Star-hopping is going from stars you know … to stars you don’t know. On April evenings, you can look west after sunset to star-hop from the constellation Orion the Hunter to Sirius. Chart via EarthSky.
Star-hop from Orion to Sirius
One very easy constellation to find at this time of the year is the magnificent Orion the Hunter, now descending in the west after sunset. It’s easy because Orion contains a very noticeable pattern of three medium-bright stars in a short straight row. These stars are known as Orion’s Belt. Find Orion, and continue the line of his belt to star-hop to Sirius. Found in the constellation Canis Major, this is the sky’s brightest star!
As Earth revolves around the sun, both the constellation Orion and the star Sirius are about to disappear for a while. They always drop into the sun’s glare shortly after this time of the year, as Earth’s motion brings the sun between us and them. So be sure to look for them while you can, soon after the sun goes down. We’ll see them again in the east before dawn, beginning around late July or early August.
People learning to recognize the stars often use star-hopping – going from stars and constellations they know to ones they don’t know – to find and recognize new stars and constellations. The use of Orion’s Belt to find Sirius is one of the best-known star-hops in the sky, because the stars are so bright and the pattern is so definite.
Another great star-hop to try is using the Big Dipper to find Polaris, the North Star. If you’re in the Northern Hemisphere, this star-hop will allow you to always find north!
Look for the Big and Little Dipper high in the northern sky on spring evenings. This view is for the Northern Hemisphere. The 2 outer stars in the bowl of the Dipper point to Polaris, the North Star. Polaris marks the end of the handle of the Little Dipper. Chart via EarthSky.View at EarthSky Community Photos. | Cecille Kennedy in Oregon shared this image with us on March 13, 2024. Cecille wrote: “Before midnight, pointing the camera straight up into the night sky, there is the Big Dipper and the Little Dipper. When you are looking at Polaris, you are facing north. While other constellations move around, Polaris stays still as it’s found at the north celestial pole. Thus Polaris is a very useful star for navigators and sailors. The 2 front stars in the asterism of the Big Dipper are called Pointers because they point to the North Star or Polaris.” Thank you, Cecille!
Bottom line: Star-hopping is going from stars you know to stars you don’t know. Star-hop from the constellation Orion the Hunter to Sirius, the sky’s brightest star, before they’re gone!
Star-hopping is going from stars you know … to stars you don’t know. On April evenings, you can look west after sunset to star-hop from the constellation Orion the Hunter to Sirius. Chart via EarthSky.
Star-hop from Orion to Sirius
One very easy constellation to find at this time of the year is the magnificent Orion the Hunter, now descending in the west after sunset. It’s easy because Orion contains a very noticeable pattern of three medium-bright stars in a short straight row. These stars are known as Orion’s Belt. Find Orion, and continue the line of his belt to star-hop to Sirius. Found in the constellation Canis Major, this is the sky’s brightest star!
As Earth revolves around the sun, both the constellation Orion and the star Sirius are about to disappear for a while. They always drop into the sun’s glare shortly after this time of the year, as Earth’s motion brings the sun between us and them. So be sure to look for them while you can, soon after the sun goes down. We’ll see them again in the east before dawn, beginning around late July or early August.
People learning to recognize the stars often use star-hopping – going from stars and constellations they know to ones they don’t know – to find and recognize new stars and constellations. The use of Orion’s Belt to find Sirius is one of the best-known star-hops in the sky, because the stars are so bright and the pattern is so definite.
Another great star-hop to try is using the Big Dipper to find Polaris, the North Star. If you’re in the Northern Hemisphere, this star-hop will allow you to always find north!
Look for the Big and Little Dipper high in the northern sky on spring evenings. This view is for the Northern Hemisphere. The 2 outer stars in the bowl of the Dipper point to Polaris, the North Star. Polaris marks the end of the handle of the Little Dipper. Chart via EarthSky.View at EarthSky Community Photos. | Cecille Kennedy in Oregon shared this image with us on March 13, 2024. Cecille wrote: “Before midnight, pointing the camera straight up into the night sky, there is the Big Dipper and the Little Dipper. When you are looking at Polaris, you are facing north. While other constellations move around, Polaris stays still as it’s found at the north celestial pole. Thus Polaris is a very useful star for navigators and sailors. The 2 front stars in the asterism of the Big Dipper are called Pointers because they point to the North Star or Polaris.” Thank you, Cecille!
Bottom line: Star-hopping is going from stars you know to stars you don’t know. Star-hop from the constellation Orion the Hunter to Sirius, the sky’s brightest star, before they’re gone!
Watch this video of some of our editor’s pics for the best deep-sky photos of March 2025, and then see more below!
Stunning deep-sky photos from our community
The EarthSky community has many talented astrophotographers who capture stunning images of the deep sky. We gathered some of our favorite deep-sky photos we received in March 2025 for you to enjoy. Do you have some of your own images to share? You can submit them to us here. We love to see them!
View at EarthSky Community Photos. | Scott Smith in Palmetto, Florida, captured the Trifid nebula on March 27, 2025. Scott wrote: “The Trifid nebula illustrates 3 different types of astronomical nebulae in a single deep-sky object. A red emission nebula (light from hydrogen atoms), a blue reflection nebula (dust reflected by starlight), and dark nebula, with dense dust that silhouettes the light beneath it. The Trifid nebula (catalogued as Messier 20 or M20 and as NGC 6514) lies in the northwest of Sagittarius. Charles Messier discovered it on June 5, 1764.” Thank you, Scott!
Deep-sky photos of open star clusters
View at EarthSky Community Photos. | Our own Marcy Curran from EarthSky, in Cheyenne, Wyoming, captured open clusters Messier 36, Messier 37 and Messier 38 on March 26, 2025. Marcy wrote: “Auriga is a constellation prominent in the winter months of the Northern Hemisphere. It contains 3 bright Messier objects, all of them are open star clusters. M38 (the Starfish cluster) is about 4,200 light-years away and lies almost in the middle of the constellation. M36 (the Pinwheel cluster) is next in line to M38 and lies about 4,100 light-years distant. Next is M37, the brightest, richest and largest of the 3 open clusters. It’s about 4,500 light-years away.” Thank you, Marcy!View at EarthSky Community Photos. | Muhammad Alaa in Sanabu, Assiut, Egypt, captured the Pleiades in the constellation Taurus the Bull on March 20, 2025. Thank you, Muhammad!
Globular star clusters
View at EarthSky Community Photos. | Scott Smith in Palmetto, Florida, captured Omega Centauri on March 3, 2025. Scott wrote: “Omega Centauri is a globular cluster in the constellation of Centaurus. Located at a distance of 17,090 light-years, it is the largest known globular cluster in the Milky Way, at a diameter of roughly 150 light-years. It contains approximately 10 million stars, making it the most massive known globular cluster in the Milky Way.” Thank you, Scott!View at EarthSky Community Photos. | Tom Cofer in Lakewood Ranch, Florida, captured this telescopic view of Messier 13, the Hercules Cluster, on March 14, 2025. Tom wrote: “A snow globe of stars!” Thank you, Tom!
Galaxies in the deep-sky
View at EarthSky Community Photos. | Gwen Forrester in DeKalb County, Tennessee, captured Messier 81, a bright galaxy in the constellation Ursa Major, on March 26, 2025. Gwen wrote: “Messier 81, Bode’s Galaxy, a grand design spiral galaxy 12 million light-years away.” Thank you, Gwen!View at EarthSky Community Photos. | David Hoskin in Halifax, Nova Scotia, Canada, captured this telescopic view of Messier 82 on March 4, 2025. David wrote: “Messier 82, the Cigar Galaxy, lies in the constellation Ursa Major and is about 12 million light-years from Earth. Stars are forming at a high rate in this galaxy.” Thank you, David!View at EarthSky Community Photos. | Josh Wright in Cleethorpes, England, captured Messier 51 in the constellation Canes Venatici on March 19, 2025. Josh wrote: “The Whirlpool Galaxy, an interacting grand-design spiral galaxy 31 million light-years away. Taken with my smart telescope from my back garden.” Thank you, Josh!View at EarthSky Community Photos. | Steven Bellavia in Staunton River State Park, Virginia, captured NGC 3628, the Hamburger Galaxy, in the constellation Leo, on March 26, 2025. Steven wrote: “This is the fainter sibling of the Leo Triplet, which contains M65 and M66, which are not in this close-up image. It is an unbarred spiral galaxy about 35 million light-years away, discovered by William Herschel in 1784.” Thank you, Steven!
