The Joint Dark Energy Mission is an Einstein probe that will focus on investigating dark energy. JDEM is a partnership between NASA and the U.S. Department of Energy.

Supernova 1994D and the Unexpected Universe. [More...]

Each group plans to measure how the universe's expansion rate has changed over time by studying Type Ia supernovae: the explosive deaths of white dwarfs. Type Ia supernovae are relatively uniform in their luminosities and other properties, and they are extremely luminous. So they are ideal "standard candles" for measuring distances to remote galaxies.

By observing many Type Ia events in their host galaxies, both near and far, scientists can determine how fast galaxies are moving away from us, and this in turn yields crucial information about how fast our universe was expanding at different epochs. In fact, this is how two independent teams of astronomers discovered dark energy in 1998.

Yet each proposed mission incorporates at least one additional measurement technique as well, unique to that spacecraft. The combination of multiple techniques provides independent and complementary checks on the history of cosmic expansion. These additional methods all delve into the infrared regime, and for good reason: the most distant stars and galaxies glow primarily in infrared. The expanding universe has literally stretched (or redshifted) their visible light into the infrared portion of the electromagnetic spectrum.