As NASA develops its next "flagship" mission to the outer solar system, Jupiter's enigmatic moon Europa should be the target, says Arizona State University professor Ronald Greeley. Although Europa lies five times farther from the Sun than Earth, he notes it may offer a home for life.
Greeley, a Regents' Professor, heads the Planetary Geology Group in ASU's School of Earth and Space Exploration. He is presenting the Europa proposal today (Feb. 18) at the annual meeting of the American Association for the Advancement of Science in San Francisco.
"Europa is unique in our solar system," says Greeley. "It's a rocky object a little smaller than our Moon, and it's covered with a layer of water 100 miles deep." This holds more water than all the oceans on Earth, he explains. Greeley adds that Europa also has the two other basic ingredients of life -- organic chemistry and a source of energy.
Scientists have identified four candidate worlds beyond Earth that might contain life, either now or in the past, Greeley says. These four are Mars, Saturn's moons Titan and Enceladus, and Jupiter's moon Europa.
Mars is the target of numerous ongoing missions, and NASA's Cassini spacecraft is studying both Titan and Enceladus at present. Cassini's results, however, show that Titan and Enceladus have temperatures hundreds of degrees Fahrenheit below zero and may not hold any liquid water.
NASA's Galileo mission surveyed Europa in the late 1990s. Greeley notes the mission found that Europa's surface ice was mixed with organic minerals that came up from the solid rocky part of the moon or were deposited by meteorite and comet impacts at the surface. Yet Galileo's results raised more questions than answers.
"We know Europa's surface is frozen," Greeley says. "But we don't know if it's frozen all the way down, or if there's an ocean under an ice shell."
The ice thickness is a key question, notes Greeley.
"Ultimately, we want to get down through that ice shell and into the ocean where any action is," he says. "So it matters whether the ice is 10 yards thick, or 10 miles or more. The data we have today will never answer that question."
Europa's place in the Jovian system, however, provides a possible means of measuring the ice shell's thickness. As Europa circles Jupiter every 3.6 days, it orbits in lockstep with two other moons, Ganymede and Callisto. The gravity of these bodies, plus Jupiter itself, raises tides in Europa that heat it by friction.
"Geophysical models show that if the ice goes all the way down, the amount of tidal flexing will be small, only a few feet or so," Greeley explains. "But if the ice shell is thin, say 30 feet thick, the tidal flexing could range 130 feet." What's needed, Greeley adds, is an instrument that can measure the flexing on a continuing basis.
To do that, he says, requires the spacecraft to orbit Europa while it measures the surface with a high-precision altimeter. It might be possible, Greeley notes, to measure the flexing from orbit around Ganymede, the next moon out from Europa. A Ganymede orbit would ease the task for spacecraft and instrument designers, he says, "because the radiation environment at Europa's orbit is extremely harsh." Calculations show radiation levels are high enough to damage instruments in a few months.
Mission details still need to be developed, Greeley notes, along with basic specifications for instruments and performance. He is working with Robert Pappalardo, an ASU graduate now at the Jet Propulsion Laboratory, to define more carefully the Europa orbiter mission. They expect to finish their work by the end of this summer.
The U.S. National Academy of Sciences published a report in 2003 summarizing what planetary scientists felt were the highest priority missions for the decade ahead. A Europa geophysical mission stood at the top of the list.
"In the minds of many researchers," says Greeley, "Europa is of primary importance."
Skip Derra | EurekAlert!
Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa
Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik
A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.
In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...
A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.
By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...
Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
23.02.2018 | Physics and Astronomy
23.02.2018 | Health and Medicine
23.02.2018 | Physics and Astronomy