As interstellar visitor Comet 3I/ATLAS hurtles through the Solar System, scientists from around the world are taking advantage of this rare opportunity to actively study this visitor from distant worlds. The results of two new studies shed light on its remarkable properties, which challenge conventional wisdom about comet behavior.

The spectrum obtained by the 4.1-meter SOAR telescope on July 3, 2025, when the comet was far from the Sun, revealed a red tint in the reflected light. However, no signs of radiation from typical cometary gases (CN, C3, C2, CO+) or atomic oxygen were detected. This creates a paradox: the comet became active early, but without the usual sublimation of ice. Scientists suggest that dust release may occur through a different, unusual mechanism characteristic of ancient interstellar “travelers.”

A second study conducted by David Jewitt’s team based on images from the Hubble Space Telescope between July 4 and 5 made it possible to estimate the size of the comet’s nucleus. It turned out to be very compact – only 0.32 to 5.6 kilometers in diameter. This is consistent with preliminary predictions based on the limited availability of durable material in the interstellar medium. However, this tiny nucleus is surrounded by an impressively large cloud of dust, which makes up the bulk of the visible object.

Amazing glow in an unusual place

The most unexpected discovery made by Hubble was the structure of the coma of 3I/ATLAS. Instead of the classic tail extending from the Sun, the telescope detected a diffuse glow ahead of the comet’s movement toward our star. This contradicts the usual picture for comets.

An explanation for this phenomenon was proposed back in early August: the comet’s nucleus rotates very slowly. The sun heats only one side of it. The dust evaporation occurs precisely there. If the nucleus does not rotate fast enough, this hot daytime side does not have time to cool down significantly. Consequently, dust continues to be actively released from the “illuminated” part, creating a glowing effect in front. This hypothesis has been confirmed.

Remaining mystery

The latest ground-based observations complete the picture: the rotation period of 3I/ATLAS is 16.16 hours (±0.01 hours). This means that “night” and “day” on its surface last about 8 hours each. During these 8 hours, dust particles released from the day side are carried away from the nucleus to a distance of up to 10,000 km. In Hubble images, this corresponds to 0.35 arcseconds — the scale at which the elongated forward glow is observed.

The key point is that the surface of the nucleus has to cool down quickly after it goes into shadow, meaning in less than 8 hours. Otherwise, the release of dust would become more uniform and would not produce a clear frontal effect.

The main mystery that remains is the combination of intense dust release, visible by its glow, with the complete absence of any traces of gases that usually “carry” this dust in comets.

As it approaches the Sun, 3I/ATLAS will become brighter. The greatest hopes for unraveling its mystery are pinned on the James Webb Space Telescope. Its infrared vision will help analyze the comet’s thermal radiation and dust composition in greater detail, possibly finally answering questions about its true nature and the mechanism behind its unusual activity.

Earlier, we reported on how Juno, instead of dying, got a new chance at life by hunting 3I/ATLAS.

• According to medium.com

The European Space Agency has published a series of new images obtained by the Mars Express spacecraft. They show a region whose geological history holds memories of the Red Planet’s turbulent past. 

Modern Mars is a cold and desert world where, at first glance, no significant geological processes are taking place. But this was not always the case. Over billions of years of its existence, the Red Planet has gone through periods of water bodies, eruptions of giant supervolcanoes, and numerous glaciation cycles. All of them left distinctive marks on its surface.

One of the most striking examples demonstrating the tumultuous past of Mars is the Acheron Fossae region. It is located 1,200 km from Olympus Mons, the largest volcano in the Solar System, whose formation directly influenced the appearance of this area. Acheron Fossae is a surprisingly diverse mix of rugged and smooth terrain, covered with ancient faults, craters, and solidified lava. In April, Mars Express already photographed its eastern part. Now the vehicle returned to it to show the western edge, where the landscape is equally diverse: deep cracks, valleys, and winding channels carved out and filled by slowly moving streams of ice and rocks.

According to scientists, this structure emerged more than 3.7 billion years ago, when Mars was most geologically active, as a result of hot material rising beneath the Martian crust associated with the formation of supervolcanoes. This rise in molten rock stretched and tore the surface, creating cracks and valleys kilometers deep, some of which are hundreds of kilometers long.