Messier 101, the Pinwheel Galaxy
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured Messier 101, the Pinwheel Galaxy in the constellation Ursa Major, on March 2, 2025. Andy wrote: “I never would have imagined how much more detail I could get from data using PI (PixInsight). The difference is astonishing. Imagine how much better I can get when I have some real understanding of PixInsight. This experience has proved to me that software is as important if not more important than the hardware.” Wonderful image. Thank you, Andy!View at EarthSky Community Photos. | Muhammad Alaa in Sanabu, Assiut, Egypt, captured the Pinwheel Galaxy on March 25, 2025. Muhammad wrote: “The Pinwheel Galaxy is one of the most beautiful spiral galaxies. It lies in the Ursa Major constellation, about 21 million light-years from Earth.” Thank you, Muhammad!View at EarthSky Community Photos. | Jelieta Walinski at Desert Bloom Observatory in St. David, Arizona, captured the Pinwheel Galaxy on March 3, 2025. Jelieta wrote: “Marvel at the breathtaking beauty of the Pinwheel Galaxy. This celestial wonder is home to hundreds of billions of stars, with estimates suggesting around 100 billion stellar inhabitants. As we gaze upon this cosmic masterpiece, we’re reminded of the awe-inspiring beauty and mystery that awaits us in the vast expanse of the universe. Don’t forget to look up!” Thank you, Jelieta!
Bottom line: Enjoy this gallery of deep-sky photos for March 2025 from our EarthSky community. If you have a great photo to share, send it in, too. We love to see them!
Watch this video of some of our editor’s pics for the best deep-sky photos of March 2025, and then see more below!
Stunning deep-sky photos from our community
The EarthSky community has many talented astrophotographers who capture stunning images of the deep sky. We gathered some of our favorite deep-sky photos we received in March 2025 for you to enjoy. Do you have some of your own images to share? You can submit them to us here. We love to see them!
View at EarthSky Community Photos. | Scott Smith in Palmetto, Florida, captured the Trifid nebula on March 27, 2025. Scott wrote: “The Trifid nebula illustrates 3 different types of astronomical nebulae in a single deep-sky object. A red emission nebula (light from hydrogen atoms), a blue reflection nebula (dust reflected by starlight), and dark nebula, with dense dust that silhouettes the light beneath it. The Trifid nebula (catalogued as Messier 20 or M20 and as NGC 6514) lies in the northwest of Sagittarius. Charles Messier discovered it on June 5, 1764.” Thank you, Scott!
Deep-sky photos of open star clusters
View at EarthSky Community Photos. | Our own Marcy Curran from EarthSky, in Cheyenne, Wyoming, captured open clusters Messier 36, Messier 37 and Messier 38 on March 26, 2025. Marcy wrote: “Auriga is a constellation prominent in the winter months of the Northern Hemisphere. It contains 3 bright Messier objects, all of them are open star clusters. M38 (the Starfish cluster) is about 4,200 light-years away and lies almost in the middle of the constellation. M36 (the Pinwheel cluster) is next in line to M38 and lies about 4,100 light-years distant. Next is M37, the brightest, richest and largest of the 3 open clusters. It’s about 4,500 light-years away.” Thank you, Marcy!View at EarthSky Community Photos. | Muhammad Alaa in Sanabu, Assiut, Egypt, captured the Pleiades in the constellation Taurus the Bull on March 20, 2025. Thank you, Muhammad!
Globular star clusters
View at EarthSky Community Photos. | Scott Smith in Palmetto, Florida, captured Omega Centauri on March 3, 2025. Scott wrote: “Omega Centauri is a globular cluster in the constellation of Centaurus. Located at a distance of 17,090 light-years, it is the largest known globular cluster in the Milky Way, at a diameter of roughly 150 light-years. It contains approximately 10 million stars, making it the most massive known globular cluster in the Milky Way.” Thank you, Scott!View at EarthSky Community Photos. | Tom Cofer in Lakewood Ranch, Florida, captured this telescopic view of Messier 13, the Hercules Cluster, on March 14, 2025. Tom wrote: “A snow globe of stars!” Thank you, Tom!
Galaxies in the deep-sky
View at EarthSky Community Photos. | Gwen Forrester in DeKalb County, Tennessee, captured Messier 81, a bright galaxy in the constellation Ursa Major, on March 26, 2025. Gwen wrote: “Messier 81, Bode’s Galaxy, a grand design spiral galaxy 12 million light-years away.” Thank you, Gwen!View at EarthSky Community Photos. | David Hoskin in Halifax, Nova Scotia, Canada, captured this telescopic view of Messier 82 on March 4, 2025. David wrote: “Messier 82, the Cigar Galaxy, lies in the constellation Ursa Major and is about 12 million light-years from Earth. Stars are forming at a high rate in this galaxy.” Thank you, David!View at EarthSky Community Photos. | Josh Wright in Cleethorpes, England, captured Messier 51 in the constellation Canes Venatici on March 19, 2025. Josh wrote: “The Whirlpool Galaxy, an interacting grand-design spiral galaxy 31 million light-years away. Taken with my smart telescope from my back garden.” Thank you, Josh!View at EarthSky Community Photos. | Steven Bellavia in Staunton River State Park, Virginia, captured NGC 3628, the Hamburger Galaxy, in the constellation Leo, on March 26, 2025. Steven wrote: “This is the fainter sibling of the Leo Triplet, which contains M65 and M66, which are not in this close-up image. It is an unbarred spiral galaxy about 35 million light-years away, discovered by William Herschel in 1784.” Thank you, Steven!
Messier 101, the Pinwheel Galaxy
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured Messier 101, the Pinwheel Galaxy in the constellation Ursa Major, on March 2, 2025. Andy wrote: “I never would have imagined how much more detail I could get from data using PI (PixInsight). The difference is astonishing. Imagine how much better I can get when I have some real understanding of PixInsight. This experience has proved to me that software is as important if not more important than the hardware.” Wonderful image. Thank you, Andy!View at EarthSky Community Photos. | Muhammad Alaa in Sanabu, Assiut, Egypt, captured the Pinwheel Galaxy on March 25, 2025. Muhammad wrote: “The Pinwheel Galaxy is one of the most beautiful spiral galaxies. It lies in the Ursa Major constellation, about 21 million light-years from Earth.” Thank you, Muhammad!View at EarthSky Community Photos. | Jelieta Walinski at Desert Bloom Observatory in St. David, Arizona, captured the Pinwheel Galaxy on March 3, 2025. Jelieta wrote: “Marvel at the breathtaking beauty of the Pinwheel Galaxy. This celestial wonder is home to hundreds of billions of stars, with estimates suggesting around 100 billion stellar inhabitants. As we gaze upon this cosmic masterpiece, we’re reminded of the awe-inspiring beauty and mystery that awaits us in the vast expanse of the universe. Don’t forget to look up!” Thank you, Jelieta!
Bottom line: Enjoy this gallery of deep-sky photos for March 2025 from our EarthSky community. If you have a great photo to share, send it in, too. We love to see them!
The April birthstone is the diamond. And a diamond solitaire ring is a popular choice for engagement rings. Image via EarthSky’s Marcy Curran.
