Dome-shaped shield provides protection to InSight seismometer
The Seismic Experiment for Interior Structure (SEIS), the seismometer part of NASA’s Mars InSight lander mission, was provided with a third layer of protection from the Red Planet’s extreme temperature variations in the form of a dome-shaped shield.
Deployed by InSight’s robotic arm on Dec. 19, 2018, just weeks after the lander’s Nov. 26 touchdown on the Red Planet, the seismometer, labeled the mission’s “highest priority instrument,” will examine the Martian interior by measuring marsquakes or subsurface ground motion.
Mission scientists hope to determine the depth and composition of the interior of Mars by analyzing the way seismic waves pass through the planet’s underground layers.
“Having the seismometer on the ground is like holding a phone to your ear,” said SEIS Principal Investigator Philippe Lognonne of the Institut de Physique du Globe de Paris in a news release. “We’re thrilled that we’re now in the best position to listen to all the seismic waves from below Mars’ surface and from its deep interior.”
Seismometers on Earth are placed in vaults approximately four feet (1.2 meters) below the surface to protect them from temperature changes, which adversely affect their measurements.
Because InSight cannot construct such subsurface vaults on Mars, mission engineers have had to resort to multiple alternative protection methods from temperature changes as extreme as 170 degrees Fahrenheit (94 degrees Celsius) between Martian day and night.
These temperature changes can cause parts that make up the seismometer, including metal springs, to expand and contract, a major impediment to its collecting accurate data.
“Think of the shield as putting a cozy over your food on a table,” said InSight Principal Investigator Bruce Banerdt of NASA’s Jet Propulsion Laboratory in Pasadena, California. “It keeps SEIS from warming up too much during the day or cooling off too much at night. In general, we want to keep the temperature as steady as possible.”
Officially titled the Wind and Thermal Shield, the aerodynamic dome was placed atop the seismometer on Feb. 2. It protects the instrument from winds, which could render its measurements inaccurate, by pressing the instrument down onto the Martian surface, preventing it from falling over. The dome’s bottom is equipped with a “skirt” composed of chain mail and thermal blankets that hold in heat and enable the device to remain stable on top of rocks.
SEIS is also equipped with several internal temperature variation protections in addition to the dome. To protect its sensitive parts, the seismometer is vacuum-sealed in a titanium sphere that provides insulation and another level of protection from temperature changes. Some of the seismometer’s parts counter the impacts of temperature changes by expanding and contracting in the direction opposite those caused by conditions on the Martian surface.
Surrounding the titanium sphere is yet another protective layer, a hexagon-shaped insulating container that traps carbon dioxide gas from Mars’ atmosphere in hexagon-shaped cells. InSight is also equipped with weather sensors capable of picking up any other interference from the planet. Using the sensors’ data, scientists can filter out such interference, allowing them to obtain accurate data.
Next week, mission scientists hope to deploy InSight’s other crucial instrument, the Heat Flow and Physical Properties Package (HP3), which is designed to burrow deeper than ever previously done into the Martian surface.
HP3 is designed to hammer down to nearly 16 feet (5 meters) where it will measure the heat coming from Mars’ interior to identify that heat’s source and determine how much of it is leaving the planet. Scientists hope this data will provide new insight into the formation of rocky planets and into whether Mars formed from the same materials as the Earth and Moon.
“We’ve been waiting for this moment for a long time,” Lognonne said. “It’s been 130 years since the first seismic record on Earth and almost 50 years since a seismometer was placed on the Moon during the Apollo program. What we learn from SEIS will shed light on how Mars formed and evolved.”
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.