Among our solar system's many moons, Saturn's Titan stands out—it's the only
moon with a substantial atmosphere and liquid on the surface. It even has a
weather system like Earth's, though it rains methane instead of water. Might
it also host some kind of life?
NASA's Dragonfly mission, which will send a rotorcraft relocatable lander to
Titan's surface in the mid-2030s, will be the first mission to explore the
surface of Titan, and it has big goals.
On July 19, the Dragonfly science team published "Science Goals and
Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander" in The
Planetary Science Journal. The paper's lead author is Jason Barnes,
Dragonfly deputy principal investigator and a professor of physics at the
University of Idaho.
The goals for Dragonfly include searching for chemical biosignatures;
investigating the moon's active methane cycle; and exploring the prebiotic
chemistry currently taking place in Titan's atmosphere and on its surface.
"Titan represents an explorer's utopia," said co-author Alex Hayes,
associate professor of astronomy in the College of Arts and Sciences and a
Dragonfly co-investigator. "The science questions we have for Titan are very
broad because we don't know much about what is actually going on at the
surface yet. For every question we answered during the Cassini mission's
exploration of Titan from Saturn orbit, we gained 10 new ones."
Though Cassini has been orbiting Saturn for 13 years, the thick methane
atmosphere on Titan made it impossible to reliably identify the materials on
its surface. While Cassini's radar enabled scientists to penetrate the
atmosphere and identify Earth-like morphologic structures, including dunes,
lakes and mountains, the data could not reveal their composition.
"In fact, at the time Cassini was launched we didn't even know if the
surface of Titan was a global liquid ocean of methane and ethane, or a solid
surface of water ice and solid organics," said Hayes, also director of the
Cornell Center for Astrophysics and Planetary Science and the Spacecraft
Planetary Image Facility in A&S.
The Huygens probe, which landed on Titan in 2005, was designed to either
float in a methane/ethane sea or land on a hard surface. Its science
experiments were predominantly atmospheric, because they weren't sure it
would survive the landing. Dragonfly will be the first mission to explore
the surface of Titan and identify the detailed composition of its
organic-rich surface.
"What's so exciting to me is that we've made predictions about what's going
on at the local scale on the surface and how Titan works as a system," Hayes
said, "and Dragonfly's images and measurements are going to tell us how
right or wrong they are."
Hayes has been working on Titan for almost the entirety of his career. He's
particularly eager to answer some of the questions raised by Cassini in the
area of his specialty: planetary surface processes and surface-atmosphere
interactions.
"My primary science interests are in understanding Titan as a complex
Earth-like world and trying to understand the processes that are driving its
evolution," he said. "That involves everything from the methane cycle's
interactions with the surface and the atmosphere, to the routing of material
throughout the surface and potential exchange with the interior."
Hayes will be contributing significant expertise in another area as well:
operational experience from Mars rover missions.
"The Dragonfly mission benefits from and represents the intersection of
Cornell's substantial history with rover operations and Cassini science,"
Hayes said. "It brings those two things together by exploring Titan with a
relocatable moving craft."
Cornell astronomers are currently involved in the the Mars Science
Laboratory and Mars 2020 missions, and led the Mars Exploration Rovers
mission. The lessons learned from these rovers on Mars are being relocated
to Titan, Hayes said.
Dragonfly will spend a full Titan day (equivalent to 16 Earth days) in one
location conducting science experiments and observations, and then fly to a
new location. The science team will need to make decisions about what the
spacecraft will do next based on lessons from the previous location—"which
is exactly what the Mars rovers have been doing for decades," Hayes said.
Titan's low gravity (around one-seventh of Earth's) and thick atmosphere
(four times denser than Earth's) make it an ideal place for an aerial
vehicle. Its relatively quiet atmosphere, with lighter winds than Earth,
make it even better. And while the science team doesn't expect rain during
Dragonfly's flights, Hayes noted that no one really knows the local-scale
weather patterns on Titan—yet.
Many of the science questions outlined in the group's paper address
prebiotic chemistry, an area that keenly interests Hayes. Many of the
prebiotic chemical compounds that formed on early Earth are also formed in
Titan's atmosphere, and Hayes is eager to see how far down the road of
prebiotic chemistry Titan has really gone. Titan's atmosphere might be a
good analogue for what happened on early Earth.
Dragonfly's search for chemical biosignatures will also be wide-ranging. In
addition to examining Titan's habitability in general, they'll be
investigating potential chemical biosignatures, past or present, from both
water-based life to that which might use liquid hydrocarbons as a solvent,
such as within its lakes, seas or aquifers.
Reference:
Jason W. Barnes et al, Science Goals and Objectives for the Dragonfly Titan
Rotorcraft Relocatable Lander, The Planetary Science Journal (2021).
DOI: 10.3847/PSJ/abfdcf
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