Scientists say a planet is likely to be sterile and lifeless without oceans, because of the impact oceans have on climate.
Oceans are vital to Earth-like life evolving on other planets, a new study has found.
Computer simulations of an alien world similar to Earth revealed the vital role the oceans play in moderating climate.
Without large expanses of water on a planet's surface, seasonal temperature rises would be too rapid and weather too extreme to provide a comfortable home for life, scientists discovered.
Even a planet in the habitable zone of its star - the orbital region where temperatures are mild enough to permit liquid surface water - is likely to be sterile and lifeless without oceans.
In our own solar system, barren Mars has no oceans despite being in the Sun's habitable zone, the researchers point out. As a result, its air temperature swings over a range of 100C.
Professor David Stevens, who led the team from the University of East Anglia's School of Maths, said: "The number of planets being discovered outside our solar system is rapidly increasing. This research will help answer whether or not these planets could sustain alien life.
"We know that many planets are completely uninhabitable because they are either too close or too far from their sun. A planet's habitable zone is based on its distance from the sun and temperatures at which it is possible for the planet to have liquid water.
"But until now, most habitability models have neglected the impact of oceans on climate.
"Oceans have an immense capacity to control climate. They are beneficial because they cause the surface temperature to respond very slowly to seasonal changes in solar heating. And they help ensure that temperature swings across a planet are kept to tolerable levels.
"We found that heat transported by oceans would have a major impact on the temperature distribution across a planet, and would potentially allow a greater area of a planet to be habitable."
Factoring oceans into climate models was vital to knowing whether a planet could develop and sustain life, he added.
The research is published in the latest edition of the journal Astrobiology.
Scientists have so far confirmed the existence of 1739 planets outside our solar system, according to latest information from the Nasa Exoplanet Archive.
There are thousands more unconfirmed "candidates", and a total of 452 multiple planet systems have also been logged.