New Horizons at Jupiter
New Horizons, a spaceship bound for Pluto, took a good look at the Jupiter system when passing by on Feb. 28. The scientific findings were featured in a special section of Science last week, with 11 articles. Joanne Baker said in the Introductory article,1 “The papers in this special issue record how the probe witnessed lightning and aurorae in Jupiter’s atmosphere, volcanic eruptions on the moon Io, and the pulsing of Jupiter’s magnetosphere, a cocoon of charged particles that swathes the entire system.”
- Io’s magnetic personality: Of special interest is Io, the volcanic inner moon of Jupiter. The spacecraft witnessed a major eruption of a polar volcano seen earlier by the Galileo mission:
An eruption of the Tvashtar volcano on the satellite Io was caught in the act, allowing the mechanics of the sulfurous plume and the lava temperature to be measured. Pollution from Io’s volcanoes has even reached the shores of Europa, an icy moon that may harbor oceans beneath its frozen surface. Io’s volcanic emissions feed extra sulfur and oxygen ions into a vast particle cloud that circles the entire Jupiter system, held in place by the planet’s strong magnetic field. Behind the planet, it is pulled into a magnetic shadow billions of kilometers long, streaming away from the Sun as the solar wind deflects around Jupiter. Acting like a giant pipe, this magnetic tail drains half a metric ton of charged particles out of the jovian system each second.
Apparently the mass lost down the magnetotail is just half of Io’s output. Norbert Krupp, in another introductory article,2 said that Io is ejecting one metric ton per second of sulfur dioxide particles. “Data from all of the previous missions have shown that Jupiter’s moon Io is the most important player in the configuration and dynamics of the jovian magnetosphere,” he exclaimed. Keep in mind that Jupiter has the largest magnetosphere by far of any planet in the solar system. This little moon is shedding a lot of responsibility (picture).
- Polar eruption: Spencer et al described the volcanoes on Io in another paper (picture).3 The 350-km-high plume from Tvashtar (picture) contained “remarkable time-variable filamentary structures” (movie). Tvashtar, erupting steadily during the eight days of the observations (picture), was just one of several active volcanoes witnessed in action (picture). They measured lava temperatures nearly 2000° F. – consistent with basaltic lavas and not requiring “exotic high temperature magmas” inferred from some Galileo observations, they claimed (compare this 2002 abstract from Galileo scientists).
- Ring things: Jupiter’s faint rings were the subject of a paper by Showalter et al (picture).4 They were surprised that clumps appeared in some new tenuous rings; these clumps “challenge our theoretical understanding,” they said (movie). Another puzzle is that “The dusty jovian ring system must be replenished continuously from embedded source bodies,” but they could not find any new small moons capable of feeding the ring system other than the previously-known Metis and Adrastea (movie). Jupiter’s rings showed significant variation since Galileo: a pattern matched by the thinnest rings at Saturn and Uranus. “We conclude that the general class of dusty rings may be much more dynamic and time-variable than was previously supposed, with variations on 10- to 20-year time scales not the exception but the norm.”
- Europa dope: New Horizons also got looks at Europa and Ganymede.5 It appears that Io is coating Europa with some of the non-ice material observed earlier on “thousand-year time scales” (picture). The “young” crater Pwyll on Europa showed less contamination than others, supporting the idea that the salty material comes from outside the moon. If so, this raises hopes that the ocean under the ice is not so salty as to inhibit life (09/17/2002). Yet if Europa is undergoing “active resurfacing,” as they said, it might seem plausible that the accumulated salts from Io would contaminate the interior ocean over billions of years.
- Ganymede scarface: Ganymede appears to be accumulating “a globally distributed dark material except where relatively recent impacts have excavated cleaner ice from below the surface.” New Horizons observed three bright, rayed craters not mapped by earlier missions (picture).
1. Joanne Baker, “Grand Tour,” Science, 12 October 2007: Vol. 318. no. 5848, p. 215, DOI: 10.1126/science.318.5848.215.
2. Norbert Krupp, “New Surprises in the Largest Magnetosphere of Our Solar System,” Science, 12 October 2007: Vol. 318. no. 5848, pp. 216-217, DOI: 10.1126/science.1150448.
3. Spencer et al, “Io Volcanism Seen by New Horizons: A Major Eruption of the Tvashtar Volcano,” Science, 12 October 2007: Vol. 318. no. 5848, pp. 240-243, DOI: 10.1126/science.1147621.
4. Showalter et al, “Clump Detections and Limits on Moons in Jupiter’s Ring System,” Science, 12 October 2007: Vol. 318. no. 5848, pp. 232-234, DOI: 10.1126/science.1147647.
5. Grundy et al, “New Horizons Mapping of Europa and Ganymede,” Science, 12 October 2007: Vol. 318. no. 5848, pp. 234-237, DOI: 10.1126/science.1147623.
We could not find where any of the scientists ventured to explain how these short-lived phenomena, sometimes called “dramatic,” could be sustained for 4.5 billion years. New Horizons has shown that the Jupiter system’s dynamic activity, first observed in 1979 by the Voyagers, was not a fluke. Volcanic eruptions, ring erosion and active resurfacing have continued unabated for the last 28 years. How far back in time can these evidences of youth be extended?
Remember that nearly all of these phenomena were a complete surprise when first discovered. Believers in a billions-of-years-old solar system did not predict them then, and cannot explain them now. Some open-minded researcher should take the collective data and model it without the a priori constraint of billions of years. Planetary science needs new horizons.