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WWW.ASTRONOMY.COM 25
as the world’s first deep-space interplan-
etary CubeSats.
Unpacking for a long stay
Although the cameras started taking pic-
tures and TWINS began collecting Mars
weather data soon after landing, it took
more than three months to truly complete
the landing process. That’s because many
of InSight’s key geophysics instruments
were packed on the lander’s deck during
the journey to Mars. To work properly,
the Instrument Deployment Arm (IDA)
had to carefully unpack and then set
them in contact with the rocky surface.
The InSight team deployed SEIS first,
on December 18, or sol 22. (Mars scien-
tists typically express time on the planet’s
surface in sols. One sol is the length of
a martian day, and equals 24 hours
39 minutes 35 seconds.) It would take
until sol 66 (early February 2019) to com-
plete the adjustments of the seismometer’s
tether back to the rover and to cover the
instrument with its protective Wind and
Thermal Shield (WTS) designed to lower
background noise that the sensitive
instrument would otherwise pick up.
HP^3 was deployed to the surface on
sol 76 (February 12), and it began ham-
mering the mole into the subsurface on
sol 92 (February 28). After a long wait,
the mission team could finally begin to
collect all the different kinds of measure-
ments it had set out to make.
In a sense, then, the InSight mission
has only just started. The SEIS team
detected its first probable marsquake on
sol 128 (April 6), but as of early July, it
has yet to pick up a second. The quake
had a magnitude between 2.0 and 2.5
— a quiver, really, that a human would
not have felt if it had occurred on Earth.
Despite the apparent calm on Mars, the
seismometers are operating beautifully,
detecting ground motions on the scale
of 25 picometers — just 20 percent the
diameter of a hydrogen atom! SEIS’s
high sensitivity has also recorded the
effect of what team members presume to
be numerous dust devils as well as other
kinds of low-frequency atmospheric tur-
bulence, known as infrasound, passing
over the seismometer.
The scarcity of detected marsquakes
in SEIS’s first few months of operations
already rules out the possibility that Mars’
interior is as seismically active as Earth’s.
Although not unexpected, the team is
eager to see if continued monitoring will
reveal Mars to have as little activity as the
Moon, or whether it slots in somewhere
between Earth and the Moon. InSight
should have plenty of time to sort this out
— its primary mission lasts a full martian
year, or just over two Earth years.
HP^3 ’s mole hasn’t fared as well.
Shortly after hammering began, the mole
became stuck some 12 inches (30 centi-
meters) below the surface, perhaps
because the soil is not providing enough
friction or because the instrument
encountered one or more rocks. The
team continues to diagnose the problem
and hopes to devise a strategy that will
allow the instrument to do its work. The
InSight’s deck bristles with science instruments December 4, 2018, before controllers on Earth had the robotic
arm deploy the devices. The copper-colored hexagonal structure in the foreground is a cover to protect the
seismometer. The gray dome behind it is the Wind and Thermal Shield, which would be placed over the
seismometer February 2.
InSight’s seismometer detected its first probable marsquake April 6 (sol 128). The instrument recorded three
distinct types of ground vibrations: Noise from the martian wind came first, followed by the seismic event
itself, and finally the motion of the spacecraft’s robotic arm as it swung around to take pictures.
NASA/JPL-CALTECH/CNES/IPGP/IMPERIAL COLLEGE LONDON
A tremor at the surface of Mars