Do "Dark Comets" Pose a Danger to Earth?

 You have probably seen pictures of comets with their long tails of dust and ice sweeping majestically behind them. That tail is one of the defining characteristics of comets. Small objects orbiting the sun that do not sprout a tail have long been considered to be asteroids. While astronomers have found some “dead” comets, those with no tail being pushed off by the sun, they have become asteroids.

As the ice melts from the comet by the sun’s heat, it pushes off the comet with a small force. Think of a pot of water evaporating. Even though you can’t feel the “wind” caused by this water vapor leaving the water, it’s there, and it pushes back on the water with a tiny but persistent force. With comets, this force of the vaporized ice leaving the comet acts like a tiny rocket motor. It can push the comet in its orbit in a way that astronomers can measure. The orbit of a comet isn’t controlled solely by the gravity of the sun, planets, and other objects in our solar system, but also due to this outgassing. Asteroids don’t behave this way.

Or so astronomers thought.

In 2016, astronomer David Farnocchia, with NASA’s Center for Near-Earth Object Studies, discovered something quite puzzling. He found an asteroid, 2003 RM, whose motion through the solar system couldn’t be fully accounted for by the gravity of other bodies. It behaved like a comet shooting water vapor into space, except that he could find no evidence of that.

There is another force, known as the Yarkovsky effect, which can alter the orbit of small bodies around the sun. As photons from the sun impact a space rock, they deliver an almost imperceptible push on the rock. Though minuscule, it can, over time, affect the rock’s orbital path. Also, the sunward side heats up from the sun’s thermal energy. But, as the asteroid rotates, the heated side rolls into the dark and radiates the excess heat into space, again providing a tiny bit of thrust. Farnocchia took all of that into account for 2003 RM, yet it still couldn’t explain the small deviation of the asteroid’s orbit.

Comet Tsuchinshan-ATLAS credit Wladimir Bulgar - Science Photo Library via Getty Images

With all comets, as the ice is vaporized and outgassed from the sun’s heat, it also releases dust trapped in the ice. That beautiful tail we see coming from a comet is actually composed of dust. But even using our biggest and best telescopes, no one has found any dust trailing 2003RM. It behaved as if it had a tiny rocket engine attached to it. Eventually, Farnocchia and other astronomers found thirteen more such objects. They dubbed them “dark comets.”

This is more than just a curiosity for astronomers. Farnocchia’s job is to search for asteroids that have a possibility of hitting Earth. “My job,” he says, “is to predict how things move in space. So if there’s something novel or unexpected, that’s where the advance in the field lies for us.”

Current telescopes can easily see any dust that might be coming off of a comet, but none has been found to date. New telescopes planned or already under construction will be able to detect any tiny bits of water vapor that may be puffing off these dark comets. And since some are close enough that they might have a chance of collision with Earth down the road, being able to predict their position and movement may become more crucial in the future. For now, he will monitor them and track their movements, just in case one wanders too close to us.  

Do Cosmic Events Cause Mass Extinctions on Earth?

 Scientists recognize five major mass extinctions in Earth’s history, episodes when a large fraction of life all over our planet went extinct in a very short time on geological time scales. Scientists blame various causes for these extinctions. Climate change was often the real killer, but the cause of climate change varied.

The most recent mass extinction, the K-T extinction 66 million years ago, is perhaps the most famous and best understood of the major extinctions. It led to the end of the dinosaurs and most marine reptiles. At that time, an asteroid 6 miles in diameter slammed into Earth just off the coast of what is now the Yucatan Peninsula in Mexico. It threw hot ash and molten rock into the air that covered the planet, resulting in worldwide fires, killing off many species. The resulting cloud of debris and smoke then reduced sunlight from reaching the planet’s surface for a period of years, causing the death of many plant species which dramatically diminished the entire food chain.

A new study suggests an astronomical cause for two other extinction episodes. The Ordovician extinction event occurred 443.8 million years ago. This was a time known for rapid diversification in marine life and the appearance of the first plants on land. Scientists estimate that 71% of species disappeared during this event.

