Aheliocentric orbit (also calledcircumsolar orbit) is anorbit around thebarycenter of theSolar System, which is usually located within or very near the surface of theSun. Allplanets,comets, andasteroids in the Solar System, and the Sun itself are in such orbits, as are many artificialprobes and pieces ofdebris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits, as they orbit their respective planet (although the Moon has a convex orbit around the Sun).
The barycenter of the Solar System, while always very near the Sun, moves through space as time passes, depending on where other large bodies in the Solar System, such asJupiter and other largegas giants, are located at that time. A similar phenomenon allows the detection ofexoplanets by way of theradial-velocity method.
Thehelio- prefix is derived from theGreek word "ἥλιος", meaning "Sun", and alsoHelios, thepersonification of the Sun inGreek mythology.[1]
The first spacecraft to be put in a heliocentric orbit wasLuna 1 in 1959. An incorrectly timed upper-stage burn caused it to miss its planned impact on theMoon.[2]
Atrans-Mars injection (TMI) is a heliocentric orbit in which apropulsive maneuver is used to set aspacecraft on atrajectory, also known asMars transfer orbit, which will place it as far asMars orbit.
Every two years,low-energy transfer windows open up, which allow movement between the two planets with the lowest possibleenergy requirements. Transfer injections can place spacecraft into either aHohmann transfer orbit orbi-elliptic transfer orbit. Trans-Mars injections can be either a single maneuver burn, such as that used by theNASAMAVEN orbiter in 2013, or a series of perigee kicks, such as that used by theISROMars Orbiter Mission in 2013.[3][4]
