NASA is considering launching missions to Venus after potential evidence emerged of life on the planet.
On Monday, an international research team reported that phosphine had been discovered in Venus' atmosphere.
On Earth, the gas is produced by bacteria inhabiting oxygen-free environments.
It is seen by many astrobiologists as a so-called "biosignature" – an indicator of the possible presence of life.
In February, NASA shortlisted four proposed space missions that are now being reviewed by a panel, two of which would involve robotic probes to Venus.
One of those, called DAVINCI+, would send a probe into the Venusian atmosphere.
David Grinspoon, an astrobiologist working on DAVINCI+, told the Reuters news agency: "Davinci is the logical one to choose if you're motivated in part by wanting to follow this up – because the way to follow this up is to actually go there and see what's going on in the atmosphere.”
In light of Monday's findings, NASA Administrator Jim Bridenstine said it is "time to prioritise Venus".
In a statement, Bridenstine said the selection process for the new potential missions will be tough "but I know the process will be fair and unbiased".
The three other proposals include IVO, a mission to Jupiter's volcanically active moon Io, Trident, a fly-by trek to map Neptune's icy moon Triton, and VERITAS, the second of the proposed Venus missions that instead would focus on understanding the planet's geological history.
NASA has said it may choose one or two of the missions.
The phosphine in Venus’ atmosphere was detected by the Atacama (ALMA) array telescope located in Chile, and the James Clerk Maxwell Telescope in Hawaii.
The research team included members from the University of Manchester, Cardiff University and the Massachusetts Institute of Technology (MIT).
A paper on the findings has appeared in the latest issue of Nature Astronomy.
Researchers found that so much phosphine has been discovered in Venus' atmosphere that abiotic mechanisms – which don't involve life but might produce phosphine – can't account for all of it.
The phosphine detected in the region with the planet's atmosphere is considered by some to be potentially habitable.
Venus, a toxic and overheated planet where temperatures at the surface can often hit heights of 427C, has long been considered by scientists to be somewhere no living thing could survive.
The surface has no breathable air, but scientists believe small liveable pockets could be uncovered in its atmosphere.