The Late Devonian mass extinction occurred 372 million years ago leading to the extinction of nearly 70% of species. It is the least understood of the five major events, and scientists have offered several possible explanations for it. The new study provides plausible astronomical explanations for both of these events.

In both the Ordovician and late Devonian extinction events, there is evidence that Earth’s ozone layer was severely depleted. A new study led by Dr. Alexis Quintana at the University of Alicante in Spain, including other researchers from Keele University in England, puts the blame for both events on nearby supernovas.

When a massive star runs out of fuel, it explodes with so much energy that a single supernova can temporarily release more energy than its entire host galaxy. The debris includes not only high-energy radiation, like X-rays and gamma rays, it also includes cosmic rays, charged particles moving at nearly the speed of light. A nearby supernova can blast enough energy to destroy our ozone layer. With that protective shield gone, the high-energy cosmic rays and the deadly radiation can bathe Earth’s surface at lethal levels.

The Crab Nebula, a supernova remnant in the constellation of Taurus. 

Credit NASA, ESA, and the Hubble Space Telescope Institute.

Life on our planet owes its existence to supernovas, as all elements heavier than hydrogen and helium – including oxygen, carbon, calcium, iron, and all the chemical elements that make us up – are created in those stellar explosions. As the authors say in the study, it is "a great illustration for how massive stars can act as both creators and destructors of life".

Dr. Quintana states, "Supernova explosions bring heavy chemical elements into the interstellar medium, which are then used to form new stars and planets. But if a planet, including the Earth, is located too close to this kind of event, this can have devastating effects."

It seems the universe can give us life, but can also take it away.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Are We Close to Finding Extraterrestrial Life?

 The topic of many of my articles involves the search for extraterrestrial life. I look at what conditions are needed to support life on Earth and see if such environments exist elsewhere. For example, we found seasonal variations of methane in the Martian atmosphere. On our planet, methane is almost exclusively associated with life. I’ve written about astronomers’ efforts to find and study planets orbiting other stars to determine if they orbit in the habitable zone where water can exist on the surface. On Earth, virtually wherever we find water, we find living creatures. That may only be microbial life, such as that found in acidic hot springs or water trapped far below the surface, but life nonetheless.

Even if we only find such microbial life, that would be an astounding discovery. It would tell us that life can develop in locations other than Earth which at the moment is the only location in the universe where life is known to exist.

Recently, a newsletter called The Conversation ran an article in which the authors polled astrobiologists and other scientists on their belief in extraterrestrial life. The Conversation is an online source of articles written by researchers and academics across all disciplines. It gives them a platform to present their work to the public. We often read articles that say finding extraterrestrial life is “only a matter of time”, or “we are close to finding alien life.” And yet, we still await that discovery.

Exoplanets in their star's habitable zone. Are we close to discovering exo-life?

In 2024, three researchers – Peter Vickers, a Professor in Philosophy of Science at Durham University, Henry Taylor an Associate Professor in the Department of Philosophy at the University of Birmingham, and Sean McMahon, of the University of Edinburgh – did surveys, polling a number of astrobiologists, those scientists who study and look for the chances of life elsewhere, and scientists in other fields on their beliefs of the existence of alien life. They asked about their beliefs, based on all the research to date, of the existence of basic lifeforms, i.e. microbial life, complex forms, i.e. multicellular life, and intelligent extraterrestrial life.

Altogether, they received responses from 521 astrobiologists and 534 non-astrobiologists. Of the astrobiologists, 86.6% said they “agree” or “strongly agree” that extraterrestrial life, at least at the basic level, exists elsewhere. Less than 2% disagreed with the sentiment and 12% claimed to be neutral on the possibility. Of the non-astrobiologists, 88.4% also marked “agree” or “strongly agree” with the question. Scientists who don’t study the possibility of extraterrestrial life are not more skeptical than those who do. The authors of the survey felt that to be a rather significant result.

The survey asked about each level of life – basic, complex, and intelligent – separately. The results when asked specifically about whether “intelligent” aliens exist were not quite as optimistic. Only 67.4% of astrobiologists and 58.2% of other scientists agreed, still more than half. Only 10.2% of astrobiologists disagreed with that statement.