After their formation, these valleys continued to transform. Now their bottom is relatively flat, with soft, winding lines reminiscent of a flowing river. It is believed that these valleys were once filled with a slow, viscous flow of ice-rich rock, very similar to the rock glaciers found on Earth. 

Rock glaciers are very sensitive to climate change and are therefore good indicators of how the planet’s climate has changed over time. Here, they point out that this region of Mars experienced alternating periods of cooling and warming, freezing and thawing. 

These temperature fluctuations are caused by the tilt of Mars’ axis of rotation. Unlike Earth, whose axis maintains a relatively stable and moderate tilt thanks to the stabilizing influence of the Moon, Mars’ tilt varies significantly over time. This leads to alternating warm periods and ice ages, resulting in ice periodically advancing toward the planet’s equator and then retreating back to the poles.

Although our Earth also experiences similar fluctuations, they are much stronger on Mars. Over the past 10 million years, Mars’ tilt has fluctuated between 15 and 45 degrees, while Earth’s tilt has varied between 22 and 24.5 degrees. These regular shifts, known as Milankovitch cycles, play an important role in our planet’s climate, but their influence is more subtle than on Mars. 

• According to ESA

Dark matter — an invisible substance that holds galaxies together like glue — remains the main cosmological mystery. Efforts to find it using traditional methods have reached an impasse. Against the backdrop of this crisis, physicist Stefano Profumo of the University of California, Santa Cruz, proposed two revolutionary, albeit speculative, scenarios for the origin of this mysterious matter.

Scientists discovered dark matter only because of its gravitational influence: galaxies rotate faster than they should, considering only visible matter. The difficulty lies in the fact that this mysterious substance does not emit or absorb light at all, making direct detection impossible. Decades of searching have been fruitless. Hypothetical particles that dark matter is supposed to consist of, such as WIMPs, have never been found. This deadlock forces scientists to seek radical alternatives, which may even be fantastical.

Mirror Universe

In his first article, Profumo addresses quantum chromodynamics, the theory of the strong nuclear force. He suggests the existence of a parallel “mirror” universe, where similar but invisible forces and particles — analogues of protons and neutrons — act. In the early Universe, the concentration of these dark particles could have been extremely high. This resulted in the formation of compact objects – dark matter black holes. They interact with our world exclusively through gravity, explaining the observed effects.

Birth on the edge

Profumo’s second article offers an even more exotic idea. He considers the cosmic horizon — the boundary of the observable Universe, similar to the event horizon of a black hole, but on a global scale. During the period of extremely rapid expansion of the Universe (inflation) after the Big Bang, quantum fluctuations at this cosmic horizon could spontaneously generate dark matter particles with a wide range of masses. These particles, born at the very edge of our existence, could also be a source of invisible mass.

Verification methods

“Both mechanisms are highly speculative,” Profumo notes, “but they offer self-sufficient and calculable scenarios that are independent of problematic traditional models.”

Although the theories are based on modern physics, they require significant refinement and verification in future experiments and observations. Despite this, Profumo’s work opens up new, bold avenues for unraveling one of the deepest mysteries of the cosmos — the nature of dark matter, which shapes our universe.

• According to Science Alert

The European spacecraft Hera, located in the asteroid belt, managed to obtain images of several of its objects. These observations served as both a successful test of the instruments and a demonstration of capabilities that could be useful for protecting our planet. 

The Hera spacecraft was launched to study the double asteroid Didymos. In 2022, NASA’s DART probe deliberately crashed into its companion, Dimorphos. The aim of the experiment was to study the possibility of deflecting dangerous celestial bodies away from Earth.

This spring, Hera flew past Mars and used its gravity to accelerate and change its trajectory. Shortly thereafter, the spacecraft entered the Main Asteroid Belt. Hera’s flight path does not suggest that it will encounter any asteroids along the way. Nevertheless, the mission specialists decided to take advantage of this opportunity to test the instrument. They chose the asteroid Otero, located 3 million km from Hera.

On May 11, 2025, Hera took pictures of Otero with its AFC camera. This navigation and science instrument will be used to guide the spacecraft as it gets closer to Didymos. According to experts, Otero’s imaging was conducted under conditions similar to the ones that would occur next year – when Hera reaches its destination and needs to keep the asteroid in the center of the camera’s field of view. 

