photochemistry

Twelve stars have received X-ray passports. Now, for each of them, we know the exact radiation dose received by a planet in the habitable zone, the region where liquid water is possible.

In July 1969, as Apollo 11 flew toward the Moon, astronauts noticed something unusual: brief flashes of light that appeared even with their eyes closed. At first, this was attributed to fatigue, but the flashes recurred in different crews. Gradually, it became clear: cosmic rays were to blame — tiny particles hurtling through space at tremendous speeds.

The lifetime of the entangled triplet pair in the protein is about 60 picoseconds, which is eight times longer than in solution. Sunlight is like a continuous stream of balls flying at a wall.

In dark interstellar clouds where new stars are born, chemistry starts with a tiny particle — the trihydrogen ion (H₃⁺). It collides with other atoms and sets off a cascade of reactions that build ever more complex molecules. For a long time, it was thought that the main reaction producing it, H₂⁺ colliding with H₂, only happens in the gas phase.

A planet in the habitable zone is no guarantee of life. Like a conductor leading an orchestra, a star dictates the tempo and character of planetary atmosphere evolution over billions of years.

When the JWST telescope breaks the light of a distant exoplanet into a spectrum, it reads a chemical chronicle. But this chronicle is not a monolithic truth; it's an atmosphere constantly rewritten by the star's radiation.

Erwin Schrödinger pondered how life maintains order despite the second law of thermodynamics. He could never have imagined that part of the answer lies hidden in the instability of giant stars.

Imagine an artist whose canvas is an entire planet, and whose palette is molecules drinking starlight. His brush is billions of years of evolution, and his painting is a spectral portrait visible even from another star system.

For years, the Sun teased astrophysicists. In its atmosphere, refractory elements, like spices in a basic recipe, were slightly less abundant than in nearly identical twin stars. Suspicion arose: could our star be modest, skipping the planetary "dessert" that others devour with gusto?

A pot of porridge boiling over a high flame: bubbles carry grains from the bottom to the surface. A similar mechanism works on a neutron star. As it accumulates hydrogen and helium from a companion star, it occasionally triggers a powerful nuclear explosion — an X-ray burst.

When astronomers peer at distant worlds, they often don't see crisp lines of water vapor or methane, but a blurry silhouette, as if the planet has thrown on a thick veil. This veil, a haze of organic particles, behaves like a temperamental photographic plate: it darkens under harsh ultraviolet light, revealing hidden chemical patterns.

A giant cloud of gas and dust, so cold that its warmth barely flickers, just a few degrees above absolute zero. This is TMC-1 in the constellation Taurus, one of the darkest and densest cradles of molecules in our Galaxy. In recent years, it has become a true treasure trove for astrochemists: the number of substances found there has more than doubled.

A high-speed camera capable of capturing the motion of electrons is an attosecond interferometer. It sends two laser pulses at a substance with a tiny delay. The first, ultraviolet, acts like a flash, knocking an electron out of the molecule. The second, infrared, like an invisible hand, gently nudges or slows this electron in flight.

In the cold gas cloud where a star is born, chemistry sleeps. Molecules barely collide, reactions stall. But when a charged particle zips through the cloud, it knocks electrons off atoms — ionizing them. That's how active ions appear in a dormant cloud, ready to build new molecules.

Inside the Sun, invisible nuclear transformations occur every second. One of them is the birth of boron-8: a beryllium-7 nucleus captures a passing proton and momentarily becomes a new element. This step kicks off a chain that ends with the emission of a neutrino — a particle capable of passing straight through Earth.

Water isn't the only thing life needs. To assemble the first RNA-like chains from simple molecules, you need ultraviolet light, like the sunlight that helps plants, but harsher and with shorter wavelengths. Big stars like the Sun emit plenty of this light. Small, dim stars, however, have almost none: they shine mostly in red and infrared, like a glowing ember.

When a sunbeam hits a leaf, a relay race begins inside it. The energy of light passes from one chlorophyll molecule to the next until it reaches the reaction center — the place where the chemistry of life kicks off. This relay runs with astonishing accuracy: nearly every quantum of light finds its way.

In a dark, cold cloud between the stars, a dust grain a thousandth of a millimeter across catches light molecules. Carbon monoxide and hydrogen stick to its surface like raindrops to glass and react. After a few steps, methanol is produced — the same alcohol found in windshield washer fluid.

Cometary ice slams into the young Earth. The pressure at the impact point is like stacking six aircraft carriers on your thumbnail. In the lab, such conditions are reproduced by squeezing a tiny sample between two rotating anvils. This time, adenosine monophosphate — one of the letters of future RNA — was placed under the anvils.

An ordinary chemical reaction is like a ball rolling down a hill: it has one natural path. But if you place molecules in a tiny mirrored box, an optical microresonator, the light inside starts to interfere with the ball's motion. It can nudge it, hold it back, or even split its trajectory. In a new study, physicists traced exactly how this happens.

In every leaf, in the light, a factory works that splits water into oxygen and hydrogen. The oxygen goes into the air we breathe, and the plant uses the hydrogen for food. The heart of this factory is a protein complex with four manganese atoms and one calcium atom.

Throw pebbles along a tight row of posts: they ricochet into a dense spray. Throw at an angle, and they scatter. Gamma rays in a crystal do the same: they spawn particle cascades that spread out unless the crystal’s atomic rows are perfectly aligned. Align them within a hair’s width, and the cascade sharpens into a tight beam. A small crystal then outperforms a large one.

Life began with molecules akin to natural sunscreen — based on carbon, they soaked up the mild ultraviolet of the young Sun and turned it into heat. This way of dissipating energy wasn’t just heating: it made molecules self-organize, like chefs kneading structured dough out of a chaos of ingredients. But ultraviolet is a finicky tool.

Sunlight collected by a Fresnel lens and passed through 20 meters of plastic fiber had a power of just 3 microwatts, a million times less than a typical laser pointer. That was enough to generate photon pairs correlated in position inside a nonlinear crystal. One photon from each pair passed through the object, the second was scanned by a detector, and coincidences built up the image.