This survey cannot in any way offer proof of life elsewhere, but the preponderance of scientific research and evidence leads most scientists, at least in these fields, to accept the likelihood. Astronomers estimate that in our galaxy alone a trillion extrasolar planets, those orbiting other stars, exist. They further estimate that billions of Earth-like planets orbit in the habitable zone of their parent star.

Life on Earth is proving to be far more robust than we previously thought. Microbes called extremophiles can survive in all kinds of environments once thought unable to support any kind of life. Creatures called tardigrades, or water bears, have even been shown to survive in airless, radiation-filled outer space beyond our planet. I suspect that the existence of such extremophiles that survive in these hazardous or toxic locations is a large part of the thought processes of these scientists.

Perhaps it really is only a “matter of time” before we discover alien life forms. And. Some scientists say we may not even recognize alien creatures as living at first. We have no idea if “life as we know it” is all that there can be.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Did Planets from the Inner Disk of the Milky Way Become Rogue Planets?

 We think of a planet as a non-luminous body that orbits a star, like the planets of our solar system. But that’s not always the case.

All stars form from clouds of gas and dust that collapse inward due to the pull of gravity. The pressure caused by the gravitational crunch squeezes gas in the center of each cloud so tightly that it heated the gas to extreme temperatures, generating thermonuclear reactions, and a new star is born. Our sun flared into existence four and a half billion years ago, far younger than the oldest stars, which are born in other parts of the galaxy.

But there was still quite a bit of leftover gas and dust surrounding the young sun which formed a disk around the new star. This leftover bit eventually becomes all of the planets, moons, comets, and asteroids that orbit our sun.

Our solar system lives in the spiral arms of the Milky Way galaxy. Most of the galaxy’s younger stars like our sun are in the spiral arms. Astronomers estimate that virtually all of these stars have planets, an average of two and a half planets per star.

The older stars of our galaxy mostly reside in a bulge surrounding the center of the Milky Way. Stars there have on average barely one planet per star.  MIT astrophysicist Tim Hallatt thinks he knows why. “The puzzle is, these planets (in the spiral arms) are very common,” Hallatt says. “And yet when we look at this other dominant population of stars in the Milky Way, they’re less common. So what’s going on?”

As is the case with all large galaxies like ours, when the Milky Way first formed some 12 billion years ago, star formation was fast and furious, a time Hallatt describes as galactic chaos, what astronomers generally refer to as “cosmic noon.” Also, the stars there were more closely bunched together than the stars in our neighborhood. The greater levels of energetic radiation from the process of rapid star formation plus the relative proximity of stars meant that the stars during cosmic noon experienced ten million times greater levels of radiation. This intense radiation would have heated the gas surrounding all these rapidly forming stars. The greater levels of radiation and heat blew away much of the remaining gas, leaving less raw material for planets.

When astronomers search for planets beyond our own solar system, they look at other stars. We currently know of more than 5000 such exoplanets, and the more we look, the more we find. Astronomers also find lots of rogue planets, planets that don’t orbit any star. They may have formed around a star but were ejected from their home stellar system, perhaps due to close passage of another star. The gravity of the passing star can rip a planet away from its home. Astronomers estimate that perhaps as many as four trillion rogue planets exist in our galaxy alone. That’s a huge number.

Artist's conception of a Rogue Planet

It’s likely that some of those rogue planets formed on their own, not as part of a stellar system. Perhaps some of the gas and dust blown out by the stars formed during the crowded cosmic noon eventually coalesced into rogue planets. Many of these rogue planets could have orbited a star but for the early period of rapid star growth.

Rogue planets may easily outnumber the stars in our galaxy. And some of those rogue stars may be causalities of the cosmic noon timeframe of our Milky Way galaxy.

Each month, I write an astronomy-related column for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and Oklahoman.com.

The New Space Race

 NASA has plans to return to the Moon, first with a space station orbiting it and soon after that a permanently manned lunar research facility. China also plans to establish a permanent research station on the Moon. India is preparing for a second lunar landing with the eventual goal of a manned presence in the near future.

