A pile of solar panels announces that NASA’s Mars lander InSight will end its role this summer. For the first time in history, InSight has brought a seismograph to Mars and has detected more than 1,300 “fire earthquakes” on Mars. Since the Mars data reflects the internal structure of Mars, on the contrary, it reveals the internal structure from the nucleus to the surface of the earth, which cannot be seen directly, and elucidates the formation and evolution of Mars. We provide information that is indispensable in. In other words, the detection of fire quake is of great scientific value.
Examining the velocities and waveforms detected by InSight revealed that Mars has an unexpectedly large nucleus. It was also confirmed that the core of Mars is in a state of being melted by heat like the core of the earth. Since Mars is much smaller than Earth, it was thought that it would cool faster than Earth (it would lose the heat it had when the planet was formed), so the core of Mars would be solid. There was a theory. InSight also revealed that the density of Mars’ cores is low. At the same time, it is suggested that iron and nickel, which are the main constituents of the nucleus, are mixed with light elements to lower the melting point and slow down solidification.
Seismic observations of celestial bodies outside the Earth do not end with InSight. NASA’s Dragonfly mission is scheduled to launch in 2027, and its destination is the Saturn moon Titan. The JAXA-developed seismograph installed in Dragonfly will look inside the Titan whose surface is covered with ice. Unlike the lander InSight, the Dragonfly is a multi-rotor drone that flies and travels in different parts of Titan. The JAXA seismograph mounted on it was developed (needed to be) as light as 300g compared to the 11kg weight of the InSight seismograph package.[Dragonfly搭載予定の地震計に関する過去の記事はこちら（英語）]
InSight and Dragonfly each have one seismograph, but JAXA has a plan to install multiple seismographs on the moon. It is believed that the lunar earthquake (moonquake) observed by astronauts with an seismometer on the surface of the moon in the Apollo project is caused by the bending of the moon due to the tidal force generated by the gravity of the earth. Professor Takanao Saeki of the Interdisciplinary Science Research Department says that elucidating the inside of the moon will not only help us understand the Earth-Moon system, but will also provide us with the information we need to build a manned base in the future.
The long-term observation of InSight’s fire quake and the elucidation of the internal structure of Mars are truly wonderful achievements. Exploration of internal structures is a major theme for future solar system exploration. Japan, which is an earthquake-prone country, is also considering a plan to arrange its own high-sensitivity moonquake meter on the moon in a network and to know the internal structure of the still uncertain moon in detail. We believe that this will be an important finding when deploying large-scale structures such as the lunar base and the lunar observatory on the moon.
Takanao Saeki (Professor, Interdisciplinary Science Research)
While seismic measurement is the main method for revealing the internal structure of rock-shaped objects, there are alternatives if the interior is not solid. The ESA-led JUICE (Jupiter Ice Satellite Exploration Program / Ganymede Orbiting Satellite) aims to launch in 2023, with multiple Jupiter ice satellites believed to have a huge inner sea beneath the surface ice. At the end of the exploration and planning, the ice satellite Ganymede will be orbited and scrutinized. JAXA will be in charge of some of the hardware to be installed in JUICE, such as GALA (Ganymede Altimeter). Professor Yoshifumi Saito of the Solar System Science Research Department says that GALA may reveal details of the inner ocean of the ice satellite Ganymede.
I have been very interested in the internal structure of celestial bodies for a long time, so I am excited about the news of the exploration of the underground structure of Mars by the seismic observation of InSight. As planetary exploration progresses, the internal structure of celestial bodies other than the Earth will gradually become clear. Jupiter’s ice satellite exploration satellite JUICE (Jupiter Icy Moons Explorer) is said to be inside the ice satellite after making fly-by observations of Europa, Ganymede, and Callisto, which are called Jupiter’s ice satellites. We will explore the possible liquid sea (underground sea).
The JUICE-GALA (Ganymede Laser Altimeter), which Japan is in charge of part of the observation equipment, measures the distance between the JUICE satellite and Ganymede to capture changes in the shape of the Ganymede satellite that orbits Jupiter. We plan to clarify the underground sea structure of the Ganymede satellite. The JUICE satellite will be launched in April next year. Please look forward to the future success of JUICE.
Yoshifumi Saito (Professor, Department of Solar System Science)
InSight showed us the detailed internal structure of planets other than Earth for the first time. InSight’s legacy will continue to accumulate, with far more insight into the formation of planets and satellites.
(Sentence: Elizabeth Tasker / Translation: Masumi Isobe)
The “Overseas Space News” series focuses on the important developments of space exploration around the world and is a place for us researchers to share their interest in these achievements.
Overseas Space News: NASA’s INSIGHT Peeks Inside Mars – Cosmos
(The following are all English pages)
Measuring the wave thought Titan: ISAS builds a seismometer for NASA’s Dragonfly mission (past Cosmos article)
Scientific achievements of the NASA Insight mission (NASA website)
Dragonfly Mission (NASA / Johns Hopkins website)