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---------------------- 2715 - MOLECULES - discovered in outer space?
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- Let’s start with rocks. The name of the rock comet is 2I/Borisov. It was discovered on August 30, 2019, by an amateur astronomer. Following the appearance of another interstellar object 'Oumuamua in 2017, this was the second object from another solar system ever discovered wandering through our cosmic neighborhood.
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- On December 15, and 16, in 2019, astronomers took a closer look at 2I/Borisov using the Atacama Large Millimeter/submillimeter Array (ALMA), a giant radio telescope in Chile Atacama Desert.
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- The researchers found that the gas coming from the comet contained more carbon monoxide (CO) than has been detected in any other comet this close to the Sun, less than 186 million miles. The concentration of CO in the gas coming from this comet was between 9 and 26 times higher than in the average comet in our solar system.
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- The team detected both CO and hydrogen cyanide (HCN). However, they found a similar amount of HCN in 2I/Borisov that's found in other comets in our solar system, so that discovery wasn't much of a surprise.
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- But, the unexpectedly high quantities of CO offered a major clue as to where this comet came from. The comet must have formed from material very rich in CO ice, which is only present at the lowest temperatures found in space, below minus 420 degrees Fahrenheit.
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- The gases show that the comet may have formed in a different way than our own solar system comets, in an extremely cold, outer region of a distant planetary system.
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- Astronomers suspect that 2I/Borisov came from a cold region in a larger protoplanetary disk, or rotating disk of dust and gas around a young star from which planets and planetary objects form.
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- Many of these protoplanetary disks extend well beyond the region where our own comets are believed to have formed, and contain large amounts of extremely cold gas and dust.
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- 2I/Borisov was traveling 21 miles per second when it zoomed through our solar system. Researchers think that, whichever solar system it came from, it was likely torn from that system by the gravity of a passing star or large planet. After a long trip through space, it has made history as one of only two interstellar visitors ever identified in our solar system.
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- Further studies and possible future observations of other interstellar comets will add to this understanding and also show whether 2I/Borisov and its unusual makeup is typical for such an object.
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- It is not just comets that tell us about the makeup of our Solar System, the molecules in space gas can also tell us the story of our existence.
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- Molecules containing the noble gases should not even exist. By definition, these chemical elements like helium, neon, argon, krypton, xenon and radon, occupy the rightmost column of the periodic table and refuse to make molecules here on Earth.
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- No one has ever seen any naturally occurring noble gas molecules on Earth. Earlier this decade, however, astronomers accidentally discovered one of these elements in molecules in space.
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- This newly found molecule lends insight into the chemistry of the early universe, before any stars began to shine or any galaxies had formed. The discovery may even help astronomers understand how the first stars arose.
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- Most chemical elements readily share electrons with other elements to make molecules, but noble gases normally do not. That is because the outer shell of a noble gas atom already has its fill of electrons, so it won’t ordinarily exchange electrons to bond with other atoms and form molecules, at least, not here on Earth.
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- Space is the perfect place to seek noble gas molecules, because these gases abound in the cosmos. Helium is the second most common element in the universe, after hydrogen, and neon ranks fifth or sixth. And in interstellar space, where extreme temperatures and densities are the rule, noble gases do things they would never do on Earth. That includes forming molecules.
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- In addition to providing insight into the universe’s infancy, these exotic molecules tell scientists about the current conditions in the space between the stars, the gases that make up the interstellar medium. The interstellar medium is the place where stars and planetary systems are born.
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- Here on Earth, scientists have been concocting noble gas molecules for nearly a century. In 1925, laboratory scientists were able to force the noble gas helium into a bond with hydrogen to form helium hydride, or HeH+. This is termed a molecule by astronomers but, because it’s electrically charged, it is called a molecular ion by chemists.
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- In 1962 chemists coaxed xenon to mate with fluorine and platinum, yielding a mustard-colored compound that was the first substance consisting of electrically neutral molecules which both astronomers and chemists are happy to say is full of noble gas molecules. Still, no one has ever seen any naturally occurring noble gas molecules on Earth.
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- Argon is more than 20 times as common in Earth’s atmosphere as carbon dioxide but gets far less press. In fact, it is the third most abundant gas in the air you breathe. Nitrogen and oxygen make up 78 percent and 21 percent of Earth’s atmosphere, respectively, while argon accounts for most of the remaining 1 percent.
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- Nobody was looking for an interstellar molecule containing argon. Noble gases are known for being chemically non-reactive and don’t naturally bond with other atoms to form molecules on Earth.
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- In 2009 the Herschel Space Observatory lifted off for space carrying a tank of frigid liquid helium that lasted four years. This allowed Herschel to observe far-infrared wavelengths from distant objects without the interference its own warmth would have produced. Because many molecules absorb and emit far-infrared light, this spectral range is a good place to seek new space molecules.
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- Within a year of Herschel’s launch, astronomers began noticing that something in interstellar space was absorbing far-infrared light at a wavelength of 485 microns, a spectral line that hadn’t been observed before. Nobody could figure out what it was. No known molecule matched the observed wavelength of 485 microns.
