Hello,

This is a surprisingly tricky question to answer. A while ago, some of the scientists in our department were discussing this very topic. Before we had this discussion, I would have told you that the Mariner 10 spacecraft sent to study the planet Mercury had made the closest approach to the Sun so far. I am not sure what the orbit of the MESSENGER spacecraft (http://messenger.jhuapl.edu/) that is currently studying Mercury is like, but I assume it is similar to Mariner 10 in terms of its closet approach to the Sun. The orbit of the planet Mercury has its perihelion (closest approach to the Sun) at about 0.31 AU (1 AU = 1 Astronomical Unit, the distance between the Earth and the Sun). However, the Helios 2 spacecraft, which studied gamma ray bursts, was launched into a solar orbit with a perihelion of 0.29 AU, which is inside the orbit of Mercury. It seems likely that the Helios 2 satellite has actually made the closest approach to the Sun by a spacecraft so far. You can read more about Helios 2 here: http://heasarc.nasa.gov/d...issions/helios2.html

NASA may be planning missions in the future that will get even closer to the Sun, but I don't know much about them. Maybe one of the solar physicists participating in Solar Week can tell you more.

Kris