Our natural satellite is a treasure trove of valuable minerals. Nations that develop lunar mining capabilities will gain access to important resources. One such lunar resource you might not immediately think of is Helium 3. Normal helium contains two protons and two neutrons in its nucleus. Helium 3 has only one neutron. Why would this be important? That isotope of helium is extremely significant in the production of non-polluting energy.

Currently, our primary source of non-renewable energy on Earth comes from burning fossil fuels which releases copious amounts of carbon dioxide, a major cause of global warming. The process also releases a lot of sulfur which combines with water to create sulfuric acid, acidifying our lakes and oceans and leading to the possible extinction of numerous species. The acid rain leaches minerals from the soil that trees and other plants need for proper growth. The particulates that fossil fuel burning puts in the air are a major health risk for all animals, including us humans.

Many countries also rely on nuclear power plants for energy production. These plants rely on nuclear fission, the splitting of uranium and plutonium atoms to generate energy, but also generate tons of radioactive waste materials for which we currently have no safe disposal methods.

So what does the Moon have to do with all of this? Helium 3. With no atmosphere or magnetic field to protect it from the harsh solar wind, the Moon’s surface is bombarded with charged particles, and helium 3 is one product of this. The surface of our Moon has an abundance of it. Helium 3 can be used in fusion reactors to make clean, pollution-free energy, the same process that powers our sun. Scientists have recently figured out how to create fusion reactors that deliver more energy than it takes to power them, giving us the promise of almost unlimited energy production that won’t destroy our forests or threaten extinction.

Artists conception of Lunar Helium-3 mining. Credit ESA

We’ve found a lot of water in the form of ice at the south pole of the Moon. Water can be used for drinking, oxygen for breathing, and rocket fuel. It is much easier to blast off from the Moon than it is from Earth due to the Moon’s weaker gravity. That gives us an easier stepping stone to explore the solar system. Easier and cheaper access to space allows us greater opportunity to explore the asteroid belt.

One goal of space exploration is to mine asteroids for rare minerals, such as lithium, cobalt, manganese, and nickel, all important for creating electronic devices like smartphones, computers, and batteries that can store electrical energy and power vehicles that don’t burn fossil fuels. Asteroids also contain copious amounts of iron, silver, gold, and platinum, all valuable in modern society.

There are, of course, a tremendous number of scientific reasons for having a lunar base. The Moon itself still holds many secrets for us to discover. The relative ease of access to space from the Moon provides scientists the opportunity to study our solar system in great detail. Telescopes located on the Moon’s far side give us the chance to study the cosmos without interference from Earthly sources of radio noise and light pollution, not to mention the huge and growing number of satellites in orbit around Earth that interfere with astronomical studies.

Our Moon holds many riches, both economic and scientific, making it a goal to create a permanently manned scientific colony there. That is the new space race.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Should We Call Pluto a Planet?

Astronomers once called Pluto the ninth planet. In 2006, the International Astronomical Union, IAU, downgraded Pluto to the status of dwarf planet. After the New Horizons craft flew by Pluto in 2015, it showed us a very dynamic world. Many astronomers and a large percentage of the public now believe we should reconsider Pluto’s demotion.

Pluto as seen by the New Horizons spacecraft. 

Since before written history, humans have known of seven regularly observed heavenly bodies that didn’t behave like the vast majority of stars. They called them planets, Greek for “wanderer.” In those ancient times, they considered anything that changed its position relative to the “fixed stars” to be a planet. Since both the sun and the Moon moved relative to the fixed stars, they were also considered planets until Copernicus proved that planets circled the sun and the Moon circled Earth.

Astronomers then recognized six planets, Mercury, Venus, Earth, Mars, Jupiter, and Saturn. Comets also orbited the sun, but because they had weird orbits and grew a tail, they were considered different types of celestial objects. That changed in 1781 when William Herschel discovered Uranus and Italian astronomer Giuseppe Piazzi discovered Ceres in 1801 between Mars and Jupiter while searching for comets. Both orbited the sun.

Ceres, the largest member of the Asteroid Belt.

Initially, astronomers called Ceres the smallest planet until many more such objects were discovered in the same area of our solar system. They reclassified Ceres and all those other even smaller objects as “asteroids,” calling that region the Asteroid Belt.