The April birthstone
The April birthstone is the diamond. It’s treasured for its exceptional hardness and purity of color. Although the diamond is not the rarest of gems, it’s still one of the most popular gemstones.
As a result of a diamonds’ cold, sparkling fire, it’s held us spellbound for centuries. What’s more, it’s inspired rich, passionate myths of romance, intrigue, power, greed and magic. Today, the diamond is a symbol of enduring love, and often graces engagement rings.
Ancient Hindus, finding diamonds washed out of the ground after thunderstorms, believed bolts of lightning created them.
Of course, we know different now. In fact, diamonds are the rich cousins of graphite. Both are crystalline forms of pure carbon. But the enormous differences in their properties are a result of the way the carbon atoms bond together. In graphite, carbon atoms form in sheets that easily slide past each other, which makes graphite ideal as a lubricant and, of course, as pencil lead. On the other hand, diamond crystals are a tight-fisted network of carbon atoms securely bound in four directions. Thus, making diamonds the hardest naturally-occurring substance in the world.
So to achieve such a compact and strongly-held network of carbon atoms, it’s believed that diamonds crystallized deep under the Earth’s surface. At these depths – 90 to 120 miles deep (145 – 193 km) – the proper conditions for the formation of diamonds exist. That’s because pressures are more than 65,000 times that of the atmosphere at the Earth’s surface, with temperatures exceeding 2,700 degrees Fahrenheit (1,500 degrees Celsius). And as a matter of fact, such pressures and temperatures are reproduced in laboratories successfully creating synthetic diamonds.
This is the typical shape of a rough diamond crystal. Its lustrous faces also indicate that this crystal is from a primary deposit. Image via Géry Parent/ Wikipedia (Public domain).
The quality of diamonds
There are many kinds of diamonds: transparent, translucent, or opaque; ranging from colorless to sooty black, with many colors in between. Mostly transparent diamonds, those that are colorless or tinted, end up in jewelry. And then lower grade diamonds are for industrial use.
The color of a diamond depends on the kind of impurities embedded inside it. For example, yellow diamonds betray minute quantities of nitrogen, while boron imparts a bluish hue. As a matter of fact, some inclusions in diamonds have great scientific value. That’s because they are time capsules containing valuable information about conditions deep in the Earth’s upper mantle where diamonds form. Additionally, they offer clues to the formation and age of the diamond.
Different types of rough diamonds. Image via James St. John/ Wikipedia (CC BY 2.0).
Sources of the April birthstone
Diamonds are found in alluvial deposits or gravel swept away by streams, rivers, glaciers and ocean currents. Also, they are in sedimentary rock where gravel deposits and organic material are compressed into rock. Diamonds are in some samples of kimberlite, a type of volcanic rock first identified in Kimberley, South Africa. Also, the diamonds in kimberlite may be very old, perhaps as much as three billion years old. And even meteorites – bits of rocky space debris that land on Earth – often contain tiny flecks of diamonds.
Diamonds are crystals. Crystals are the ultimate form of symmetry in nature. Their shape reflects the internal orderly arrangement of atoms within the crystal. In diamonds, atoms of carbon are held tightly by covalent bonding, where two neighboring atoms share an electron, endowing the diamond crystal with great strength. But despite that hardness, diamonds can be cut with saws and polished with grinding wheels coated with tiny industrial diamond fragments. In their natural form, diamonds can appear quite unimpressive. But they are cut and polished by skilled craftsmen in a pattern that reflects and refracts the light among their facets to reveal the hidden beauty of the stone.
One of the most famous diamonds, the Hope Diamond, shown here in the National Museum of Natural History in Washington, D.C. Image via David Bjorgen/ Wikipedia (CC BY-SA 3.0).
Diamond lore
Some diamonds seem to have lived lives of their own. One legendary stone in the diamond hall of fame is the Koh-i-noor (“Mountain of Light”). The Koh-i-noor diamond is believed to be 5,000 years old, and was featured in the great Sanskrit epic The Mahabharata.
Originally owned by the Rajah of Malwa in India, the Koh-i-noor has since been a player in victories and defeats spanning India, Persia and Afghanistan. It was in the possession of the great Mogul dynasty from 1526 to 1739. Its owners included Shah Jehan, who built the Taj Mahal in memory of his queen Mumtaz. The Persian invader Nadir Shah briefly possessed it until his assassination in 1747. The jewel then fell into the hands of Afghan rulers who eventually surrendered it to the Rajah of Punjab, Ranjit Singh.
Two years after Ranjit Singh’s death in 1839, Punjab became part of India under British rule and they presented the stone to Queen Victoria. Then she had it cut from its original 187 carats to 108 carats to further enhance its beauty. After her death, the diamond became part of the British crown jewels. Queen Elizabeth (later the Queen Mother) wore it in her crown at her 1937 coronation. However, Camilla chose to wear another crown to Charles III coronation in 2023.
Find out about the birthstones for the other months of the year.
The April birthstone is the diamond. And a diamond solitaire ring is a popular choice for engagement rings. Image via EarthSky’s Marcy Curran.
The April birthstone
The April birthstone is the diamond. It’s treasured for its exceptional hardness and purity of color. Although the diamond is not the rarest of gems, it’s still one of the most popular gemstones.
As a result of a diamonds’ cold, sparkling fire, it’s held us spellbound for centuries. What’s more, it’s inspired rich, passionate myths of romance, intrigue, power, greed and magic. Today, the diamond is a symbol of enduring love, and often graces engagement rings.
Ancient Hindus, finding diamonds washed out of the ground after thunderstorms, believed bolts of lightning created them.
Of course, we know different now. In fact, diamonds are the rich cousins of graphite. Both are crystalline forms of pure carbon. But the enormous differences in their properties are a result of the way the carbon atoms bond together. In graphite, carbon atoms form in sheets that easily slide past each other, which makes graphite ideal as a lubricant and, of course, as pencil lead. On the other hand, diamond crystals are a tight-fisted network of carbon atoms securely bound in four directions. Thus, making diamonds the hardest naturally-occurring substance in the world.
So to achieve such a compact and strongly-held network of carbon atoms, it’s believed that diamonds crystallized deep under the Earth’s surface. At these depths – 90 to 120 miles deep (145 – 193 km) – the proper conditions for the formation of diamonds exist. That’s because pressures are more than 65,000 times that of the atmosphere at the Earth’s surface, with temperatures exceeding 2,700 degrees Fahrenheit (1,500 degrees Celsius). And as a matter of fact, such pressures and temperatures are reproduced in laboratories successfully creating synthetic diamonds.
This is the typical shape of a rough diamond crystal. Its lustrous faces also indicate that this crystal is from a primary deposit. Image via Géry Parent/ Wikipedia (Public domain).
The quality of diamonds
There are many kinds of diamonds: transparent, translucent, or opaque; ranging from colorless to sooty black, with many colors in between. Mostly transparent diamonds, those that are colorless or tinted, end up in jewelry. And then lower grade diamonds are for industrial use.
The color of a diamond depends on the kind of impurities embedded inside it. For example, yellow diamonds betray minute quantities of nitrogen, while boron imparts a bluish hue. As a matter of fact, some inclusions in diamonds have great scientific value. That’s because they are time capsules containing valuable information about conditions deep in the Earth’s upper mantle where diamonds form. Additionally, they offer clues to the formation and age of the diamond.
Different types of rough diamonds. Image via James St. John/ Wikipedia (CC BY 2.0).
Sources of the April birthstone
Diamonds are found in alluvial deposits or gravel swept away by streams, rivers, glaciers and ocean currents. Also, they are in sedimentary rock where gravel deposits and organic material are compressed into rock. Diamonds are in some samples of kimberlite, a type of volcanic rock first identified in Kimberley, South Africa. Also, the diamonds in kimberlite may be very old, perhaps as much as three billion years old. And even meteorites – bits of rocky space debris that land on Earth – often contain tiny flecks of diamonds.
