After a long journey of about 7 months, which began at the Vanderberg Air Force base, California, on May 5, InSight is expected to finally reach the Martian surface on November 26. This will be a huge step forward for the scientific endeavor of our solar system and more particularly of its interior rocky planets, as the seismometer carried on its lander is supposed to be the first of its kind to ever be deployed on the surface of another planet, out of Earth.
InSight was launched on an Atlas V 401 rocket, provided by United Launch Alliance. Its landing time is expected to be at 19:47 UTC. Because it takes about 8 minutes for light to travel from Mars to Earth, this means the landing “signal” will be received in Mission Control as early as around 19:54 UTC. This is referred to as “Earth Receive Time” (ERT). At the Mars landing site, it will be mid-afternoon on a winter day.
The landing site is near the equator, about 4.5 degrees north latitude, 135.9 degrees east longitude, in Elysium Planitia. The eventual landing will be the finish point of a 146 million kilometers journey for the spacecraft. The primary mission duration is defined for one Martian year plus 40 Martian days, until November 24, 2020.
The US investment in InSight mission is $813.8 million, including about $163.4 million for the launch vehicle and launch services, and the rest for the spacecraft and operations through the end of the prime mission. In addition, France and Germany, the major European participants, have invested about $180 million in InSight’s investigations, primarily the seismometer investigation (SEIS) and heat flow investigation (HP3).
A brief timeline of planetary seismology
20th century was a period when the humanity encountered a drastic evolution in terms of scientific progress. New domains of knowledge were chartered for the first time in the map of the discoveries of our species and their frontiers were continuously tending to be expanded. Among others, modern seismology was a scientific domain born in the late 19th century, as it can be defined by the milestone invention of the first seismometer with viscous damping by E. Wiechert, in 1898, providing the maiden recordings for the entire duration of an earthquake. Since the, the evolution of our ability to measure, understand and model the propagation of seismic waves lead seismology to be considered as the most powerful tool to explore the interior of the Earth and consequently other planetary and celestial bodies.
The success of a seismic experiment on another planet can be a major contribution for understanding its interior , the size, composition and physical state of its crust, mantle and core. It will contribute to obtain constraints on fundamental questions about the formation and evolution of the Solar System. Moreover, it will help to better understand the formation of planets which can sustain life and provide useful information linked to the habitability of a planet.
The evolution of Earth seismology, for more than a century, contributed to discover very important features of the interior of our home planet. A hundred years ago, humanity was not aware of the composition of the interior of Earth, the depth of the discontinuities between different phases. Even the existence of tectonic plates, which provoke phenomena that literals shock the population of the occurrence region was not known. It turns that seismology is an excellent tool in order to provide in detail information about the interior of a planetary body, on local, regional or global scale. Therefore, performing a seismic experiment with a seismometer deployed on the surface of another planet is of paramount importance in order to understand an extraterrestrial interior.
The adventure of Planetary Seismology begins with the seismometer developed for the Ranger 3 mission, supposed to land on the Moon. The seismometer was installed in a lunar capsule. Unfortunately, Ranger 3 never made it to the Moon and this was also the fate of Ranger 4 and 5. Therefore, the objective of the unmanned deployment of a seismometer on another planetary object, was not yet accomplished.
Thereafter, another seismometer was designed for the Surveyor program. The seismometer was supposed to be fixed on the lander. Even if 5 out of 7 Surveyor missions made successfully the travel and landing on the Moon, finally none of them carried any seismometer.
The first successful deployment of a seismometer outside of our planet was deployed by the astronauts of the Apollo 11 mission. The “great leap for humanity” was also revolutionizing seismology and opened the doors to the interior of another world. The instrument of the Passive Seismic Experiment (PSE) recorded meteorite impacts and moonquakes with about 4 hits by meteorites per day during its lifetime of about 21 days. The installation of the seismometer on the lunar surface was performed by the first humans to have ever walked on it, Neil Armstrong and Buzz Aldrin, on July 20, 1969.
The successful installation of the seismometer by the crew of Apollo 11 mission led to the inclusion of a better, nuclear powered seismic station, by the rest of Apollo missions that successfully made id to the Moon (Apollo 12, 14, 15 and 16). This set of instruments was operational for more than 6 years, until September 1977.
