Quasi-satellite

A quasi-satellite's orbit around the Sun takes the same time as the planet's, but has a different eccentricity (usually greater), as shown in the diagram.

In contrast to true satellites, quasi-satellite orbits lie outside the planet's Hill sphere, and are unstable.

Over time they tend to evolve to other types of resonant motion, where they no longer remain in the planet's neighborhood, then possibly later move back to a quasi-satellite orbit, etc.

A quasi-satellite is similar to an object in a distant retrograde orbit, in a different context.

The latter term is usually used for a space probe or artificial satellite in a retrograde orbit around a moon, and the period may be much shorter than that of the moon, whereas the term "quasi-satellite" usually refers to an object like an asteroid whose period is similar to that of the planet of which it is considered to be a quasi-satellite.

But in both cases, the object (asteroid, space probe) viewed in a reference frame that rotates with the two main objects (once a year for Sun-Earth, once a month for Earth-Moon) appears to move retrograde compared to that rotation, thus lengthening its sidereal period.

In 2005, aerospace engineer Thomas Gangale proposed a quasi-satellite orbit for spacecraft to provide communications relays between Earth and crews on Mars when Mars is in solar conjunction and direct communication is blocked by the Sun for several weeks.

[15] This dynamical behavior is recurrent where Arawn becomes a quasi-satellite of Pluto every 2.4 Myr and remains in that configuration for nearly 350,000 years.