Diamonds are crystals. Crystals are the ultimate form of symmetry in nature. Their shape reflects the internal orderly arrangement of atoms within the crystal. In diamonds, atoms of carbon are held tightly by covalent bonding, where two neighboring atoms share an electron, endowing the diamond crystal with great strength. But despite that hardness, diamonds can be cut with saws and polished with grinding wheels coated with tiny industrial diamond fragments. In their natural form, diamonds can appear quite unimpressive. But they are cut and polished by skilled craftsmen in a pattern that reflects and refracts the light among their facets to reveal the hidden beauty of the stone.
One of the most famous diamonds, the Hope Diamond, shown here in the National Museum of Natural History in Washington, D.C. Image via David Bjorgen/ Wikipedia (CC BY-SA 3.0).
Diamond lore
Some diamonds seem to have lived lives of their own. One legendary stone in the diamond hall of fame is the Koh-i-noor (“Mountain of Light”). The Koh-i-noor diamond is believed to be 5,000 years old, and was featured in the great Sanskrit epic The Mahabharata.
Originally owned by the Rajah of Malwa in India, the Koh-i-noor has since been a player in victories and defeats spanning India, Persia and Afghanistan. It was in the possession of the great Mogul dynasty from 1526 to 1739. Its owners included Shah Jehan, who built the Taj Mahal in memory of his queen Mumtaz. The Persian invader Nadir Shah briefly possessed it until his assassination in 1747. The jewel then fell into the hands of Afghan rulers who eventually surrendered it to the Rajah of Punjab, Ranjit Singh.
Two years after Ranjit Singh’s death in 1839, Punjab became part of India under British rule and they presented the stone to Queen Victoria. Then she had it cut from its original 187 carats to 108 carats to further enhance its beauty. After her death, the diamond became part of the British crown jewels. Queen Elizabeth (later the Queen Mother) wore it in her crown at her 1937 coronation. However, Camilla chose to wear another crown to Charles III coronation in 2023.
Find out about the birthstones for the other months of the year.
View larger. | Artist’s concept of a collision between 2 rocky bodies in the early solar system. A new study suggests an event like this, although with more similarly sized bodies, created Mercury. Image via NASA/ JPL-Caltech/ Wikimedia Commons (Public domain).
How did planet Mercury form? Scientists have been pondering this question for a long time.
According to new research, Mercury originated from the massive grazing collision of 2 similarly-sized bodies.
Collisions like this one were common in the early solar system billions of years ago. In fact, they likely accounted for about 1/3 of all impacts.
Mercury is the smallest and innermost planet in our solar system. It looks a lot like our moon at first glance, but it’s its own world, with unique geology and history. Scientists have been trying to figure out how it formed for a long time. And now, a new study from researchers in Brazil, Germany and France has shed some new light on the question. In a new preprint paper published on March 4, 2025, they said that a grazing giant collision between two similar-sized rocky bodies likely created Mercury a few billion years ago.
Mark Thompson wrote about the latest findings in Universe Today on March 25, 2025.
Despite its superficial resemblance to our moon, Mercury is a unique and strange world. Researchers have found evidence for a possible 10-mile-thick (16 km) layer of diamonds between the core and mantle of this planet, along with salty glaciers that could even be habitable.
And until now, scientists haven’t fully understood how Mercury formed. Surrounding its iron core is a relatively thin silicate mantle. In fact, the solid inner core and the molten outer core together take up nearly 85% of the planet’s radius. That’s much more than any of the other rocky planets. This posed a mystery. As the paper states:
The origin of Mercury still remains poorly understood compared to the other rocky planets of the solar system. One of the most relevant constraints that any formation model has to fulfill refers to its internal structure, with a predominant iron core covered by a thin silicate layer.
View larger. | Diagram depicting the interior structure of Mercury as currently understood. The overall core is nearly 85% of the planet’s radius, much more than other rocky planets in our solar system. This supports the theory that Mercury formed from the grazing impact of 2 similarly-sized bodies. Image via NASA/ Goddard Space Flight Center.
Collisions in the early solar system
The early solar system was a chaotic place, with frequent collisions between rocky bodies. And Mercury’s strangely large core has led scientists to hypothesize that a giant collision with a much larger body might have stripped away its outer layers.
But simulations of the early solar system have found colossal impacts between very differently sized objects to be relatively rare. On the other hand, recent simulations suggest that grazing ‘hit-and-run’ collisions between similarly-sized bodies are much more common. In fact, they likely accounted for about 1/3 of all impacts in the early solar system. And this, the new study says, is how Mercury likely formed.
One of the newest images of Mercury, from the 3rd flyby of the BepiColombo spacecraft on June 19, 2023. Image via ESA/ BepiColombo/ MTM.
Did a massive collision create Mercury?
Patrick Franco at the National Observatory in Brazil led the new study into whether two similar-sized rocky bodies could form a planet similar to Mercury.
Their study used a main body – a proto-Mercury – with a mass just over 10% of Earth’s, and a 30% iron makeup. In the simulations, the researchers experimented with variously sized secondary bodies, with varying amounts of iron.
They also varied the impact velocities between the two bodies, from 2.8 to 3.8 times the mutual escape velocity. The escape velocity is the minimum speed needed for an object to escape the orbit of or contact with a primary body.
Within these parameters, the researchers experimented with collision scenarios that could have occurred billions of years ago in the early solar system.
And they eventually found a setup in which Mercury grazed a similarly sized rocky object in a hit-and-run collision, leading it to lose much of its outer material. This scenario produced a planet that matched Mercury’s mass with a 5% margin, and left a core of 65-75% iron, matching Mercury’s current value of 70%. It’s strong evidence, they said, that a collision like this produced the planet we know today.
Patrick Franco at the National Observatory in Brazil is the lead author of the new Mercury study. Image via LinkedIn.
Bottom line: A new study says Mercury was formed from a huge collision between 2 similarly-sized rocky bodies.
View larger. | Artist’s concept of a collision between 2 rocky bodies in the early solar system. A new study suggests an event like this, although with more similarly sized bodies, created Mercury. Image via NASA/ JPL-Caltech/ Wikimedia Commons (Public domain).
How did planet Mercury form? Scientists have been pondering this question for a long time.
According to new research, Mercury originated from the massive grazing collision of 2 similarly-sized bodies.
Collisions like this one were common in the early solar system billions of years ago. In fact, they likely accounted for about 1/3 of all impacts.
Mercury is the smallest and innermost planet in our solar system. It looks a lot like our moon at first glance, but it’s its own world, with unique geology and history. Scientists have been trying to figure out how it formed for a long time. And now, a new study from researchers in Brazil, Germany and France has shed some new light on the question. In a new preprint paper published on March 4, 2025, they said that a grazing giant collision between two similar-sized rocky bodies likely created Mercury a few billion years ago.
Mark Thompson wrote about the latest findings in Universe Today on March 25, 2025.
Despite its superficial resemblance to our moon, Mercury is a unique and strange world. Researchers have found evidence for a possible 10-mile-thick (16 km) layer of diamonds between the core and mantle of this planet, along with salty glaciers that could even be habitable.
And until now, scientists haven’t fully understood how Mercury formed. Surrounding its iron core is a relatively thin silicate mantle. In fact, the solid inner core and the molten outer core together take up nearly 85% of the planet’s radius. That’s much more than any of the other rocky planets. This posed a mystery. As the paper states:
The origin of Mercury still remains poorly understood compared to the other rocky planets of the solar system. One of the most relevant constraints that any formation model has to fulfill refers to its internal structure, with a predominant iron core covered by a thin silicate layer.
View larger. | Diagram depicting the interior structure of Mercury as currently understood. The overall core is nearly 85% of the planet’s radius, much more than other rocky planets in our solar system. This supports the theory that Mercury formed from the grazing impact of 2 similarly-sized bodies. Image via NASA/ Goddard Space Flight Center.
