A small bit of the sun has been trapped by an orbiting satellite, the Smithsonian Astrophysical Observatory reported last week.

Scientists have discovered a quantity of tritium, a radioactive variation of the hydrogen atom, on the capsule of Discoverer 17. Normally most tritium is lost in the atmosphere.

Launched Nov. 12, 1960, from Vandenberg Air Force Base, Calif, the satellite encountered radiation from an intense solar flare within a few hours. The capsule from the satellite was recovered off Hawaii two days later. The solar flare--a vast magnetic storm or explosion on the sun's surface--had caused a great increase in the amount of tritium in the earth's upper atmosphere.

Smithsonian scientists said they found more than 100 times the amount of tritium imbedded near the surface of the capsule than they would normally expect in a satellite making a similar orbit during a period of no flares.

Tritium is produced when great solar explosions cause hydrogen and helium to combine at energies of over a million electron volts. The effect can be duplicated on earth with a cyclotron.