The next step was the deployment of a seismometer by an unmanned mission in another planet. This era began with the development of the seismometer for Viking missions. Unfortunately, the original idea to deploy the seismometer on the ground was abandoned due to its weight and the increased complexity of the operation. Therefore, the instrument operated on the lander. In this position, the noise level of the lander and due to wind activity, was increased. The objectives of the seismic experiment were to characterize the seismic noise environment at the landing sites, to detect local events and large events at teleseismic distances. The first goal was a success in some level, as a first determination of the noise level due to wind activity was obtained. However, with the lack of clear detection, only preliminary estimation were made for the seismic activity, which appeared to be reasonably lower than on Earth.
The next two instruments developed in order to reach the Red Planet never made their interplanetary journey to its end. Instruments were onboard the landers of Phobos 1 and 2, which were both lost in different phases before their landing and deployment respectively. Some years later, the long period vertical axis seismometer, which was onboard of Mars 96 mission, was lost after the failure of the propulsion system and the Earth re-entry of the spacecraft, which plummeted in the Pacific Ocean.
More recently, the first landing of instruments able to detect seismic activity, reached the surface of comet 67P/Churyumov-Gerasimenko, more precisely accelerometers and piezoelectric sources, situated at the feet of the Philae lander of Rosetta mission.
The InSight mission and the Seismic Experiment of Internal Structure of Mars
On May 5, 2018, at 4:05 AM, the seismometer of the Seismic Experiment of Internal Structure (SEIS) of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission, was launched from the Vanderberg Air Force Base in California. It is supposed to perform its landing on the Western Elysium Planitia, on Mars, on November 26.
InSight is a NASA Discovery mission which is supposed to be the first to perform in situ experiments to investigate the internal structure of Mars. One of the main instruments of InSight is the SEIS instrument. In comprises two independent, 3-axis seismometers: an ultra sensitive very broad band (VBB) and a short period (SP) seismometer. This combined architecture of a VBB and an SP instrument was also used for previous missions, as NetLander, ExoMars and SELENE-2.
The second main instrument of the mission is HP3, a heat flow probe which is going to provide data for determining the heat flux on the first meters of Martian subsurface.
The main instruments are supposed to be deployed on the Martian surface by a robotic arm situated on a lander using the same technology with Phoenix mission, which landed successfully on Mars about a decade before the expected InSight landing, on May 25, 2008.
The scientific goals of the InSight mission are summed up as:
- Determine the size composition and physical state of the core
- Determine the thickness and structure of the crust
- Determine the composition and structure of the mantle
- Determine the thermal state of the interior
- Measure the rate and distribution of internal seismic activity
- Measure the rate of impacts on the surface
An in situ geophysical experiment on another planet than Earth, with the use of a seismometer, will contribute to understand geological features of the planet which do not exist on Earth, due to the tectonic activity. Furthermore, it can provide constraints for understanding unique martian characteristics, as the hemispherical dichotomy, which origin is still unknown.
The actual knowledge for Mars interior is provided by the observation of the planet, its moment of inertia, which provides evidence for it differentiation and numerous missions, which mapped its surface and measured its gravity. The actual “aerodynamic” model is the stagnant lid, which means that the lithosphere remains immobile. However, various scenarios for the evolution of Mars are proposed. The experiments performed by InSight can provide evidence for the processes of the mantle, which are associated to the dynamic regime. Investigate in further detail this dynamics regime can provide more information for the habitability of planets, in addition to plate tectonics regime, which is considered fundamental for life on Earth.
The important of an eventual mission success for InSight is high for the evolution of Planetary Seismology, as the efficiency of a seismic experiment performed in distance, to provide satisfactory results in terms of knowledge for planetary interiors would eventually lead to the development of a martian seismic network, which is supposed to work with the principle of Apollo. In addition, it will contribute to the seismic exploration of other objects, as the development of a new seismic experiment and the exploration of the Jovian moon, Europa.
Things to know about landing
Only about 40% of the missions ever sent to Mars – by any space agency – have been successful. The US is the only nation whose missions have survived a Mars landing. The thin atmosphere – just 1% of Earth’s – means that there is little friction to slow down a spacecraft. Despite that, NASA has had a long and successful track record on Mars. Since 1965, it has flown by, orbited, landed on and roved across the surface of the Red Planet.