Collisions in the early solar system
The early solar system was a chaotic place, with frequent collisions between rocky bodies. And Mercury’s strangely large core has led scientists to hypothesize that a giant collision with a much larger body might have stripped away its outer layers.
But simulations of the early solar system have found colossal impacts between very differently sized objects to be relatively rare. On the other hand, recent simulations suggest that grazing ‘hit-and-run’ collisions between similarly-sized bodies are much more common. In fact, they likely accounted for about 1/3 of all impacts in the early solar system. And this, the new study says, is how Mercury likely formed.
One of the newest images of Mercury, from the 3rd flyby of the BepiColombo spacecraft on June 19, 2023. Image via ESA/ BepiColombo/ MTM.
Did a massive collision create Mercury?
Patrick Franco at the National Observatory in Brazil led the new study into whether two similar-sized rocky bodies could form a planet similar to Mercury.
Their study used a main body – a proto-Mercury – with a mass just over 10% of Earth’s, and a 30% iron makeup. In the simulations, the researchers experimented with variously sized secondary bodies, with varying amounts of iron.
They also varied the impact velocities between the two bodies, from 2.8 to 3.8 times the mutual escape velocity. The escape velocity is the minimum speed needed for an object to escape the orbit of or contact with a primary body.
Within these parameters, the researchers experimented with collision scenarios that could have occurred billions of years ago in the early solar system.
And they eventually found a setup in which Mercury grazed a similarly sized rocky object in a hit-and-run collision, leading it to lose much of its outer material. This scenario produced a planet that matched Mercury’s mass with a 5% margin, and left a core of 65-75% iron, matching Mercury’s current value of 70%. It’s strong evidence, they said, that a collision like this produced the planet we know today.
Patrick Franco at the National Observatory in Brazil is the lead author of the new Mercury study. Image via LinkedIn.
Bottom line: A new study says Mercury was formed from a huge collision between 2 similarly-sized rocky bodies.
Watch this video on white-necked jacobins, a hummingbird species whose chicks look like caterpillars.
A hummingbird chick that looks like a caterpillar
A team of scientists from the University of Colorado Boulder were studying white-necked jacobin hummingbirds in Panama when they made an interesting discovery. They said on March 17, 2025, that the newborn chicks of this hummingbird species appear to be born with long, thin, yellowish feathers on their backs. This plumage resembles the hair that surrounds caterpillars. Coincidence? Scientists think not. It appears to be a defense mechanism for these tiny birds’ wee chicks.
The scientists published their peer-reviewed findings in the journal Ecology on March 17, 2025.
What’s new in the tiny world of hummingbirds?
The discovery begins with Jay Falk, a U.S. National Science Foundation postdoctoral fellow working at the University of Colorado and at the Smithsonian Tropical Research Institute (STRI). Falk was studying adult white-necked jacobins (Florisuga mellivora) in Panama. This is a neotropical hummingbird species that lives in southern Mexico, Central America and northern South America, in countries such as Brazil, Peru and Bolivia. The species also lives in Trinidad and Tobago.
Falk has studied this species for over a decade, but only adult hummingbirds. Then, co-authors Michael Castaño-Díaz and Sebastián Gallan Giraldo, a PhD student and a research assistant also working at STRI, spotted a hummingbird nest with an attentive mother caring for her egg. This caught the scientists’ attention, so they told Falk.
Since this was the first white-necked jacobin nest scientists had seen so far, they decided to visit it every day to check on its progress. They also enlisted videographer Joe See to record the events that followed.
About 18 to 20 days later, the egg hatched, and the scientists saw something spectacular. The tiny chick had long, fluffy feathers on its back. This made the newborn hummingbird look like a dangerous caterpillar.
A female white-necked jacobin on her nest, incubating her eggs. Falk had previously found that about 20% of the females in this species resemble males, likely to improve their chances of getting food. This chick’s mother was one of them. Image via Michael Castaño-Díaz/ University of Colorado Boulder.
A new strategy to scare off predators?
And why is a caterpillar dangerous? Because some caterpillars have a hairy covering that causes painful skin reactions. One of the most obvious symptoms is hives (itching). In some humans, contact with this hair even causes headaches, nausea and fever.
So, is this cute little animal also dangerous? Nope! Apparently, this creature disguises itself as a caterpillar, but its feathers don’t provoke skin reactions like the hairy coverings of caterpillars do.
The researchers also observed that the nest was covered with hairy-looking tree seeds. These are the local balsa trees (Ochroma pyramidale). This suggests that these hummingbirds use this strategy to camouflage themselves.
On the other hand, the scientists observed another curious fact. A carnivorous wasp approached the chick, and the newborn began to move its head, as some caterpillars do when a predator is nearby. It seems that this imitation serves the chicks as a method of protection against predators.
A newly hatched white-necked jacobin. Check out its back feathers! Image via Michael Castaño-Díaz/ University of Colorado Boulder.
Are other hummingbird species born with this characteristic?
The scientists looked for photos of other similar newborn animal species to verify how special this characteristic is. The cinereous mourner (Laniocera hypopyrra), endemic to South America, also begins life with feathers that look like caterpillar hair.
However, most hummingbird species are born without these distinctive feathers.
It’s not surprising that this species has developed this mimicry or camouflage ability. White-necked jacobins build their nests open, that is, in a cup shape. They also place them on exposed branches close to the ground. This makes them easy prey.
Scientists believe this species has evolved to the point of mimicking caterpillars and thus protecting itself from potential predators. However, to support these hypotheses, they’ll need to observe more individuals.
Nope, not a hummingbird. Some caterpillars have hair coverings that cause painful skin reactions. Image via Ronan Hello/ Unsplash.
Bottom line: The white-necked jacobin hummingbird might be small, but it has an interesting form of protection. This species is born with feathers similar to dangerous caterpillar hair.
Watch this video on white-necked jacobins, a hummingbird species whose chicks look like caterpillars.
A hummingbird chick that looks like a caterpillar
A team of scientists from the University of Colorado Boulder were studying white-necked jacobin hummingbirds in Panama when they made an interesting discovery. They said on March 17, 2025, that the newborn chicks of this hummingbird species appear to be born with long, thin, yellowish feathers on their backs. This plumage resembles the hair that surrounds caterpillars. Coincidence? Scientists think not. It appears to be a defense mechanism for these tiny birds’ wee chicks.
The scientists published their peer-reviewed findings in the journal Ecology on March 17, 2025.
What’s new in the tiny world of hummingbirds?
The discovery begins with Jay Falk, a U.S. National Science Foundation postdoctoral fellow working at the University of Colorado and at the Smithsonian Tropical Research Institute (STRI). Falk was studying adult white-necked jacobins (Florisuga mellivora) in Panama. This is a neotropical hummingbird species that lives in southern Mexico, Central America and northern South America, in countries such as Brazil, Peru and Bolivia. The species also lives in Trinidad and Tobago.
Falk has studied this species for over a decade, but only adult hummingbirds. Then, co-authors Michael Castaño-Díaz and Sebastián Gallan Giraldo, a PhD student and a research assistant also working at STRI, spotted a hummingbird nest with an attentive mother caring for her egg. This caught the scientists’ attention, so they told Falk.
Since this was the first white-necked jacobin nest scientists had seen so far, they decided to visit it every day to check on its progress. They also enlisted videographer Joe See to record the events that followed.
About 18 to 20 days later, the egg hatched, and the scientists saw something spectacular. The tiny chick had long, fluffy feathers on its back. This made the newborn hummingbird look like a dangerous caterpillar.
A female white-necked jacobin on her nest, incubating her eggs. Falk had previously found that about 20% of the females in this species resemble males, likely to improve their chances of getting food. This chick’s mother was one of them. Image via Michael Castaño-Díaz/ University of Colorado Boulder.
A new strategy to scare off predators?