In 1846, two astronomers independently discovered Neptune, adding an 8^th planet to the solar system. Clyde Tombaugh added Pluto in 1930, making nine planets, and there it stayed for years.

In the 1990s, astronomers began finding many more objects beyond Neptune. They were small like Pluto and in the area of our solar system that was relatively crowded, unlike the inner parts. Some astronomers feared that it might be time to get a more scientifically based definition of “planet.”  

At the 2006 IAU meeting, astronomers agreed to redefine what constitutes a planet. There were two camps: geophysicists and dynamists. They all agreed that it had to orbit a star. Geophysicists said that any object big enough that its gravity pulled it into a spherical or nearly spherical shape should be a planet. Dynamists argued that a planet must also be large enough to “clear its orbital area of debris.” Ceres couldn’t be a planet since, even though it is round, there were many asteroids in the same region. Likewise, round Pluto shared its region with many thousands of objects.

The dynamists won. Pluto, Ceres, and other round solar system bodies became dwarf planets. Along with those two, astronomers now recognize three others, Haumea, Makemake, and Eris, all beyond Neptune, as dwarf planets. There may be many more that we just don’t have enough data on yet.

Count me in the camp of the geophysicists. If it’s big enough to pull itself into a nearly circular shape, technically called hydrostatic equilibrium, then I believe it should be a planet. I’m convinced that the dynamists just didn’t want to remember that many planet names.

  

    Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After publishing it there, I post that same column to my blog page.

   This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Did Earth Once Possess a Ring Like Saturn?

 When I show people astronomical sights through my telescope, the one view that elicits the most comments is Saturn with its rings. Many times I’ve heard people say “Wow! That’s amazing.” Or, “Oh, that’s not real. You have a picture in there.” Saturn, more than any other common backyard telescope target, looks like the pictures you’ve seen in books.

Saturn.

Saturn isn’t the only planet with a ring system. Jupiter, Uranus, and Neptune also have rings but are only visible with very powerful telescopes or spacecraft passing nearby.

Imagine the sense of awe if we lived on a planet with rings, something we sometimes see in science fiction movies. Had you been around on Earth 466 million years ago, you might have been able to enjoy that very experience. A recent study suggests that Earth may very well have sported a ring like Saturn.

Artist's conception of Earth with rings.

Planetary rings are ephemeral. They don’t last forever, although they do exist for millions of years. The evidence for Earth’s possible ring is circumstantial but quite intriguing. Starting about 466 million years ago, Earth experienced a period of enhanced meteor cratering, a period known as the Ordovician impact spike. During that cratering period, virtually all of the impacts on Earth, centered on a narrow band along the equator. Typically, impacts should occur randomly over the Earth’s surface.

This narrow cratering band implies that the objects striking Earth all came from that area of the sky over the equator. The easiest explanation for such a narrow band of cratering events along the equator is a ring of debris encircling our planet. If a ring forms around a planet, it will always settle over the equator.

During the same time frame, sedimentary rocks show a large increase in L chondrite material. L chondrite-type asteroids are common in the asteroid belt. Denizens in the asteroid belt occasionally collide, scattering debris around the solar system. 

Artist's conception of two asteroids colliding. 

The researchers, led by Andrew G. Tomkins, a geologist at Monash University in Australia, suggest that one large fragment came close to Earth, passing so closely that Earth’s gravity shattered it and the debris formed a ring.

Based on the cratering record, the study participants claimed the ring lasted approximately 40 million years, a typical lifetime for a planetary ring. During that same period of time, Earth experienced one of its most intense glaciation events and mass extinctions known as the Hirnantian global icehouse period. The researchers suggest that shading from the ring decreased solar radiation reaching the planet’s surface, triggering the short but intense glaciation period. “The existence of such a ring, forming around 466 million years ago and persisting for a few tens of millions of years could explain several puzzles in our planet’s past,” Tomkins wrote.

None of this evidence is absolute proof that we once had a ring like Saturn’s, but it is strongly suggestive. More work needs to be done to help corroborate their conclusion.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After publishing it there, I post that column on my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.