Jupiter's Largest Moon Has Thin Oxygen Atmosphere

October 23, 1996

Astronomers using the Hubble Space Telescope have found evidence for a thin oxygen atmosphere on Jupiter's moon Ganymede, the largest of the Jovian satellites.

The same team of scientists had previously found a tenuous veil of oxygen around another Jupiter moon, Europa.

The observations also suggest that Ganymede, like Earth and Jupiter itself, has polar aurorae -- light displays created when charged particles collide with atmospheric gases.

The findings will be presented as a poster paper on display throughout a meeting of the American Astronomical Society's Division of Planetary Sciences, from Oct. 23 to Oct. 26 at the Tucson Convention Center in Tucson, Ariz.

A team of astronomers used the Hubble telescope's Goddard High Resolution Spectrograph on June 21 to make ultraviolet observations of Ganymede. The astronomers were excited when they saw the spectrum had the characteristic fingerprint that indicates the presence of oxygen gas. But they were puzzled because the spectrograph had detected two peaks, where the astronomers were expecting to see at most a single spike. They soon realized, however, that the two spikes could be explained by the existence of light emitted from two regions near Ganymede's north and south poles.

"The bright spikes correspond nicely to the poles of Ganymede," said Doyle Hall, the Johns Hopkins University astronomer who led the team making the oxygen discovery. Hall called the data "very tentative evidence for the existence of polar aurorae."

Ganymede and Europa are both at least partially covered with water ice. The scientists believe that the atmospheric oxygen comes from the icy surfaces, where oxygen atoms are split off from water molecules that are bombarded by charged particles; exposure to sunlight and meteor impacts also could create some of the gas, Hall said.

The atmosphere on Ganymede is likely to be as thin as the gas previously detected on Europa, comparable in pressure to Earth's atmosphere at an altitude of several hundred kilometers, roughly as high as the space shuttle orbits.

"I want to emphasize that all of the results that we have seen related to oxygen do not require nor imply the presence of life," Hall said. This is in contrast to the oxygen in Earth's atmosphere, which is generated by biological activity. "In fact, the surfaces of these moons, as far as we can tell, are completely inhospitable to any life form that we can imagine."

The other members of the research team were Paul Feldman, a professor in the Johns Hopkins Department of Physics and Astronomy; Darrell Strobel, a professor in the Department of Earth and Planetary Sciences; and astronomer Melissa McGrath from the Space Telescope Science Institute in Baltimore -- the same scientists who used the Hubble telescope to detect an oxygen atmosphere on Europa about two years ago.

Polar aurorae are created when charged particles are guided by a planet's magnetic field toward its poles. As the charged particles collide with atmospheric gases they create brilliant and colorful emissions, which on Earth are known as the Northern and Southern lights. Earth, Jupiter, Saturn, Uranus and Neptune are known to have polar aurorae.

If confirmed, the Ganymede findings "would be the first detection of polar aurorae on any planetary satellite," Hall said.

The astronomers observed ultraviolet light from Ganymede because in the visible spectrum the faint oxygen emissions would have been overwhelmed by bright sunlight reflecting off the moon's surface.

Scientists believe there are three prerequisites for the existence of polar aurorae on a planet or satellite: an atmosphere, a magnetic field, and a population of charged particles. At nearly the same time that the astronomers were using the Hubble telescope to detect the atmospheric oxygen, scientists operating NASA's Galileo spacecraft discovered both a magnetic field and charged particles around Ganymede.

The research is being funded by a two-year grant from the Space Telescope Science Institute totaling $76,000.

Johns Hopkins University

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.