Meteorites bring messages from other worlds and they must be protected

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Meteorites bring messages from other worlds and need to be protected

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The carbonaceous chondrite ALH77307 in transmitted light allows the identification of the glassy spherules known as chondrules. It is representative of a pristine carbonaceous asteroid. J.M. Trigo CSIC/IEEC, Author provided
Josep M. Trigo Rodríguez, Institute of Space Sciences (ICE - CSIC)

Every day in some corner of the Earth fall free samples of the stars that surround us. And they arrive by cosmic messenger, the result of multiple processes that launch these rocks from asteroids and planetary bodies in orbits around the Sun through which they move for tens of millions of years until, after a carambola, they finally find our planet. Meteorite falls, announced by glowing fireballsThe rocks are fascinating rocks that carry a message in a bottle from remote parts of the Solar System.

Their extraterrestrial origin captivates us. Most humans will never reach space and no one will ever be able to visit all the worlds from which meteorites reach us.

Your messages

In expert hands, their minerals provide scientific information capable of delving into the past. They tell stories about the formative processes of asteroids and planets in the early days of our planetary system, long before Earth was formed.

Thanks to the dating of minerals produced by aqueous alteration, we know that carbonaceous chondrites were the first hydrated bodies in the Solar System, before the Earth came into existence.. Even the tiny components inside, formed before the Sun, speak to us, telling us the history of our galaxy. Because it contains presolar grains and certain isotopes that are the product of the disintegration of radioactive elements formed in other stars, we know, for example, that the Sun was born in an association of stars more massive than itself..

Thus, we can extract from them fascinating stories waiting to be told. For this reason, a branch of space sciences is devoted to their study and cataloguing, also as representative samples of the bodies from which they originate.

Rocks surviving their abrupt encounter with the Earth

They do not have it easy in their abrupt and tortuous encounter with our planet. The rocks that cross the interplanetary medium reach the ceiling of the atmosphere at hypersonic speeds (between 11 and 72 km/s), so they suffer friction with the atmosphere and the process called ablation. This is how the luminous phase is generated, which we call bolide or fireball in which more than 95% of the initial mass is usually lost, and the rock tends to fragment, crumble and evaporate.

It is good news that the Earth's atmosphere provides a shield for these projectiles to fragment effectively without being a hazard. In fact, meteorites have such a low thermal conductivity that they cool down during the fall: it is a myth that they reach the ground incandescent.

We could agree that these fascinating rocks, arriving from distant corners of our planetary systemshould be the heritage of all. Any country that is passionate and respectful of science takes measures to preserve this legacy offered by Mother Nature. Spain included them in the Geological Heritage Law and since then the meteorites fallen in Spain are protected by law, they must be made known, preserved, and it is illegal to sell them.

We know where they come from

From the CSIC we have made technological advances applicable to the digital detection of these luminous phenomena to identify and catalog the fireballs that sometimes produce meteorites. Some of them are as luminous as the Moon and we monitor them from the CSIC's Bolide and Meteorite Research Network (SPMN), which for more than 25 years has been keeping an updated list of the most important meteorites in the world. fruit of a citizen science project.

By reconstructing their trajectories, we measure their degree of deepening and survival, and calculate the places of possible fall. In addition, we reconstruct their orbits in the Solar System to know the dynamic routes that transport them to Earth.

For example, seventeen years ago we managed, for the first time in Spain and the ninth in the world, to reconstruct the orbit of a meteorite, the ordinary chondrite Villalbeto de la Peña.. Since then we have obtained the orbits of other meteorites and have been increasing our knowledge about the origin of these rocks. The last four meteorite falls we have recovered and identified in Spain so far: Ardón (1931), Villalbeto de la Peña (2004), Puerto Lápice (2007) and, recently, Puerto Lápice (2007), Traspena (2022).

