What are Sun Grazers and Earth Grazers?
These are small number of asteroids with highly elliptical orbits in relation to the Earth or the Sun, known as Earth Grazers and Sun Grazers, respectively.
How close to the Sun can a Sun Grazer Approach?
The notable example is the asteroid Icarus discovered in 1949 which is about 1.5 km in diameter and whose highly elliptical orbit takes it from an aphelion position beyond the orbit of Mars to a perihelion position within 28 million km of the Sun (less than half the mean distance of mercury from the Sun).
How close to the Earth Grazers approach?
Hermes, an asteroid less than 1 km in diameter, occasionally approaches the Earth within twice the Moon’s distance from Earth. Another asteroid Eros can approach the Earth within 23 million km.
What is Vulcan?
Vulcan was an imaginary planet never detected from Earth, but postulated by some astronomers to account for perturbations in the orbits of mercury.