Which planet is most like Earth?
Venus is most like Earth in size and mass and is sometimes called Earth's twin, but its surface is extremely hot. Mars is more like Earth in other ways, such as day length and seasons.
Venus is about 95 percent of Earth's diameter and about 81 percent of its mass, and it is our closest planetary neighbor. But its thick carbon dioxide atmosphere creates a runaway greenhouse effect, with surface temperatures around 465 degrees Celsius and crushing pressure. It could not support life as we know it.
Mars is about half Earth's size, but its day is just over 24 hours and its axis is tilted about 25 degrees, giving it seasons like Earth. It has polar ice caps, ancient riverbeds and evidence of past water. Its thin atmosphere and cold temperatures make it harsh, but it is considered the most habitable other planet.
Earth-like exoplanets
Beyond our solar system, astronomers have found rocky planets in habitable zones, such as Kepler-452b and some of the TRAPPIST-1 planets. Whether any of them has liquid water or life is still unknown.
Did You Know?
Some scientists think Venus may have had liquid water oceans for billions of years before its climate changed.