Free Astronomy Magazine January-February 2018

SOLAR SYSTEM 5 I n astronomy, each discovery adds a piece to the great puzzle of the universe. A cen- tury ago, we thought our galaxy repre- sented the whole cosmos. Thirty years ago, we could only imagine there were planets around other stars, and interstellar space was always considered empty or, at best, just filled with a few atoms of gas per cubic meter. To tell the truth, as early as the 1930s, erstellar T his artist’s im- pression shows the first interstellar asteroid: Oumua- mua. This unique object was discov- ered by the Pan- STARRS 1 telescope in Hawaii. [ESO/M. Kornmesser] JANUARY-FEBRUARY 2018 on several occasions, someone hypothe- sized the existence of numerous dark bod- ies of various sizes in free movement in the empty spaces separating the stars. Verifying the hypothesis seemed difficult, as these bodies did not emit enough radiation to be distinguished from the black background of the night sky. In the last twenty years, however, exploitation of what is called