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- In the Crab Nebula’s spectrum astronomers found two unidentified spectral lines. One was the same mysterious line everyone else had been seeing at 485 microns; the other had exactly half the wavelength, the spectrum of a molecule containing two atoms. It was the first noble gas molecule ever found in nature.
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- The discovery was a shock. Astronomers had been seeing that same 485 micron spectral line elsewhere. The scientists were the victims of a down-to-earth mix-up. They thought they knew the wavelengths argonium produced, because scientists had created it in the lab decades earlier and measured its spectrum.
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- But these laboratory molecules contained argon-40, which is by far the most common argon isotope on Earth. But that’s only because the argon we breathe comes from the radioactive decay of potassium-40 in rocks.
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- The universe is different. In the interstellar medium, argon-36 is by far the most abundant. Argonium made with argon-36 absorbs and emits light at slightly different wavelengths than it does with argon-40, explaining why the scientists had missed the identification.
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- What ere argonium’s cosmic Origins? Based on standard calculations of how chemical reactions proceed in space, scientists know the formation of the interstellar argonium molecule requires two steps. First, a cosmic ra, a high-speed charged particle, strips an electron from an interstellar argon atom, making Ar+.
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- Then, that argon ion can steal a hydrogen atom from a hydrogen molecule (H2) to create argonium, ArH+, because the hydrogen atom is more attracted to the argon ion than to the hydrogen.
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- But argonium is fragile, and the same hydrogen molecules it requires for its formation can also destroy it. The noble gas molecule can therefore exist only where there is just enough molecular hydrogen to create argonium but not so much as to tear it apart.
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- Interstellar gas in our part of the Milky Way comes in two main types: atomic and molecular. The first and more common type consists primarily of individual hydrogen and helium atoms. Because atomic gas is diffuse, it rarely makes new stars. Instead, most stars arise in denser gas where atoms crowd together to create molecules.
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- It can be difficult to tell apart the interstellar clouds that consist mostly of atomic gas from those that consist mostly of molecular gas, and that’s where argonium comes in. Although argonium is a molecule, it exists only in gas that’s 99.9 to 99.99 percent atomic.
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- Because cosmic rays lead to the creation of argonium, its abundance in interstellar space has also helped nail down the number of cosmic rays darting through the galaxy.
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- Even after the discovery of interstellar argonium, astronomers continued their quest for the simplest noble gas molecule, helium hydride, the one that theorists had predicted decades ago. This is thought to be the first chemical bond that formed in the universe shortly after the Big Bang.
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- The molecule arose because hydrogen and helium were the two chief elements to emerge from the Big Bang. At the beginning, the universe was so hot that any electrons either element managed to capture would immediately be stripped away by high-energy radiation generated by the extreme heat.
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- As space expanded, it cooled, and about 100,000 years after the Big Bang, each helium nucleus grabbed two electrons and became neutral. Put H+ and He together and you have the universe’s first molecule, HeH+.
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- So far helium hydride and argonium are the two noble gas molecules astronomers have found in space. To this day no one has ever detected any helium hydride in the early universe. That would require the unprecedented feat of looking across more than 13 billion light-years of space to the dawn of time and discerning the faint spectral line that the molecule produces.
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- In April 2019 the discovery was made not with a spacecraft but with a specialized airplane that flies above nearly all of the atmosphere’s water vapor, which blocks infrared radiation. The “Stratospheric Observatory for Infrared Astronomy” hunted for the coveted molecule using a telescope with a sensitive new high-resolution spectrometer. This instrument successfully detected the far-infrared signature of HeH+ at a wavelength of 149 micrometers.
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- By searching the same nebula in the constellation Cygnus, where 600 years ago, an aging star known as a red giant shed its atmosphere, which is something our own Sun will do in about 7.8 billion years.
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- This exposed the dying star’s hot core, which shines at a blistering 340,000 degrees Fahrenheit, and emits extreme ultraviolet light that tears electrons from helium atoms, creating He+. Combine that with neutral hydrogen atoms from other parts of the nebula and you have HeH+.
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- In the early universe it was the other way around, charged hydrogen and neutral helium, but the end result was the same: HeH+, the first molecule to form after the Big Bang.
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- The detection proves that the calculations predicting the exotic molecule’s existence were correct, lending credence to expectations that the molecule did indeed take shape soon after the universe’s birth.
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- There might be other noble gas molecules, too. In space, neon atoms greatly outnumber argon, so neonium, or NeH+, could exist. If so, its abundance and the places it exists will further illuminate conditions in the interstellar medium.
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- On the other hand, krypton is so rare that kryptonium probably poses little threat to any interstellar detection, and xenon is rarer still.
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- But it’s a vast universe with temperatures and densities that vary wildly from place to place and differ dramatically from those on Earth. Somewhere, in the nook of some distant interstellar cloud, the most unlikely atoms may have come together to create molecules even more bizarre than any yet found, awaiting only an intrepid observer to detect their spectral signature in the depths of space.
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- Astronomers are detectives searching for evidence to understand how we came to exit in the first place. There are some 90 elements in the Periodic Table and it all started with these simplest of those elements, hydrogen and helium. You are the chemistry of the cosmos.
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- April 22, 2020 2715
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--------------------- Wednesday, April 22, 2020 -------------------------
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