/Borisov suggest that interstellar objects pass through the inner solar system at a rate of about 0.1 to 1 per year. However, many are likely small and faint, making them hard to detect with current telescopes. The LSST will improve detection capabilities significantly. If the true population is larger than current estimates, a confirmation before 2027 is more likely. If the population is smaller, or if most objects are dark and small, the wait could be longer. The market also factors in the possibility that an object might be detected but not confirmed as interstellar until after 2026.

Historical Context

The concept of interstellar objects has been discussed for decades, but no confirmed detections existed before 2017. In the 1970s and 1980s, astronomers speculated that comets from other star systems might occasionally enter the solar system. However, detection technology was too primitive to find them. The first serious search efforts began in the 1990s with the Spacewatch and LINEAR surveys, which focused on near-Earth objects. These surveys occasionally found objects with unusual orbits, but none were definitively interstellar. The discovery of 'Oumuamua on October 19, 2017, changed this. The object was first spotted by the Pan-STARRS1 telescope as a faint point of light moving at 26 kilometers per second relative to the Sun. Within weeks, astronomers calculated its orbit and confirmed it came from outside the solar system. It was designated 1I/2017 U1 ('Oumuamua), with the 'I' standing for interstellar. The object had an unusual shape: it was 10 times longer than it was wide, with a reddish color. It showed no comet-like activity, meaning it had no gas or dust escaping from its surface. This made it hard to classify as either an asteroid or a comet. Two years later, on August 30, 2019, Gennady Borisov discovered a comet that was soon confirmed as interstellar. It was designated 2I/Borisov. Unlike 'Oumuamua, it had a visible coma and tail, and it released cyanogen gas. Its orbit was hyperbolic with an eccentricity of 3.36. The comet was about 1 kilometer in diameter. It passed closest to the Sun on December 8, 2019, at a distance of 2 astronomical units. Observations from the Hubble Space Telescope showed that the comet's nucleus was small, about 0.4 kilometers across. These two objects provided the first direct samples of material from other star systems. Since 2019, no other interstellar objects have been confirmed. However, several candidates have been reported. In 2020, the object 2020 SO was initially thought to be interstellar but turned out to be a rocket booster from the 1966 Surveyor 2 mission. In 2022, the object 2022 AB was considered a possible interstellar object but was later determined to be a solar system asteroid. These cases highlight the difficulty of confirming interstellar origin. The International Astronomical Union maintains a working group for interstellar objects and has established naming conventions. The field is still young, with many open questions about the population size, composition, and origin of these objects.