For centuries people have mused about life in outer space. Novelists have explored space colonies on other planets, while tabloids have made millions on UFO sightings and abductions. Despite the demand, scientists have yet to find our neighbors in the vast backyard of outer space.
Physicists identify areas of space capable of sustaining life as circumstellar habitable zones (CHZ), or Goldilocks zones. For a Goldilocks zone to exist it must have temperatures that allow for liquid water. Scientists believe that about 40 percent of red dwarf stars have Goldilocks zones, making the likelihood of extraterrestrial life extremely high. There are scientists, however, who believe other requirements exist, such as geological conditions involving surface water, as well as biochemical factors.
It's possible that lifeforms could exist in areas of space uninhabitable to human beings. Tardigrades, or water bears, are known to withstand harsh physical conditions, such as high pressure levels and extreme temperatures above and below freezing. Some scientists have suggested that creatures like water bears might live in the oceans of other planets and moons and that one such ocean might lie beneath the icy shell of Jupiter's moon, Europa.
As scientists continue their search for life on other planets, aliens remain confined to the realm of science fiction. But for how long, who can say?