And why is a caterpillar dangerous? Because some caterpillars have a hairy covering that causes painful skin reactions. One of the most obvious symptoms is hives (itching). In some humans, contact with this hair even causes headaches, nausea and fever.
So, is this cute little animal also dangerous? Nope! Apparently, this creature disguises itself as a caterpillar, but its feathers don’t provoke skin reactions like the hairy coverings of caterpillars do.
The researchers also observed that the nest was covered with hairy-looking tree seeds. These are the local balsa trees (Ochroma pyramidale). This suggests that these hummingbirds use this strategy to camouflage themselves.
On the other hand, the scientists observed another curious fact. A carnivorous wasp approached the chick, and the newborn began to move its head, as some caterpillars do when a predator is nearby. It seems that this imitation serves the chicks as a method of protection against predators.
A newly hatched white-necked jacobin. Check out its back feathers! Image via Michael Castaño-Díaz/ University of Colorado Boulder.
Are other hummingbird species born with this characteristic?
The scientists looked for photos of other similar newborn animal species to verify how special this characteristic is. The cinereous mourner (Laniocera hypopyrra), endemic to South America, also begins life with feathers that look like caterpillar hair.
However, most hummingbird species are born without these distinctive feathers.
It’s not surprising that this species has developed this mimicry or camouflage ability. White-necked jacobins build their nests open, that is, in a cup shape. They also place them on exposed branches close to the ground. This makes them easy prey.
Scientists believe this species has evolved to the point of mimicking caterpillars and thus protecting itself from potential predators. However, to support these hypotheses, they’ll need to observe more individuals.
Nope, not a hummingbird. Some caterpillars have hair coverings that cause painful skin reactions. Image via Ronan Hello/ Unsplash.
Bottom line: The white-necked jacobin hummingbird might be small, but it has an interesting form of protection. This species is born with feathers similar to dangerous caterpillar hair.
A view from above of Interlaken, Switzerland. A new study analyzed residential trees and mortality in Switzerland. Image via Kelly Kizer Whitt.
Urban trees enhance residents’ well-being. A long-term Switzerland-wide study has found that neighborhoods with numerous, well-arranged trees exhibit lower mortality risks than other areas.
Aggregated, connected tree clusters seem to provide greater health benefits than fragmented green spaces at the neighborhood level.
In fact, the study identified a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies.
Beyond creating a serene and open atmosphere in urban areas, trees and parks also contribute to human well-being. There are various reasons for this: trees filter pollutants out of the air, provide shade, lower the ambient temperature in hot weather and encourage people to spend more time outdoors. Many governments have set ambitious tree-planting targets for the decades ahead, partly in response to climate change and rising temperatures. In densely developed cities, however, space for new green space is at a premium. In this context, the key question is how to plant trees in existing green spaces to optimal effect.
This is a question that occupies urban planning researchers and practitioners alike, because any answer must take into account specific, local spatial circumstances and climatic conditions. ETH researchers are tackling this issue … not only in Switzerland, but also in Asia. In the course of their work, researchers from Future Cities Lab operated in Singapore by ETH Zurich and the National University of Singapore (NUS) discovered interesting links between tree management and the health of urban residents.
To begin with, the researchers examined high-resolution tree canopy data to determine the structure of tree-covered green spaces within a radius of 500 meters (1,640 feet) of a person’s place of residence. In addition to recording the total area covered by all tree clusters, they also identified the proximity and connectedness of tree clusters, their geometrical complexity and the fragmentation level.
They linked this information with the survival time of the residents in the respective neighborhood for over 6 million adults. That is, they looked exclusively at natural-cause deaths due to illness and old age. The Swiss Federal Statistical Office supplied this data, which covers a 10-year period (2010–2019). In order to protect privacy, the Federal Statistical Office rounded the coordinates of citizens’ residences to the nearest 50 meters (164 feet).
Residential trees: quantity and positioning both matter
The analysis showed that both the tree canopy cover in residential areas and their spatial arrangement correlate with mortality. The study identified a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies. That’s versus people who live in areas with fewer, fragmented areas of tree canopies with complex geometries. This correlation is particularly evident in densely developed peri-urban and urban areas with poor air quality and high temperatures. If such areas feature well-structured forested green spaces, the residents may receive more health benefits than other areas.
Yet, while this study represents an important first step, it is still not possible to draw conclusions regarding the causes. The researchers are not yet able to state with precision the pathways through which tree canopy configuration influences human health. Nevertheless, the study’s findings at the individual level are generally consistent with the results of similar studies at the community level in Philadelphia, Tehran and Taipei.
Isolated forested green spaces should be joined up
Dengkai Chi, a postdoctoral researcher at the ETH Future Cities Lab and the first author of the study, said:
Although we can’t yet define a direct causal link, when we have addressed factors such as age, gender and socio-economic status, the data show clear correlations. Our results provide plausible indications that human health may be influenced not only by the quantity of trees but also by their spatial distribution.
The findings underline the importance of carefully considering the layout of forested green spaces and adopting a targeted approach to tree placement. Chi said:
In order to fully exploit trees’ potential to support human health, cities should strive to not only increase the number of trees but also to connect isolated green spaces, including by creating tree-lined boulevards.
The study also suggested that compact, geometrically simple areas of tree canopy – including circular and rectangular forms – could have a greater positive effect on health than irregular, fragmented tree coverage. One possible explanation is that simply structured areas offer a larger core area, promote biodiversity and consequently attract residents to use these spaces.
The study was unable to take account of many specific influencing factors, such as whether people have preexisting illnesses, smoke or actually use green spaces. In addition, the results of this study pertain to the neighborhood level. They do not necessarily translate to an entire municipal area. Initial indications suggest that, at the level of an entire city, the health-promoting effects of green spaces correlate with their more even distribution throughout the city. That way, as many residents as possible have access to them. The researchers hope to examine these issues in further studies to better understand these links.
Chi explained that, when it comes to developing recommendations for future action by political decision-makers and urban planners, the researchers will have to quantify their results more effectively and define specific thresholds.
Bottom line: A new study examined residential trees in Switzerland and found a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies.
A view from above of Interlaken, Switzerland. A new study analyzed residential trees and mortality in Switzerland. Image via Kelly Kizer Whitt.
Urban trees enhance residents’ well-being. A long-term Switzerland-wide study has found that neighborhoods with numerous, well-arranged trees exhibit lower mortality risks than other areas.
Aggregated, connected tree clusters seem to provide greater health benefits than fragmented green spaces at the neighborhood level.
In fact, the study identified a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies.
Beyond creating a serene and open atmosphere in urban areas, trees and parks also contribute to human well-being. There are various reasons for this: trees filter pollutants out of the air, provide shade, lower the ambient temperature in hot weather and encourage people to spend more time outdoors. Many governments have set ambitious tree-planting targets for the decades ahead, partly in response to climate change and rising temperatures. In densely developed cities, however, space for new green space is at a premium. In this context, the key question is how to plant trees in existing green spaces to optimal effect.
This is a question that occupies urban planning researchers and practitioners alike, because any answer must take into account specific, local spatial circumstances and climatic conditions. ETH researchers are tackling this issue … not only in Switzerland, but also in Asia. In the course of their work, researchers from Future Cities Lab operated in Singapore by ETH Zurich and the National University of Singapore (NUS) discovered interesting links between tree management and the health of urban residents.
To begin with, the researchers examined high-resolution tree canopy data to determine the structure of tree-covered green spaces within a radius of 500 meters (1,640 feet) of a person’s place of residence. In addition to recording the total area covered by all tree clusters, they also identified the proximity and connectedness of tree clusters, their geometrical complexity and the fragmentation level.
They linked this information with the survival time of the residents in the respective neighborhood for over 6 million adults. That is, they looked exclusively at natural-cause deaths due to illness and old age. The Swiss Federal Statistical Office supplied this data, which covers a 10-year period (2010–2019). In order to protect privacy, the Federal Statistical Office rounded the coordinates of citizens’ residences to the nearest 50 meters (164 feet).
