NASA Spacecraft Closes in on Comet Tempel 1

NASA is about to discover how solar heat devours a comet.

"For the first time, we'll see the same comet before and after its closest approach to the sun," explains Joe Veverka, principal investigator for NASA's Stardust-NExT mission.

The comet is Tempel 1, which NASA's Deep Impact probe visited in 2005. Now another NASA spacecraft, Stardust-NExT, is closing in for a second look on Valentine's Day, Feb. 14, 2011. The two visits bracket one complete orbit of the comet around the sun--and a blast of solar heat.

"Close encounters with the sun never go well for a comet," says Veverka. "Fierce solar heat vaporizes the ices in the comet's core, causing it to spit dust and spout gas. The cyclic loss of material eventually leads to its demise."

Researchers suspect the flamboyant decay doesn't happen evenly all over a comet's surface*, but until now they've lacked a way to document where, exactly, it does occur. Stardust NExT will image some of the same surface areas Deep Impact photographed 6 years ago, revealing how these areas have changed and where material has been lost.

"Deep Impact gave us tantalizing glimpses of Temple 1," says Veverka. "And we saw strange and unusual things we'd like a closer look at."

At a January 2011 press conference, Veverka and other Stardust-NExT team members listed the features they're most interested in seeing again:

For starters, parts of the comet's surface are layered like pancakes.

"Earth has layers because water and wind move dirt and debris around here, but layering on a comet was a surprise – and a mystery," says Veverka.

Proposed Mission to Jupiter System Achieves Milestone

With input from scientists around the world, American and European scientists working on the potential next new mission to the Jupiter system have articulated their joint vision for the Europa Jupiter System Mission. The mission is a proposed partnership between NASA and the European Space Agency. The scientists on the joint NASA-ESA definition team agreed that the overarching science theme for the Europa Jupiter System Mission will be "the emergence of habitable worlds around gas giants."

The proposed Europa Jupiter System Mission would provide orbiters around two of Jupiter's moons: a NASA orbiter around Europa called the Jupiter Europa Orbiter, and an ESA orbiter around Ganymede called the Jupiter Ganymede Orbiter.

"We've reached hands across the Atlantic to define a mission to Jupiter's water worlds," said Bob Pappalardo, the pre-project scientist for the proposed Jupiter Europa Orbiter, who is based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The Europa Jupiter System Mission will create a leap in scientific knowledge about the moons of Jupiter and their potential to harbor life."

The new reports integrate goals that were being separately developed by NASA and ESA working groups into one unified strategy.

The ESA report is being presented to the European public and science community this week, and the NASA report was published online in December. The NASA report is available at http://www.lpi.usra.edu/opag.

The proposed mission singles out the icy moons Europa and Ganymede as special worlds that can lead to a broader understanding of the Jovian system and of the possibility of life in our solar system and beyond. They are natural laboratories for analyzing the nature, evolution and potential habitability of icy worlds, because they are believed to present two different kinds of sub-surface oceans.

The Jupiter Europa Orbiter would characterize the relatively thin ice shell above Europa's ocean, the extent of that ocean, the materials composing its internal layers, and the way surface features such as ridges and "freckles" formed. It will also identify candidate sites for potential future landers. Instruments that might be on board could include a laser altimeter, an ice-penetrating radar, spectrometers that can obtain data in visible, infrared and ultraviolet radiation, and cameras with narrow- and wide-angle capabilities. The actual instruments to fly would be selected through a NASA competitive call for proposals.

Ganymede is thought to have a thicker ice shell, with its interior ocean sandwiched between ice above and below. ESA's Jupiter Ganymede Orbiter would investigate this different kind of internal structure. The Jupiter Ganymede Orbiter would also study the intrinsic magnetic field that makes Ganymede unique among all the solar system's known moons. This orbiter, whose instruments would also be chosen through a competitive process, could include a laser altimeter, spectrometers and cameras, plus additional fields-and-particles instruments

The two orbiters would also study other large Jovian moons, Io and Callisto, with an eye towards exploring the Jupiter system as an archetype for other gas giant planets.