Radiation from Jupiter can destroy molecules on Europa's surface. Material from Europa's ocean that ends up on the surface will be bombarded by radiation, possibly destroying any biosignatures, or chemical signs that could imply the presence of life. Image credit: NASA/JPL-Caltech. Large View
Map of Europa's surface showing the regions that receive the highest radiation dose (pink). Image credit: U.S. Geological Survey, NASA/JPL-Caltech, Johns Hopkins Applied Physics Laboratory, Nature Astronomy
New comprehensive mapping of the radiation pummeling Jupiter's icy moon Europa reveals where scientists should look -- and how deep they'll have to go -- when searching for signs of habitability and biosignatures.
Since NASA's Galileo mission
yielded strong evidence of a global ocean underneath Europa's icy shell in the
1990s, scientists have considered that moon one of the most promising places in
our solar system to look for ingredients to support life. There's even evidence
that the salty water sloshing around the moon's interior makes its way to the
surface.
By studying this material from the interior,
scientists developing future missions hope to learn more about the possible
habitability of Europa's ocean.However,
Europa's surface is bombarded by a constant and intense blast of radiation from
Jupiter. This radiation can destroy or alter material transported up to the
surface, making it more difficult for scientists to know if it actually
represents conditions in Europa's ocean.
As scientists plan for upcoming exploration of
Europa, they have grappled with many unknowns: Where is the radiation most
intense? How deep do the energetic particles go? How does radiation affect what's
on the surface and beneath - including potential chemical signs, or
biosignatures, that could imply the presence of life.
A new scientific study, published today in
Nature Astronomy, represents the most complete modeling and mapping of
radiation at Europa and offers key pieces to the puzzle. The lead author is Tom
Nordheim, research scientist at NASA's Jet Propulsion Laboratory,
Pasadena, California.
"If we want to understand what's going on at
the surface of Europa and how that links to the ocean underneath, we need to
understand the radiation," Nordheim said. "When we examine materials that have
come up from the subsurface, what are we looking at? Does this tell us what is
in the ocean, or is this what happened to the materials after they have been
radiated?"
Using data from Galileo's flybys of Europa two
decades ago and electron measurements from NASA's Voyager 1 spacecraft,
Nordheim and his team looked closely at the electrons blasting the moon's
surface. They found that the radiation doses vary by location. The harshest
radiation is concentrated in zones around the equator, and the radiation
lessens closer to the poles.
Mapped out, the harsh radiation zones appear
as oval-shaped regions, connected at the narrow ends, that cover more than half
of the moon.
"This is the first prediction of radiation
levels at each point on Europa's surface and is important information for
future Europa missions," said Chris Paranicas, a co-author from the Johns
Hopkins Applied Physics Laboratory in Laurel, Maryland.
Now scientists know where to find regions
least altered by radiation, which could be crucial information for the JPL-led
Europa Clipper, NASA's mission to orbit Jupiter and monitor Europa with about
45 close flybys. The spacecraft may launch as early as 2022 and will carry
cameras, spectrometers, plasma and radar instruments to investigate the
composition of the moon's surface, its ocean, and material that has been
ejected from the surface.
In his new paper, Nordheim didn't stop with a
two-dimensional map. He went deeper, gauging how far below the surface the
radiation penetrates, and building 3D models of the most intense radiation on
Europa. The results tell us how deep scientists need to dig or drill, during a
potential future Europa lander mission, to find any biosignatures that might be
preserved.
The answer varies, from 4 to 8 inches (10 to
20 centimeters) in the highest-radiation zones - down to less than 0.4 inches
(1 centimeter) deep in regions of Europa at middle- and high-latitudes, toward
the moon's poles.
To reach that conclusion, Nordheim tested the
effect of radiation on amino acids, basic building blocks for proteins, to
figure out how Europa's radiation would affect potential biosignatures. Amino
acids are among the simplest molecules that qualify as a potential
biosignature, the paper notes.
"The radiation that bombards Europa's surface
leaves a fingerprint," said Kevin Hand, co-author of the new research and
projectscientist for the potential Europa Lander
mission. "If we know what that fingerprint looks like, we can better understand
the nature of any organics and possible biosignatures that might be detected
with future missions, be they spacecraft that fly by or land on Europa.
Europa Clipper's mission team is
examining possible orbit paths, and proposed routes pass over many regions of
Europa that experience lower levels of radiation, Hand said. "That's good news
for looking at potentially fresh ocean material that has not been heavily
modified by the fingerprint of radiation."
JPL, a division of Caltech in Pasadena,
California, manages the Europa Clipper mission for NASA's Science Mission
Directorate in Washington.
For more information about NASA's Europa
Clipper mission, visit: https://www.nasa.gov/europa
News Media Contact
Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-6215
gretchen.p.mccartney@jpl.nasa.gov
Dwayne Brown / JoAnna Wendel
NASA Headquarters, Washington
202-358-1726 / 202-358-1003
dwayne.c.brown@nasa.gov / joanna.r.wendel@nasa.gov
Source: JPL-Caltech/News