Residential trees: quantity and positioning both matter
The analysis showed that both the tree canopy cover in residential areas and their spatial arrangement correlate with mortality. The study identified a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies. That’s versus people who live in areas with fewer, fragmented areas of tree canopies with complex geometries. This correlation is particularly evident in densely developed peri-urban and urban areas with poor air quality and high temperatures. If such areas feature well-structured forested green spaces, the residents may receive more health benefits than other areas.
Yet, while this study represents an important first step, it is still not possible to draw conclusions regarding the causes. The researchers are not yet able to state with precision the pathways through which tree canopy configuration influences human health. Nevertheless, the study’s findings at the individual level are generally consistent with the results of similar studies at the community level in Philadelphia, Tehran and Taipei.
Isolated forested green spaces should be joined up
Dengkai Chi, a postdoctoral researcher at the ETH Future Cities Lab and the first author of the study, said:
Although we can’t yet define a direct causal link, when we have addressed factors such as age, gender and socio-economic status, the data show clear correlations. Our results provide plausible indications that human health may be influenced not only by the quantity of trees but also by their spatial distribution.
The findings underline the importance of carefully considering the layout of forested green spaces and adopting a targeted approach to tree placement. Chi said:
In order to fully exploit trees’ potential to support human health, cities should strive to not only increase the number of trees but also to connect isolated green spaces, including by creating tree-lined boulevards.
The study also suggested that compact, geometrically simple areas of tree canopy – including circular and rectangular forms – could have a greater positive effect on health than irregular, fragmented tree coverage. One possible explanation is that simply structured areas offer a larger core area, promote biodiversity and consequently attract residents to use these spaces.
The study was unable to take account of many specific influencing factors, such as whether people have preexisting illnesses, smoke or actually use green spaces. In addition, the results of this study pertain to the neighborhood level. They do not necessarily translate to an entire municipal area. Initial indications suggest that, at the level of an entire city, the health-promoting effects of green spaces correlate with their more even distribution throughout the city. That way, as many residents as possible have access to them. The researchers hope to examine these issues in further studies to better understand these links.
Chi explained that, when it comes to developing recommendations for future action by political decision-makers and urban planners, the researchers will have to quantify their results more effectively and define specific thresholds.
Bottom line: A new study examined residential trees in Switzerland and found a significantly lower mortality risk in people who live in neighborhoods with large, contiguous and well-networked areas of tree canopies.
The faint dot fixed in the center of this starfield is asteroid 2024 YR4. This is a sequence of observations from ESO’s Very Large Telescope in January 2025, shortly after the asteroid was discovered to have a greater than 3% chance of hitting Earth in 2032. Further observations have revealed that this asteroid won’t hit us in the foreseeable future. But, owing to a specific orbital resonance, it – and others – will keep coming back into our vicinity. Via Wikimedia Commons/ ESO/ O. Hainaut et al.
Astronomers have determined that asteroid 2024 YR4 will not hit Earth in 2032, as had been feared.
But asteroids like this one will keep coming back regularly, thanks to a strange orbital resonance.
These dangerous space rocks sit in an orbital “Kirkwood gap,” populated by asteroids that are pushed and pulled by Jupiter’s gravity until they either leave their orbit or hit a planet like Earth.
In late 2024, astronomers spotted asteroid 2024 YR4 on a trajectory that could potentially threaten Earth. This observation triggered a fervid series of observations to determine that the object, which is large enough to cause city-level damage, will not hit.
Then in January of this year, the near approach of asteroid 887 Alinda – perhaps a million times more massive than 2024 YR4 – went almost unnoticed. This asteroid is large enough to cause a global extinction event.
Alinda remains just outside Earth’s orbit, while 2024 YR4 continues to cross our orbit and still could impact Earth, although not in the foreseeable future. But, thanks to a strange orbital resonance, these asteroids are of a variety that will come back worryingly regularly. That is, until they’re ejected from their orbit … or until they collide with a planet like Earth.
A radar image of asteroid 887 Alinda taken in January 2024. The rectangular region at the top of the asteroid is about 3 kilometers (2 miles) a side. Image via NASA/ JPL.
Asteroids 2024 YR4 and 887 Alinda have dangerous orbits
Both 887 Alinda and 2024 YR4 orbit the sun three times for every time the massive planet Jupiter goes around once. Since Jupiter’s orbit takes 12 years, the asteroids will take four years to be back on similar paths in 2028. This special kind of asteroids is dangerous, since they come back regularly.
Alinda was discovered in 1918 and has made several sequences of near passes at four-year intervals. 2024 YR4 has made what NASA considers close passes every four years since 1948, but was only recently noticed.
Not since the 1970s has so much attention been paid to asteroids with a three-to-one orbital relation to Jupiter. Such relationships had already been noted as a curiosity by American astronomer Daniel Kirkwood in the late 1800s. Working with very sparse data, since few asteroids were known at the time, he noted that none went around the sun twice for each Jupiter orbit, nor three times, nor in more complex ratios like seven-to-three or five-to-two.
These statistical voids are known as Kirkwood gaps. And they’re not obvious, as they only show up when you plot the average distance of asteroids from the sun. The gaps remained a mere curiosity of the solar system for about 100 years.
This chart shows asteroid quantities by averaged distance from the sun, showing the Kirkwood gaps. The gap labelled 3:1 harbors both 887 Alinda and 2024 YR4, located at an average distance 2.5 times Earth’s distance from the sun. Chart via NASA/ JPL.
Understanding the Kirkwood gaps
The use of new computer technologies to calculate orbits revealed the effects of resonance to scientists in the 1970s. Resonance occurs when asteroids appear to move at the same speed that an external object orbits, or a multiple of the speed. In this case, that external object is the gravitationally dominant gas giant Jupiter.
The Kirkwood gaps are explained by asteroids interacting with Jupiter to leave the asteroid belt, even while their average distance from the sun does not change. That is, their orbits become more elliptical or oval-shaped, so they dip farther in and then farther out of the asteroid belt during each single orbit of the sun.
By dipping into the inner solar system, these asteroids are often removed by hitting an inner planet like Mars, Venus or Earth. And that’s one reason there are very few asteroids remaining with these particular orbits. Alternatively, if they don’t hit an inner planet, their orbits can become so elongated that they escape the solar system. Or Jupiter’s gravity can simply move them to a different, more stable orbit.
However, scientists have found that these Kirkwood gaps are not completely empty. They discovered 887 Alinda, for example, in the three-to-one gap. Many more such asteroids have been found, and they are generically named “Alindas” after that first discovery.
Asteroids 2024 YR4 and 887 Alinda will keep returning
So the bad news is that Kirkwood gaps are partly due to asteroids hitting inner planets, including Earth. Can it get much worse? For Alinda-class asteroids, it does. Alindas follow their pumped-up, elongated orbit every four years. So certain Alindas get a chance to hit Earth about that often.
Near passes of these asteroids tend to happen spaced by gradually longer intervals. But when perfectly aligned, they come back several times with four-year spacing. A limiting factor is how tilted their orbits are. If they are quite tilted, they are not often at a “height” matching Earth’s, so are less likely to hit.
The bad news about that is that both 887 Alinda and 2024 YR4 are very nearly in the plane of Earth’s orbit, and are not tilted much, so are more likely to hit.
The resonant “pumping” that stretches the orbit both inward and outward from the asteroid belt has already made 2024 YR4 cross Earth’s orbit, giving it a chance to impact. The much more dangerous Alinda is still being pumped; in about 1,000 years, it may be poised to hit Earth.
One piece of good news is that 2024 YR4 will not only miss in 2032, but it will come close enough that our planet’s gravity will kick it out of its Alinda orbit. It will no longer come back every four years.
