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"A pretty elegant and simple solution," says a researcher from the Technical University of Denmark (DTU).
The Mars Curiosity mobile was sent to the red planet without gravimeter in November 2011. At that time, NASA considered it was too expensive and difficult to send it with a 20-kg box. But you should never say never.
Researchers at Johns Hopkins University have nevertheless found a way to use Curiosity's instruments to measure gravity. And it's the first time that a rover performs gravity measurements on a foreign planet, reads in the research article published in the journal Science and in a press release from the research laboratory. propulsion by reaction of NASA.
– It's an easy way to save the billions it costs to send with a typical gravitometer. John Leif Jørgensen of DTU Space, who heads the department of measurement and instrumentation of the department, is a rather elegant solution.
Curiosity is packed with electronics, including inertial measurement units (IMUs), which contain both gyroscopes and accelerometers. But they are basically too inaccurate to measure gravity on Mars.
– The problem is that when you turn them on – as researchers do every morning on Mars – they work a lot, but at the same time they are very sensitive to temperature, explains John Leif Jørgensen.
Facts on curiosity
- On August 6, 2012, Curiosity landed at Gale Crater on Mars.
- Curiosity weighs 899 kilos, of which 80 kilograms are scientific instruments.
- It is 2.9 meters long, 2.7 meters wide and 2.2 meters high.
- The mission of Curiosity is to explore the climate and geology of Mars and, among other things, to search for the possible presence of water in the planet.
- It takes an average of 14 minutes and 6 seconds to send a signal from Earth to Mars.
- It is the fourth unmanned space probe sent to Mars since 1996.
But an old rover like Curiosity can, so to speak, build on his experiences, learn from mistakes and become more specific. Every morning for six years, scientists calibrated Curiosity's equipment, "a bit like removing an old clock from the drawer and having to adjust it every time." And in the case of Curiosity, researchers can rely on six years of data without calibration each morning. This allows them to calculate an average that they can use to perform gravimetric measurements. With old data, they can filter effects such as temperature and slope.
In order to reinforce the gravity calculation, they also collected satellite measurements of the gravity field on Mars and incorporated knowledge based on Martian samples of the mineral composition at the surface.
– There is still data filled with noise, but the instrument is accurate enough to give an idea of the composition of clips under Curiosity, says John Leif Jørgensen.
The substrate is surprisingly porous
The apparent density actually affects low energy measurements, and recently the gravity field has decreased faster than expected, while Curiosity has slowly started its journey along the five-kilometer Mount Sharp Mountain.
This gives scientists a clue that the soil is more porous than previously thought and that this could be a crucial element in solving the mystery of the formation of Mount Sharp, which is a mountain in the middle of the Gale crater.
This article was first published at ing.dk.
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