Hera accomplished the task. The device successfully tracked Otero for three hours, taking one photo every six minutes. On July 19, Hera conducted a new photo shoot. This time, the camera was aimed at the asteroid Kellyday. Despite being approximately 40 times dimmer than Otero, the device managed to get an image of it.

Although science was not the primary goal of these observations, they demonstrate how a spacecraft in space can quickly perform accurate observations of a new object. This ability can be very useful for protecting our planet.

One example is asteroid 2024 YR4. Earlier this year, astronomers around the world pointed their telescopes at it because they were worried it might hit Earth in 2032. If a spacecraft similar to Hera were in the right place, it could conduct impromptu observations of the asteroid. Additional information about its size and orbit would help astronomers better assess the danger it poses to Earth.

Similarly, a spacecraft located at a suitable point could be used to observe interstellar objects passing through the Solar System, such as the recently discovered comet 3I/ATLAS. At the end of this year, it will fly past Mars, and right now the scientific community is assessing whether any of the spacecraft orbiting the Red Planet will be able to observe it.

• According to ESA

A person who is just beginning to learn about astrophysics may think that there are any possible combinations of star color and size. But in reality, this is not the case, and the actual state of affairs is described by the Hertzsprung-Russell diagram, which reveals the fundamental dependencies according to which stars function.

The most important diagram in astrophysics

When describing the characteristics of a particular star that has caught the attention of astronomers, they are often presented by indicating its position on the Hertzsprung-Russell diagram. Experts understand perfectly well what this means, but for most people it sounds like gibberish.

However, all this can be explained to ordinary people. In the 19th century, scientists discovered that the apparent magnitude of stars in the sky depends on both their luminosity and their distance. At the same time, the color of a star correlates with its temperature. But both parameters can vary greatly for different objects.

Can they form any combination? It became possible to answer this question after spectroscopic studies conducted in the second half of the 19th century and the early 20th century at the Harvard Observatory. It was Annie Jump Cannon, an employee of the observatory, who developed the system of designating spectral classes with Latin letters, which we still use today.

Based on this data, Danish astronomer Ejnar Hertzsprung and American scientist Henry Russell independently conducted an analysis and placed known stars in a coordinate system, with luminosity on the vertical axis and color on the horizontal axis, ranging from blue to red. It turned out that the stars do not cover it evenly, but form several elongated groups, which are conventionally called sequences.

Main sequence

The largest number of stars on the Hertzsprung-Russell diagram is found in the so-called main sequence. If the axes are positioned in the standard way, it stretches from the lower right corner to the upper left. Ninety percent of all stars observed by scientists in the Milky Way are found in this sequence.

The main sequence is not just a line on a graph. It shows the normal state of a star in the middle of its life cycle: the first millions of years it spent as a protostar are already over, and its transformation into a subgiant or red giant is still a long way off.

The coldest and smallest stars, red dwarfs, are located in its lower part. Brown dwarfs are not usually considered stars, but if they are placed on the main sequence, they will continue it further into the infrared zone and toward decreasing luminosity.

Red dwarfs are a fairly diverse group of stars, with luminosities varying by a factor of ten between members. What unites them all is that, unlike other stars, helium reactions are impossible inside them, so they never turn into red giants.

It is believed that at the end of their lives, they should contract, heat up, and become blue dwarfs. However, no one has ever seen such a star, since their lifespan is tens of billions or even trillions of years, which is much longer than the existence of the Universe. The surface temperature of red dwarfs ranges from 2 to 4 thousand degrees Celsius.

Next come orange dwarfs. These are stars whose mass is tens of percent of the Sun’s, and whose surface temperature is 4–5 thousand degrees Celsius. Unlike red dwarfs, they turn into red giants at the end of their existence, but no one has ever seen such a star, since the time of their evolution exceeds the age of the Universe.

They are followed by yellow stars, which include our Sun. Their surface temperatures range from 5,000 to 7,000 degrees Celsius, and their time on the main sequence is 8 to 15 billion years. Moving further to the left, we first see yellowish stars of spectral class F, then white stars of class A, white-blue stars of class B, and finally blue stars of class O.

