Radio image of Jupiter made with ALMA. Bright bands
indicate high temperatures and dark bands low temperatures. The dark
bands correspond to the zones on Jupiter, which are often white at
visible wavelengths. The bright bands correspond to the brown belts on
the planet. This image contains over 10 hours of data, so fine details
are smeared by the planet's rotation. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello
Flat map of Jupiter in radio waves with ALMA (top) and visible light with the Hubble Space Telescope (bottom). The eruption in the South Equatorial Belt is visible in both images.
Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/Hubble. Hi-res image
Burke and Franklin's antenna array.
Credit: Carnegie Institution of Washington. Hi-res image
Radio image (bottom) captured by the VLA of Jupiter's Great
Red Spot, compared with a visible-light image (top) from the Hubble
Space Telescope. Credit: de Pater, et al., NRAO/AUI/NSF; NASA. Hi-res image
A 2003 image of Jupiter. The lobes on each side of the planet are caused by Jupiter's strong magnetosphere.
Credit: NRAO/AUI/NSF. Hi-res image
Jupiter is the largest planet in our solar system. It is also the
brightest planet at radio frequencies. While radio astronomy often
focuses on more distant objects such as nebulae and galaxies, the radio
astronomy of planets begins with Jupiter.
While other planets in our solar system emit radio light,
Jupiter is by far the most radio bright. When charged particles in
space interact with Jupiter’s magnetic field, they emit radio light
through a process known as synchrotron radiation. The first radio
observation of Jupiter was made by Bernard Burke and Kenneth Franklin in
1955. They weren’t expecting such a signal, so they initially thought
it was the radio noise of a farm-hand driving home. But subsequent
observations showed the signal was Jovian in origin.
In addition to its synchrotron emissions, Jupiter also gives off
radio light due to thermal emissions. These fainter emissions were first
mapped by the Very Large Array (VLA). The VLA’s antennas can work
together in a wide configuration to capture faint and high-resolution
radio images.
When the VLA was upgraded in 2011, it greatly increased its sensitivity and imaging capabilities. In 2013 the VLA gathered the first radio images of Jupiter’s atmosphere.
It allowed us to peer into Jupiter’s thick atmosphere. Observations in
visible light are limited by the cloud layer of Jupiter. But radio light
penetrates these cloud layers more easily. The VLA observations let us
see 100 kilometers below the visible clouds. They captured details of
the great red spot, and how ammonia within Jupiter’s cloud layer rises
and falls.
Recently the Atacama Large Millimeter/submillimeter Array (ALMA) also captured even higher resolution images of Jupiter’s thermal emissions.
ALMA operates at shorter wavelengths than the VLA. Since shorter
wavelengths are absorbed more readily by Jupiter’s atmosphere, ALMA’s
observation only penetrates about 50 kilometers below Jupiter’s cloud
layer. But ALMA’s high resolution allowed astronomers to create a
three-dimensional map of ammonia gas within the atmosphere. This helps
us understand the mechanisms that drive storms on Jupiter.
As radio technology has advanced, the radio astronomy of Jupiter has
become much more accessible. With only modest radio equipment, you can
observe the radio light of Jupiter for yourselves. Projects such as
NASA’s Radio JOVE
encourage students and amateur scientists to observe radio emissions
from Jupiter and other bright radio sources. The project teaches
students about radio astronomy and engages in citizen science research
projects.
Jupiter has long inspired humanity to look toward the stars. From
Galileo’s first view through his telescope, to the radio arrays of the
VLA and ALMA, the light of Jupiter at all wavelengths has much to offer.
Reference: de Pater, Imke, et al. “Peering through Jupiter’s clouds with radio spectral imaging.” Science 352.6290 (2016): 1198-1201.
Reference: de Pater, Imke, et al. “First ALMA Millimeter-wavelength Maps of Jupiter, with a Multiwavelength Study of Convection.” The Astronomical Journal 158.4 (2019): 139.