Most meteorites reach the Earth following tortuous routes from their parent body, in an asteroid-plagued region called the main beltlocated between the orbits of Mars and Jupiter. This is what happened to the metric-sized rock that originated the Villalbeto de la Peña fall. Measuring its age of exposure to cosmic rays we deduced that it needed about 48 million years to reach our planet since it was previously launched by another impact on the surface of its parent asteroid. A real cosmic billiards game.

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Appropriate terminology to refer to these phenomena. In space we speak of asteroids and, if they are rocks with a diameter of less than one meter, meteoroids. Luminous phenomena are meteors and, if they are more luminous than the planet Venus, bolides. Finally, we reserve the term meteorite for any rock of extraterrestrial origin that reaches the surface (Image adapted by the author of TermCat).

Where and how to find meteorites

Meteorites are not easy to find. They are not common and erode quickly when they are on the surface of the earth. The reason is that they contain minerals that are reactive to the action of water and atmospheric oxygen. As a result, they oxidize easily, weakening the consistency of the rock, which eventually disintegrates.

Only in desert regions are these processes minimized by environmental dryness and survive longer, as Phil Bland's studies have shown.. But, as if this were not enough of a challenge, recognizing a meteorite will also depend on knowing how to distinguish them from certain terrestrial rocks and minerals that, when altered by the action of the elements, adopt shapes and shades reminiscent of a meteorite (in the English-speaking world they are known as meteorites). meteorwrongs).

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Main features to learn to recognize meteorites (Image adapted from FRIPON-SPMN Network)

Its characteristics

Meteorites have partially or totally a thin fusion crust produced when they enter the atmosphere. This layer is less than a millimeter thick, is usually dark or black and alters with the passage of time. They also have generally flat faces and edges, rounded by the friction to which they are subjected during their course through the atmosphere at hypervelocity. Due to the overpressure they suffer when penetrating the deeper and denser layers of the atmosphere, they fragment and some show their interior, where shiny metallic grains are usually found. If they have just fallen, their melt crusts are dark and the minerals are shiny, making them easier to find.

Meteorites are also usually heavier than terrestrial rocks. If in doubt, we do not recommend any kind of test that destroys or alters the sample, not even subjecting it to a magnet so as not to alter its primary magnetic field.

The experts will give a quick answer and inform about the procedure to follow to be recognized as discoverers, in case it was indeed a meteorite. As an anecdote, I remember the meteorite we named in 2014, Ardon, a small chondrite fallen in 1931 in front of a girl who preserved it beautifully for 80 years..

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The ordinary Ardon chondrite shows the bright metallic grains and the condyules inside, as well as the thin fusion crust (J.M. Trigo/CSIC/IEEC).

Where should the meteorites end up?

In any case, they should be in expert hands and in an official center that makes them available to the scientific community and, for the most part, on public display. Meteorites should be in museums and research centers that preserve them and where they are in charge of showing them to the public.

Our specialization in the Institute of Space Sciences of CSIC has allowed us to become the only Spanish center with an international repository of Antarctic meteorites from NASA. In addition, as members of the Meteoritical SocietyWe have given official names to many meteorites, so we have a unique collection that is available to young researchers so that they can acquire training in those materials that form the bodies of the Solar System.

Rigorous classification requires time, chemical and mineralogical analysis starting at the time of classification. our Meteorite and Space Sample Return Clean Room at ICE-CSIC. In the case of identifying a new meteorite, we will study and characterize it in order to name it at no cost to the person who provides us with the sample and return most of it to its owner, advising him/her on the steps to be taken.

Sadly, all too often, public interest in meteorites is focused on their economic value, even though the most common ones are much less valuable than precious metals. That bias diverts us from the more relevant aspect: scientifically they are unique, having carved into their materials the evolutionary processes undergone by the asteroids or planetary bodies from which they originate. Incredible stories of cosmic resilience waiting to be told if they fall into expert hands.The Conversation

Josep M. Trigo Rodríguez, Principal Investigator of the Meteorites, Minor Bodies and Planetary Sciences Group, Institute of Space Sciences (ICE - CSIC)

This article was originally published in The Conversation. read the original.