You are living through a monumental period of astronomical science. Just over four centuries ago, a handful of pioneering explorers first turned their telescopes – a novel invention at the time – toward the sky. On the grand scale of the human timeline, almost nothing separates us from them, but today our collective understanding of the Universe is developing at an astonishing pace. Sometimes I wonder how the first scientific astronomers, such as Thomas Harriot, Galileo Galilei, and Johannes Kepler would react if confronted with the wealth of knowledge that generations of their disciples have collected.
After all, they penned a handful of the earliest volumes in what has become a library of staggering size and depth, and some of their foundational ideas continue to permeate the subject today. Yet the way we now observe and think about the Universe in the 21st Century has been completely transformed through the age of technology. What would Harriot and his contemporaries make of it? Well, it seems likely that future generations will ask the same of us. For everything we now know, we are also aware of just how much more is yet to be discovered. Looking back through astronomy’s modern history up to the current day, I collected 101 discoveries, topics and questions for my new book, Diamonds Everywhere. It’s written for anyone with even a passing interest in astronomy or space science, and my hope is that it will change the way you think about the Universe. Here are three surprising findings from the book’s pages, which would have been unbelievable just 400 years ago.
Moonquakes rock our celestial companion
While earthquakes have been known about since ancient times, the theory of plate tectonics emerged as recently as the 20th Century. Remarkably, today, we can measure similar events on our celestial companion – The Moon – and they cause it to ring like a bell. Moonquakes, also known as lunar seismic activity, resonate through the Moon, providing vital insights into its interior and serving as a cornerstone of selenology, akin to geology on Earth. The study of moonquakes began in 1969 with the placement of a seismometer on the lunar surface during Apollo 11, and subsequent Apollo missions deployed more instruments whose results continue to be analysed.
These lunar tremors have diverse origins, each yielding distinctive signals for seismometers. Moonquakes are attributed to the Moon's ongoing cooling, causing it to contract, and tidal forces exerted by Earth's gravitational pull. "Deep moonquakes," occurring around 700 km below the surface, likely result from these combined effects. However, moonquakes at depths of 50–220 km remain enigmatic, possibly arising from thermal expansion as the Moon's crust alternates between extreme cold and intense sunlight. Collapses within shallow crater walls due to crust size changes are another plausible cause, as are meteorite impacts, which send vibrations through the Moon's interior.
Compared to Earth, the Moon has a thinner crust and a more rigid mantle, suggesting lower internal activity throughout its similar lifespan. Notably, major moonquakes tend to cluster near the rims of large impact basins, hinting at these regions as stress points where energy is frequently released, akin to Earth's fault lines. In recent times, NASA's Lunar Reconnaissance Orbiter (LRO) has monitored lunar seismic activity from orbit, detecting thousands of seismic events, including numerous shallow moonquakes. Ongoing observations and analysis promise a deeper understanding of the Moon's seismic behaviour, which could prove crucial for designing safe habitats for future lunar settlers.
The nearest star system to the Sun hosts a terrestrial exoplanet
Credit: ESO/M. Kornmesser
When astronomers began making detailed charts of the night sky, the had no way of knowing the distances to the stars. But in the modern age, we can measure quite precisely how far many if not most of the stars we see actually are. We’ve also unearthed the existence of other worlds and systems of worlds orbiting these stars, and it now appears they’re much more common that first thought. Yet even astronomers were surprised to learn that the Sun’s nearest neighbouring star is home to a terrestrial world. Proxima Centauri, a red dwarf star just 4.24 light-years away from the Sun, hosts a rocky extra-solar planet – exoplanet for short – called Proxima b. Discovered in August 2016, this Earth-sized exoplanet has piqued interest due to its proximity and potential habitability. Despite its short 11.2-day orbit around its host star, the planet's distance from the fainter Proxima Centauri makes it a candidate for liquid water and habitability.
Yet, much remains unknown about Proxima b. Scientists are investigating its atmosphere for signs of water vapor or other life-indicating molecules. The presence of a magnetic field, essential for shielding potential life from radiation, is also under scrutiny. Proxima b is tidally locked, with one side in perpetual day and the other in constant night, raising questions about the possibility of a stable atmosphere given strong stellar winds and erosion.
Exploring this intriguing world directly is challenging. The fastest spacecraft available today would take thousands of years to reach the Proxima Centauri system, necessitating a revolutionary advancement in space technology for a closer examination of our neighbouring exoplanet.
Colliding black holes and neutron stars release ripples in space-time that change the shape of the Earth
Credit: NSF/LIGO/Sonoma State University/A. Simonnet
It’s trivial to understand that a nearby explosion can exert a force on you. Even a distant explosion, if it’s powerful enough, can level structures and cause significant damage. The compression of air by a shockwave is made visible when a condensation cloud forms behind it in sufficiently humid conditions, and colossal explosions – such as those created by nuclear bombs – create seismic waves in the Earth’s crust. Astronomers have discovered something enormously more powerful, however, released by cataclysmic events at tremendous astronomical distances, that are capable of influencing the Earth in a rather unusual way.
Gravitational waves, predicted by Albert Einstein's theory of relativity in 1915, were directly detected for the first time in 2015. These waves are created by massive objects, like black holes or neutron stars, rapidly orbiting each other, causing ripples in space-time that propagate at the speed of light. As they do, they sap energy from the system, prompting the objects to spiral towards a dramatic collision, with the gravitational wave intensity surging just before the merger.
However, detecting these faint waves over vast distances is incredibly challenging. Scientists employ interferometers, which split a laser beam into two beams, send them down several-kilometre-long arms, and recombine them at a central detector. If a gravitational wave passes through, it subtly alters the arm lengths, leading to a phase shift in the recombined beams. This shift allows scientists to measure the presence and strength of gravitational waves, as they minutely reshape the Earth itself!
The Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first detections, beginning with the collision of two black holes located 1.3 billion light-years away, confirming Einstein's theory and revolutionizing astronomy. Subsequent detections by LIGO and its European counterpart, the Virgo detector, included collisions of black holes and neutron stars, yielding valuable insights into their behaviour. Neutron star collisions, in particular, play a pivotal role in the Universe's chemical evolution, making their indirect observation a milestone in astronomy.
These are just three of the 101 cosmic topics explored in Diamonds Everywhere: Awe-Inspiring Astronomy Discoveries, available to pre-order now.
About the author
Tom Kerss is an astronomer, astrophotographer, writer and speaker, specialising in the rewarding task of connecting people to their shared universe. He is the author of Northern Lights, Moongazing, Stargazing, Observing Our Solar System, Children’s Picture Atlas of the Stars and You Can Explore the Universe, all of which are available now.