As seen in Forbes Science | November 30, 2018
But more importantly, what can Mars’ inner workings tell us about the formation of planets like our own?
In December, the InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) spacecraft will position its French-built surface seismometer only a few feet from where it landed. That is, on a flat, smooth expanse of lava, says NASA.
In early January, InSight’s robotic arm will drop its German-built HP3 (The Heat Flow and Physical Properties Probe) instrument at a location that is rock-free and sandy as possible. From there, HP3 will start self-hammering down to a depth of 16 feet. Once in place, it’s expected that HP3’s sensors will continually take two years of temperature data in this Martian subsoil. The hope is that it will tell the researchers just how much heat the interior is still emitting today.
That’s, in large part, because the technology for the surface seismometer literally took over twenty years to develop. However, NASA did attempt to measure Marsquakes with its Viking landers in the late 1970s. The first Viking mission’s seismometer never functioned.
Viking 2’s seismometer worked well in fact, Ray Arvidson, a planetary scientist at Washington University in St. Louis, told me. But as far we can tell the seismic record was dominated by vibrations from the lander as the winds blew, he says.
“No unequivocal Mars quakes were registered in this noisy environment,” said Arvidson.
In contrast, InSight’s seismometer will be deployed via the robotic arm onto a prepared flat surface. This will mean the instrument will be less subject to signal noise and will have good contact with the ground, he says.
Yet Arvidson contends that to understand Mars as a planet, seismic and heat flow measurements should have been done before now. But he says a shortage of funds and feasible geophysical mission proposals have been the main impediments to making such research strides.
Based on its density, we know Mars has a metallic core, but we don’t know much beyond that, Kevin Lewis, a planetary geophysicist at Johns Hopkins University, told me. InSight can determine whether the core is liquid or solid, the thickness of the crust, and the current temperature of the interior, he says. Lewis says this will among other things help us understand why Mars no longer has a magnetic field, and whether there could be places in the subsurface where liquid water might still be stable today.
What sort of follow-on Mars missions is needed to further this research?
A network of seismometers would allow researchers to triangulate the location of detected earthquakes, says Lewis. He notes this was done for the moon, where seismometers placed by Apollo 12,14,15, and 16 were used to understand the lunar interior.
But the Moon is pretty much tectonically dead. Thus, how is Mars’ interior different than Earth’s?
“We don’t know,” said Lewis. “Certainly, there will be a core, mantle, and crust like Earth. But beyond that, we don’t know what the structure might look like .”
Mars will also likely be cooler than the earth, says Lewis, since it is smaller and more easily loses heat. But it’s his hope that InSight will provide researchers with a better idea of how terrestrial planets retain their heat as a function of size.
But understanding Venus’ deep interior would arguably make more sense. Almost an earth twin in size, Venus may have briefly been habitable in its earliest history.
Still, in the near term, extrasolar planet hunters are more likely to detect orbitally close-in Venus-like planets around other stars than earthlike planets around other stars.
“Unfortunately, seismology often involves a fair amount of waiting for the quakes,” said Lewis. On Venus, extreme temperatures make it difficult for spacecraft to operate for long periods of time. He notes that the current record holder for an operational spacecraft on Venus is the soviet Venera 13, which lasted only 127 minutes in 1982.
The best bet for Venus, Arvidson says, is to use a balloon system, descend to the surface, do a sample collection, and then ascend high into the cooler atmosphere.
As for InSight’s ultimate findings?
If Mars is found to be warmer and more seismically active than current interior models predict, says Arvidson. It’s likely the Red planet might have undergone relative recent outgassing and greenhouse warming. But if Mars has lower internal heat flow than previously thought and only a few Mars quakes, he says it’s likely that Mars’ interior had long ago passed its geodynamical heyday.
I’m a science journalist and author of “Distant Wanderers: the Search for Planets Beyond the Solar System” who writes about over-the-horizon technology, primarily astronomy and space science. I’m a former Hong Kong bureau chief for Aviation Week & Space Technology magaz…