Answer: mercury

AnswerCrossword Clue
MERCURY

First mission to put an American astronaut in space

MERCURY

It falls in winter

MERCURY

Thermometer element

MERCURY
First rock from the sun
MERCURY
Sun's immediate neighbor
MERCURYGod of science.
MERCURYPlanet nearest the sun.
MERCURYElement from cinnabar.
MERCURYEcologists' concern
MERCURYPlanet nearest to the sun
MERCURY60's space project
MERCURYHermes, to Horace
MERCURYIt orbits the sun in 88 days
MERCURYBarometer filler
MERCURYNearest planet to the sun