What is the distance between Mercury and the earth in light years?

Answer

Mercury and the earth both rotate around the sun, and therefore the distance between these two planets is not always the same.

If Mercury passes between the earth and the sun, the distance is at least: 77 million kilometers.

If Mercury is on the other side of the sun, the distance is a maximum of: 224 million kilometers.

You now ask that distance in light year. Well, a light year is so huge that the 77 million or the 224 million kilometers sink into nothing. In light year, always 9 671,000,000 kilometers is.

So: 77 million kilometers = 0.,000 008 light year = 4.28 light minutes
and: 224 million kilometers = 0,000 02316 light year = 12.4 light minutes

You see, if you express distances in the solar system in light years you get very small numbers.
That is why astronomers use another concept to measure distances, for objects in the solar system. There they use the Astonomic unit. That is the average distance from the earth to the sun, and it is 149 598,000 km.

So: 77 million kilometers = 0.51 astronomical units
and: 224 million kilometers = 1.50 astronomical units

By expressing distances in astronomical units in the solar system, you get numbers that are not too large or too small. But for stars you use light years!