Volcanoes may be erupting on the planet Venus, scientists believe.
Surges in levels of sulphur dioxide high in the planet's atmosphere could be an indication of volcanic activity.
Venus is covered by hundreds of volcanoes, but whether any are still active today is a hotly debated question.
An earlier study of infrared radiation from the surface of Venus suggested that one volcano may have erupted in the planet's recent past.
For the new study, researchers analysed six years of sulphur dioxide observations by the European Space Agency orbiter Venus Express.
On Earth, most of the pungent toxic gas found in the atmosphere is generated by volcanic activity.
Sulphur dioxide is easily destroyed by sunlight. This means that any detected above the thick cloud deck that blankets Venus must have been recently supplied from below.
The study found evidence of big increases in sulphur dioxide followed by sharp decreases.
Venus Express investigator Dr Jean-Loup Bertaux said: "A volcanic eruption could act like a piston to blast sulphur dioxide up to these levels, but peculiarities in the circulation of the planet that we don't yet fully understand could also mix the gas to reproduce the same result."
The findings are published in the latest issue of he journal Nature Geoscience.