Why does the sun's energy reach us through radiation only?

In heat transfer by radiation, energy is carried by electromagnetic waves from a starting point to the space surrounding it and does not involve contact with matter. The other forms of heat transfer cannot produce any of the energy that arrives to Earth through the vacuum of space.

Explanation:

All of the energy from the Sun that reaches the Earth arrives as solar

radiation, part of a large collection of energy called the electromagnetic

radiation spectrum. Solar radiation includes visible light, ultraviolet light,

infrared, radio waves, X-rays, and gamma rays.Radiation is one way to transfer heat. To

“radiate” means to send out or spread from a

central location. Whether it is light, sound,

waves, rays, flower petals, wheel spokes or pain,

if something radiates then it spreads outward

from a starting point. You experience radiation

personally whenever you get out of the shower,

soaking wet, in the dead of winter and enjoy the

warmth of the heat lamp in your bathroom. The heat lamp beams out

heat to you and keeps you warm through radiation.

Explanation:

https://www.esrl.noaa.gov/gmd/education/info_activities/pdfs/LA_radiation.pdf