Lab experiment shows that a sugar key to genetic material on Earth can form on ice around young stars
An essential ingredient for life as we know it might have formed in space. Later, it might have rained down on a young Earth. That’s the finding of a new study.
The ingredient is the simple sugar ribose (RY-bose). It is a crucial piece of the chemical machinery inside cells. This sugar can form when a blend of ices are blasted with ultraviolet radiation. That’s what Cornelia Meinert and her colleagues reported April 8 in Science. Meinert is a chemist at University Nice Sophia Antipolis in France.
The ices that her term worked with are common on comets. Scientists believe they also coat the grains of interstellar dust that swirl around young stars.
“This is an amazing result,” says Conel Alexander. He is a planetary scientist at the Carnegie Institution for Science in Washington, D.C. For years researchers have been looking at ices exposed to radiation. Yet none, he notes, has ever seen ribose show up. Ribose is the backbone of RNA, a molecule that helps carry out the instructions encoded in genes. RNA is found in all life on Earth. It might have evolved billions of years ago, before DNA.
Other pieces of biological machinery have been found in space. Some have been produced in a lab in ways similar to what might happen in space. Last year, for instance, researchers created uracil (YUR-uh-sil), cytosine (SY-to-seen) and thymine (THY-meen) under conditions that simulated space. These chemicals are three of the molecular letters in the genetic alphabets of DNA and RNA. Researchers also have found amino acids in meteorites. Those molecules link together to form proteins. And in 2014, scientists spied isopropyl (EYE-so-PRO-pul) cyanide (SY-uh-nyde) in a gas cloud near the center of our galaxy. This molecule resembles amino acids. A decade earlier, scientists found the simple sugar glycoaldehyde (GLY-ko-AL-duh-hyde) in the same cloud.
Meinert and her colleagues started with water, ammonia and methanol. Each exists in comets as ices. The researchers cooled the substances to –195° Celsius (–319° Fahrenheit) inside a vacuum chamber. They then simulated the radiation given off by a young star by exposing the ice to ultraviolet light. Later, the cosmic goop was warmed back to room temperature.
The researchers then examined chemicals that had formed on the ice. They found about 55 different organic (or carbon-based) molecules. Ribose was one of them.
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The results aren’t too surprising, says Reggie Hudson. He is a chemist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Researchers had suspected sugars could form on interstellar ice. And the chemistry at work here has been understood for 155 years, he says. But no one had actually done the experiment before.
One challenge: The compounds that formed are really common. People carry many of the sugars in their bodies. And one chemical that turned up is ethylene glycol (ETH-uh-leen GLY-kol). It’s best known as antifreeze. Any of these could have accidentally contaminated the experiment. To probe for signs of that, the researchers used methanol ice that contained a type of atoms known as carbon-13. Any contaminants would have carried the more common carbon-12. By seeing carbon-13 show up in the ribose and other sugars, the researchers could be sure that these were due to chemical reactions in the ice.
It is, however, hard to tell whether the molecules formed when the ices were cold or as the samples warmed up, notes Hudson. The study’s authors agree. But both Hudson and Meinert point out that warm temperatures can occur around interstellar ice grains. Young stars will periodically warm the belts of debris that surround them. And grains that fall to Earth will heat up as they fall through Earth’s atmosphere. Instead of forming in space, then, ribose might have formed as its ingredients rained down upon Earth.
No one has seen ribose in comets or asteroids. A few upcoming missions, however, might get a chance to look for it. Japan’s Hayabusa2 spacecraft is on course to pilfer material from asteroid (162173 Ryugu). And NASA’s OSIRIS-REx mission will launch in September. It will bring pieces of an asteroid named Bennu back to Earth.
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amino acids Simple molecules that occur naturally in plant and animal tissues and that are the basic constituents of proteins.
ammonia A colorless gas with a nasty smell. Ammonia is a compound made from the elements nitrogen and hydrogen. It is used to make food and applied to farm fields as a fertilizer. Secreted by the kidneys, ammonia gives urine its characteristic odor. The chemical also occurs in the atmosphere and throughout the universe.
asteroid A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
astronomy The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.
biology The study of living things. The scientists who study them are known as biologists.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
carbon-12 The most abundant form of carbon. Each of its atoms has 6 protons and 6 neutrons in the nucleus. This isotope of carbon has a lower weight than carbon-13.
carbon-13 A carbon atom with 6 protons and 7 neutrons in the nucleus. This isotope of carbon has a magnetic spin that allows researchers to detect its presence.
cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) The term is used to refer to the recipe of a compound, the way it’s produced or some of its properties.
comet A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”
cosmic An adjective that refers to the cosmos — the universe and everything within it.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
encode (adj. encoded) To use some code to mask a message.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
interstellar Between stars.
meteor A lump of rock or metal from space that hits the atmosphere of Earth. In space it is known as a meteoroid. When you see it in the sky it is a meteor. And when it hits the ground it is called a meteorite.
methanol A colorless, toxic, flammable alcohol, sometimes referred to as wood alcohol or methyl alcohol. Each molecule of it contains one carbon atom, four hydrogen atoms and an oxygen atom. It is often used to dissolve things or as a fuel.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nebula A cloud of space gas and dust existing between major adult stars. Telescopes can detect these clouds by the light they emit or reflect. Some nebulas also appear to serve as the nurseries in which stars are born.
nucleotides The four chemicals that, like rungs on a ladder, link up the two strands that make up DNA. They are: A (adenine), T (thymine), C (cytosine) and G (guanine). A links with T, and C links with G, to form DNA. In RNA, uracil takes the place of thymine.
organic (in chemistry) An adjective that indicates something is carbon-containing; a term that relates to the chemicals that make up living organisms. (in agriculture) Farm products grown without the use of non-natural and potentially toxic chemicals, such as pesticides.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and it must have cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, it must be big enough to pull neighboring objects into the planet itself or to sling-shot them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
planetary science The science of other planets besides Earth.
proteins Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins.Medicines frequently work by latching onto proteins.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
ribose A type of sugar that forms the backbone for RNA.
RNA A molecule that helps “read” the genetic information contained in DNA. A cell’s molecular machinery reads DNA to create RNA, and then reads RNA to create proteins.
simulate To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.
star Thebasic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
stellar An adjective that means of or relating to stars.
ultraviolet A portion of the light spectrum that is close to violet but invisible to the human eye.
vacuum Space with little or no matter in it. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.
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Original Journal Source: C. Meinert et al. Ribose and related sugars from ultraviolet irradiation of interstellar ice analogs. Science. Vol. 352, April 8, 2016, p. 208. doi: 10.1126/science.aad8137.