Sky & Telescope - July 2023 - 21

NASA / JPL / SPACE SCIENCE INSTITUTE
Titania
Oberon
atmosphere, burning it up in the planet's icy air. This disposal
method avoids harm to any potential habitable environment
on the moons.
The baseline orbital mission would last less than five years.
But history suggests that once an orbiter is safely at Uranus,
NASA would consider mission-extension scenarios that would
send the orbiter on additional tours, perhaps studying the
anti-Sun side of the magnetosphere or performing dedicated
gravity-tracking flybys of moons, as Cassini did at Saturn. The
availability of gravity assists from four moons at different distances
from Uranus make the options nearly endless.
RING PEAKS This Cassini image reveals vertical structures rising
abruptly from Saturn's icy B ring. The peaks tower as high as 2.5 km
(1.6 mi) above the rings and may be " splash-ups " created by passing
moonlets. They appear stark thanks to the low illumination angle of
equinox, when sunlight shines obliquely along the ring plane and causes
structures jutting out of the plane to cast long shadows. An orbiter at
Uranus might see similar structures during the planet's own equinox.
masses and gravitational tugs on each other. The spacecraft
could spend a long time in such an orbit; the lifetime of the
mission will ultimately be limited by the waning power available
from its radioisotope power source.
The end would eventually come. To prepare, the orbiter
would execute multiple flybys of the innermost thousandkilometer-size
moon, Ariel - which may have the geologically
youngest surface of the bunch - to pull the spacecraft
into a death spiral. Finally, a rocket burn at apoapsis would
reduce the orbital periapsis to one that intersects Uranus's
To Infinity, and Beyond!
We still don't know exactly what the first dedicated ice-giant
mission will look like, or what it will discover. The scenario
I've outlined here, as detailed as it is, is just one concept. It
also doesn't include how other space agencies might collaborate
with NASA. The European Space Agency, for example,
contributed the Huygens probe to Cassini and is also considering
building an ice-giant orbiter.
One thing we do know is that the scientists and engineers
developing a future mission to Uranus - or Neptune - will
not be the ones operating it when it arrives. The mid- and
late-career scientists who have the professional standing and
the time to propose future missions will be edging toward
retirement by the time a spacecraft actually enters orbit. This
mission will belong to today's early-career scientists.
Studying the outer outer planets requires patience, faith,
and hope - an optimistic view that, two or three decades
from now, today's children will be enjoying the opportunity
to be the first to study a new kind of planet from orbit. These
days, such optimism is a breath of fresh air. So tell your kids:
It's time to probe Uranus!
¢ Contributing Editor EMILY LAKDAWALLA is a freelance science
writer and space artist based in Los Angeles. Find her
work, socials, and shop at Lakdawalla.com/emily.
In kilometers, Oberon lies 1.5 times farther from Uranus than the Moon does from Earth, but
because Uranus is so much bigger than Earth, that's less than 23 Uranian radii out - the Moon
orbits 60 Earth radii away. Imagine Uranus's size in its moons' skies!
sk yand tele scope .o r g * JULY 2023 21

http://www.Lakdawalla.com/emily http://skyandtelescope.org

Sky & Telescope - July 2023

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