In 2008, NASA’s Jet Propulsion Laboratory successfully landed the Phoenix spacecraft near Mars’ North Pole. InSight is based on the Phoenix spacecraft, both of which were built by Lockheed Martin Space. Despite tweaks to the heat shield and parachute, the overall landing design is still very much the same: After separating from a cruise stage, an aeroshell descends through the atmosphere. The parachute and retrorockets slow the spacecraft down, and suspended legs absorb some shock from the touchdown.
One of the benefits of InSight’s science instruments is that they can record equally valuably data almost regardless of where they are on the planet. That frees the mission from needing anything more complicated than a flat, stable surface (ideally with few boulders and rocks). That’s why the mission’s team considers the landing site at Elysium Planitia “the biggest parking lot on Mars”.
InSight’s engineers have built a tough spacecraft, able to touch down safely in adult storm if it needs to. The spacecraft’s heat shield is designed to be thick enough to withstand being “sandblasted” by suspended dust. It also has a parachute that was tested to be stronger than Phoenix’s, in case it faces more air resistance due to the atmospheric conditions expected during a dust storm.
The entry, descent and landing sequence also has some flexibility in handling shifting weather. The mission team is receiving daily weather updates from NASA’s Mars Reconnaissance Orbiter in the days before landing so that they can adjust when InSight’s parachute deploys and when it uses radar to find the Martian surface.
Entry, Descent and Landing
InSight’s aeroshell, with the lander enclosed, will enter the top of the Martian atmosphere at about 12,300 mph (5.5 kilometers per second). In roughly 6.5 minutes, InSight will endure heat-generating atmospheric friction on its aeroshell, deploy a parachute and fire descent thrusters to decelerate to only about 5 mph (2.24 meters per second) before touching down on its shock-absorbing legs. This is the riskiest sequence in the entire mission. With dozens crucial steps required for success, it is often referred to as “the seven minutes of terror.” Those minutes and the preceding few hours of preparatory events are more formally called the mission’s entry, descent and landing (EDL) phase.
The top of Mars’ atmosphere is actually a gradual transition to interplanetary space, not a sharp boundary. The atmospheric entry interface point — the target point for the flight to Mars — is set at 2,188.6 miles (3,522.2 kilometers) from the center of Mars. At this point, InSight is about 80 miles (128 kilometers) above the ground elevation of the planned landing site at Elysium Planitia, though the entry point is not directly above the landing site, but about 440 miles (708 kilometers) west of it.
At the interface point elevation, the entry target for the mission’s navigation team is a rectangle about 6 miles wide (10 kilometers) by 15 miles high (24 kilometers). In proportion to the distance of about 298 million miles (479 million kilometers) that InSight will fly from Earth to Mars, hitting a target that size is like scoring a soccer goal from about 80,000 miles (130,000 kilometers). Or like hitting a fast-moving target the size of a smart phone from the distance between New York and Denver.
Compared to the cross-section area of this target at the top of Mars’ atmosphere, the landing ellipse on the surface of Mars is larger — about 81 miles (130 kilometers) generally west-to-east by about 17 miles (27 kilometers) north-to-south. The spacecraft has odds better than 99 percent of reaching the surface within this landing ellipse. Uncertainties that make the landing ellipse so much larger than the entry target include not only the precision of hitting the entry target but also aerodynamic factors, such as how much lift or drag the spacecraft will experience, and atmospheric variables, such as wind velocity and atmospheric density.
Experience the last part of the journey
Experience the NASA InSight approach to Mars with the NASA Eyes on the Solar System app (https://eyes.nasa.gov/). You can regulate the rate of the simulation, in order to follow the trajectory of the capsule as it is going to be during the next days, until its entrance in the Martian atmosphere.
How to watch!
News briefings and launch commentary will be streamed on NASA TV, NASA.gov/live, YouTube.com/NASAJPL/live and Ustream.tv/NASAJPL. On-demand recordings will also be available after the live events have finished on the YouTube and Ustream pages. A clean feed of landing from Mission Control will be streamed and archived on Ustream.tv/NASAJPL2 and YouTube.com/JPLRaw/live.
*Part of the article was written thanks to the NASA Press Kit for InSight landing