All these stars have several features in common. First, they are all heavier and hotter than the Sun. As a result, thermonuclear reactions inside them are much more intense than on the Sun, so they age much faster. This leads to their second feature: they remain on the main sequence for only a few million to a few billion years.

The second feature of hot stars leads to the third – they are quite rare. And the more massive and hotter a star is, the rarer it is to observe something like this. For example, only a few tens of thousands of stars of spectral class O are known. It is precisely the stars on the left side of the main sequence that most often become the subjects of articles about the study of unique objects.

Subgiants and giants

The second most frequently mentioned sequence is giants. They are often referred to as red giants, as their most prominent representatives belong to the spectral class M. However, there are also extremely bright stars of spectral classes K and G.

The easiest way to explain what the giant sequence is is from the perspective of astrophysics. When a star with a mass between 0.4 and several solar masses runs out of hydrogen, it gradually begins to burn helium. The outer layers of the star expand and cool, but its luminosity only increases. If you look at the Hertzsprung-Russell diagram, it looks as if the star is shifting to the right of the main sequence. At the same time, it still consists mostly of hydrogen. Combustion begins in the core, initially in a very limited area, and then spreads to an increasingly larger volume.

However, this cannot last forever. Sooner or later, this fuel runs out, and stars of different masses begin to behave differently. All of them, in one way or another, leave the red giant sequence, but smaller ones usually end up on the horizontal branch and eventually simply shed their shell, turning into a white dwarf.

Heavier stars may even shift to the left on the diagram. Eventually, reactions involving oxygen and carbon begin inside them. They move to an asymptotic branch, which is located even higher and further to the right than the previous one. That is, they are even redder and brighter than all the others. But the outcome for all red giants is always the same – they turn into white dwarfs.

Subdwarfs

Below the main sequence and parallel to it is another narrow and long zone of stars that is not mentioned very often – subdwarfs. These are at least two different categories of stars combined. The right half of this sequence consists of stars of spectral classes G, K, and M. They are very similar to their “relatives” from the main sequence, but have lower luminosity than they should have at such temperatures.

All of these are old stars that contain very few metals, i.e., elements heavier than helium. Because of this, they emit slightly less radiation in the visible range, but more in the ultraviolet range.

Hot subdwarfs are completely different from them. Their origin remains controversial. Some scientists believe that these objects are red giants that lost their outer shells at a certain stage before exhausting all their helium fuel. Others believe that they are formed during the merger of two helium white dwarfs. In any case, they are powered by helium reactions.

White dwarfs

At the bottom of the Hertzsprung-Russell diagram is a sequence of white dwarfs. This is exactly what the vast majority of medium-sized stars turn into after passing through the red giant stage. In terms of temperature, they are very similar to main-sequence stars belonging to class A, but they are several orders of magnitude dimmer than they are.

The mass of white dwarfs can range from a few tens of percent to 1.4 times the mass of the Sun. Essentially, these are dead stars composed of helium, carbon, or oxygen. Thermonuclear reactions no longer occur on them, but they have accumulated an enormous amount of energy. By emitting it, they can shine for billions and tens of billions of years until they completely fade away.

Supergiants

The most interesting things happen at the top of the Hertzsprung-Russell diagram. This is where stars with masses greater than 10 solar masses are located. Formally, this is where the upper limit of the main sequence is, but there are several virtual ones, sometimes called supergiant and hypergiant branches.

However, in reality, all this can be discussed only in a rather conditional manner. The fact is that stars located in the upper part of the Hertzsprung-Russell diagram are, first, extremely rare, and second, evolve very quickly. They simply gradually “ignite” more and more new chemical elements, going even further than in the case of asymptotic branch giants.

Other objects in the Hertzsprung-Russell diagram

In general, astronomers use the Hertzsprung-Russell diagram to plot any objects or systems consisting of stars to better understand their nature. For example, the position of stars in a star cluster on this diagram allows us to estimate its age. The location of components in binary systems helps us to better understand their evolution. Pulsating stars form characteristic sequences on the diagram.

