Lucky for us, Earth is in the Goldilocks zone. In other words, it’s within the range where liquid water can persist (0.99 to 1.7 AU).
In other words, because Earth receives a hearty portion of sun’s rays (just 1 astronomical unit away), it can sustain liquid water and life.
Even here in our Milky Way galaxy, at least 10 possible habitable planets are within the Goldilocks zone.
This means that only light years away, there is a glimmer of hope that other life exists.
Venus and Mars are in the Goldilocks zone too
Temperature is key to sustain liquid water. Where we find liquid water, we are likely to find life.
But it’s not the only factor to harbor life on a planet. For example, Venus and Mars are in the habitable zone of our sun. But it doesn’t mean they’ll have liquid water.
As rovers wheel around the red planet, the verdict is still out for liquid water on Mars. There’s frozen water in its ice caps and trapped in permafrost. But the search for water is still on.
There is very little possibility that Venus could sustain life. Venus is even hotter than Mercury because of its runaway greenhouse effect.
Despite being nicknamed Earth’s twin, Venus may have held oceans of water on its surface. But now, any liquid water would evaporate and lost into outer space dye to its tremendous heating.
Habitable exoplanets in the universe
The distance for planetary habitability depends on the type of start. For example, bigger red dwarf stars habitable zone spans further outward because they’re that much brighter.
Based on the Kepler mission, there could be as many as 40 billion exoplanets in habitable zones. But the blueprint for life on other planets is only from what we know about our own.
Even here in our Milky Way galaxy, at least 10 possible habitable planets such as within Proxima Centauri (Alpha Centauri). This small red dwarf star is part of the triple star system in Alpha Centauri (Rigil Kentaurus).