Hyperbolic asteroid
Asteroids with unbound solar orbits and no outgassing.
A hyperbolic asteroid is an asteroid or other non-cometary object whose orbit around the Sun is not gravitationally bound, meaning its orbital eccentricity exceeds 1 when it is near perihelion. Unlike hyperbolic comets, these objects show no signs of outgassing light elements and therefore lack a cometary coma. The majority of such objects are only weakly hyperbolic and are not thought to originate from outside the Solar System.
Most planets and satellites in the Solar System follow nearly circular, elliptical orbits, with eccentricities much closer to 0 than to 1. In mathematical terms, an eccentricity of exactly 1 defines a parabolic orbit, while any value greater than 1 describes a hyperbola. Some comets travel on parabolic or hyperbolic paths, and hyperbolic asteroids share this property of having an eccentricity above 1.
To date, most discovered hyperbolic asteroids have later exhibited cometary behavior, either through outgassing or by showing motion influenced by solar radiation pressure. The object ʻOumuamua, for instance, moved like a comet but never showed outgassing, so the JPL Small-Body Database classifies it as a hyperbolic asteroid. Several recent hyperbolic comets were initially listed as hyperbolic asteroids, including C/2017 U7 (A/2017 U7), C/2018 C2 (Lemmon), C/2018 F4 (PANSTARRS), C/2019 O3 (Palomar), and C/2019 G4. Astronomer David Jewitt suggests that as the Solar System moves toward the constellation Lyra—the direction from which ʻOumuamua was observed—more hyperbolic asteroids may become visible.
Asteroids can be ejected or placed into highly eccentric orbits by gravitational interactions with planets like Jupiter. However, an orbit that appears unbound when the object is near perihelion does not guarantee it will remain unbound once it moves beyond the planetary region.
- field
- Astronomy
- known_for
- Orbital eccentricity greater than 1, no cometary coma
- characteristic
- Orbit not bound to the Sun near perihelion
Lore & Background
Hyperbolic asteroids are orbital objects with an orbit not bound to the Sun while near perihelion. So far most hyperbolic asteroids discovered have later displayed cometary behavior by either outgassing or demonstrating motion based on solar radiation pressure. ʻOumuamua had the motion of a comet but was never seen outgassing and thus it is listed as a hyperbolic asteroid by the JPL Small-Body Database.
Recent hyperbolic comets that were originally listed as hyperbolic asteroids include C/2017 U7 (A/2017 U7), C/2018 C2 (Lemmon), C/2018 F4 (PANSTARRS), C/2019 O3 (Palomar), and C/2019 G4. According to astronomer David Jewitt, it is likely that, as the Solar System moves toward the Lyra constellation, more hyperbolic asteroids will come into the view of astronomers as that is where ‘Oumuamua was observed coming from.
Asteroids can become ejected or in a highly eccentric orbit around the Sun by being ejected by planets like Jupiter. Just because an orbit solution looks unbound at an epoch when the object is near perihelion does not mean the orbit will be unbound when beyond the planets.
Reader's Guide
Hyperbolic asteroids represent a rare and intriguing class of small Solar System bodies. Their defining characteristic—an orbital eccentricity greater than 1 near perihelion—means they are not gravitationally bound to the Sun at that point, yet they lack the cometary outgassing that typically accompanies such orbits. This distinction is crucial for understanding the population of objects that may be interstellar or simply perturbed by giant planets like Jupiter. The case of ʻOumuamua, which displayed comet-like motion without outgassing, highlights the ambiguity in classifying such objects. Most hyperbolic asteroids discovered so far have later shown cometary behavior, suggesting that true hyperbolic asteroids—those that never outgas—are extremely rare. Their study helps refine models of orbital dynamics and the origins of objects that pass through the inner Solar System. As the Solar System moves toward the Lyra constellation, astronomers anticipate more discoveries, potentially increasing our understanding of these enigmatic bodies.
Did You Know?
- Hyperbolic asteroids have an orbital eccentricity greater than 1 when near perihelion.
- Unlike hyperbolic comets, they have not been seen out-gassing light elements and have no cometary coma.
- ʻOumuamua is listed as a hyperbolic asteroid by the JPL Small-Body Database because it was never seen outgassing.
- Most hyperbolic asteroids discovered have later displayed cometary behavior by outgassing or motion from solar radiation pressure.
More in Hypothetical astronomical objects 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record