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NASA's MESSENGER Mission To Crash Into Mercury In 2 Weeks
astroengine writes: NASA's MESSENGER spacecraft is in the final days of an unprecedented and unexpectedly long-lived, close-up study of the innermost planet of the solar system, with a crashing finale expected in two weeks. Out of fuel, the robotic Mercury Surface, Space Environment, Geochemistry and Ranging, or MESSENGER, probe on April 30 will succumb to the gravitational pull of this strange world that has been its home since March 2011. The purpose of the mission, originally designed to last one year, is to collect detailed geochemical and other data that will help scientists piece together of how Mercury formed and evolved. "MESSENGER is going to create a new crater on Mercury sometime in the near future ... let's not be sad about that," NASA associate administrator John Grunsfeld said Thursday.
The Johns Hopkins Applied Physics Laboratory has an excellent site for looking through the pictures MESSENGER has taken and the science it's done.
Lots of things evidently crash into it:
MESSENGER Finds Spacecraft Graveyard on Mercury
I wish people, including the official NASA press release would quit using this misleading terminology.
A spacecraft only needs fuel to "fight gravity" when changing orbits. In this case, although Mercury doesn't have much of an atmosphere, it does have one, and that's what's dragging the spacecraft down.
Normally I would agree with you on how gravity gets represented and how in a lot of situations you can replace a body with the same mass black hole with no changes (although get close enough, and things do change, e.g. innermost stable orbit).
However, in this case the problem is gravity. The primary cause of orbital decay for MESSENGER is the Kozai mechanism, which is a three body interaction between the Sun, Mercury, and the probe, causing the probe's orbit to increase in eccentricity until it hits the surface. They had to keep using fuel to keep the eccentricity reasonable, especially considering it is in a pretty low orbit.
Mercury has virtually no atmosphere, even with stuff from the Sun there is no atmospheric drag on the relevant timescales. As others point out, there is a three body physics effect here, in particular, it is the Kozai effect that makes the orbit eventually intersect the surface using just gravity alone.
I can't blame people for modding the comment up, because of how much movies and some journalists get wrong with gravity. But in this case the statement came from the actual scientists and people on the project, because it is actually gravity in this case causing orbital decay. It isn't just from Mercury, but from the Sun being so near that three-body instabilities are much larger. Other comment(s) above explain in a little more detail already.