Mercury and Earth are never fixed at a single distance; their separation varies as both planets orbit the Sun. At their closest approach (near Mercury’s inferior conjunction when Mercury is between Earth and the Sun), the distance can be about 77 million kilometers (approximately 48 million miles). At their farthest separation (when the two planets are on opposite sides of the Sun or near Mercury’s superior conjunction with Earth on the far side), the distance can reach roughly 222 million kilometers (about 138 million miles). A typical or average distance is often cited around 155 million kilometers (97 million miles), but this is a statistical average rather than a constant value. If you’d like, I can tailor the figure to a specific date or orbital configuration.