The Hertzsprung-Russell diagram is both a description of all possible types of stars and an understanding of their evolutionary paths. That is why scientists constantly refer to this diagram when describing stars to express themselves as accurately as possible. Therefore, there is no need to be afraid of it.

British scientists have discovered that icy comets colliding with exoplanets can alter their climate and atmosphere. According to computer modeling results, even a single large comet could transform a dead, cold exoplanet into a warmer and potentially habitable world.

Researchers simulated the collision of a large comet with a planet similar to TRAPPIST-1e. It is one of the most studied exoplanets in the habitable zone orbiting a red dwarf. Red dwarfs (stars of spectral class M) are cooler and less luminous than the Sun, but they are the most common type of stars in the Universe. Planets that orbit such stars are often located very close to them and may be tidally locked, meaning that they always face the star with the same side. This creates extremely harsh conditions: the daytime side can be too hot and dry, while the nighttime side can be freezing cold.

When a large comet consisting mainly of water ice collides with such a planet, a large amount of water vapor is released into the atmosphere. Part of this pair enters the upper layers of the atmosphere, where it can remain for a long time, altering the planet’s heat balance. Water vapor in the upper layers acts like a greenhouse “blanket”: it absorbs heat emitted by the planet and traps it, raising the surface temperature. This is similar to the natural greenhouse effect known on Earth.

In addition, under the influence of ultraviolet radiation, water molecules split into hydrogen and oxygen. This process, as well as subsequent chemical reactions, can lead to the formation of greenhouse gases such as methane and nitrogen oxide. They are significantly more effective at warming the planet than carbon dioxide.

Thus, modeling shows that even a single major collision could cause climate changes that would last for decades or even centuries. During this time, liquid water may appear on the planet. This creates a brief but important “window of opportunity” for the emergence of life.

This study helps us better understand how exoplanets that initially appear uninhabitable may have a chance to develop favorable conditions. Similar catastrophic events may have been significant in Earth’s past. According to one hypothesis, it was comets that brought the first supplies of water to our planet, which were necessary for the development of life.

• According to The Astrophysical Journal.

The Perseverance mission team took advantage of a rare opportunity to capture one of the clearest panoramas of Mars in history. It shows objects located up to 65 km away from the rover.

The clearest panorama of Mars in history

Mars is a very dusty place. Dust gives its surface and sky a distinctive appearance and also limits visibility. However, sometimes there are periods of calm on the Red Planet when the sky clears of dust. This is exactly what happened on May 26, 2025.

NASA specialists took advantage of a rare opportunity to obtain a panorama of Mars. Inside the Jezero crater, the Perseverance rover took 96 photos, which were then combined into a single image. According to experts, this is the clearest panorama of Mars ever taken. It shows hills located 65 km away from the rover. 

A total of two versions of the image were published: one in natural colors, where the Martian sky has a reddish hue, and one in enhanced colors, where it looks surprisingly clear and deceptively blue. 

Floating boulder

One of the details that caught the attention of the research team is a large rock that appears to be lying on a dark sand dune in the shape of a crescent to the right of the center of the mosaic, approximately 4.4 meters from the rover. Geologists call this type of rock a “floating rock” because it most likely formed elsewhere and was transported to its current location. It is unknown whether it arrived there by landslide, water, or wind, but the scientific team assumed that it was there before the dune was formed.

The bright white circle to the left of the center and at the bottom of the image was created by Perseverance using a drill. Thanks to this, the scientific team was able to see what was beneath the weathered, dusty surface of the rock before deciding to take a sample, which would be stored in one of the mission’s titanium tubes.

The rover left this track on May 22, and two days later, using instruments mounted on its manipulator, conducted a detailed analysis of Martian rocks. The scientific team wanted to study this area because it is located in one of the oldest regions Perseverance has ever explored — possibly even older than Jezero Crater.

Traces of the rover’s movement to this location can be seen on the right edge of the mosaic. About 90 meters away from it, they turn left and disappear from view at the previous rover stop.

Just over halfway across the mosaic, from one edge to the other, there is a transition from lighter to darker rocks. This is the boundary, or contact, between two geological zones. The flat, lighter-colored rocks closer to the rover are rich in the mineral olivine, while the darker rocks farther away appear to be much older clay rocks.

• According to NASA