However, its orbit will still cross ours, just not as often. The current orbit shows a somewhat close approach (farther than the moon) in 2052. Beyond that calculations are not very accurate.
Earth impacts
Although Earth is a small target in a big solar system, it does get hit.
Are dangerous asteroids out there likely to surprise us? The last damaging one to do so appeared undetected on February 15, 2013, over Chelyabinsk, Russia, injuring many people when its shock wave shattered glass in buildings.
Fallen trees from the 1908 Tunguska explosion in Siberia. Photo via the Soviet Academy of Science/ NASA/ Leonid Kulik/ Yevgeny Krinov.
Keeping watch
While astronomers work diligently to survey the night sky from Earth’s surface, space-based surveys like the upcoming Near-Earth Object (NEO) surveyor can be very efficient in detecting asteroids. The NEO surveyor will do so by watching for the heat (infrared) radiation of asteroids. And, being in space, the satellite can also study the daytime sky.
According to Amy Mainzer, lead on the NEO surveyor:
We know of only roughly 40% of the asteroids that are both large enough to cause severe regional damage and closely approach Earth’s orbit.
Bottom line: Asteroids like 2024 YR4 – which is set to pass very close to Earth in 2032 – will keep coming back into our planet’s vicinity, thanks to a strange orbital resonance.
The faint dot fixed in the center of this starfield is asteroid 2024 YR4. This is a sequence of observations from ESO’s Very Large Telescope in January 2025, shortly after the asteroid was discovered to have a greater than 3% chance of hitting Earth in 2032. Further observations have revealed that this asteroid won’t hit us in the foreseeable future. But, owing to a specific orbital resonance, it – and others – will keep coming back into our vicinity. Via Wikimedia Commons/ ESO/ O. Hainaut et al.
Astronomers have determined that asteroid 2024 YR4 will not hit Earth in 2032, as had been feared.
But asteroids like this one will keep coming back regularly, thanks to a strange orbital resonance.
These dangerous space rocks sit in an orbital “Kirkwood gap,” populated by asteroids that are pushed and pulled by Jupiter’s gravity until they either leave their orbit or hit a planet like Earth.
In late 2024, astronomers spotted asteroid 2024 YR4 on a trajectory that could potentially threaten Earth. This observation triggered a fervid series of observations to determine that the object, which is large enough to cause city-level damage, will not hit.
Then in January of this year, the near approach of asteroid 887 Alinda – perhaps a million times more massive than 2024 YR4 – went almost unnoticed. This asteroid is large enough to cause a global extinction event.
Alinda remains just outside Earth’s orbit, while 2024 YR4 continues to cross our orbit and still could impact Earth, although not in the foreseeable future. But, thanks to a strange orbital resonance, these asteroids are of a variety that will come back worryingly regularly. That is, until they’re ejected from their orbit … or until they collide with a planet like Earth.
A radar image of asteroid 887 Alinda taken in January 2024. The rectangular region at the top of the asteroid is about 3 kilometers (2 miles) a side. Image via NASA/ JPL.
Asteroids 2024 YR4 and 887 Alinda have dangerous orbits
Both 887 Alinda and 2024 YR4 orbit the sun three times for every time the massive planet Jupiter goes around once. Since Jupiter’s orbit takes 12 years, the asteroids will take four years to be back on similar paths in 2028. This special kind of asteroids is dangerous, since they come back regularly.
Alinda was discovered in 1918 and has made several sequences of near passes at four-year intervals. 2024 YR4 has made what NASA considers close passes every four years since 1948, but was only recently noticed.
Not since the 1970s has so much attention been paid to asteroids with a three-to-one orbital relation to Jupiter. Such relationships had already been noted as a curiosity by American astronomer Daniel Kirkwood in the late 1800s. Working with very sparse data, since few asteroids were known at the time, he noted that none went around the sun twice for each Jupiter orbit, nor three times, nor in more complex ratios like seven-to-three or five-to-two.
These statistical voids are known as Kirkwood gaps. And they’re not obvious, as they only show up when you plot the average distance of asteroids from the sun. The gaps remained a mere curiosity of the solar system for about 100 years.
This chart shows asteroid quantities by averaged distance from the sun, showing the Kirkwood gaps. The gap labelled 3:1 harbors both 887 Alinda and 2024 YR4, located at an average distance 2.5 times Earth’s distance from the sun. Chart via NASA/ JPL.
Understanding the Kirkwood gaps
The use of new computer technologies to calculate orbits revealed the effects of resonance to scientists in the 1970s. Resonance occurs when asteroids appear to move at the same speed that an external object orbits, or a multiple of the speed. In this case, that external object is the gravitationally dominant gas giant Jupiter.
The Kirkwood gaps are explained by asteroids interacting with Jupiter to leave the asteroid belt, even while their average distance from the sun does not change. That is, their orbits become more elliptical or oval-shaped, so they dip farther in and then farther out of the asteroid belt during each single orbit of the sun.
By dipping into the inner solar system, these asteroids are often removed by hitting an inner planet like Mars, Venus or Earth. And that’s one reason there are very few asteroids remaining with these particular orbits. Alternatively, if they don’t hit an inner planet, their orbits can become so elongated that they escape the solar system. Or Jupiter’s gravity can simply move them to a different, more stable orbit.
However, scientists have found that these Kirkwood gaps are not completely empty. They discovered 887 Alinda, for example, in the three-to-one gap. Many more such asteroids have been found, and they are generically named “Alindas” after that first discovery.
Asteroids 2024 YR4 and 887 Alinda will keep returning
So the bad news is that Kirkwood gaps are partly due to asteroids hitting inner planets, including Earth. Can it get much worse? For Alinda-class asteroids, it does. Alindas follow their pumped-up, elongated orbit every four years. So certain Alindas get a chance to hit Earth about that often.
Near passes of these asteroids tend to happen spaced by gradually longer intervals. But when perfectly aligned, they come back several times with four-year spacing. A limiting factor is how tilted their orbits are. If they are quite tilted, they are not often at a “height” matching Earth’s, so are less likely to hit.
The bad news about that is that both 887 Alinda and 2024 YR4 are very nearly in the plane of Earth’s orbit, and are not tilted much, so are more likely to hit.
The resonant “pumping” that stretches the orbit both inward and outward from the asteroid belt has already made 2024 YR4 cross Earth’s orbit, giving it a chance to impact. The much more dangerous Alinda is still being pumped; in about 1,000 years, it may be poised to hit Earth.
One piece of good news is that 2024 YR4 will not only miss in 2032, but it will come close enough that our planet’s gravity will kick it out of its Alinda orbit. It will no longer come back every four years.
However, its orbit will still cross ours, just not as often. The current orbit shows a somewhat close approach (farther than the moon) in 2052. Beyond that calculations are not very accurate.
Earth impacts
Although Earth is a small target in a big solar system, it does get hit.
Are dangerous asteroids out there likely to surprise us? The last damaging one to do so appeared undetected on February 15, 2013, over Chelyabinsk, Russia, injuring many people when its shock wave shattered glass in buildings.
Fallen trees from the 1908 Tunguska explosion in Siberia. Photo via the Soviet Academy of Science/ NASA/ Leonid Kulik/ Yevgeny Krinov.
Keeping watch
While astronomers work diligently to survey the night sky from Earth’s surface, space-based surveys like the upcoming Near-Earth Object (NEO) surveyor can be very efficient in detecting asteroids. The NEO surveyor will do so by watching for the heat (infrared) radiation of asteroids. And, being in space, the satellite can also study the daytime sky.
According to Amy Mainzer, lead on the NEO surveyor:
We know of only roughly 40% of the asteroids that are both large enough to cause severe regional damage and closely approach Earth’s orbit.
Bottom line: Asteroids like 2024 YR4 – which is set to pass very close to Earth in 2032 – will keep coming back into our planet’s vicinity, thanks to a strange orbital resonance.
