The gorgeous aurora and Jupiter's magnetic field, is there such a connection behind them?

Scientists' new study finds that auroras cause Jupiter's "energy crisis"

Scientists believe auroras could be behind mysterious heating on Jupiter (Credit: J. O'Donoghue (JAXA)/Hubble/NASA/ESA/A. Simon/J. Schmidt)

New observations suggest that Jupiter's mysterious "energy crisis" that has puzzled astronomers for 50 years may be caused by its auroras.

Despite its great distance from the Sun, the largest planet in the Solar System is well known for its unusual heat. Jupiter is located at a distance of 5 astronomical units, or 5 Earth-Sun distances (AU) away (1 AU is several million miles (150 million kilometers)).

With so little sunlight reaching the planet, Jupiter's upper atmosphere should be extremely cold. Scientists estimate that Jupiter's atmosphere is around -100 degrees Fahrenheit (-73 degrees Celsius), according to a NASA statement. However, the average temperature in Jupiter's upper atmosphere is a scorching 800 degrees Fahrenheit (426 degrees Celsius) -- almost as hot as the surface of the hellish planet Venus.

Image: NASA's Juno mission

For decades, scientists have debated what caused Jupiter's so-called "energy crisis," but now new research suggests the planet's intense auroras, fueled by its strong magnetic field, are causing temperatures to soar.

Auroras are common in the solar system, occurring on planets with large magnetic fields, such as Earth and Jupiter. (Mars and Venus also have their own auroras, but the lights work differently on those planets because of the unstable magnetic conditions in those regions.)

In places with strong magnetic fields, like Jupiter and Earth, auroras are created when charged particles are caught in the magnetic field and spiral down toward the poles. On the way to the poles, the particles strike atoms and molecules in the atmosphere and produce light.

The theory of Jupiter's auroral heating comes in part from new data from NASA's Juno spacecraft, which is currently studying Jupiter up close as it flies in and out of intense radiation fields. Juno's close proximity to Jupiter allows scientists to track the planet's atmospheric heating in unprecedented detail.

"To use a beach analogy, if the thermosphere is water, then the magnetic field mapped by Juno is the coastline and the auroras are the oceans," lead author James O'Donoghue said in a statement from Keck Observatory. "We found that water left the oceans and flooded the land, and Juno helped us reveal where the coastline was, and thus understand the extent of the flooding."

The research team used data from Juno and the Hisaki satellite, a planetary spectroscopic observation satellite developed by the Japan Aerospace Exploration Agency (JAXA). Both satellites track Jupiter's magnetic field. They also used data from the Keck II telescope, which provided high-resolution temperature maps. These combined observations allowed scientists to observe the heat pulses of auroras shooting toward Jupiter's equator. The long-term observations from the Hisaki satellite from 2013 to the present also show the importance of the solar wind - a constant stream of particles originating from the sun - which brings its own magnetic field and likely enhances the observed auroras.

"We are very lucky to have captured this potential cooling event," said O'Donoghue, a planetary space scientist at JAXA. "If we had observed Jupiter on a night when the solar wind pressure was not high, we would have missed it."

Using its near-infrared spectrometer, the Keck telescope tracked Jupiter's heat as charged hydrogen molecules moved from the planet's poles to its equator during two observing periods, in April 2016 and January 2017. Keck II also improved its resolution by taking more temperature measurements and only including those with a high degree of certainty. The work took many years, but the result is a temperature map with as many as 10,000 individual data points, a vast improvement over past efforts in terms of resolution.

However, the high-resolution maps also reveal another unsolved temperature mystery.

"We also discovered a strange, localized region of heating far away from the aurora - a long strip of area that we had never seen before," said Tom Stallard of the University of Leicester and co-author of the paper in Keck's statement.

Jupiter's magnetic field is much stronger than Earth's. The volcanic satellites of Jupiter have been known to deliver a lot of material to Jupiter through volcanic eruptions, and many of these particles have entered Jupiter's atmosphere. Jupiter's large size and intense storms also play a role in how the limited heat from the auroras circulates around the planet.

Although the auroral heating effect is not a new theory, scientists have only now been able to prove the hypothesis.

Previously, models examining Jupiter's upper atmosphere speculated that any auroral winds would not blow toward the equator. Instead, the theory suggested that the auroral winds would be pushed westward by Jupiter's rapid rotation. Jupiter rotates once in just 10 hours, and because Jupiter is a gas giant, the rotation time varies slightly at different latitudes. The new observations disprove that idea and suggest that the westward auroral winds may be weaker than the equatorial winds, which carry away the heat of the auroras.

BY: Elizabeth Howell

FY: TMON

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