Instrumenty InSight wychwyciły zmiany spowodowane przez 30-sekundowe zaćmienia Słońca (zarejestrowana ilość światła słonecznego spadła podczas zaćmienia o 30 procent) wywołane przez Phobosa.
Zarejestrowany sygnał z magnetometru był najprawdopodobniej spowodowany spadkiem energii elektrycznej w ogniwach słonecznych na skutek zaćmienia.
Podczas zaćmienia powierzchnia gruntu marsjańskiego ochładza się, powodując najprawdopodobniej nierównomierne bardzo małe deformacje, co powoduje przechylenie sejsmometru, które jest rejestrowane.
Czujnik podczerwieni zmierzył oziębienie gruntu o dwa stopnie. Obliczenia wykazały, że w ciągu 30 sekund po zaćmieniu „zimny front” mógł wniknąć w grunt na głębokość zaledwie mikro- lub milimetrów, ale było to wystarczające, by sejsmometr zareagował.Solar eclipse measured on Mars, affects interiorby Barbara Vonarburg, ETH Zurich SEPTEMBER 4, 2020
(...) As expected, InSight's solar cells registered the transits. "When Phobos is in front of the sun, less sunlight reaches the solar cells, and these in turn produce less electricity," Stähler explains. "The decline in light exposure caused by Phobos's shadow can be measured." Indeed, the amount of sunlight dipped during an eclipse by 30 percent. However, InSight's weather instruments indicated no atmospheric changes, and the winds did not change as expected. Other instruments; however, delivered a surprise: both the seismometer and the magnetometer registered an effect.
Unusual signal from the seismometerThe signal from the magnetometer is most likely due to the decline in the solar cells' electricity, as Anna Mittelholz, a recent addition to ETH Zurich's Mars team, was able to show. "But we didn't expect this seismometer reading; it's an unusual signal," Stähler says. Normally, the instrument—equipped with electronics built at ETH—would indicate quakes on the planet. So far the Marsquake Service, led by John Clinton and Domenico Giardini at ETH, has recorded about 40 conventional quakes, the strongest of which registered a magnitude of 3.8, as well as several hundred regional, shallow quakes.
What was surprising during the solar eclipse was that the seismometer tilted slightly in a particular direction. "This tilt is incredibly small," Stähler notes. "Imagine a 5-franc coin; now, push two silver atoms under one edge. That's the incline we're talking about: 10-8." As slight as this effect was, it was still unmistakable. "The most obvious explanation would be Phobos's gravity, similar to how Earth's moon causes the tides," Stähler says, "but we quickly ruled this out." If that were the explanation, then the seismometer signal would be present for a longer period of time and every five hours when Phobos makes its pass, not only during eclipses. Researchers determined the most likely cause of the tilt: "During an eclipse, the ground cools. It deforms unevenly, which tilts the instrument," says Martin van Driel from the Seismology and Wave Physics research group.
As it happens, an infrared sensor did indeed measure a cooling of the ground on Mars of two degrees. Calculations revealed that in the 30 seconds of the eclipse, the "cold front" could penetrate the ground only to a depth of micro- or millimeters, but the effect was enough to tug at the seismometer. (...)
https://phys.org/news/2020-09-solar-eclipse-mars-affects-interior.html
Wątek: InSight (05.05.2018) (Przeczytany 268483 razy)