Microwave Radiometer (Juno)

MWR views Jupiter's microwave radiation so it can see up to hundreds of miles deep into the planet. In August 2016, as Juno swung closely by the planet MWR achieved a penetration of 200 to 250 miles (350 to 400 kilometers) below the surface cloud layer. MWR is designed to make observations below the cloud-tops, especially detecting the abundances of certain chemicals and determining dynamic features. These depths have not been observed before.

MWR was launched aboard the Juno spacecraft on August 5, 2011 (UTC) from Cape Canaveral, USA, as part of the New Frontiers program, and after an interplanetary journey that including a swingby of Earth, entered a polar orbit of Jupiter on July 5, 2016 (UTC),

The electronics for MWR are located inside the Juno Radiation Vault, which uses titanium to protect it and other spacecraft electronics. The antennas and transmission lines are designed to handle the radiation environment at Jupiter so the instrument can function.

Goals

Determining the features and abundances of oxygen, nitrogen, and sulfur at up to 100 bar of pressure (1451 psi) will shed light on the origins and nature of Jupiter. MWR is also designed to detect the amount of water and ammonia deep inside Jupiter. It should also be able to provide a temperature profile of atmosphere down to 200 bar (2901 psi). Overall MWR is designed to look down as deep as roughly 1,000 atmospheres (or bar or kPa), which is about 342 miles (550 kilometers) down inside Jupiter. (1 bar is roughly the pressure at Earth sea level, 14.6 psi.)

One of the molecules MWR is intended to look for inside Jupiter is water, which it is hoped will help explain the formation of the Solar System. By probing the interior, the insights may reveal how and where Jupiter formed, in turn shedding light on the formation of the Earth.

At the time of its use in the 2010s, it was one of only four microwave radiometers to have been flown on interplanetary spacecraft. The first was Mariner 2, which used a microwave instrument to determine the high surface temperature of Venus was coming from the surface not higher up in the atmosphere. There were also radiometer-type instruments on the Rosetta comet probe, and Cassini-Huygens. Previously, the Galileo probe directly measured Jupiter's atmosphere in situ as it descended into the atmosphere, but only down to 22 bars of pressure. However, MWR is designed to look down as deep as 1000 bar of pressure. (1000 bar is about 14,500 psi, or 100000 kPa)