Nasa is set to make a major announcement about which missions it has selected for the Discovery Programme. The space agency is set to host a media teleconference at 4pm EST (9pm GMT), during which it will discuss the results with the scientists involved.

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The candidate missions will be ones that, "unlock the mysteries of the solar system". The event will be attended by Thomas Zurbuchen, associate administrator of Nasa's Science Mission Directorate, Jim Green, director of Nasa's Planetary Science Division in Washington and – in a cryptic statement – the "principal investigator(s) of the selected mission(s)".

In 2015, Nasa announced it had narrowed down five missions as part of the Discovery selection process. These missions were awarded $3m (£2.4m) each – with which scientists were expected to refine them. At the time, Nasa said it expected to choose one or two missions for flight opportunities "as early as 2020".

The five missions shortlisted were:

Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI)

A mission to study the chemical composition of Venus' atmosphere over a 63-minute descent. This would provide a better understanding of whether there are still active volcanoes on the surface of Venus, and how the surface interacts with the atmosphere.

The Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy mission (VERITAS)

This mission would provide a high-resolution, global topography and imaging of the surface of Venus – providing the first maps of deformation and the plant's surface.

Psyche

This mission looks at the origin of planetary cores by studying the metallic asteroid Psyche. This asteroid appears to have survived a violent collision with another object, the consequence of which was that it stripped the outer, rocky layers of a protoplanet.

Near Earth Object Camera (NeoCam)

NeoCam would help to discover 10 times more near-Earth objects than the total number discovered to date.

Lucy

The Lucy mission would visit the Jupiter Trojan asteroids, an understanding of which could help us understand the history of our Solar System.

The Discovery Programme was founded in 1992 as a new avenue for Nasa's space exploration. Missions that have been part of the programme include the Dawn mission to Vesta and Ceres, the Mars Pathfinder and the Kepler space telescope – which looks for Earth-size habitable planets outside of our Solar System.

Following the mission announcement, the public can ask questions by using the #AskNasa hashtag on Twitter.

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Nasa's Discovery Programme Nasa
NASA