Sundiver Book 1 of 6: Uplift: A Journy into the fires of the sun... in search of those made us human

In all the universe, no species reached for the stars without "uplift" guidance, except possibly humankind. Did some cryptic patron race begin the job long ago, then abandon us? Or did we leap all by ourselves? That question burns, yet a greater mystery looms ahead, in the furnace of a star. Under the caverns of Mercury, Expedition Sundiver prepares for the most momentous voyage in our history – into the boiling inferno of the sun, seeking our destiny in the cosmic order of life.
David Brin's Uplift novels are among the most thrilling and extraordinary science fiction ever written, comprising one of the most beloved sagas of all time. This freshly revised re-issue includes a substantial author's introduction about the personal and scientific journeys leading to his now-classic first novel.

Sundiver is the first book in David Brin's magnificent Uplift series, including also:
Startide Rising
The Uplift War
Brightness Reef
Infinity's Shore
Heaven's Reach