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The hunt for alien life has so far focused on planets that may contain water, but scientists claim we should be looking further afield.

A new study argues that alien species could exist on planets that contain an exotic substance known as 'supercritical' carbon dioxide.

This type of CO2 is created when liquids and gases reach their temperature and pressure thresholds, creating a supercritical fluid that has features of both a liquid and gas.

The hunt for alien life has so far focused on planets that may contain water, but scientists claim we should be looking further afield. A new study argues that bacteria (pictured) could exist on planets that contain an exotic substance known as 'supercritical' carbon dioxide

Carbon dioxide becomes supercritical when its temperature exceeds 305 degrees Kelvin (32°C) and its pressure goes beyond 72.9 the standard atmosphere at sea level.

On Earth, it's increasingly used in application such as dry cleaning or to sterilise medical equipment, but astrobiologists at Washington State University believe it could also be capable of sustaining life.

'I always have been interested in possibly exotic life and creative adaptations of organisms to extreme environments,' study co-author Professor Dirk Schulze-Makuch told Charles Choi at Space.com.

'Supercritical CO2 is often overlooked, so I felt that someone had to put together something on its biological potential.'

Professor Schulze-Makuch and his team compared enzymes in carbon dioxide and in water, and found that they were more stable in supercritical CO2.

SCIENTISTS FIND 'PARALLEL UNIVERSE' OF LIFE BENEATH THE OCEANS 

An international team of scientists found evidence of tiny creatures living inside the basalt of the Pacific Ocean floor - covered by 2.5km of water and hundreds of metres of sediment

A parallel universe of life exists hidden beneath our planet's ocean floors and could help us search for life on other planets, research last year claimed.

An international team of scientists found evidence of tiny creatures living inside the basalt of the Pacific Ocean floor - covered by 2.5km of water and hundreds of metres of sediment.

The results of their studies revealed evidence of a vast ecosystem whose characteristics are entirely different from any previously investigated.

Core samples taken from the sea floor off the west coast of the U.S. contained traces of micro-organisms living in the total absence of light, and almost entirely disconnected from the world above.

'We're providing the first direct evidence of life in the deeply buried oceanic crust,' said microbiologist Mark Lever, who worked on the study as a PhD student at North Carolina.

'Our findings suggest that this spatially vast ecosystem is largely supported by chemosynthesis.'

Supercritical carbon dioxide makes enzymes choosier about the molecules they bind to, leading to fewer side reactions.

They also found that a number of species of bacteria are tolerant of supercritical carbon dioxide.

Previous studies have found that microbes can live near liquid carbon dioxide trapped under Earth's oceans – and area where the fluid can become supercritical.

The researchers believe that supercritical carbon dioxide may be present on Venus (pictured), whose atmosphere is mostly carbon dioxide. If it is, it may have trapped remnants of life once existed on the planet

For instance, Core samples taken from the sea floor off the west coast of the U.S. contained traces of micro-organisms living in the total absence of light, and almost entirely disconnected from the world above.

'It would be great to drill into areas with supercritical carbon dioxide on Earth and investigate those environments in detail, but this is obviously difficult because of practical limitations and huge expenses,' Professo Schulze-Makuch told Space.com.

The researchers believe that supercritical carbon dioxide may be present on Venus, whose atmosphere is mostly carbon dioxide. 

If it is, it may have trapped remnants of life that may have once existed on the planet.