Definition of planet object can be irregular in shape, but beyond that point gravity begins to pull an object towards its own centre of mass until the object collapses into an ellipsoid. (None of the large objects of the Solar System are truly spherical. Many are spheroids, and several, such as the larger moons of Jupiter and Saturn and the dwarf planet , have been further distorted into ellipsoids by rapid rotation or tidal forces, but still in hydrostatic equilibrium.) However, there is no precise point at which an object can be said to have reached hydrostatic equilibrium. As Soter noted in his
Parker Solar Probe the early 2010s, plans for the "Solar Probe" mission were incorporated into a lower-cost "Solar Probe Plus". The redesigned mission uses multiple Venus gravity assists for a more direct flight path, which can be powered by solar panels. It also has a higher perihelion, reducing the demands on the thermal protection system. In May 2017, the spacecraft was renamed "Parker Solar Probe" in honor of astrophysicist Eugene Parker, coiner of the term "solar wind". The solar probe cost NASA US$1.5 billion. The launch rocket bore a dedication in memory of APL engineer Andrew A. Dantzler who had worked on the