An examination of data from the past mission MESSENGER from NASA has revealed that this spacecraft most likely witnessed the first observed meteoroid impact on the surface of another planet.
Before, meteoroid impacts had only been observed with telescopes on Earth and the Moon:
“It’s just amazing that MESSENGER could see this happen,” Jamie Jasinski, a space physicist at the Jet Propulsion Laboratory in Pasadena, California, and lead author of the study, said in a statement. “
This data plays a very important role in helping us understand how meteoroid impacts contribute material to Mercury’s exosphere. “
At two-fifths the size of Earth, Mercury has just one sliver of atmosphere, called the exosphere, with a pressure that is one quadrillionth of that felt at sea level on Earth.
The exosphere forms on Mercury’s Sun-facing side from material originally on the planet’s surface, including sodium and about a dozen other molecules. Scientists believe that the impacts of the meteoroids, in part, are responsible for placing the material in the exosphere of Mercury.
“Large meteoroid impacts can blast a huge amount of material off the surface, briefly exceeding the mass of the entire exosphere of Mercury,” Jasinski said.
Meteoroids come from the asteroid belt, more than 300 million kilometers away, where gravitational interactions between asteroids and Jupiter or Mars send small space rocks spiraling into the inner solar system. Some of them should inevitably hit Mercury, throwing particles thousands of kilometers into its exosphere.
But such an impact had never been registered, it was purely hypothetical.
The scientists hedged their bets on MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging), which would orbit Mercury for four years. They expected the spacecraft to experience two impacts per year during its mission. But two and a half years after entering orbit, MESSENGER had seen none.
“It just shows how rare it is to have the spacecraft in the right place and time to be able to measure something like this,” said Leonardo Regoli, study co-author and space physicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, where he was built and then operated MESSENGER.
On December 21, 2013, when MESSENGER glided over Mercury’s side toward the sun, one of its instruments, the Rapid Imaging Plasma Spectrometer (FIPS), saw something strange: an unusually large amount of sodium and silicon ions. that blew in the sun’s solar wind, the gale that spews laden gases from the sun. Interestingly, these particles traveled in a narrow beam, almost all in the same direction and at the same speed.
When Regoli, Jasinski, and other team members reviewed the data years later, those details came as a signal. They indicated that the particles were probably “young”, having recently floated in the solar wind. But where did they come from?
Using the speed and direction of the particles, the researchers rewound the clock, tracing the movement of the particles back to their origin. They found the particles clustered in a dense column, one that had risen from the surface of Mercury and had spread nearly 5,000 kilometers into space.
The researchers considered several possible causes for the plume, but the impact of a meteoroid made more sense. They estimate that the meteoroid was probably just over a meter long, relatively small, but large enough for models to suggest that it would create a column with a height and density very close to those detected by FIPS.
“This was a special observation, and really cool to see how the story came together,” Regoli said.
The team plans to leverage a FIPS-like instrument on the European Space Agency’s BepiColombo mission, which launched for Mercury in 2018 and will approach the planet in late 2025, to conduct analog observations and look for more meteorite impacts during its year in orbit around Mercury.
Regoli noted that researchers will need to refine their models before using BepiColombo to make new observations, but the opportunity to see another Mercury impact would be invaluable.
Coat of arms
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