Sky & Telescope - July 2020 - 28

p ROVER
Another mission was originally intended
GROUNDED A
for the 2020 flight window: ExoMars, a
reduced-scale
joint mission between the European Space
model of Franklin
Agency and the Roscosmos agency in Rus- roves a Mars-like
sia, would have put the Rosalind Franklin
terrain in prepararover on the Red Planet's surface in 2021 as tion for the second
leg of the ExoMars
well. However, parachute problems put the
mission, now set
mission behind schedule, causing the team
for launch in 2022.
to delay to a 2022 launch.
Like Perseverance, the Rosalind Franklin
will be on the lookout for life, but it will take a different tack to
the search for biosignatures. Rather than caching samples for
future study, Franklin will drill as deep as two meters into Mars,
retrieving samples to analyze in the lab within its belly. It will
study each sample using infrared and Raman spectrometers,
before using lasers to zap it into gases for analysis with an
organic-sniffing gas chromatograph mass spectrometer.
Team scientists hope that the rover's deep drill will provide
access to rocks that have been shielded from the oxidizing
atmosphere and space radiation. If Mars has life in the form of
microbes living beneath the surface, there is a faint but nonzero
possibility that ExoMars could discover it immediately, without
the need for future missions to recover and return samples.
ESA's Rosalind Franklin rover is much smaller than Perseverance, comparable to the size of NASA's earlier rovers Spirit and
Opportunity. Unlike NASA's rovers, though, Rosalind Franklin
will not bounce to a safe landing inside airbags. Rather, it will
ride down to the surface atop a Russian-built lander.
Once it rolls off the lander, Rosalind Franklin will visit Oxia
Planum, a flat plain along the eastern edge of Chryse Planitia.
There is abundant evidence that rivers once flowed across this
landscape toward a northern sea. The rocks are slightly older
than those at Jezero and contain minerals that formed in liquid
water, but what kind of water? The rocks may well have been
inundated by the salty waters of the northern ocean, a different
environment than Jezero's closed lake basin.
Rosalind Franklin will be in a hurry: Its nominal mission lasts
only a third of a Martian year. Over a traverse path of 1.5 km,
the team hopes to drill as many as six holes. The scientists plan
to drill to more than one depth at each place to compare the
condition of near-surface rocks to those underground.

J U LY 2 0 2 0 * S K Y & T E L E S C O P E

After landing, Perseverance will ﬁnd itself inside a crater named Jezero. At Jezero, the mission's goal will be "to
explore the history of water and chemistry in an ancient
crater lake basin and associated river-delta environments
to probe early Martian climates and search for life." In
particular, the team hopes to sample rocks that contain
biosignatures, evidence for the existence of ancient life (see
next page).
Jezero Crater, which is 45 kilometers in diameter, once
held a lake that could have been as deep as 250 meters
(820 feet). When the lake was full of water, two river systems emptied into it, depositing a thickly layered, spreadﬁngered river delta. The crater, delta, river, and river source
regions have all been mapped by dozens of planetary geologists poring over every data set that every Mars orbiter has
to offer. These regions contain a wide variety of rocks that
geologists would dearly love to sample.
A detailed plan for Perseverance's scientiﬁc traverse
has already been hashed out. The rover will land on a ﬂat
section of the crater ﬂoor to the east of the delta, possibly
atop some volcanic rocks that ﬁlled the crater after the
lake dried up. A lava rock sample, if returned to Earth,
could be radiometrically dated to pin down when in Mars's
history the water activity ended.
Before drilling their ﬁrst sample, though, team members will execute a number of shakedown activities,
which should include the ﬂight of the ﬁrst-ever Martian
helicopter. The helicopter is an experimental technology
that doesn't need to work for the overall mission to be
considered successful. But it could, like the Pathﬁnder's
Sojourner rover did back in 1997, pave the way for future
exploration. The helicopter might provide the most dramatic moments (after landing) of the early phases of the
new Mars mission.
The minicopter weighs only 1.8 kg and has twin
counter-rotating carbon-ﬁber blades that span 1.2 m. It
will drop off the bottom of the rover, then wait until the
rover has driven a safe distance away before it begins to
operate, popping up in brief ﬂights as long as 1½ minutes. Each ﬂight will take its cameras high enough to
photograph potential traverse areas, then it will land and
recharge for another go a few days later. It's designed to ﬂy
up to 5 times, but one bad landing could end its mission
more quickly.
Once the rover acquires its ﬁrst sample, the team will
drive to some rocks in the delta area. Geologists understand deltas very well. Consequently, they know exactly
how they want to traverse Jezero's delta for samples.
They've zeroed in on locations that will answer questions
about Mars's history while also maximizing the opportunity to sample rocks that preserve biosignatures.
The team plans to sample at the base and surface of the
delta, at the ancient lake shoreline (there may be several
such shorelines), and up on the crater rim. If all goes to
plan, the rover will reach the rim by the end of the nomi-

ALT EC

ExoMars:
A Mission
Delayed

Sky & Telescope - July 2020

Table of Contents for the Digital Edition of Sky & Telescope - July 2020