JDEM for General Audience
Every now and then in science, a discovery comes along that is so contrary to expectations that it changes the way we think about the cosmos.
Two teams announced such a finding in 1998. In direct contrast to what scientists thought, the universe's expansion is speeding up.
Imagine the universe as a balloon, with galaxies painted on its surface. As air is pumped into the balloon, the balloon expands, and the galaxies move away from one another. Ever since Edwin Hubble discovered in 1929 that the universe is expanding, scientists assumed that the gravity of galaxies would slow down cosmic expansion, as if air is pumped into the balloon at a slower and slower rate. Instead, the two teams in 1998 discovered that cosmic expansion is accelerating, as if the balloon's size is growing at a faster and faster rate.
What form of energy is acting against gravity and causing the universe's expansion to accelerate?
Scientists have concocted dozens of ideas, but we don't know which one, if any, is correct. Physicist Michael Turner coined the term "dark energy" to describe this mysterious phenomenon. Dark energy, combined with dark matter, seem to be the dominant components of the universe.
The NASA and DOE Dark Energy Mission:
The Joint Dark Energy Mission (JDEM) will explore the properties of dark energy and measure how cosmic expansion has changed over time using multiple techniques. The JDEM observatory is a space-based, medium-aperture, wide field, optical telescope with visible and near-infrared (NIR) imaging and spectroscopic instrumentation.
JDEM will survey the sky to accurately measure the magnitude and redshift of a large sample of Type Ia supernovae (SNe Ia), spectroscopic redshifts of a large, uniform sample of galaxies for Baryon Acoustic Oscillation (BAO) studies, and accurate shape parameters and photometric redshift measurements of a very large sample of galaxies for Weak Lensing (WL) studies.
JDEM is a partnership between NASA and the DOE. The two agencies will work together to develop the science and the instrumentation to carry out the space-based dark energy investigation. Lawrence Berkeley National Laboratory (LBNL) has lead responsibility for the DOE work. The Mission will be managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland.