The water that makes up the oceans acted as a key ingredient for the development of life on Earth. However, scientists still do not know where the water here on Earth came from in the first place.

One leading idea is that space rocks such as comets and asteroids delivered water to the Earth through impacts. As a planetary scientist, I’m curious about the kinds of space objects that could have led to the formation of the oceans. For the past few years, I’ve been studying a type of object that I called a dark comet – which could be just the culprit. In a new study my colleagues and I published in December 2024, we discovered two classes of these elusive dark comets

What is a comet?

The solar system is teaming with small bodies such as comets and asteroids. These space rocks were fundamental building blocks of planets in the early solar system, while the remaining leftovers are the comets and asteroids seen today.

These objects are also avenues by which material can be transported throughout the solar system. These small worlds can contain things such as rubble, ice and organic material as they fly through space. That’s why researchers see them as good potential candidates for delivering ices such as water and carbon dioxide to the Earth while it was forming.

Traditionally, the difference between comets and asteroids is that comets have beautiful cometary tails. These tails form because comets have ice in them, while asteroids supposedly do not.

When a comet gets close to the Sun, these ices heat up and sublimate, which means they turn from ice into gas. The gas heats up because of the sunlight and is then blown off the comet’s surface in a process called outgassing. This outgassing brings with it rubble and small dust grains, which reflect sunlight.

Asteroids, on the other hand, do not have cometary tails. Presumably, they are more like classic rocks – without ice on their surfaces.

What is a nongravitational acceleration?

The outgassing material from the surface of a comet produces a cometary tail and a rocketlike recoil. The fast moving gas pushes on the surface of the comet, and this causes it to accelerate. This process drives comets’ motion through space on top of the motion set by the gravitational pull of the Sun.

So, when comets outgas, they have what planetary scientists call nongravitational acceleration – motion that isn’t caused by the gravity of objects in the solar system. Planetary scientists typically measure the nongravitational accelerations of comets after detecting their cometary tails.

What are dark comets?

Our team identified a class of small bodies in the solar system that take some of the properties of both comets and asteroids. We called them dark comets.

These dark comets have nongravitational accelerations like comets, so they experience a rocketlike recoil from comet outgassing. However, they don’t have the dusty tails that most comets have.

In other words, they look like typical asteroids, but gravity alone can’t explain their motion.

The first interstellar object, ’Oumuamua, was the first comet or asteroid-size body that was detected in the solar system that came from outside of the solar system.

’Oumuamua displayed this same mysterious combination of no dust tail but a cometlike nongravitational acceleration, which led to many theories trying to explain what the object could have been. One option is that it was outgassing like a comet but not producing a dusty tail.

Since ’Oumuamua was first spotted in 2017, my colleagues and I have identified other dark comets within the solar system. In our study, we found seven new dark comets, bringing the total to 14.

Now that we’ve found more dark comets, we’ve noticed that they come in two flavors. Outer dark comets are larger – about a mile wide in size – and on more elliptical orbits farther out in the solar system. Inner dark comets are smaller – typically 1,000 feet in size – and on circular orbits close to the Earth.

Contributions to the Earth’s oceans?

It’s still not clear exactly what these dark comets are. They may not even be traditional comets if they don’t have icy surfaces.

However, the most likely answer for their nongravitational accelerations is that they outgas water, like a comet, but don’t produce a dusty tail – at least not one we can see when we look at them with our telescopes.

If this is the case, there are sure to be many more of these objects, parading around like asteroids, still yet to be identified.

Since scientists don’t know for sure where the Earth’s water came from, if there really are lots of dark comets that have water near Earth, it is possible that these dark comets contributed water to the early Earth.

These dark comets could tell researchers more about the origins of Earth’s oceans and the development of life here on Earth.

Reasons to be excited for the future

This research is really just the tip of the iceberg, because we only just started finding these dark comets in 2023.

The Vera C. Rubin Observatory’s Legacy Survey of Space and Time, which comes online in 2025, will start scanning the entire southern sky almost every night to spot anything that moves. This telescope, located on a mountain in Chile’s Atacama desert, is home to the largest camera ever built.

It will give astronomers almost five orders of magnitude greater sensitivity for detecting moving objects in the night sky. It will likely help my colleagues and me discover lots of new dark comets in the near future.

Telescopes that are already operating, such as the Hubble Space Telescope and the James Webb Space Telescope, could also help my team watch for outgassing or ice on the surface of the 14 dark comets we’ve already identified.

Finally, the JAXA Hayabusa2 extended mission is slated to rendezvous with one of the inner dark comets, 1998 KY26, in 2031. Therefore, we will be able to see the surface of a dark comet in exquisite detail.

Darryl Z. Seligman, Postdoctoral Fellow in Physics and Astronomy, Michigan State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Powerful Santa Ana winds, with gusts reaching hurricane strength, swept down the mountains outside Los Angeles and spread wildfires into several neighborhoods starting Jan. 7, 2025, creating a terrifying scene.

Thousands of homes and other structures, including several schools, had burned by Jan. 9, and at least five people had died. Officials urged more than 180,000 residents to evacuate at the height of the fires. With the winds so strong, there was little firefighters could do to control the flames.

Jon Keeley, a research ecologist in California with the U.S. Geological Survey and adjunct professor at UCLA, explains what causes extreme winds like this in Southern California, and why they create such a dangerous fire risk.

What causes the Santa Ana winds?

The Santa Ana winds are dry, powerful winds that blow down the mountains toward the Southern California coast. The region sees about 10 Santa Ana wind events a year on average, typically occurring from fall into January.

When conditions are dry, as they are right now, these winds can become a severe fire hazard.

The Santa Ana winds occur when there is high pressure to the east, in the Great Basin, and a low-pressure system off the coast. Air masses move from high pressure to low pressure, and the more extreme the difference in the pressure, the faster the winds blow.

Topography also plays a role.

As the winds rush downslope from the top of the San Gabriel Mountains, they become drier and hotter. That’s a function of the physics of air masses. By the time the winds get to the point where the Eaton Fire broke out in Altadena on Jan. 7, it’s not uncommon for them to have less than 5% relative humidity, meaning essentially no moisture at all.

Canyons also channel the winds. I used to live in the Altadena area, and we would get days during Santa Ana wind events when the wind wasn’t present at all where we lived, but, a few blocks away, the wind was extremely strong.

These strong, dry winds are often around 30 to 40 mph. But they can be stronger. The wind gusts in early January 2025 were reported to have exceeded 80 mph.

Why was the fire risk so high this time?

Typically, Southern California has enough rain by now that the vegetation is moist and doesn’t readily burn. A study a few years ago showed that autumn moisture reduces the risk of Santa Ana wind-driven fires.

This year, however, Southern California has very dry conditions, with very little moisture over the past several months. With these extreme winds, we have the perfect storm for severe fires.

It’s very hard to extinguish a fire under these conditions. The firefighters in the area will tell you, if there’s a Santa Ana wind-driven fire, they will evacuate people ahead of the fire front and control the edges – but when the wind is blowing like this, there’s very little chance of stopping it until the wind subsides.

Other states have seen similar fires driven by strong downslope winds. During the Chimney Tops 2 Fire in Tennessee in November 2016, strong downslope winds spread the flames into homes in Gatlinburg, killing 14 people and burning more than 2,500 homes. Boulder County, Colorado, lost about 1,000 homes when powerful winds coming down the mountains there spread the Marshall Fire in December 2021.

Have the Santa Ana winds changed over time?

Santa Ana wind events aren’t new, but we’re seeing them more often this time of year.

My colleagues and I recently published a paper comparing 71 years of Santa Ana wind events, starting in 1948. We found about the same amount of overall Santa Ana wind activity, but the timing is shifting from fewer events in September and more in December and January. Due to well-documented trends in climate change, it is tempting to ascribe this to global warming, but as yet there is no substantial evidence of this.

California is seeing more destructive fires than we saw in the past. That’s driven not just by changes in the climate and the winds, but also by population growth.

More people now live in and at the edges of wildland areas, and the power grid has expanded with them. That creates more opportunities for fires to start. In extreme weather, power lines face a higher risk of falling or being hit by tree branches and sparking a fire. The area burnt because of fires related to power lines has greatly expanded; today it is the major ignition source for destructive fires in Southern California.

The Eaton Fire, which has burned many homes, is at the upper perimeter of the San Gabriel Basin, at the base of the San Gabriel Mountains. Fifty years ago, fewer people lived there. Back then, some parts of the basin were surrounded by citrus orchards, and fires in the mountains would burn out in the orchards before reaching homes.

Today, there is no buffer between homes and the wildland. The point of ignition for the Eaton Fire appears to have been near or within one of those neighborhoods.

Homes are made of dried materials, and when the atmosphere is dry, they combust readily, allowing fires to spread quickly through neighborhoods and creating a great risk of destructive fires.

This article, originally published Jan. 8, has been updated with new details on the fires.

Jon Keeley, Research Ecologist, USGS; Adjunct Professor, University of California, Los Angeles

This article is republished from The Conversation under a Creative Commons license. Read the original article.

In 2024, space exploration dazzled the world.

NASA’s Europa Clipper began its journey to study Jupiter’s moon Europa. SpaceX’s Starship achieved its first successful landing, a critical milestone for future deep space missions. China made headlines with the Chang’e 6 mission, which successfully returned samples from the far side of the Moon. Meanwhile, the International Space Station continued to host international crews, including private missions like Axiom Mission 3.

As an aerospace engineer, I’m excited for 2025, when space agencies worldwide are gearing up for even more ambitious goals. Here’s a look at the most exciting missions planned for the coming year, which will expand humanity’s horizons even further, from the Moon and Mars to asteroids and beyond:

Scouting the lunar surface with CLPS

NASA’s Commercial Lunar Payload Services, or CLPS, initiative aims to deliver science and technology payloads to the Moon using commercial landers. CLPS is what brought Intuitive Machines’ Odysseus lander to the Moon in February 2024, marking the first U.S. Moon landing since Apollo.

In 2025, NASA has several CLPS missions planned, including deliveries by companies Astrobotic, Intuitive Machines and Firefly Aerospace.

These missions will carry a variety of scientific instruments and technology demonstrations to different lunar locations. The payloads will include experiments to study lunar geology, test new technologies for future human missions and gather data on the Moon’s environment.

Surveying the sky with SPHEREx

In February 2025, NASA plans to launch the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer, or SPHEREx, observatory. This mission will survey the sky in near-infrared light, which is a type of light that is invisible to the naked eye but that special instruments can detect. Near-infrared light is useful for observing objects that are too cool or too distant to be seen in visible light.

SPHEREx will create a comprehensive map of the universe by surveying and collecting data on more than 450 million galaxies along with over 100 million stars in the Milky Way. Astronomers will use this data to answer big questions about the origins of galaxies and the distribution of water and organic molecules in stellar nurseries – where stars are born from gas and dust.

Studying low Earth orbit with Space Rider

The European Space Agency, or ESA, plans to conduct an orbital test flight of its Space Rider uncrewed spaceplane in the third quarter of 2025. Space Rider is a reusable spacecraft designed to carry out various scientific experiments in low Earth orbit.

These scientific experiments will include research in microgravity, which is the near-weightless environment of space. Scientists will study how plants grow, how materials behave and how biological processes occur without the influence of gravity.

Space Rider will also demonstrate new technologies for future missions. For example, it will test advanced telecommunication systems, which are crucial for maintaining communication with spacecraft over long distances. It will also test new robotic exploration tools for use on future missions to the Moon or Mars.

Exploring the Moon with M2/Resilience

Japan’s M2/Resilience mission, scheduled for January 2025, will launch a lander and micro-rover to the lunar surface.

This mission will study the lunar soil to understand its composition and properties. Researchers will also conduct a water-splitting test to produce oxygen and hydrogen by extracting water from the lunar surface, heating the water and splitting the captured steam. The generated water, oxygen and hydrogen can be used for enabling long-term lunar exploration.

This mission will also demonstrate new technologies, such as advanced navigation systems for precise landings and systems to operate the rover autonomously. These technologies are essential for future lunar exploration and could be used in missions to Mars and beyond.

The M2/Resilience mission is part of Japan’s broader efforts to contribute to international lunar exploration. It builds on the success of Japan’s Smart Lander for Investigating Moon, or SLIM, mission, which landed on the Moon using a precise landing technique in March 2024.

Investigating an asteroid with Tianwen-2

China’s Tianwen-2 mission is an ambitious asteroid sample return and comet probe mission. Scheduled for launch in May 2025, Tianwen-2 aims to collect samples from a near-Earth asteroid and study a comet. This mission will advance scientists’ understanding of the solar system’s formation and evolution, building on the success of China’s previous lunar and Mars missions.

The mission’s first target is the near-Earth asteroid 469219 Kamoʻoalewa. This asteroid is a quasi-satellite of Earth, meaning it orbits the Sun but stays close to Earth. Kamoʻoalewa is roughly 131-328 feet (40-100 meters) in diameter and may be a fragment of the Moon, ejected into space by a past impact event.

By studying this asteroid, scientists hope to learn about the early solar system and the processes that shaped it. The spacecraft will use both touch-and-go and anchor-and-attach techniques to collect samples from the asteroid’s surface.

After collecting samples from Kamoʻoalewa, Tianwen-2 will return them to Earth and then set course for its second target, the main-belt comet 311P/PANSTARRS. This comet is located in the asteroid belt between Mars and Jupiter.

By analyzing the comet’s materials, researchers hope to learn more about the conditions that existed in the early solar system and possibly the origins of water and organic molecules on Earth.

Solar system flybys

Besides the above planned launch missions, several space agencies plan to perform exciting deep-space flyby missions in 2025.

A flyby, or gravity assist, is when a spacecraft passes close enough to a planet or moon to use its gravity for a speed boost. As the spacecraft approaches, it gets pulled in by the planet’s gravity, which helps it accelerate.

After swinging around the planet, the spacecraft is flung back out into space, allowing it to change direction and continue on its intended path using less fuel.

BepiColombo, a joint mission by ESA and the Japan Aerospace Exploration Agency, JAXA, will make its sixth flyby of Mercury in January 2025. This maneuver will help the spacecraft enter orbit around Mercury by November 2026. BepiColombo aims to study Mercury’s composition, atmosphere and surface geology.

NASA’s Europa Clipper mission, which launched in October 2024, will make significant progress on its journey to Jupiter’s moon Europa. In March 2025, the spacecraft will perform a flyby maneuver at Mars.

This maneuver will help the spacecraft gain the necessary speed and trajectory for its long voyage. Later in December 2026, Europa Clipper will perform a flyby of Earth, using Earth’s gravity to further increase its momentum so it can arrive at Europa in April 2030.

The ESA’s Hera mission will also perform a flyby of Mars in March 2025. Hera is part of the Asteroid Impact and Deflection Assessment mission, which plans to study the Didymos binary asteroid system. The mission will provide valuable data on asteroid deflection techniques and contribute to planetary defense strategies.

NASA’s Lucy mission will continue its journey to explore the Jupiter Trojan asteroids, which share Jupiter’s orbit around the Sun, in 2025. One key event for Lucy is its flyby of the inner main-belt asteroid 52246 Donaldjohanson, scheduled for April 20, 2025.

This flyby will provide valuable data on this ancient asteroid’s composition and surface features, which can help researchers gain insights into the early solar system. The asteroid is named after the paleoanthropologist who discovered the famous “Lucy” fossil.

ESA’s Jupiter Icy Moons Explorer, or JUICE, mission will perform a Venus flyby in August 2025. This maneuver will help JUICE gain the necessary speed and trajectory for its journey to Jupiter. Once it arrives, JUICE will study Jupiter’s icy moons to understand their potential for harboring life.

2025 promises to be a groundbreaking year for space exploration. With NASA’s ambitious missions and significant contributions from other countries, we are set to make remarkable strides in humanity’s understanding of the universe. These missions will not only advance scientific knowledge but also inspire future generations to look to the stars.

Zhenbo Wang, Associate Professor of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee

This article is republished from The Conversation under a Creative Commons license. Read the original article.