When a meteoroid strikes the surface of the earth

The team plans to leverage an instrument similar to FIPS on the European Space AgencyвЂ™s BepiColombo mission, which launched for Mercury in 2018 and will approach the planet in late 2025, to make analogous observations and look for more meteoroid impacts during its year orbiting Mercury. вЂњThis was a special observation, and really cool to see the story come together,вЂќ Regoli said. They estimate the meteoroid was likely just a little over three feet long - relatively small, but large enough that models suggest it would create a plume with a height and density closely matching what FIPS detected. The researchers considered various possible causes for the plume, but a meteoroid impact made the most sense. They found the particles clustered in a dense plume, one that had erupted from MercuryвЂ™s surface and extended nearly 3,300 miles into space. Using the particlesвЂ™ speed and direction, the researchers rewound the clock, tracking the particlesвЂ™ motion back to their source. They indicated the particles were likely вЂњyoung,вЂќ having only recently floated into the solar wind. When Regoli, Jasinski and other team members looked over the data years later, those details were like a signpost. Oddly, these particles were traveling in a tight beam, nearly all in the same direction, and at the same speed. On December 21, 2013, as MESSENGER glided over MercuryвЂ™s sunward side, one of its instruments - the Fast Imaging Plasma Spectrometer (FIPS) - saw something strange: an unusually large number of sodium and silicon ions blowing in the SunвЂ™s solar wind, a powerful gale that spews charged gases from the Sun. вЂњIt just shows how rare it is to have the spacecraft at the right place and time to be able to measure something like this,вЂќ said Leonardo Regoli, a space physicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland - where MESSENGER was built and operated - and study co-author. But 2 1/2 years after falling into orbit, MESSENGER hadnвЂ™t seen any. They expected the spacecraft to see two impacts per year during its mission. Scientists hedged their bets on MESSENGER, which would orbit Mercury for four years. Some of them should inevitably hit Mercury, throwing particles thousands of miles into its exosphere.Д«ut such an impact had never been recorded - it was purely hypothetical. The meteoroids come from the asteroid belt, more than 200 million miles away, where gravitational interactions between asteroids and either Jupiter or Mars send small space rocks spiraling into the inner solar system. вЂњLarge meteoroid impacts can blast off an enormous amount of material from the surface, briefly exceeding the mass of MercuryвЂ™s entire exosphere,вЂќ Jasinski said. Scientists believe meteoroid impacts, in part, are responsible for putting such material into MercuryвЂ™s exosphere.

The exosphere forms on MercuryвЂ™s Sun-facing side from material originally on the planetвЂ™s surface, including sodium and around a dozen other molecules. вЂњThis data plays a really important role in helping us understand how meteoroid impacts contribute material to MercuryвЂ™s exosphere.вЂќДЄt two-fifths the size of Earth, Mercury has just a sliver of an atmosphere, called an exosphere, with a pressure thatвЂ™s one-quadrillionth of that felt at sea level on Earth. вЂњItвЂ™s just incredible that MESSENGER could watch this happen,вЂќ said Jamie Jasinski, a space physicist at the Jet Propulsion Laboratory in Pasadena, California, and the lead author on the study. Before, meteoroid impacts had been observed by telescopes only on Earth and the Moon. Now, a recent study in Nature Communications shows the spacecraft can add one more feather to its cap (or, perhaps more aptly, winged feet): It very likely witnessed a large meteoroid impact on Mercury - the first ever observation of an impact on the surface of another planet. NASAвЂ™s MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission to Mercury has been out of operation for nearly six years, but the data it collected keeps on giving, from revealing new insights about VenusвЂ™ atmosphere to providing a new way to measure the length of time neutrons can survive on their own.

When a meteoroid strikes the surface of the earth