Microwave Radiometer (MWR) is an instrument on the ''Juno'' orbiter sent to planet

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

.Spacecom - Jupiter's Stripes Go Deep, and Other Surprises from Juno Probe - October 2016
/ref> MWR is a multi-wavelength

microwave radiometer A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally ...

for making observations of

's deep

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

. MWR can observe radiation from 1.37 to 50 cm in

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

, from 600 MHz to 22 GHz in frequencies. This supports its goal of observing the previously unseen atmospheric features and chemical abundances hundreds of miles or kilometers into Jupiter's atmosphere. MWR is designed to detect six different frequencies in that range using separate antennas. 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 Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

) from Cape Canaveral, USA, as part of the

New Frontiers program The New Frontiers program is a series of space exploration missions being conducted by NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the ...

, and after an interplanetary journey that including a swingby of Earth, entered a

polar orbit A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of abo ...

of Jupiter on July 5, 2016 (UTC), The electronics for MWR are located inside the ''

Juno Radiation Vault Juno Radiation Vault is a compartment inside the '' Juno'' spacecraft that houses much of the probe's electronics and computers, and is intended to offer increased protection of radiation to the contents as the spacecraft endures the radiation ...

'', which uses

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

to protect it and other spacecraft electronics.Key and Driving Requirements for the Juno Payload Suite of Instruments
/ref> 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 Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

, and

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

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 Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

and

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

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 Mariner 2 (Mariner-Venus 1962), an American space probe to Venus, was the first robotic space probe to report successfully from a planetary encounter. The first successful spacecraft in the NASA Mariner program, it was a simplified version of t ...

, 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 Rosetta ( ) or Rashid (, ; ) is a port city of the Nile Delta, east of Alexandria, in Egypt's Beheira governorate. The Rosetta Stone was discovered there in 1799. Founded around the 9th century on the site of the ancient town of Bolbitine, R ...

'' 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)

Antennas

MWR has six separate antennas of different size that are mounted to the sides of the ''Juno'' spacecraft body. As the spacecraft turns (it is a spin-stabilzed spacecraft) each antenna takes a "swath" of observations of the giant. Five of the six antennas are all on one side of the spacecraft. The sixth and biggest antenna entirely fills another side the ''Juno'' body. MWR antennas: There are two patch

array antennas An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called ''elements'') are usually connected to a single receiver ...

, three slot arrays, and one

horn antenna A horn antenna or microwave horn is an antenna (radio), antenna that consists of a flaring metal waveguide shaped like a horn (acoustic), horn to direct radio waves in a beam. Horns are widely used as antennas at Ultrahigh frequency, UHF and m ...

. *600 MHz/0.6 GHz frequency/50 cm wavelength (biggest antenna takes up one side of spacecraft body and is a patch array antenna) *1.2 GHz (also a patch array antenna, but located with other five antennas on one side) *2.4 GHz (waveguide slot array) *4.8 GHz (waveguide slot array) *9.6 GHz (waveguide slot array) *22 GHz frequency/1.3 cm light wavelength (horn antenna on upper deck of ''Juno'') As ''Juno'' turns the antennas sweep across Jupiter, each frequency/wavelength capable of seeing a certain distance below the visible cloud tops. See also

Reflective array antenna In telecommunications and radar, a reflective array antenna is a class of directive antennas in which multiple driven elements are mounted in front of a flat surface designed to reflect the radio waves in a desired direction. They are a type ...

and

Slot antenna A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven element, driven as an antenna (radio), antenna by an applied radio frequency current, the slot radiates electromag ...

Results

During a close pass in summer of 2017 when MWR was operated at Jupiter, it detected temperature changes deep within the Great Red Spot (GRS) storm. On Perijove 7, which was the sixth science orbit MWR took readings of Jupiter's great red storm down to dozens of kilometers/miles of depth below the surface layers. The distribution of ammonia gas was reported on in 2017, and analyzed. An ammonia rich layer was identified, as well as a belt of ammonia poor atmosphere from 5 to 20 degrees north. During the first eight orbits, MWR detected hundreds of lightning discharges, mostly in the polar regions.

References

External links

NASA ''Juno'' Spacecraft and InstrumentsPIA22177: Slices of Jupiter's Great Red Spot
{{Junojupiternav Spacecraft instruments Juno (spacecraft)