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.

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 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.

nasa discovery mission
Nasa's Discovery Programme Nasa