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Space Topics: New Horizons

The Year in Pictures: 2007

New Horizons: The Fire Fountains of Tvashtar

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Io erupts, in color
Credit: NASA / JHUAPL / SwRI

Jupiter’s moon Io put on a spectacular fireworks show for New Horizons as the Pluto-bound spacecraft picked up a gravity assist from Jupiter in January and February. The primary reason for the Jupiter flyby was to shave time off the long cruise to Pluto, but the New Horizons team used the opportunity to conduct a thorough test of systems, instruments, and personnel, packing the flyby with observations from Jupiter, its rings, and its moons.

A few months before New Horizons' arrival, Hubble images revealed new volcanic activity near the north pole of Io, and science team members realized that the volcano known as Tvashtar probably was erupting. They were not sure whether the eruption would last until New Horizons made it to the system, but Tvashtar didn't disappoint. Because of its north polar location and New Horizons' nearly equatorial approach to the Jupiter system, the plume of Tvashtar was silhouetted against the sky in every shot that the spacecraft captured of the violent moon.

This image represents the combined effort of two of New Horizons' instruments: the Long Range Reconnaissance Imager (LORRI), which has high resolution but no color capability, and the Multispectral Visual Imaging Spectrometer (MVIC), which has only one fourth the resolution of LORRI but is capable of multicolor images. The approximately true color image was taken just after New Horizons' closest approach, so Io is seen in crescent phase.

Tvashtar in motion
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Tvashtar in motion
In this amazing animation from the New Horizons flyby of Jupiter, the 300-kilometer-high plume erupting from Io's Tvashtar volcano is visibly in motion, its fountains of lava spraying up, out, and back down to the Ionian surface. New Horizons captured the motion fortuitously; the images were part of an observation of the ring system designed to search for structures in the rings, and because Io was close by the science team planned the ring images to encompass Io in the same frame. The animation contains five images taken over an eight-minute span of time beginning at 23:50 UT on March 1, 2007. Credit: NASA / JHUAPL / SwRI

Tvashtar is erupting on Io's night side. The volcano's incandescent fire fountains, which are a thousand meters tall, are too small to be resolved in this image, but the fiery eruption lights the neck of Tvashtar's plume from within so that it glows red. The hot gas chills as it shoots through space until it condenses into frost, making an umbrella-shaped plume that soars 330 kilometers (205 miles) above the moon. The uppermost reaches of the plume rise above Io's shadow to be lit by sunlight.

On the lower right side of Io's dark limb is another, dimmer plume, actually a pair of plumes from a long eruption and lava flow at Marduk. Marduk is one of many areas where New Horizons' images revealed many changes since the moon was imaged by Voyager or even Galileo.