The Atmosphere of Uranus Is Literally Leaking Gas Into Space
MICHELLE STARR27 MARCH 2020
Poor old Uranus just can’t seem to catch a break. Something already tipped the planet on its side, so its orbit is perpendicular to those of the other Solar System planets. It probably smells terrible. And now scientists have discovered that the atmosphere of Uranus is leaking out into space.
Hidden in the data from Voyager 2’s historic 1986 encounter with the icy planet, and undiscovered until now, was the presence of a plasmoid – a pocket of atmospheric material being funnelled away from Uranus by the planet’s magnetic field.
It’s the first time a plasmoid has been spotted in connection with an ice giant, and it doesn’t just show us that Uranus’ atmosphere is leaking. It’s also revealing some of the dynamics of this planet’s peculiar, twisted magnetic field.
Actually, leaky atmospheres aren’t that uncommon. It’s called atmospheric escape, and it’s how Mars, for example, turned from what we think was quite a damp planet into a dusty barren wasteland. Venus is leaking hydrogen. Jupiter’s moon Io and Saturn’s moon Titan are leaking. Even Earth is losing about 90 tonnes of atmospheric material a day (don’t worry, we have around 5,140 trillion tonnes, it will take a long time to completely disappear).
Uranus is unquestionably weird. Swirling with mostly water, methane and ammonia, the solar system’s seventh planet is tipped over at 98 degrees, so its magnetic poles take turns directly facing the sun. And its magnetic field is strangely misaligned with the planet’s rotation, causing it to wildly lurch about.
Back in 1986, the ice giant world got what remains its only visitor from Earth — Voyager 2, which is now more than 11 billion miles from Earth, but at that time flew a mere 50,600 miles above Uranus’s cloudy skies. As it passed, Voyager 2 heard an odd magnetic whisper, a signal so ephemeral that it went unnoticed.
More than three decades later, scientists were taking a deep dive into the venerable spacecraft’s data pool, hoping to find scientific mysteries that could help support a return mission to Uranus and its ice giant sibling, Neptune.
They unearthed that magnetic hiccup, and realized it represented the detection of a mass of electrically excited gas with a width 10 times Earth’s circumference.
This ginormous bubble was a jettisoned part of Uranus’s atmosphere. Although only one was spotted, other gassy missiles may also be launched every 17 hours, the time it takes Uranus to complete one rotation.
CNN: Only one spacecraft has flown near Uranus and Neptune, the mysterious ice giant planets on the edge of our solar system.
Yet the wealth of data captured by NASA’s Voyager 2 spacecraft some 34 years ago is still revealing tantalizing hints and reminding scientists of why we need to go back.
Voyager 2 flew by Uranus in 1986, and now, thanks to a little blip discovered in some data, NASA scientists know it also flew through a plasmoid. A plasmoid is a giant magnetic bubble that likely pinched off part of the planet’s atmosphere, sending it out into space.
They found it while looking through old data to find questions they wanted to answer on future potential missions to Uranus.
It’s not unusual for planets to lose their atmospheres. Venus, Jupiter, Saturn and even Earth leak their atmospheres into space, according to NASA.
from official NASA press release:
Unbeknownst to the entire space physics community, 34 years ago Voyager 2 flew through a plasmoid, a giant magnetic bubble that may have been whisking Uranus’s atmosphere out to space. The finding, reported in Geophysical Research Letters, raises new questions about the planet’s one-of-a-kind magnetic environment.
A wobbly magnetic oddball
Planetary atmospheres all over the solar system are leaking into space. Hydrogen springs from Venus to join the solar wind, the continuous stream of particles escaping the Sun. Jupiter and Saturn eject globs of their electrically-charged air. Even Earth’s atmosphere leaks. (Don’t worry, it will stick around for another billion years or so.)
The effects are tiny on human timescales, but given long enough, atmospheric escape can fundamentally alter a planet’s fate. For a case in point, look at Mars.
“Mars used to be a wet planet with a thick atmosphere,” said Gina DiBraccio, space physicist at NASA’s Goddard Space Flight Center and project scientist for the Mars Atmosphere and Volatile Evolution, or MAVEN mission. “It evolved over time” — 4 billion years of leakage to space — “to become the dry planet we see today.”
Atmospheric escape is driven by a planet’s magnetic field, which can both help and hinder the process. Scientists believe magnetic fields can protect a planet, fending off the atmosphere-stripping blasts of the solar wind. But they can also create opportunities for escape, like the giant globs cut loose from Saturn and Jupiter when magnetic field lines become tangled. Either way, to understand how atmospheres change, scientists pay close attention to magnetism.
That’s one more reason Uranus is such a mystery. Voyager 2’s 1986 flyby revealed just how magnetically weird the planet is.
Old gas blob from Uranus found in vintage Voyager 2 data
Buried inside data that NASA’s iconic Voyager 2 spacecraft gathered at Uranus more than 30 years ago is the signature of a massive bubble that may have stolen a blob of the planet’s gassy atmosphere.
That’s according to scientists who analyzed archived Voyager 2 observations of the magnetic field around Uranus. These measurements had been studied before, but only using a relatively coarse view. In the new research, scientists instead looked at those measurements every two seconds. That detail showed what had previously been missed: an abrupt zigzag in the magnetic field readings that lasted just one minute of the spacecraft’s 45-hour journey past Uranus.
The tiny wobble in the Voyager 2 data represents something much larger since the spacecraft was flying so fast. Specifically, the scientists behind the new research believe the zigzag marks a plasmoid, a type of structure that wasn’t understood particularly well at the time of the flyby in January 1986.
But by now, plasmoids have earned scientists’ respect. A plasmoid is a massive bubble of plasma, which is a soup of charged particles. Plasmoids can break off from the tip of the sleeve of magnetism surrounding a planet like a teardrop.
Scientists have studied these structures at Earth and nearby planets, but never at Uranus or its neighbor Neptune, since Voyager 2 is the only spacecraft to date ever to visit those planet
A magnetosphere controls a planet’s evolution by suppressing or enhancing atmospheric loss to space. In situ measurements of Uranus’ magnetosphere from the Voyager 2 flyby in 1986 provide the only direct evidence of magnetospheric transport processes responsible for this atmospheric escape at Uranus.
Analysis of high-resolution Voyager 2 magnetic field data in Uranus’ magnetotail reveals the presence of a loop-like plasmoid filled with planetary plasma traveling away from the planet.
This first plasmoid observation in an Ice Giant magnetosphere elucidates that (1) both internal and external forces play a role in Uranus’ magnetospheric dynamics, (2) magnetic reconnection contributes to the circulation of plasma and magnetic flux at Uranus, and (3) plasmoids may be a dominant transport mechanism for mass loss through Uranus’ magnetotail.